LETTER

The masquerade of alkaline–carbonatitic tuffs by zeolites:a new global pathfinder hypothesis

L. S. Campbell & A. Dyer & C. Williams & P. R. Lythgoe

Received: 18 August 2011 /Accepted: 2 December 2011 /Published online: 21 December 2011# Springer-Verlag 2011

Abstract Rapid and progressive reaction of alkaline–car-bonatitic tuffs with magmatic and crustal fluids disguisestheir initial character and origin. This is collectively indicat-ed from (a) the extensive literature on zeolite formation fromvolcanic glass precursors and alkaline fluids, (b) mineralog-ical characteristics of specific zeolite species, (c) a compar-ative review of global distributions of alkaline–carbonatitesuites and of zeolite minerals, and (d) new trace elementdata from zeolite samples. A unifying conceptual modelbased on tectonic and geological settings, hydrological re-gime and mineralogy is presented that helps to explain theglobal distributions and current understanding of occurren-ces. The model will assist in resource exploration by contrib-uting deeper understanding of the economically importantbedded zeolite deposits and further, serve as a guide to thediscovery of new alkaline–carbonatitic suites, potentially ofeconomic significance (metallic ores and rare earth elements).

It follows that future testing of the hypothesis will impact onmodels of natural carbon cycling as volcanic contributions ofCO2 are reviewed.

Keywords Natural zeolites . Alkaline magmatism .

Carbonatites . Mineral reactivity . Trace elements

Introduction

In the last 50 years, the recognition of widespread occur-rences, both of primary carbonatites (igneous rocks com-posed largely of carbonate minerals, Tuttle and Gittins 1966;Bell 1989; Woolley and Kjarsgaard 2008a) and of naturalzeolites (hydrated aluminium silicate minerals with openframework structures and important cation exchangeproperties, Mumpton 1981; Tschernich 1992), has beenconsiderable. The successive growth of scientific understand-ing in these traditionally disparate fields has accelerated withmulti-disciplinary advances in fundamental science, and alsowith the discovery and utilization of their respective naturalresource potentials (Colella and Mumpton 2000; Bish andMing 2001; Mitchell 2005; Wall and Zaitsev 2004; Woolleyand Kjarsgaard 2008a, b). However, recognition of a globalgenetic link between these systems has, to date, not beenconceptualized. The reasons are evident; with an emphasison properties and applications of zeolite-group minerals, andon elucidating the highly complex composition–zonation pat-terns in zeolite occurrence studies, global patterns of funda-mental geological/tectonic setting are not readily apparent.Further, the complex, partially understood and controversialassociation between carbonatites and the huge diversity ofalkaline rocks that exist would tend to make this highlyspecialized discipline less readily accessible to other scientists.In carbonatite science, the big questions are on magma origins

Electronic supplementary material The online version of this article(doi:10.1007/s00126-011-0394-z) contains supplementary material,which is available to authorized users.

L. S. Campbell (*) : P. R. LythgoeSchool of Earth, Atmospheric and Environmental Sciences,University of Manchester,Williamson Building, Oxford Road,Manchester M13 9PL, UKe-mail: Linda.Campbell@manchester.ac.uk

A. DyerDepartment of Chemistry, Loughborough University,Ashby Road,Loughborough, Leicestershire LE11 3TU, UK

C. WilliamsSchool of Applied Science, University of Wolverhampton,Wulfruna Street,Wolverhampton WV1 1SB, UK

Miner Deposita (2012) 47:371–382DOI 10.1007/s00126-011-0394-z

and evolution including the examination of alkaline and per-alkaline rock associations (Woolley and Kjarsgaard 2008a, b),the relationship with large igneous provinces, “LIPs” (Ernstand Bell 2010), and on the considerable resource potential ofthese deposits (Wu 2008; Castor 2008).

Fluid–magma separation and fluid–rock interaction (feni-tization) studies in deeper crustal settings have received muchattention (Bailey and Hampton 1990; Le Bas 2008), but lowtemperature near-surface alteration, especially of extrusiveoccurrences, has only sparsely been addressed by the carbo-natite community (Mitchell 2005; Zaitsev and Keller 2006;Barker and Milliken 2008). Yet nearly half a century ago, Hay(1964) detailed the zeolitization of trachytic and nephelinitictuff beds of the Olduvai Gorge lacustrine deposits, and further,compared them directly with the saline lake deposits of thewestern USA, listing silica-undersaturated glass compositions(e.g., nephelinite) as precursors in the Eocene Green RiverFormation. Ironically, he later discussed magma compositionsin the Tanzanian Olduvai Gorge and the German Kaiserstuhllocalities, suggesting that carbonatite magmas might morecommonly erupt as natrocarbonatitic lavas as seen at Old-oniyo Lengai, losing their alkalis to subsequent alterationreactions (Hay and O’Neil 1983). A full and detailedcounter-discussion on this issue is given by Mitchell (2005),citing experimental and textural evidence against very wide-spread occurrences of natrocarbonatite, yet acknowledgingthat extreme reactivity would mask their recognition. Zaitsevand Keller (2006) reported the presence of highly concentrat-ed alkaline brines in pore fluids accompanying natrocarbona-tite mineral reactions at Oldoniyo Lengai. In the presenthypothesis, we do not suggest that zeolite beds representaltered natrocarbonatite, but that alteration of the associatedalkaline glasses to zeolites could have been promoted by highconcentrations of hydrophilic alkalis released into the localnear-surface hydrosphere from erupted natrocarbonatite-typecompositions, or from composite eruption products as de-scribed by Bailey et al. (2006) for Limagne, France.

Thus the present study demonstrates the pertinence of thevast literature on highly reactive alkaline-glass precursor tuffsfor bedded zeolite occurrences (especially the rift-type “sedi-mentary” saline lake deposits, Hay and Sheppard 2001) to therecognition of, and exploration for, extrusive alkaline–carbo-natitic rocks. It demonstrates the value and potential of theglobal database “mindat.org” (Hazen et al. 2011) for resourceexploration. It also highlights the value of carbonatite sciencein better understanding the global patterns of distribution andcontrols on evolution of different types of zeolites.

The hypothesis

We hypothesize that “sedimentary” zeolite deposits are re-lated to alkaline–carbonatite systems through fluid reaction

of extrusive alkaline volcanic products. Our rationale isbased on the well-documented control of highly reactiveprecursor glass compositions for zeolite formation in beddeddeposits and also on the hydrological regime identified ineach occurrence, which influences progressive zeolitic reac-tions. We further hypothesize that many cavity-type zeolites(vugs, amygdales and veins) are also genetically linked tolow silica alkaline–carbonatitic suites through fluid sources.We do not consider marine or metamorphic zeolites in thepresent discussion.

Thus we predict that the global incidence of alkaline–carbonatitic rocks is more extensive than presently under-stood, and that new discoveries of carbonatite suites shall bemade easier with the use of pathfinder criteria based onzeolite occurrences and compositions, including new traceelement data (this study). We also suggest that our hypoth-esis contributes a unifying landscape for natural zeoliteformation and evolution, consistent with current understand-ings of global zeolite occurrences.

Analytical methods

Digestions

We selected acid digestion of powdered zeolite samples forextraction of extra-framework cations in this pilot study.Duplicate sub-samples were accurately weighed anddigested for 18 h in 50% HCl (room temperature agitation).Precise aliquots were taken and dilutions were prepared byserial methods, for 5% acidified (HCl) solutions. 1,000 ppmKNO3 was added to one set to suppress ionization of Li andRb during ICP-AES analysis. The ICP-MS set did notcontain added KNO3. Analytical standards were made upfrom stock single and mixed element standards supplied byAlpha Aesar, VWR and Johnson Matthey to match thesample solutions. High-purity reagents and deionized water(to 18.2 MΩ) were used throughout in the preparation ofsample solutions and analytical standards.

Instrument specifications and operating conditions

The rare earths, Y, Cs, U and Th were analysed by induc-tively coupled plasma mass spectrometry (ICP-MS) and Li,Rb, Sr and Ba by inductively coupled plasma atomic emis-sion spectroscopy (ICP-AES).

ICP-MS The ICP-MS is an Agilent model 7500cx. Operat-ing conditions were standard: plasma condition RF Power1,550 W; sample depth 8 mm; plasma gas 15 l/min; carriergas 1.05 l/min; peripump 0.08 rpm. Data acquisition param-eters: peak pattern full quantification; integration time 0,1 s;3 repeats. Mass list: 89Y, 133Cs, 139La, 140Ce, 141Pr, 146Nd,

372 Miner Deposita (2012) 47:371–382

147Sm, 153Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm,172Yb, 175Lu, 232Th and 238U. Internal standards (Ge, Rh)were prepared from 1,000 mg/l stock single element standards(VWR).

ICP-AES The ICP-AES is an Optima 5300 DV manufac-tured by Perkin-Elmer. The sample introduction system iscomprised of a concentric glass nebulizer system fitted to acyclonic spray chamber. The spectrometer has the capabilityof viewing the plasma radially and axially. Viewing theplasma axially improves ICP detection limits by approxi-mately an order of magnitude over the radial view plasma.While both plasmas have about the same linear concentra-tion range, the radial plasma can measure at higher concen-trations because of the reduction in sensitivity. Thespectrometer is based on an echelle polychromator with asegmented-array charge-coupled-device and has a wave-length range of 163–782 nm. Wavelength specifications(nm) for this study were Li 670.784, Rb 780.023, Sr460.733 and Ba 233.527. Two point background correctionswere made on each peak and the average of three readingsper analysis was calculated (relative standard deviationswere generally within 5%). Operating conditions used werestandard; plasma gas 15 ml/min; auxiliary gas 0.2 ml/min;nebuliser gas 0.75 ml/min; RF power 1,300 W; samplepump speed 1.5 ml/min.

X-ray diffraction The instrument is a Phillips PW1710 dif-fractometer running a copper X-ray tube at 40 kV and30 mA. The detector step size was 0.02° θ and the samplestep time was 1.0 s. Approximately 100 mg of each samplewas mounted on glass slides with a small well. The mineraldata analysis was performed using Phillips APD softwarerunning on a MicroVax 3100.

Quality assurance

Analytical quality control factors were evaluated; reproduc-ibility from replication, instrument drift checks with repeat-ed analysis of standard solutions, use of analytical andprocedural blanks, and analysis of duplicated reference sam-ples with each batch. The relative standard deviations ofanalytical standards and sample solutions were generallywithin 5% and no contaminations were detected in theblanks for any element. Duplicate samples were well-matched; 10% precision was achieved by 93% of samples,as assessed by the Thompson and Howarth (1978) method.The Mudhills sample was chosen as a reference sample as ithas a good history of independent verification by othermethods (neutron activation analysis in Dyer et al. 1993,and ICP-MS with acid digestion (HF–HClO4–HNO3), Stre-kopytov 2009, personal communication).

Method development

For the digestions, HCl was preferred over an earlier experi-mental HF batch (microwave digested with an evaporationstage and made up to 2% acidification with HNO3) whichgenerated sparingly soluble Al–F species. Where thisoccurred, the analyses were rejected. However, the Lovelock,Bowie and Rotorua samples displayed excellent reproducibil-ity with further confidence from the quality assurance factorsdescribed above, and have therefore been included in the dataset. All other samples were HCl digested in the main method,as described above.

Map construction

The maps of Fig. 1 were created using ESRI ArcGIS 9.2software. Using a summarized geological basemap afterChorlton (2007), we overlaid carbonatite and zeolite mineraloccurrence data. Carbonatite co-ordinates were taken fromWoolley and Kjarsgaard (2008b) and zeolite co-ordinateswere compiled visually from Google Maps, using localityinformation from Mindat.org. Spatial accuracy has thereforebeen limited by the variable detail of source information.The mineral/carbonatite occurrence data uses a WGS84geographic coordinate system whereas the basemap usesWGS1972. This can result in a locational error of under20 m typically. Note: Chorlton (2007) © Department ofNatural Resources Canada. All rights reserved.

Rationale and evidence

Here we explain the basis and rationale (a–d) of our hypoth-esis, highlighting key aspects of the two main disciplines. Weexplore evidence embedded in the literature and in globaldatabases and begin to test the primary relationship withcomparative maps and new trace element data.

(a) Precursor volcanic glasses and alkaline fluids: theassociation of zeolites with low-Si alkaline and basicrock compositions is well known, as seen numerouslyin the review volume on natural zeolites (Bish andMing 2001). Specifically, the role of rock/glass com-position on zeolite formation is explained by Chiperaand Apps (2001), Hay and Sheppard (2001) and Lan-gella et al. (2001). However, significant contributionsto understanding the role of glass composition to spe-cific alteration products has been given by De’Gennaroet al. (1995, 2000) in experimental studies. This re-search has shown how starting compositions of trachyt-ic/phonolitic rocks from European pyroclastic deposits(all, incidentally, known carbonatitic provinces), com-bined with temperature, fluid pH and time to progress

Miner Deposita (2012) 47:371–382 373

a

b

c

374 Miner Deposita (2012) 47:371–382

zeolitization. It is worthy of note here that De’Gennaroet al. (1995) explain how high concentrations of Mg insolution keep the pH low, favouring smectite clayprecipitation. Low Mg allows a rise in pH such thatzeolite stability fields are reached (e.g. for phillipsite,analcime). Thus dolomitic carbonatites extruding explo-sively with nephelinite glass (as in Limagne, France,Bailey et al. 2006), should be less likely to displayphillipsite alteration (subject to carbonate buffering).

Whilst it is clear from studies on western USA andsome European deposits that rhyolitic precursors arecapable of becoming zeolitized (Broxton et al. 1987;Kirov et al. 2010), all apparently require alkali-rich, highpH fluid interaction. A key source of such fluids is fromalkaline–carbonatitic magmas; they are also known asfenitizing fluids in their subsurface context (Le Bas2008; Mitchell 2005; Woolley and Church 2005). Aninsightful discussion on the types of carbonatite andalkaline magmas in which alkaline fluids separate fromthe melt is given inWoolley and Kjarsgaard (2008a), andare suggested as those that are differentiated in the crust,rather than ascended directly from the mantle. In theirreview of known extrusive carbonatites, Woolley andChurch (2005) consider the relationship of the alkalicontent with different eruptive styles as categorized bylarge volcanoes (V—differentiated sources), and smallvolcanic edifices (SVE—rapid ascent from the mantle).

The review of saline lake type bedded zeolite depositsby Hay and Sheppard (2001), describing work on EastAfrican bedded zeolites and numerous studies on theextensive western USA deposits of this type (e.g. Eugsterand Surdam 1973 on the Green River Formation, directlycompared with beds of Lake Magadi, Tanzania), aredemonstrative of occurrence patterns of low-Si volcanicglass reaction with alkaline fluids, often in arid environ-ments. Although the precursor glasses may not always bepreserved, the regional significance of East African

volcanism and alkaline hot spring feeders for the salinelakes is overwhelming. This region is an important studyarea as most of the volcanic rocks, including the beddedzeolites, rest on exposed Precambrian basement and arethus effectively isolated from a silica-rich hydrologicalregime. The saline lake type zeolites of the western USArest on covered basement (Phanerozoic sedimentary andpyroclastic sequences), and are thus subject to much widersources of fluids (see chapters on open and closed hydro-logical systems in Bish and Ming 2001). Consequently,progressive zeolitic reactions have dominated in theUSA province, giving rise to suites of zeolite beds withhigh Si/Al ratios (clinoptilolites, mordenites, etc.).

(b) Mineralogical characteristics: most minerals of thezeolite group considered here are hydrated open frame-work structures with a significant proportion of Alsubstituting for Si in the tetrahedral sites. Structuretype and variation in R Si/(Si+Al+Be) as well asextra-framework cation composition result in over 50distinct natural zeolite mineral species (www.iza-online.org/natural/). Large ion lithophile elementsdominate the extra-framework cations but Mg and Liare also known (Passaglia and Sheppard 2001). In ourhypothesis and conceptual model, we propose to relatevariations in R and major extra-framework cation com-position to origin of the precursor glass and subsequentreactive fate. Thus, we ask whether fluids and glassessourced directly from alkaline–carbonatite magmasgive rise to low-R zeolites, and whether the extra-framework cation composition (both major and tracecations) is consistent with this. We also considercation selectivity as a control on mineral composi-tions (Dyer 2007). The well-documented cation selec-tivity series determined for specific zeolite types andindeed, for specific deposits, urge vigilance in interpre-tation of major and trace element compositions in zeo-lites that might have undergone progressive stages ofreaction involving framework transformation. For exam-ple, Trummer and Barth-Wirsching (2000) describea phillipsite to mordenite or clinoptilolite transfor-mation (phillipsite selectivity: Cs>K≈Rb>Na>Li,Barrer and Munday 1971; clinoptilolite selectivity:Cs>K>Sr0Ba>Ca>>Na>Li, Vaughan 1978), intheir reaction experiments starting with a natural volca-nic glass from California, USA. They discuss chemicalgradients and reaction rates as additional parameters thatinfluence observed zonal distributions in bedded, salinelake type zeolite deposits. Thus, mineralogical processesbeyond simple ion-exchange with fluids will have takenplace, influencing the overall composition of the resul-tant zeolite.

It should be noted here that studies of other micropo-rous mineral groups with rare and transition elements

Fig. 1 Comparative map of selected zeolite mineral occurrences andknown carbonatites. Carbonatite data after Woolley and Kjarsgaard(2008b) and geological base map summarized from Chorlton (2007),© Department of Natural Resources Canada, all rights reserved. Min-eral data from Mindat.org, include bedded and cavity-type zeolites.General chemical formulae for zeolite minerals are from Passaglia andSheppard (2001). a Global occurrences. Excellent matches are seen inthe well-studied carbonatites of the Kola Peninsula, Russia, Mont St.Hilaire and Ice River, Canada, Eifel and Hegau, Germany, the Romeprovince, Italy, the Canary Islands, Cerro Sapo, Bolivia, Jacupiranga,Brazil and East African localities. b Central Europe. Note the distribu-tion of merlinoite, a rare K-rich zeolite, in the Italian ultrapotassicprovince around Rome. c The Colorado Plateau, USA. Whilst thereare no direct matches of known carbonatites with zeolites specificallyselected for this study, collectively the data trend in an arcuate patternaround the plateau, likely relating to deep lithospheric processes (seeLevander et al. 2011). Note the position of the Mountain Pass REEdeposit, within the arcuate trend

�

Miner Deposita (2012) 47:371–382 375

have been strongly associated with alkaline and peralka-line rocks and accompanied by zeolites. An overview ofthese other microporous minerals is given in Pekov andChukanov (2005).

(c) Global distributions: in their landmark publication onthe world distribution of carbonatites and alkaline rocks,Woolley and Kjarsgaard (2008b) discuss the patterns ofknown occurrences in relation to regional tectonic settingand other criteria. It is suggested that the global distribu-tion of zeolite-group minerals should display similar pat-terns with a considerable degree of spatial localitymatching, on the basis of their hypothetically linkedorigins. To test this notion, a compilation of locality datawas made for all known occurrences of the low-Si zeolitephillipsite, (frequently reported as an early alterationphase), and for occurrences of the rare Ba, Sr, and Kzeolite species, all from the online, open-source database“Mindat.org” (Hazen et al. 2011). These data were thenused in conjunction with the Woolley and Kjarsgaard(2008b) carbonatites data set to produce a new compara-tive world map (Fig. 1a). Two regions have been expand-ed; central Europe in Fig. 1b, and the Colorado Plateauarea in Fig. 1c.

A critical examination of the map figures reveals (a)major locality matching in the central European prov-ince, especially in Italy and Germany, (b) good matchingin parts of the western USA and the Canadian Mont St.Hilaire district, plus the Kola peninsula of Russia, Boli-vian and Brazilian localities and a few East Africanoccurrences, (c) a strong association of phillipsite and afew carbonatites with oceanic island volcanism, notablyin the Canary Islands, (d) intense clusters of carbonatite-absent phillipsite occurrences in the western USA (theBasin and Range and rimming the Colorado Plateau) andin Tasmania/eastern Australia. Collectively, carbonatiteand zeolite occurrences describe an arc on the sourthernperiphery of the Colorado Plateau (Fig. 1c), where nu-merous deep magmatic bodies have recently been iden-tified (Levander et al. 2011).

Visually striking are the comparative distributions ofthe rare Ba, Sr and K zeolites, bellbergite, brewsterite,edingtonite, perlialite, paulingite and merlinoite. Theultrapotassic rocks of the Rome Province are expressedin the K-rich, low-Si zeolite merlinoite (Fig. 1b) and alsoin montesommaite (not illustrated). Bellbergite onlyoccurs at carbonatite localities, with a similar pattern forperlialite. With regard to Ba and Sr, the distributions ofedingtonite and brewsterite are suggestive of additionalcontrols on (origin?) and mobility of Ba-rich fluids, withfurther preservation factors relating to Ba precipitates.Nevertheless, the co-occurrences are worthy of note.

(d) Trace element data: reports of trace element analysesin natural zeolites are scarce (Dyer et al. 1993;

Terakado and Nakajima 1995; Stamatakis et al.1996; Vitali et al. 2000; Godelitsas et al. 2010),yet potentially offer valuable geochemical insightsas to fluid sources and processes affecting thereactive history of these industrial mineral deposits.Alkaline–carbonatite sources offer a tantalizingREE signature in the rocks and minerals that theyproduce; those that are plagioclase-absent displaychondrite-normalized REE patterns that lack a neg-ative Eu anomaly (e.g. Hornig-Kjarsgaard 1998).Products of alteration (zeolites) would therefore beexpected to adhere to these controls, in addition tolight rare earth enrichment, fluid controls, and tozeolite-specific mineralogical selectivity for theREE, yet to be determined. For the trace alkalisRb and Cs, elevated concentrations mimicking thebehaviours of Na and K might be expected inalkaline rocks and fluids.

Our second test of the hypothesis therefore, is inthe trace element analysis of selected zeolites,Tables 1 and 2. The samples were mainly zeoli-tized tuffs from the USA, the Middle East, Africa,Europe and New Zealand, with mineralogical com-positions either published or determined by X-raydiffraction (XRD; this study). Chondrite-normalizedREE data are displayed in Fig. 2, showing a groupof samples with no, or minimal, Eu anomalies.These patterns generally demonstrate plagioclase-minimal or plagioclase-absent controls in virtuallyall the East African and Middle Eastern samplesand in the Italian laumontite (Ossola sample), acavity-type occurrence. For the USA, the Mudhills,Bowie and Lovelock samples display negative Euanomalies similar to the Rotorua (New Zealand)sample, but in the Pine Valley phillipsite whereREE concentrations are comparatively low, theanomaly is weak. Low La/Lu are noted in theRotorua and Lovelock samples (Table 2), consistentwith a high-Si context. The Ossola cavity samplealso has a low La/Lu ratio, but La/Gd is compara-ble to the highest ratios as seen in the East Africanand Middle Eastern samples. Its signature reflectshydrothermal transportation and aqueous geochem-ical controls on the REE. It is noted that theTanzanian Olduvai 478-118 sample (Tables 1 and2, Fig. 2) has a REE pattern closely matching thatof average foidite glass that is coupled with carbo-natite (Oricola), in Stoppa et al. (2005). Tracealkali concentrations are generally too low to de-termine any pattern except that in the Mudhillssample, Rb and particularly Cs are significantlyelevated relative to our other samples. From sparse dataavailable, only the zeolitic deposits of Greece appear to

376 Miner Deposita (2012) 47:371–382

Tab

le1

Detailsof

thenaturalzeolite

samples

Sam

ple

label

Locality

Map

co-ordinates

(latitu

de,

long

itude,in

decimal

degrees)b

Mineral

prop

ortio

ns(%

)aSup

plier

References

Mud

hills

Mud

Hills,Barstow

Formation,

Death

ValleyJunctio

n,California,USA

34.894

182,

−117.01

6811

Clin

optilolite

>95

%Phelps-Dod

geDyerandJozefowicz

(199

2),Dyeret

al.

(199

3)

Lov

elock

Lov

elock,

Nevada,USA

40.177

299,

−118.48

1712

Mordenite

>95

%MineralsResearchUSA,no

wNevadaSpeciality

Minerals

Riceet

al.(199

2)

PineValley

PineValley,Nevada,USA

40.596

397,

−116.17

5814

Phillipsite

>95

%MineralsResearch,

NY,USA

DyerandJozefowicz

(199

2)

Bow

ieEZChabazite

Mine,Bow

ie,Arizona,

USA

32.434

444,

−10

9.45

7778

Na-chabazite

>95

%GSA

Resou

rces,no

wmined

byUOPLLC

DyerandZub

air(199

8)

Syrian

MkehelatDeposit,

SW

Syria

32.859

98,37

.260

13Zeolites

50–70

%(Chabazite,

Phillipsite,Analcim

e),+

impu

rities

S.S

oulyman,D

amascusHigherInst.

App

liedScience

andTechn

olog

yTorossian

and

Moh

ammadnejad

(200

8)

JordanianC

Aritain

Volcaniclastic

Formation,

Jabal

Hanno

un,Baida

Regionof

NEJordan

32.387

222,

37.628

889

Faujasite

37%,Phillipsite

40%,

impu

rites23

%H.Kho

ury,The

University

ofJordan,Amman

Kho

uryet

al.(200

3/4)

JordanianZ

Tulul

Unq

arRustum,approx

imately

50km

ENEof

AsSafaw

i,Jordan

32.330

24,37

.615

64Chabazite

94%

aH.Kho

ury,The

University

ofJordan,Amman

Kho

uryet

al.(200

3/4)

Olduv

ai47

8-18

Bed

II,1

stfault,N.sideOlduv

aiGorge,

Tanzania

−2.98

09,35

.406

Merlin

oite

65%

Sod

alite

35%

aT.

Teagu

e,The

University

ofCalifornia,Berkeley,USA

Hay

andKyser

(200

1)

Olduv

ai47

8-118

Locality

49,Olduv

aiGorge,Tanzania

−2.96

687,

35.310

917

Phillipsite

>95

%a

T.Teagu

e,The

University

ofCalifornia,Berkeley,USA

Hay

andKyser

(200

1)

Olduv

ai47

8-41

0Locality

34Bed

IIA,Olduv

aiGorge,

Tanzania

−2.99

0699

,35

.375

805

Phillipsite

70%

Analcim

e30

%a

T.Teagu

e,The

University

ofCalifornia,Berkeley,USA

Hay

andKyser

(200

1)

Slovakian

Nizny

Hrabo

vec,Slovakia

48.856

894,

21.751

342

Clin

optilolite

86%

Cristob

alite

14%

aZeocem,Bystré,Slovakia

www.zeocem.com

/en

Ossola

Formazza,Ossolavalley,Italy

46.378

083,

8.42

514

Laumon

tite>95

%a

A.Dyer

Sersale

(197

8)

Rotorua

Ngaku

ru,Rotorua,North

Island

,New

Zealand

−38

.321

592,

176.19

2551

Clin

optilolite

>95

%App

liedZeoliteDevelop

ments,N

ewZealand

Brathwaite

(200

3)

aXRD,thisstud

y(≤5%

error)

bEstim

ated

from

Mindat.o

rginform

ationandGoogleMaps

Miner Deposita (2012) 47:371–382 377

Tab

le2

Trace

elem

entdata

forzeolite

samples.Con

centratio

nsin

ppm

(μg/g)

Mean

Procedural

Blanks

(thisstudy)

Reference

sample—

USA

USA

EastAfrican

andMiddleEastern

Rift

Europe

New

Zealand

Mudhills

(Dyeret

al.1993)

Mudhills

(Strekopytov

2009

pers.

comm.)

Mudhills

(this

study)

Lovelock

Bow

iePine

Valley

Syrian

Jordanian

CJordanian

ZOlduvai

478-18

Olduvai

478-118

Olduvai

478-

410

Slovakian

Ossola

Rotorua

Li

<0.0025

n.d.

n.d.

<0.0025

n.d.

n.d.

<0.0025

<0.0025

<0.0025

<0.0025

<0.0025

<0.0025

0.0254

<0.0025

<0.0025

n.d.

Rb

<0.003

n.d.

140.9

0.1526

n.d.

n.d.

0.0456

<0.003

<0.003

0.0646

0.0492

0.1016

0.0794

0.0771

<0.003

n.d.

Cs

<0.0188

n.d.

121

50.6973

3.3127

1.0195

0.2816

0.1809

0.0320

0.1350

0.1612

0.4623

1.9689

2.3463

0.5608

7.3016

Sr

<0.0025

n.d.

n.d.

2.1270

n.d.

n.d.

0.0251

0.5612

0.7161

1.0175

0.8687

0.9457

0.3543

0.2126

0.1626

n.d.

Ba

<0.0025

2100

a991a

0.2761

n.d.

n.d.

0.1014

0.3546

0.4599

0.0786

0.6877

0.9258

0.4866

0.6562

<0.0025

n.d.

Th

<0.0004

24.293

1812.6938

5.7014

6.6954

0.3696

1.9915

0.8191

1.1042

7.7646

3.2604

4.8717

9.6856

0.0144

11.0933

U<0.0022

1.3

1.91

1.2277

4.8582

1.4653

7.0391

1.6742

0.9131

0.6399

0.3410

8.6210

1.9284

1.5785

0.0097

1.9668

Y<0.0016

n.d.

16.7

8.5186

18.5469

12.1910

1.3266

14.3761

8.4277

3.6820

22.0208

6.9466

15.9653

12.6765

1.6090

32.6682

La

<0.002

2828.9

28.5971

13.3438

19.9103

1.9603

20.2544

16.7660

12.5959

72.5469

77.8543

50.8654

24.8742

1.5063

23.3064

Ce

<0.0056

5051.4

54.3635

37.1458

41.7073

4.5038

39.5797

17.5679

22.9374

111.2720

126.0434

85.7224

42.9965

3.6345

50.4031

Pr

<0.0012

n.d.

6.03

6.1536

4.4168

5.2577

0.4635

5.1111

4.0106

2.7880

14.4053

13.3075

9.3777

5.3616

0.2720

6.8592

Nd

<0.0028

n.d.

19.8

19.5070

17.5516

18.6613

1.7652

20.4213

16.0999

10.2689

51.2369

41.8436

33.0648

18.9063

0.8549

27.1669

Sm

<0.0028

4.0

3.82

3.6048

4.0879

3.7403

0.3529

4.1826

3.0626

1.8003

8.7065

5.4390

5.7622

3.5778

0.1403

6.1278

Eu

<0.0012

0.5

0.338

0.3079

0.1076

0.2490

0.0711

1.4486

1.1086

0.5804

2.5561

1.2238

1.7996

0.5294

0.0482

0.8292

Gd

<0.0016

n.d.

3.18

3.4879

4.1547

3.5729

0.3440

4.3003

2.9317

1.6938

8.3593

4.9703

5.8361

3.6917

0.1616

6.2415

Tb

<0.0012

n.d.

0.545

0.4425

0.7188

0.5694

0.0489

0.6215

0.3926

0.2128

1.1046

0.4921

0.7771

0.5618

0.0274

1.0057

Dy

<0.0012

n.d.

3.05

2.0149

4.2021

3.0128

0.2489

3.1368

1.8031

0.9040

5.1905

1.7685

3.7293

2.9097

0.1822

5.7683

Ho

<0.0012

n.d.

0.593

0.3614

0.8913

0.5795

0.0489

0.6011

0.3243

0.1480

0.9608

0.2848

0.6927

0.5586

0.0526

1.2509

Er

<0.0012

n.d.

1.73

0.9462

2.5774

1.5836

0.1326

1.5603

0.7791

0.3324

2.4907

0.7396

1.7827

1.4247

0.2191

3.7057

Tm

<0.0012

n.d.

0.264

0.1289

0.3890

0.2164

0.0177

0.2034

0.0914

0.0344

0.3128

0.0828

0.2197

0.1791

0.0489

0.5613

Yb

<0.0012

n.d.

1.72

0.8078

2.4644

1.2156

0.1083

1.2076

0.5087

0.1671

1.7767

0.4842

1.1989

0.9821

0.4187

3.6214

Lu

<0.0012

0.9

0.251

0.1209

0.3696

0.1629

0.0170

0.1829

0.0780

0.0216

0.2582

0.0713

0.1653

0.1333

0.0766

0.5778

La/Lu

31.11

115.14

236.58

36.10

122.20

115.18

110.71

215.07

582.82

281.03

1091.89

307.66

186.67

19.65

40.34

La/Gd

9.09

8.20

3.21

5.57

5.70

4.71

5.72

7.44

8.68

15.66

8.72

6.74

9.32

3.73

La/Y

1.73

3.36

0.72

1.63

1.48

1.41

1.99

3.42

3.29

11.21

3.19

1.96

0.94

0.71

Th/U

18.69

9.42

10.34

1.17

4.57

0.05

1.19

0.90

1.73

22.77

0.38

2.53

6.14

1.49

5.64

Sr/Ba

7.70

0.25

1.58

1.56

12.95

1.26

1.02

0.73

0.32

Overall:

10%

duplicateprecisionachieved

(Tho

mpson

andHow

arth

1978

)

n.d.

notdeterm

ined

aSignificant

Sdeterm

ined

inthissampleby

Strekop

ytov

—baryte

contam

inationindicated.

Might

also

applyto

Dyeret

al.(199

3)sample

378 Miner Deposita (2012) 47:371–382

have comparable Cs concentrations (Stamatakis et al.1996; Godelitsas et al. 2010). Alkaline fluids in

combination with mineralogical selectivity for Cs areindicated as controlling factors here.

Discussion

In our first test of the hypothesis, zeolite–carbonatite localitymatches are most evident in the intensively studied regions ofEurope, North America and the Kola peninsula of Russia.Beyond these regions, matches are less evident, and this ispartly attributed to the differential focus of research in the twokey disciplines. For East Africa and the Middle East, naturalzeolite commodities have not been extensively exploited,unlike for metallic resources concentrated in continental in-trusive and metamorphic terrains where known carbonatiteoccurrences dominate, and that have experienced a long his-tory of mineral exploration (e.g. the African continent). An-other consideration is that carbonatite rocks sensu strictu arefar less voluminous than their accompanying alkalinerocks, at least as far as patterns of intrusive rocks tend to show(Woolley and Kjarsgaard 2008a). Further, our second testlinking REE patterns of zeolites with geological criteria hasshown how the regional hydrological regime is an integral partof interpretation of altered mineral compositions, highlightingthe masquerading phenomenon of our hypothesis.

Criteria development with conceptual model

To encapsulate the evidence and ideas of the hypothesis, wepresent here a simplified conceptual model, schematicallyillustrated in Fig. 3. Five main controls on the occurrenceand fate (progressive reaction/alteration) of extrusive alka-line–carbonatitic rocks, and on the compositional profiles ofresultant zeolites are listed: (C1) rift or extensional tectonics(or deep crustal disturbance). (C2) Original glass/magmacomposition. (C3) Hydrological regime. (C4) Trace elementpartitioning and mobility. (C5) Zeolite mineral properties.

Deeper explanation of the hydrological regime (controlnumber C3) is required here. Fluid origins and composi-tions, flux, temperatures and time collectively influence theprogression and nature of alteration reactions, and many ofthese are very well-documented in terms of open and closedhydrologic systems (articles in Bish and Ming 2001). Forexample, it is well established that high concentrations ofNa+ and K+ with low activity of Si and high pH are favouredfor high initial reactivity (Chipera and Apps 2001). We notethat juvenile fluids derived directly from alkaline magmashave these properties (Fig. 3a, C3.1) and are thereforeindicated for initial zeolitization in which magmatic REEpatterns in extruded glass are mirrored by the zeolitic REEpatterns. Access to wider fluid compositions (Fig. 3b, C3.2)results in “the masquerade”; a progression of reactions

0.1

1

10

100

1000

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sam

ple

/ch

on

dri

te

Syrian

Jordanian C

Jordanian Z

Olduvai 478-18

Olduvai 478-118

Olduvai 478-410

Ossola, Italy

0.1

1

10

100

1000

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sam

ple

/ch

on

dri

te

Rotorua

Slovakian

Mudhills

Pine Valley

Lovelock

Bowie

a

b

Fig. 2 Chondrite-normalized rare earth element patterns in zeolitesamples. a The absence of an Eu anomaly in nearly all the East Africanand Middle Eastern samples reflects their plagioclase-absent precursorglass compositions and isolation from wider crustal fluids (see Fig. 3afor a schematic illustration). The Ossola cavity sample (Italy) alsodepicts plagioclase-absent, light rare earth-enriched origins. b NegativeEu anomalies indicate the influence of a higher Si/Al environment inthe reactive history, such as in the USA samples of Mudhills, Lovelockand Bowie, in Rotorua (New Zealand) and in the Slovakian sample(see Fig. 3b for a schematic illustration)

Miner Deposita (2012) 47:371–382 379

b

a

380 Miner Deposita (2012) 47:371–382

towards more silica-rich zeolite assemblages and new REEpatterns reflecting re-equilibration with these different flu-ids. Authigenic feldspars, smectite clay and other silicatesmay also occur in zoned zeolitic successions as widelyreported, further disguising the origin of the rocks.

Hydraulic conductivity of the country rock impacts fluidflux, with Precambrian cratonic basement rocks generallycharacterized by low hydraulic conductivity, and Phanerozoicsediments by high hydraulic conductivity (Fig. 3b, C3.3). Thismajor difference represents a critical control on the accessi-bility of wider fluid compositions with their concomitantreactive power. It helps to explain the apparent scarcity ofcarbonatite occurrences in Phanerozoic sequences (Woolleyand Kjarsgaard 2008a, b), especially with regard to extrusivecarbonatites. Considering temperature and temporal controls,many zeolitic reactions are possible at low temperatures asexemplified in ocean bottom sediments, but where volcaniceruptive sequences are rapidly buried with juvenile water(phreatomagmatic), elevated temperatures favourable to rapidzeolitization are achieved. Such “geoautoclave” type processesare not illustrated here, but described by Langella et al. (2001).

Conclusions

We conclude that our hypothesis is consistent with extensivepast work from both key disciplines and is comprehensivelytestable. We suggest that more extrusive alkaline–carbona-tite suites exist than have been recognised, due to zeoliticmasquerade of bedded volcanics of appropriate composi-tions. Our simple, schematic, unifying model draws together

the key controls and processes, to be refined as more detailedstudies and evidence emerge. Rare earth patterns in zeolites ofthe present study suggest that pathfinder criteria based partlyon trace element signatures could be useful in the search fornew alkaline–carbonatite suites.

Acknowledgements This work was inadvertently inspired by a car-bonatite seminar session given by Ken Bailey, Alan Woolley andFrances Wall at the University of Manchester in 2008. Laboratoryand technical assistance were given by staff of the Universities ofManchester and Wolverhampton; Cath Davies, Al Bewsher, KarlHennermann (Fig. 1), Richard Hartley (Fig. 3), with resources fromDave Polya and Richard Pattrick. Permissions from Natural Resources/Geological Survey of Canada and preliminary responses to mappingqueries from Alan Woolley, Bruce Kjarsgaard and Beth Hillary (Geo-logical Survey of Canada) are acknowledged. S. Strekopytov (TheNatural History Museum, London) provided independent analyticalverification for the Mudhills sample. Special thanks are due to zeolitesample suppliers, Alan Dyer for relinquishing some of his personalcollection, Timothy Teague (University of Berkeley, California) forsub-samples of R. Hay’s Tanzanian rocks, Hani Khoury (Universityof Jordan, Amman) for the Jordanian samples, S. Soulyman (DamascusHigher Institute of Applied Science and Technology), and commercialzeolite producers. All the zeolite contributors to Mindat.org areacknowledged, without whom the global perspective would have beenlimited.

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