ORIGINAL ARTICLE

Christopher P. Reed Æ Malcolm W. Wallace

Zn-Pb mineralisation in the Silvermines district, Ireland: a productof burial diagenesis

Received: 04 April 2002 / Accepted: 22 July 2003 / Published online: 19 November 2003� Springer-Verlag 2003

Abstract Carbonate-sulphide cement stratigraphic rela-tionships in the host rock and ore have been used toconstrain the age of mineralisation at the Silvermineszinc-lead-barium deposit. The base-metal sulphidespost-date planar dolomite and replace stylolites. Fur-thermore, the pre-mineralisation planar dolomites alsoreplace stylolites. These and other diagenetic observa-tions indicate that the base-metal sulphides formed atburial depths greater than 800 m, but probably predatethe Variscan deformation (since pressure shadowsovergrow base metal sulphides). This indicates that thesulphides are of epigenetic origin, constraining the age ofmineralisation to between the late Chadian (�347 Ma)and the late Westphalian (�307 Ma). However, the mostlikely age for mineralisation, (based on widespreadmacro-stylolite development) is Asbian (�339 Ma) oryounger. No evidence of synsedimentary sulphides (inthe form of hydrothermal chimneys, vent faunas, orsulphides intergrown with marine cements) was ob-served at Silvermines. Mineralised breccias (black matrixbreccias), late-stage internal sediments, and dissolutionzones within the carbonate cements all appear to beproduced by hydrothermal karsting that occurred dur-ing the mineralisation process. Fluid inclusion homog-enisation temperatures for ore-stage calcites (up to300 �C) approach the peak temperature estimates de-rived from regional maturation parameters (270 to310 �C from conodont alteration indices and vitrinitereflectance). This suggests that homogenisation temper-atures represent maximum heating temperatures (prob-ably during Variscan time) rather than mineralisationtemperatures.

Keywords Irish-type Æ Mississippi Valley-type ÆCarbonate diagenesis Æ Epigenetic Æ Sulphidemineralisation

Introduction

With a combined tonnage of about 160 Mt at anaverage grade of 7.2% Zn and Pb, the Lower Carbon-iferous carbonate sequence of the Irish Midlands is hostto one of the world�s major Zn-Pb ore-fields (Bankset al. 2002) (Fig. 1). Currently much of this minerali-sation is classified in the literature as ‘‘Irish-type’’mineralisation (e.g. Derry et al. 1965; Taylor and An-drew 1978). Although similar to the mineralisationmodel used for Mississippi Valley-type deposits (MVT),the ‘‘Irish-type’’ model differs in that the deposits aresuggested to contain a component of synsedimentarymineralisation. They also exhibit hotter ore-stagehomogenisation temperatures. The Silvermines deposithas been described as a classic ‘‘Irish-type’’ deposit, andhas been used in the literature to define this geneticmodel (Taylor and Andrew 1978; Taylor 1984; Andrew1986; Samson and Russell 1987).

While Ireland is regarded as the type locality for thisstyle of deposit, a number of studies have questioned thevalidity of the ‘‘Irish-type’’ classification (Schultz 1966;Hitzman and Beaty 1996; Johnston 1999; Peace andWallace 2000; Reed and Wallace 2001; Peace et al.2003). The discovery of epigenetic base-metal minerali-sation at Harberton Bridge, Lisheen and Galmoy(Fig. 1) has further fuelled the debate (Hitzman et al.2002). As a result, there is no consensus regarding thenature and origin of this mineralisation.

The Silvermines district has been the subject of manyindustry and academic studies, and these have focusedmainly on the structural setting and style of minerali-sation (i.e. Rhoden 1958; Taylor and Andrew 1978;Taylor 1984; Andrew 1986; Samson and Russell 1987;Mullane and Kinnaird 1998). In this study we describe

Editorial handling: J. Mengue

C. P. Reed (&) Æ M. W. WallaceSchool of Earth Sciences, University of Melbourne,3010 Victoria, AustraliaE-mail: c.reed@pgrad.unimelb.edu.auTel.: +61-3-8344-5994Fax: +61-3-83447761

Mineralium Deposita (2004) 39: 87–102DOI 10.1007/s00126-003-0384-x

the diagenesis of the Silvermines district at a regionaland deposit scale, and provide age constraints for themineralisation using this diagenetic data. Reed andWallace (2001) used similar diagenetic observations toconstrain the timing of mineralisation at the Court-brown deposit; concluding that mineralisation was epi-genetic (Fig. 1). The degree of thermal maturation of thedeposit and host carbonates is also discussed in relationto mineralisation temperatures.

Geological setting and mineralisation

The base-metal mineralisation at Silvermines is hostedwithin a Lower Carboniferous transgressive carbonatesequence on the faulted southern limb of the KilmastullaSyncline (Andrew 1986) (Fig. 2). The transgressive se-quence is characterised by a progression from (oldest toyoungest) fluvial and deltaic clastic sediments (the OldRed Sandstone) and shallow-water mixed bioturbatedcalcareous and non-calcareous shales and sandstones(the Lower Limestone Shale), to deeper water fossilif-erous argillaceous bioclastic limestones (the BallysteenLimestone) and non-argillaceous micrites (the Waul-sortian Limestone). The Waulsortian Limestone wasdeposited as a series of mudmound complexes of poorlybedded, pale-grey micrite, with abundant sparry calcitefilled stromatactis cavities (Bruck 1982; Hitzman andBeaty 1996; Archer et al. 1996). Locally, well-bedded,

cherty limestones that resemble the underlyingBallysteen Limestone may flank individual Waulsortianmudmounds (Bruck 1982). The supra-Waulsortian (orCalp) stratigraphy of the Silvermines district comprises amore complex succession of shallow and deep-waterlimestones that record a transition to more structurallycontrolled sedimentation (Bruck 1982; Hitzman andBeaty 1996) (Fig. 2).

Economic concentrations of base-metal mineralisa-tion in the Silvermines district are confined to twostratigraphic horizons. The upper ore-zones at the Sil-vermines (Upper G and B zones) and Magcobar depositsare tabular, stratiform ore-bodies on the boundary be-tween the Ballysteen and Waulsortian limestones (Tay-lor and Andrew 1978; Andrew 1986) (Fig. 2). The lowerore-zones (Lower G, K, and P zones) are confined to anextensively dolomitised interval within the BallysteenLimestone (the Lower Dolomite) (Fig. 2). Sphalerite,galena and pyrite occur as open space filling cementswithin primary and secondary porosity and as fine-grained massive and disseminated mineralisation. AtMagcobar, barite occurs as fine-grained, grey or pale-brown acicular crystals in a fine-grained groundmass(Mullane and Kinnaird 1998). The ore-zones are inplaces brecciated, and are cemented by additional sul-phide mineralisation, quartz and dolomite cement(Taylor and Andrew 1978). Minor mineralisation alsooccurs at Shallee within the Old Red Sandstone as openspace filling and disseminated sulphides and barite(Bruck 1982; Andrew 1986) (Fig. 2).

Methods of study

The major methods used in this study are described byReed and Wallace (2001). For this study, samples werecollected from drill core held at the Shallee and Mogul(Ennex) core stores. Additional surface samples werecollected from the Ballynoe open pit. Sample numbersused in this paper are formatted: drill hole name-depthin drill hole. The drill hole name refers to the ore-zone(e.g. B zone). The NX prefix refers to the Cooleen zone(Fig. 2). A record of drill hole localities is available fromthe Geological Survey of Ireland (GSI).

For stable isotope analyses, samples of calcite anddolomite were collected using a high-speed hand drilland grinding bit from polished blocks. A 4 mg minimumsample size was used for analyses. Values of d13C andd18O are reported as per mil relative to the Pee DeeBelemnite (PDB).

Results

Diagenetic phases

The Lower Carboniferous rocks of the Silvermines dis-trict preserve a range of cements and replacement phasesthat document the diagenetic history of the region.

Fig. 1 Location map of Ireland outlining the location of: theRathdowney Trend, including the Lisheen and Galmoy deposits(Shearley et al. 1996); the Harberton Bridge deposit, Courtbrowndeposit, Navan, Silvermines, Tynagh, and Gortdrum deposits(Hitzman and Beaty 1996)

88

While pervasive dolomitisation, mineralisation, andfracturing have commonly destroyed the earlier sedi-mentary and diagenetic textures in the ore-zones, pri-mary cements are still preserved distal to the deposits.Synsedimentary and burial cements are preserved withinintra- and inter-skeletal, inter-granular, and secondaryporosity. Replacement diagenetic phases are observedreplacing the host lithologies, earlier diagenetic cements,and stylolites.

Calcite cements

Isopachous calcite cements

Radiaxial fibrous calcite cement is the first cavity-fillingphase, and is most commonly observed lininglarge stromatactis cavities (Fig. 3 and Fig. 4A, B). Indi-vidual crystals have a columnar growth habit that isperpendicular to the substrate. The cement has a cloudy

Fig. 2 Geology of theSilvermines Deposit (top) withtwo north–south cross-sectionsthrough the mineralisation(middle and bottom). Geology isfrom Taylor and Andrew (1978)and Andrew (1986). Position ofthe Cooleen Zone from Leeet al. (2001)

89

appearance under plane-polarised light, and unduloseextinction under crossed-polars. Cathodoluminescencemicroscopy shows the cement to be dominantly non-luminescent, although some patchy dull or bright lumi-nescence is observed within some generations. The d13Cand d18O values range from +2.56 and +3.59& PDBand from )4.56 and )7.94& PDB, respectively (Table 1).This cement is equivalent to the stage A crypto-fibrouscements (CFC) of Lees and Miller (1995).

Equant calcite cement

Clear equant calcite cements post-date the isopachouscalcite cements, occluding primary and secondary

Fig. 3 Photomicrographs of major carbonate diagenetic phasesat Silvermines. A Plane-light view of primary pore with earlyradiaxial fibrous calcite cements (RF) overlain by clear equantcalcite. Sample NX19-711 ft. B cathodoluminescence view ofsame area with, from oldest to youngest, radiaxial fibrous calcite(RF), non-luminescent calcite (N), bright luminescent calcite (B),ore-stage calcite (OS) and dull luminescent calcite cements (D).Blue arrows highlight undulating surfaces indicating probabledissolution. Sample NX19-711 ft. C plane-light view of largeprimary cavity with internal sediments (IS). Planar dolomitecrystals (PD) and radiaxial fibrous calcite (RF) underlie theinternal sediments. Sample B42-575 ft. D same area incathodoluminescence. The cavity is filled by (from oldest toyoungest); radiaxial calcite (RF), non-luminescent calcite (N),bright luminescent calcite (B), planar dolomite (PD), dolomiticinternal sediments (IS), ore-stage calcite (OS), and saddledolomite cement (SD). Sample B42-575 ft

90

porosity. Individual crystals are inclusion-rich or inclu-sion-poor, and display uniform to undulose extinctionunder crossed-polarised light. The equant calcitecements can be divided into four generations based ontheir observed luminescence and relationship to sulp-hides: non-luminescent; bright luminescent and ore-stage; and dull luminescent cement. These luminescentzones are observed variably as growth bands within asingle crystal or as individual crystals (Fig. 3B, D). Leesand Miller (1995) have previously described the non-bright-dull luminescent stratigraphy from the Waulsor-tian Limestone as cement stages B–D. Lees and Millers(1995) did not describe the ore-stage calcite cement astheir study concentrated on unmineralised carbonates.

Non-luminescent calcite cements (stage B) overgrowthe isopachous cements, and where these are absent,they grow directly on depositional constituents. Thecrystals are commonly equigranular, and under plane-polarised light they either have a clear or cloudyappearance.

The bright luminescent calcite cement (stage C) di-rectly overgrows the non-luminescent generation and isgenerally observed as a bright luminescent band over-growing an earlier core of non-luminescent calcite ce-ment (Fig. 3B, D). The thickness of the brightluminescent band is variable, ranging from a few mi-crons to 100�s of microns.

Ore-stage calcite represents a generation of stronglyzoned, dominantly bright luminescent equant calcitecement that has developed contemporaneously with themain sulphide minerals (Fig. 4A, B). It has a variableappearance, commonly exhibiting a zoned luminescenceof alternating bright and dull luminescent growthzones, or, blotchy bright or dull luminescence (Fig. 3B,D and Fig. 4B). Partial alteration of the earlier calcitecements may accompany ore-stage calcite cementation,and is especially prevalent in more mineralised samples(Fig. 4B). This may obscure the original luminescentcharacter of the earlier calcite cements. Lees and Miller(1995) record a similar episode of alteration accompa-nying the precipitation of the bright luminescent calcitecements from unmineralised regions. Under cross-po-larised light, individual ore-stage calcite crystals displayundulose extinction while abundant fluid inclusionsgive the cement a cloudy appearance under plane-po-larised light. Homogenisation temperatures for theprimary two-phase inclusions in the ore-stage calciteyield a mode at 230 to 240 �C, with the homogenisa-tion temperatures spread from 150 to 330 �C (Fig. 5).The d13C and d18O values range from +1.33 and+2.69& PDB and )10.50 and )7.53& PDB, respec-tively (Table 1).

Dull luminescent calcite cement (stage D) is generallythe youngest generation of equant calcite cement(Fig. 3B), occurring as the final cavity-occluding phasein primary and secondary porosity. The cement iscoarser-grained than the preceding varieties, and isordinarily observed as an individual, uniform dullluminescent crystal. A sample of dull luminescent calcite

cement yields a d13C value of +1.85& and d18O value of)10.46& (Table 1).

Irregular, wavy contacts are observed between someluminescent cement generations, particularly the non/bright luminescent and the ore-stage/dull luminescentcement boundaries (Fig. 3B). Miller (1986) and Lees andMiller (1995) documented similar irregular boundariesat the same stage (their stage B/C and C/D boundaries)and have attributed these to periods of dissolution.

Dolomite

Planar dolomite

Planar dolomite occurs as a replacement phase and ce-ment within primary and secondary porosity within theWaulsortian and Ballysteen limestones (Fig. 3C, D andFig. 4A–F). The planar replacement dolomite also re-places primary synsedimentary and secondary hydro-thermal karst geopetal sediments, and insoluble residualalong micro- and macro-stylolites (Fig. 4C, D andFig. 6A, B). The degree of dolomitisation varies fromisolated crystals or crystal clusters, to completely per-vasive dolomitisation. Pervasive dolomitisation appearsrestricted to well-defined sub-facies, i.e. the LowerDolomite (Fig. 2). In extensively dolomitised zones, theplanar replacement dolomite consists of an interlockingmosaic of euhedral to subhedral planar dolomiterhombs 30 to 200 lm in diameter (Fig. 4C–F). Individ-ual crystals are commonly zoned, with cloudy inclusion-rich cores surrounded by alternating inclusion-rich andinclusion-poor zones (Fig. 4E).

Planar dolomite cement overgrows the bright lumi-nescent calcite cement, or where this generation is ab-sent, the earlier isopachous and non-luminescentcements (Fig. 3C, D and Fig. 4C, D). In extensivelydolomitised areas, the planar dolomite cement is the firstcavity-occluding phase infilling secondary dissolutionporosity.

In any one sample, the planar dolomite cement andreplacement dolomite exhibit the same luminescentzonation (from oldest to youngest): (1) a red luminescentcore; (2) banded dull luminescent dolomite; and (3)banded bright yellow or red luminescent dolomite(Fig. 4F). Within the upper ore zones, the first stage ofred luminescent planar dolomite dominates. The d13Cvalues of the planar replacement dolomite range from+1.55 to +3.57& PDB and the d18O values range from)7.68 to )5.5& PDB (Table 1).

Saddle dolomite

Saddle dolomite cement occurs as medium to coarselycrystalline (1 to 3 mm), non-planar, euhedral to sub-hedral crystals with sweeping extinction. It post-datesthe bright luminescent planar dolomite. Individualsaddle dolomite crystals are commonly zoned with acloudy inclusion-rich core, surrounded by alternating

91

inclusion-rich and inclusion-poor zones (Fig. 3C andFig. 4E). Two varieties of coeval saddle dolomite canbe distinguished using cathodoluminescence. Uniformlynon-luminescent and inclusion poor saddle dolomiteoccurs in the Lower Dolomite zones (Fig. 4F). In theupper ore-zones, the saddle dolomite is uniformly or-ange-red luminescent (Fig. 3D). It commonly exhibits apronounced zonation towards the crystal rim, withnon-luminescent inclusion-poor zones and is commonlydedolomitised to uniform dull luminescent calcitewithin mineralised zones.

The d13C values of the saddle dolomite range from)0.41 to +3.12& PDB, and the d18O values range from)11.33 to )6.11& PDB (Table 1).

Mineralisation phases

The sulphide minerals occur as cements within primaryand secondary porosity and as replacement phaseswithin the host-rock and along stylolites and dissolutionseams (Fig. 4A–F, and Fig. 6A, B). The same sulphide

92

generations present in the economic zones of minerali-sation can also be recognised in the host-rocks sur-rounding the deposits.

Gangue phases

Minor barite is observed as a diagenetic phase distal tothe economic barite deposits. In these distal localities,barite occurs predominantly as cement in primaryporosity within the Waulsortian Limestone and sec-ondary dissolution or intra-granular porosity within theLower Dolomite (Fig. 4C, D) and as a replacementphase (Fig. 6E). Individual crystals are elongate, non-luminescent and display undulose extinction. Replace-ment barite may be partially replaced by bright-blueluminescent barium feldspar and contain associatedexsolution growths of galena (Fig. 6E).

Diagenetic quartz is a minor gangue phase that occurspredominately as cement within primary intra-granular,secondary dissolution, and intra-crystalline porosity.Quartz cements occur as euhedral to subhedral crystalsand crystal clusters andasmassivemicrocrystalline quartzthat commonly completely occludes intra-crystallineporosity within the Lower Dolomite (Fig. 4C, D andFig. 6D). The quartz grains are inclusion-poor but maycontain small (1–15 lm) inclusions of barite in the latestgenerations. It is weakly luminescent (Fig. 6D).

Fig. 4 Photomicrographs of the relationship between carbonatesand sulphides at Silvermines. A Plane-light view of carbonateand sulphide cements filling a large primary pore. RF radiaxialfibrous calcite, PD planar dolomite, OS ore-stage calcite, Ppyrite, LS late sphalerite. Sample NX14-1346 ft. B same area incathodoluminescence. The cavity is filled by, from oldest toyoungest, radiaxial calcite (RF), planar dolomite (PD), pyrite (P),ore-stage calcite (OS), and late coarsely crystalline greensphalerite (LS). The ore-stage calcite cement overgrows thepyrite and planar dolomite cement, and is in turn overgrown bythe late sphalerite cement. The original luminescent character ofthe earlier isopachous and non-luminescent cements has beenoverprinted during ore-stage diagenesis to patchy bright/dullluminescence. Sample NX14-1346 ft. C cross-polarised view ofearly zoned sphalerite (ES), with strongly zoned equantsphalerite and dark colloform sphalerite generations. Quartz(Q) is intergrown with the colloform sphalerite. The sphaleriteovergrows planar dolomite (PD) and is overlain by pyrite (P),internal sediments (IS) and barite cements (BA). Sample 75-84-39-159 ft. D plane-light view of from oldest to youngest, planarreplacement dolomite (PD), early zoned sphalerite cement (ES)and quartz (Q), late coarsely crystalline sphalerite cement (LS),and barite cement (BA). Opaque minerals are galena (G) andpyrite (P). Sample 75-84-39-159 ft. E plane-light view of (fromoldest to youngest), planar replacement dolomite (PD), saddledolomite cement (SD), and late sphalerite cement (LS). Sample75-84-39-224 ft. F same area as (E) in cathodoluminescence.Planar replacement dolomite has three major luminescent zones,from oldest to youngest, a red luminescent planar dolomite(RLPD), dull luminescent planar dolomite (DLPD), and brightluminescent planar dolomite (BLPD). The saddle dolomite (SD)and late sphalerite (LS) are both non-luminescent. Sample 75-84-39-224 ft

b

Table 1 Stable isotopecomposition of the calcitecements and dolomites fromSilvermines

Sample Phase d18O & PDB d13C & PDB

B189@460� Non-luminescent calcite cement )4.87 3.13B42@575� Non-luminescent calcite cement )4.56 3.59NX19@711� Non-luminescent calcite cement )4.98 3.36NX19@760� Non-luminescent calcite cement )7.94 2.56

Mean )5.59 3.16B189@525� Ore-stage calcite cement )8.31 2.66NX19@760� Ore-stage calcite cement )8.19 2.41NX19@741� Ore-stage calcite cement )8.54 2.69NX19@741� Ore-stage calcite cement )10.50 1.33NX19@741� Ore-stage calcite cement )7.53 1.6372RP-17@648� Ore-stage calcite cement )9.36 2.52

Mean )8.74 2.21NX14@1346� Dull luminescent calcite cement )10.46 1.85K28@253� Planar replacement dolomite )7.44 1.61K28@163� Planar replacement dolomite )7.04 1.49K28@254� Planar replacement dolomite )7.53 1.3175-84-39@159� Planar replacement dolomite )7.68 1.5572RP-17@646� Planar replacement dolomite )7.20 3.57Magcobar pit hand sample Planar replacement dolomite )5.50 3.09

Mean )7.07 2.10B42@575� Saddle dolomite cement )6.50 2.85B63@925� Saddle dolomite cement )6.11 2.63B63@925� Saddle dolomite cement )11.33 2.72B181@683� Saddle dolomite cement )6.96 2.72NX19@749� Saddle dolomite cement )8.31 2.69NX19@741� Saddle dolomite cement )7.33 2.73K28@253� Saddle dolomite cement )8.54 )0.23K28@163� Saddle dolomite cement )7.89 )0.4172RP-17@646� Saddle dolomite cement )7.66 3.1272RP-17@648� Saddle dolomite cement )7.75 2.95

Mean )7.84 2.18

93

Sulphide minerals

Pyrite is the most abundant regional sulphide mineralobserved in the area, and occurs in many localitiesdevoid of other sulphides. It first occurs as a primarycement within the bright luminescent calcite cementsand may also replace the isopachous cements, internalsediments, stylolites and dissolution seams, and themicritic matrix of the host limestone (Fig. 4A–D andFig. 6A, B). It is typically the first sulphide phase, andoccurs mainly as aggregates of individual anhedral tosubhedral crystals, a few microns to hundreds of mi-crons in diameter. The replacement pyrite has a sim-ilar habit to the cement and is most common withinthe more argillaceous facies of the host carbonates.In cleaner carbonates, the pyrite occurs adjacent to,and along, well-developed stylolites. Lees and Miller(1995) also identified pyrite that had precipitatedcontemporaneously with the bright luminescent (stageC) carbonate cements in otherwise unmineralisedregions.

Sphalerite occurs as cement within primary andsecondary porosity, and as a replacement phase alongstylolites and dissolution seams (Fig. 6A, B). Twomajor generations of sphalerite are present: (1) Anearly strongly zoned generation consisting of greenand brown equant crystals (250 lm average) interla-minated with finely crystalline colloform sphalerite(Fig. 4C, D); (2) A later generation of unzoned coar-sely crystalline (500 lm average) greenish sphalerite(Fig. 4A, B, D–F). The early, zoned sphalerite isgenerally observed rimming breccia clasts andcementing intra-granular porosity in the LowerDolomite (Fig. 4C). Rhoden (1960) identified this asFe- and Cu-rich sphalerite that overlaps the formationof pyrite. This early-zoned sphalerite may also containsmall inclusions of chalcopyrite or pyrrhotite (Rhoden1960). The unzoned coarsely crystalline late sphaleriteis commonly the last sulphide to precipitate. It occurspredominantly as cement within secondary intra-crys-talline, and dissolution porosity. Individual sphaleritecrystals are uniformly green or brown and containabundant single-phase inclusions.

Galena exhibits a similar distribution and habit as theother sulphide minerals. It is typically subhedral to eu-hedral, and occurs predominantly as a minor replace-ment phase along stylolites and dissolution seams. Italso occurs as a cavity-occluding phase within primaryand secondary porosity (Fig. 4D).

Diagenetic textures

Mechanical and chemical compaction

The effects of mechanical compaction are most evidentin the skeletal packstones and grainstones of the Waul-sortian equivalent facies and the Ballysteen Limestone.These facies are closely packed, with a preferred orien-tation of grains. The closely packed fabric is furtheraccentuated by grain-to-grain pressure solution. This isdemonstrated by swarms of parallel to non-parallel,

Fig. 5 Fluid inclusion homogenisation data for ore-stage calcitefrom the Cooleen Zone. Histogram of homogenisation tempera-tures (bottom) and homogenisation temperature versus fluidinclusion diameter (top). Sample NX19@741 and NX19@760

Fig. 6 Photomicrographs of various textural relationships atSilvermines. A Plane-light view of a high amplitude stylolite inthe Waulsortian Limestone. The stylolite is bedding parallel and isreplaced by pyrite (dark material) and early sphalerite (blue arrow).Sample NX14-1335 ft. B same area as (A) in cathodoluminescence.The stylolite is also replaced by the early red luminescent planardolomite. Note the surrounding rock is almost devoid ofreplacement sulphides and dolomite. This would suggest that thesephases have preferentially developed along the stylolite. SampleNX14-1335 ft. C black matrix breccia from the Magcobar pit.Details discussed in text. Light clast in the centre consists ofchalcedonic silica. D cathodoluminescence view of planar dolomite(PD) overgrown by blue-purple luminescent quartz (Q). SampleK28-254 ft. E non-luminescent barite (B) replaced by blueluminescent barium feldspar (F). Sample P4-201 ft. (F) cathodo-luminescence view of dull luminescent calcite pressure shadows (D)surrounding pyrite (P) hosted by planar dolomite (PD). Sample 75-84-11

c

94

reticulate multi-grain sutured seams. In the WaulsortianLimestone, pressure solution is characterised by thedevelopment of bedding parallel, single, widely spaced,micro- and macro-stylolites (Fig. 6A, B). In the Ballys-teen Limestone, non-sutured bedding parallel seams, orswarms of bedding-parallel to reticulate micro-seams arepresent. Planar replacement dolomite and sulphideminerals may overprint these pressure solution fabrics,including high-amplitude stylolites and thick (<1 cm)dissolution seams (Fig. 6A, B). These replacement pha-ses can be correlated with the ore-stage sulphides anddolomites.

Mineralised internal sediments and breccias

Two generations of geopetal internal sediments can beidentified in the Silvermines area. In the unmineralisedand undolomitised Waulsortian facies, there are abun-dant micritic internal sediments preserved associatedwith stromatactis cavities and other large primary pores.They are either overlain by, or more rarely, interspersedwith the isopachous calcite cements. Lees and Miller(1995) described similar synsedimentary sediments fromthe Waulsortian Limestone.

95

Of more significance to this study are the cavity-fillingore-stage internal sediments. These internal sedimentsdiffer from the marine internal sediments because theyare: (1) of later diagenetic origin as they overlie isopac-hous and non-luminescent calcite cement, and planardolomite cements, and may be interspersed with thebright luminescent calcite cement (Fig. 3C, D); (2) theyare coarser grained, varying from 20 to 80 microns; and(3) they consist of a finely intergrown mixture of car-bonate (dolomite or calcite), organic matter and sulp-hides (Fig. 3C, D and Fig. 4C).

Various breccia types are present in the Silverminesarea. Similar breccia types have also been recognised atother Irish base-metal deposits (e.g. Galmoy, and Lish-een; Doyle et al. 1992; Hitzman et al. 1992) and on thebasis of morphology these breccias have been dividedinto black matrix breccias and white matrix breccias(Hitzman et al. 1992, 2002).

At Silvermines, the black matrix breccias consist ofpoorly sorted clasts (a few millimetres to metres indiameter) within a poorly sorted fine-grained matrix ofplanar dolomite and pyrite, together with minordetrital quartz grains (Fig. 6C). Breccia clasts arecommonly angular and may have a fitted fabric(Fig. 6C). Individual breccia clasts may be partially ortotally replaced by planar replacement dolomite and/orpyrite. In some instances, extensively dolomitised clastsare juxtaposed against undolomitised fragments. Simi-larly, marine and burial cements within breccia frag-ments may be truncated along clast boundaries. Insome breccias, a thin band of pyrite and planardolomite cement (up to 2 mm thick) rims the brecciafragments. These pyrite and dolomite cements may befurther brecciated. Under cathodoluminescence, thedolomite matrix and planar replacement dolomite thatreplaces the breccia clasts have the same bright redluminescence as the first stage of planar dolomitecement.

White matrix breccias are cemented rather thanmatrix-supported. The breccias are cemented vari-ably by planar dolomite, pyrite, ore-stage calcite andsaddle dolomite cement. Dull luminescent calcitecement may occlude the remaining porosity betweenclasts.

Deformation micro-structures

The most prominent deformation microstructures ob-served in the Silvermines mineralisation are well-devel-oped pressure shadows that surround sulphide minerals.Pressure shadows are associated with sphalerite andpyrite in both the Ballysteen and Waulsortian lime-stones. The pressure shadows consist of fibrous andinclusion-free, dull luminescent calcite cement (Fig. 6F).Pressure shadows are best developed where isolatedmasses of pyrite and/or sphalerite are surrounded bycarbonates, regardless of whether the host is calcite ordolomite.

Discussion

Paragenesis

The paragenesis of the Silvermines district is illustrateddiagrammatically in Fig. 7 and in detail in Fig. 8. Themineralisation at Silvermines post-dates the isopachousand non- and bright luminescent calcite cements, theearliest planar replacement dolomite and planar dolo-mite cement, and post-dates the onset of mechanicalcompaction and stylolitisation. This paragenesis is sim-ilar to those previously documented by Miller (1986),and Lees and Miller (1995) for unmineralised Waulsor-tian Limestone. It is also comparable with the para-genesis of the Courtbrown deposit (Reed and Wallace2001) and the ore-stage paragenesis of Shallee (Rhoden1960). This similarity suggests that the carbonate cementstratigraphy is of regional significance. As such, anunderstanding of the relative timing of these phases canprovide important constraints on the timing of the sul-phide mineralisation.

Fig. 7 Diagrammatic representation of the major phases and theirparagenetic relationships at Silvermines

96

Marine diagenesis

Miller (1986) and Lees and Miller (1995) proposed amarine origin for the isopachous cements, and indeedthese cements share many characteristics that are similarto other Palaeozoic marine cements (e.g. James andChoquette 1984; Tucker 1991; Prezbindowski 1985). Themain evidence to support a marine origin from this studyincludes:

1. The early paragenetic timing of the cement. Thesecements are the first cavity-occluding phases, and areattached directly to the substrate, and the micriticwalls of skeletal remains.

2. The isopachous cements of this study have an isoto-pic composition comparable to Carboniferous marinecalcite values (i.e. Bruckschen and Veizer 1997).

3. The cement is commonly interlaminated with marineinternal sediments.

Burial diagenesis

The equant calcite cements provide a record of theprecipitation environment following the marine isopac-hous cements. Importantly, this sequence of cementsalso preserves the relative timing of the sulphide min-eralisation and the dolomite phases. While the non-bright-dull cement stratigraphy found at Silvermines ismost commonly attributed to a change in the redoxpotential of the precipitating fluid (Machel 1985; Bar-naby and Rimstidt 1989; Frank et al. 1982), a number ofdifferent environments have been proposed for its for-mation (e.g. Hendry 1993; Meyers and Lohmann 1978,1985). In the case of the Irish Midlands, Miller (1986)and Lees and Miller (1995) proposed a shallow sub-surface environment to explain the luminescent stratig-raphy of the calcite cements. This model was largelydeveloped in relation to unmineralised Waulsortian

Limestone and did not encompass the underlying Bal-lysteen Limestone, or the timing of the dolomites rela-tive to the calcite cement stratigraphy.

Non-luminescent calcite cements represent the firstgeneration of calcite precipitation following the isopac-hous cements. These cements commonly post-datemechanical compaction and are often further truncatedby tectonic fractures. This indicates that some of thiscement was precipitated after the rocks were at leastpartly lithified and compacted (Choquette and James1987). The non-luminescent character of the cement alsosuggests that it precipitated from oxidised waters thatinhibited the mobilisation of trace elements into solution(Barnaby and Rimstidt 1989; Machel 1985). A near-surface oxidised environment consistent with that ofMiller (1986) and Lees and Miller (1995) can thereforebe envisaged for the non-luminescent equant calcite ce-ments.

Bright luminescent calcite cements post-date theisopachous and non-luminescent calcite cements and arecommonly observed healing fractures within the earliercement types. This cement is also brightly luminescent,implying that it precipitated from a fluid with a loweroxidation potential (relative to the earlier non-lumines-cent calcite). Lees and Miller (1995) attributed thischange in conditions to the transition of the WaulsortianLimestone into a suboxic zone.

Planar dolomite occurs close to the boundarybetween non- and bright luminescent calcite cements(Fig. 3C, D). It is also the first replacement dolomitephase that overprints macro-stylolites. Stylolites areburial diagenetic structures that are common withinmineralised and unmineralised carbonate sequencethroughout the world (Scholle and Halley 1985; Bar-naby and Read 1992; Moss and Tucker 1995; Tobinet al. 1997). They generally post-date marine and earlynear surface cements and may in turn be overprinted byreplacement dolomite (e.g. Wallace et al. 1991; Barnabyand Read 1992). It is unlikely that stylolites could have

Fig. 8 Paragenetic relationshipsof diagenetic and mineralisationprocesses at Silvermines. Theappropriate diagenetic realm,discussed in text, is includedacross the top

97

formed in the near seafloor environment given thatstylolite formation post-dates mechanical compactionand requires significant host-rock lithification (Cho-quette and James 1987). Previous work by Nicolaidesand Wallace (1997), and Lind (1993), indicate that aminimum burial depth of about 800 m is required for theformation of macro-stylolites. As planar dolomiteoverprints high amplitude stylolites, a minimum depthof at least 800 m can therefore also be assigned to theplanar dolomite and the bright luminescent calcitecement.

This paragenesis does not exclude the possibility ofother different dolomite types existing within the Irishore-field. It is probable that a number of geneticallydifferent dolomite types are preserved within the Car-boniferous succession of Ireland (e.g. Gregg et al. 2001).However, the common dolomite types (planar and sad-dle dolomite) documented in this study from around theSilvermines deposit are of burial diagenetic origin andprecipitated after significant physical and chemicalcompaction of the host-rocks.

The dull luminescent calcite is the final cavity-occluding phase. It cements the remaining primary andsecondary porosity and later fractures that truncate allearlier phases. This is consistent with precipitationwithin a later burial diagenetic setting.

The stable isotope composition of the carbonatecements and replacement phases also supports a burialdiagenetic origin (Fig. 9). Burial cements generally havelower oxygen isotopic compositions than earlier marinecements (Choquette and James 1987). Meteoric cementsare most commonly inferred to have followed a separate,distinct path that is defined by lighter d13C values(Meyers and Lohmann 1985). The isotopic trend of thisstudy is clearly more consistent with a burial diageneticorigin for these cements (Fig. 9).

The diagenetic history outlined by this study for theSilvermines deposit is not unlike that proposed by Miller

(1986) and Lees and Miller (1995) for the WaulsortianLimestone from unmineralised localities. However,whereas Lees and Miller (1995) attributed the non- tobright luminescent transition to shallow subsurfaceprocesses, the evidence from this study suggests that thetransition to more reduced conditions (i.e. bright lumi-nescent cement) occurred at a considerable burial depth(in the order of 800 m or more). Importantly, miner-alisation at Silvermines can be shown to unequivocallypost-date the planar replacement dolomite and dolomitecement that are themselves of burial origin (post-datestylolites). We therefore suggest that the base-metalmineralisation at Silvermines is entirely epigenetic inorigin.

Absolute ages for diagenetic events

The depth required for stylolite development and thetiming of the Variscan deformation can be used toprovide maximum and minimum ages on the timing ofthe mineralisation (Reed and Wallace 2001) (Fig. 10).As the formation of macro-stylolites requires a mini-mum burial depth of about 800 m, a maximum age ofabout the late Chadian (�347 Ma; Harland et al. 1990)can be assigned to the mineralisation (Fig. 10). How-ever, since high amplitude macro-stylolites only becomecommon at depths of around 1.5 km or greater (Lind1993), an Asbian (�339 Ma; Harland et al. 1990) oryounger age is most likely for the mineralisation.

The main phase of Variscan deformation occurredbetween about the late Westphalian and pre-UpperPermian (Coller 1984; Hitzman 1999). We interpret thepressure shadows around sulphide minerals to mostlikely be the result of the Variscan deformation. As thepressure shadows overprint ore-stage sulphide miner-alisation, this constrains the timing of mineralisation tobefore about the late Westphalian (�307 ma; Harlandet al. 1990) (Fig. 10).

Thermal constraints on mineralisation

Reed and Wallace (2001) noted the possible influence ofpost-entrapment heating on ore-stage homogenisationtemperatures during Variscan deformation at theCourtbrown deposit (Fig. 1). The same conclusion canbe made for the Silvermines deposit. Homogenisationtemperatures from ore-stage calcite range from 150 to330 �C with a mode at 230 to 240 �C (Fig. 5). Thesetemperatures are less than temperature estimates frompublished vitrinite (Ro%) and conodont (CAI) valuesfor the Silvermines area. These indicate Variscan peakburial temperatures of between 270 and 310 �C (Claytonet al. 1989; Jones 1987; Fitzgerald et al. 1994). There-fore, as Variscan temperatures exceed ore-stagehomogenisation temperatures it is possible that stretch-ing has occurred and that anomalous temperatures haveresulted.

Fig. 9 The stable isotopic composition of the calcite and dolomitecements, and planar replacement dolomite from Silvermines. Theburial and meteoric diagenesis trends depicted on the diagram arediscussed in the text

98

A plot of homogenisation temperatures versus mea-sured fluid inclusion size shows no correlation (Fig. 5).This has been used to suggest that fluid inclusion popu-lations have not been stretched (Goldstein and Reynolds1994). However, previous studies of fluid inclusionstretching have suggested that a stretching trend is bestpreserved in large inclusions (Goldstein and Reynolds1994). Ore-stage calcite from this study yielded only smallinclusions (i.e. <12 lm). It is possible then that astretching trend is not preserved in this instance as all theinclusions in the sample set have been stretched to thesame degree. Tobin and Claxton (2000) have also shownthat a distribution will remain unimodal during post-entrapment heating. These simple checks may not there-fore be adequate to test for fluid inclusion stretching.

Hitzman and Large (1986) noted that mineralisationtemperatures (as documented from homogenisationtemperatures) increase towards the south of Ireland. Thesame trend of increasing temperatures to the south wasdocumented by Clayton et al. (1989) for regional mat-uration data (CAI and Ro) and was interpreted as beingdue to the increasing intensity of Variscan deformationto the south. From this data, it seems reasonable tosuggest that fluid inclusion populations from the IrishZn-Pb deposits may actually reflect Variscan peak

temperatures rather than mineralisation temperatures. Ifhomogenisation temperatures for the ore-stage phases inIreland approximate peak Variscan temperatures, thenthe original precipitation temperatures for the miner-alisation may have been significantly cooler and indeedmay have been more in line with temperatures attainedduring regional burial.

Origin of the mineralisation

A number of recent publications have helped define thenature of the ore-forming fluids responsible for the IrishZn-Pb mineralisation (i.e. Banks et al. 2002; Everettet al. 1999, 2003). However, these papers do not directlyaddress the problem of the timing of mineralisation (themajor subject of this study). Of more importance to thisstudy are the reported examples of synsedimentarysulphides that are used to support the Irish-type modelfor the Silvermines deposit.

In the Cooleen zone of the Silvermines deposit(Fig. 1), Lee et al. (2001) and Lee and Wilkinson (2002)cite the inclusion of dolomitised and mineralised clastswithin limestone breccias (interpreted as sedimentary) asevidence of near-surface mineralisation. Reed and

Fig. 10 Burial historyreconstruction for theSilvermines area. The columnon the right shows thereconstructed stratigraphicsection for the Silvermines areabased on the regionalstratigraphy. Present daythickness� were corrected forcompaction using BasinMod1D. The Courceyan to earlyHolkerian stratigraphy of theSilvermines area is after Bruck(1982). The remaining LowerCarboniferous stratigraphy isreconstructed from sectionspreserved in the RathdowneyTrend described by Sevastopuloand Wyse Jackson (2001) andArcher et al. (1996). TheNamurian and Westphaliangeology is poorly preservedonshore, but Fitzgerald et al.(1994) provides an estimate ofthe total thickness of UpperCarboniferous sediments basedon onshore and offshoresections from the west ofIreland. The post-Variscanuplift history is not included.Stages for the Carboniferous(after Harland et al. 1990) areincluded along the bottom. Thesolid black line denotes thestratigraphic position andpossible relative age of the base-metal mineralisation based onthe paragenetic considerationsdiscussed in the text

99

Wallace (2003) have questioned this interpretation,suggesting instead that the breccias documented by Leeet al. (2001) and Lee and Wilkinson (2002) are theproduct of hydrothermal dissolution at depth. A near-surface origin for the mineralised and dolomitised clastsis not compatible with the paragenesis outlined by thisstudy. The sulphide mineralisation and dolomite docu-mented by this study (including the mineralised whiteand black matrix breccias; Fig. 4 and Fig. 6C) are epi-genetic, and formed at depths in excess of about 800 m.Furthermore, the identification of irregular dissolutionboundaries in the non- and bright luminescent calcitecements (overlain by ore-stage internal sediments;Fig. 3A, B) demonstrates that carbonate dissolutionoccurred during the emplacement of mineralisation. Wetherefore suggest that hydrothermal dissolution was themain process responsible for the formation of the min-eralised breccias at Silvermines. Hitzman et al. (2002)has also proposed a similar origin for the mineralisedbreccias at Lisheen (Fig. 1).

Several researchers have suggested that exhalativemineralisation exists at Silvermines and this has beenused to support a partly synsedimentary origin for themineralisation. The evidence for exhalative mineralisa-tion includes features interpreted as pyrite hydrothermalchimneys (Larter et al. 1981). Restricted in distribution,and rarely preserved in-situ, these features have beeninterpreted as small (a few centimetres tall) hydrother-mal vents that exhaled sulphide-bearing fluids onto theseafloor in reduced conditions. Interpreted pyritised ventfaunas from Silvermines have also been compared withhydrothermal chimneys on the East Pacific Rise, andPhanerozoic VMS deposits (Larter et al. 1981; Boyceet al. 1983, 1999; Mullane and Kinnaird 1998).

We find the reported evidence of exhalative miner-alisation at Silvermines to be unconvincing. The inter-preted hydrothermal chimneys and most of theinterpreted vent faunas from Silvermines (Larter et al.1981; Boyce et al. 1983) resemble cavity-filling stalactiticsulphides (similar to those from the Navan deposit,Peace et al. 2003). The problematic pyritised fossil fromSilvermines described by Boyce et al. (1999) and inter-preted as a vent tube worm may also be a pyritisednormal marine organism and it appears tenuous to basea synsedimentary origin for the Silvermines mineralisa-tion on this single pyritised fossil.

It is also important to note that diagenetic evidence ofsynsedimentary mineralisation at Silvermines is lacking.For example, given the abundance of marine cementa-tion in the Waulsortian mound facies (i.e. the isopac-hous calcite cements), synsedimentary base-metalsulphide cements (if they are present) should be inter-laminated with these marine cements. After an extensivesearch for interlaminated sulphides and marine cementsin both core and thin sections, we can find no evidenceof this and in fact no study has made this observationfrom any locality in Ireland.

Playford and Wallace (2001) described unequivocalsynsedimentary barite mineralisation on the Lennard

Shelf. It is intergrown with stromatolitic limestone and istruncated by veins of Fe-sulphides. The barite itself iscoarse grained and displays a distinct plumose texture,with unidirectional growth textures. This is quite unlikethe barite mineralisation described for the Ballynoebarite deposit, which occurs variably as microcrystalline,randomly orientated acicular crystals and coarse cavity-filling cements (Fig. 4C, D and Fig. 6E, and Mullaneand Kinnaird 1998). Significantly, the synsedimentarybarite mineralisation on the Lennard Shelf pre-datesmarine cements, burial calcite cements, dolomites andMississippi Valley-type mineralisation (Playford andWallace 2001). The barite mineralisation at Silverminesis significantly later as it post-dates the burial calcite andsaddle dolomite cements (Fig. 7 and Fig. 8).

The paragenesis described by this study is not con-sistent with suggestions of synsedimentary mineralisa-tion from Silvermines. The mineralisation and dolomitedocumented by this study are entirely epigenetic as theypost-date significant burial. Any hypothetical synchro-nous exhalative mineralisation at Silvermines wouldhave to have formed at a stratigraphic level that wasgreater than 800 m above the host Waulsortian car-bonates. If synsedimentary sulphides do exist at Silver-mines, then they must be temporally unrelated to themajority of epigenetic sulphides that make up the de-posit. With the absence of unequivocal synsedimentarymineralisation and abundant evidence for epigeneticsulphide precipitation, we propose that the mineralisa-tion at Silvermines is entirely epigenetic.

Conclusions

In the absence of any unequivocal evidence for synse-dimentary sulphides and with the abundance of diage-netic evidence indicating the base metal sulphides are ofburial origin, we conclude that the economic minerali-sation in the Silvermines area is entirely epigenetic inorigin. The mineralisation post-dates the onset of styl-olite formation and extensive replacement dolomitisa-tion. This requires that a minimum burial depth of atleast 800 m was achieved prior to the beginning of sul-phide precipitation. As mineralisation pre-dates pressureshadows of probable Variscan origin, it can also beconcluded that the mineralisation preceded this orogenicevent, constraining the timing of mineralisation tobetween the late Chadian and the late Westphalian.

Elevated regional palaeotemperatures for the Silver-mines area suggest that the Variscan Orogeny resulted inpost-entrapment temperatures that exceeded thehomogenisation temperatures for the calcite cement. Theclose agreement between ore-stage calcite homogenisa-tion temperatures and regional peak temperature esti-mates (from CAI and Ro), suggests that fluid inclusionstretching has occurred. Instead, homogenisation tem-peratures from ore-stage calcite probably approximatepeak temperatures reached during Variscan deforma-tion. As a result, fluid inclusion homogenisation

100

temperatures from ore-stage phases probably overesti-mate mineralisation temperatures.

References

Andrew CJ (1986) The tectono-stratigraphic controls to minerali-zation in the Silvermines area, County Tipperary, Ireland. In:Andrew CJ, Crowe RWA, Finlay S, Pennell WM, Pyne JF (eds)Geology and genesis of mineral deposits in Ireland. Irish AssocEcon Geol, pp 377–417

Andrew CJ (1995) The Silvermines district, Co. Tipperary, Ireland.In: Anderson IK, Ashton J, Earls G, Hitzman M, Tear S (eds)Irish carbonate-hosted Zn-Pb deposits. Soc Econ Geol, pp 247–258

Archer JB, Sleeman, AG, Smith DC (1996) A geologicaldescription of Tipperary and adjoining parts of Laois, Kil-kenny, Offaly, Clare and Limerick, to accompany the BedrockGeology 1:100,000 Scale Map Series, Sheet 18, Tipperary, withcontributions by K. Claringbold, G. Stanley (Mineral Re-sources) and G. Wright (Groundwater Resources). Geol SurvIreland, pp 77

Banks DA, Boyce AJ, Samson IM (2002) Constraints on theorigins of fluids forming Irish Zn-Pb-Ba deposits: evidencefrom the composition of fluid inclusions. Econ Geol 97:471–480

Barnaby RJ, Rimstidt JD (1989) Redox conditions of calcitecementation interpreted from Mn and Fe contents of authigeniccalcites. Geol Soc Am Bull 101:795–804

Barnaby RJ, Read JF (1992) Dolomitization of a carbonate plat-form during late burial: Lower to Middle Cambrian ShadyDolomite, Virginia Appalachians. J Sediment Petrol 62(6):1023–1043

Boyce AJ, Coleman ML, Russell MJ (1983) Formation of fossilhydrothermal chimneys and mounds from Silvermines, Ireland.Nature 306:545–550

Boyce AJ, Fallick AE, Little CTS, Wilkinson JJ Everett CE (1999)A hydrothermal vent tube worm in the Ballynoe baryte deposit,Silvermines, Ireland: implications for timing and ore genesis. In:Stanley CJ, Rankin AH, Bodnar RJ, Naden J, YardleyBWD,Criddle AJ, Hagni RD, Gize AP, Pasava J, Fleet AJ, SeltmannR, Halls C, Stemprok M, Williamson B, Herrington RJ, HillRET, Prichard HM, Wall F, Williams CT, McDonald I, Wil-kinson JJ, Cooke D, Cook NJ, Marshall BJ, Spry P, Zaw K,Meinert L, Sundblad K, Scott PW, Clark SHB, Valsami-JonesE, Beukes NJ, Stein HJ, Hannah HJ, Neubauer F, Blundell DJ,Alderton DHM, Smith MP, Mulshaw S and Ixer RA (eds)Mineral deposits: processes to processing. Balkema, Rotterdam,pp 825–827

Bruck PM (1982) The regional lithostratigraphical setting of theSilvermines zinc-lead and the Ballynoe barite deposits, Co.Tipperary. In: (eds) Mineral exploration in Ireland—Progressand developments 1971–1981, Irish Assoc Econ Geol, pp 162–170

Bruckschen P, Veizer J (1997) Oxygen and carbon isotopic com-position of Dinantian brachiopods: paleoenvironmental impli-cations for the Lower Carboniferous of western Europe.Palaeogeogr Palaeoclimatol Palaeoecol 132:243–264

Choquette PW, James NP (1987) Diangenesis #12. Diagenesis inLimestones - 3. The deep burial environment. Geosci Can 14:3–35

Clayton G, Haughey N, Sevastopulo GD, Burnett R (1989)Thermal maturation levels in the Devonian and Carboniferousrocks of Ireland. Geol Surv Ireland, 36 pp

Coller DW (1984) Variscan structures in the Upper Palaeozoicrocks of west central Ireland. In: Hutton DHW, Sanderson DJ(eds) Variscan tectonics of the north Atlantic region. Geol SocLond Spec Publ 14, pp 185–194

Derry DR, Clark GR, Gillatt N (1965) The Northgate base-metaldeposit at Tynagh, County Galway, Ireland: a preliminarygeological study. Econ Geol 60:1218–1237

Doyle E, Bowden AA, Jones GV, Staley GA (1992) The geology ofthe Galmoy zinc-lead deposits, Co. Kilkenny. In: Bowden AA,Earls G, O�Connor PG, Pyne JF (eds) The Irish mineralsindustry 1980–1990. Irish Assoc Econ Geol, pp 211–225

Everett CE, Wilkinson JJ, Rye DM (1999) Fracture-controlledfluid flow in the Lower Palaeozoic basement rocks of Ireland:implications for the genesis of Irish-type Zn-Pb deposits. In:McCaffrey KJW, Lonergan L, Wilkinson JJ (eds) Fractures,fluid flow and mineralisation. Geol Soc Lond Spec Publ 155, pp247–276

Everett CE, Rye DM, Ellam RM (2003) Source or sink? Anassessment of the role of the Old Red Sandstone in the genesisof the Irish Zn-Pb deposits. Econ Geol 98(1):31–50

Fitzgerald E, Feely M, Johnston JD, Clayton G, Fitzgerald LJ,Sevastopulo GD (1994) The Variscan thermal history of westClare, Ireland. Geol Mag 131(4):545–558

Frank MH, Carpenter AB, Oglesby TW (1982) Cathodolumines-cence and composition of calcite cement in Taum Sauk Lime-stone (Upper Cambrian), southeast Missouri. J Sediment Petrol52:631–638

Goldstein RH, Reynolds TJ (1994) Systematics of fluid inclusionsin diagenetic minerals. SEPM Short Course 31, pp 199

Gregg JM, Shelton KL, Johnson AW, Somerville ID, Wright WR(2001) Dolomitisation of the Waulsortian Limestone (LowerCarboniferous) in the Irish Midlands. Sedimentology 48:745–766

Harland WB, Armstrong RL, Cox AV, Craig LE, Smith AG,Smith DG (1990) A geologic time scale, 1989. CambridgeUniversity Press, New York, 263 pp

Hendry JP (1993) Calcite cementation during bacterial manganese,iron and sulphate reduction in Jurassic shallow marine car-bonates. Sedimentology 40:87–106

Hitzman MW, Large D (1986) A review and classification of theIrish carbonate-hosted base metal deposits. In: Andrew CJ,Crowe RWA, Finlay S, Pennell WM, Pyne JF (eds) Geologyand genesis of mineral deposits in Ireland. Irish Assoc EconGeol, pp 217–238

Hitzman MW, O�Connor P, Shearley E, Schaffalitzky C, BeatyDW, Allan JR, Thompson T (1992) Discovery and geology ofthe Lisheen Zn-Pb-Ag prospect, Rathdowney Trend, Ireland.In: Bowden AA, Earls G, O�Connor PG, Pyne JF (eds) TheIrish minerals industry 1980–1990. Irish Assoc Econ Geol, pp227–246

Hitzman MW, Beaty DW (1996) The Irish Zn-Pb-(Ba) orefield. In:Sangster DF (eds) Carbonate-hosted lead-zinc deposits. SocEcon Geol, pp 112–143

Hitzman MW (1999) Extensional faults that localise Irish syndia-genetic Zn-Pb deposits and their reactivation during Variscancompression. In: McCaffrey KJW, Lonergan L, Wilkinson JJ(eds) Fractures, fluid flow and mineralisation. Geol Soc LondSpec Publ 155, pp 233–245

Hitzman MW, Redmond PB, Beaty DW (2002) The carbonate-hosted Lisheen Zn-Pb-Ag deposit, County Tipperary, Ireland.Econ Geol 97:1627–1656

James NP, Choquette PW (1984) Diagenesis 6. Limestones—thesea floor diagenetic environment. Geosci Can 10:162–179

Johnston JD (1999) Regional fluid flow and the genesis ofIrish Carboniferous base metal deposits. Miner Deposita34:571–598

Jones GL (1987) Irish carboniferus conodonts record maturationlevels and the influence of tectonism, igneous activity andmineralization. Terra Nova 4:238–244

Larter RCL, Boyce AJ, Russell MJ (1981) Hydrothermal pyritechimneys from the Ballynoe Baryte deposit, Silvermines,County Tipperary, Ireland. Miner Deposita 16:309–318

Lee MJ, Wilkinson JJ, Earls G (2001) Textural and cathodolumi-nescence evidence for the origin of black matrix breccias in theIrish Zn-Pb orefield. In: Piestrzynski AEA (ed) Mineral depositsat the beginning of the 21st century. Balkema, Rotterdam, pp161–164

Lee MJ, Wilkinson JJ (2002) Cementation, hydrothermal alter-ation, and Zn-Pb mineralization of carbonate breccias in the

101

Irish Midlands: textural evidence from the Cooleen Zone, nearSilvermines, County Tipperary. Econ Geol 97:653–662

Lees A, Miller J (1995) Waulsortian banks. In: Monty CLV, Bo-sence DWJ, Bridges PH, Pratt BR (eds) Carbonate mud-mounds—Their origin and evolution. Blackwell Science, Ox-ford, pp 191–273

Lind IL (1993) Stylolites in chalk from leg130, Ontong Java Pla-teau. Proceedings of the Ocean Drilling Program, ScientificResults 130:445–451

Machel HG (1985) Cathodoluminescence in calcite and dolomiteand its chemical interpretation. Geosci Can 12(4):139–147

Meyers WJ, Lohmann KC (1978) Microdolomite-rich syntaxialcements: proposed meteoric-marine mixing zone phreatic ce-ments from Mississippian limestones, New Mexico. J SedimentPetrol 48:475–488

Meyers WJ, Lohmann KC (1985) Isotope geochemistry ofregionally extensive calcite cement zones and marine compo-nents in Mississipian Limestones, New Mexico. In: Schneider-mann N, Harris PM (eds) Carbonate cements. Soc EconPaleontol Mineral, pp 223–239

Miller J (1986) Facies relations and diagenesis in Waulsortianmudmounds from the Lower Carboniferous of Ireland and N.England. In: Schroeder JH, Purser BH (eds) Reef diagenesis.Springer, Berlin Heidelberg New York, pp 311–335

Moss S, Tucker ME (1995) Diagenesis of Barremian-Aptian car-bonates (the Urgonian Limestone Formation of SE France):near-surface and shallow-burial diagenesis. Sedimentology42:853–874

MullaneMM,Kinnaird JA (1998) Synsedimentarymineralisation atBallynoe barite deposit, near Silvermines,Co.Tipperary, Ireland.Trans Inst Min Metall (Sect B: Appl Earth Sci) 107:48–61

Nicolaides S, Wallace MW (1997) Pressure-dissolution andcementation in an Oligo-Miocene non-tropical limestone (Clif-ton Formation), Otway Basin, Australia. In: James NP, ClarkeJAD (eds) Cool-water carbonates. Soc Econ Paleontol Mineral,pp 249–261

Peace WM, Wallace MW (2000) Timing of mineralisation at theNavan Zn-Pb deposit: a post-Arundian age for Irish minerali-sation. Geology 28(8):711–714

Peace WM, Wallace MW, Holdstock MP, Ashton JH (2003) Oretextures within the U lens of the Navan Zn-Pb deposit, Ireland:Miner Deposita, DOI 10.1007/s00126-002-0340-1

Playford PE, Wallace MW (2001) Exhalative mineralization inDevonian Reef Complexes of the Canning Basin, WesternAustralia. Econ Geol 96:1595–1610

Prezbindowski DR (1985) Burial cementation—is it important? Acase study, Stuart City Trend, South Central Texas. In:Schneidermann N, Harris PM (eds) Carbonate cements. SocEcon Paleontol Mineral, pp 241–264

Reed CP, Wallace MW (2001) Diagenetic evidence for an epige-netic origin of the Courtbrown Zn-Pb deposit, Ireland. MinerDeposita 36(5):428–441

Reed CP, Wallace MW (2003) Cementation, hydrothermal alter-ation, and Zn-Pb mineralization of carbonate breccias in theIrish Midlands: textural evidence from the Cooleen Zone, nearSilvermines, County Tipperary: a discussion. Econ Geol98(1):191–198

Rhoden HN (1958) Structure and economic mineralization of theSilvermines District, Co. Tipperary, Ireland. Trans Inst MinMetall (Sect B: Appl Earth Sci) 92:67–71

Rhoden HN (1960) Mineralogy of the Silvermines district, Co.Tipperary, Eire. Mineral Mag 32:128–139

Samson IJ, Russell MJ (1987) Genesis of the Silvermines zinc-lead-barite deposit, Ireland: fluid inclusion and stable isotope evi-dence. Econ Geol 82:371–394

Scholle PA, Halley RB (1985) Burial diagenesis: out of sight, out ofmind! In: Schneidermann N, Harris PM (eds) Carbonate ce-ments. SEPM Spec Publ No 36, pp 309–334

Schultz RW (1966) The Northgate base-metal deposit atTynagh, County Galway, Ireland: discussion. Econ Geol61:1443–1449

Sevastopulo GD, Wyse Jackson PN (2001) Carboniferous (Di-nantian). In: Holland CH (ed) The geology of Ireland. DunedinAcademic Press, Edinburgh, pp 241–288

Shearley E, Redmond P, King M, Goodman R (1996) Geologicalcontrols on mineralisation and dolomitisation of the LisheenZn-Pb-Ag deposit, Co. Tipperary, Ireland. In: Strogen P,Somerville ID, Jones GL (eds) Recent advances in LowerCarboniferous geology. Geol Soc Lond Spec Publ 107, pp 23–33

Taylor S, Andrew CJ (1978) Silvermines orebodies, County Tip-perary, Ireland. Trans Inst Min Mineral (Sect B: Applied EarthSci) 87:111–124

Taylor S (1984) Structural and paleotopographic controls of lead-zinc mineralization in the Silvermines orebodies, Republic ofIreland. Econ Geol 79:529–548

Tobin KJ, Walker KR, Goldberg SG (1997) Burial diagenesis ofmiddle Ordovician carbonate buildups (Alabama, USA): doc-umentation of the dominance of shallow burial conditions.Sediment Geol 114:223–236

Tobin RC, Claxton BL (2000) Multidisciplinary thermal maturitystudies using vitrinite reflectance and fluid inclusion microth-ermometry: a new calibration of old techniques. AAPG Bull 84(10):1647–1665

Tucker ME (1991) Sedimentary petrology: an introduction tothe origin of sedimentary rocks. Blackwell Scientific, London,260 pp

Wallace MW, Kerans C, Playford PE, McManus A (1991) Burialdiagenesis in the Upper Devonian reef complexes of the GeikieGorge Region, Canning Basin, Western Australia. Am AssocPet Geol Bull 75(6):1018–1038

102