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Abstracts

Abstracts from the 34th Annual Winter

Meeting of the Geological Society’s Mineral

Deposit Studies Group and the Applied

Mineralology Group of the Mineralogical

Society and the 14th CERCAMS Workshop

on Ore Giants of Asia was held on 5th–7th

January 2011 at the Natural History Museum,

London.

The meeting was dedicated to Nick Badham

(12th May 1947–19th June 2010). In June

2010, MDSG lost one of its greatest supporters.

For those who knew him, they will always

remember his enthusiasm for Mineral Deposits

science and his contagious humour.

‘What is the difference between Roast Beef

and Pea Soup?

Anyone can roast beef’

Nick Badham

Asia’s golden architecture: tectonic foundations for EastAsian orogenic gold

Craig J. R. Hart1, Richard J. Goldfarb2

1Mineral Deposit Research Unit, Department of Earthand Ocean Sciences, The University of British Columbia,6339 Stores Road, Vancouver, BC V6T 1Z4, Canada(chart@eos.ubc.ca)2US Geological Survey, PO Box 25046, Mail Stop 973,Denver Federal Center, Denver, CO 80225-0046, USA

Orogenic gold systems comprise the largest number ofgold deposits and greatest gold endowment of easternAsia. Despite this enrichment and considerable prospec-tivity for new discoveries, there is a poor overallunderstanding of the controls that localise the ores, themost appropriate genetic model, and the geologicalsettings of the deposits at their time of formation. Muchof this uncertainty is related to two factors, poor ageconstraints, and geological settings that do not fitcurrent models for orogenic gold deposits. Theseuncertainties conspire to cause a re-evaluation of thegeological settings and fluid sources regarded to beintegral to the orogenic gold deposit model.

The vast landmass of Eastern Asia (China, Mongolia& eastern Russia) is an assembly of Precambriancratonic nuclei, variably rimmed with Neoproterozoicto Early Palaeozoic pericratonic passive margin assem-blages that were assembled through collision andaccretion from Permian to Cretaceous time. Theamalgamated blocks were subsequently modified byreverse and strike-slip dominated structural activity andoverprinted by episodic magmatism. Gold deposits anddistricts formed preferentially in the margins or mar-ginal assemblages of the cratonic blocks, but despite theabundance of Archaean and Palaeoproterozoic rocks

that comprise the cratons, significant Precambriangreenstone-gold deposits have not been, and are unlikelyto be, discovered.

The oldest gold ores are the orogenic gold deposits onthe margins of the Siberian craton, specifically those in theYenisei Ridge gold province (e.g. Olimpiada, Sovetskoe)which likely formed between 700 and 450 Ma. These,and probably the deposits of the East Sayan region (e.g.Zun Holba, Sora, Aksug), are part of the broader lateNeoproterozoic-Early Palaeozoic orogenic belt that formedalong the southwestern margin of Siberian craton. Thisapparent ‘Cordilleran-style’ belt is characterised by arcaccretion with deposits forming in metasedimentaryassemblages that were either flysch basins, or more likely,inverted, off-shelf pericratonic passive margin assemblages.The geological setting was similar along the easternSiberian cratonic margin where the Sukhoi Log depositformed, potentially at a similar time, but this region isdominated by deformation and plutonism associated withCarboniferous terrane accretion, the earliest assembly ofthe Central Asian Orogenic Belt (CAOB).

Permian collision of the North (NCC) and South China(SCC) cratonic blocks, and amalgamation of the CAOBwith rifted cratonic fragments, resulted in some middlePalaeozoic orogenic gold deposits such as those on thenorthern margin of the NCC (e.g. Wulashan). Permianstrike-slip faulting along terrane sutures and cratonicmargins formed a continental-scale gold episode (e.g.Muruntau, Kumtor, Bakyrchik, Saidu, Olon Ovoot).

Permo-Triassic amalgamation of the NCC and SCCformed orogenic gold deposits (e.g. Yangshan, Bagu-aniao) in the sutured terranes of the western Qinling foldbelt. Although their tectonic evolution is still very poorlyunderstood, the reactivated marginal regions of the SCCcontain Permo-Triassic(?) orogenic deposits (e.g. Boka)and mid-Mesozoic(?) Carlin-like deposits (e.g. Jinfeng).The orogenic gold deposits likely correlate with subduc-tion/accretion episodes along the trailing margins of theSCC, whereas the Carlin-like deposits indicate hydro-thermal events during extension in SCC carbonate/basinsequences.

Asian gold systems related to Palaeo-Pacific Oceanevents may be as old as Jurassic with the final mid-Mesozoic closure of the Mongol-Okhotsk Ocean.Deformation of turbidites was associated with forma-tion of Middle to Late Jurassic orogenic gold ores innorthern Mongolia (e.g. Boroo) and central to easternTransbaikal (e.g. Darasun, Tokur). Arc collision andsubsequent extension, also during the Jura-Cretaceous,but along the Siberian continental margin farther to thenorth, was associated with orogenic (e.g. Natalka), aswell as epithermal gold deposits (e.g. Dukat, Julietta)throughout northeastern Russia.

Significant Early Cretaceous gold provinces formed inthe northern and eastern margins of the NCC (e.g.Jiaodong, Qinling), the eastern SCC (e.g. Jiagnan) to thesouth, and eastern, southern Siberia to the north. ThesePhanerozoic orogenic gold districts are globally unique

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� 2010 Mineral Deposits Study GroupPublished by Maney on behalf of the Institute and The AusIMMDOI 10.1179/1743275811Y.0000000004 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2

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as they are mostly hosted in high-grade Archaean toPalaeoproterozoic metamorphic rocks. Reorganisationof Pacific oceanic plates at y125 Ma re-initiated Pacificplate subduction which led to the reactivation of majorfault systems and the formation and uplift of the high-grade metamorphic core complexes which host manyof the gold districts. The initiation of Pacific platesubduction also resulted in the subsequent loss of morethan 150 km of cratonic lithosphere for .2000 km alongthe eastern Asian Pacific margin. This region of litho-sphere loss has a remarkable association with theorogenic gold provinces that developed at this time. Theoccurrence of orogenic gold deposits in high-grademetamorphic rocks requires an exotic reservoir for thehydrothermal systems since the Precambrian host rockswere devolatilised billions of years prior to ore formation.

The Kupol epithermal gold deposit Chukotka Region, NERussiaH. C. Golden11/13 Proletarskaya Street, Magadan, 685000 Russia(howard.golden@kinross.com)

The Kupol deposit is located in the ChukotkaAutonomous Okrug in the Far East of the RussianFederation. The deposit is located in the 3000 km long NEtrending Cretaceous Okhotsk-Chukotka volcanogenicbelt. This belt is interpreted to be an Andean volcanicback-arc type tectonic setting, intersected normally by theMesozoic Anui sedimentary fold belt in which sits theKupol epithermal gold deposit. Kupol hosts measuredand indicated resources of 22?6 thousand tonnes of goldore grading 15?48 g t21 yielding 12 thousand ounces. Thedeposit is owned 75% by Kinross Gold Corporation and25% by the government of Chukotka.

The Kupol deposit area is centred within a 10-km widecaldera, along the western margins of the 100-km wideMechkerevskaya Upper Cretaceous bimodal nested vol-canic complex. The 1300 m thick volcanic succession iscomprised of a lower sequence of felsic tuffs andignimbrites, a middle sequence of andesitic to basaltic-andesitic flows and fragmentals, and is capped by felsictuffs and flows. These sequences are cut and discordantlyoverlain by basalts of reported Palaeogenic age. Thevolcanic rocks unconformably overlie and intrude foldedJurassic sediments.

The deposit is associated with a north-south trendingsplay off a regional fault of similar orientation. Themagnitude of displacement along the Kupol structure isunknown but the direction is inferred to be normal-rightlateral due to fault geometry.

Gold and silver mineralisation at Kupol is hosted bycolloform to crustiform-banded quartz-adularia veinsand polyphase breccias. The mineralised veins includemassive to sugary, very fine to fine-grained quartz withsulphosalt rich colloform banded veins; banded collo-form and crustiform veins; brecciated quartz veins;quartz breccia with a dark sulphide-rich matrix; stock-work veins; and stringer veining with sheeted, non-crosscutting veinlets.

The predominant gold and silver minerals are elec-trum, native gold, silver-rich tetrahedrite (freibergite),acanthite, and a variety of sulphosalts. Arsenic andantimony-rich end members of a variety of mineralgroups are present reflecting different solution chemistryin the evolution of the deposit and/or zonation in the

deposit. Mineral associations occur in five phases ofquartz-adularia veins and breccias. The Ag/Au ratio inthe deposit is 10 : 1.

Evolution of the Sukhoi Log and Kumtor gold ore giantsV. V. Maslennikov1, R. R. Large2, A. Shevkunov3, V. A.Simonov1

1Institute of Mineralogy, Urals Branch RAS, Miass,Russia2CODES, Hobart, Tasmania, Australia (maslennikov@mineralogy.ru)3Kumtor Mining Company, Bishkek, Kyrgyzstan

The evolution of gold concentration in ‘orogenic golddeposits’ is poorly understood, with recent geneticmodels challenging the conventional view (Large et al.,2007; 2009). Textural, mineral and chemical evolution ofsulphide mineralisation has been studied in the SukhoiLog (Lena province in southern margin of Siberiacraton, Siberia) and Kumtor (northern flank of theTarim craton, Kyrgyzstan) black shale-hosted golddeposits. Both deposits have been metamorphosed tolower greenschist facies.

The sulphide mineral evolution in black shales whichhost the Sukhoi Log group of gold deposits has thefollowing stages: (1) banded or nodular early-diageneticsooty or framboidal pyrite (py1) with moderate invisiblegold (0?1 to 12 ppm); (2) recrystallised framboidal py1to fine-grained anhedral and subhedral py2,3 with raremicronuggets of native gold; (3) subhedral arsenopyriteand/or pyrrhotite pseudomorphs after py1,2,3, and/orsubhedral arsenopyrite with inclusions of py1,2,3; (4)syntectonic euhedral py4 with inclusions of pyrrhotite,native gold, chalcopyrite, sphalerite and folded sedi-mentary matrix; (5) clear inclusion-free py5 overgrowingpy3,4 within bedding parallel folded quartz veinletscarrying inclusions of gold, tellurides, galena andfahlores in the py3,4 cores; (6) latest postmetamorphicpseudocolloform marcasite-pyrite intergrowth, formedby replacement of pyrrhotite (Large et al., 2007; 2009).

Detailed petrography has revealed a similar gold-bearing mineral paragenesis in the black shale-hostedKumtor gold deposits: (1) fine-grained disseminated,banded or nodular diagenetic framboidal pyrite (py1);(2) recrystallised of framboidal py1 to fine grainedanhedral py2 overgrown by nodular radial py3 (aftermarcasite); (3) pyrrhotite veinlets parallel to cleavageand banded disseminated pyrrhotite pseudomorphs afterframboidal and granular pyrite in association withquartz, rutile, chalcopyrite and rare arsenopyrite; (4)syntectonic euhedral to subhedral pyrite with inclusionsof pyrrhotite and chalcopyrite; (5) subhedral, corrodedand/or euhedral py5 with inclusions of rutile, goldtellurides, native gold, chalcopyrite, sphalerite, fahloresand galena in association with quartz, carbonate,scheelite and feldspar veins; (6) fine intergrowth of py6and marcasite generated after pyrrhotite and othermineral assemblages.

Laser ablation ICP-MS analyses of trace elements inthe various pyrite types from both Sukhoi Log andKumtor have revealed two distinct episodes of goldenrichment: an early synsedimentary stage and laterepigenetic ‘metamorphic or hydrothermal’ stage. In thefirst stage, invisible gold was concentrated in arsenianearly diagenetic mostly, framboidal, sooty, nodular orfine grained pyrite along with other trace elements, in

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particular, As, Ni, Pb, Ag, Zn, Mo, Te, V and Se.During late diagenesis and early metamorphism thediagenetic arsenian pyrite was recrystallised to formcoarser grained pyrite generations, and the organicmatter was cooked to bitumen. Under higher grademetamorphism (lower greenschist facies and above)arsenian pyrite in carbonaceous shales was convertedto pyrrhotite. These processes were critical in the releaseof gold, tellurium and arsenic from the black shales tobecome concentrated by hydrothermal processes, locallyto ore grades, in structural sites such as fold and shearzones (Sukhoi Log) or breccia zones (Kumtor) within orabove the black shale sequence.

This research was achieved with support from themining companies at Sukhoi Log and Kumtor.

Large, R. R., Danyushevsky, L. V., Hollit, C., Maslennikov, V. V.,

Meffre, S. C., Bull, S., Scott, R., Emsbo, P., Thomas, H., Singh, B.

and Forster J. 2009. Gold and trace element zonation in pyrite

using a laser imaging technique: implication for the timing of gold

in orogenic and Carlin-style sediment-hosted deposits. Econ. Geol.,

104, 635–638.

Large, R. R., Maslennikov, V. V., Robert, F., Danyushevsky, L. V. and

Chang, Z. 2007. Multistage sedimentary and metamorphic origin

of pyrite and gold in the giant Sukhoi Log deposits, Lena gold

province, Russia. Econ. Geol., 102, 1232–1267.

Multiple sources for mineralising fluids: case studiesMuruntau and Charmitan

T. Graupner1, U. Kempe2, R. Seltmann3

1Federal Institute for Geosciences and Natural Resources(BGR), Stilleweg 2, 30655 Hannover, Germany (torsten.graupner@bgr.de)2Institute of Mineralogy, TU Bergakademie Freiberg,Brennhausgasse 14, 09596 Freiberg, Germany3Centre for Russian and Central EurAsian MineralStudies (CERCAMS), Department of Mineralogy,Natural History Museum, London SW7 5BD, CromwellRoad, UK

Verification of sources for giant gold deposits is crucialfor the development of appropriate exploration modelsand strategies. There are two aspects to be considered inthis respect: (i) verification of the gold source itself and(ii) determination of the ‘driving force’ for the enrich-ment of gold up to economically significant ore gradesand recoverable tonnages. The latter means a determi-nation of the nature of the gold-bearing fluids in mostcases. Whereas it is still difficult to constrain the goldsource(s) directly, results of modern analytical methodsgive a good basis for understanding the formation andevolution of the related ore-forming fluids.

The latter point is examined in more detail for theworld-class gold deposits of Muruntau (Kyzylkum,Western Uzbekistan) and Charmitan (Nuratau, Cen-tral Uzbekistan), which are both located within theSouth Tien Shan orogenic belt (Khamrabaev et al.,1971). Samples from other gold systems located in thisbelt (Kumtor, Kyrgyzstan; Amantaitau, Uzbekistan) areused for comparative purposes.

Investigation of vein mineralisation by modernmicroscopic and fluid inclusion techniques, micro-beamchemical analysis, isotope methods and luminescencespectroscopy strongly suggests that fluids from multiplesources took part in the formation of both, Muruntauand Charmitan deposits. Geological position and

geochronology (Seltmann et al., 2010) point to a genesiswithin the framework of late collisional magmaticactivity (Re–Os sulphide and U–Pb zircon SHRIMPages define a narrow interval of time about 290–285 Ma). The most intriguing aspect, however, is theinvolvement of mantle-related sources clearly indicatedby noble gas (He, Ar) analysis notwithstanding the felsicstyle of the magmatism at this time (Graupner et al.,2006; 2010).

The consequences for exploration strategies within theorogenic belt under consideration and beyond arediscussed.

Graupner, T., Niedermann, S., Kempe, U., Klemd, R. and Bechtel, A.

2006. Origin of ore fluids in the Muruntau gold system:

constraints from noble gas, carbon isotope and halogen data.

Geochim. Cosmochim. Acta, 70, 5356–5370.

Graupner T., Niedermann, S., Rhede, D., Kempe, U., Seltmann, R.,

Williams, C. T. and Klemd, R. 2010. Multiple sources for

mineralizing fluids in the Charmitan gold (-tungsten) mineraliza-

tion (Uzbekistan), Mineral. Dep., 45, 667–682.

Khamrabaev, I. Kh., et al. 1971. Some geologic and mineralogic

characteristics of the gold ore deposit of Charmitan, western

Uzbekistan, Uzb. Geol. Zhur, 1–7.

Seltmann, R., Konopelko. D., Biske, G., Divaev, F. and Sergeev, S.

2010. Hercynian post-collisional magmatism in the context of

Paleozoic magmatic evolution of the Tien Shan orogenic belt.

J. Asian Earth Sci., doi:10?1016/j.jseaes.2010?08?016.

The volcanogenic massive sulphide giants of centralEurasiaR. J. Herrington1, S. Mills2, C. Halls1

1The Natural History Museum, London, UK(R.Herrington@nhm.ac.uk)2Redback Mining, Vancouver, Canada

This presentation will review the major VMS camps ofthe Uralides, the Rudny Altai, the Khandiza district ofUzbekistan as well as the Kyzyl Tashtyg deposit in Tuvaand the giant Ozernoe camp in Buryatia (see Fig. 1).

Crustal growth and continental construction an exampleof the Central Asian Orgenic BeltK. Schulmann1, J. Lehmann2, O. Lexa3

1 Major arc systems of Central Eurasia with the location

of key deposts highlighted

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1IPGS, UMR 7516, Universite de Strasbourg, F-67084Strasbourg, France (schulman@unistra.fr)2Czech Geological Survey, Prague 1, Klarov 3, 11000,Czech Republic3Charles University, IPSG, Albertov 6, 128 43, Prague,Czech Republic

We discuss a new concept of continental growthexemplified by the structure of the Central AsianOrogenic Belt in Mongolia, which represents the largestaccretionary orogenic belt on the Earth. This work isbased on a combination of geological, geochronologicaland geochemical data which show that the developmentof this crust was episodic, with one peak (centred at530 Ma) representing a period of acceleration accretionvia the obduction process, another peak correspondingto a period of massive addition of juvenile continentalmaterial (420–300 Ma). This period is associated withthe formation of oceanic crust which was laterincorporated into the Euroasian continent. The crustalgrowth event is responsible for the origin of N–Strending magmatic arcs and back arcs and subductionzones parallel to continental ribbons. Finally, during thethird distinct event (290 to 270 Ma), the Belt wasassembled by the accretion of previously grown crustonto the continental blocks associated with magmaticreworking and crustal reworking. Abundant orogenicgranites were intruded at this stage. We argue that thecrust was constructed via Permo-Triassic oroclinalbending mechanism pulse during which major part ofAsian continent was assembled. The new model isproposed as an alternative to existing tectonic models ofaccretion of CAOB proposed earlier and provides amechanistic explanation of oroclinal bending processwhich is not satisfactorily explained so far. We arguethat the CAOB continental crust was constructed in anextremely short period of time during which thedeformation was dominated by crustal scale folding.The orientation of the N–S trending large-scale aniso-tropic system (inherited from crustal growth stage)represented by Mongol-Okhotsk subduction zone,Dabzkhan-Baydrag continental ribbon, compressional(Gobi-Altay magmatic arcs) and N-S trending oceanicdomain of the Trans-Altay Zone. This complex systemwas subparallel to the Permo-Mesozoic orientation ofplate tectonic stress that enabled the crust to behave as amultilayer system. This configuration allowed the crustto deform by folding at a relatively low stress andprecluded the formation of localised subduction zoneperpendicular to the original mechanical anisotropyuntil the folds locked up. The mechanical activity alongthe subduction zone parallel to the mechanical aniso-tropy in the core of the fold is considered to be the mainaccommodating mechanism that facilitates this folding.This model proposes a unified theory of deformationand accretion of oceanic crust using three contrastingmechanisms. (1) The Mongol-Okhotsk oceanic domainin the inner part of the fold is closed due to lateralshortening and gravity driven pull of progressivelysteepened subduction zone. (2) The Dabzkhan-Baydragribbon and steeply folded passive margin reveal classicalflexural slip/flow folding accompanied by developmentof steep crustal crenulation cleavage and folds with steephinges. (3) The westerly oceanic domain accommodatesfolding of inner arc by reactivation of transform faults

and passive folding mechanism i.e. translation of rigidoceanic blocks parallel to strike slips. The presentedmodel is conserving volume in the oceanic domain of theTrans Altai Zone, Gobi Altai Zone and Dabzkhancontinent but is marked by loss of material in the innerpart of the fold structure – the Mongol Okhotsk Oceanwhich is the major pre-requisite of oroclinal bending.

Uranium potential of CIS and Mongolia: with emphasison volcanic related deposits

M. Cuney

G2R, Nancy-Universite, CNRS, CREGU, B.P. 239,54506 Vandoeuvre les Nancy, France(Michel.cuney@g2r.uhp-nancy.fr)

The largest uranium resources of the Commonwealth ofIndependent States (CIS) and Mongolia are located in theso- called ‘Central Asia Uranium Province’ (CAUP),distributed around the Altai Mountains. The CAUPrepresents the second largest U province of the world withnearly 1/4 of the world U resources. The most significantdeposits occur in Kazakhstan, Uzbekistan, SouthernSiberia, Mongolia, and extend in northern China. Iden-tified Resources reaches 1?3 Mt U at 130 US$/kg U with652 000 t U in Kazakhstan, 480 000 t U in Russia,115 000 t U in Uzbekistan, 50 000 t U in Mongolia(IAEA, 2009). Total production of CAUP has reachedone-third of the world production in 2008 and Kazakhstanis now the leading U producing country in the world.

Uranium deposit types are dominated by those relatedto meteoric water infiltration systems in continentalsandstone: predominantly of roll front subtype (inKazakhstan, Uzbekistan, Mongolia, Inner Mongolia)and of palaeovalley subtype of much lesser importance(Vitim, Russia; NW Mongolia), and to hydrothermalhigh level postorogenic systems developed in volcaniccaldera (Streltsovka, Russia; Dornot and others inMongolia, and also some in northern Kazakhstan)according to the genetic classification of Cuney (2009).Another major deposit, Elkon in Russia associated withK-metasomatism belongs to a rather unique model, stillpoorly known. The CAUP has the specificity to be avery young U province compared to most others (e.g.Australia, Canada) which are rooted in Archaean toPalaeoproterozoic domains (Cuney, 2010). The main Usource for CAUP deposits is recent intrusive to effusive(as ignimbrites or as volcanic ash deposited in con-tinental sandstones) highly fractionated magmatism,mainly of peralkaline (A1 type) and high-K calc-alkaline(A2 type) nature massively produced within a widenearly EW extensional domain, exceeding 1000 km fromTransbaıkalia in Russia to Northern China. Nearly allthese deposits have been formed from Cretaceous toCainozoic. The main reducing trap was considered to bedetrital continental plants disseminated within thesandstone, but increasing evidences are in favour ofthe involvement of reducing gas infiltration from deepseated oil/gas reservoir Cai et al. 2007.

The giant U deposits in the CAUP according tothe definition of Laznicka (1983), with a tonnageaccumulation index: t.a.i.5quantity of accumulatedore metal (potentially economic)/mean crustal content(Clarke) higher than 1011, are the Inkai and Mynkudukroll front deposits in Kazakhstan. Other giants Udeposits correspond in fact to a series of small depositsbelonging to large regional structures extending over a

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few tens to several tens of kilometres such as the Elkondistrict in Aldan, the Streltsovka and the Dornotcaldera systems. Considered as a whole and includingprognosticated resources, the roll front district ofsouthern central Kazhakstan (Shu Sarysu andSyrdarya basins) potentially represent a supergiant Uaccumulation (t.a.i..1012).

Cai, C., Li, H., Qin, M., Luo, X., Wang , F., Ou, G. (2007). Biogenic

and petroleum-related ore-forming processes in Dongsheng

uranium deposit, NW China. Ore Geol Rev 32, 262–274.

Cuney, M. (2009) The extreme diversity of uranium deposits. Min.

Deposit, 44, 3–9.

Cuney, M. (2010). Evolution of uranium fractionation processes

through time: driving the secular variation of uranium deposit

types. Econ. Geol., 105(3), 449–465.

IAEA (2009) Uranium 2009 - Resources, production and demand.

NEA/OCDE - International Atomic Energy Agency. 454 p.

Laznicka, P. (1983) Giant ore deposits: A quantitative approach:

Global Tectonics and Metallurgy. 2, 41–63.

The Noril’sk model and its application in the Emeishanand Tarim basin areas of China

A. J. Naldrett1, X.-Y. Song2, H. Zhong2

1University of Toronto, Canada, CERCAMS NHMLondon, UK (ajnaldrett@yahoo.com)2SKLODG, Institute of Geochemistry, Chinese Academyof Sciences, Guiyang, Guizhou, China

The objective of this paper is to discuss key aspects ofthe Siberian Permo-Triassic (250 Ma) Large IgneousProvince (SLIP) relating to the development of theNoril’sk-Talnakh Ni–Cu–PGE ores and evaluate twoother Asian LIPs of similar age, the Emeishan (ELIP)(5257–263 Ma) and Tarim (TLIP) (5285–292 Ma). TheSLIP originally covered an area of 4?56106 km2,whereas the other two are an order of magnitude lessextensive (ELIP>6105 km2; TLIP52?56105 km2).

In the Noril’sk region of the SLIP the basalts stand upas mesas above the underlying sediments. A 500 m basalsuccession of Ti-rich (Ti/Y.440), high Gd/Yb (52–3)olivine-normative basalts (some of which are alkalic) aresucceeded by 3000 m of low Ti (Ti/Y 250–440), low Gd/Yb (,2), low La/Sm (,2?8), low 87/86Sri (50?7053–0?7062), variable eNd (524?6 to z7?3) largely olivinenormative basalts, some of which have high La/Sm (2?6–4?7), low eNd (27 to 28?5) and high 87/86Sri (50?7075–0?7090) that is attributed to contamination by a crustalpartial melt. Picritic basalts occur in two units of theNoril’sk succession. Average Mg#s for the differentbasaltic units range from 53 to 62.

The ELIP is well exposed in upfolds and faultingcaused by the Himalayan event impacting the Yangtsecraton. The central part of the ELIP is characterised bytwo units of Ti-poor (Ti/Y5285–426), olivine- andquartz-normative basalts with Gd/Yb52?1–2?7, variableLa/Sm51?4–4?1, and relatively low 87/86Sri (50?7053–0?7067) that are capped by Ti-rich (Ti/Y5449–773),Gd/Yb52?5–3?5, 87/86Sri50?7039–0?7069. A sequence ofalkalic, nepheline-normative basalts forms the base of theELIP succession in places, and much of the outer zone tothe east comprises Ti-rich basalt. Picritic rocks occur inthe central part of the ELIP, some of which have aferropicritic composition. Mg#s for the basalts aremostly ,50, except for the lower of the two Ti-poor units.

Much of the TLIP is covered by younger rocks andinformation is restricted to the peripheries of the regionunderlain by basalt. Ti/Y ratios tend to be high (.500),

Gd/Yb.2 and La/Sm ratios vary from 3 to 5. Isotopicwork is limited, but one group has been identified with87/86Sri50?705–0?708, eNd522 to 25 and another with87/86Sri50?703–0?706, eNd5z3 to z5. Mg#s are mostlybetween 35 and 45. Some associated ultramafic dykeshave been observed.

At Noril’sk the basalts overly a sequence of Silurianshales, Devonian shales and anhydrite beds, LowerCarboniferous limestones and Upper Carboniferouscoal measures. The ores occur within intrusions in theunderlying shales, anhydrite beds and coal measures thathave been interpreted as feeders to the overlyingvolcanics. The intrusions are exposed, or brought toaccessible depths as a result of anticlinal structures thathave resulted in the lavas being removed by erosion. A500 m sequence within the overlying volcanics isremarkably depleted in Ni, Cu and PGE, as isdemonstrated by plots of Ni/MgO versus MgO, Cu/Zrversus MgO and Cu/Pd versus Pd, and the missingmetals are regarded as the source of those forming theores. The current model for Noril’sk is that fertilemagma generated from a plume became ponded in amidcrustal magma chamber, interacted with a partialcrustal melt, became sulphide saturated, deposited poolsof sulphide, and reached the surface, depleted inchalcophile metals and bearing the traces of crustalcontamination. The interaction of a continuing flow ofundepleted, sulphide-unsaturated magma through theconduit with the early formed sulphide, resulted in FeSbeing removed from and Ni, Cu and PGE added to thesulphide. Subsequent magmas equilibrating and dissol-ving these enriched sulphides became highly enrichedthemselves in these metals. These continued closer tosurface where they interacted with the anhydrite bedsand became sulphide-saturated, depositing the rich ores.

Turning to the ELIP, the bulk of the mineralisationoccurs in the central region where faulting associated withthe Himalayan event has brought the underlying base-ment to surface. Three principal types of mineralisationare found, world-class Fe–Ti–V deposits, small Ni–Cusulphide deposits and low-sulphide PGE-rich deposits. Inone case (Xinjie) the intrusion, that is thought to havebeen derived from a ferropicritic magma, hosts both Fe–Ti–V and PGE–Ni–Cu deposits. Jinbaoshan is typical ofthe sulphide-poor, PGE-rich type; mineralisation occursin wherlite that occupies a magma conduit, and its PGE-rich character is attributed to upgrading of sulphides bysuccessive waves of magma flowing through the conduit.The Limahe deposit is typical of the Ni–Cu type, wheresulphides are concentrated towards the base of a multi-phase intrusion in rocks thought to have been derivedfrom picritic magma that had gained sulphur throughreaction with country rocks.

Several deposits occur in the region of the TLIPincluding Kalatongke, the largest, but their structuralsetting and/or geochemistry of associated rocks ruleout any direct genetic connection. Most of them arethought to be associated with the emplacement ofmafic/ultramafic rocks in a post-collisional tectonicenvironment.

The basalts of the ELIP and TLIP have beenevaluated in terms of the chalcophile depletion criteriathat are so prominent at Noril’sk. Relatively few of theanalysed samples of basalt from the central ELIP showup as depleted on the Ni/MgO versus MgO plot,

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whereas more than half show up as depleted on the Cu/Zr and Cu/Pd plots. In the Tarim area, data are sparseand more scattered, with no PGE results available atpresent. Basalts and mafic dykes from the western tonorthwestern part of the TLIP appear depleted on a Ni/MgO versus MgO plot, and all rocks appear depleted ona Cu/Zr plot. The latter may be due to assuming that theundepleted Cu/Zr ratios that are characteristic of thebasalts at Noril’sk are the same for rocks of the TarimLIP.

In general, the massive chalcophile depletion thatcharacterises a 500 m succession of basalts at Noril’skhas not been confirmed in the ELIP and TLIP.Depletion is present in the latter two provinces, but itis more localised and less extreme. Further investigation,particularly of the TLIP, may change this conclusion.

Almalyk district and its porphyry epithermal depositsR. Seltmann1, R. Creaser2, R. Koneev3, V. Shatov4,D. Konopelko5

1Centre for Russian and Central EurAsian MineralStudies (CERCAMS), Department of Mineralogy,Natural History Museum, London, UK(R.Seltmann@nhm.ac.uk)2University of Alberta, Edmonton, Alberta, Canada3National University of Uzbekistan, Tashkent,Uzbekistan4VSEGEI, St. Petersburg, Russia5St. Petersburg State University, St. Petersburg, Russia

The Almalyk porphyry Cu–Au system of easternUzbekistan encompasses the giant ore deposits atKal’makyr (2?5 Gt at 0?38% Cu, 0?5 g t–1 Au) andDalnee (2?8 Gt at 0?36% Cu, 0?35 g t–1 Au). TheSarycheku orebody (200 Mt at 0?5% Cu, 0?1 g t–1 Au) ispart of the Saukbulak porphyry Cu–Au system, some18 km to the south. Both systems are associated with thesecond, Middle- to Late-Carboniferous, pulse of magmaticactivity within the Devonian-Carboniferous Valerianov-Bel’tau-Kurama volcano-plutonic belt that is the mainelement of the Middle Tien Shan terrane in Central Asia.Previous K–Ar dating of the ore-related porphyryintrusive and the mineralisation has returned ages in therange of 310 to 290 Ma, whereas recent U-Pb zircon datingreported for the intrusive sequence in the Almalyk districtpartially overlaps in the range of 320 to 305 Ma, with ore-related porphyries 315 to 319 Ma. Re–Os molybdenitedating resulted in ages at about 314 to 316 Ma.

Mineralisation at both Kal’makyr and Dalnee ispredominantly in the form of stockworks with lesserdisseminations, and is associated with Late Carboni-ferous quartz monzonite porphyry plugs intrudingearlier dioritic and monzonitic intrusive rocks of thesame magmatic complex. The orebodies take the formof a cap-like shell developed above and draped over theflanks of the related quartz monzonite porphyry stock.The dominant hosts to ore are the monzonite anddiorite wall rocks, with the quartz monzonite porphyryonly containing ore in its outer margins, surroundingand/or overlying a barren core. The focus of stockworkdevelopment is fracturing related to both the intrusivecontact of the porphyry stock and to crosscuttingfaulting. Alteration comprises an early K-silicate phasefollowed by albite-actinolite and peripheral epidote-chlorite-carbonate-pyrite propylites, overprinted by anabundant phyllic episode which is closely related to the

final distribution of the ore. Associated mineralisationcommenced with barren quartz-hematite veining,followed by quartz-magnetite, quartz-pyrite-molybde-nite-chalcopyrite with the bulk of the contained gold,quartz-carbonate-polysulphide with lesser gold, then byzeolite-anhydrite, and finally carbonate and barite vein-ing. Subsequent oxidation and uplift developed a layer ofoxide ore, a limited leached cap and supergene sulphideenrichment, largely in zones of fault related fracturing.

Golovanov, I. M., Seltmann, R. and Kremenetsky, A. A. 2005. The

Porphyry Cu-Au/Mo Deposits of Central Eurasia: 2. The

Almalyk (Kal’makyr-Dalnee) and Saukbulak Cu-Au Porphyry

Systems, Uzbekistan, in Super porphyry copper & gold deposits:

a global perspective, (ed. T. M. Porter), Vol. 2, 513–523;

Adelaide, PGC Publishing.

Oyu Tolgoi and porphyries of South Mongolia

R. N. Armstrong1, R. Seltmann1, D. Crane2 the CercamsTeam1CERCAMS, Department of Mineralogy, The NaturalHistory Museum, London SW7 5BD, UK(R.Armstrong@nhm.ac.uk)2Ivanhoe Mines Mongolia Inc., Mongolia

The South Gobi Region of Mongolia is composed of aseries of Island Arc terranes including the extensiveGurvansayhan terrane (Badarch et al., 2002). Theregion contains 82 known porphyry style deposits andoccurrences including the deposits of the Oyu Tolgoidistrict (Gerel et al., 2010). The majority of theseoccurrences and deposits are coincidental with a strongSW–NE striking magnetic high anomaly at easternmargin of the Gurvansayhan terrane. The East Mon-golian Fault, a major tectonic feature of the region,delineates the eastern boundary of this terrane. Re-gional sampling completed during the Altaids Projecthas demonstrated through the application of wholerock Nd/Sm and Lu/Hf measurements from zirconsthat the melt sources for the granitoids of the region isprimitive with no contribution from cratonic crystal-line basement. Existing and new chronological datademonstrate two clear periods of porphyry mineralisa-tion, the Famennian which includes Oyu Tolgoi andTsagaan Suvarga, and the Serpukhovian-Visean whichincludes the Shuuten and Kharmagtai Cu–Mo–Auprospects. Whole rock chemistry from the granitoidsregion shows that the intrusions from the UpperDevonian to the Upper Carboniferious have strong I-type and primitive volcanic arc affinities. Furthermore,the REE chemistry from the intrusions suggests thathornblende crystallisation was a significant control inthe evolution of these magmas. Intrusions of lowerPermian age in the region possess A-type like signa-tures and are significantly more fractionated suggestingthat these magmas are related to post-subductionmagmatic processes.

The Oyu Tolgoi mineral district strikes NNE for over22 km and includes the named mineralised centres fromnorth to south of Heruga, South Oyu Tolgoi, SW OyuTolgoi, Hugo Dummett South, Hugo Dummett Northto the Ulan Kud. The current measured and indicatedresource for the camp is 1390 Mt at 1?33% Cu, 0?47 g t–1

Au, and an inferred resource of 2200 Mt at 0?83% Cu,0?37 g t–1 Au (at 0?6% Cu equiv. cut-off) (Khashgerel

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et al., 2009). Within the Oyu Tolgoi deposits the mostsignificant porphyry style mineralisation is spatially andtemporally associated with quart-monzodiorites dykes.At Central Oyu Tolgoi and the Hugo Dummett depositsCu and Au-rich high sulphidation style mineralisationhas partially telescoped on to underlying Cu–AuPorphyries. These mineralising intrusions are cross-cutby later biotite-granodiorites.

Badarch, G., Cunningham, W. D. and Windley, B. F. 2002. A new

terrane subdivision for Mongolia; implications for the

Phanerozoic crustal growth of Central Asia, J. Asian Earth Sci.,

21, (1), 87–110.

Gerel, O., Amar-Amgalan, S., Oyungerel, S., Myagmarsuren, S.,

Kirwin, D., Armstrong, R., Herrington, R. and Seltmann, R.

2010. GIS of the Granitoid petrology, tectonics and mineral

deposits of Mongolia in Mineral Deposit Research: Meeting the

Global Challenge (ed. J. Mao and F. P. Bierlein), The Natural

History Museum London.

Khashgerel, B.-E., Rye, R. O., Kavalieris, I. and Hayashi, K.-I. 2009.

The sericitic to advanced argillic transition: stable isotope and

mineralogical characteristics from the Hugo Dummett porphyry

Cu-Au deposit, Oyu Tolgoi District, Mongolia, Econ. Geol., 104,

1087–1110.

Taldybulak Au–Cu–Mo deposit: a new .5 Moz Au(11?7 Moz Au eq) ordovician porphyry hosted gold systemin Kyrgyzstan, Central AsiaA. Yakubchuk1, J. Schloderer2, J. Woodcock3,A. Wurst4

1Orsu Metals Corporation, London, UK (ayakubchuk@orsumetals.com)2Gold Fields Limited, Perth, Australia3Gold Fields Limited, Bishkek, Kyrgyzstan4Gold Fields Limited, Denver, USA

The Taldybulak prospect in the Kyrgyz Ridge innorthwestern Kyrgyzstan was originally identified inthe late 1970s during regional search for the Cuporphyry systems in Central Asia, but was abandoneddue to low copper grade, although gold potential inexcess of 0?5 g t–1 was recognised.

From 2006 until 2010, the 40/60 joint venture betweenOrsu Metals Corporation and Gold Fields Limiteddrilled in excess of 30 000 m and delineated a major pit-constrained Au–Cu–Mo resource of 11?7 Moz Au eq atthe Taldybulak deposit. As of September 2010, theTaldybulak deposit consists of an indicated resource of127 Mt, comprising 2?6 Moz gold at 0?64 g t21, 477Mlb copper at 0?17%, and 29?4 Mlb molybdenum at0?01%, and an inferred resource of 296 Mt, comprised of3?71 Moz gold at 0?4 g t21, 1098 Mlb copper at 0?17%,and 69?2 Mlb molybdenum at 0?01%.

The deposit is currently viewed as a Cu2Au2Moporphyry system with superimposed Au-only event,which produced a high-grade gold overprint. Theisotopic dating suggests that formation of the porphyrysystem took place at 475–455 Ma, and it was thenintruded by post-mineral trachyte dykes at 450 Ma.Presence of the Devonian cover was essential inpreservation of the Ordovician system.

An exploration history and evolution of thoughts onthe architecture of the Taldybulak deposit as well asmost recent advances in the understanding of thegeodynamic evolution of the Kyrgyz Ridge against thesetting of the Taldybulak porphyry system will bepresented.

The Koshrabad massif as host of intrusion-related goldmineralisation at Charmitan and Guzumsay: an exampleof post-collisional A-type granites from Southern TienShan, UzbekistanD. Konopelko1, K. Kullerud2, R. Seltmann3, F. Divaev4

1St. Petersburg State University, 7/9 UniversityEmbankment, St. Petersburg 199034, Russia (konopelko@inbox.ru)2University of Tromsoe, Norway3CERCAMS, Natural History Museum, London, UK4Geological Production Association, Tashkent,Uzbekistan

The Koshrabad massif (y200 km2) is situated inNorthern Nurata range, Uzbekistan. It is emplaced inthe Southern Tien Shan fold and thrust belt formed as aresult of the Late Paleozoic collision between theKarakum-Tarim and Palaeo-Kazakhstan continents.The Koshrabad massif and other intrusions ofNorthern Nurata range were recently dated aty285 Ma and defined as Hercynian post-collisionalintrusions (Seltmann et al., 2010). Peculiar features ofthe Koshrabad rocks include their elevated alkalinityand presence of rapakivi-textured varieties. Besides, themassif hosts two large intrusion-related gold depositscontaining y100 tons of gold each (Abzalov, 2007). Inthis paper we present new geochemical data and useexisting analytical data sets to discuss the evolution andpossible sources of the Koshrabad magmas and theorigin of the gold deposits. The Koshrabad rockassemblage includes pyroxene-amphibole¡olivine alka-line gabbro, syenite, monzonite, quartz syenite, grano-syenite and amphibole-biotite granite. Amphibole-biotitequartz syenite and granite with rapakivi texturecomprise 80% at present day erosion surface. Maficrocks, mapped in the central part of the massif,demonstrate signatures of coeval intrusion of meltswith different compositions. All rock-types form dykeswhich are structurally controlled and form two swarmsin the SE part of the massif striking roughly in theeast2west direction. The rocks of Koshrabad are richin FeO, K2O and Na2O, they have extremely high FeO/(FeOzMgO) ratios and low contents of CaO andMgO. They plot into fields of A-type rocks in thediscrimination diagrams. Iron-rich mafic minerals andpresence of olivine indicate reduced nature of the melts.We think that evolution of alkaline mafic melts at mid-crustal levels produced main volume of felsic composi-tions which dominate at present day erosion surface ofthe massif. This evolution probably included assimila-tion of quartzo-feldspathic crustal material. The struc-ture of gold deposits shows that the gold veins wereemplaced in brittle fractures striking in the samedirection as the dyke swarms. Other features of thedeposits are their low sulphide character with main oremineral being pyrite, and lack of significant alterationassociated with the gold veins (Abzalov, 2007). There isa positive correlation of Au contents with SiO2 contentsin the late dykes; this may indicate accumulation ofgold in the reduced melt at the final stages of crystal-lisation and rapid emplacement of Au-rich veins in thesame structures which previously controlled emplace-ment of dykes.

Abzalov, M. 2007. Zarmitan granitoid-hosted gold deposit, Tian Shan

belt, Uzbekistan, Econ. Geol., 102, 519–532.

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Seltmann, R., Konopelko, D., Biske, G., Divaev, F. and Sergeev, S.

2010. Hercynian post-collisional magmatism in the context of

Paleozoic magmatic evolution of the Tien Shan orogenic belt.

J. Asian Earth Sci., doi:10?1016/j.jseaes.2010?08?016.

Exploration potential of the Lena gold fieldsA. Mikhailov1, V. Voitenko2

1SRK Exploration Services Ltd, 16 Park Grove, Cardiff,CF10 3BN, UK (amikhailov@srk.co.uk)2St. Petersburg University, Russia

Unlike most other countries, about 80% of Russian goldwas mined from alluvial deposits. The grade andresources of these alluvial gold deposits were so highthat it detracted attention from primary gold explora-tion. But even the limited amount of exploration thattargeted primary gold deposits had led to the discoveryof a number of world-class deposits: the Lena gold fieldsis one of the best examples. Accumulative gold produc-tion from the Lena gold fields well exceed 30 Moz withless than 1% of gold mined from primary deposits. Thesame time the Lena gold fields contain the biggestRussian gold deposit – Sukhoi Log.

Based on comprehensive data compilation andanalysis it is possible to come to conclusion that theLena gold fields is still underexplored and that it is oneof the most attractive exploration targets in the world.

Benevolskiy, B. I. 2002. Gold of Russia, Moscow, Geoinformmark.

Buryak, V. A. and Khmelevskaya, N. M. 1997. Sukhoy Log, one of the

greatest gold deposits in the world: genesis, distribution patterns,

prospecting criteria, Vladivostok, Dalnauka.

Distler, V. V., Yudovskaya, M. A., Mitrofanov, G. L., Prokof’ev, V. Y.

and Lishnevskiy, E. N. 2004. Geology, composition and genesis

of the Sukhoi Log noble metals deposit, Russia, Ore Geol. Rev.,

24, 7–44.

Kazakevich, Y. P. 1971. Lena gold-bearing region, stratigraphy,

tectonics, magmatism and occurrences of hard rock gold,

Moscow, Nedra Press.

Kuz’min, M. I., Yarmolyuk, V. V., Spiridonov, A. I., Nemerov, V. K.,

Ivanov, A. I. and Mitrofanov, G. L. 2006. Geodynamic setting of

gold ore deposits of the Neoproterozoic Bodaibo trough, Doklady

Earth Sci., 407A, 397–400.

Smirnov, V. I., 1997. Ore deposits of the USSR. London-San

Francisco-Melbourne, Pitman Publishing.

Mineralisation and alteration patterns at the Damanggold mine, Ghana: ore genesis and explorationapplications in tropical terrainsA. J. White1, L. J. Robb1, D. J. Waters1, V. M. Robb2

1Oxford Centre for Tectonics and Metallogenic Studies,Department of Earth Sciences, University of Oxford,South Parks Road, Oxford, OX1 3AN, UK (alistair.white@earth.ox.ac.uk)211 The Green, Ascott-under-Wychwood, OX7 6AB, UK

Mineralisation at Damang mine is significantly differentto most other known orogenic gold deposits of Ghana,comprising two distinct styles of mineralisation – astratigraphically controlled quartz-pebble conglomeratepalaeoplacer deposit overprinted by later orogenic goldmineralisation hosted in flat-dipping fault-fracture veinarray and surrounding hydrothermal alteration assem-blages (Tunks et al., 2004).

The host Tarkwaian stratigraphy comprises anupward-fining sequence of clastic sediments intruded bydoleritic dykes and sills, all overprinted before miner-alisation by amphibolite facies mineral assemblages. Apotassic alteration signature during mineralisation,

accompanied by the extensive development of sulphideand carbonate phases, suggests that the mineralising fluidwas similar to that responsible for other Birimian-hostedorogenic gold deposits in Ghana and indeed otherorogenic gold deposits globally (Goldfarb et al., 2005).This implies that the Tarkwaian of Ghana is alsoprospective for gold mineralisation.

Limited exposure in a tropical terrain providesspecific challenges to a better understanding of theDamang ore genesis. The lack of a major, large-scalestructural control on the Damang deposit introducescomplications to traditional geophysical explorationmethodologies. At Damang however, portable, field-based infrared reflectance spectroscopy has been usedin a systematic study and has proven to be a valuableexploration tool (White et al., 2010). Sedimentary andigneous lithological groups are readily distinguishedusing diagnostic spectral parameters, such as theferrous-iron response, the AlOH/H2O absorption dep-th ratio, and automated mineral identification. Vectorsto gold mineralisation are provided by systematicvariations to these parameters, observable both down-hole and in 3D models. The speed of data collectionand ease of analysis of spectral data make infraredreflectance spectroscopy a useful methodology thatcan be readily incorporated into both pre-existing andestablished exploration programs in other tropicalterrains.

Goldfarb, R., Baker, T., Dube, B., Groves, D. I., Hart, C. J. R. and

Gosselin P. 2005. Distribution, character, and genesis of gold

deposits in metamorphic terranes, Econ. Geol. 100th Ann. Vol.,

407–450.

Tunks, A. J., Selley, D., Rogers, J. R. and Brabham, G. 2004. Vein

mineralization at the Damang Gold Mine, Ghana: controls on

mineralization, J. Struct. Geol., 26, 1257–1273.

White, A., Robb, V. M., Robb, L. J., Waters, D. J. et al. 2010. Portable

infrared spectroscopy as a tool for the exploration of gold

deposits in tropical terrains: a case study at the Damang deposit,

Ghana, Soc. Econ. Geol. Spec. Publ., 15, 67–84.

The role of regolith mapping in gold exploration in deeplyweathered terrains of West Africa

E. Arhin, G. R. T. Jenkin, D. W. Cunningham

Geology Department, University of Leicester, UniversityRoad, Leicester, LE1 7RH, UK (ea163@le.ac.uk)

Gold discovery, particularly in the tropical regions, hasdeclined over the past two decades. In part this isbecause the conventional geochemical explorationapproach is best suited to areas with outcrop and somedegree of exposure and less successful in detectingmineralisation under cover. The geochemical expressionof mineralisation in areas where tropical weatheringprocesses have developed complex regoliths are com-monly variable anomalies or mixed signals consisting ofweak, subtle and highly discontinuous anomalies whichare difficult to interpret. Gold occurrence in the savannaareas of Ghana was reported in 1937 but subsequentexploration failures may be linked to a lack of regolithstudies (e.g. Griffis et al., 2002; Arhin and Nude, 2009).Despite the inadequate knowledge of the regolithenvironment some gold discoveries have been made(e.g. Ashanti-AGEM Alliance). However, furtherexploration was discontinued as anticipated depositsizes were disappointing. Recently, Azumah Resources

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commenced a new geochemical sampling programmeand exploration re-assessment. Their work highlightedthe importance of understanding and modelling rego-lith impacts on geochemistry. Regolith terrain mapswere produced by remote sensing with no groundtruthing. The regolith terrain maps fail to clearlydistinguish between transported and residual regolithsbut did yield new geochemical targets. The presentresearch seeks to generate a detailed regolith map byprocessing digital terrain data (e.g. SRTM/DEMmodels, landsat, ASTER and radiometric) complemen-ted by ground truth mapping. Recent mapping cha-racterised regolith stratigraphy and established geneticand geomorphological models for varying regolithtypes.

Arhin, E. and Nude, P. M. 2009. Significance of regolith mapping and

its implication for gold exploration in northern Ghana: a case

study at Tinga and Kunche. Geochemistry: exploration, environ-

ment and analysis. Geol. Soc. Lond., 9, 63–69.

Griffis, J., Barning, K., Agezo, F. and Akosah, F. 2002. Gold deposits

of Ghana, prepared on behalf of Ghana Mineral Commission,

Accra, Ghana.

Diagenetic study of the host rocks of the Kipushi oredeposit, Democratic Republic of Congo

J. van Wilderode1, W. Heijlen2, Ph. Muchez1, D. DeMuynck3, J. Schneider1, F. Vanhaecke3

1Geodynamics and Geofluids Research Group,Department of Earth and Environmental Sciences,K.U.Leuven, Celestijnenlaan 200E, B-3001 Leuven,Belgium (jorik.vanwilderode@ees.kuleuven.be)2GF Consult bvba, Antwerpsesteenweg 644, B-9040Ghent, Belgium3Department of Analytical Chemistry, U. Ghent,Krijgslaan 281-S12, B-9000 Ghent, Belgium

The vein-type Kipushi Cu2Zn deposit is located in theCentral African Copperbelt, Democratic Republic ofCongo. The aim of the present study is to investigate theinfluence of the mineralisation on the dolomite hostrocks using a combination of petrographic techniquesand both stable and radiogenic isotope analysis.

The petrographic study (transmitted and incidentlight microscopy, cathodoluminescence and SEM-ima-ging techniques) quantified the relative abundance ofdiagenetic carbonate and silicate phases in the hostrocks (Nguba Group, Katanga Supergroup). The resultsshow an erratic and lithostratigraphic controlled varia-tion of their distribution, without obvious trendstowards the ore body.

Most host rock samples have a bulk oxygen isotopiccomposition between 27?50 and 22?54% V-PDB, whichis within or above the range of Neoproterozoic marinedolomites. Given the petrographic observations and thegeological context, this suggests that the host rockdolomites formed by reflux dolomitisation. A few sampleshave depleted d18O values (down to 29?9% V-PDB).They could reflect the influence of a fluid with a lowerd18O composition or recrystallisation at higher tempera-tures in a more open geochemical system. However, theselower d18O values do not show a clear spatial correlationwith the mineralisation.

All carbon isotopic signatures lie within the range ofNeoproterozoic marine dolomites (21?46,d13C,z

3?44% V-PDB). However, the most negative valuesoccur in more carbonaceous lithologies, indicating astratigraphic control on the carbon isotopic signature.

The host rock samples have a strontium isotopiccomposition that lies within or above the range ofNeoproterozoic marine carbonates (0?7056,87Sr/86Sr,0?7087 (Jacobsen and Kaufman, 1999). Radiogenicsignatures between 0?7087 and 0?77788 represent impuredolomites. A 87Sr/86Sr–87Rb/86Sr diagram indicates apossible stratigraphic control on the strontium isotopiccomposition. There is no spatial relation between theseresults and the presence of the ore body.

In conclusion, the petrographic observations and theoxygen, carbon and strontium isotopic analyses suggestthat the sulphide mineralisation had no widespreadinfluence on the diagenetic evolution of the dolomitehost rocks.

Jacobsen, S. B. and Kaufman, A. J. 1999. The Sr, C and O isotopic

evolution of Neoproterozoic seawater. Chem. Geol., 161, 37–

57.

Uranium mineralisation at the Lumwana Cu (¡Co)deposits: evidence of initial mineralisation subsequentlyremobilisedJ. P. Nowecki1, S. Roberts1, M. Richards2,M. McGloin3

1School of Ocean and Earth Science, NationalOceanography Centre, University of Southampton,European Way, Southampton, SO14 3ZH, UK(jpn205@soton.ac.uk)2Equinox Minerals PLC, Ground Floor, Scott House, 46–50 Kings Park Road, West Perth, WA, 6005, Australia3School of Geosciences, Building 28, Monash University,Clayton, Victoria, 3800, Australia

The Lumwana Cu (¡Co ¡U) deposits of NW Zambiaare large, tabular, disseminated ore bodies, hostedwithin the Mwombezhi Dome of the Lufilian Arc. Thehost rocks to the Lumwana deposits are typicallygneisses, which comprise quartz-feldspar¡muscovite¡-biotite/phlogopite¡hematite. Sulphide ore horizons aredeveloped within a muscovite-phlogopite-quartz-kyanite‘ore schist’. Contacts between the ore and host rocks aretransitional and characterised by a loss of feldspar.Kinematic indicators suggest a top-to-the-north shearsense, with sulphides deformed by an S1 fabric andsubsequently enclosed within kyanite or concentratedinto low strain zones and pressure shadows aroundkyanite porphyroblasts, suggesting that the coppermineralisation was introduced either syn or pre-peakmetamorphism.

Uranium mineralisation within the Lumwanadeposits is located on the boundaries between hangingwall and footwall gneiss units and the ore schist inorebodies elongated in a north-south direction con-sistent with the S1 fabric and stretching lineation. Twotypes of uranium mineralisation are observed: Ura-ninite and brannerite grains and aggregates areenclosed and sheared within the S1 fabric, indicatingthat initial uranium mineralisation predates the maindeformational phase. SEM reveals a relationshipbetween this early uranium enrichment and zircon,rutile, ilmenite and apatite formation, with REE-richcarbonates and phosphates. These phases can be

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observed enclosed within kyanite and copper sul-phides, indicating initial uranium enrichmentoccurred before the copper-mineralising event.Brannerite has been remobilised, showing progres-sively U-depleted edges, leaving Ti as rutile rims. U isremobilised as uraninite and coffinite in mica clea-vages, grain boundaries, and within retrogressivechlorite. Fluid inclusions in early quartz boudinsand discordant veins (which locally remobilise sul-phides) are sheared, necked-down and decrepitated.Decrepitated primary inclusions show a variety ofdaughter minerals indicating passage of highly salinefluid through the shear zone, similar to that reportedat the Nchanga and Kansanshi deposits. These veinsalso show an overprint of a fluid contained in laterdiscordant veins, which most likely remobilised theuranium. This fluid is moderately saline (y15 wt-%NaCl equiv.) with minor CO2 and first meltingtemperatures about 230uC, indicating a fluid compo-sition of H2O2NaCl2MgCl22KCl¡FeCl2. Homogenisa-tion temperatures are typically 110–270uC. Pressure correc-tion suggests this late fluid formed at around 250–350uCbetween 6 and 9 km depth, consistent with a retrogressive,post-peak metamorphic fluid likely diluted by interactionwith meteoric water.

Micro-analysis of early magmatic Fe(Ni,Cu) sulphideinclusions in the Platreef, northern Bushveld Complex,South AfricaR. E. Jones1, I. McDonald1, H. M. Prichard1, I. B.Butler2, G. Chunnett3, D. A. Holwell41School of Earth and Ocean Sciences, Cardiff University,Main Building, Park Place, Cardiff, Wales, CF10 3AT,UK (JonesRE5@cardiff.ac.uk)2School of Geosciences, University of Edinburgh, GrantInstitute, The King’s Buildings, West Main Road,Edinburgh, EH9 3JW, UK3School of Geosciences, University of the Witwatersrand,Johannesburg, South Africa4Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK

The Platreef, located on the northern limb of theBushveld Complex in South Africa, is one of the largestand most valuable Ni2Cu2PGE orebodies on Earth.The relationship between the Platreef and the mainBushveld stratigraphy is uncertain. The Platreef mayrepresent the northern limb equivalent of the CriticalZone, equating with the Merensky Reef (e.g. Cawthornet al., 2002; Kruger, 2005; Maier et al., 2008) or mayhave formed from a combination of magmas unique tothe northern limb.

The sill-like morphology of the Platreef and theabsence of an overlying magma impose a mass balanceparadox (Lee, 1996) and a staging chamber model(McDonald and Holwell, 2007) was developed in orderto account it. This model can be tested using sulphideinclusions in chromites. These inclusions are proposedto represent the preserved remnants of an early sulphideliquid that was highly enriched in Ni2Cu2PGE and issuggested to have formed in an earlier magma chamberbefore the Platreef magma was intruded.

Using new techniques, the polyphase sulphide inclu-sions are homogenised and analysed by laser ablationICP-MS in order to study PGE tenor variations alongstrike and down-dip across the central Platreef sector

(comprising the farms Zwartfontein, Overysel andSandsloot).

Cawthorn, R. G., Merkle, R. K. W. and Viljoen, M. J. 2002. Platinum-

group element deposits in the Bushveld Complex, South Africa, in

The geology, geochemistry, mineralogy and mineral beneficiation

of platinum-group elements, (ed. L. J. Calbri), Vol. CIM Special

Volume 54, 582; Canadian Institute of Mining, Metallurgy and

Petroleum.

Kruger, F. J. 2005. Filling the Bushveld Complex magma chamber:

lateral expansion, roof and floor interaction, magmatic uncon-

formities, and the formation of giant chromitite, PGE and Ti-V-

magnetitite deposits, Miner. Dep., 40, 451–472.

Maier, W., Klerk, L., Blaine, J., Manyeruke, T., Barnes, S. J., Stevens, M.

and Mavrogenes, J. 2008. Petrogenesis of contact-style PGE

mineralization in the northern lobe of the Bushveld Complex:

comparison of data from the farms Rooipoort, Townlands,

Drenthe and Nonnenwerth, Miner. Dep., 43, 255–280.

Lee, C. A. 1996. A review of mineralization in the Bushveld Complex

and some other layered mafic intrusions, in Layered Intrusions,

(ed. R. G. Cawthorn), 103–146; Amsterdam, Elsevier Science.

McDonald, I. and Holwell, D. A. 2007. Did lower zone magma

conduits store PGE-rich sulphides that were later supplied to the

Platreef? South Afr. J. Geol., 110, 611–616.

Geochronology of granites and gold in the Lupa Goldfield,Southwest TanzaniaC. J. M. Lawley1, D. Selby1, D. J. Condon2, M. S. A.Horstwood2, Q. G. Crowley3, J. Imber1, C. MacKenzie4

1Department of Earth Sciences, Durham University,Science Labs, Durham, DH1 3LE, UK (c.j.lawley@durham.ac.uk)2NERC Isotope Geoscience Laboratory, BritishGeological Survey, Keyworth, NG12 5GG, UK3School of Natural Sciences, Department of Geology,Trinity College, Dublin 2, Ireland4Helio Resources Corp, Suite 580, 625 Howe Street,Vancouver, British Columbia, V6C 2T6, Canada

The Lupa goldfield in southwest Tanzania displays aclear spatial relationship between granites and shear-hosted gold deposits. To evaluate the temporal re-lationship between magmatism and sulphide (Au)mineralisation we present U2Pb zircon and Re2Osmolybdenite geochronology.

LA2ICP2MS U2Pb zircon analysis for the shearedgranitic host of the Kenge deposit provides a weightedaverage 207Pb/206Pb age of 2728¡6 Ma (MSWD55?4;n523). All 24 analyses from 15 zircons possess U2Pbisotopic compositions that overlap with Concordia;however, individual 207Pb/206Pb ages range from 2666to 2753 Ma. This spread of ages may reflect re-workingof zircon in the magmatic system (i.e. inherited zirconswith a range of U-Pb ages), and/or some Pb loss. Incontrast, the sulphide and by inference gold mineralisa-tion at Kenge post-dates the granite host by y700 Myr(Re2Os molybdenite dates5y1939 Ma).

Three other granitoids from the Lupa goldfield weredated by ID-TIMS U2Pb zircon geochronology. TheIlunga granite and a granodiorite dyke that crosscutsthe Archaean granite possess weighted 207Pb/206Pb agesof 1960¡1 Ma (MSWD51?1; n56) and 1960¡1 Ma(MSWD50?4; n52), respectively. The Saza granitepossesses a weighted 207Pb/206Pb age of 1935¡1 Ma(MSWD51?7; n55). This latter age is in close agree-ment with the timing of gold mineralisation as datedby three molybdenite and gold bearing veins fromthe Kenge deposit, which provide a weighted average

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Re2Os molybdenite model age of 1939¡4 Ma (MSWD50?50; n56). This suggests that gold deposition at theKenge deposit was broadly coeval with emplacement ofthe nearby Saza granite and that hydrothermal fluidsrelated to granites could have played an important rolein gold genesis. These results highlight the importanceof combining mineralisation (i.e. Re2Os molybdenite)and magmatic (i.e. U2Pb zircon) geochronology to-wards the understanding of Precambrian shear-hostedgold deposits.

Structural, fluid and geochemical controls of the Tongongold deposit, northern Cote d’Ivoire

C. French1, P. Treloar1, A. Rankin1, D. Lawrence1,Sarah Herbert2, Paul Harbidge2

1Kingston University, Penrhyn Road, Kingston uponThames, Surrey, KT1 2HX, UK (k0849561@kingston.ac.uk)2Randgold Resources (UK) Ltd, 1st Floor, 2 SavoyCourt, Strand, London, WC2R 0EZ, UK

The Birimian of West Africa currently hosts a number ofworld class orogenic gold deposits, and is one of thefastest growing gold producing regions in the world. TheTongon mine is located within the Nielle mining districtnorthern Cote d’Ivoire, with current indicated resourcesof 3?61 Moz gold. Tongon lies within the NNE-trendingBirimian-aged, Senofou volcanic belt which formed atthe margin of the Archaean Sao Luis Craton at ca2?35–2?30 Ga. Belt evolution included emplacement oftonalitic and granodioritic plutons into volcano-sedi-mentary basins. The Senofou belt is dominated by aseries of ENE (060–080) and NE (035–045) trending D1thrust faults. During D2 (2?10–1?98 Ga), the ENE-trending thrusts were dextrally reactivated due to a re-orientation of the principal shortening direction toWNW–ESE. Hydrothermal activity related to miner-alisation was linked to the D2 deformation event.

Tongon hosts two main ore bodies, North Zone (NZ)and South Zone (SZ). These are mineralogically andstructurally distinct. Gold in the NZ is predominatelyoccluded within arsenopyrite or occurs as free goldwithin quartz veins. In the SZ gold is dominantly presentas free gold within quartz or occluded within pyrrhotiteand to a lesser extent arsenopyrite. The NZ ore body islocated within a steeply dipping simple shear zone withcarbonaceous shale (CS) units on both its hanging walland footwall. The carbonaceous shale likely represents areduced buffering system that encouraged gold precipi-tation. The SZ ore body has a ramp flat geometry withinwhich mineralisation was encouraged bvdilation thatwas the result of D2 re-activation. A well constrainedand highly conductive arsenic anomaly extends from thesouth of the permit and lies directly to the SE of bothNZ and SZ, marking a potential fluid pathway.

Preliminary fluid inclusion studies show a dominanceof H2O–NaCl inclusions of low to moderate salinity(12–18 wt-% NaCl equiv.), but with no obvious CO2

present. This is atypical of most orogenic gold depositswhich are sourced by metamorphic fluids. These dataneed to be considered in the context of data fromTreloar et al. (2009) from the Loulo permit of westernMali and Hammond and Robb (2009) from the Moriladeposit of southern Mali each of whom providecompelling evidence to support a significant magmatic

fluid signature linked to orogenic gold mineralisation inthe West African Birimian terrane.

Hammond, N. Q. and Robb, L. 2009. Controls on mineralisation at the

Morila mine, Mali5petrographic, mineral-chemical, isotopic and

fluid aspects. Abstract for Society for Geology Applied to

Mineral Deposits meeting 2009.

Treloar, P. J., Lawrence, D., Rankin, A. H., Harbidge, P. 2009.

Hypersaline metalliferous fluids associated with orogenic gold

deposits in the Loulo mining district, West Mali: significance to

ore genetic model: Goldschmidt 20009 Abstract, Geochim.

Cosmochim. Acta, 73, (13), 1 A1345.

Mineralogical footprints and insights from GarnetChemistry from the Red Lake Gold Mines, NorthwesternOntario, Canada

E. D. Stock, G. M. Dipple, F. Bouzari, R. M. Tosdal

Mineral Deposit Research Unit, Department of Earth andOcean Sciences, University of British Columbia, 6339 StoresRoad, Vancouver, BC, Canada (estock@eos.ubc.ca)

The Archaean Red Lake Gold Mines (40 Mt at20 g t21) in the Superior Province, Canada, is a lode-gold deposit hosted in metamorphosed Mesoarchaeansubmarine tholeiitic and less-common komatiitic basalt(Sanborn-Barrie et al., 2001). Overprinting relation-ships indicate polyphase hydrothermal alteration andmetamorphism. All rocks are metamorphosed; hencehydrothermal alteration reflects pre-metamorphic events(Penczak and Mason, 1997). Despite the complex his-tory, variations in hydrothermal mineral assemblagesand mineral compositions form a regular zonal pattern(Penczak and Mason, 1997; Bouzari et al., 2009). Distalassemblages include albite, pervasive biotite and carbo-nate, and pervasive chloritezamphibole¡epidote. Pro-ximal to ore are carbonate-quartz veins, garnetz-chlorite¡magnetite, carbonate-magnetite veins, alumino-silicate bleaching and silicification. Abundant garnetoccurs proximal to the deposit in a concentrated haloapproximately 500 m from the ore, thus garnet provides apossible indicator mineral.

Garnet ranges from 0?5 to 3 mm in diameter withpoikiloblastic cores. Garnet growth predates ore deposi-tion, and is associated with magnetite, grey birefringentchlorite¡biotite. Ti-magnetite, blue birefringent chlorite,biotite, quartz, carbonate and feldspar are inclusions,whereas quartz-carbonate veins and sulphides overgrowor cut the garnet. Garnet unusually has Mn-rich coresand Fe-enriched rims (Mathieson, 1982) compared tonormal metamorphic garnet in mafic volcanic rocks(Harte and Graham, 1975). Mn is known to preferentiallyconcentrate into garnet (Makanjuola and Howie, 1972).The chemical changes indicate metamorphic growthfollowing Fe and Mn-enrichment during a pre-orehydrothermal event. Subsequent hydrothermal activityformed abundant carbonate-quartz veins, which weresubsequently silicified and overprinted by sulphide-goldmineralisation. Recognition of the early-stage Fe- andMn-enrichment in garnet halos to the ore bodies mayprovide a regional vectoring tool.

Bouzari, F. Tosdal, R. M., Hart, C. J. R., Penczak, R. S., Crick, D.,

Stock, E. and Dipple, G. et al. 2009. Alteration and geochemical

footprints of gold mineralization at Red Lake Mine, Ontario.

Portland GSAAnnual Meeting Abstracts with Programs, 41,

682.

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Mathieson, N. A. 1982. Geology and Mineralization in the area of the

East South ‘C ore zone, Dickenson Mine, Red Lake, Northwestern

Ontario. Unpublished MSc thesis, Queen’s University.

Harte, B. and Graham, C. M. 1975. The graphical analysis of

greenschist to amphibolite facies mineral assemblages in metaba-

sites, J. Petrol., 16, 347–370.

Makanjuola, A. A. and Howie, R. A. 1972. The mineralogy of the

galucophane schists and associated rocks from Ile de Groix,

Brittany, France, Contrib. Miner. Petr., 35, 83–118.

Penczak, R. S. and Mason, R., 1997. Metamorphosed Archean

Epithermal Au-As-Sb-Zn-(Hg) vein mineralization at the

Campbell Mine, Northwestern Ontario, Econ. Geol., 92, 696–719.

Sanborn-Barrie, M., Skulski, T. and Parker, J. 2001. Three hundred

million years of tectonic history recorded by the Red Lake

greenstone belt Ontario, GSC Open File 4594, Current Research,

2001–C19, 1–30.

Reinterpreting the most historically prolific chromitedepositA. Jones1, D. C. Cliff2, L. Hoxha3

1Department of Geology, University of Leicester,Leicester, LE1 7RH, UK (aj112@le.ac.uk)2Empire Mining Corporation 307–475 Howe St,Vancouver, BC, Canada3Empire Mining Albania, Rruga Rerxhepi, Pallati UnikonLati 6-te Ap. 28 Tirana, Albania

Despite the collapse of the communist regime in Albaniasome 20 years ago, Albania is struggling to regain itsstrong hold in the production of high grade chromite.Albania was the third largest producer of chromite inthe world though it produced much lower volumes butmuch higher grades than South Africa. Most of thischromite production came from the Bulqiza ophiolite-hosted orebody, one of the largest of its type in theworld.

The deterioration of the state owned mines, little statesupport for national companies and the country beingclosed to western companies left only one significantchromite producer in Albania in the 1990s. With the risein demand from China, and other emerging economies,and the welcoming mining laws of the Albaniangovernment the Bulqiza chromite deposit has becomea style well worth exploring for western companies. Thedeposit is largely mined by artisanal miners who carryout no geological exploration.

The long-held view is that the Bulqiza-Batra orebodyforms an anticline with thickening and improved gradeat its crest. However, the cusp of the fold was missingover part of the structure and the eastern limb provedimpossible to follow despite intensive efforts over theyears to locate it through underground development anddrilling.

Following the acquisition of 64?5 km2 of license areain 2009 Empire has devoted much of its time to digitisinganalogue data into a digital format so that it can bereinterpreted. The data review allowed Empire geolo-gists to go back to the basic informational buildingblocks and re-draw the sections. This showed thatthrusting tectonics play a dominant role in ore distribu-tion with important implications for exploration.

Targeting lower environmental impact secondary copperdeposits in the Troodos Ophiolite, CyprusD. B. Parvaz1, B. J. Williamson1, R. J. Herrington2,J. Naden3

1The Camborne School of Mines, Tremough Campus,Penryn, Cornwall, TR10 9EZ, UK (dbp201@exeter.ac.uk)

2The Natural History Museum, Cromwell Road, London,SW7 5BD, UK3The British Geological Survey, Kingsley Dunham Centre,Keyworth, Nottingham, NG12 5GG, UK

Volcanogenic massive sulphides (VMS) within theTroodos Ophiolite have been exploited for thousandsof years, but may only represent a portion of themineral potential for Cyprus. Secondary Cu depositsprovide an attractive alternative to VMS. They form asa result of weathering of VMS due to oxidation andhydrolysis of sulphide minerals, either on the seaflooror, following uplift, in the terrestrial environment. Thebenefits of exploiting secondary copper deposits are: (1)their oxides and sulphides are more amenable to heapleaching than pyrometallurgy for chalcopyrite in VMS,reducing SO2 emissions; (2) acid waters producedduring leaching can be recycled, reducing cost; (3)leaching technologies allow the processing of muchlower grade ores than VMS, permitting the mining ofstrategically important European deposits; (4) produc-tion of high purity ‘electrical grade’ Cu, with no furtherprocessing.

Seafloor or terrestrial weathering of primary VMSdeposits results in the oxidation of pyrite, generatingsulphuric acid which leaches metals from the host rock(basaltic/dacitic-andesites). The metals enter the aqueousphase, being stripped from the rocks and leaving behind abrightly coloured oxidised sulphide deposit known as agossan. The resultant metal rich fluids can then migrate toa new location according under gravity/groundwater flowregimens, often being precipitated at deeper levels asoxides and carbonates (e.g. tenorite, cuprite and mala-chite) above the water table, or sulphides (e.g. chalcocite,covellite and bornite) in the reducing environment belowthe water table. A secondary deposit is produced, whichmay or may not be sufficiently enriched in copper towarrant a mining operation.

The most obvious exploration indicator for thepresence of VMS is surface gossans. Many gossans inCyprus, and in other VMS provinces, overlie miner-alisation dominated by pyrite, with very little or nopotential for Cu. At the moment, the science does notexist to determine the potential for secondary copperdeposits presence beneath a gossan. Low cost, reliableexploration tools are therefore required to discriminategossans overlying Cu-rich VMS. The presence orabsence of secondary copper deposits is likely to relateto both the initial composition of the VMS (Cu-rich/poor) and whether the conditions were right forleaching, transport and enrichment of Cu in suitablezones. This project aims to develop gossan science intoan exploration tool, by attempting to mineralogicallyand chemically classify gossans overlying Cu richdeposits, and Cu poor deposits.

A multi-disciplinary approach to volcanogenic massivesulphide exploration in ancient collision zones: theIreland–Newfoundland connection

S. P. Hollis1, S. Roberts1, G. Earls2, R. Herrington3,S. M. Archibald4, M. R. Cooper5, S. J. Piercey6

1School of Ocean and Earth Science, NationalOceanography Centre, Southampton, UK (steven.hollis@noc.soton.ac.uk)2Dalradian Gold, Belfast, Northern Ireland, UK

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3Department of Mineralogy, Natural History Museum,London, UK4Aurum Exploration Services, Kells Business Park, CountyMeath, Ireland5Geological Survey of Northern Ireland, Belfast, NorthernIreland, UK6Department of Earth Sciences, Memorial University ofNewfoundland, Canada

The Caledonian–Appalachian orogen is one of the bestpreserved and most intensely studied examples of a long-lived collision zone within the geologic record. EarlyPalaeozoic closure of the Iapetus Ocean resulted in theaccretion of a diverse set of arc terranes, ribbon-shapedmicrocontinents and oceanic tracts to the Laurentianmargin during the Grampian–Taconic event. Many ofthese within Newfoundland, Canada, such as theAnnieopsquotch Accretionary Tract, are sequentiallydivisible into a series of ophiolitic, arc and back-arcassemblages that host substantive volcanogenic massivesulphide (VMS) deposits (e.g. Buchans Camp, 16 Mt ofore at 14?5% Zn, 7?6% Pb, 1?3% Cu, 126 g t21 Ag and1?4 g t21 Au) (van Staal, 2007). Within the British andIrish Caledonides, peri-Laurentian-hosted VMS depos-its remain to be discovered.

New mapping across the Tyrone Igneous Complex ofNorthern Ireland, supported by extensive major-, trace-element and Nd-isotope geochemistry, and nine newU2Pb zircon dates, suggests a correlation to the VMS-rich Annieopsquotch Accretionary Tract of Newfound-land. Synthesis of more than 30 years of exploration datain Co. Tyrone, coupled with new lithogeochemistry andhigh-resolution geophysics, has defined stratigraphichorizons favourable for VMS mineralisation, coincidentwith: (i) extensive sericitic alteration, (ii) mineralised float,(iii) bedrock silica-iron exhalites, (iv) strike parallel km-scale deep overburden anomalies and (v) geophysicalanomalies (EM, magnetic and IP).

For example, talc and chlorite altered felsic tuffs atGreencastle contain bands of pyrite-galena-sphalerite-chalcopyrite mineralisation assaying up to 10% Zn,2?8% Pb and 1?2% Cu coincident with a 3 km strikelength Zn deep overburden anomaly and a series of EManomalies. Silicified and chloritic altered felsic tuffsaround Tullybrick and Broughderg are coincident with aseries of EM anomalies and a 5 km strike length Zn(with Cu and minor Pb) deep overburden anomaly. Thisrevised and detailed correlation between the twoterranes, integrated with encouraging exploration datahas defined exploration fairways in Co. Tyrone withpotential to host VMS deposits.

van Staal, C. R. 2007. Pre-carboniferous tectonic evolution and

metallogeny of the Canadian Appalacians, in Mineral Deposits

of Canada, (ed. W. D. Goodfellow), Geological Association of

Canada special publication no. 5, 793–818.

Magmatic-hydrothermal Cu2Au and Zn2Pb (Ag2Au)deposits in the kassandra mining district, N Greece: firststeps towards an integrated metallogenetic modelA. Hahn1, P. J. Treloar1, J. Naden2, S. P. Kilias3,A. H. Rankin1, P. Forward4

1School of Geography, Geology & the Environment,Kingston University, Surrey, KT1 2EE, UK(K0849560@kingtson.ac.uk)

2British Geological Survey, Kingsley Dunham Centre,Keyworth, Nottingham, NG12 5GG, UK3National and Kapodistrian University Athens,Zographou, GR-15784 Athens, Greece4European Goldfields (Services) LTD, London, W1J8DS, UK

The Kassandra mining district (KMD) in N Greecehosts various styles of economically important mag-matic-hydrothermal mineralisation located in theSerbo-Macedonian Rhodope metallogenic provinceof SE Europe (Heinrich and Neubauer, 2002). Baseand precious metal deposits are spatially related toNeogene magmatism on the southern limb of acontemporaneously exhumed metamorphic core com-plex. Available data are insufficient to develop anoverarching metallogenetic district model linking hy-drothermal mineralisation to magmatism and meta-morphic core complex formation. In addition the roleof ophiolites in constraining the metallogenic signatureis unclear.

Olympias and Mavres Petres are Pb–Zn (Au–Ag)carbonate-hosted massive sulphide replacement de-posits (Olympias: 11?5 Mt at 9?0 g t21 Au and 137?5g t21 Ag, 0?53 Mt at 4?6% Pb, 0?70 Mt at 6?1% Zn;Mavres Petres: 1?76 Mt at 177 g t21 Ag, 0?11 Mt at 6?3%Pb, 0?15 Mt at 9?3% Zn). Skouries is a nearby Cu–Auporphyry resource (146?20 Mt at 0?83 g t21 Au, 0?79 Mtat 0?54% Cu (European Goldfields, 2010). Both deposittypes are linked to Neogene I-type, calc-alkaline plutonsemplaced into a tectonic stack of Palaeozoic toPrecambrian (amphibolite facies) gneisses, marbles andan ophiolitic melange unit containing peridotite anddunite. These are supra-subduction zone systems likelylinked to high heat flows that result from crustal thinningrelated to slab-rollback located in a local transtensionalstress field along the detachment of a metamorphic corecomplex.

Unusual PGE concentrations of PtzPd (max. 80ppm) in ore concentrates from the Cu–Au porphyry atSkouries as well as Fe–Ni–Co–V sulphides and Cu-enriched rims in magnetite in a porphyry-style alterationsystem in vicinity to Skouries suggests that metamorphicfluids derived from the ophiolitic units provide anunusual chemical bias to the mineralisation (Elio-poulos and Economou-Eliopoulos, 1991).

Preliminary results of a multidisciplinary analyticalprogram are presented in order to establish anintegrated ore genetic model for the Kassandra miningdistrict. These include LA-ICP-MS single grain U2Pbgeochronology; Lu2Hf isotope, REE and melt inclusiongeochemistry of zircon; and magnetite mineral andwhole-rock geochemistry.

Heinrich, C. A. and Neubauer, F. 2002. Miner. Dep., 37, 533–540.

European Goldfields. 2010. Reserves (P&P) Statement 10th August

2010. www.egoldfields.com

Eliopoulos, D. and Economou-Eliopoulos, M. 1991. Econ. Geol., 86,

740–749.

Timing and evolution of Tertiary magmatism andepithermal mineralisation in the southern Sierra MadreOccidental, Mexico

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A. R. Rosique1, S. Bryan2, L. Ferrari3, M. Lopez-Martinez4, A. Rankin1, A. Camprubı5, C. Allen6,T. Uysal7, Y. Feng8, P. Reiners9

1Centre for Earth and Environmental Research, KingstonUniversity, UK (a.ramos@kingston.ac.uk)2Biogeoscience, Queensland University of Technology,Australia3Centro de Geociencias, UNAM, Queretaro, Mexico4Laboratorio de Geocronologıa, CICESE, BajaCalifornia, Mexico5Departamento de Geoquımica, Instituto de Geologıa,UNAM, Mexico6Research School of Earth Sciences, ANU, Australia7Queensland Geothermal Energy Centre of Excellence,The University of Queensland, Australia8Centre for Microscopy & Microanalysis, The Universityof Queensland, Australia9Department of Geosciences, University of Arizona, USA

The mid-Tertiary Sierra Madre Occidental (SMO) ofwestern Mexico, a young and continuous silicic vol-canic province hosts the world’s largest silver province,and the spatial2temporal distribution of Ag2Auepithermal deposits is intimately related to SMO igne-ous activity.

New field mapping, geochemical, and combined U2

Th/Pb2He, 40Ar/39Ar and Rb2Sr geochronologicalstudies provide insights into the timing and evolutionof magmatism and epithermal mineralisation in thecentral Bolanos graben (southern SMO). The exposedvolcanic pile spans at least y10 Myr. The lower part ofthe succession yielded Oligocene (29–28 Ma) U2Pbzircon ages, and is dominated by rhyolitic ignimbritesinterbedded with resedimented pyroclastics. TheAlacran ignimbrite (23?1¡0?5 Ma, 40Ar/39Ar) was partof a new pulse of bimodal volcanism, with theemplacement of crystal-poor rhyolitic ignimbrites anddomes, and basaltic lavas. Domes emplaced betweenabout 24–22 Ma are distinctive in being generally Zrundersaturated rhyolites containing high proportions ofantecrystic zircons with very high UzHREE contents.At the top of the erupted pile is the non-welded Chimaltuff (18?4 Ma; 40Ar/39Ar), followed by a y200 msedimentary sequence.

The graben faults have been considered as conduitsfor magmas and mineralising fluids, and that miner-alisation was closely related to rhyolitic domes. Our fieldobservations and age data show that mineralisationpost-dates dome emplacement. We obtained an Rb/Srillite age of 20?57¡0?5 Ma from the argillic alterationrelated to mineralisation. Ore veins are mostly alongE2W and NNE trending faults at San Martın deBolanos and Bolanos, respectively; these faults alsopartition extensional deformation along the graben. TheN2S graben faults have thus exposed mineralisationrather than controlled it: a U2Th/He zircon age of15?4¡0?9 Ma from a host ignimbrite unit to theZuloaga vein dated at 26?2¡0?24 Ma (U/Pb zircon)records post-volcanic exhumation of the succession.

Our data indicate that Early Miocene rhyoliticmagmas spatially related to, and building up tomineralisation, were sourced from crustal igneous rockssignificantly pre-enriched in metals over the lifespan ofSMO magmatism. Hydrothermal alteration may alsohave concentrated metals in the crustal source for theEarly Miocene rhyolitic magmas.

Basement vein microthermometry and isotopiccomposition, Kagusa high-sulphidation deposit,Kagoshima, Japan

T. D. Tindell1, A. Imai2, R. Takahashi3, A. J. Boyce4

1Faculty of Engineering, Kyushu University, Fukuoka819-0395, Japan (tindell-tom@mine.kyushu-u.ac.jp)2Faculty of Engineering and Resource Science, AkitaUniversity, Akita 010-8502, Japan3Faculty of Engineering, Hokkaido University, Sapporo060-8628, Japan4SUERC, East Kilbride, Rankine Avenue, Glasgow G750QF, Scotland, UK

The Nansatsu ore district is regarded as a type examplefor high-sulphidation Au/Ag/Cu deposits (Hedenquistet al., 1994). The Nansatsu district is dominated by threedeposits; Kasuga, Iwato and Akeshi, ranging in agefrom 4?3 to 3?7 Ma (Izawa et al., 1984), mirroring theeastward migration of a volcanic front.

Kasuga, a disseminated Au deposit exploited since1908, is hosted in andesite of the Nansatsu UpperVolcanic Sequence, which unconformably overlies thesandstone and sandy mudstone of the Shimanto-Supergroup Formation (89?3 to 83?5 Ma) (Teraokaet al., 1986). In 1999, core 11MANU-1 was drilled1200 m below Kasuga to elucidate feeder veining andstructure. Veining was recognised below 300 m, andoccurs in 8 discrete batches of veins, distributed every100–150 m. Veins, usually 0?1–3 cm wide, are commonlybarren of ore minerals, but occasionally contain pyrite,chalcopyrite, galena and sphalerite. Gangue minerals aredominated by quartz, calcite and epidote (the latterrestricted to below 800 m depth). Veins typically have acomb structure; however, there are a number ofoccurrences composed of vuggy silica, especially whereleaching of host rock and illitic alteration is abundant.Calcite is absent above 400 m depth, largely attributedto the strongly acidic conditions, whereas below 1100 m,quartz is subordinate to calcite. Our preliminary studyfocuses on the microthermometric and isotopic compo-sition of these veins, with a view to establishing thegeochemical anatomy of the feeder system to theoverlying deposit.

Fluid inclusion microthermometry was conducted onsamples of quartz and calcite from veins at each veingroup interval. Homogenisation temperature and sali-nity were measured in two-phase liquid/vapour andpolyphase halite/liquid/vapour inclusions. Polyphaseinclusions in quartz were observed from 900 to 1054 mdepth. Generally, above 600 m depth, temperature isbelow 250uC, increasing to 310uC at the base of the drillcore.

d13C isotopic composition from calcite is dominantlymagmatic. Calculated fluid d18O from quartz and calcitevaries significantly with depth: above 640 m, it rangesfrom z0?8 to 1?1%, whereas below this, the range isfrom z4?2 to z8?6%. These data indicate that therewas a mixing of magmatic and surface fluid, with agreater influence of magmatic fluids generally noted withdepth, as might be intuitively anticipated.

Izawa, E., Urashima, Y. and Okubo, Y. 1984. Mining Geol., 34, 343–

351.

Hedenquist, J. W., Matsuhisa, Y., Izawa, E., White, N. C.,

Giggenbach, W. F. and Aoki, M. 1994. Econ. Geol., 89, 1–

30.

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Teraoka, Y. and Kurimoto, C. 1986. Bull. Geol. Surv. Japan, 37, (8),

417–453.

The creation of Au-enriched oceanic crust by the Icelandplume and implications for Au mineralisation in the arcsystem

A. Webber1, S. Roberts1, I. Pitcairn2, Rex Taylor1,C. Dale3

1School of Ocean and Earth Science, NationalOceanography Centre, University of Southampton, SO143ZH, UK (a.webber@noc.soton.ac.uk)2Department of Geology and Geochemistry, StockholmUniversity, Stockholm 10691, Sweden3Department of Earth Sciences, Durham University,Science Labs, Durham DH1 3LE, UK

It has been suggested that the subduction of gold-enriched crust, such as oceanic plateaus formed byplume activity, can increase the chances of developinggold mineralisation in the overlying arc (Bierlein et al.,2006; 2008; Kerrich et al., 2000). Such material isassumed to have a higher Au concentration than normalmid-ocean ridge basalt since plumes should carrysiderophile elements into the upper mantle. Here weshow the Iceland plume is creating subductable enrichedoceanic crust with Au concentrations of up to4?3¡0?2 ppb, which is 6 to 7 times the normal mid-Atlantic MORB Au concentration. This enrichmentextends over 100 s of kilometres and would represent asignificant enrichment to an arc system if it weresubducted.

However, we do not yet know whether Au carried bythe subducting slab is recycled into the arc system. Inorder to answer this question, we are analysing samplesof eclogitised basalt from the Zermatt-Saas ophiolite,Switzerland. These eclogites are thought to have beensubducted to y90 km depth before being uplifted andemplaced in the Alpine orogeny. Pt, Pd and Re havebeen shown to be depleted in this material by up to 80%(Dale et al., 2009), and so are inferred to move into themantle wedge during subduction. By comparing the Auconcentration of these samples with their PGE content,and with global MORB data, we will be able to detectany flux of Au from the slab to the mantle wedge.

Bierlein, F. P., Groves, D. I., Goldfarb, R. J. and Dube, B. 2006.

Lithospheric controls on the formation of provinces hosting giant

orogenic gold deposits, Miner. Dep., 40, 874–886.

Bierlein, F. P. and Pisarevsky, S. A. 2008. Plume-related oceanic

plateaus as a potential source of gold mineralization, Econ. Geol.,

103, 425–430.

Dale, C. W., Burton, K. W., Pearson, D. G., Gannoun, A., Alard, O.,

Argles, T. W. and Parkinson, I. J. 2009. Highly siderophile

element behaviour accompanying subduction of oceanic crust:

Whole rock and mineral-scale insights from a high-pressure

terrain, Geochim. Cosmochim. Acta, 73, 1394–1416.

Kerrich, R., Goldfarb, R. J., Groves, D. I. and Garwin, S. 2000. The

geodynamics of world-class gold deposits; characteristics, space-

time distribution, and origins, Rev. Econ. Geol., 13, 501–555.

Don’t pass the salt: stable chlorine isotopes inhydrothermal systems

S. A. GleesonDepartment of Earth & Atmospheric Sciences, Universityof Alberta, Edmonton, Alberta, T6G 2E3, Canada(sgleeson@ualberta.ca)

Chlorine is the most abundant anion in most hydro-thermal solutions and is the dominant metal complexingagent in many ore forming environments. Furthermore,Cl (and Br) have often been regarded geochemicallyfairly conservative elements in many systems, and, thus,have been used to elucidate the origins of metal bearingbrines and other fluids. Stable chlorine isotopes (d37Cl)are a relatively new geochemical tool that may also helpto constrain the origin of the salinity in mineralisingfluids and the role that hydrothermal fluids play in theglobal cycle of Cl.

Studies have suggested that the crustal reservoir for Clis dominated by seawater and evaporites and has valuesof 0¡1% (Eastoe et al., 2007). The composition of themantle is not well known but recent studies of mid oceanridge basalts suggest that mantle values may range from0 to 23% (Bonifacie et al., 2008). It is known thatboiling and condensation can fractionate Cl isotopes atlow temperatures but there are no experimental data onfluid-mineral fractionations at elevated temperaturesand pressures although theoretical models suggest thatsuch fractionations will be small (Schauble et al., 2003).The potential for isotopic analyses of small mineralsamples by secondary ion mass spectrometry is high(Godon et al., 2004) and as a result fractionation dataare likely to become available in the near future.

Two case studies utilising a combination of Cl, Br andd37Cl data from fluid inclusion leachates will bepresented. The first focuses on the compositions ofintermediate density fluids from the Butte (Montana)and Bingham Canyon (Utah) porphyry-Cu deposits andsuggests that the fluids that formed Butte derived Clfrom the mantle reservoir, whereas fluids at Binghammay in part retain a low temperature d37Cl signaturerelated to a subducting slab. In the second case study,fluid inclusions from a series of metamorphic Ag-Zn-Pbveins from the Kokanee district of British Colombiawere analysed. These halogen data suggest that themineralising fluids ultimately derived their salinity fromthe dissolution of evaporites and, therefore, that thepresence of evaporite bearing carbonate units in the areawas a fundamental control on the ability of these fluidsto complex Ag and base metals.

Bonifacie, M., Jendrzejewski, N., Agrinier, P., Humler, E., Coleman, M.

and Javoy, M. 2008. The chlorine isotope composition of Earth’s

mantle, Science, 319, 1518–1520.

Eastoe, C. J., Peryt, T. M., Petrychenko, O. Y. and Geisler-Cussey, D.

2007. Stable chlorine isotopes in Phanerozoic evaporates, Appl.

Geochem., 22, 575–588.

Godon, A., Webster, J. D., Layne, G. D. and Pineau, F. 2004. SIMS

for the determination of d37Cl Part II: intercalibration of SIMS

and IRMS for aluminosilicate glasses, Chem. Geol., 207, 291–303.

Schauble, E. A., Rossman, G. R. and Taylor, H. P. 2003. Theoretical

estimates of equilibrium chlorine-isotope fractionations, Geochim.

Cosmochim. Acta, 67, 3267–3281.

Evolution of sediment-hosted Cu2Co ore mineralisationin the Central African CopperbeltPh. Muchez1, H. El Desouky1, A. Boyce2, D. Brems1,A. De Cleyn1, S. Dewaele3, L. Lammens1, J. Cailteux4,O. Sikazwe5

1Geodynamics and Geofluids Research Group,K.U.Leuven, Celestijnenlaan 200E, B-3001 Leuven,Belgium (philippe.muchez@ees.kuleuven.be)2SUERC, Scotland

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3Royal Museum for Central Africa, Belgium4E.G.M.F., Groupe Forrest International, Lubumbashi,D.R.Congo5University of Zambia, School of Mines, Zambia

The Central African Copperbelt is one of the largest andrichest Cu2Co metallogenic provinces in the world. Arecent consensus suggests these high-grade stratiformdeposits resulted from multiple mineralisation/remobili-sation stages (Cailteux et al., 2005; Selley et al., 2005;Dewaele et al., 2006; El Desouky et al., 2009; 2010).During initial rifting, Cu and Co sulphides formed dueto convective circulation of brines in the underlying rockpile including the pre-Katangan basement, from whichmetals were leached. Interaction of these brines withbacteriogenic sulphide resulted in early diagenetic(y820 Ma) stratiform mineralisation (Muchez et al.,2008). This stage occurs in the DRC, but is absent orobscured in Zambia. Ore events then occurred duringthe Lufilian Orogeny (Brems et al., 2009) at approxi-mately 583–526 Ma. In Zambia, layer-parallel veinsformed at lithostatic pressures during basin inversion.Subsequently, rocks and layer-parallel veins were folded,concentrating minerals in the hinge zones of the folds.Highly irregular veins formed at high pressures duringthe main phase of the orogenesis. Unfolded massiveveins crosscut all preceding stages. In the DRC, ores areremobilised in veins and late stage nodules, and cementtectonic breccias (El Desouky et al., 2009; Cailteux andKampunzu, 1995).

To unravel this complex metallogenesis, mineralogicaland geochemical studies must be carried out onindividual stages. d34S increases from early diageneticstratiform sulphides to syn-orogenic sulphides (ElDesouky et al., 2010; Muchez et al., 2010), reflectingthe evolution from early bacteriogenic sulphides tosulphur derived from thermochemical sulphate reduc-tion (Muchez et al., 2010; McGowan et al., 2003). Fluidsassociated with the first Cu2Co mineralisation stagehad moderate temperature (115u to (220uC) andsalinity (11?3 to 20?9 eq. wt-% NaCl). In the DRC (ElDesouky et al. 2009), the second Cu2Co stage is relatedto a hydrothermal fluid with a higher temperature(.270uC) and salinity (35–45 eq. wt-% NaCl). Although,the barren host-rock carbonates show Sr isotopesignatures compatible with Neoproterozoic marine sea-water, carbonates associated with all the mineralisation/remobilisation stages in Zambia and with the earlydiagenetic mineralisation stage in the DRC are sig-nificantly more radiogenic, reflecting the interaction ofthe fluids with basement rocks or basement-derivedsiliciclastic sediments derived from it (El Desouky et al.,2010; Muchez et al., 2008; Muchez et al., 2010; Robertset al., 2009).

Brems, D., Muchez, Ph., Sikazwe, O. and Mukumba, W. 2009.

Metallogenesis of the Nkana copper-cobalt South Orebody,

Zambia, J. Afr. Earth Sci., 55, 185–196.

Cailteux, J. and Kampunzu, A. B. 1995. Musee Royal de l’Afrique

Centrale, Tervuren, Belgique, Annales des Sciences Geologiques,

101, 63–76.

Cailteux, J., Kampunzu, A. and Batumike, M. 2005. J. Afr. Earth Sci.,

42, 134–158.

Dewaele, S., Muchez, Ph., Vets, J., Fernandez-Alonzo, M. and Tack, L.

2006. J. Afr. Earth Sci., 46, 455–469.

El Desouky, H., Muchez, Ph. and Cailteux, J. 2009. Ore Geol. Rev., 36,

315–332.

El Desouky et al. 2010. Miner. Dep., DOI10.1007/s00126-010-0298-3.

Roberts et al. 2009. Miner. Dep., 44, 881–891.

Selley, D., Broughton, D., Scott, R., Hitzman, M., Bull, S., Large, R.,

McGoldrick, P., Croaker, M., Pollington, N. and Barra, F.

2005. A new look at the geology of the Zambian Copperbelt, in

Econ. Geol. 100th Ann. Vol., (ed. J. W. Hedenquist et al.), 965–

1000.

McGowan, R. R., Roberts, S., Foster, R. P., Boyce, A. J. and Coller, D.

2003. Origin of the copper-cobalt deposits of the Zambian

Copperbelt: an epigenetic view from Nchanga, Geology, 31, 497–

500.

Muchez, P., Vanderhaeghen, P., Desouky, H., Schneider, J., Boyce,

A., Dewaele, S. and Cailteux, J. 2008. Anhydrite pseudomorphs

and the origin of stratiform Cu-Co ores in the Katangan

Copperbelt (Democratic Republic of Congo), Miner. Dep., 43,

575–589.

Muchez, Ph., Brems, D., Clara, E., De Cleyn, A., Lammens, L., Boyce, A.,

De Muynck, D., Mukumba, W. and Sikazwe, O. 2010. Evolution of

Cu–Co mineralizing fluids at Nkana Mine, Central African

Copperbelt, Zambia, J. Afr. Earth Sci., 58, 457–474.

Cu2Co mineralisation and geotectonic evolution of theZambian BasinS. RobertsSchool of Ocean and Earth Science, NationalOceanography Centre, University of Southampton, SO143ZH, UK (sr1@noc.soton.ac.uk)

A range in the timing and style of Cu2Co mineralisa-tion is evident in the Cu2Co mineralisation of theZambian Copperbelt. The Zambian base metal depositsrange from disseminated stratabound mineralisation tovein hosted, with mineralisation evidently occurringthroughout the evolution of the basin. For example,some of the deposits show geological and isotopiccharacteristics consistent with low temperature diage-netic mineralisation. Elsewhere, the deposits containevidence of high temperature thermochemical sulphatereduction and mineralisation during the onset of basininversion. In addition, base metal deposits are increas-ingly recognised within the metamorphic basement tothe sedimentary basin and in veins which postdatefabrics generated during the closure of the basin. Thesenew data indicate that successful base metal explorationin the Zambian basin involves recognition of thecontrasting styles and timing of mineralisation, whichin turn significantly expand the potential explorationtargets beyond the traditional exploration paradigm inthe region.

Secondary zinc deposits – an African focusM. BoniDipartimento Scienze della Terra Universita di Napoli‘Federico II’, Via Mezzocannone, 8 80134 Napoli, Italy(boni@unina.it)

Until recently, the search for base metal deposits in theAfrican continent has been mainly limited to sulphideores: nonsulphide zinc concentrations (both hypogeneand supergene) have been relatively poorly investigated.Consequently, the genetic understanding, and the abilityto explore these mineralogically and geochemicallycomplex deposit types are still incomplete. In the lastdecades, though, the Skorpion success in Namibia hastriggered a renewed interest in the scientific andeconomic research of nonsulphide ores. We will discusshere some examples of Zn-nonsulphide prospects/deposits of different age, framed in the geologicalevolution of the African continent.

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Hypogene: Lusaka region (Zambia)

The prospects of the Lusaka area occur in the marbles ofthe late Proterozoic Zambezi Belt. The main ore mineralis willemite, associated with hematite, franklinite, andthe Zn-spinel gahnite. High homogensation tempera-tures suggest a hypogene-hydrothermal origin for theores, with brines derived from highly evaporatedseawater. A similar paragenesis is a vector towardsmassive sulphides in other parts of the world; thereforeit is possible that the Lusaka showings may be part of astill unexplored zinc province.

Hypogene/Supergene: Otavi region (Northern Nami-bia); Kabwe (Zambia)

The willemite ores from the Otavi region in Namibia arehosted by Neoproterozoic carbonates of the OtaviGroup. In the main occurrences (Berg Aukas andAbenab West), the nonsulphide ores clearly replace basemetal sulphides and/or the carbonate host. Willemitemineralisation in Namibia is related to hydrothermalprocesses, which followed the main Damaran deforma-tional events. The same genesis and age (post-Lufilianorogeny) can be assigned to the willemite prospects ofthe Kabwe area (Zambia). Neither of these deposits hasbeen exploited for willemite so far. Both primarysulphides and willemite ores have been subjected inboth areas to late supergene enrichment processes.

Supergene: Skorpion (Southern Namibia); Kihabe-Nxuu (Namibia-Botswana)Skorpion is a nonsulphide deposit, hosted by volcano-sedimentary rocks of the Proterozoic Gariep Complex.Supergene ore-forming processes involve wallrock-replacement, as well as direct-replacement. The zinc-silicate (sauconite)-smithsonite ore is treated by acidleach, solid liquid separation, zinc solvent extraction andelectro-winning to produce high-purity zinc on site.

The Kihabe-Nxuu Project is located in siliciclasticNeoproterozoic sedimentary rocks, on the border ofBotswana and Namibia, and contains total resources of33 mtons of Zn.Pb ore. Zinc in the oxidised zone isfound in the minerals smithsonite and baileychlore.Metallurgical test work has shown that the ore isamenable to tank acid leaching and electro-winning onsite.

How geothermal exploration led to gold exploration: acase history – the Afar DepressionD. JamesStratex International plc., London, UK

The term epithermal derives from the genetic classifica-tion scheme for hydrothermal ore deposits proposed byLindgren. On the basis of stratigraphic relationships involcanic sequences, and by analogy with mineral andmetal occurrences and mineral textures in active hydro-thermal systems, Lindgren inferred that epithermaldeposits formed at ,200uC and ,100 atmospheres(y100 bars). It was early recognised that clear parallelsexist between the near surface (y500 m) depositionalenvironment of these deposits and that of modern hotspring systems and these were emphasised by the resultsof exploration activity through the Western USA (e.g.McLaughlin deposit, CA).

Bonanza epithermal veins are defined informally asthose containing roughly 1 million metric tonnes ormore averaging at least y1 oz t21 Au (i.e. y30 metrictonnes gold) and occur sparingly in the epithermal

environment. However, somewhat surprisingly nearly60% of them occur in rifts with bimodal volcanism.

The Afar Depression lies within the Afro-ArabianRift System. This rift system extends from Syria in thenorth and passes through Jordan valley, Dead Sea, RedSea, Afar Depression and the East African Rift andterminates in southern Africa. The Main Ethiopian Rift,the southern Red Sea and the western Gulf of Aden liewithin the Afar Depression forming a rift-rift-rift triplejunction between the Nubian, Somalian and ArabianPlates.

The volcanism within the rift is strongly bi-modal.Many petrological indications suggest that silicic rocksmay have generated by fractional crystallisation oftransitional basaltic magmas in shallow level magmachambers with some degree of crustal assimilation.

Geothermal exploration has been undertaken in theTendaho graben of Ethiopia and in Republic of Dji-bouti. Hydrothermal activity, both active and extinct,was reported in the Tendaho Graben. The extincthydrothermal activity is indicated by silica depositionwithin NW to NNW sub-vertical fractures cross-cutting the rift sediments. No extinct hydrothermalactivity was reported by the geothermal work in Dji-bouti however, epithermal potential had been recog-nised by the USGS.

Bonanza gold deposits make attractive targetsbecause of their potential to yield high rates of return.The need for the discovery of high quality, high profitmargin gold deposits is essential to sustain a competitiveindustry position.

Stratex initiated a programme in January 2008 toprove the concept of gold potential of the African Riftvalley. In March 2009 work commenced in the LakesDistrict of the Main Ethiopian Rift based on data fromgeothermal reports. In October 2009, the Tendahograben was visited to investigate in and around knownhot springs. This resulted in discovery of the Megentahot spring gold prospect.

Review of nickel exploration in eastern Africa

D. M. Evans1,2

1Carrog Consulting, Canada House, Eastcote, HA4 9NA,UK2Natural History Museum, Cromwell Road, London,SW7 1BB, UK (Evans_dave_m@hotmail.com)

The Precambrian terranes of eastern Africa mayrepresent an emerging exploration province for bothsulphide and laterite nickel deposits. I define easternAfrica as including Kenya, Uganda, Tanzania, Burundi,Rwanda, Malawi, Zambia, the eastern part of DRC andthe northern part of Mozambique. This area hasexcellent deep water ports on the Indian Ocean, but asyet poorly developed transport and energy infrastruc-ture inland.

Two factors are driving the emergence of easternAfrica as a potential source of nickel. (1) The perceivedimbalance of supply/demand for nickel from emergingeconomies around the Indian Ocean such as India andChina in the near to medium future. (2) The possibilityof acceleration of infrastructure development led by theWorld Bank’s transit corridors project, aiming toreplicate the success of the Maputo corridor farthernorth.

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There is one operating nickel mine in the region, therelatively small producer at Munali in Zambia. Twomain advanced projects stand out: the laterite deposit atMusongati in Burundi, and the sulphide nickel depositat Kabanga, Tanzania, for which the results of afeasibility study are imminent. Other deposits for whichmineral resources have been estimated are the lateritedeposits at Mibango and Dutwa, and the small but high-grade sulphide deposits at Nachingwea (all in Tanzania).

All of the deposits mentioned so far were discovered inthe 1965–1975 global nickel boom, or even earlier, but laynearly idle until the last 10–15 years. However, continu-ing exploration and new geological appraisal, togetherwith the evolving economic situation have led to thepossibility that all or most of these deposits may becomeviable operations in the near future. In addition, brandnew deposits are beginning to be uncovered in previouslyunprospected terranes such as northern Mozambique.

The known nickel deposits are situated in a diversityof geological settings, but the main prospective belt isthe Mesoproterozoic Karagwe-Ankole Belt of north-western Tanzania, Uganda, Burundi and Rwanda. Thiscontains the major deposits of Musongati, Kabanga andMibango, plus several less important occurrences, allassociated with intracontinental high-Mg basaltic mag-matism. Exploration in this belt is not yet mature, andthe discovery of significant new deposits at Kabanga(Tembo and Safari) since 2006 indicates the continuingpotential for new sulphide deposits.

Other geological settings include the Archaean craton(Dutwa), and Neoproterozoic orogenic belts (Munali,Nachingwea, northern Mozambique). The backgroundgeological knowledge of many of these terranes israpidly improving, and as it does, it suggests that somereceived ideas about favourable tectonic settings andgeological eras based on other parts of the world maynot be applicable in eastern Africa.

Lamproite and a possible carbonatite in the Tromsø area,North NorwayK. Kullerud1, D. R. Zozulya2, E. J. K. Ravna1

1Department of Geology, University of Tromsø, N-9037Tromsø, Norway (kare.kullerud@uit.no)2Geological Institute, Kola Science Centre, 14 FersmanStr, 184209 Apatity, Russia

A lamproite dyke and a possible high-pressure carbo-natite have recently been discovered near Tromsø,North Norway. The lamproite dyke occurs within the1?79 Ga Ersfjord granite at the island Kvaløya west ofTromsø. The dyke rock shows high concentrations ofK2O (9–10?3 wt-%), TiO2 (3?2–4?0 wt-%), BaO (0?55–1?47 wt-%), P2O5 (2?5–3?0 wt-%), Zr (2650–3000 ppm),Sr (2300–2500 ppm), Cr (270–350 ppm), Ni (240–320 ppm) and SREE (900–1260 ppm), and low concen-trations of Fe2O3 (4–5 wt-%), Al2O3 (8?5–10 wt-%) andCaO (3?2–4?2 wt-%). The SiO2 content is 54?8–56?8wt-%. In consequence of the high K2O content, the dykerock shows high element ratios K/Na (2?3–2?9) and K/Al(1?0–1?2).

The rock is porphyritic, with 1–3 mm long phenocrystsof phlogopite in a fine-grained matrix. The fine-grainedmatrix is principally composed of K-magnesioarfvedso-nite (y25 modal%), orthoclase (y40 modal%) andquartz (y10 modal%). Accessory minerals include apa-tite (5–7 modal%), baotite [Ba4Ti4(Ti,Nb,Fe)4Si4O28Cl;

up to 3 modal%], rutile (1–3 modal%), barite and zircon.Several unknown phosphates, including a Na2Mg2Baphosphate have been observed.

Baotite formed at an advanced stage of crystallisation,probably as a result of (1) an abnormally high content ofBaO and TiO2 in the melt, and (2) rapid crystallisationof the melt. Also important for baotite formation wasthe low calcium content of the melt. Most likely, allcalcium was consumed during early apatite formingreactions, leaving no Ca for titanite. Titanium in excessfrom the baotite forming reactions resulted in thecrystallisation of rutile. Furthermore, when all Ca hadbeen consumed during the apatite forming reactions,excess P was responsible for the formation of moreuncommon phosphates.

High pressure carbonatite-like rocks occur spatiallyassociated with eclogite, garnet pyroxenite, (kyanite)-garnet-phengite schist and, and marble within theuppermost tectonic unit in the northern ScandinavianCaledonides. Veins of carbonatite-like rock cross-cut themetamorphic fabric defined by alternating laminae ofgarnet and omphacite in eclogite and foliation in marble.The rock is variably deformed, but locally massive partsexhibiting isotropic texture are present. Potassic feniti-sation resulted in phlogopitisation of the host rock(eclogite, pyroxenite -. glimmerite) and a consequentK-depletion in the carbonatite-like rock along contacts.

Gold particle characteristics in vein-gold deposits:implications for evaluation and metallurgyS. C. Dominy1,2, I. M. Platten1, Y. Xie3, R. C. A.Minnitt4, R. L. Abel51Snowden Mining Industry Consultants Limited, AbbeyHouse, Wellington Way, Brooklands Business Park,Weybridge, Surrey KT13 0TT, England, UK2School of Science and Engineering, University ofBallarat, Mount Helen, Vic 3353, Australia3Department of Minerals Engineering, University ofScience and Technology Beijing, Xueyuan Road, HaidianDistrict, Beijing 100083, China4School of Mining Engineering, University ofWitwatersrand, Private Bag 3, WITS 2050, South Africa5Micro-Tomography Specialist, Department ofMineralogy, Natural History Museum, Cromwell Road,London SW7 5BD, England, UK

Vein gold mineralisation generally contains both fine(,100 mm) and coarse (.100 mm) gold particles. Thein-situ size and shape, deportment, distribution andabundance of the particles controls deposit samplingcharacteristics, grade distribution and metallurgicalproperties (Dominy and Platten, 2007; Dominy et al.,2008; Dominy et al., 2010) Particles can range fromindividual disseminated grains, clusters of particles andmasses above 1 cm in size (Dominy and Platten, 2007).At each end of the coarse-gold to fine-gold spectrum, thesamplability of a deposit ranges from relatively simplefor fine-grained disseminated gold particles (e.g. Carlinstyle deposits), through to extremely difficult for verycoarse particles (e.g. Bendigo-Ballarat mineralisation).Most vein-gold deposits show a background grade ofmineralisation dominated by disseminated fine goldparticles. Drilling will resolve the background graderelatively well, though is likely to considerably under-state the grade related to the coarser gold particles –depending upon drill density, support and sampling

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protocols. Knowledge of gold particle sizing anddistribution enables evaluation programmes to beoptimised. Gold mineralogy has a significant impacton metallurgy, with key factors affecting recovery beingparticle size, deportment, liberation parameters andsilver content of gold minerals (Dominy et al., 2010).For coarse gold particles the focus should be onliberation and the early removal of the particles fromthe mill circuit by gravity concentrators and gold traps.Finer particles will require more grinding to liberateprior to flotation or cyanide extraction. Early goldparticle determination enables metallurgical recoveryparameters to be defined prior to detailed feasibilitystudies. The determination of gold particle sizing is thusrequired to minimise evaluation and geometallurgicaluncertainty and lower project risk.

Dominy, S. C. and Platten, I. M., 2007. Gold particle clustering 2 a

new consideration in sampling applications, Trans. Inst. Min.

Metal, 116, B130–B142.

Dominy, S. C., Xie, Y. and Platten, I. M., 2008. Characterisation of in-

situ gold particle size and distribution for sampling protocol

optimisation, in Proceedings of the Ninth International Congress

on Applied Mineralogy 2008, 175–185; Melbourne, The

Australasian Institute of Mining and Metallurgy.

Dominy, S. C., Platten, I. M. and Xie, Y., 2010. Determining gold

particle size in gravity ores for sampling and metallurgical

characterisation – discussion and test protocol, in Proceedings

of Gravity Gold Conference 2010, 83–95; Melbourne, The

Australasian Institute of Mining and Metallurgy.

Fracture prediction for mine planning using 3D kinematicstructural modelling, Bingham Canyon mine, UtahA. Kloppenburg1, J. Grocott1, X. Guifen2

1Midland Valley Exploration Ltd, 144 West GeorgeStreet, Glasgow, G2 2HG, UK (armelle@mve.com)2Schlumberger, 10 The Courtyard, Eastern Rd, BracknellBerkshire RG12 2XB, UK

Discrete fracture network modelling can inform minedevelopment where it helps rock mass characterisation,including block size and block size anisotropy for minedesign and for flow property prediction for optimumground water handling. Traditionally, fracture predic-tions are made by interpolating and extrapolatingobservations from surface and/or drill-hole data usingcontouring techniques. This approach may carry highrisk depending on the heterogeneity of the controls onfracturing and on the observation density.

Our 3D kinematic approach involves identifyingfracture causes, both spatially and through time. Weuse 3D kinematic modelling software (MoveTM) torestore the 3D model and determine the associatedvolumetric strain, both for discrete sequential stepsthrough time and cumulatively. Strain quantificationprovides volume dilatation and strain tensors withorientation and magnitude of the principal strain axes.Strain values and ratios of specific restoration steps canthen be selected to govern fracture density and orienta-tion of particular fracture sets, depending on the appliedgeological concept for that particular deformation stage.

For the area of interest in Bingham Canyon, a 7-stepgeological history (Kloppenburg, 2010) served as a basisfor the 11-set fracture network ‘recipe’. Lack of drill-hole data and direct field observations, required thefracture modelling to largely build on theoreticalconstraints. Early fracture sets are fold related and for

these both tensile and shear fractures, mode 1 and 2,respectively, were built. Applied density governingattributes include strain ratio E1/E3 and deviation fromcylindricity. Quantifying these attributes required sev-eral restoration steps. Subsequent fault related fractureswere built using fault plane orientations and estimateddamage zone widths.

The optimum discrete fracture network, and the rangeof scenarios, aims to honour the geological history, withnumber of sets, predicted lateral variation, and crosscutting relationships. It can now be fine-tuned as soon asdrill-hole data comes in. Characteristics of the fracturenetworks, including sigma value, block size and perme-ability tensor, can be output using a geocellular grid andprovide input parameters for geotechnical and hydro-logical modelling.

Kloppenburg, A., Grocott, J. and Hutchinson, D. 2010. Structural

setting and syn-plutonic fault kinematics of a cordilleran Cu-Au-

Mo porphyry mineralization system, Bingham Mining District,

Utah, Econ. Geol., 105, (4), 743–761.

Isotope study of hydrothermal deposits and geothermalactivity: implication to resource exploration inKamchatka

R. Takahashi1, H. Matsueda2, V. M. Okrugin3,E. D. Andreeva4, S. Ono1, N. Shikazono5, A. Imai6,K. Yonezu7, K. Watanabe7

1Faculty of Engineering, Hokkaido University, Sapporo060-8628, Japan (ryoheit@eng.hokudai.ac.jp)2Hokkaido University Museum, Hokkaido University,Sapporo 060-0810, Japan3Institute of Volcanology and Seismology FEB, RussianAcademy of Sciences, Petropavlovsk- Kamchatsky683006, Russia4Graduate School of Science, Hokkaido University,Sapporo 060-0810, Japan5Faculty of Science and Technology, Keio University,Yokohama 223-8522, Japan6Faculty of Engineering and Resource Science, AkitaUniversity, Akita 010-8502, Japan7Faculty of Engineering, Kyushu University, Fukuoka819-0387, Japan

There are a hundred of hydrothermal mineral occur-rences in Kamchatka, Far Eastern Russia. This studyfocuses on sulphur isotopes of sulphide minerals fromhydrothermal gold, silver and base metal deposits andoxygen and hydrogen isotopes of fluids from the presentgeothermal fields, in order to elucidate the genesis of oreformation and the potential of geothermal activity.

In Kamchatka peninsula, Cenozoic hydrothermalAu2Ag and base metal mineralisation is recognised inCentral Koryak, Central Kamchatka and EastKamchatka metallogenic belts. However, Sn-bearingbase metal deposits occur only in Central Koryak,whereas porphyry-like deposits are only in CentralKamchatka. The sulphur isotope study on Au2Agand base metal deposits resulted in particularly negatived34S values (25?2 to 20?8%, av. 22?8%) for CentralKoryak metallogenic belt, indicating an assimilationprocess of 32S-enriched sedimentary sulphur. Themagma in Central Koryak metallogenic belt would havebeen reduced during the intrusion process through a

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thick turbidite terrane (Ukelayat-Lesnaya River trough)and thus causing the Sn-bearing mineralisation.

Oxygen and hydrogen isotopes and dissolved chemicalcompositions were analysed for volcanic gas, hot springwater and meteoric water in Central Kamchatka andEastern Kamchatka volcanic belts. The d18O and dDanalysis revealed a mixing of magmatic water andmeteoric water for the present hydrothermal system inthe Eastern Kamchatka volcanic belt. Geothermometryusing Na, K, Ca and Mg indicates a definitively higherequilibrium temperature in the underground of EasternKamchatka (170–380uC) compared to that of CentralKamchatka (155–232uC). Geothermal scale from pro-duction wells of Mutnovskie geothermal power stationin Eastern Kamchatka contains relatively high Au andAg, at maximum 8?8 and 33 ppm respectively. Theresults suggest that the epithermal gold mineralisation isstill on going in geothermal fields of the EasternKamchatka volcanic belt.

It is expected that above results, with previouslyreported ore-forming ages, would become a guideline forexploration of hydrothermal deposits in Kamchatkapeninsula.

The hydrothermal gold system of the Archaeangreenstones in the Nuuluk area, Sermiligaarsuk Fjord,South West Greenland

D. M. Schlatter, J. Kolb

Geological Survey of Denmark and Greenland,Copenhagen (dms@geus.dk)

Nuuluk is located about 75 km SE of Paamiut, and goldexploration has been carried out since the early 1970s(Evans and King, 1993; Appel and Secher, 1984).Exploration work at surface defined two ore horizonswhich were tested by Winkie and diamond drilling(Petersen and Madsen, 1995). In this paper, we discussnew geological, petrographical and lithogeochemicaldata from the Nuuluk gold prospect with the aim tocharacterise the host rocks and hydrothermal alterationassociated with gold mineralisation. The rocks aremetamorphosed to greenschist facies grade, comprisegreenstone, quartz-feldspar-garnet schist and carbonatealtered metavolcanic rocks of Archaean age, which inturn were thrust over an Archaean gneiss basement tothe east. The Nuuluk area comprises two distinct NNEstriking, 40 to 60 degrees WNW-dipping, 50 to 100 mthick and 5 km long zones containing gold mineralisa-tion and hydrothermal carbonate-white mica alteration(Petersen and Madsen, 1995). The distance between thetwo zones is about 500 m and both zones are intimatelyassociated with thrust contacts. The western carbonatezone was studied from a 60 m long surface profile, whichcomprises hydrothermal altered greenstones consistingof ankerite-muscovite-chlorite-pyrite-arsenopyrite, nar-row quartz veins and minor magnetite and graphiteschist. A three metre thick layer of brownish white mica-ankerite schist yielded up to 900 ppb Au. The easterncarbonate zone was studied from a 130 m long surfaceprofile and the lithologies comprise mainly massive andhydrothermal carbonate altered greenstones. A narrow15 cm quartz vein rimmed by thin ankerite alterationyielded up to 1300 ppb Au. The hydrothermal alterationis similar in both zones, but in the eastern carbonatezone magnetite and graphite schists are lacking.Application of immobile-element methods show that

the rocks from both zones are mainly tholeiitic basaltswith flat REE patterns and only few ankerite-whie micaaltered metavolcanic rocks from the western carbonatezone are mildly calc-alkaline basaltic andesites. The goldreefs of Nuuluk typically occur in pervasively ankeritealtered metavolcanic rocks or are hosted in quartz veinsrimmed by ankerite halos. Fluid flow and mineralisationis suggested to be confined to high-strain zones withinthe greenstones confirming a structurally controlledlodegold origin for both horizons (Petersen andMadsen, 1995).

Appel, P. W. U. and Secher, K. 1984. On a gold mineralization in the

Precambrian Tartoq Group, S. W. Greenland, J. Geol. Soc.

Lond., 141, 273–278.

Evans, D. M. and King, A. R. 1993. Sediment and shear-hosted gold

mineralization of the Tartoq group supracrustals, southwest

Greenland, Precambr. Res., 62, 61–82.

Petersen, J. S. and Madsen, A. L. 1995. Shear-zone hosted gold in the

Archaean Taartoq greenstone belt, South-West Greenland, in

Gold mineralization in the Nordic countries and Greenland.

Extended abstracts and field trip guide (ed. P. M. Ihlen), 95/10:

Copenhagen, Open File Series Grønlands Geologiske

Undersøgelse, 65–68.

The nature and genesis of marginal Cu2PGE2Ausulphide mineralisation in palaeogene macrodykes of thekangerlussuaq region, east Greenland

D. A. Holwell1, T. Abraham-James2, R. R. Keays3,A. J. Boyce4

1Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK (dah29@le.ac.uk)2Platina Resources Limited, PO Box 4192, Robina,Queensland 4226, Australia3School of Geosciences, Building 28, Monash University,Victoria 3800, Australia4Scottish Universities Environmental Research Centre,Scottish Enterprise Technology Park, Rankine Avenue,East Kilbride, G75 0QF, UK

The Kangerlussuaq region of east Greenland hosts avariety of extrusive and intrusive igneous rocks of earlyTertiary age including the spectacularly layered andiconic Skaergaard Intrusion. Spatially and temporallyrelated to Skaergaard are a series of gabbroic macro-dykes, two of which: the Miki Fjord Macrodyke, andthe newly discovered Togeda Macrodyke, containCu2PGE2Au sulphide mineralisation along theirmargins. Sulphides occur as disseminated interstitialblebs and rounded globules of chalcopyrite and pyr-rhotite with some Fe2Ti oxides and platinum groupminerals, comprised largely of Pd-bismuthides andtellurides. The globules are interpreted to have formedfrom fractionation of trapped droplets of an immiscibleCu- and Pd-rich sulphide melt and high resolution X-raycomputer tomography has revealed that the dropletsshow geopetal indicators.

Sulphur isotopes indicate that the source of S in thesesulphides is of crustal origin, sourced locally fromisotopically light pyritic sediments of the KangerlussuaqBasin. Thus, generation of these sulphide occurrences iscontrolled by local country rock type. Low Ni/Cu andPt/Pd, also present in the Platinova reefs in theSkaergaard Intrusion, indicate that early fractionationof olivine may have depleted the magma of Ni and

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suggest the likely presence of large magma chamber atdepth. Xenoliths of olivine-rich cumulates found withinthe Miki Fjord Macrodyke may have been sourced fromsuch a body which may be analogous to the ‘HiddenZone’ postulated to be present beneath the exposed partof the Skaergaard Intrusion.

During emplacement of the macrodyke magma,interaction with sulphides in the local sediments mayhave induced further sulphide saturation, producingCu- and Pd-rich sulphides which were then entrainedand emplaced along the macrodyke margins. Thelocation of thus far unidentified conduit or feeder zonesbeneath the present day surface may represent potentialtargets for more massive sulphide orebodies.

Geochemical pattern recognition of lead and zinc depositsin the central part of Sanandaj-Sirjan Zone (WesternIran)B. Mehrabi1, A. Meshkani1,2, A. Yaghubpur1,Y. Fadakar3

1Department of Geology, Tehran Tarbiat MoallemUniversity, Tehran 15614, Iran (mehrabi@tmu.ac.ir)2Geological Survey of Iran, PO Box 13185-1494, Tehran,Iran3School of Earth Sciences, University of Queensland,Brisbane, Australia

The Sanandaj-Sirjan Zone (SSZ) is a magmatic-meta-morphic belt with a NW2SE trend located between theZagros and Urmieh-Dokhtar volcanic zone of Iran. It isa major metallogenic zone in Iran, containing gold,copper, iron, lead and zinc deposits. In the central partof the SSZ, lead and zinc mineralisation is widespreadand hitherto exploration has been based on geologicalcriteria. In this study, representative mineralised sampleswere collected from 104 active and abandoned minesand prospects. After ICP-OES multi-element chemicalanalyses (Amdel Lab., Australia) of representativesamples the data were processed and a database created.Using hierarchical cluster analysis, ore- and rock-forming elements were separated. As, Au, Co, Ni, Cu,Fe, Cd, Sb, Ag, Pb, Zn and Mo clustered as an elementalassociation with Pb2Zn mineralisation whereas Ca, Mg,Mn, Ba and Sr grouped as carbonate hosts rocks.

The derived elemental associations were put throughK-means clustering and the outcomes plotted asscattered plot. Well-separated element groups possesspractical geochemical significance, representing distincttypes of mineralisation, were plotted on a map usingArcGIS. Based on the hierarchical clustering andelemental associations, it is shown that lead and zincdeposits in the central SSZ belong to two genetic groups:an MVT type hosted by limestone and dolomites and anSEDEX type hosted by shale, volcanic rocks andsandstone. The elemental associations and spatialdistribution of the lead and zinc deposits exhibit zoningin the central part of the SSZ. The ratios of ore-formingelements (Sb, Cd, Zn) versus (Pb, Ag) show zoningalong an E2W trend, while host rock-forming elements(Mn, Ca, Mg) versus (Ba, Sr) show a zoning along anSE2NW trend. Large and medium deposits occurmainly in the centre of the studied area. The patternrecognition methods were able to uncover elementalzoning, identify key elemental associations for furthergeochemical exploration and indicate exploration targetareas for large to medium size ore deposits in the central

SSZ. Our conclusions justify further exploration aroundoccurrences and abandoned mines in the centre of thestudy area, as there is potential for medium to large Pb-Zn deposits. This methodology can be applied in asimilar way to search for new ore deposits in a widerange of known metallogenic zones.

Metallogeny of gold of the northwestern part of the Altay-Sayan fold belt

A. I. Chernykh

FGUP ‘SNIIGGiMS’, Novosibirsk, Russia (cherntkhai@mail.ru)

The main gold deposits in the Altai-Sayan fold belt(ASFB) are lode gold-quartz, gold-skarn and placerones. Formation of endogenic gold mineralisationoccurred in the Late Cambrian – Early Ordovicianmetallogenic epoch and is related to collision stage of theregion development. Gold ore is localised in near-contact parts of polyphase essentially granitoid massifs,breaking through Vendian – Early Cambrian volcano-genic-sedimentary rocks of ophiolitic and island-arccomplexes. In recent years we received data testifying toprospects of the north-western part of the ASFB fornon-conventional gold mineralisation of four ore-formational types.

1. Gold-sulphide mineralisation in carbonaceousstrata is confined to Late Riphean EarlyCambrian and Devonian metamorphosed terrige-nous complexes. These rocks are formed inmarginal sea basins. They show enhanced averagecontent of noble metals. Metamorphism andrepeated tectono-magmatic activisation of theregion resulted in gold concentration. We estimateundiscovered potential gold resources of categoryP3 in carbonaceous strata of the north-westernASFB at the level of 550 t.

2. Gold-sulphphde mineralisation in carbonate strata(Karline type) is confined to Vendian and LateDevonian-Carboniferous carbonaceous dolomiteand limestone. Formation of such epithermalmineralisation is associated with Siberian plumeevolution in Mesozoic. Gold mineralisation isconfined to major tectonic zones, is accompaniedby listwanite, jasperoid and argillisite as well asbarite, polymetallic and mercury mineralisation.Gold-sulphphde mineralisation in carbonate rocksis most widely represented within the Kuznetskzone. We estimate undiscovered potential goldresources of category P3 in carbonaceous carbonatestrata of the north-western ASFB at the level of350 t.

3. Gold-porphyry mineralisation is confined to thehabitat of small massifs and dyke fields of diorite,granitoid, monzonite, and syenitoid compositions.Such massifs are distributed within collision com-plexes (Kuznetsk-Altai zone), Early-Middle Devo-nian volcanic2plutonic associations and habitatof granitoids of Mesozoic intraplate activisation(Pezass-Kurai and Salair zones). There is a closeassociation of gold with copper and molybdenumreflecting general regularities in formation ofporphyry orogenic systems. We estimate undiscov-ered potential gold resources of category P3 ofgold-porphyry type at the level of 300 t.

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4. Gold in crusts of weathering is found inCretaceous-Paleogene deposits within Salair ridge,Gornaya Shoria and northern Altai. Crusts ofweathering represent clay and clay-rubbly rocksdeveloped after gold-bearing sulphidised rocks.Salair region is one of the most promising. Weestimate undiscovered potential gold resources ofcategory P3 in crusts of weathering of the north-western ASFB at the level of 500 t.

Hence, despite the lack in the region of specialisedprospecting work for gold mineralisation of the typesconsidered, their resources of category P3 are estimatedat the level of 1700 t. Further development of goldmining in the north-western Altai-Sayan region willdirectly depend on this resource base development.

Dhezkazgan-style copper deposits in Kazakhstan

A. Dolgopolova1, R. Seltmann1, B. Syusyura2

1Natural History Museum, CERCAMS, Cromwell Road,London, SW7 5BD, UK (allad@nhm.ac.uk)2Mining Economic Consulting (MEC), Almaty,Kazakhstan

Kazakhstan ranks in the 10th position with regard tocopper resources of the world. The annual production ofcopper is relatively small, contributing 470–490 tons ofthe total world production of 13?6–13?9 Mt. The StateInventory of Mineral Resources of Kazakhstan includes90 mineable copper deposits with an average coppergrade of 0?65%. Some 26 deposits with an averagecopper grade of 1?22% account for about 50% of thetotal reserves. The remaining 64 deposits contain low-grade ores of copper porphyry type with an averagecopper content of 0?40%.

Unlike a number of major copper producing countrieswhere the porphyry type is of greatest industrialimportance, more than two-third of the production inKazakhstan comes from the sandstone-hosted copperdeposits of the Dzhezkazgan area, which make up 30%of the total copper reserves in Kazakhstan. In additionto copper, the ores of these deposits contain significantamounts of lead, zinc, silver, rhenium, osmium andsulphur. These co-products, together with the highaverage grades of copper (.1%), ensure the profitabilityof the mining operations in the main copper depositsand have guaranteed the stability of the copper miningindustry in Kazakhstan over the period of more than35 years.

Economic sandstone-hosted deposits are the basis ofmineral resources of the Dzhezkasgantsvetmet CopperMining and Metallurgical Combine of the KazakhmysCorporation. They have been explored within theDzhezkazgan Basin in the northern part of the largeDzhezkazgan–Chu–Sarysu Depression and are groupedinto the Dzhezkazgan and Dzhilandy, and Zhaman-Aybat copper ore clusters.

The Dzhezkazgan and Dzhilandy copper ore cluster(Dzhezkazgan, Zhartas, Itauz, Saryoba, Qipshakbay,Qarashoshak, Shilisay deposits) is a type of coppersandstone in Eurasia. This copper giant occupies about1000 km2 as a common structural-metallogenic zone ofcopper ore localised in the epigenetic sandstonescontrolled by the Qengir Brachyanticline complicatedby regional faults. The anticline is a synsedimentationstructural unit that grew during accumulation of fluvial

sediments of the Permian-Carboniferous red beds. Thethickness of this formation regularly increases from core(800 m) to limbs (1500 m) of the anticline. Thisdetermined a paragenesis of gas, oil, and bitumenaccumulating in structural trap and copper depositionfrom formation water in discharge area of elisionartesian basin. The epigenetic nature of copper sand-stones of the Dzhezkazgan region is confirmed by U–Pband Ar/Ar isotopic age of about 210 Ma and bybiogenic sulphur source of sulphides (prevalence of thelight isotope with a wide variation of d34S) against thebackground of heavier sulphur of sulphates (gypsum,anhydrite) in the host red beds and sulphur of diageneticpyrite.

The Dzhezkazgan-group deposits attracted efforts ofgeologists over more than a century. These efforts werefocused on the parametrisation of ore zone and study ofore composition. Despite this activity, copper miner-alisation in this district remains incompletely contouredat flanks and deep levels because of (i) complexmorphology of ore zone (multistage mineralisation inthe section, apron- and ribbon-shaped ore layers in planview); (ii) complex internal structure (small folds,numerous flexures, thrust faults, intraformational off-sets, and regional faults); (iii) multi-component compo-sition of ore (Cu, Pb, Zn, Ag, Re, Os, Cd) along withlinear and concentric mineralogical zoning; and (iv)insufficient exploration of flanks of the deposits, whichtend to merging into a single superlarge deposit withsubstantial growth of resources.

The Zhaman-Aybat copper ore cluster (Zhaman-Aybat, Taskura deposits) is situated 200 km southeastof the Dzhezkazgan deposit in the Azat–Zhaman-AybatAnticline, which complicates the eastern margin of theDzhezkazgan-Sarysu Basin as a structural nose. Thenorthern limb of the anticline is downfaulted along theAzat Fault. The latter is a sharp flexure more than500 m in amplitude. In structure and metallogeny, thiscopper ore cluster is similar to the Dzhezkazgan clusterbut better preserved owing to the significant depth (600–800 m) of ore-bearing layers. Copper ore of theZhaman-Aybat deposit is hosted in the middle andlower parts of a large lens composed of epigeneticallyaltered grey sandstones. The ore-bearing lens is25612 km (.250 km2) in area; the composite area ofore beds is about 30 km2. The ore is multi-component(Cu, Pb, Zn, Ag, Re, Os, Cd) with elevated Ag grade upto appearance of ‘silver sandstone’. The localisation ofore reveals distinct linear and concentric zoning relativeto cores of small anticlines (undulation of axis of themain fold). The chalcocite–bornite ore that occurs in theouter zone gives way to the chalcopyrite–galena–sphalerite ore in the inner zone.

Because of retention of the Zhaman-Aybat Anticlineas a structural petroleum trap, sandstones in the orezone are enriched in bitumen and hydrocarbon gases,clearly demonstrating close links between petroleum andcopper accumulation. The ore zone at the Zhaman-Aybat deposit has not been contoured at flanks and deeplevels and currently is an object of follow-up explorationwith expected substantial growth of copper oreresources. In general, Zhaman-Aybat is estimated as alarge deposit.

The Taskura deposit is hosted at the bottom ofcalcareous marly rocks that overlie the ore-bearing red

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beds. Thus, the position of copper ore in section issimilar to the Mansfeld stratigraphic level in theZechstein of Central and East Europe.

A number of similar anticlinal structures, which aresuggested in the Dzhezkazgan-Sarysu Basin at adepth of 500–1000 m from geophysical data, can beregarded as potential Dzhezkazgan-type copper orezones.

Ore mineralisation of the Karashokho diatreme, WesternUzbekistanA. V. Golovko, F. K. DivaevCentral geological–geophysical expedition of the StateCommittee on Geology & Mineral Resources ofUzbekistan Republic (divaev2749@mail.ru)

The diamond-bearing diatreme of Karashokho is1256525 m; and is composed of massive lamproitesand their eruptive breccias. It is located in BukantauMts (the Central Kyzylkum desert) in the westernborder of the Kokpatas gold deposit. The diatreme hasa complicated multistage formation, and is composedof two submeridional elongated, stocks-like bodiesof lamproites of ultramafic, mafic and intermediatecomposition. There are also two stages of eruptivebreccias.

Diamonds were found within ultramafic and mafictypes of massive lamproites and their breccias. In thediatreme, fine crystals (up to 1 mm) are more commonthan rather large ones. The latter (up to 2?2 mm) makesup 7–10%. Predominated crystal habit is octahedron,rarely, transitional forms from octahedron to rhombicdodecahedron. The main morphological crystal typesare diverse, often distorted octahedrons and dodecahe-drons. Cubes and cub-octahedrons are rare. Most of thecrystals are colourless and transparent.

Morphological peculiarities of diamonds from Kara-shokho diatreme and preliminary data on contain anddistribution nitrogen in them were obtained byspecialists of the Institute of Geology, Mineralogyand Ore-forming of Ukraine Academy of Sciences(Kvasnitsa et al.) in the Centre of GeologicalResearches (Germany, Potsdam) using methods ofInfrared and Raman Spectroscopy. These data indi-cate that surroundings of diamond crystallisation werecarbonaceous and silicate melts with active participa-tion of fluids. Most of the diamonds are among thelaB1 or laAzlaB1 spectral type. This testifies toevolution of nitrogen centres within crystals and toprolonged time in mantle conditions, as a resultlargediamonds were formed.

Gold mineralisation in rocks of the Karashokhodiatreme has many shapes in common with mineralisa-tion of Kokpatas gold-sulphide deposit.

Gold-sulphide mineralisation within diatreme islocated in tectonic zones of latitudinal and north-western strikes and is accompanied by the samehydrothermal metasomatic alterations (listvenitisation,brecciation and silicification).

The same three generations of hypogenic gold form asat the Kokpatas deposit: (1) gold-pyrite-arsenopyrite; (2)polysulphide-quartz-dolomite; (3) quartz-calcite-stibnite.

The differences consist in the following: gold-sulphidemineralisation is superposed both on country sedimen-tary-metamorphic rocks of Kokpatas suite of Pre-Cambrian age and on lamproites of the Karashokho

complex, Lower Permian age, and granitoid dykes of theCentral Bukantau complex of the Upper Permian age.The other important difference is the additionalindependent generation of native gold, which wasgenerated by lamproitic magma. It was establishedwithin the latest variety of micro granular porphyriclamproites, which did not undergo metasomatic change.This gold has forms of thin plates and films of yellowcolour measuring up to 1 mm (assay number 782–911),contains heightened quantity of copper (6?18–14?36%)and nickel (0?29–1?36%) but admixtures of arsenic andantimony are practically absent. On the contrary goldfrom granitoid dykes and country rocks is characterisedby low copper and nickel and elevated arsenic andantimony.

The largest gold contents are incataclasite andbrecciation in granitoid dikes and breccias of thefirst stage of injection, i.e. to places which are themost favourable for circulation of hydrothermalsolutions.

Co-existence of gold and diamonds jointly withinKarashokho diatreme raise perspectives of its economicsignificance.

The Bugdaya Au–Mo(W) porphyry deposit(Transbaikalia, Russia): geology, mineralisation sequence,formation conditions

G. D. Kiseleva, V. A. Kovalenker, T. L. Krylova

Institute of Geology of Ore Deposits, Petrography,Mineralogy, and Geochemistry (IGEM RAS), 35,Staromonetny per., 119017, Moscow, Russia (kis60@rambler.ru)

The Bugdaya deposit is the largest Mo-deposit inTransbaikalia (ore 436?2 Mt, Mo 347 500 t, Au 11?2 t,Ag 193?5 t, Pb 41 400 t). It is located in the zone of thecollisional of the Mongol-Okhotsk fold belt in the areaof the main structural S-like bend (Zonenshine et al.,1990). The deposit is confined to the central part ofvolcanic dome-like radial-concentric structure of3?5 km diameter. This dome is located in the SE partof large pluton of Variscan granitoids, which wasintruded by Jurassic subvolcanic bodies of rhyolite-granite-porphyry. The deposit comprises a net ofdiversely oriented quartz-molybdenite veins and vein-lets, located around a small stock of silicified rhyoliteporphyry. The stockwork has a shape of verticalcolumn with 11006800 m (in plane). It was traced bydrilling to a depth of 1200 m without pinching out.Gold concentrations (from few to 100–150 ppm) occurin steeply dipping gold-base metal veins crosscuttingMo–W stockwork. Mo–W mineralisation is mainlyconfined to submeridional and north-east trendingfaults and the gold-base metal veins – to north-westand submeridional faults.

The most widespread metallic minerals of more then70 minerals of the deposit are molybdenite, pyrite,galena, sphalerite, less common chalcopyrite andscheelite. Subordinated are arsenopyrite, fahlores,wolframite, magnetite. More rare are various sulpho-bismutites (aikinite, matildite, berryite and others),sulphoantimonides (polybasite, Te-polybasite, pear-ceite, bournonite, boulangerite), sulphotellurides (tetra-dimite, cervelleite), and extremely rare cassiterite. Goldof varying fineness (962–223) was found only in basemetal veins. Gangue minerals are represented by quartz

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(most widespread), chalcedony, carbonates, white mica,K-feldspar, phlogopite, kaolinite, smectite and others;fluorite is present in rather low concentrations. Theearliest wall-rock alterations were K-feldspathisationand silicification which followed intrusion of rhyolite-porphyry stock and predated molybdenite mineralisa-tion, both of them (alteration and ore) being parts ofearly quartz-molybdenite stage. Following gold-base-metal stage started from phyllic alteration (white micaplus pyrite) and formation of gold-base metal ores.These two stages were divided by a drastic change ofregional pattern of tectonic deformations with breccia-tion. Post-ore stage was manifested as argillisationfollowed by formation of chalcedony-carbonate veinsand veinlets with some remobilisation of earlierminerals. Supergene processes are rather weak butproduced unusual Mo-rich stolzite, native Ag-Ag-amalgams in assemblage with greenockite, and exoticdzhalindite.

Fluid inclusions study. Preore mineralisation stagewas formed at the final of magma crystallisation, whensalt and vapour fluids exsolved from the melt asindicated by syngenetic melt (silicate and salt), andvapour fluids in the FIs of the rhyolite-porphyryfestoon-like early quartz. Later salt melt transformedto aqueous salt melt-brine, and then – to hydrothermalfluid. Preore quartz and quartz-molybdenite veinsprecipitated in similar T intervals (580–420 and 550–290uC respectively). At T.400uC the immiscible low-density vapour and Na2Ca2Mg2Cl high-density(1?5–1?2 g cm23) brine (70?5–40 wt-%, equiv. NaCl)coexisted. The vapour fluid inclusions are dominant,pointing to a significant role of the gas fluidsparticulary at the early deposit formation period. AtT,400uC mineral precipitation took place from Na–Clfluid (,25 wt-%). MoS2 daughter crystals were detectedin all types of fluid inclusions of quartz-molybdenitestage. The next gold-base metal stage mineralisationprecipitated at 360–140uC from Na–K–Cl(HCO3?,SO4?)fluids of moderate to low salinity. The first generationof native gold was deposited by Na–Cl (23–21 wt-%)fluid at 330–260uC, more common electrum (2ndgeneration) – by lower temperature (240–190uC) Na–Cl (HCO3) (16–7 wt-%) fluids. The main gas componentof the fluids was CO2. Molybdenite, base metals, and goldprecipitation could be triggered by appearance of H2, N2

and H2S (no more than 2 mol.-%) in fluid composition.

dS34 H2S aq values are within a range of 0¡5%, andcorrespond to magmatic S source.

A comparison of Bugdaya and Climax-type depositsshows their similarity, but there are some distinctionthat include simpler magmatic system, low F, Sn,relatively low Re-content in MoS2, mineral diversity incomparison with the rhyolite subtype porphyry depos-its and economic Au based metals in the Bugdayadeposit. Large Mo reserves of the deposit can beexplained by convergence of many factors: formationof the dome-like structure in the anisotropic area of themain structure S-like bend, multiple magmatic system,stockwork localisation at the centre of the volcanicstructure, simple shape of the ore-forming stockfavourable for fluid focusing, fluids peculiarities(unique high density and salt content in the brine)and others.

This work was supported by RFBR (10-05-00354).

Zonenshine, L. P., Kuz’min, M. I. and Natapov, L. M. 1990.

Lithospheric plates tectonics of the USSR territory, 1, 297–318.

Permo-Triassic gold deposits of Eastern Kazakhstan andSouth Siberia: types of mineralisation and connection withmagmatic events

E. A. Naumov1, A. S. Borisenko1, K. R. Kovalev1,Yu. A. Kalinin1, G. S. Fedoseev1, R. Seltmann2,A. V. Travin1

1Institute of Geology and Mineralogy SB RAS, pr.Koptyuga, 3, Novosibirsk, 630090, Russia (naumov@igm.nsc.ru)2Natural History Museum, Mineralogy, CERCAMS,Cromwell Road, London, SW7 5BD, UK

The junction of Caledonides and Hercynides structuresin West Siberia and Eastern Kazakhstan hosts manydeposits of various types, including gold-arsenic (Au–As), gold-telluride (Au–Te), gold-quartz (Au–Q), andgold-mercury (Au–Hg). These are localised in two majorore regions: Eastern Kazakhstan (Shcherba et al., 2000)and Ob-Salair (Sotnikov et al., 1999). In the EasternKazakhstan gold mineralisation is represented by Au–As (Bakyrchik, Suzdal, Zherek), Au–Te (Sekisovskoe),Au–Q (Balazhal, Boko), Au–Sb–Hg (Kyzyl-Char, Vera-Char) and other types. Recent detailed isotopic-geo-chronological studies have revealed a clearer scheme ofthe development and evolution of magmatism in thisregion (Vladimirov et al., 2008; Lyons et al., 2002).However, the absence of data on the age of goldmineralisation of Eastern Kazakhstan makes it difficultto correctly correlate it with the occurrence of granitoidand mafic magmatism. With this aim, we used 40Ar/39Ardating of sericite from various types of ores from gold-ore deposits in this region (analyses were performed inthe Analytical centre of the IGM SB RAS, Novosibirsk).For analysis we selected newly formed sericite from orevein and veinlets and/or from pervasively hydrothermallyaltered terrigenous and magmatic rocks, consisting ofrelict and newly formed quartz, sericite, and gold-bearingarsenopyrite. The oldest age (306?6¡3?8 Ma) was es-tablished for the ores of the Sekisovka gold-telluridedeposit. This deposit lies within the Rudnyi-Altai belt,within hydrothermally altered gabbro-diorites. The ageof mineralisation distinctly correlates with small intru-sions of plagiogranites and diorites of the Kunushcomplex and palaeovolcanic structures of similar ages(306?7¡8?7 and 299¡2?3 Ma; U–Pb, SHRIMP (Vladi-mirov et al., 2008). According to the U–Pb data, the ageof contact zones between plagiogranite and porphyrieswith molybdenum mineralisation in the black-schistseries at the Zherek gold-sulphide deposit is 309¡3?5 Ma (U–Pb analysis were performed in the Centre ofIsotope Researches of VSEGEI, St. Petersburg). The40Ar/39Ar age of mineralisation of hydrothermally al-tered endocontact zones with gold-sulphide mineralisa-tion is 286?7¡3?4 Ma. Of a younger age is the gold-sulphide (Au–As) mineralisation widely spread withinEastern-Kalba and Kalba-Narym belts and localisedamong carbonaceous terrigenous rocks. The age of Au–As mineralisation of Bolshevik deposit is 285?6¡3?3 Ma. The age of the main gold-ore stage of Suzdaldeposit, dated using sericite from quartz-sericite-pyrite-arsenopyrite metasomatites, is 281¡3?3 Ma. At theSuzdal deposit, within a zone of early metasomatic

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Au–As mineralisation, one can observe younger anti-mony and antimony-ore cluster-veinlet mineralisation,whose sericite is dated at 248?3¡3?4 Ma. This con-forms to the time of formation of trachybasalt-trachyrhyolite association in the Semeitau volcano-plutonic structure (248?2¡0?5 Ma), (Lyons et al.,2002), which is in the ore field of this deposit. Inbrecciation zones of metasomatic gold-arsenic ores,there are veinlets of lepidolite whose age 241?9¡2?7 Ma, is quite close to the stage of emplacement ofthe Monastyrskii complex granitoid intrusions withLi2Ta. Moreover, the Suzdal deposit hosts dykes ofaltered granite-porphyries dated at 257?8¡2?1 Ma (U–Pb, SHRIMP), containing redistributed gold-polysul-phide mineralisation. The muscovite-dated younger ageof Au–As mineralisation from the Daubai (BelayaGorka) deposit is 254?3¡3?1 Ma is, most likely, relatedto contact metamorphism effects by the Late Permiangranitoid intrusions on primary ore-arsenic ores. Thus,three basic age boundaries of formation of ore miner-alisation are established in Eastern Kazakhstan: LateCarboniferous (Au–Te), Early Permian (Au–As) andEarly Triassic. Redistribution of primary Au–As ores ortheir transformation is related to the Early Triassic. Asimilar sequence and age of formation of gold miner-alisation was revealed in the Ob-Salair gold-ore region,with localisation in the Early Palaeozoic structures ofNW Salair, which were activated in the MiddlePalaeozoic, and in Hercynides of the Kolyvan-Tomskfold zone. This region abounds in mafic rocks andgranitoid complexes related to the Late Hercynian andLate Permian – Early Triassic stages of intraplatemagmatism (Shcherba et al., 2000; Vladimirov et al.,2008). The earliest type of ore mineralisation is Au–Te,represented by quartz veins and stockworks withchalcopyrite, galena, sulphosalts of Cu, Ag and Pb,tellurides of Pb, Ag, Au and Hg (Novolushnikovskoyedeposit, gold-quartz stockworks at the Salair and Urskdeposits). According to our data, the age of thismineralisation is 299?8¡2?7 Ma (40Ar/39Ar). It is pre-ceded by the Cu-Mo-porphyry mineralisation in theapical part of the Novolushnikovsky plagiograniteintrusion. A younger (with respect to Au–Te) mineralisa-tion is Au–As mineralisation represented by quartz-arsenopyrite veins, stockworks and zones of phenocrystsof arsenopyrite mineralisation (Baturinskoe, Larinskoe,Legostaevskoe). It is younger relative to the Ob Complexgranitoids (252–249 Ma, Ar–Ar, (Fedoseev et al., 2005)and younger than quartz veins with Au–Te mineralisa-tion. The terminal stage of hydrothermal activity in thisregion is related to Hg and Au–Hg mineralisation, whichoverprints the Triassic (241?6–238 Ma, Ar–Ar, (Fedoseevet al., 2005) dykes of dolerite and lamprophyre(Semiluzhenskoe Au–Sb–Hg deposit).

Our data suggest the similarity of metallogeny of thetwo above-discussed gold-ore regions and a single trendof evolution of magmatism and ore formation. As to theage aspects, magmatism and metallogeny correlate inthese regions with similar structures of NW China andCentral Asia. The age of all large Au–As deposits in thisregion (Muruntau, Kumtor, Suzdal, Zherek, Khatu,Saerbulak) fits within a narrow time interval: 285¡3 Ma.

Fedoseev G. S., Sotnikov, V. I. and Rikhvanov, L. P. 2005.

Geochemistry and geochronology of Permo-Triassic basites in

the Northwestern Altai-Sayan folded area, Russ. Geol. Geophys.,

46, (3), 287–301.

Lyons, J. J., Coe, R. S., Zhao, X., Renne, P. R., Kazansky, A.Y.,

Izokh, A. E., Kungurtsev., L. V. and Mitrokhin, D. V. 2002.

Paleomagnetism of the early Triassic Semeitau igneous series,

Eastern Kazakhstan, J. Geophys. Res., 107, 2139.

Shcherba, G. N., et al. 2000. Great Altai: geology and metallogeny.

Book 2. Metallogeny. Almaty.

Sotnikov V. I., et al. 1999. Geodynamics, magmatism, and metallogeny

of the Kolyvan-Tomsk folded zone. Scientific Publishing Centre,

IUGGM Novosibirsk.

Vladimirov, A. G., et al. 2008. Permian magmatism and lithospheric

deformation in the Altai caused by crustal and mantle thermal

processes, Russ. Geol. Geophys., 49, (7), 468–479.

Map of mineral resources of the Kyrgyz Republic Scale1 : 500 000

V. V. Nikonorov1, R. D. Djenchuraeva2, Yu. V.Karaev1, T. S. Zamaletdinov1

1Ministry of Natural Resources of the Kyrgyz Republic,Bishkek, Kyrgyzstan (nikonorov99@mail.ru)2Institute of Geology of the Academy of Science, Bishkek,Kyrgyzstan

The Kyrgyz Republic has a significant mineral potential.Geologists discovered several thousands deposits andoccurrences of metal and non-metal resources. Complexand prolonged geological evolution of the Kyrgyz TienShan created favourable conditions for the formation ofdeposits of various mineral resources.

Gold, antimony, mercury, tin, coal and oil, gas andbuilding materials are mined at present in Kyrgyzstan.Fresh, mineral and thermal waters are being exploited.There exists a possibility for future mining of tungsten,iron, titanium, vanadium, aluminium, copper, stron-tium, molybdenum, beryllium, tantalum and many othernon-metal commodities.

Information about existing mineral resources becamevery important after entering the market economy. Thefirst overview on mineral resources of the Republic wascompiled in 1986. At that time a lot of information wasnot included due to either existing limitations on datarelease or information that was not any longer up-to-date. As a result, compilation of a new version of themap of mineral resources of Kyrgyzstan was needed.

Scheme of distribution of large structural complexesthat show the main geological features within theterritory of the Kyrgyz Republic was taken as ageological base for the new map. Different structuralcomplexes are formed as a result of various geodynamicconditions (passive and active margins, island arcs,ophyolite, collisions, rift zones) in Northern, Middle andSouthern Tien-Shan. Therefore, with some reservations,the base for the new map can be called geodynamic.

More than 2000 deposits, mineral occurrences andaureoles of more than 150 types of mineral resources areshown on the new map. The following commodities areshown on the map (number of large and medium-sizeddeposits in brackets): oil – 11 (-); oil and gas – 6 (1); gas– 5 (-); coal – 30 (-); brown coal – 23 (7); iron – 11 (2);manganese – 5 (1); chromium – 2 (-); iron-titanium-vanadium – 1 (1); aluminium (bauxites) – 14 (-);aluminium (nepheline syenite) – 5 (2); copper – 74 (1);copper-base metals – 6 (1); nickel – 2 (-); cobalt – 6 (-);lead – 87 (-); zinc-lead – 64 (-); zinc – 4 (1); tin – 59 (1); tin-tungsten – 4 (1); tungsten – 47 (1); arsenic – 9 (4);molybdenum – 21 (3); molybdenum-tungsten – 12 (2);beryllium – 30 (-); mercury – 98 (2); arsenic-antimony – 13

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(2); antimony – 25 (5); antimony-base metals – 11 (-);strontium – 9 (1); rare earth elements – 20 (2); tantalum-niobium – 7 (2); hafnium – 1 (-); zirconium – 3 (1); lithium– 4 (1); gold – 218 (11); gold-copper – 30 (5); gold-basemetals – 14 (1); gold-antimony – 25 (5); gold-mercury – 1(-); gold-cobalt – 1 (1); gold-tungsten – 2 (-); gold-bismuth– 9 (2); silver – 9 (2); silver-base metals – 10 (3); uranium –31 (-); thorium – 2 (-); uranium-molybdenum-tungsten –11 (2); gold placers – 85 (2); uranium-thorium placer – 1(1); litho-chemical aureoles – 100; black sand aureoles –50; gemstones – 77 (18); optical materials – 35 (-);chemical raw materials – 29 (14); raw materials formetallurgy – 31 (18); ceramic raw materials – 129 (45);abrasive raw materials – 11 (2); salts and brines – 20 (6);building materials – 197 (110); other non-metallicmaterials – 57 (23); underground waters – 88 (69).

From all mineral resources within the territory ofKyrgyzstan the largest number of deposits belong to thecommodities of gold (300 deposits), base metals (155deposits), mercury (111 deposits), copper (80 deposits) andtin (51 deposits). 85 large and medium size deposits areamongst those. The Republic is also rich in deposits of coal,non-metal mineral resources and underground waters.

A Catalogue of all deposits shown on the map isavailable. For each deposit and mineral occurrence itshows administrative and geographic coordinates, scale(large, medium, small deposit or occurrence), shortgeological characteristics of mineralisation, averagegrades and quality of mineral components, reserves orprognostic mineral resources. Notes show some infor-mation about infrastructure, exploration maturity andits perspectivity.

At present this is the most complete summary onmineral resources of the Kyrgyz Republic.

Ore potential of Kazakhstan for rare earth elements(Lanthanides)B. Syusyura1, I. Gorlachev2, D. Berezovskiy2

1Eurasian Mining Gelogical Company LLC, Almaty,Kazakhstan (boris.euras@gmail.com)2Institute of Nuclear Physics of National Nuclear Centre,Almaty, Kazakhstan

In the Republic of Kazakhstan rare earth elements(REEs) have been explored as admixtures in eightdeposits belonging to different types: uranic phosphor-ite, essentially argillaceous rare earth residual soils, anduranium as bedded infiltration type in undergroundleaching of uranium.

Main prospects of expansion of REE raw materialsources in Kazakhstan are related to the followingindustrial ore objects:

(i) albitite-greisen type of complex deposits con-taining REE of yttrium group

(ii) network type of rare metal deposits (REE influorite and turnerite)

(iii) titan-zirconium placers with turnerite;(iv) argillaceous residual soils of churchite-rhabdo-

phanite type;(v) molybdenum-vanadium, phosphoritic, uranium

and coal deposits.

The major deposit of Kundybai (South Urals) is locatedin kaolin residual soil within exo-interface of ancientserpentinite intrusive massif. Areal ore bodies are

deposited at a depth of 5–10 m at seam thickness from2 to 40 m. REEs in ores are presented as ion-sorbateformed on argillaceous minerals (50%) and forming theirown mineral – churchite [Y(Ce, Ca)[PO4]2H2O (50%).

The sum of the rare earth oxidesin ores varies withinthe range from 300 to 28 kg m23 (average is 2 kg m23).Spectrum of lanthanides in ores is characterised by theuniquely high contents of yttrium (more than 50% ofsamarium and rare earth sum), scare lanthanides –europium (2?0%), neodymium (15?2%), samarium (4?6%)and the more expensive heavy lanthanides (thulium,lutetium, erbium and ytterbium) being 26?7%. BesidesREE there are ore reserves of Ta, Nb and Ti.

In the central part of Kazakstan (Ulitauski andKokchetauski anticlinorium, the West and East side ofTurgay yield) are known a number of prospects withsimilar ores in residual soils (the largest are Mayatas andKoshkargai).

Complex (Ta–Nb–Be–REE–U–Th) multiple minera-lisation is the major deposit Maytyube located in zone oflarge massif of granosyenite on Karsakpay plateau thatis only lightly explored. The deposit is characterised byradiometric anomaly with the intensity of gammabackground up to 100 micro roentgens per hour, at adepth of logging of a exploratory well up to 1300 microroentgens per hour. Ore bodies with thickness of 10–40 m contain up to 330 g t21 REE of cerium grouplight lanthanides and increased contents of middleyttrium lanthanides (10–12%) due to dysprosium (upto 7?4 g t21).

Anomaly 308 has Ta–Nb–REE–Zr ores in Chingizanticlinorium of East Kazakhstan where REE total400 g t21.

High REEs are in uranium and phosphorus depositswhich have a practical importance as the valuableextraction co-components. Overall, the territory of theRepublic of Kazakstan has significant REE raw materialpotential but the detailed ore geological examination hasjust started.

Review on copper porphyry deposits in Kazakhstan – pastinvestigations, actual situation, future perspectives

I. Ussoltsev

K.I.Satpaev Institute of Geological Sciences, Almaty,Kazakhstan (ussolt@yahoo.com)

The territory of Kazakhstan is a large copper porphyryprovince exists – Kounrad, Bozshakol, Aktogay, Nur-kazgan. These are associated with Devonian (orogenic)and Caledonian (island arc) volcano-plutonic belts.

Largest copper reserves in the Country belong toKazakhmys, the leading natural resources group withmain operations in Kazakhstan and the surroundingcountries of Central Asia.

The copper division of the Kazakhmys consists of 20mining entities of various mineral types with 14 under-ground mines and 6 open pit mines. The mineral reservesand resources of these mines are sufficient to supportprojected production for at least 20 years. The minedore is processed in 10 concentrators and 2 smelters. Inaddition to producing copper, the division producessignificant quantities of zinc, silver and gold, which aresold as by-products. The division has spare smeltingcapacity and copper concentrate is purchased, providingadditional output.

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Kounrad copper porphyry deposit, proud of Kaza-khmys, was depleted and closed in 2009. Nurkazgan is theonly copper porphyry deposit in production.

Kazakhmys Copper has two major long-term expan-sion projects comprising the large copper porphyrydeposits at Bozshakol and Aktogay managed by aspecialist internal team, Kazakhmys Projects.

The technical studies for the development of theAktogay deposit have progressed during 2009 with acombined pre-feasibility study completed in October2009 that incorporated the deposit’s sulphide and oxideore bodies. The study demonstrates that Aktogay is alarge resource containing nearly 5 Mt of copper alongwith silver and molybdenum by-products.

The current estimated mineable oxide resourcecontains 119 Mt of ore with 0?37% copper grade, anda mineable sulphide resource of 1268 Mt of ore with0?38% copper grade. Scope exists to expand theresource in the Aktogay deposit with further explora-tion work.

The deposit would be mined using a conventionalopen pit truck and shovel system. Based on theestimated production levels, the resource base supportsa mine life of 40 years. The project would involvethe construction of a processing plant and a copperconcentrator. Kazakhmys is currently evaluating theresults of the 2009 pre-feasibility study to identifyopportunities for improving the economics of the projectand assessing financing options prior to its potentialadvancement to feasibility stage.

The pre-feasibility study was successfully completedfor the Bozshakol sulphide ore deposit in April 2009.The study confirmed that Bozshakol is an economicallyviable project.

The Bozshakol deposit is substantial with a manage-ment estimated geological resource of 1169 Mt of ore anda copper grade of 0?36%, a gold grade of 0?21 g t21, asilver grade of 4?9 g t21 and molybdenum and rheniumby-products. Based on current projections of productionlevels, the resource base supports a mine life of 40 years.

Geology and geochemistry of the shear zone-related golddeposits in west Tianshan, Xinjiang, NW ChinaY. ZhuSchool of Earth and Space Sciences, Peking University,Beijing 100871, China (yfzhu@pku.edu.cn)

Gold has been introduced syn-deformationally during aperiod of brittle-ductile shear development of shear zonewith the gold-bearing sulphides subsequently deformedin the brittle field (Allibone, 1998; Klemm and Krautner,2000; Voicu et al., 1999). Gold introduction is post-deformational and related to a brittle fracture event(Zhu et al., 2007).

The Tianger (also called Bingdaban) shear zonestrikes roughly E-W, varies between 500 and 2000 min width and extends over 100 km. This shear zone cutsa Silurian gneissic granite dated at 442 Ma by zirconSHRIMP. The shear zone is comprised of mylonitisedgranite with yellowish alteration. Disseminated sul-phides are abundant in sheared rocks and rare in weaklydeformed rocks.

Three gold deposits have been found in the Tiangershear zone: Wangfeng, Tianger and Saridala. The orebo-dies and their wall rocks in these deposits are hetero-geneously mylonitised. The degree of mylonitisation of the

wall rocks increases gradually towards the orebodies. Sub-horizontal fractures are filled with syntaxial quartz-fibresand antitaxial fibrous muscovite, which was dated at220 Ma by Ar–Ar techniques. Pyrite is mainly dissemi-nated in mylonite consisting of quartz subgrains, albite,muscovite and calcite. The pyrite-bearing mylonite is cutby a late-stage sulphide-quartz vein which generally is 1–2 mm wide and consists of pyrite and quartz showingundulose distinction. Such pyrite-quartz veins formed afterthe major ductile deformation stage of the Tianger shearzone. They are, in turn, crosscut by micro-scale veinscarrying pyrite, mica and quartz.

Stable isotope characteristics and high initial 87Sr/86Srratio suggested that no magmatic process was relatedwith the ore-forming process of gold deposits during theTriassic period in west Tianshan, and the ore-formingmaterials were solely derived from the continental crust.

Allibone, A. 1998. Synchronous deformation and hydrothermal activity

in the shear zone hosted high-sulphidation Au–Cu deposit at Peak

Hill, NSW, Australia, Miner. Dep., 33, 495–512.

Klemm, D. D. and Krautner, H. G. 2000. Hydrothermal alteration and

associated mineralization in the Freda-Rebecca gold deposit -

Bindura District, Zimbabwe, Miner. Dep., 35, 90–108.

Voicu, G., Jebrak, M. B. M. and Crepeau, R. 1999. Structural,

mineralogical, and geochemical studies of the Paleoproterozoic

Omai Gold Deposit, Guyana, Econ. Geol., 94, 1277–1304.

Zhu, Y. F., Zhu, J. Zeng, Y. 2007. The Tianger (Bingdaban) shear zone

hosted gold deposit, west Tianshan, NW China: Petrographic and

geochemical characteristics, Ore Geol. Rev., 32, 337–365.

Geology and tectonic implications of Early Palaeozoicophiolitic belts in west Junggar, Xinjiang, NW China

Y. Zhu1, B. Chen, J. J. Tan

School of Earth and Space Sciences, Peking University,Beijing 100871, China (yfzhu@pku.edu.cn)

The Ordovician Tajin – Taerbahatai – Kujibai –Honguleleng ophiolitic belt accreted to the Chingiz-Taerbahatai arc, while the Ordovician Tangbale - Mayila– Baijiantan-Baikouquan ophiolitic belt (TMBB) accretedto the Junggar plate, Xinjiang (Xu et al., 2006; Zhu and Xu,2006; He et al., 2007; Zhu et al., 2007; Chen et al., 2008; Zhuet al., 2008). The spreading of the Ordovician Oceanprobably started from the Precambrian and lasted toDevonian. TheOrdovician Baijiantan-Baikouquan ophiolitemelanges in the TMBB consist of different rock unitsincluding serpentinised lherzolite, spinel serpentinite, meta-gabbro, garnet amphibolite, basalt, spinel-bearing marble,and abyssal radiolarian-bearing chert. Metagabbro ismainly composed of clinopyroxene and plagioclase pseu-domorph consisting of zoisitezalbite¡garnet¡ilmenite¡chlorite. The garnet amphibolite, occurring together withspinel serpentinite, mainly consists of hornblende, garnetand assemblage of zoisitezalbite with minor amounts ofclinopyroxene, ilmenite, sphene, epidotite, chlorite, quartz,rutile, biotite and apatite. Geochemical data demonstratethat the spinel lherzolite, metagabbro, and garnet amphi-bolite resemble N-type MORB with enrichments of largeion lithophile elements. The high eNdT values (.z9)indicate that the spinel lherzolite represents a depletedmantle. Insignificant depletions of high field strengthelements in metagabbro, and the slightly enrichments ofHFSE in garnet amphibolite suggest that strong fluidmodification or partial melting did not happen duringmetamorphism in subduction zone.

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Thermodynamic calculations indicate that metagab-bro has undergone metamorphism at 6?6–8?3 kbar (420–470uC), whereas metamorphic pressure recorded ingarnet amphibolite is much higher (y15 kbar at520uC). The clockwise P-T path reflects a subductionchannel condition in which the Baikouquan ophioliticmelange was recycled. The metagabbro exhumated fromthe shallow part of the subduction channel, while garnetamphibolite from the deeper part.

Chen, B., et al. 2008. Acta Petrol. Sin., 24, 1034–1040.

He, G. Q., et al. 2007. Acta Petrol. Sin., 23, 1573–1576.

Xu, X., et al. 2006. Geol. China, 33, 470–475.

Zhu, Y. F. and Xu, X. 2006. Acta Petrol. Sin., 22, 2833–2842.

Zhu, Y. F., et al. 2007. Acta Petrol. Sin., 23, 1075–1086.

Zhu, Y. F., et al. 2008. Acta Petrol. Sin., 24, 2767–2777.

The geological significance and mining-related problemsassociated with framboidal pyrite-rich ore at Navan,Ireland

G. J. Barker, J. F. Menuge

UCD School of Geological Sciences, University CollegeDublin, Belfield, Dublin 4, Ireland (gareth.barker1@gmail.com)

The Navan deposit, Co. Meath, Ireland is a world-classzinc–lead (Zn–Pb) orebody with pre-production re-sources of y105 Mt at 8?1%Zn, 2?0%Pb, and is cur-rently Europe’s largest Zn producer. Around 3% of oreoccurs as lenses termed the Conglomerate Group Ore(CGO), hosted by a sequence of fault talus and debrisflows known locally as the Boulder Conglomerate. CGOcontains volumetrically significant Fe-sulphides (dom-inantly framboidal pyrite) amounting to y23% of thetotal 3?15 Mt of ore (Ashton et al., 2010). These depositsoverlie an erosion surface and both are considered to bethe product of gravitational instability caused by ex-tensional faulting during the Chadian (Boyce et al.,1983; Philcox, 1989).

Pyrite framboids are microscopic spheroidal to sub-spheroidal clusters of discrete, equant, equidimensionaland equimorphic microcrystals packed with varyingdegrees of ordering (Ohfuji and Rickard, 2005). CGOframboidal pyrite shows extreme variation in size, shapeand internal ordering of individual pyrite framboids,with the prevailing shape of microcrystals beingoctahedral. The morphology and size distribution ofthe CGO framboidal pyrite gives insights into thebiogeochemical processes of the ancient depositionalenvironment suggesting that precipitation occurred bothsyngenetically and diagenetically. CGO framboidalpyrites are frequently overgrown by later phases ofpyrite filling the pore space between microcrystals,masking their original internal structure. CGO framboi-dal pyrite may be amalgamated to various extentseventually forming massive pyrite.

Overall CGO mineralisation is mainly replacive withreactive carbonate clasts and plant material completelyreplaced. Other styles of mineralisation occur includingopen-space infilling and entrained reworked clasts ofsulphide ore sourced from exhumed, stratigraphicallylower, mineralised lenses.

Historically at Navan, high Fe grades result in sub-optimal Pb recovery. Mill feed with high Fe gradecorrelates with reduced Pb recovery but early results

suggest that, high Fe is not the only factor in sub-optimal Pb recovery.

Ashton, J. H., et al. 2010. The giant Navan carbonate-hosted Zn-Pb

deposit – a review. IAEG Extended Abstracts Volume ZINC 2010,

97–102.

Boyce, A. J., Anderton, R. and Russell, M. J. 1983. Rapid subsidence

and early Carboniferous base-metal mineralization in Ireland,

Trans. Inst. Min. Metall., 92, B55–B66.

Philcox, M. E. 1989. The mid-Dinantian unconformity at Navan,

Ireland, in The role of tectonics in Devonian and Carboniferous

sedimentation in the British Isles, (ed. R. S. Arthurton et al.),

Yorkshire Geol. Soc., Occasional Publ., 6, 67–68.

Ohfuji, H. and Rickard, D. 2005. Experimental syntheses of

framboids—a review, Earth Sci. Rev., 71, 147–170.

The Algtrask Au-deposit, northern Sweden, an example ofa higher level Au-bearing hydrothermal system related tothe Palaeoproterozoic Tallberg porphyry Cu deposit?

T. Bejgarn1, H. Areback2, C. Broman3, R. Large4,J. Nylander2, P. Weihed1

1Division of Geosciences, Lulea University of Technology,SE-971 87 Lulea, Sweden (Therese.Bejgarn@ltu.se)2Boliden Mineral AB, SE-936 81 Boliden, Sweden3Division of Geosciences, Stockholm University, SE-10691 Stockholm, Sweden4CODES, University of Tasmania, Private Bag 126,Hobart TAS 7001, Australia

The Palaeoproterozic Tallberg porphyry Cu andAlgtrask Au deposits are situated in the northern partof the Skellefte district, northern Sweden. These depositsare hosted by the early orogenic-synvolcanic JornGranitoid Complex (JGC) that is coeval with a remnantof a volcanic arc succession, hosting several 1?89 GaVMS deposits (Allen et al., 1996). Mineralisation inTallberg occurs as disseminated and quartz vein stock-work sulphides associated with mainly propylitic andphyllic alteration and quartz-feldspar porphyritic (QFP)dykes dated at 1886 Ma (Weihed, 1992). The AlgtraskAu deposit (indicated mineral resource of 2?9 Mt at2?6 g t21 Au), situated approximately 3 km east of theTallberg deposit, is mainly hosted by a coarse grainedgranodiorite of the JGC. The Algtrask deposit ischaracterised by several steeply dipping, subparallel,NE–SW striking zones of varying width with dissemina-tions and veins of mainly pyrite, locally enriched inchalcopyrite, sphalerite, arsenopyrite, accessory Te-minerals and Au (Bejgarn et al., 2011). The mineralisedzones are structurally controlled and display intenseproximal phyllic-silicic alteration and pervasive distalpropylitic alteration of the host rock. QFP dykes withcomparable composition as in Tallberg predate theAlgtrask mineralisation (Bejgarn et al., 2011), whereassimilar style Au-mineralisation as in Algtrask is com-monly associated with the QFP dykes in the southernTallberg area. However, no porphyry style mineralisa-tion has yet been observed in the Algtrask area.Preliminary results from microscopic and LA-ICP-MSstudies of sulphide minerals from both deposits suggestat least two different stages of mineralisation. Fluidinclusions from the Algtrask deposit have variable CO2/H2O proportions, low salinity and suggest formationtemperature of 150–200uC. The Tallberg porphyry Cu-deposit and adjacent Au bearing zones formed at highertemperatures and possibly from two unmixed salinity

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groups (Weihed, 1992). The fluid forming the Algtraskdeposit is interpreted to represent a higher level laterphase of the hydrothermal system forming the Tallbergdeposit, or alternatively a similar but different, deeperlying porphyry system.

Allen, R. L., Weihed, P. and Svenson, S.-A. 1996. Setting of Zn-Cu-Au-

Ag massive sulfide deposits in the evolution and facies architec-

ture of a 1?9 Ga marine volcanic arc, Skellefte district, Sweden,

Econ. Geol., 91, 1022–1053.

Bejgarn, T. et al. 2011. Geology, petrology and alteration geochemistry

of the Palaeoproterozoic intrusive hosted Algtrask Au deposit,

Northern Sweden, in Granite-related ore deposits, (ed. A. N. Sial

et al.), Geol. Soc., Lond. Spec. Publ., 350, 105–132.

Weihed, P. 1992. Geology and genesis of the Early Proterozoic Tallberg

porphyry-type deposit, Skellefte district, northern Sweden, PhD

thesis, University of Gothenburg, Sweden, Publication A72.

Platinum-group mineralogy of ‘hybrid’ norites within thePlatreef at Zwartfontein and Overysel, northern BushveldComplex, South Africa

A. P. Bevan, D. A. Holwell

Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK(ab381@le.ac.uk)

The Platreef is a platinum group element (PGE)-enriched pyroxenite unit, located in the northern limbof the Bushveld Complex, South Africa, which containsbase metal sulphide mineralisation with associated highgrades of PGE. The Platreef was intruded into countryrocks made up of Palaeoproterozoic sediments andArchaean gneiss, and is overlain by gabbronorites of the‘Main Zone’ (Holwell et al., 2005). The base of the MainZone consists of norites and gabbronorites that have‘eaten’ into the Platreef and in some cases intrudedalong serpentinised shear zones within the Platreef,formed prior to the emplacement of the Main Zonemagma (Holwell and Jordaan, 2006). In addition, anumber of intrusive norite bodies referred to as ‘hybridnorites’ intrude the Platreef. It is thought these latterintrusions may represent ‘hybrid’ magmas of Platreefmagma and melted floor rocks, or Main Zone magmaand melted Platreef rocks.

This study has investigated examples of these intrusivenorites that are both PGE-bearing and PGE-barren. Sofar an intrusive norite from Anglo Platinum’s Overyselproperty has yielded range of telluride-dominant plati-num group minerals (PGM) with a palladium mineralmajority as well as unnamed germanides (Pd,Pt)2Ge andPtGeS and a minor amount of arsenides. The vastmajority of PGM occur either as part of polyphasesulphide (pentlandite with secondary amounts of chal-copyrite and pyrrhotite) grains enclosed in amphibole onthe edge of massive interstitial sulphides or as a ‘coating’to secondary amphibole crystals surrounded by theinterstitial sulphides.

Similarities between the norite, Platreef, main zonemagma and floor-rock whole-rock geochemistry arebeing used to help determine an origin for the hybridmagma. (Pd,Pt)2Ge is the dominant PGM of thehangingwall gabbronorite in the Sandsloot pit to thesouth of Zwartfontein and Overysel (Holwell et al.,2006). Also like Sandsloot, the PGMs are oftenassociated with polyphase pentlandite-secondary amphi-bole contacts. The intention is to define nomenclatures

for barren and potentially ore-bearing norites that canbe used during mining and exploration processes.

Holwell, D. A., McDonald, I. and Armitage, P. E. B. 2005.

Observations on the relationship between the Platreef and its

hangingwall, Appl. Earth Sci. (Trans. Inst. Min. Metall. B), 114,

B199–B207.

Holwell, D. A. and Jordaan, A. 2006. Three-dimensional mapping of

the Platreef at the Zwartfontein South mine: implications for the

timing of magmatic events in the northern limb of the Bushveld

Complex, South Africa, Appl. Earth Sci. (Trans. Inst. Min.

Metall. B), 115, 41–48.

Holwell, D. A., McDonald, I. and Armitage, P. E. B. 2006. Platinum-

group mineral assemblages in the Platreef at the Sandsloot Mine,

northern Bushveld Complex, South Africa, Miner. Mag., 70, 83–

101.

The origin and economic significance of dioritic sillswithin the Skaergaard Intrusion, Kangerlussuaq region,east Greenland

P. J. Bird1, D. A. Holwell1, T. Abraham-James2

1Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK (pjb44@le.ac.uk)2Platina Resources Limited, PO Box 4192, Robina,Queensland 4226, Australia

Greenland’s east coast is host to an extensive igneoussuite consisting of flood basalt, ultramafic to alkalineplutons and mafic dyke swarms, produced during theearly Tertiary in association with the opening of theNorth Atlantic, and the ancestral Icelandic plume. Ofthese, the most well known is the Skaergaard Intrusion,famous for its world class example of igneous differ-entiation and layering. The discovery of significantstratiform Au–Pd mineralisation within the SkaergaardIntrusion, termed the Platinova Reefs, during the late1980s resulted in renewed study of the SkaergaardIntrusion and its surrounding area. Platina ResourcesLimited are currently conducting a resource definitiondrilling program and, during the 2010 field season,identified previously uncharacterised ‘dioritic’ sillsoccurring in multiple drill cores within the Skaer-gaard intrusion above the Platinova Reefs. Thesestructures are particularly notable because of theirgreat thickness, unusual composition and presence ofsulphide mineralisation.

Sill material shows variable composition away fromthe wall contacts graduating through chilled margin-xenolith rich flanks-xenolith poor centre with progres-sively increasing assimilation of small (,3 cm) crustalxenoliths towards the centre of the sill. Sill exhibits aplagiocalse-biotite-chlorite mineralogy. Sulphides, prin-cipally pyrite, are dispersed throughout the sills butshow a propensity to cluster around the xenoliths andchlorite masses, possibly indicating a link between theassimilation of xenoliths and the precipitation ofsulphides. It has been shown that assimilation of pyriticshales within the Togeda and Miki Fjord Macrodykes,located to the northeast of Skaergaard, resulted in theprecipitation of Pd- and Cu-bearing sulphides (Holwellet al., 2010) and a similar process may have occurredwithin these newly discovered intrusive bodies. Initialstudies using bulk geochemistry have shown distinctcompositional variations and grouping of samples basedupon their relative location.

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Holwell. D. A., et al. 2010. Marginal Cu-Au-PGE mineralisation in the

newly discovered Togeda Macrodyke, Kangerlussuaq region,

East Greenland, in 11th International Platinum Symposium,

Extended Abstracts, (ed. P. Jugo), Sudbury, Ontario Geological,

Miscellaneous Release, Data 269.

A possible iron oxide-copper-gold (IOCG) style of goldmineralisation at Laka, Northwest Nigeria

A. E. Bullimore, L. J. Robb

Department of Earth Sciences, University of Oxford,South Parks Road, Oxford, OX1 3AN, UK (aebullimor-e@hotmail.co.uk)

Nigeria lies in the heart of the West African Craton,underlain by ancient orogenic terranes, with provengold endowment. Despite a more recent record ofpetroleum, tin and coal extraction, Nigeria is virtuallyunknown as a producer of gold. Recent explorationin Laka, Kebbi State in the northwest of Nigeria, hasdiscovered potentially economically viable goldmineralisation. Gold-in-soil anomalies have beenfound over a 7 km long, WNW-trending zone, thecentral portion of which has soils with up to 300 ppbAu. The gold-in-soil anomalies coincide broadly withshallow hills comprising resistant pods of quartz-magnetite rock, and associated, highly altered quartz-epidote-garnet-hematite rocks. These bodies are spa-tially related to a probable Pan-African granitoidintrusion that cuts across one of several NNEtrending schist belts that underlie the NW sector ofthe country, and which may be Palaeoproterozoic inage (and therefore be Birimian correlatives). Preli-minary ground based magnetic surveys suggest thatthe granitoid underlies much of the mineralised areaand possibly is genetically associated with the quartz-magnetite bodies.

The quartz-magnetite and quartz-epidote-garnet-hematite rocks exhibit anomalous gold values andoccasionally show evidence of copper mineralisation inthe form of malachite staining. Detailed geologicalmapping of the area suggests that the irregular iron-rich bodies are discordant to the regional fabric and maybe hydrothermal in origin – possibly associated with thegranitoid intrusion. The close proximity of the depositto a granitoid intrusion, as well as the abundance ofiron-oxide minerals associated with gold and copperanomalies, suggest that the Laka deposit bears affinitieswith iron oxide-copper-gold deposits such as those inwestern Zambia (Mumbwa, Kasempa, Dunrobin) orMauritania (Guelb Moghrein). Such deposits have notpreviously been described in Nigeria, or elsewhere in theWest African Craton.

Developing an exploration model for gold mineralisationassociated with Archaean basement rocks at Sortekap,East Greenland

K. G. Butterworth1, D. A. Holwell1, T. Abraham-James2

1Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK(kb165@le.ac.uk)2Platina Resources Limited, PO Box 4192, Robina,Queensland 4226, Australia

East Greenland has a history of mineral exploration,mostly concentrating on the numerous Tertiary intru-sives and basalts concentrated around the Kanger-lussuaq area, which include the world famousSkaergaard Intrusion. However, little to no explora-tion has taken place focusing on the Archaean countryrock in the region. Sortekap is a remote locality inEast Greenland, approximately 30 km north of theSkaergaard Intrusion. It comprises a series of ridgescomposed of Archaean basement gneiss and a supra-crustal unit of amphibolite and ultramafic rocks, witha number of gabbroic Tertiary intrusions that cut thebasement sequence.

Initial exploration of the area was undertaken byPlatina Resources Ltd during the summer of 2009. Theydiscovered extensive quartz veining within the basementamphibolite, with associated sulphide mineralisation.Samples returned gold values of up to 3–4 g t21 Au.

Numerous gold grains have been identified using SEManalysis; the first positive identification of gold in theArchaean of East Greenland. The grains range in sizefrom 2 mm to almost 10 mm. More importantly, twogenerations of gold have been identified:

(i) those hosted in the Ca silicates of the host rockamphibolite

(ii) those as inclusions within arsenopyrite (thedominant sulphide).

The larger grains appear to be within the host rocksilicate minerals whereas the gold inclusions in arseno-pyrite are much smaller. A variety of sulphides havebeen discovered, with arsenopyrite, pyrite, chalcopyriteand small amounts of lollingite and galena. The sulphideand gold mineralisation is primarily within the host rockand not in the quartz veins.

Comparison to other similarly hosted gold deposits inGreenland will provide a framework on which to basethe model of mineralisation. The mineralisation ob-served at Sortekap appears to be quite similar to theNalunaq gold mine in South Greenland, but furtherdata will be required in order to make a full comparisonand help to construct an exploration model forArchaean gold in the region.

The evolution of tungsten vein-type deposits in Rwanda: afluid inclusion and stable isotope study

F. De Clercq1, Ph. Muchez1, S. Dewaele2,M. Fernandez-Alonso2, K. Piessens4

1Department of Earth and Environmental Sciences,Katholieke Universiteit Leuven, Celestijnenlaan 200E,B-3001 Leuven, Belgium(Friso.Declercq@ees.kuleuven.be)2Department of Geology and Mineralogy, Royal Museumfor Central Africa, Leuvensesteenweg 13, B-3080Tervuren, Belgium3Isotope Geoscience Unit, Scottish UniversitiesEnvironmental Research Centre (SUERC), RankineAvenue, East Kilbride G75 0QF, Glasgow, UK4Geological Survey of Belgium, Royal Belgian Institute ofNatural Sciences, Jennerstraat 13, B-1000 Brussels,Belgium

The Central African Kibara orogen consists mainly ofPalaeo- to Mesoproterozoic rocks which were intrudedby different generations of granite (G1–G4). At 986¡

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10 Ma G4-granites were emplaced. After emplacementof these granites, pegmatites formed between 975 and960 Ma. The entire set has been crosscut by quartz veinswhich may contain cassiterite or wolframite. This studyfocuses on the W vein-type deposits in the northern partof the Kibara belt, in Rwanda.

The W deposits are hosted by pyritiferous black shalesand grey sandstones. W-mineralisation is present in twotypes of cm to m thick quartz veins: (i) bedding parallelveins restricted to pelitic host-rocks, and (ii) veinscrosscutting both host-rocks and bedding parallel veins.Wolframite formed during a late stage of the veindevelopment. Afterwards, wolframite was altered toporous crystals. Muscovite crystals related to theformation of the W-mineralised veins were dated atabout 990–960 Ma (40Ar–39Ar), which overlaps with thetiming of G4-granite emplacement. Fluid inclusions inboth quartz and wolframite were analysed by (IR-)microthermometry and Raman analysis. The W-miner-alising fluid was most likely a low to medium salineH2O–CO2–N2–CH4–NaCl fluid with a minimal forma-tion temperature between 240 and 320uC.

All quartz veins have relatively homogeneous d18Ovalues (14?4 to 16?0%V-SMOW), but the dD values varysignificantly (233 to 264%V-SMOW). In a d18O-dDisotopic diagram, these values plot in the area typical formetamorphic water, with a small overlap with the areaof primary magmatic water (De Clercq et al., 2008). TheW-mineralised quartz veins show a similar oxygencomposition as the metapelitic rocks in the area, whichranges between 13?5 and 16?0%V-SMOW. The d18Odata of the wolframite crystals range between 23?3 and3?4%V-SMOW, and the dD values between 287 and2133%V-SMOW. The wolframite samples plot belowthe field typical for metamorphic and magmatic water.Based on the d18O data wolframite and quartz did notprecipitate in isotopic equilibrium. The dD values ofwolframite might indicate fluid-rock interactions withlow dD host-rocks or the involvement of a low dD fluid.The W-mineralised veins most likely formed from ahydrothermal fluid which strongly interacted withmetasedimentary rocks.

De Clercq, F., Muchez, Ph., Dewaele, S. and Boyce, A. 2008. The

tungsten mineralisation at Nyakabingo and Gifurwe (Rwanda):

preliminary results, Geol. Belgica, 11, 251–258.

Sphalerite isotopic constraints (Fe, Zn, S, Pb) on thegenesis of the Navan Zn-Pb ore body: evidence for fluidmixing and kinetic fractionationD. Gagnevin1, J. F. Menuge1, C. D. Barrie2,A. J. Boyce2, M. A. Murphy1, R. J. Blakeman3

1UCD School of Geological Sciences, University CollegeDublin, Belfield, Dublin 4, Ireland (damien.gagnevin@ucd.ie)2Scottish Universities Environmental Research Centre,East Kilbride, Glasgow G75 0QF, Scotland3Boliden Tara Mines Ltd, Navan, County Meath, Ireland

This study investigates the giant carbonate-hostedNavan Zn–Pb ore body, Ireland, the largest of theLower Carboniferous Irish midlands ore field, using amulti-isotopic approach on micro-drilled sphaleritesamples (Fe, Pb, Zn), as well as in-situ S isotopicanalyses. Sphalerite in Navan provides evidence of

sequential growth along well-defined layers (i.e. collo-form texture), which have been targeted for isotopicanalyses. The investigated samples are from the 5 Lens,which corresponds to the stratigraphically lowest andlargest body of mineralisation within the so-called ‘PaleBeds’.

A New-Wave device was used for mineral microsam-pling along sphalerite layers at a spatial resolution of50–100 mm. Zn, Fe and Pb were purified using AG1-X8anion exchange resin and isotopic analyses were carriedout using a Thermo Scientific Neptune MC-ICPMSinstrument in UCD.

A large spread in Fe and Zn isotopic composition hasbeen obtained from sphalerite microsamples, which isespecially dramatic in the case of d56Fe (from 22?20 to20?24%) compared to d66Zn (from 20?27 to 0?28%).This contrasts with uniform Pb isotopic composition. Aclear correlation between d66Zn and d56Fe is alsoobserved, which is exemplified by both inter- andintra-sphalerite colloform layers. In-situ S isotopicanalyses in sphalerite equally display a substantial rangeof variation (of 24%), and can be imperfectly correlatedwith d66Zn and d56Fe variations.

It is proposed that kinetic, Rayleigh-type, Fe and Znisotopic fractionation occurred and was due to rapidprecipitation at a high degree of supersaturation(Wilkinson et al., 2005), with negligible metal sourcevariations. Intra-grain S isotopic data indicate thatkinetic fractionation was intimately associated with themixing of two fluids at the site of deposition. It is thusproposed that early precipitated sphalerite had ahydrothermal signature (d34S.0), light Zn and Feisotopes, and precipitated at relatively high temperature(.150uC). Conversely, later precipitated sphalerite had amore bacteriogenic signature (d34S,0), heavier Zn andFe isotopes, and precipitated at lower temperature(about 50–150uC). The possible role of other processeswill also be discussed.

Wilkinson, J. J., Weiss, D. J., Mason, T. F. D. and Coles, B. J. 2005.

Zinc isotope variation in hydrothermal systems: preliminary

evidence from the Irish Midlands ore field, Econ. Geol., 100, (3),

583–590.

Geological, geochemical and metamorpho-tectonic settingof gold mineralisation at the Kiaka deposit, SouthernBurkina Faso

J. O. Garman, L. J. Robb

Department of Earth Sciences, University of Oxford,South Parks Road, Oxford, OX1 3AN, UK(Jack.garman@st-annes.ox.ac.uk)

Although artisanal gold exploration and extraction havedominated Burkina Faso for centuries, modern explora-tion is a relative newcomer to the country. Primary golddeposits in the Palaeoproterozoic Birimian Belt aresignificant, yet there is little detailed research into theirformation and occurrence, especially in southernBurkina Faso. This study focuses on the Kiaka golddeposit in Southern Burkina Faso, which occurs wherethe Boromo and Gourma greenstone belts intersect theNNE trending Markoye Fault zone. Two styles of goldmineralisation occur within this sheared fault zone andshow similarities to many other epigenetic West Africanorogenic gold deposits. Gold mineralisation occurs both

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in high grade, low tonnage quartz vein systems, as wellas in disseminated, wall rock hosted deposits of hightonnage and low grade. Both types of mineralisation areeconomically significant; their genesis and parageneticsequence need to be ascertained in order to advanceexploration in Burkina Faso.

Analysis of geochemical down-hole elemental data, aswell as petrography and mineral chemistry were used toidentify the nature of the host rocks, their mineralogyand alteration assemblages and the gold deportment.These data are complemented by portable XRFelemental data taken from cores in the main zone ofthe exploration site, which were plotted against AU fireassay data for the corresponding pulped cores. Fieldmapping and core log extrapolation, combined withregional gravity and magnetic data, provide structuralinsights into the regional metamorphic and tectonicsetting of the Kiaka deposit, allowing it to be comparedwith others in the West African Craton.

Detailed ore genesis studies of this nature have notpreviously been undertaken in this remote part ofBurkina Faso and should contribute to a better under-standing of important new deposits such as Kiaka, fromwhich a resource of 1?4 millions ounces of gold hasalready been ascertained.

Towards a genetic model for targeting gold mineralisationin the Scottish DalradianN. J. Hill1, G. R. T. Jenkin1, D. A. Holwell1,D. Catterall2, A. J. Boyce3, D. Mark3, J. Naden4,G. Gunn4, C. M. Rice5

1University of Leicester, LE1 7RH, UK (njh35@le.ac.uk)2Scotgold Resources Ltd, Tyndrum, FK20 8RY, UK3Scottish Universities Environmental Research Centre,G75 0QF, UK4British Geological Survey, NG12 5GG, UK5University of Aberdeen, AB24 3UE, UK

The Cononish deposit is an economic gold prospectsituated within the Grampian Highlands, y4 km SSWof Tyndrum. Scotgold Resources Ltd currently controlsthe project and has exploration licences throughout theScottish Dalradian. Cononish has a JORC compliantresource, with 31 000 oz of Au at 17?9 g t21 inMeasured, 24 000 oz of Au at 10?2 g t21 in Indicatedand 108 000 oz with a grade range of 10?8 to 16 g t21 inInferred. This project aims to increase understanding ofCononish and place it in the context of the widergeology and mineralisation of the Tyndrum area, with aview to enhancing its own and the surrounding areaspotential for gold exploration.

Mineralisation at Cononish is hosted in a ,6 m widesteeply-dipping quartz vein running parallel to the NE-trending Tyndrum Fault. The vein cuts units of Argylland Appin age including psammites, pelites, and somecalcareous units. Gold is hosted in electrum and withinsulphides, with a lack of visible gold. Pyrite dominatesthe sulphide assemblage, with sporadic galena, sphaler-ite and chalcopyrite. The deposit has undergone multiplephases of fluid input: an early quartz phase, sulphide-rich quartz, clean white quartz and late calcite andchlorite veins.

There are large variations in the relative abundance ofelements at Cononish. Highest gold grades are asso-ciated with high Cd and Te. Enrichment of Pb and Znmay be associated with later base metal mineralisation

utilising pathways associated with earlier Au mineralisa-tion. On a deposit scale, no consistent As enrichment isobserved. However, within a more regional settinganomalous As values (up to 300 ppm) are common.Mo abundances appear to be decoupled from Augrades.

The heat source for hydrothermal activity is unclear;there is no surface outcrop at Cononish of igneousbodies. However, a regional gravity anomaly aroundTyndrum may represent an igneous body. A lateCarboniferous quartz-microgabbro dyke cross cuts thevein in the adit and microgranite is exposed 1?5 km fromthe adit entrance. At Glen Orchy (y8 km NNW of adit)there are microgranite and lamprophyre intrusions.

Metamorphic and fluid infiltration history of the TambienGroup, Ethiopia; a Neoproterozoic pre-Snowball Earthsequence

M. R. S. Hodgkinson, G. R. T. Jenkin

University of Leicester, LE1 7RH, UK (mh227@le.ac.uk)

Sediments of the Tambien Group, Ethiopia weredeposited over a period of approximately 65 Ma from800 to 735 Ma (Alene et al., 2006). The Tambien Groupis exposed in four different inliers in the Tigrai region,Northern Ethiopia; from west to east, these are the MaiKenetal, the Tsedia, the Chemit and the Negash Inliers(Alene et al., 2006). The Tambien Group is the youngerof the two sequences that together make up theNeoproterozoic basement of the Nafka Terrane andforms part of the Arabian Nubian Shield (Sifeta et al.,2005). The region is also being investigated for gold byStratex with the potential for many different depositgroups such as mesothermal lode gold, orogenic gold,VMS (Sifeta et al., 2005) as well as overlapping in agewith host rocks of the Zambian Copperbelt.

The region has experienced two major stages oftectonic compression, the first being N–S and the secondE–W (Alene et al., 2006). The first stage has given rise toa penetrative foliation with folds from millimetres totens of metres in wavelength and the second, lesscompressive stage formed folds up to 10 km inwavelength (Alene et al., 2006). Peak regional meta-morphism has PT conditions in the pumpellyite-actino-lite facies and occurred during the first stage ofdeformation (Alene et al., 2006).

The Tambien group sequence comprises metamor-phosed carbonates and slates with the dominantlithologies being black limestones featuring up to 95%calcite and finely laminated green-grey slates (Aleneet al., 2006). At the base of the Tambien Group, there amajor negative carbon isotope anomalies of 24% thatare is not attributed to one of the major glaciations seentowards the end of the Neoproterozoic (Alene et al.,2006; Halverson et al., 2007). There are only foursequences featuring deposition at this time and two ofthe other studied groups are the AkademikerbreenGroup in north east Svalbard, Greenland and theBitter Springs Formation, Central Australia (Hal-verson et al., 2007). They all have the same carbonisotope anomaly which has been called the ‘BitterSprings Anomaly’. However as the region has experi-enced metamorphism and hydrothermal alteration it ispossible that the original isotopic data has been altered.This project aims to characterise the conditions of the

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metamorphism and the hydrothermal alteration so thatnew and existing isotope data from the Tambien Groupcan be characterised and a possible model can be madefor explaining the reasons behind the carbon isotopeanomaly. Since it examines the fluid history of thisregion the results will also have implications for mineralexploration in the area.

Alene, M., Jenkin, G. R. T., Leng, M. J. and Fiona Darbyshire, D. P.

2006. The Tambien Group, Ethiopia: an early Cryogenian (ca

800–735 Ma) Neoproterozoic sequence in the Arabian-Nubian

shield, Precambr. Res., 147, 79–99.

Halverson, G. P., Hoffman, P. F., Schrag, D. P. and Kaufman, A. J.

2007. Stratigraphy and geochemistry of a ca 800 Ma negative

carbon isotope interval in northeastern Svalbard, Chem. Geol.,

237, 5–27.

Sifeta, K. et al. 2005. Geochemistry, provenance, and tectonic setting of

Neoproterozoicmetavolcanic and metasedimentary units, Werri

area, Northern Ethiopia, J. Afr. Earth Sci., 41, 212–234.

The Senegal-Mali shear zone: interaction of two fluiddomains along a sinistral strike-slip system and theirinfluence on Au mineralisation

J. S. Lambert-Smith1, P. J. Treloar1, D. M. Lawrence1,R. Harbidge2

1Centre for Earth & Environmental Science Research,Kingston University London, Penrhyn Road, Kingstonupon Thames, Surrey, KT1 2EE, UK(J.Lambert-Smith@kingston.ac.uk)2Randgold Resources (UK) Ltd, 1st Floor, 2 SavoyCourt, Strand, London, WC2R 0EZ, UK

The Senegal-Mali shear zone (SMSZ), which parallels theSenegal-Mali border, hosts a number of world classorogenic gold deposits in the highly prospectivxicKedougou-Kenieba Inlier, West Africa. The depositsare typically hosted along second and higher order splaysoff the main shear zone. New mineral stretching lineationand shear criteria data reported here confirm the sinistralstrike-slip nature of the SMSZ.

This study builds on that of Lawrence (Lawrence,2010) who showed that some deposits feature fluidcompositions and paragenetic characteristics atypical oforogenic gold deposits. Two distinct hydrothermal fluidswere involved in mineralisation in the Loulo permit areaof western Mali. (1) A high temperature, hypersaline,Na–Fe–Cl–B bearing magmatic sourced fluid and (2) alower temperature, low salinity, CO2–N2–H2S richmetamorphic fluid. The magmatic fluid is absent at theYalea deposit, which represents a typical orogenic golddeposit formed from unmixing of the CO2 rich fluid. TheGara deposit is thought to have formed due to mixing ofthe two fluids, resulting in a deposit with an unusuallyFe-rich paragenesis.

The Bambadji permit area lies to the west of the Loulopermit and straddles the SMSZ. It contains numerousprospective Au targets that surround two large albititebodies in the metasedimentary rocks of the Kofi Series inthe east as well as several iron skarn deposits associatedwith dioritic intrusions in the Faleme Volcanic Belt.Preliminary analyses of diorite and Fe-rich hydrother-mal breccia indicate the presence of a regionallydistributed magmatic fluid similar to that at Gara.SEM analysis of the iron endoskarns shows enrichmentin LREEs, P, Cu, U, Ni, Co and As. Combined withtheir association with widespread sodic alteration and

nearby Au mineralisation this indicates potential affi-nities with IOCG or Kiruna type Iron ore deposits. Thediorite bodies are a potential source for this fluid, whichhas influenced mineral parageneses in Au ore bodiesthroughout the Bambadji permit as well as at Gara. It issuggested that the SMSZ represents a boundary betweentwo distinct fluid domains, with a magmatic sourcedfluid dominant to the west and a metamorphic fluiddominant in the east. The primary aim of this study is toeffectively map these two fluids in order to gain anunderstanding of how they interact and mix along andacross the SMSZ, and to test the potential link betweenIOCG and orogenic gold mineralisation.

Lawrence, D. M. 2010. Characterisation and evolution of Au

mineralisation in the Loulo mining district, Western Mali, PhD

thesis, Kingston University London.

The genesis of base and precious metal vein mineralisationin the Amdrup Fjord area, east Greenland: arelamprophyres the key?S. P. Lawrence1, D. A. Holwell1, T. Abraham-James2

1Department of Geology, University of Leicester, UniversityRoad, Leicester, LE1 7RH, UK (sl230@le.ac.uk)2Platina Resources Limited, PO Box 4192, Robina,Queensland 4226, Australia

The Kangerlusuuaq region of east Greenland hostsintrusive and extrusive rocks associated with the passingancestral Icelandic plume and continental break upassociated with the opening of the North Atlantic.These basic and alkaline intrusions include the 50 MaKangerlusuuaq Alkaline Intrusion (KAI), and a numberof satellite intrusions which both pre and postdate it. TheKAI is located on the western side of the KangerlusuuaqFjord, 20 km to the northwest of the world famousSkaergaard Intrusion. Platina Resources Ltd currentlyholds the exploration licence for the Kangerlusuuaq areaand is prospecting for base and precious metals.

A suite of lamprophyre dykes intrude syenites of theKAI in the Amdrup Fjord area, and are spatially asso-ciated with hydrothermal base and precious metal veinmineralisation, and surround the porphyry Mo deposit ofFlammefjeld (Brooks et al., 2004). Mineralised epithermalstyle quartz-carbonate breccia veining is found along thecontact between the dykes and the unaltered syenite.

Through field observations the veins have beenclassified into four groups:

1. Pb–Zn with prominent galena and calcite quartzgangue

2. pyrite veins within syenite with associated Augrades up to 33 g t21

3. pyrite with tetrahedrite that may host Ag mineralisation4. quartz veins in dyke material (Thomassen and

Krebs, 2001). Further analysis of the vein materialwill determine any petrological, geochemical andgenetic relation between the dykes and the veins.

Analysis of the dykes indicates that they are alkalinelamprophyres based on their bulk geochemistry. Theyhave been dated between 43 and 34 Ma (Gleadow andBrooks, 1979) which is considerably younger than thehost syenite, and this overlaps the 39?7 Ma porphyryMo mineralisation at Flammefjeld (Brooks et al., 2004)

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representing the most recent magmatic event in theregion. This project aims to constrain the temporalrelationship between these poorly studied veins anddykes in what is a hugely significant region in terms ofearly Tertiary magmatic and metallogenic activity.

Brooks, C. K., Tegner, C., Stein, H. and Thomassen, B. 2004. Re-Os

and 40Ar/39Ar ages of porphyry molybdenum deposits in the east

Greenland volcanic-rifted margin, Econ. Geol., 99, 1215–1222.

Gleadow, A. J. W. and Brooks, C. K. 1979. Fission track dating,

thermal histories and tectonics of igneous intrusions in east

Greenland, Contrib Miner. Petrol., 7, 45–60.

Thomassen, B. and Krebs, J. D. 2001. Reconnaissance for noble metals

in Precambrian and Palaeogene rocks, Amdrup Fjord, southern

east Greenland, Geol. Greenland Surv. Bull., 189, 76–82.

The Massawa Au deposit, Kedougou-Kenieba Inlier,Senegal, West AfricaD. Senghor1, D. M. Lawrence2, P. J. Treloar2

1Randgold Resources, 3rd Floor Unity Chambers, 28Halkett Street, St Helier, Jersey, UK(D.M.Lawrence@kingston.ac.uk)2Kingston University, Penrhyn Road, Kingston-Upon-Thames, London, KT1 2EE, UK

The Massawa Au deposit is located within theSenegalese part of the highly prospective/productiveKedougou-Kenieba Inlier, which hosts several world-class orogenic goldfields in western Mali (e.g. Loulo andSadiola). Massawa is located in the Kounemba explora-tion permit along the eastern margin of the Palae-oproterozoic (Birimian) Mako volcano-sedimentarybelt, with mineralisation focussed along splays off amajor terrane-bounding dextral shear known as theMain Transcurrent Shear Zone (MTZ). The deposit is atleast 8?5 km long and has a current resource of3?01 Moz at an average grade of 3?96 g t21.

The Massawa structure trends NE (030u) with highgrade zones situated along N–S dilational shears that areinterpreted to be right-hand flexures developed duringdextral reactivation. Exploration is currently focussedon the northern 4?5 km section of the structure wherethe deposit is split in two separate mineralised zones(Central and Northern). Host rocks strike sub-parallelto the main shear direction and consist of a package oflow grade regionally metamorphosed volcaniclasticsedimentary rocks (tuffs and ash-tuffs), quartz-feldsparand lithic wackes, carbonaceous shales, hydrothermalbreccias, and gabbro and porphyry sills. These sedimen-tary rocks have undergone pervasive silica alteration(Central zone) followed by a sericite-ankerite-dolomitealteration event related to mineralisation (both zones).

Two major styles of mineralisation are recognised atMassawa from field and laboratory studies. The firststage of sulphide-Au mineralisation is associated withdisseminated arsenopyrite-pyrite accompanied by car-bonate-sericite alteration, which follows shear bands inthe sedimentary-igneous host rocks. The second stageconsists of quartz-stibnite¡tetrahedrite veining (con-fined to the Central zone) distinguished by coarsevisible gold mineralisation (100 mm to a few mm).A distinctive trace assemblage is linked to stibniteformation including multiple Sb phases such aschalcostibnite, zinkerite, roschinite, aurostibite, jame-sonite and robinsonite. This Sb-Au mineralisation islikely to represent a shallower (,6 km) late stage

overprint according to the Groves model for orogenicgold (Groves et al., 1998). Shallow-level mineralisa-tion is also suggested by fluid inclusion studies onquartz-stibnite veins which show the predominance oflow temperature (homogenisation temperatures be-tween 115–200uC) H2O–NaCl fluids (,6 wt-% NaClequiv).

Groves, D. I., Goldfarb, R. J., Gebre-Mariam, M., Hagemann, S. G.

and Robert, F. 1998. Orogenic gold deposits: a proposed

classification in the context of their crustal distribution and

relationship to other gold deposit types, Ore Geol. Rev., 13, 7–

27.

Mesothermal gold mineralisation in the Southern Alps,New Zealand: comparisons between mineralised andbarren veins

C. D. Menzies1, D. A. H. Teagle1, S. C. Cox2,A. J. Boyce3

1School of Ocean and Earth Science, NationalOceanography Centre Southampton, University ofSouthampton, SO14 3ZH, UK (cdm1g08@soton.ac.uk)2Dunedin Research Centre, GNS Science, 764Cumberland Street, Dunedin 901, New Zealand3SUERC, Rankine Avenue, Scottish EnterpriseTechnology Park, East Kilbride, G75 0QF, UK

The Alpine Fault in the South Island of New Zealandmarks the transpressional boundary between theAustralian and Pacific plates. Rapid uplift (8–10 mm/year) along the dextral strike slip fault has formed the.3000 m high Southern Alps. Theoretical models(Koons, 1987; 1989) indicate that the combination ofrapid uplift with highly asymmetric erosion results inhigh (.200uC km21) geothermal gradients in the upper-most crust, raises the brittle–ductile transition to shallow levels (around 5–6 km), and fuels hydrothermalcirculation.

The Southern Alps are commonly presented as amodern analogue for mesothermal gold mineralisation,such as the significant Mesozoic gold deposits in Otago,New Zealand (Pitcairn et al., 2006). In the SouthernAlps gold mineralisation is restricted to quartz¡calcite¡ankerite¡chlorite¡adularia veins in steeply dippingvein networks in low grade schists and greywacke in thehigh mountains (Craw et al., 1987). Quartz¡calcite¡chlorite veins hosted in ampibolite grade mylonites inthe Alpine Fault Zone are barren. These veins form atvarying structural levels, defined by ductile versus brittledeformation styles.

Rare earth element patterns of calcite from barrenductile veins in the Alpine Fault Zone and mineralisedveins in the high mountains suggest vein fluids hadsimilar ligand chemistries. However, the mineralisedveins have more radiogenic 87Sr/86Sr (87Sr/86Sr5y0?705to 0?708 versus y0?710 to 0?711) and lower d18O(d18O(vsmow) fluid5y4 to 6 % versus y6 to 13 %). Theradiogenic signature of the mineralised veins is attrib-uted to interaction with pelitic host rocks which have ahigher 87Sr/86Sr than the host rocks of the barren ductileveins. These low grade metamorphic rocks also containmore gold than high grade rocks which host the barrenveins (Pitcairn et al., 2006). The lower d18O signature ofthe mineralised veins is inferred to be due to mixing withmeteoric waters at shallow depth (y1 km), which also

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serves as the mechanism for gold precipitation (Crawet al., 1987).

Koons, P. O. 1987. Some thermal and mechanical consequences of

rapid uplift: an example from the Southern Alps, New Zealand,

Earth Planet. Sci. Lett., 86, 307–319.

Koons, P. O. 1989. The topographic evolution of collisional mountain

belts: a numerical look at the Southern Alps, New Zealand, Am.

J. Sci., 86, 1041–1069.

Pitcairn, I. K., Teagle, D. A. H., Craw, D., Olivo, G. R., Kerrich, R.

and Brewer, T. S. 2006. Sources of metals and fluids in orogenic

gold deposits: insights from the Otago and Alpine schists, New

Zealand, Econ. Geol., 101, 1525–1546.

Craw, D., et al, 1987. Structural geology and vein minseralisation in the

Callery River headwaters, Southern Alps, New Zealand, New

Zealand J. Geol. Geophys., 30, 273–286.

In search of the lost zinc: Zn-dolomite in supergenenonsulphide oresN. Mondillo, M. Boni, G. BalassoneDipartimento Scienze della Terra, Universita di Napoli‘Federico II’, Via Mezzocannone 8 80134 Napoli, Italy(nicolamondillo@libero.it)

The supergene nonsulphide zinc and lead ores resultfrom the weathering of original sulphide-bearing depos-its (SEDEX, MVT and CRD), whose host rocks aremainly carbonates. Until now, the best-known interac-tion between the sulphide-hosting carbonate rocks andsupergene fluids was limited to the exchange between thehost rocks and the Zn and Pb ions carried in the fluids,commonly resulting in the precipitation of smithsonite,hydrozincite, cerussite and hemimorphite (Hitzmanet al., 2003).

However, during our research in the nonsulphidemining districts of Jabali (Yemen), Yanque (Peru) andSouthwest Sardinia (Italy), we could detect an unex-pected widespread replacement of the host dolomitesby newly formed zincian dolomite phases. The zinciandolomites from these mining districts are extensivelydistributed around the main deposits, and replace thepredecessor dolomite phases. Their characteristics,which include the presence of variable amounts ofZn, Pb and Cd in the crystal lattice, are quite similar inall the investigated districts. The precipitation of Zn-dolomites is commonly followed by several Fe- andMn(hydr)oxide phases and, eventually, by sparrycalcite and/or (Mg-) smithsonite. From the paragenesisobserved in many samples, we envisage the replace-ment of the dolomite host as a supergene multi-stepprocess, starting with a progressive ‘zincification’ of thedolomite crystals controlled by microfractures, fol-lowed by a patchy dedolomitisation (resulting in theformation of calcitezFe-Mn(hydr)oxides), and theneventually concluded by the complete substitution ofdolomite by smithsonite. Part of the magnesiumderived from the dolomite replacement is hosted inzoned smithsonite concretions. On the base of texturalevidence, we interpret the Zn-dolomite phases occur-ring in the supergene zone of sulphide zinc deposits asthe ‘missing link’ between dolomite and smithsonite inthe wall-rock replacement process (Boni et al., inpress).

The ample extent of these replacement bodies ofzincian dolomite in several mining districts, under-estimated so far, is important for the exploration ofnonsulphide zinc ores, because Zn-dolomite currently

represents a non-economically recoverable phase. Thismay lead to an incorrect evaluation of the extractablemetallic resources calculated from the assay data, andfrom non-specific mineralogical analyses.

Hitzman, M. W., Reynolds, N. A., Sangster, D. F., Allen, C. R.,

Carman, C. E. 2003. Classification, genesis, and exploration

guides for nonsulphide zinc deposits, Econ. Geol., 98, 685–714.

Boni, M., Mondillo, N., Balassone, G. (in press). Zincian dolomite: a

peculiar dedolomitization case? Geology.

Sedimentary copper mineralisation within the Yozgat-Delice-Yerkoy Basin, Middle Anatolia, Turkey

J. P. Nowecki1, S. Roberts1, R. P. Foster2, Bahri Yildiz3

1School of Ocean and Earth Science, NationalOceanography Centre, University of Southampton,European Way, Southampton, SO14 3ZH, UK(jpn205@soton.ac.uk)2Stratex International PLC, Wessex House, UpperMarket Street, Eastleigh, Hampshire, SO50 9FD, UK3Stratex Madencilik Sanayi ve Ticaret Ltd. sti. IranCaddesi 53/6, G.O.P./Ankara, Turkey

The Yozgat-Delice-Yerkoy basin (y145 km east ofAnkara) is part of the Cankiri basin, which formedduring the Late Cretaceous to Tertiary closure of theNeo-Tethys Ocean, represented by the collision betweenthe Kirsehir and Sakarya continental blocks. Mineralisation primarily occurs at three main horizons withinthe Incik Formation of Middle to Late Eocene ageterrestrial conglomerates and sandstones, in sedimentarychannel structures. The Incik Formation is in closestratigraphic association with evaporite sequences, andcontains gypsum veinlets. Host sediments are bothtexturally and compositionally immature, comprisingsiltstones to sandstones of all sizes to fine grainedconglomerates. Clasts are moderately sorted and aregenerally sub-angular to sub rounded. A variety of clasttypes are observed, including quartz, feldspar (mostlyplagioclase), biotite, ilmenite, lithofragments and lignite.Lithofragments include choritised basalt, metaquartzite,schists, andesites, and reworked sandstones, indicatingthat the source region for the sedimentary rocks wasdiverse, containing lithologies from the nearby AnkaraMelange and various volcanics in the region.

Cu (and minor V–Pb–U–Co–Mo) mineralisationconsists almost solely of oxidised copper minerals,likely formed by supergene alteration of primarysulphide phases. Malachite and azurite are the majorcopper minerals, with minor chrysocolla and cuprite.Malachite mineralisation occurs within the metasedi-mentary rocks, filling pore spaces with a fibrous habitand coating clasts. It is also observed within micro-crystalline quartz veinlets, filling fractures in clasts,penetrating schistosity in metamorphosed lithoclasts,and intruding and expanding mica cleavages. Azuriteshows an affinity for areas of high fluid flow, forming asnear-spherical concretions in pore space around micro-crystalline quartz veins and on porosity and perme-ability boundaries, as well as near organic clasts. Raresulphides were observed penetrating cleavage withinbiotite phenocrysts in an andesite clast within aconglomerate. The similarities between this method ofsulphide emplacement and the sites of malachiteemplacement indicate that the deposits probably con-tained sulphides before widespread supergene oxidation

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occurred. Organic material is common as large ligniteclasts within the sediments, and can frequently beobserved with significant malachite formed on the edgesand in cracks. Thin lenses contain abundant blockyorganic material (interpreted as degrading lignitefragments) partially replaced by malachite surroundedby microcrystalline quartz. These organic phases likelyacted as a reductant for copper bearing fluids, whichwere channelled along areas of enhanced permeabilityand porosity.

Mineral exploration using whole rock multi-elementgeochemistry on the Chirano Shear Zone, Ghana, WestAfricaM. J. Roberts1, G. R. T. Jenkin1, C. Smeathers2,H. Stuart2

1Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK(mjr39@le.ac.uk)2Hugh Stuart Exploration Consultants, Lower FarmBarns, Brandon Lane, Coventry, CV3 3GW, UK

The Chirano Gold District covers a strike length of9 km within the Sefwi-Bibiani volcanic belt in Ghana,y100 km southwest of Kumasi, Ghana’s second city.The district comprises 14 mesothermal gold deposits,hosted within altered mafic rocks of the BirimianSupergroup. All of these deposits are located along theChirano Lode Horizon, an intensely altered anddeformed fault bound package of rocks, displayingalbite and later carbonate alteration with intensebleaching surrounding and within the ore zone.

Exploration at Chirano is at a relatively mature stageand is becoming more conceptual in order to search fordeeper blind thrust deposits along the Chirano LodeHorizon.

A total of 458 drill core samples have been analysedfor their whole rock geochemistry covering a range ofdepths and distances from the ore zone. These sampleshave been correlated against 17 hand specimen andpolished thin section samples to further classify thealteration zones and deformation present. Samplingfocused on mafic rocks within the Chirano LodeHorizon at two deposits, Paboase and Akwaaba.These underground deposits were chosen for study asthey represent the largest proportion of gold within theChirano District and have associated undergroundresources which are the continued focus of the explora-tion team at Chirano.

Whole rock geochemical analysis of drill core samplesfrom the deposits has produced mixed results byhighlighting the immediate lack of pathfinder elementstypically associated with mesothermal gold deposits.Low amounts of arsenic and undetectable levels oftellurium within the mafic samples are prompting acloser study of the chemical patterns and alterationdetected in association with increasing gold levels.

Any correlations or anomalies within the data set willbe used to increase the precision of drill holes targetingmineralisation, generating new drill targets and to helpfind deeper blind deposits such as the Akwaaba andPaboase underground deposits which have added over1?5 Moz to the Chirano deposits total gold reserves.

The potential for rare earth element resources in SouthWest England: a reconnaissance study

R. A. Shaw

British Geological Survey, Keyworth, Nottingham, NG125GG, UK (rashaw@bgs.ac.uk)

The rare earth elements (REEs) have a wide range ofindustrial uses including important applications inenvironmental technology. The REE have recently beenidentified by the European Commission as critical to theEU, chiefly because 95% of global production is fromChina and because for many applications no substitutesexist.

Rock samples from various settings within andaround the Cornubian batholiths in SW England havebeen studied to determine: the distribution and abun-dance patterns of individual REE; the nature andcomposition of REE minerals; and the controls onREE mineralisation in granitic rocks.

Total REE concentrations range from less than 10 togreater than 500 ppm. The highest values occur inskarns and metasedimentary rocks surrounding granitebodies. The light-REE (La-Sm) is concentrated inmonazite and allanite; whereas the middle-REE (Pm-Ho) and heavy-REE (Gd-Lu) are concentrated inxenotime. Monazites are either of primary magmaticorigin and occur as inclusions in biotite, ilmenite andapatite, or of hydrothermal origin, occurring as fram-boids and fine-grained aggregates within cavities.Allanite is almost exclusively restricted to skarns.

REE distribution is predominantly controlled bymagmatic processes and melt composition. Alteration(e.g. chlorite) of granitic rocks results in small scale re-distribution and local upgrading of REE. Mixing ofmagmatic fluids containing REE with meteoric/meta-morphic fluids causes the precipitation of hydrothermalmonazite in metasedimentary units surrounding graniteintrusions. Reaction of magmatic fluids carrying REEwith calcic-skarns results in the formation of hydro-thermal allanite.

Data from this study suggest that, REE concentra-tions in South West England are generally sub-economic. However, metasedimentary units surroundinggranites and calcic-skarns have the greatest potentialfor higher REE concentration.

Alteration mineralogy, geochemistry and elemental massbalance through the hydrothermal alteration zones ofMaher Abad Cu–Au porphyry deposit, Khusf, Iran

K. Siahcheshm1, A. Abedini2

1Geology Department, Faculty of Natural Sciences,Tabriz University, Tabriz, Iran (kl_siahcheshm@tabrizu.ac.ir)2Geology Department, Faculty of Sciences, UrmiehUniversity, Urmieh, Iran

The Maher Abad porphyry Cu–Au deposit is located inKhusf, South Khorasan province, East of Iran. Copper–gold mineralisation is related to the emplacement ofmultiple stages of granodiorite porphyries. The hydro-thermal alteration and mineralisation developed in threetemporally and spatially stages, namely, (1) The earlystage which is divided into potassic (biotite) andpropylitic (chlorite-epidote) zones. (2) The transitionalalteration stage is typified by a phylic (quartz, whitemica and chlorite) zone. (3) The late alteration stage ischaracterised by destruction of feldspar and formationof argillic (muscovite, paragonite and kaolinite) zone.

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The potassic zone is enriched in Si, Fe, K, Rb, S, Cuand Au with a decrease in mass and volume of5?44¡1?67% respectively. Copper and gold enrichmentsin the potassic zone represent the abundance of copper–gold bearing sulphides consist of bornite, digenite andchalcopyrite. The early propylitic alteration zone isrelatively unchanged. The transitional phyllic zoneshows general depletion of ferromagnesian oxides andalkalis, which is consistent with a decrease in mass andvolume. The late argillic zone is characterised by acomplete destruction of pre-existing mafic mineralsand plagioclase, expressed by an overall decreaseof mass and volume (8?65¡6?61 and 17?76¡6?88%respectively).

In general, as a consequence of breakdown ofhornblende, biotite and plagioclase, major elements(Ca, Mg, Na and K) and REE decrease from leastaltered rocks towards the late alteration zones. Based onelemental mass balance calculations by using the isoconmethod, degree of mass and volume losses increasesfrom early, through transitional to late alteration stages.This is compatible with a general decrease of elementalactivities in hydrothermal fluids during the alteration.

Platinum group mineralogy within the Grasvally-Norite-Pyroxenite-Anorthosite member in the Rooipoort area,Northern Limb, Bushveld Complex, South AfricaJ. W. Smith1, D. A. Holwell1, I. McDonald2,T. Pearton3

1Department of Geology, University of Leicester,University Road, Leicester, LE1 7RH, UK (jws14@le.ac.uk)2School of Earth and Ocean Sciences, Cardiff University,Park Place, Cardiff, CF10 3YE, UK3Caledonia Mining Corporation, Johannesburg, SouthAfrica

The northern limb of the 2?06 Ga Bushveld Complex ishost to the PGE-rich Platreef which forms the base of themagmatic succession north of the town of Mokopane.The area to the south of Mokopane is considerably lesswell understood and differs in its magmatic succession.This region consists of ultramafic Lower Zone lithologies, aunique layered package referred to as the Grasvally-Norite-Pyroxenite-Anorthosite (GNPA) member and Main Zonegabbronorites and gabbros. The GNPA member hasbeen divided into the Lower Mafic (LMF) unit, theLower Gabbronorite (LGN) and an upper MottledAnorthosite (MANO) unit. Seven sulphide and PGEmineralised horizons have been identified within theGNPA member. The origin of this unit is highlydisputed with some equating it to the critical zone ofthe eastern and western limbs and thus the mineralisedhorizons with the Merensky Reef and UG2 chromitite,whereas others suggest it is a facies of the Platreef.These discrepancies exist due to the lack of research,especially on the fine scale mineralogy undertaken inthis area and on the PGM assemblages.

A preliminary SEM study has revealed each reef isdistinguishable by its unique platinum group mineral-ogy. The platinum group mineral (PGM) assemblage ofthe four reefs present within the LMF and underlyingquartzite are dominated by Pd antimonides and Pdtellurides. These PGMs are associated with the principalsulphides, namely millerite, pyrite and chalcopyrite andsilicates. In contrast, PGMs present within a chromitite

layer occur predominantly as the Pd-bismuthotelluride,micheneriteand primarily associated with silicates. ThePGM assemblage within the LGN is overwhelminglydominated by Pd antimonides which occur in associa-tion with sulphide blebs comprised of pyrite andmillerite. Additionally, this reef also contains themercury-rich PGM, temagamite which appears to beunique to the northern limb. The PGMs present in theMANO unit occur predominantly as Pd tellurides andbismuthotellurides which exhibit a strong associationwith silicates.

Future work will aim to understand the genesis ofeach reef and to put the GNPA member and itsmineralisation into context with the rest of theBushveld Complex. The dominance of Pd PGMs, andthe presence of abundant millerite and pyrite within theGNPA member noticeably contrasts with the MerenskyReef which is rich in the Pt and Ru PGMs, cooperiteand laurite, and sulphides such as pyrrhotite andpentlandite. Additionally, the GNPA member alsoevidently differs to the Platreef as millerite andtemagamite dominant assemblages do not occur withinthe Platreef.

Petrogenesis of Silurian-Devonian intrusive and volcanicrocks of Western Argyll, Scotland: implications for Cu–Au mineralisation

E. Spencer1, R. N. Armstrong2

1Department of Earth Science and Engineering, RoyalSchool of Mines Prince Consort Road, Imperial CollegeLondon, SW7 2BP, UK (edward.spencer06@imperial.ac.uk)2Department of Mineralogy, The Natural HistoryMuseum, London, SW7 5BD, UK

The Lorne Plateau Lavas (LPL) and KilmelfordIntrusive Suite (KIS) of Western Argyll, Scotland, formpart of the extensive Argyll Suite of igneous rocks. TheKIS hosts widespread sub-economic Cu–Mo–Au por-phyry-style mineralisation. To further develop regionalexploration models, greater understanding of the tem-poral and petrological relationships with the LPL isessential. Recent geochronological and geochemicalstudies demonstrate equivalent mineralisation ages(y425 Ma) and a unifying shoshonitic signaturebetween the LPL and KIS. The resulting proposition isof cogenesis in a post-subduction environment that, todate, has only been tested using whole rock majorelement chemistry and a limited trace element suite. Inthis study, 27 collected samples from the KIS and LPLwere forwarded for thin section examination and multi-element analysis (ICP-AES and ICP-MS using 47elements). Geochemical type for KIS and LPL samplesvaried from basic to acid, but many distinct majorelement trends, such as SiO2 versus TiO2, remainedconsistent suggesting common fractionation patterns forboth suites. Results also demonstrate that using SiO2

versus highly fluid mobile K2O to classify the rocks asshoshonites is flawed due to extensive alteration of bothsuites. Observed trace element patterns on REE/Chondrite and multi-element/Primitive Mantle plotsshow remarkably consistent patterns across all sampleswith variations in the LaN/YbN and DyN/YbN explainedby the more fractionated nature of the KIS. Immobileelement plots for samples follow the Calc-Alkaline trendand exhibit a strong affinity to Volcanic Arc Granites.

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Preliminary melt modelling suggests that both suitesoriginate from the partial melt and consequent fractio-nation of a primitive mantle source. Considering thestrong spatial and temporal links between the two suites,and the additional observed geochemical similarities it isclear that the LPL and KIS stem from the same meltsource. This suggested that a wider tract of WesternArgyll may host porphyry-style mineralisation.

To make a mineral deposit: geothermal systems in ophiolitesas examples of novel solutions for CO2 sequestrationA. L. Stephen1, G. R. T. Jenkin1, J. Naden2,M. T. Styles2, D. J. Smith1, A. J. Boyce3

1University of Leicester, LE1 7RH, UK (als46@leicester.ac.uk)2British Geological Survey, Keyworth, NG12 5GG, UK3Scottish Universities Environmental Research Centre,East Kilbride, G75 0QF, UK

Rising atmospheric CO2 concentrations are driving theneed to greatly reduce anthropogenic emissions in orderto avoid global warming (Meinshausen et al., 2009).Mineral carbonation is a natural process in which CO2

reacts with ultramafic minerals to form carbonates(Lackner, 2003). Our aim is to provide geologicalunderstanding of the mechanisms and rates of naturalcarbonation in Tethyan ophiolites in order to aid thedevelopment of industrial mineral carbonation – inessence to make a mineral deposit.

Ultrabasic rocks are particularly reactive with CO2

and undergo natural carbonation in a range of settings,from the formation of vein carbonates from hydro-thermal fluids at moderate depths and temperatures,through to rapid carbonate formation in ultrabasic minetailings (Wilson et al., 2009). Since the reactions arefluid-mediated the techniques used for investigating oregenesis are equally applicable here.

Our study is focused on the UAE section of the Semailophiolite. Whereas numerous studies have examinedparticular generations of carbonate developed in ophio-lites, we intend to undertake a holistic study of allcarbonates developed within an area. This will determinehow much carbon has been derived from the atmospherecompared to that which has been recycled from oldersources, and accurately assess natural carbonation rates.

Fieldwork undertaken in 2010 involved detailedexamination and mapping of the spatial and geologicalrelations of the different carbonate phases present. Thishas identified multiple generations, with some sitesdisplaying up to 12 separate phases. Those identifiedinclude: (i) carbonate veins within host peridotite; (ii)travertines; (iii) cements in Quaternary conglomerates;(iv) modern carbonates precipitating from hyperalkalinesprings and in irrigation channels; (v) carbonate crustson stagnant water surfaces; and (vi) carbonate efflores-cence. These materials are currently being analysed forcarbon isotopes to constrain the origin of the carbonand the rates of carbonate deposition.

Meinshausen, M., Meinshausen, N., Hare, W., Raper, S. C. B., Frieler, K.,

Knutti, R., Frame, D. J. and Myles, R. A. 2009. Greenhouse-gas

emission targets for limiting global warming to 2uC, Nature, 458,

1158–1162.

Lackner, K. S. 2003. A guide to CO2 sequestration, Science, 300,

1677–1678.

Wilson, S. A., Dipple, G. M., Power, I. M., Thom, J. M., Anderson,

R. G., Raudsepp, M., Gabites, J. E. and Southam, G. 2009.

Carbon dioxide fixation within mine wastes of ultramafic-

hosted ore deposits: examples from the Clinton Creek and

Cassiar chrysotile deposits, Canada, Econ. Geol., 104, 95–

112.

‘Invisible’ gold mineralisation in high-sulphidationepithermal LuzoniteS. Tapster1, A. J. Berry2,3

1Department of Geology, University of Leicester, LE17RH, UK (srt9@le.ac.uk)2Department of Earth Science and Engineering, ImperialCollege London, South Kensington, London, SW7 2AZ,UK3Department of Mineralogy, Natural History Museum,Cromwell Road, London, SW7 5BD, UK

The distribution and geochemical association of ‘invi-sible’ gold within luzonite provides new evidence as tothe mechanism by which Au is precipitated in high-sulphidation epithermal systems during mineral growthof the Cu3(AsxSb12x)S4 enargite-luzonite-famatinitepolymorphs. Inversion between the polymorphs iscontrolled by temperature and the fluid Sb concentra-tion (Posfai et al., 1998). Luzonite is the tetragonal, low-temperature and high Sb form.

Analyses of enargite and luzonite samples fromthe Chinkuashih (Taiwan) high-sulphidation epithermaldeposit were conducted using reflected light microscopyand spectroscopy. WDS electron microprobe analyseswere used to produce elemental maps, which show that‘invisible’ Au is only associated with luzonite polymorphand occurs at concentrations up to 600 ppm.

The crystal structure of enargite limits the Cu3(Sb)S4

component to a maximum of 6% of enargite. Incontrast, this component ranges from 1 to 14% inluzonite. Within a luzonite crystal Sb concentration iscontrolled by compositional twinning between Sb-richand Sb-poor domains. These compositional variationsappear to mirror the well documented polysynthetictwining (Gaines, 1957) seen optically in reflected light.Tellurium shows little substitution into the enargitelattice, however, readily substitutes into luzonite above athreshold of y5% Cu3(Sb)S4.

The mechanism of Au incorporation is substitution ofTe into the (As-Sb)5z site of Cu3(AsxSb12x)S4 as Te4z,rather than as Te22, which is commonly found intelluride minerals. Analysis of the Au rich zones usingXANES spectroscopy indicates that gold occurs asAu3z rather than Au0, suggesting that Au may besequestered into luzonite to charge balance the substitu-tion of Te. However, the existence of Te rich zoneswithout Au shows that these two elements are notinherently coupled within the hydrothermal fluid duringluzonite growth. When they do occur together in a fluid,the favourable partitioning of Te into luzonite creates amechanism by which Au may also be incorporated, thusremoving it from solution. In the absence of Te, Au willeither be fixed in other mineral phases or possiblytransported to a more distil part of the hydrothermalsystem.

Posfai, M. and Buseck, P. R. 1998. Relationships between micro-

structure and composition in enargite and luzonite, Am. Miner.,

83, 373–382.

Gaines, R. 1957. Luzonite, famatinite and some related minerals, Am.

Miner., 42, 766–779.

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Temperature dependence on arsenate adsorption onminerals in the presence of oil

W. Wainipee1, D. J. Weiss1,2, M. A. Sephton1,J. Cuadros2

1Department of Earth Science and Engineering, ImperialCollege London, London, UK (w.wainipee07@imperial.ac.uk)2Department of Mineralogy, Natural History Museum,London, UK

Our previous study shows that oil affects arsenate[As(V)] adsorption on goethite (Wimolporn et al., 2010)and clay minerals but there is a lack of study oftemperature dependence. This research has been con-ducted to investigate the temperature effect on As(V)adsorption on goethite, illite and montmorillonite. Theaim is to examine the effect of temperature on As(V)adsorption by comparing the magnitude of As(V)adsorption in the absence and presence of oil. Thesegoethite and clay minerals selected due to the fact thatthey are typically found in the marine environment. Thebatch experiments have been performed using marineconditions at pH 8 and 0?7M NaCl concentration. Theamount of oil used to coat 100 mg goethite is 3?5 mg.Oil of 35 mg was used to coat illite and montmorillonitebecause the effect of oil on As(V) adsorption could notbe identified if too small amount of oil coated on theseclays.

The adsorption of As(V) fits well with Langmuirisotherm model. The thermodynamic parameters werecalculated from the adsorption experiments at 5, 25, 35,45 and 55 uC. In the presence of oil, Ea, nH, nS, andnG are not significantly different from those of oil-freegoethite and oil-free clays. The exception is nH, nG,and nS between oil-free illite and oil-coated illitesystems. The positive nH suggests that the adsorptionmechanisms are endothermic and the As(V) adsorptionincreases with increasing temperature. The magnitude ofnH is related to the bond strength at the mineralsurface. The nG values are in the range of small negativeand positive values suggesting that a trend of adsorptioncould be spontaneous or requires small amount ofenergy to be more feasible.

Wimolporn, W., Dominik, J. W., Mark, A. S., Barry, J. C., Catherine, U.

and Richard, C. 2010. The effect of crude oil on arsenate

adsorption on goethite, Water Res., 44, (19), 5673–5683.

Gold sources of the Klondike placers

R. J. Chapman1, J. K. Mortensen2, E. C. Crawford2,W. L. LeBarge3

1School of Earth and Environment, The University, Leeds,LS2 9JT, UK (r.j.chapman@leeds.ac.uk)2Earth and Ocean Sciences, University of BritishColumbia, 6339 Stores Road, Vancouver, BritishColumbia, V6T1Z4, Canada,3Yukon Geological Survey, 102-300 Main St, Whitehorse,Yukon, Canada

Attempting to identify the primary sources of the 13(z)million ounces of placer gold recovered from theKlondike District, Yukon Territory Canada, has chal-lenged prospectors and explorationalists for more than acentury. Characterising the placer gold itself in terms ofalloy composition and mineral inclusions provides a

powerful method for geochemically ‘fingerprinting’ goldand in ideal cases provides conclusive evidence forplacer-lode relationships (Knight et al., 1999; Chapmanet al., 2000).

The determination of the alloy compositions andassociated inclusion assemblages from 5877 placer goldgrains (from 61 localities) and 1723 gold grains (from 24lode localities) in the Klondike goldfield permittedidentification of several gold types of coherent geogra-phical distribution (Chapman et al., 2010a; 2010b). Theidentification of systematic compositional variation ingold signatures around Lone Star Ridge and upper LastChance Creek in the north of the Klondike is interpretedas evidence for geographical and temporal zonationwithin two separate hydrothermal systems. This varia-tion is consistent with predicted changes in fluids withinevolving orogenic hydrothermal systems and the asso-ciated influences on alloy composition (Chapman et al.,2010b). Gold in the south of the Klondike exhibits afurther distinctive signature and appears to be derivedfrom several sources, as yet undiscovered.

This work has identified the most economicallyimportant gold signature within the placer inventoryand shown that other signatures evident in placer goldhave not yet been identified in lode occurrences.Furthermore, the proposed model indicates that excep-tionally rich orogenic gold mineralisation can be derivedfrom geographically constrained hydrothermal systems.

Chapman, R. J., Leake, R. C., Moles, N. R., Earls, G., Cooper, C.,

Harrington, K. and Berzins, R. 2000. The application of

microchemical analysis of gold grains to the understanding of

complex local and regional gold mineralization: a case study in

Ireland and Scotland, Econ. Geol., 95, 1753–1773.

Chapman, R. J., Mortensen, J. K., Crawford, E. and LeBarge, W.

2010a. Microchemical studies of placer and lode gold in Bonanza

and Eldorado creeks, Klondike District, Yukon, Canada:

evidence for a small, gold-rich, orogenic hydrothermal system,

Econ. Geol., 105, 1369–1392.

Chapman, R. J., Mortensen, J. K., Crawford, E. C. and LeBarge, W. P.

2010b. Microchemical studies of placer and lode gold in the

Klondike District, Yukon, Canada: 2. Constraints on the nature

and location of regional lode sources, Econ. Geol., 105, 1393–1410.

Knight, J. B., Mortensen, J. K. and Morison, S. R. 1999. Lode and

placer gold composition in the Klondike District, Yukon

Territory, Canada: implications for the nature and genesis of

Klondike placer and lode gold deposits, Econ. Geol., 94, 649–664.

Discovery of the Gounkoto Au Deposit, Loulo Permit,Western Mali, West Africa

D. M. Lawrence1, J. Holliday2, P. J. Treloar1,A. H. Rankin1, P. Harbidge2,1Kingston University, Penrhyn Road, Kingston-Upon-Thames, London, KT1 2EE, UK(D.M.Lawrence@kingston.ac.uk)2Randgold Resources, 3rd Floor Unity Chambers, 28Halkett Street, St Helier, Jersey, UK

The Loulo Au mining district, in Western Mali,represents one of the most prospective terrains in WestAfrica, with current resources exceeding 11?5 Moz atproduction rates of 365 000 oz/year. The recent dis-covery of the world-class Gounkoto deposit has addedfurther resource value to the Loulo permit and is theresult of over a decade of focused exploration. The mostrecent phase of this work included the reintegration ofall layers of data across the region, in addition to an

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Airborne EM survey. The subsequent revised explora-tion model generated a number of conceptual targetswhich all received follow-up work. The first diamonddrillhole at the Gounkoto target returned 46?6 m at13?63 g t21. Two years later the Gounkoto feasibilitystudy is approaching completion with recent drilling(e.g. 31?7 m at 23?9 g t21 and 15?05 m at 30?16 g t21)increasing the mineral resource by 100% to 5?76 Moz atan average grade of 5?28 g t21. Gounkoto has promotedLoulo to the largest West African gold district outside ofGhana, with current resources of 17?3 Moz.

The Gounkoto orebody is a moderate- to steep-dipping shear zone-hosted orogenic gold deposit situ-ated in Palaeoproterozoic metasedimentary rocks of theKedougou-Kenieba Inlier. Mineralisation extends alongstrike of the sinistral Gounkoto N2S structure for1?7 km and to a depth of 520 m (open in all directions),with high grade zones situated along dilational NW-trending jogs or intersections. The deposit has a complexhydrothermal history with multiple deformation, altera-tion and mineralisation events. Intensely sheared semi-pelitic and carbonate sedimentary rocks show evidenceof early albite-ankerite-quartz alteration followed bymagnetite-chlorite-tourmaline and then hematite-sul-phide-Au mineralisation. Chlorite replacement of Fe-bearing phases represents the last phase of hydrothermalalteration. Two styles of sulphide-Au mineralisation areobserved. The main mineralisation zone is characterisedby a magmatic (granitic) Loulo-type ore assemblage(Lawrence, 2010) consisting predominantly of pyrite (Cuand Ni bearing), accessory Ni-sulphides and arsenopyr-ite, and REE phosphates. Hangingwall mineralisedzones hosted in limestones/dolostones contain a poly-metallic Fe–Ni–Co–Cu–As–Pb–Se–Au–Bi signaturewith sulphide phases of pyrite, Ni-pyrite (bravoite),cobaltite, chalcopyrite, clausthalite, sphalerite, polydy-mite and millerite. This distinct ore assemblage could becontrolled by host chemistry driven processes (eO2

causing selective deposition of metals within thecarbonate units) and/or be representative of shallow‘epithermal’ environments (as indicated by the wide-spread presence of Te–Bi minerals).

Lawrence, D. M. 2010. Characterisation and evolution of Au

mineralisation in the Loulo mining district, Western Mali, PhD

thesis, Kingston University.

Geology and geochemistry of the Jalal Abad IOCGDeposit, central IranB. Mehrabi1, B. Karimi1, D. A. Banks2,B. W. D. Yardley2

1Geology Department, Tehran Tarbiat MoalemUniversity, Tehran 15614, Iran (earbme@leeds.ac.uk)2School of Earth and Environment, University of Leeds,Leeds LS2 9JT, UK

The Central Iran iron ore province is located inthe Kashmar-Kerman Zone (KKZ) which is an?X>over 1000 km long and up to 80 km wide arcuatefault-bounded structural zone. The world class BafqIron Province (BIP) is located in the central section ofthe KKZ and is host to major iron oxide ores(y1?8 Gt). The Jalal Abad hydrothermal iron depositis located in the southern part of the KKZ, outside theBIP. It contains 200 Mt iron ore with an average

composition of Fe545%, S51?18% and P50?08%. Themineralisation occurs within Early Cambrian felsicvolcanic tuffs in a volcanic–sedimentary sequence. Theigneous activity in the area is bimodal and has apredominantly felsic character of calc-alkaline affinitywith subordinate amounts of mafic intrusive bodies andlate diabase dykes with alkalic character, as found in theBIP. The main ore mineral in the Jalal Abad is low Ti,V, Cr magnetite with a wide range of textures: massive,cataclastic, disseminated, open space filling and breccia-tion. Primary hematite is rare and secondary hematiteformed mainly at shallow depth along fractures.Actinolite shows extensive intergrowth with magnetitein depth. Apatite is and only found in microscopicstudies. Small inclusions of uranium oxide and cassiter-ite have been identified in magnetite ore. Pyrite,chalcopyrite, arsenopyrite, chalcocite, bismuthinite,co<?show=fo]baltite, and tsumite are the sulphide-sulphosalt minerals in the Jalal Abad deposit. The Na–Ca–K metasomatism is widespread and ferroactinolite,talc, chlorite, and white mica are the main alterationminerals. The homogenisation temperature of LzVzSinclusion in quartz veins is between 280 and 450uC witha peak frequency at 340–360uC. Salinity is between 37and 51 wt-% NaCl equivalent with a peak frequency of37–39 wt-%. LA-ICP-MS analyses of fluid inclusionsindicate that the concentration of Fe, Mn, Zn and Pbincreases with the temperature, while Cu does not showsany trend. The Ca/K ratio of higher than 1, and Fe andCu concentration above 10 000 and 1000 ppm respec-tively, indicate magmatic fluids. The iron oxide–apatite(IOA) deposits of the KKZ are often referred to asKiruna-type, which is a member of the iron oxide-(Cu-Au) deposit style. Recent studies have concluded thatthe Central Iran iron ore deposits of the BIP show noassociation with Cu¡Au. In contrast, the Jalal Abadiron ore deposit contains 0?17 to 0?90% copper and traceof gold. The preliminary studies in the Jalal Abaddeposit may indicate that it is the first IOCG deposit inthe Central Iran.

Carlin type Au deposit potential of the Central AsiaHg–Sb beltD. E. Rickleman1, A. Archangelski1, M. Jackson2,V. Lysenko1, T. Zholdoshov1

1Manas Resources Ltd, 30 Ledgar Road Balcatta, WA,6021, Australia (daniel.rickleman@explorer.ktnet.kg)2CSA Global Pty Ltd, West Perth, WA, 6872, Australia

The recent discoveries of the Obdilla and Shambesaigold deposits in the Southern Tianshan of Kyrgyzstanrepresent a new deposit style previously unknown in theregion. These deposits are considered Carlin Style, mostsimilar to the Chinese Carlin examples.

The ore is hosted primarily, but not limited to thrustbreccias within Carboniferous carbonate rich fore-reefsiltstones at the contact with a massive Carboniferouslimestone. Notably the ore is oxidised both at surfaceand below sulphide ore, indicating an oxidisationcontrol other than proximity to surface.

This region was historically a mercury and antimonyproducing area where mineralisation is similarly asso-ciated with the limestone and upper sediments contact.These deposits occur within the highly folded anddeformed units of the Alay Segment of the SouthernTianshan which, with over 300 km of strike length, is

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now considered to have excellent discovery potential forsimilar style gold deposits.

Brookfield, M. E. 2000. Geological development and Phanerozoic

crustal accretion in the western segment of the southern Tien

Shan (Kyrgyzstan, Uzbekistan and Tajikistan), Tectonophysics,

328, 1–14.

Cline, J. S., Hofstra, A. H., Muntean, J. L., Tosdal, R. M. and Hickey,

K. A. 2005. Carlin-type gold deposits in Nevada: Critical geologic

characteristics and viable models, Econ. Geol. 100th Ann. Vol.,

451–484.

Fillipova, I. B., Bush, V. A. and Didenko, A. N. 2001. Middle

Paleozoic subduction belts: the leading factor in the formation of

the Central Asian fold-and-thrust belt, Russ. J. Earth Sci., 3, 405–

426.

Jackson, M. and Louw, G. 2009. Geology and Mineral Resource

Evaluation at the Shambesai Gold Project, CSA Global Pty Ltd,

Technical Report Report No. R204.2009.

Konopelko, D., Biske, G., Seltmann, R., Eklund, O. and Belyatsky, B.

2007. Hercynian post-collisional A-type granites of the Kokshaal

Range, Southern Tien Shan, Kyrgyzstan, Lithos, 97, 140–160.

Li, Z. P. and Peters, S. G. 1998. Comparative geology and geochemistry

of sedimentary-rock-hosted (Carlin-Type) gold deposits in the

People’s Republic of China and in Nevada, USA. USGS Open

File Report 98–466.

Nikonorov, V. V., Karaev, Yu. V., Borisov, F. I, Tolsky, V. I.,

Zamaletdinov, T. S., Larina, T. V. and Gorbaneva, T. V. 2007.

Gold Resources of Kyrgyzstan. State Agency for Geology and

Mineral Resources under the Government of the Kyrgyz

Republic. The Kyrgyz Methodical Expedition for Geological

and Economical Research.

Hydrothermal alteration and Cu–Mo mineralisation inKighal porphyry stock, north of Varzeghan, East-Azarbaidjan, Iran

V. Simmonds, A. A. Calagari

Geology Department, Faculty of Science, TabrizUniversity, Iran (Simmonds_vartan@yahoo.co.uk)

Quartz monzonitic porphyry stock of Kighal is locatedabout 12 km north of Varzeghan, East-Azarbaidjanprovince of Iran. It intruded upper Eocene andesitic-latitic and andesitic-basaltic units during magmaticactivities of Pyrenean orogenic phase (upper Oligocene-lower Miocene) and its hydrothermal activities coupledwith boiling caused shattering and hydro-fracturingwithin the cupola leading to the development of variouskinds of pervasive alteration zones such as potassic,phyllic, argillic, advanced argillic and propylitic.

Hypogene sulphide mineralisation principally occurredwithin potassic, transitional potassic–phyllic and phyl-lic zones as disseminations, veinlets-microveinlets, andopen-space fillings. Pyrite is the most abundant sul-phide mineral occurring as disseminations and also asdominant phase within quartz-sulphide, anhydrite-gypsum, carbonate-sulphide, and pyrite veinlets andmicro-veinlets. The main copper mineral is chalcopyriteoccurring as disseminations, as replacement of pyrite,and as minor phase within quartz-sulphide andcarbonate-sulphide veinlets and microveinlets. Moly-bdenite is disseminated within the early-stage quartzveinlets as well as in the matrix of potassic alterationzone. Sphalerite and galena are mainly present inperipheral parts of the porphyry stock occurring asdisseminations within the matrix and quartz-sulphideand carbonate-sulphide veinlets as well. They replacechalcopyrite and/or show intergrowth with it. Theaverage grades of Cu and Mo in hypogene ores areabout 760 and 30 ppm respectively. Hypogene oxides

include magnetite and lesser amounts of hematite whichare sporadically present within the potassic zone.

The presence of chalcopyrite and low-Fe sphalerite inthe area testifies to intermediate sulphidation state(Einaudi et al., 2003). The estimated values for pH ofthe ore-bearing hydrothermal fluids are ,5 and thelogfO2 of these fluids ranges from 236 to 239 (Graham,I).

Supergene processes developed both alteration andmineralisation zones. Goethite is the main supergenemineral within the leached and oxidised zone accom-panied by lesser amounts of jarosite, hematite, malachiteand azurite. Supergene enriched zone with an averagethickness of 25 m, contains chiefly covellite along withlesser amounts of bornite replacing chalcopyrite.

Einaudi, M. T., Hedenquist, J. W. and Inan, E. E. 2003. Sulfidation

state of fluids of active and extinct hydrothermal systems:

transitions from porphyry to epithermal environments, in

Volcanic, geothermal and ore forming fluids: rulers and witnesses

of processes within the earth, (ed. S. F. Simmonds and

I. Graham), Soc. Econ. Geol., 10, 285–313.

John, D. A., Garside, L. J. and Wallace, A. R. 1999. Magmatic and

tectonic setting of late Cenozoic epithermal gold-silver deposits in

northern Nevada, with an emphasis on the Pah Rah and Virginia

ranges and the northern Nevada rift, Geol. Soc. Nevada, 29, 65–

158.

Crystal chemistry of niobium mineralisation at BayanObo, China: constraints on the formation of hydrothermalNb resources

M. Smith1, J. Spratt2

1School of Environment and Technology, University ofBrighton, Brighton, UK (martin.smith@brighton.ac.uk)2Department of Mineralogy, The Natural HistoryMuseum, London, UK

The Bayan Obo Fe–REE–Nb deposit is the world’slargest known rare earth element resource, with esti-mated reserves of up to 1500 Mt of iron ore (35 wt-%Fe)and 48 Mt REE (6 wt-%REE2O3). It also hosts reservesof 1 Mt Nb at 0?13%Nb). These reserves are relativelysmall compared the prime Nb producers of Araxa andCatalao, Brazil, and Niobec, Canada, but are significantboth for their association with world class REE reservesand for the fact that Nb mineralisation is unequivocallyhydrothermal. In this study, we have examined thetextural setting and chemistry of niobates and associatedminerals from Bayan Obo in order to constrain theprocesses of mineralisation and the differences betweenNb mineralisation here and at other major depositsword wide.

Nb mineralisation is dominated by the mineralaeschynite (REE,Ca,Fe)(Ti,Nb)2(O,OH)6, but smalleramounts of other Nb bearing minerals occur. Notablyminerals such as baotite [Ba4(Ti,Nb)8Si4O28Cl] maypre-date aeschynite in the paragenesis. Aeschyniteoccurs as aggregates cutting across the banding in themonazite-bastnasite-fluorite-magnetite ores, as coarsegrained, acicular, euhedral crystals accompanying andcross-cutting undeformed aegirine, and as a hydro-thermal vein phase accompanied by aegirine, barite andcalcite. All these settings clearly indicate a hydrother-mal origin for Nb mineralisation. In all cases aeschyniteoccurs as either aeschynite-(Ce) or aeschynite-(Nd),with a normalised abudance peak from Ce to Pr and

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frequently a slight positive Eu anomaly. All aeschynaitecontains significant Th (up to 15 wt- % ThO2) and insome instances shows primary zonation with respect toTh and Y. Aeschynite also preserves evidence ofhydrothermal alteration, possibly enhanced by meta-mictisation, with increasing contents of Ca, Si and F,and reduced concentrations of Nb and the REE. Biotiteand riebeckite amphibole associated with niobiummineralisation both have elevated concentrations of Frelative to other paragenetic settings within the oredeposits, indicating the importance of high HFactivities for Nb, REE and Th transport in hydro-thermal fluids. Complexation of Nb with F in bothcarbonatite melts and hydrothermal fluids may in partbe responsible for the fraction of Nb from Ta in thesedeposit types.

Fault-valve action, fluid mixing and gold deposition:identification of grade controlling mechanisms in Nalunaqgold mine, GreenlandM. Smith1, F. Bowers2

1School of Environment and Technology, University ofBrighton, Brighton, UK (martin.smith@brighton.ac.uk)2Angel Mining plc, 6 Station Road, Morton, Lincolnshire,UK

Nalunaq is a vein-type shear zone-hosted gold deposit.The host lithologies are largely amphibolite faciesmetabasic rocks: metabasalt and metadolerite sills (withminor metatuffs and meta-agglomerate), which arebelieved to be co-magmatic and relatively contempora-neous in terms of timing of emplacement, cut by graniticaplite dykes. Significant mineralisation occurs within a

0?5–2?0 m wide shear zone (known as the main vein)where gold is largely found within sheeted quartz veinsand with associated calc-silicate alteration. The goldgrade is irregularly developed along the main vein, withgrades varying from 1 to over 200 g t21.

Fluid inclusion microthermometric investigations ofeight samples from the main vein at Nalunaq gold minehave been carried out in order to investigate possiblecontrols on the Au grade distribution in the mine. Thesample set included both high (.18 g t21) and low grade(,1 g t21) samples. The internal structure of thesamples is consistent with repeated vein opening duringcrack seal vein growth. Later cross-cutting fractures mayindicate a changing stress regime with time. Four mainfluid inclusion populations have been identified. (i):salinities from 32 to 44 wt-% NaCl equivalent andhomogenisation temperatures from 13 to 380uC. (ii):salinities from 28 to 32 wt-% NaCl eq. and homogenisa-tion temperatures from 130 to 250uC. (iii) salinities from18 to 25 wt-% NaCl eq. and homogenisation tempera-tures from 130 to 250uC. (iv) salinities from 0 to 12 wt-%NaCl eq. and homogenisation temperatures from 140 to210uC. High gold grades appear to correlate with theoccurrence of Populations (ii) and (iii). This is inter-preted to result from enhanced gold deposition as aresult of fluid mixing between high and low to moderatesalinity fluids, and rapid fluid pressure cycling on veindilation (fault valve action). Such pressure drops couldalso potentially enhance gold deposition through aqu-eous-carbonic fluid immiscibility or boiling, but noevidence for these processes has been found in thisstudy.

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