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Ore-Forming Processes in Irish-Type Carbonate-Hosted Zn-Pb Deposits: Evidence from Mineralogy, Chemistry, and Isotopic Composition of Sulfides at the Lisheen Mine

J. J. Wilkinson and S. L. Eyre^*

Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom

A. J. Boyce

Scottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 0QF, Scotland

Corresponding author: e-mail, j.wilkinson{at}imperial.ac.uk

	Abstract

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
Lisheen is a strata-bound zinc-lead deposit formed during the Mississippian by replacement of hydrothermally dolomitized, grossly stratiform breccia bodies located near the base of the Carboniferous Waulsortian Limestone. It represents one of a number of carbonate-hosted massive sulfide ore deposits in the Irish ore field that, due to several unique features, have been classified as Irish type.

Disseminated pyrite occurs in preore dolomite and around the margins of preore dolomite clasts within dolomite breccias. Early fine-grained sphalerite-pyrite mineralization occurs as infill of intergranular dolomite porosity. Locally, massive to semimassive iron sulfide is observed, mainly comprising pyrite with lesser marcasite. A complex polymetallic sulfide assemblage typifies the main ore stage, dominated by fine-grained disseminated, massive or colloform sphalerite and galena, with minor pyrite, chalcopyrite, arsenopyrite, tennantite, nickel- and cobalt-bearing minerals. Silver occurs in solid solution in tennantite, galena, and sphalerite. Dolomite and barite dominate the gangue, with lesser calcite. Main-stage mineralization involved the progressive replacement of preexisting iron sulfides and the dolomite breccias, initially by replacement of the breccia matrix and ultimately by replacement of clasts. Coarse crystalline sphalerite and euhedral galena crystals are generally restricted to fracture-fill mineralization or vugs within main ore-stage assemblages where they occur with euhedral dolomite and calcite.

Barite intergrown with main ore-stage sulfides has ³⁴S values of 14.3 to 18.1 per mil, consistent with the derivation of sulfate from coeval Carboniferous seawater. The ³⁴S values for sulfides range from –44.1 to +11.8 per mil, with a mean value of –13.7 per mil, typical of the Irish ore deposits. The dominant low ³⁴S signature is considered to be the result of bacterial reduction of coeval seawater sulfate. Extremely low ³⁴S values, in the range of –38 to –44 per mil, are only observed in preore disseminated pyrite; such extreme fractionations are thought to be due to low bacterial sulfate reduction rates coupled with oxidative cycles in near-sea floor pore waters. Main ore-stage sulfides have ³⁴S values in the range of –4 to –18 per mil, with a mode of –10 per mil, consistent with a typical bacterial fractionation from coeval seawater sulfate. Isotopic equilibrium between cogenetic sulfides is not observed. The bacteriogenic sulfur component was probably transported from bacterial colonies fringing the ore system by low-temperature brines.

The ³⁴S values of late ore-stage sulfides mainly range from –20.2 to +12.0 per mil, with the majority having relatively high values (mean = –3.0 ± 8.5, 1) interpreted as being due to the presence of a hydrothermal sulfur component, leached from the lower Paleozoic basement. For galena and sphalerite there is a general increase in ³⁴S values with depth in the system, with time, and with proximity to east-west– and northwest-trending faults. These relationships suggest that input of hydrothermal sulfur from depth via fractures became increasingly important. Hydrothermal sulfur appears to be more important at Lisheen than the other major Irish deposits.

Galena lead isotope analyses gave average ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of 18.183, 15.594, and 38.080, respectively. These data do not correlate with ore-stage, galena texture or ³⁴S. The results are comparable to previous data from Lisheen and from Silvermines, 35 km to the west, implying a common lead source in the lower Paleozoic basement.

The textural, mineral, chemical, and isotopic evidence suggests that main-stage ore was precipitated as a consequence of rapid supersaturation, caused by fluid mixing within the permeable dolomite breccias. This process involved relatively high temperature (ca. 240°C), metal-bearing solutions derived from a basement-equilibrated fluid reservoir (carrying Zn, Pb, Fe, Cd) and shallow, saline (ca. 25 wt % NaCl equiv) formation waters rich in bacteriogenic H₂S. Minor metals (Cu, As, Ni, Co) are thought to have been stripped from the footwall Old Red Sandstone during hydrothermal alteration around fault conduits. The availability of abundant seawater sulfate, operation of open-system bacterial sulfate reduction, and episodic availability of free oxygen imply that ore formation cannot have occurred at significant depth below the paleosea floor. Cessation of mineralization was due to a cut-off of the sulfur-rich brine supply, possibly by deposition of impermeable hanging-wall sediments. This process of ore formation is consistent with evidence from the other economic Irish-type deposits in the ore field.

	Introduction

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
The Lisheen deposit, situated in County Tipperary, Ireland (Fig. 1), is the most recent of six carbonate-hosted Zn-Pb deposits to have been discovered in the Irish ore field in the last 35 yr. Found in 1990 by a Chevron Mineral Corporation-Ivernia West joint venture, the deposit began production in late 1999. It contained a total premining resource (undiluted) of 16.7 million metric tons (Mt) of ore, grading 14.1 percent Zn and 2.4 percent Pb (weighted average calculated from Fusciardi et al., 2003), together with approximately 16 percent Fe and 26 g/t Ag (Elmes et al., 2000). The ore is hosted principally by carbonate breccias near the base of the Mississippian (Courceyan) Waulsortian Limestone. The deposit is the most significant of a number of mineralized occurrences in the Rathdowney trend of the southern Midlands (Fig. 1) that include the Galmoy deposit (Doyle et al., 1992), 10 km to the northeast. Lisheen, together with the deposits of Galmoy, Navan, Tynagh, and Silvermines, represents the deposit class known as "Irish-type" as redefined by Wilkinson (2003).

View larger version (55K): [in this window] [in a new window]   FIG. 1. Simplified geologic map of the Irish Midlands, showing location of major deposits.

	Geologic Setting

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
The Irish deposits are hosted by a Lower Carboniferous marine transgressive sequence that conformably overlies a terrigenous clastic red-bed succession (Old Red Sandstone) of Devonian-Carboniferous age. This lies unconformably on a peneplained basement of Silurian graywackes, siltstones, shales, and volcanic rocks that were deformed and weakly metamorphosed in the Caledonian orogeny. Mineralization is hosted by a variety of carbonate facies, primarily shallow marine deposits of the Navan Group and the deeper water mud mounds of the Waulsortian Limestone (Hitzman and Large, 1986; Phillips and Sevastopulo, 1986; Andrew, 1993; Hitzman, 1995; Hitzman and Beaty, 1996).

At Lisheen, the lower part of the Carboniferous marine sequence includes carbonate-rich shales, siliciclastic sedimentary rocks, and argillaceous bioclastic limestones (Lower Limestone Shale and Ballysteen Limestone; Philcox, 1983). The deposit is hosted by the Courceyan to early Chadian Waulsortian Limestone, which comprises coalesced wackestone or packstone mud mounds flanked by argillaceous bioclastic limestone (Philcox, 1983; Phillips and Sevastopulo, 1986). Growth fault control of sedimentation in the Courceyan-Chadian (immediately prior to and during deposition of the Waulsortian Limestone) is indicated by thickness variations across structures (Boyce et al., 1983; Hitzman et al., 2002; Carboni et al., 2003; Fusciardi et al., 2003).

	Geology of the Lisheen Deposit

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
Stratigraphy
The local stratigraphy in the Lisheen area is described by Hitzman et al. (2002) and is summarized in Figure 2. The main host to mineralization is the Waulsortian Limestone, dominantly comprising massive, pale-gray biomicrite, together with green-gray and gray argillites, wavy laminated and stylonodular micrites. The Waulsortian is commonly brecciated, particularly toward its base, and it is these breccias that host the bulk of the ore. Although there is still debate over the relative importance of sedimentary and hydrothermal controls on the genesis of Waulsortian breccias (Hitzman and Beaty, 1996; Lee, 2002; Lee and Wilkinson, 2002; Reed and Wallace, 2003; Wilkinson and Lee, 2003), their significance is clear as the primary host rocks to ore in the south and west Midlands. At Lisheen, synsedimentary breccias are present locally in the hanging wall of normal faults (Hitzman et al., 2002; Carboni et al., 2003; Fusciardi et al., 2003), but it is not clear whether these are always precursors for the hydrothermally overprinted and mineralized dolomite breccias as has been documented at Silvermines (Lee and Wilkinson, 2002).

View larger version (30K): [in this window] [in a new window]   FIG. 2. Summary stratigraphy of the Lisheen area (modified after Eyre, 1998).

View larger version (41K): [in this window] [in a new window]   FIG. 3. Simplified structural map of the Lisheen deposit, showing main ore zones and locations of drill holes sampled in the present study (Lisheen mine, 1998).

Regional dolomitization
Several phases of dolomitization occur in the Lisheen area, the origin of which are still debated (e.g., Wilkinson, 2003). The earliest is a fine- to medium-grained, subhedral to euhedral gray dolomite that preferentially replaces micritic components of the precursor Waulsortian Limestone (D_1a). This is partially recrystallized to and/or postdated by a coarse white planar to weakly nonplanar dolomite (D_1b) that preferentially replaces coarser crystalline components of the Waulsortian, such as early marine calcite cements in stromatactis cavities and bioclasts. Together, these phases form what has been described as the "regional dolomite" that occurs throughout much of the Waulsortian in southeast Ireland (Hitzman et al., 1998).

In the Lisheen area, the entire Waulsortian Complex, as well as relatively nonargillaceous beds within the lowermost part of the overlying Crosspatrick Formation, are dolomitized (Shearley et al., 1996). Regional dolomite occurs on both the hanging-wall and footwall sides of the main Killoran and Derryville faults (Hitzman and Shearley, 1991, unpub. technical report for Chevron Mineral Corporation of Ireland, Intercompany Technical Group on Carbonates Seminar LN91000514). In the northern part of the Rathdowney trend and along the margin of the Leinster massif, dolomitization of this type has been observed locally to extend higher in the stratigraphy, into the Aghmacart Formation. However, dolomite has not been observed in the Arundian-age upper portion of the Aghmacart Formation (Sheridan, 1977). The Rathdowney trend essentially marks the northwest limit of pervasively dolomitized Waulsortian, with the Lisheen and Galmoy deposits located just to the southeast of the dolomite front (Hitzman and Beaty, 1996).

The most recent studies conclude that D_1a formed during early seawater diagenesis but later underwent neomorphic recrystallization (Wright et al., 1999, 2000; Gregg et al., 2001). D_1b is thought to have developed in response to the onset of extensive fault-controlled hydrothermal circulation in the late Courceyan-Chadian (Wilkinson, 2003). The regional dolomite plays a pivotal role in arguments concerning deposit genesis because it is considered to predate ore formation at Lisheen and Galmoy (Doyle et al., 1992; Shearley et al., 1995; Eyre, 1998; Hitzman et al., 2002; Wilkinson et al., 2003), thereby providing a maximum limit for the age of mineralization.

Hydrothermal dolomitization
A weakly developed, dark-gray dolomite of uncertain genesis forms the first localized alteration phase at Lisheen (Hitzman et al., 1992). The first well-developed dolomite of inferred hydrothermal origin (D₂) forms the matrix of the grossly stratiform, wedge-shaped breccia bodies ("black matrix breccias") that occur near the base of the Waulsortian Limestone (Fig. 4). The term "matrix" is used here in a general sense to mean the material surrounding breccia clasts, rather than implying a specific origin for this material since its origin is uncertain. At Lisheen, it is not clear whether the matrix dolomite is (1) merely a replacement of the precursor dolomitized limestone, (2) a true cement to breccia clasts, or (3) predominantly a replacement of an earlier (synsedimentary) breccia matrix, as has been shown to be the case in the Silvermines district (Lee and Wilkinson, 2002). It could have formed from a combination of these processes (Hitzman et al., 2002). Fluid inclusion data from the Tynagh basin have shown that the black dolomite commonly observed associated with mineralization in the Irish ore field is likely to be a characteristic product of fluid mixing (Wilkinson and Earls, 2000), probably forming ahead of sulfides in a prograding reaction front (Hitzman et al., 2002; Lee and Wilkinson, 2002; Wilkinson et al., 2003).

View larger version (81K): [in this window] [in a new window]   FIG. 4. North-south cross section through the Derryville zone, showing major lithological units and location of main ore lens (Lisheen mine, 1998).

Crackle breccias and stockworks cemented by medium- to coarse-grained white, planar or weakly nonplanar variably ferroan dolomite (D₃), commonly referred to as "white matrix breccias," form a broad halo to the D₂ dolomite breccias and are developed through much of the thickness of the Waulsortian. These are comparable to the "crystalline dolomite breccias" at Galmoy (Doyle et al., 1992). The relative timing of these breccias is uncertain as they tend to occur above and/or lateral to D₂ dolomite breccias (Hitzman et al., 2002), such that crosscutting relationships are rarely observed. Shearley et al. (1996) inferred a post-D₂ timing, but the local presence of both crystalline white dolomite in D₂ breccia clasts and black dolomite in D₃ dolomite breccias (also observed at Silvermines; Lee et al., 2001; Lee and Wilkinson, 2002) implies a broadly contemporaneous origin (also see Fusciardi et al., 2003). The textural differences are believed to result from the mode of formation; black dolomite precipitated rapidly during fluid mixing, whereas white dolomite crystallized from a single hydrothermal fluid (Earls and Wilkinson, 2000; Wilkinson, 2003).

The dolomite breccias are crosscut by generally steeply dipping veins of ferroan dolomite, dolomite (D₄), and calcite (C₄). These phases also fill residual vuggy porosity within earlier dolomite generations. The veins typically display symmetrical drusy crystal growth and may be composite. They also commonly contain sulfides.

A late-stage, distinctive pink dolomite (D₅) crosscuts and aggressively dissolves all previous dolomite and/or sulfide generations and is often coprecipitated with minor pyrite and/or chalcopyrite (Eyre, 1998; Hitzman et al., 2002; Fusciardi et al., 2003). This is similar to late pink dolomite observed elsewhere in the Midlands (e.g., Boast et al., 1981; Wilkinson, 2003). Sometimes, residual porosity in this dolomite is filled by a white, blocky calcite (C₆).

Mineralization
Mineralization at Lisheen occurs within 30 m of the base of the Waulsortian, forming single and locally multiple, generally stratiform, sulfide lenses separated by D₂ dolomite breccias (Fig. 4). The orebodies comprise texturally complex, polymetallic massive sulfide, displaying both gradational and sharp, planar or undulating contacts with the enclosing breccias. Sometimes, postore stylolites are developed along these contacts. Sulfides are also present in the Lisduff Oolite Member (Fig. 2), predominantly in the footwall but also in the hanging wall of the Killoran and Derryville faults (Eyre, 1998; Hitzman et al., 2002; Fusciardi et al., 2003). The Lisduff Oolite is much less extensively mineralized than the basal Waulsortian and only comprises a minor proportion of the total resource.

Four main ore zones have been defined: Main, North, Derryville, and Bog (Fig. 3). The Main zone forms the largest orebody, followed by Derryville, North, and the Bog zone. Detail on metal zoning patterns in the four zones is available in Hitzman et al. (2002) and Fusciardi et al. (2003).

	Methodology

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
Textural and petrographic relationships of sulfides were determined by the detailed study of more than 200 polished blocks and thin sections in reflected light and under the scanning electron microscope (SEM). This work was based only on drill core samples collected between 1994 and 1997, prior to underground exposures becoming available for study. Representative drill core samples covering the spectrum of ore stages, mineralization styles, and a range of lateral and vertical positions within the four main ore zones (Fig. 3) were collected in order to evaluate temporal and spatial variations in sulfide mineralogy and sulfur isotope composition. Quantitative analysis of sulfides using the microprobe was carried out mainly on the ore-stage mineralization to determine the temporal and spatial distribution of trace elements, particularly in relation to putative hydrothermal feeder structures. Analyses were performed using a Cameca SX50 wavelength dispersive electron microprobe at the Natural History Museum, London. A summary of results is presented in Table 1 and full results are available from the author on request.

Lead isotope analysis
Galena samples for lead isotope analysis were drilled from core specimens. Approximately 2 to 5µg of galena was dissolved in an excess of 6M HCl. These solutions were pipetted directly onto a single rhenium filament using a standard lead loading technique with phosphoric acid and silica gel. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios were measured on a VG 54E mass spectrometer. The results were normalized to the NBS 981 international standard and corrected for instrumental mass fractionation (see Table 3).

	Ore Mineralogy and Paragenesis

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

Based on the broad textural and mineralogical associations observed within the deposit, mineralization has been classified into four stages: (1) preore stage, (2) main ore stage, (3) late ore stage, and (4) postore stage (Fig. 5).

View larger version (16K): [in this window] [in a new window]   FIG. 5. Summary paragenesis for the Lisheen deposit (after Eyre, 1998). Width of bar corresponds to relative abundance; bars for sulfides are shown hatched for clarity.

View larger version (91K): [in this window] [in a new window]   FIG. 6. Core photographs and reflected light photomicrographs of preore-stage samples. (a). Preore-stage pyrite preferentially replacing the matrix of typical black dolomite matrix breccia. Sample LK262/153.6m, Derryville zone. (b). Pale-brown early sphalerite preferentially replacing matrix of dolomite breccia. Sample LK121-189.3m, Main zone. (c). Preore-stage colloform pyrite with minor carbonate and sphalerite inclusions overgrown by subhedral pyrite (py) and marcasite (ma). Sample LK420/190.7m, Derryville zone. (d). Fine-grained granular pyrite (py) pseudomorphous after barite laths. Timing of euhedral pyrite uncertain. Subhedral-anhedral sphalerite (sp) overgrows and replaces pyrite. Sample LK262/162.1m, Derryville zone. (e). Massive sulfide sample showing colloform banding. Preore-stage fine-grained pyrite-marcasite (py-ma) with sphalerite-rich outer zone is overgrown by pyrite-marcasite band, itself succeeded and partly replaced by ore-stage sphalerite (sp), dolomite (dol), and euhedral galena (gn). Sample LK394/164.3m, Derryville zone (Derryville fault). (f). Preore-stage massive pyrite (py) and marcasite (ma) that has undergone cataclasis and cementation by dolomite (dol) and sphalerite (sp). Sample LK262/159.1m, Derryville zone.

Marcasite occurs in colloform masses, elongate radiating laths intergrown with pyrite, and as coarse subhedral grains. Sphalerite, galena, and dolomite locally occur as inclusions within the banded iron sulfides, either in discrete layers or as isolated crystals along particular iron sulfide growth bands (Fig. 6e). Galena commonly occurs as small spheres within massive iron sulfide. Sulfides displaying radial coxcomb textures are generally uncommon but are well developed in the Lisduff Oolite Member adjacent to the main fault zone.

Cataclastic textures in pyrite and marcasite are common near to major faults in the Main and Derryville zones. There is infilling and partial replacement of pyrite along fractures by sphalerite and dolomite (Fig. 6f) and also by ore-stage galena.

Main ore stage
A complex polymetallic sulfide assemblage characterizes the main ore stage, dominated by sphalerite and galena, with minor pyrite, chalcopyrite, arsenopyrite, tennantite, dolomite, and barite. Coprecipitation of some phases is suggested by the presence of mutual growth boundaries, although replacement of one sulfide by another is also common. No consistent paragenetic sequence can be defined and the assemblage appears to be the product of multiple overprinting and recrystallization events. Sulfides of the main ore stage often replace early iron sulfides (Fig. 7a) and overprint the dolomite breccias, preferentially replacing the D₂ dolomite matrix and ultimately also D_1a clasts (Fig. 7b). This sequence of progressive replacement can be clearly traced laterally into the ore from essentially pristine, unmineralized breccias. Apparently brecciated massive sulfide pseudomorphs may in fact represent preexisting dolomite breccia textures (Fig. 7b), although rebrecciation in situ during intense mineralization close to the main fault zones is also likely.

View larger version (98K): [in this window] [in a new window]   FIG. 7. Core photographs and reflected light photomicrographs of main ore-stage samples. (a). Massive fine-grained pyrite in gray Waulsortian micrite (m), crosscut and replaced by sphalerite (sp) and galena (gn) in white dolomite stockwork. Sample LK121/190.2m, Main zone. (b). Complex massive sulfide with pyrite (py) intergrown with and replaced by galena (gn) and pale-brown sphalerite (sp). Note apparent breccia texture (replaced dolomite breccia?). Sample LK262/159.85m, Derryville zone. (c). Colloform sphalerite containing thin bands of fine-grained pyrite and occasional botryoidal pyrite intergrown with dolomite and fine-grained, zinc-rich (?geopetal) carbonate. Sample LK262/159.85m, Derryville zone. (d). Pyrite (py) and sphalerite (sp) incorporated in dolomite (dol) euhedra along growth surfaces and overgrown by apparently homogeneous colloform sphalerite. Sample LK416/193.6m, Derryville zone. (e). Selective replacement of foraminifera (Endothyrid). Sphalerite (sp) preferentially replaces chamber walls with chambers filled by galena (gn) and carbonate gangue (c), the whole surrounded by pyrite (py). An unidentified Fe-As sulfide (u) with minor Ni, Co, and In forms a thin layer inside the microfossil. Sample LK137/134.9m, Derryville zone (sub-Waulsortian, footwall of Derryville fault). (f). Mixed ore-stage sulfide assemblage comprising intergrown euhedral pyrite (py) and galena (gn), together with sphalerite (sp), probably pseudomorphous after barite laths. Sample LK325/146.2m, Derryville zone. (g). Selective replacement of ooid by galena (gn), surrounded and partly replaced by sphalerite (sp) and minor pyrite (py). Galena replacement may postdate plastic deformation of ooid reflected by oval shape and curviplanar contacts that parallel distorted laminae (upper right). No replaced stylolites truncating laminae, or fractured, or spalled laminae are observed indicating replacement preceded mechanical compaction, or that mechanical compaction did not occur. Sample LK394/164.3m, Derryville zone (Derryville fault). (h). Symmetrical vug-fill sulfides comprising sphalerite (sp) intergrown with laminated and/or colloform pyrite (py), with both being replaced from the margins inward by subhedral galena (gn). Carbonate infilling in remaining space (c), with minor dissolution of sphalerite along contact. Sample LK420/196.0m, Derryville zone.

Colloform sphalerite displays marked compositional variation (Table 1). Individual samples may contain up to 40 distinct zones with significant variations in Cd, Fe, and As concentrations (Fig. 8a). Cu (up to 0.11 wt %) is also observed in some zones. The color of colloform sphalerite generally correlates with mineral chemistry. For example, in a sample from the North zone, gray-yellow bands contain up to 0.12 wt percent Fe (avg 0.06 wt % Fe), yellow sphalerite contains up to 1.95 wt percent Fe (avg 0.37 wt % Fe), and orange-brown layers contain up to 2.84 wt percent Fe (avg 0.63 wt % Fe). Other elements may also be present such as Ag (up to 0.24 wt %), Cd (up to 0.47 wt %), and As (up to 0.60 wt %). In two samples analyzed for Tl, highly variable concentrations of up to 0.54 wt percent were found. However, there are no statistically significant correlations between major or trace elements within any of the colloform sphalerite analyzed.

View larger version (9K): [in this window] [in a new window]   FIG. 8. Examples of variations in chemical composition of sphalerite as determined by microprobe analyses (supplementary information on detection limits and full data available from author on request). (a). Traverse across main ore-stage color-banded colloform sphalerite (sample 262/159.1m, Derryville zone). Note lack of correlation between element concentrations in individual bands and occasional detectable Cu. (b). Traverse across late ore-stage finely crystalline, red-amber color-zoned sphalerite (sample 471/210.4m, Main zone). This sample is unusual in that it shows elevated Cd and Fe and shows a rare correlation between Cd and Fe concentrations.

Replacement textures are common, such as the replacement of dolomite rhombs by sphalerite and/or galena. Selective replacement of microfossils by sphalerite and other sulfides is also observed locally (Fig. 7e), as has been reported at Navan (Anderson et al., 1998). Sphalerite bow-tie textures in pyrite and elongate laths of sphalerite in a mixed assemblage of pyrite and galena are probably pseudomorphs after early barite or gypsum (Fig. 7f). Sphalerite also occurs in small veinlets crosscutting and replacing pyrite (Fig. 7a) and galena.

Galena locally forms skeletal and dendritic growths, similar to those described from Navan (Anderson et al., 1998). However, ore-stage galena is predominantly coarsely crystalline or massive and replacive, as indicated by caries textures, where galena replaces D₂ dolomite, and by the selective replacement of microfossils, early marine cements, and ooids (Fig. 7g). Galena is particularly abundant in zones proximal to the Killoran and Derryville faults where it commonly contains inclusions of tennantite, especially in the Main zone. Galena inclusions are also found within tennantite. Boulangerite is commonly associated with galena.

Galena generally does not contain detectable concentrations of trace elements (Table 1). Massive Waulsortian-hosted ore-stage galena locally contains elevated Te (up to 0.27 wt %). Ag concentrations are usually below detection with the exception of a few samples located proximal to faults that contain up to 0.19 wt percent Ag. The phase that contains the highest concentrations of Ag in the deposit is tennantite (see below).

Tennantite, chalcopyrite, arsenopyrite, and barite are most abundant near the Killoran and Derryville faults, especially within the footwall Lisduff Oolite Member. In this unit, tennantite commonly occurs as irregular inclusions in galena, chalcopyrite, and sphalerite and is characterized by up to 3.91 wt percent Zn, 5.63 wt percent Fe, and 0.32 wt percent Ag (Table 1). This contrasts with tennantite in galena from the Waulsortian, which contains up to 8.55 wt percent Zn, less Fe (<1.72 wt %), and less Ag (<0.24 wt %).

Short intervals of massive chalcopyrite are observed in drill core from the footwall Lisduff Oolite of the Main zone and this contains up to 0.73 wt percent As (avg 0.16 wt %). Minor chalcopyrite in the Bog zone Lisduff Oolite also contains As, up to 0.11 wt percent (avg 0.07 wt %). Minor disseminated arsenopyrite rhombs commonly occur in ore-stage galena, proximal to faults in the Main and Derryville zones.

Main ore-stage pyrite generally comprises fine- to coarse-grained euhedra intergrown with and locally interstitial to sphalerite and galena (e.g., Fig. 7f). Trace element concentrations in ore-stage pyrite are quite variable (Table 1). Arsenic concentrations range up to 5.21 wt percent and are significantly higher than in preore pyrite. In As-rich samples, As correlates with Cu with both showing a strong antipathetic relationship with Fe. Co and Ni are usually below detection, with the notable exception of pyrite hosted by the Lisduff Oolite Member in the footwall of the Killoran fault (up to 0.44 wt % Co and 1.92 wt % Ni). This pyrite also contains up to 3.34 wt percent As, which is strongly correlated with Ni content. Elevated levels of Co and Ni are also observed in the Ballysteen Limestone close to a secondary fault (F-291) in the hanging wall of the Derryville fault (Fig. 3).

Barite was probably deposited both prior to and during the main period of sulfide mineralization. Early sulfides, in particular pyrite and sphalerite, and ore-stage sulfides (Fig. 7f) both replace barite. Later barite, associated with complex mixed sulfide assemblages, crosscuts early pyrite-sphalerite assemblages.

Late ore stage
Coarse (1–7 mm) crystalline sphalerite and euhedral galena crystals are restricted to fracture-fill mineralization that crosscuts the main ore-stage assemblages and to vugs within main-stage ore. These phases commonly predate or were coprecipitated with D₄ dolomite and C₄ calcite veins and vug-filling cements (Fig. 7h). Sphalerite was generally the last sulfide to precipitate, commonly as rims on galena. Concentrically zoned pyrite grains locally occur within these sphalerite rims and late, euhedral, fracture-filling galena is sometimes observed.

Although texturally late, there is no evidence to suggest that these phases are unrelated to the main ore stage and are therefore regarded as representing waning hydrothermal activity, precipitated within residual porosity and tectonic fractures.

View larger version (31K): [in this window] [in a new window]   FIG. 9. Variation of cadmium and iron concentrations in sphalerite as a function of textural type and location. Note that the vast majority of samples are enriched in either cadmium or sphalerite, but not both, suggesting substitution of one or other element into the same lattice site. Darker brown sphalerite may be either Cd or Fe rich. The most Cd rich sphalerites are hosted by the Lisduff Oolite; Fe-rich sphalerites are generally from within the main fault zones. Most sphalerite in the main orebodies (within thick hatched line) contains variable Fe and low Cd.

Postore stage
Sulfides that occur in veins that clearly crosscut all previous stages are defined as postore stage. At Lisheen, these sulfides are commonly associated with pink saddle dolomite (D₅), which is associated with extensive dissolution of earlier carbonates and sulfides. This often leaves extensive vuggy porosity and abundant pink dolomite typically correlates with poor ore grades. Chalcopyrite and pyrite are the dominant sulfides, typically forming encrustations on saddle dolomite crystals together with minor sphalerite and galena. There is white blocky calcite (C₆) infilling of residual porosity in some samples.

	Sulfur and Lead Isotopes

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
Sulfur Isotopes
A total of 119 analyses were carried out on 53 samples of sulfides (mainly pyrite, sphalerite, and galena) and barite from the four main ore zones and from all stages of the paragenesis (Table 2, Appendix).

The ³⁴S values show a very wide range from –44.1 to +11.8 per mil, with a mean value of –13.7 per mil (Fig. 10a). Extremely low ³⁴S values in the range of –38 to –44 per mil are only observed in preore-stage disseminated pyrite (Fig. 10b), and pyrite in general has lower values than the other sulfides, a feature typical of the Irish-type deposits (e.g., Boyce, 1990; Anderson et al., 1998; Fallick et al., 2001; Blakeman et al., 2002). Sphalerite and galena have similar ranges in isotopic composition.

View larger version (12K): [in this window] [in a new window]   FIG. 10. Histograms of sulfur isotope compositions, subdivided according to (a) sulfide phase and (b) ore stage. Sphalerite and galena have very similar ranges and average values, whereas pyrite is much more variable and trends to much lower 34S values. Preore sulfides (mainly pyrite) are characterized by very low 34S values indicative of an extreme bacteriogenic fractionation. Main ore-stage values are intermediate due to mixing between bacteriogenic and hydrothermal sulfur sources coupled with less extreme bacteriogenic fractionation during sulfate reduction. Late ore-stage sulfides are dominated by hydrothermal sulfur with high 34S. Postore-stage sulfides have low 34S values, probably indicative of sulfur remobilized from early main ore-stage sulfides.

View larger version (20K): [in this window] [in a new window]   FIG. 11. Variations in sulfur isotope composition of (a) sphalerite, (b) galena, and (c) pyrite with depth and textural type. Outliers: BZ = Bog zone, DZ = Derryville zone, MZ = Main zone, NZ = North zone. Samples from sub-Waulsortian units are indicated. Sphalerite and galena show trends toward higher 34S values with depth in the main ore zones and in sub-Waulsortian sulfides consistent with input of an 34S-enriched sulfur component from depth. Pyrite does not show such a trend in the main ore zones, suggesting that much of it formed relatively early when the flux of hydrothermal sulfur from depth was minor or absent.

Sphalerite:

Sphalerite shows a broad correlation between sulfur isotope composition and sample depth. More negative ³⁴S values occur in shallower, Waulsortian-hosted sulfides, and higher ³⁴S values occur lower in the stratigraphy at the base of the Waulsortian and in the Ballysteen Limestone Formation, including the Lisduff Oolite Member (Fig. 11a). Variation in the sulfur isotope composition of sphalerite between the ore zones is also observed. Sphalerite in the Main zone is relatively homogeneous in sulfur isotope composition (Fig. 11a). ³⁴S values for sphalerite from the Derryville zone are slightly more negative and have a wider range, and sphalerite from the Bog zone has the widest range of isotopic compositions, albeit based on only four analyses (Fig. 11a).

Galena: ³⁴S values of galena (n = 34) fall within the range of –26.8 to +3.2 per mil (avg –11.7 ± 7.5 per mil, 1; Fig. 10a). Main ore-stage galena (n = 22), like sphalerite, has a narrow range of ³⁴S values with an average of –11.2 ± 3.3 per mil. Galena hosted by the Lisduff Oolite Member and intergrown with fine-grained sphalerite has the highest ³⁴S value of +3.2 per mil. The lowest ³⁴S value, –26.8 per mil, was obtained from late- to postore-stage, vein-hosted galena associated with tennantite at the base of Waulsortian-hosted massive sulfide in the Derryville zone. Galena shows a clearly defined increase in ³⁴S values with depth and increasing heterogeneity from the Main to Derryville to Bog zones (Fig. 11b), similar to sphalerite.

Pyrite: ³⁴S values in pyrite (n = 37) range from –44.1 to +11.8 per mil (avg –22.4 ± 13.3 per mil, 1; Fig. 10a). Disseminated preore-stage pyrite hosted by well-developed hydrothermal D₂ dolomite has the lowest ³⁴S values of –44.1 to –38.1 per mil. Main ore-stage pyrite (n = 24) has a restricted range of sulfur isotope compositions but is still more variable than sphalerite and galena and also has markedly lower values than the other sulfides, with a mean of –20.1 ± 7.1 per mil. In the Waulsortian, no correlation with depth is apparent (Fig. 11c). However, the highest ³⁴S value of +11.8 per mil is from relatively deep in the system, from a vein within the upper calcarenite member of the Ballysteen Limestone Formation. Pyrite from the Main zone has a more uniform isotopic composition than in the Derryville zone, similar to the other main sulfides. Only two data from one drill hole in the Bog zone were analyzed, and these are rather similar.

Chalcopyrite: Chalcopyrite samples, all from the Main zone and representing the main ore stage, have typical ore-stage ³⁴S values ranging from –6.6 to –8.3 per mil (n = 3; Fig. 10a).

Barite: Barite intergrown with main ore-stage sulfides in the Derryville zone (n = 2) has ³⁴S values of +18.1 and +17.2 per mil (repeat analyses on splits of a single sample, Fig. 10a). Barite associated with main ore-stage sulfides in the Main zone (n = 2) has lower values (although possibly sulfide contaminated) of +14.3 and +14.5 per mil.

Lead isotopes
A preliminary study of four galena samples was carried out to provide supplementary data on the lead isotope character of the deposit and to compare the results with existing data from the Irish ore field. The samples analyzed were from massive ore-stage galena and from vein-hosted, late- to postore-stage galena (Table 3). The results are compared to data from other deposits in the ore field in Figure 12.

View larger version (17K): [in this window] [in a new window]   FIG. 12. 207Pb/204Pb vs. 206Pb/204Pb plot, showing lead isotope compositions of galena from Lisheen (this study) with error bars, compared to deposit array (encompasses average values for all Irish deposits and prospects) and average Silvermines value (see Table 3). Lisheen data fall close to the Silvermines average, implying a common lead source from local lower Paleozoic rocks. Pb growth curve of Stacey and Kramers (1975) is marked in 250 Ma increments for reference.

	Discussion

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

Since there is good evidence that mineralization is localized by the Lisheen fault array, the timing of fault movement provides some constraints on the timing of mineralization. We consider that it is highly unlikely for extensive fluid flow to exploit these potential fluid conduits except during periods of active tectonism, since any fault-related permeability would be rapidly sealed by hydrothermal precipitates in times of quiescence. Sediment thickness variations imply that fault-controlled sedimentation in the area initiated immediately prior to Waulsortian deposition, significantly earlier than previously thought (Carboni et al., 2003; Fusciardi et al., 2003). Thus, mineralization could have begun as early as the Courceyan (cf. Lee and Wilkinson, 2002). The frequent observation of cataclastically deformed preore sulfides in the Main and Derryville zones overprinted by main ore-stage mineralization (e.g., Fig. 6f) indicates that ore formation did not entirely postdate fault movements, as suggested by Sevastopulo and Redmond (1999), Hitzman et al. (2002), and Carboni et al. (2003). Synsedimentary faulting continued during deposition of the Crosspatrick Formation, suggesting that mineralization could have persisted into, or initiated in, the Chadian (Fusciardi et al., 2003).

The fact that ore-stage sulfides at Lisheen replace early marine cements and regional dolomite indicates that the main phase of mineralization must have occurred subsea-floor during or subsequent to early diagenesis of the Waulsortian Limestone. However, it is probable that ore formation occurred close in time and space to the oxic and/or suboxic transition in the connate porewaters (Wilkinson et al., 2003). Furthermore, the sulfur isotope data indicate that this must have occurred at a depth where the ore-forming system remained open to seawater sulfate. These features, coupled with the evidence for near-sea floor and exhalative mineralization in other Irish-type deposits (Wilkinson et al., 2003), suggest that mineralization probably occurred within a few tens of meters, and at most a few hundred meters below the sea floor, much sooner during burial than suggested by Hitzman et al. (2002).

Source of lead
The limited new lead isotope data from Lisheen show no obvious correlation between ore stage or galena texture and lead isotope composition and there is no indication of a covariance between lead isotopes and ³⁴S values in galenas (Table 3), as has been observed in some Mississippi Valley-type deposits (Sverjensky, 1981). This lead isotope homogeneity is consistent with results from the other Irish deposits and suggests a well-homogenized crustal reservoir. The data are comparable with those reported for Lisheen by Hitzman et al. (1992) and are similar to results from Silvermines, 35 km to the west (O’Keeffe, 1986; Fig. 12). The similarity between Lisheen and Silvermines implies a common lead source; the match between deposit galenas and estimated composition of the lower Paleozoic sequence in the southwest Midlands at the time of mineralization (Dixon et al., 1990) implicates Silurian graywackes, siltstones, and grits of the Hollyford Formation. The lead isotope data therefore support fluid-flow models involving deep basement circulation and are inconsistent with fluid flow through and derivation of lead from the Old Red Sandstone, as summarized by Everett et al. (2003).

Distribution and source of other metals
Petrographic and mineral chemical studies show that Cu-, As-, Co-, and Ni-bearing phases are abundant close to the major faults and in sub-Waulsortian mineralization, particularly within the Lisduff Oolite (also see Fusciardi et al., 2003). Similarly, these elements are enriched (and covary) in other main ore-stage phases (sphalerite, pyrite, chalcopyrite) in proximity to the major structures. The co-occurrence of these elements in a range of phases, both as major and minor constituents, suggests that they were enriched in the hydrothermal fluids active during the main ore stage. The clear spatial association with major east-west faults implies that these structures were important conduits for fluids transporting these elements from depth. Intense bleaching of the Old Red Sandstone is observed close to the main fault zones at Lisheen (Mallon, 1997; Everett, 1999; Hitzman et al., 2002; Everett et al., 2003), and results of acid leaching experiments on unaltered Old Red Sandstone samples show that Ni and Co are readily liberated (C. Everett, pers. commun., 2000). Therefore, it is suggested that Cu, As, Co, and Ni were stripped during early, localized alteration of the sandstone footwall around fault conduits and redeposited in ore-stage minerals at higher levels by buoyant hydrothermal fluids.

Trace element substitutions in sphalerite appear to have been controlled by different processes. Fe is generally enriched in vein sphalerite from close to faults, particularly in the Derryville and Bog zones and in the sub-Waulsortian stratigraphy. There is no obvious correlation with fluid inclusion homogenization temperatures (Eyre, 1998), suggesting that temperature is not a primary control on Fe content. Given the probability of high sulfur fugacity in the upper parts of the system during ore formation (see below), it is suggested that the Fe content of sphalerite is controlled by sulfur fugacity in an inverse relationship (cf. Czamanske, 1974).

Cd concentrations in sphalerite are generally decoupled from Fe and show no obvious systematic pattern in space or time. A weak correlation with sulfur isotope composition (Fig. 13) suggests that Cd may be cotransported with isotopically heavy sulfur (derived from depth; see below) and is favorably partitioned into the first sphalerite precipitated in fluid conduits. There is no evidence for liberation of Cd during alteration of the Old Red Sandstone, therefore it is suggested that Cd is sourced, with Pb, from the lower Paleozoic basement.

View larger version (8K): [in this window] [in a new window]   FIG. 13. Range of cadmium concentrations in sphalerite samples (determined by microprobe analysis) plotted against sulfur isotope composition. A weak positive correlation exists, suggesting that cadmium is associated with the hydrothermal sulfur component, both being derived from the lower Paleozoic basement.

The very low ³⁴S values observed in the early pyrite represent an extreme isotope fractionation that can only be explained by the action of sulfate-reducing bacteria in a system open to sulfate. The data represent a fractionation of around 60 per mil from contemporaneous seawater sulfate, the only viable large sulfate reservoir. Similar low ³⁴S values in pyrite have been noted at Silvermines (Boyce et al., 1983; Boyce, 1990) and Navan (Anderson et al., 1998; Blakeman et al., 2002). Typical fractionations in natural systems appear to be around 30 to 40 per mil (Canfield, 2001). However, extreme fractionations, similar to those shown by the early pyrite, are observed where low rates of bacterial sulfate reduction are combined with oxidative cycles (e.g., Canfield and Thamdrup, 1994). At Navan, it has been suggested that near-sea floor bacterial sulfate reduction resulted in the formation of pyrite with low ³⁴S during more oxidative periods at times of hydrothermal quiescence (Blakeman et al., 2002). This is consistent with the close paragenetic position of early pyrite and the silica-hematite alteration (inferred to have formed in the presence of dissolved free O₂; Cruise et al., 1999; Cruise, 2000) that is variably developed in most of the Irish deposits, including Lisheen.

Main ore-stage sulfides at Lisheen typically have ³⁴S values 22 to 38 per mil lower than coexisting sulfate. This represents a fractionation typical of bacterial sulfate reduction in natural systems open to sulfate (e.g., Goldhaber and Kaplan, 1975) and supports a bacteriogenic origin for the majority of ore-stage sulfur. A similar conclusion has been reached for all the major Irish deposits (Coomer and Robinson, 1976; Boast et al., 1981; Boyce et al., 1983; Anderson et al., 1998; Fallick et al., 2001). The predominance of bacteriogenic sulfide with low ³⁴S in Ireland is in marked contrast to the Gays River and Jubilee deposits of Nova Scotia (Sangster et al., 1998), which otherwise bear some resemblance to the Irish deposits. This characteristic sets the Irish deposits apart from Mississippi Valley-type deposits such as Pine Point (Rhodes et al., 1984) and in this respect they have more in common with the large massive sulfide deposits of the Iberian Pyrite Belt (Velasco et al., 1998; Sáez et al., 1999). This feature implies that during both the preore and main-ore stages bacterial sulfate reduction occurred in an open system; this is only likely to have been possible at, or close to, the sediment-seawater interface. However, the temperature in the immediate environment of ore deposition (ca. 140°–220°C) is likely to have been too high for sulfate-reducing bacteria, which are only known to metabolize up to 110°C (Jørgensen et al., 1999; Stetter, 1999). Therefore, bacteriogenic sulfur is most likely to have been transported to the site of ore deposition from near-sea floor sediments above or on the fringes of the deposit.

In general, there is no systematic difference in ³⁴S values between galena and sphalerite at Lisheen. Individual sphalerite-galena pairs in apparent textural equilibrium do not show fractionations consistent with isotopic equilibrium at temperatures between 240° and 100°C, the range inferred for the Irish deposits (Wilkinson et al., 2003). Similarly, all pyrite ³⁴S values are lower than those of coexisting galena or sphalerite in all of the ore stages in contrast to the higher values that would be expected for isotopic equilibrium (Sakai, 1968). These results indicate that isotopic equilibrium was not attained during any of the ore stages at Lisheen.

Although bacterially reduced sulfate is considered to be the dominant source of ore-stage sulfur at Lisheen, variations in sulfur isotope compositions indicate that a second sulfur source with higher ³⁴S was involved. The sulfur isotope compositions of sphalerite and galena show trends toward higher values with depth, irrespective of textural type or ore stage (Fig. 11a-b). This is best explained by an increasing contribution, deeper in the system, from a sulfur source characterized by ³⁴S values above 0 per mil. This source appears to dominate the late ore-stage and sub-Waulsortian sulfides at Lisheen (values of 0–12) with the highest ³⁴S values observed in more coarsely crystalline and/or euhedral sphalerite and galena (Fig. 11a-b). Such sulfur isotope compositions form a distinct grouping that has been recognized in most of the Irish deposits (Caulfield et al., 1986; Samson and Russell, 1987; Anderson et al., 1998). It has been suggested that this represents reduced sulfur, derived from diagenetic sulfides in the lower Paleozoic sequence and transported from depth by the principal ore fluid (Anderson et al., 1989; Boyce et al., 1994). Recent coupled sulfur isotope and fluid inclusion analyses on sphalerite have confirmed this association (Eyre, 1998; Everett et al., 1999b).

The trend toward higher ³⁴S values with depth in the main ore-stage sulfides, particularly galena, suggests that there was an important contribution from this source during the main stage of economic mineralization. It is noteworthy that the mean ³⁴S value for ore-stage sulfides is higher than at Silvermines (e.g., Hitzman and Beaty, 1996), consistent with a greater input of hydrothermal sulfur at Lisheen. In addition, ³⁴S values from the Main zone are generally higher than those from the Derryville zone, implying a greater contribution from the hydrothermal source, perhaps as a consequence of longer lived hydrothermal flow into the larger orebody. The greater homogeneity of sulfur isotope compositions in the Main zone could also be a product of an extended period of fluid flow and associated recrystallization.

Spatial variations in sulfur isotope compositions of main ore-stage sphalerite and galena (Fig. 14) show that higher ³⁴S values (>–10 per mil) are located in the footwall of the Killoran fault in the Main zone, in the east Main zone, and in the southwestern part of Derryville zone, close to the Derryville fault. The distribution of high ³⁴S values (>0) in late ore-stage sphalerite and galena follows a similar pattern (Fig. 14), suggesting that these zones were the foci of the principal ore fluid throughout the ore-forming event. These areas coincide with high Pb, Zn, and Ni concentrations (Hitzman et al., 2002; Fusciardi et al., 2003) and Pb-rich ores have been shown to correspond with feeder zones in other Irish deposits (Taylor, 1984; Ashton et al., 1992; Lowther et al., 2003).

View larger version (42K): [in this window] [in a new window]   FIG. 14. Spatial variations in sulfur isotope composition of sphalerite and galena from the main and late ore stages at Lisheen. Average values for multiple analyses from each drill hole sampled are shown. Main ore-stage 34S values are subdivided into those dominated by bacteriogenic sulfur (plain numbers) and those with an inferred hydrothermal sulfur component (34S > –7), shown in gray boxes. Late to postore-stage values are shown in black boxes. Higher values for both main- and late ore-stage sulfides are observed near the main east-west–trending faults and/or northwest-trending structures, suggesting that these are the main conduits for fluids transporting hydrothermal sulfur from depth. Two principal subvertical conduits for hydrothermal fluid ingress into the ore zones are suggested, one in the east Main zone and one in the west Derryville zone.

The generally low ³⁴S values of pyrite and lack of variation with depth (with the exception of two sub-Waulsortian vein pyrite samples) are significant (Fig. 11c). Given that much of the pyrite is paragenetically early, it may be that the principal ore fluid was only a minor contributor to the system at this stage. We suggest that low-temperature brines from a shallow source (see below) were largely responsible for early iron-rich mineralization (possibly including the silica ironstones) that was formed under more oxidizing conditions than the main ore-stage sulfides.

Evidence for fluid mixing
The presence of dendritic, skeletal, layered geopetal, and colloform textures are commonly interpreted to represent sulfide deposition in open space and/or by rapid precipitation of sulfides from supersaturated solution (Roedder, 1968; Honjo and Sawada, 1982). The observation of such textures in the main ore stage at Lisheen, together with the lack of correlation between trace element concentrations in colloform sphalerite and sulfur isotope disequilibrium, are suggestive of rapid precipitation at high degrees of supersaturation. The evidence from the ³⁴S data for two main sulfur sources implies that mixing between two fluids was the likely cause of sulfide supersaturation. Fluid mixing is also required to account for barite precipitation since significant concentrations of both sulfate and barium cannot be transported by the same fluid. This conclusion is supported by fluid inclusion data that suggest mixing between the principal ore fluid and a low-temperature brine occurred during the main- to late ore-stage at Lisheen (Eyre et al., 1996; Eyre, 1998). Fluid inclusion halogen data (Everett et al., 1999, 2001; Gleeson et al., 1999; Everett and Wilkinson, 2000; Banks et al., 2002) suggest that this brine is likely to have been of evaporitic origin and may have acquired H₂S while migrating through the carbonate sequence, perhaps analogous to brines reported from Cenozoic shelf carbonates on the Australian Bight (Swart et al., 2000).

The relatively uniform ³⁴S values that characterize colloform sphalerite can be accounted for if bacteriogenic sulfide dominated the total sulfur budget during its precipitation. This would have been the case for the vast majority of fluid mixtures if, as is assumed, the brine contained concentrations of (bacteriogenic) H₂S at least an order of magnitude higher than the principal ore fluid. Massive, fine-grained galena is also isotopically homogeneous and could be explained in the same way, although isotopic homogenization via recrystallization is an alternative explanation. Other types of sphalerite show much more variability (Fig. 11a) and this, together with the occurrence of intimately intergrown sulfides with widely varying compositions in some samples, is consistent with deposition from fluid mixtures dominated by the principal ore fluid. Late ore-stage euhedral sphalerite probably crystallized at low degrees of supersaturation in open vugs. The high ³⁴S values that characterize these samples suggest that only the principal ore fluid was infiltrating the system at this time, consistent with fluid inclusion data (Eyre, 1998). Thus, there appears to have been a temporal evolution from a system initially dominated by the bacteriogenic sulfur-transporting fluid (metal limited), through a main stage of fluid mixing and ore formation, to a system dominated by the deep-source hydrothermal fluid (sulfur limited). The cessation of mixing due to a cut-off of the brine supply is therefore postulated as the cause of the termination of the main ore-forming event.

Postore-stage sulfides are most likely the result of remobilization of ore-stage sulfur during the pink dolomite precipitation event. Fluid inclusion data show that the fluids responsible were low-temperature Na-Ca-Cl brines (Eyre, 1998) that may have been mobilized during the onset of Variscan compression (Everett et al., 1999a).

View larger version (68K): [in this window] [in a new window]   FIG. 15. Model for mineralization at Lisheen. (a). Stage 1: Preore dolomitization. Early diagenetic regional dolomitization of the Waulsortian Limestone driven by brine reflux from the shelf area bordering the Leinster massif predated or may have been partly synchronous with brecciation of the Waulsortian Limestone. Lisheen is located at the northwestern fringe of a zone of pervasive dolomitization, probably close to a shelf basin break controlled by propagation of Caledonian basement structures up into the overlying cover in the late Courceyan. (b). Stage 2: Fluid flow into the ore-forming environment. The high intergranular matrix porosity developed as a result of synsedimentary and/or the onset of hydrothermal brecciation was a critical ground preparation, producing a permeable lithology into which later mineralizing fluids were focused. Brecciation coupled with sufficient development of fault-related permeability resulted in connectivity between the two main fluid reservoirs (deep hydrothermal and shallow H2S-rich brine). This allowed the two fluids to penetrate into, and mix within, the breccia units. Alteration and stripping of Cu, As, Co, and Ni from the Old Red Sandstone adjacent to the main east-west–trending fault array was likely the result of focusing and upward flow of relatively reduced lower Paleozoic-equilibrated metal-bearing fluids within fault-related damage zones. Flow into the basal Waulsortian breccias was via the main Lisheen fault array and northwest-trending faults in the hanging wall. Downward flow of low-temperature saline brines occurred by migration down the upper parts of the Lisheen fault array or laterally along stratigraphy, within the dolomitized Waulsortian, the Lisduff Oolite, and also possibly along the regional dolomite front. Brine flow could have been driven by local convection induced by thermal anomalies associated with the upwelling, high-temperature fluids or by simple density contrast. (c). Stage 3: Fluid mixing. The onset of fluid mixing within the breccias led to rapid precipitation of sulfides in isotopic disequilibrium in any available pore space. Acid generated by sulfide deposition enabled dolomite dissolution, thereby creating additional porosity. The volume reduction associated with dolomite replacement by sulfide could have caused as much as a 25 percent increase in porosity, enabling further mixing and ore deposition. This, together with the elevated initial porosity and nonstoichiometry of the matrix dolomite, may explain why the lithology was such a favorable host rock to ore. Abundant evidence for multiple stages of sulfide deposition, reworking, and brecciation suggests a protracted evolution of the system in tandem with active faulting. Zone-refining processes may have led to some of the metal zonation and textural complexity observed. White matrix breccia may have developed above the ore zones due to limited downward collapse caused by the volume loss associated with sulfide replacement. (d). Stage 4: Hydrothermal sealing and progressive burial. Sulfur isotope data suggest that mineralization terminated due to exhaustion of the main H2S source and brine reservoir or blocking of brine infiltration pathways, possibly by deposition of supra-Waulsortian argillaceous sediments. The late ore stage involved choking of residual porosity by precipitation of calcite, dolomite, and sulfides from the principal ore fluid alone. Sulfide deposition at this time was probably driven by simple cooling. The late-stage calcite (C4) and dolomite (D4) veins and breccias may reflect overpressuring of the principal ore fluid in the main-flow conduits caused by progressive burial and hydrothermal sealing. A late overprint by low-temperature, high-salinity fluids resulted in remobilization of preore or main ore-stage sulfides and precipitation of D5 pink dolomite. It is suggested that these fluids represent evolved basin formation waters, mobilized as a result of the onset of Variscan compression to the south of Ireland in the Mid- to Late Carboniferous.

	Model for Mineralization

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

	Conclusions

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 
Lisheen is a strata-bound zinc-lead deposit formed by replacement of hydrothermally dolomitized, broadly stratiform breccia bodies located near the base of the Mississippian Waulsortian Limestone. Multiple stages of sulfide deposition occurred below the sea floor, with hydrothermal dolomitization and early Fe mineralization dominated by low-temperature evaporitic brines transporting bacteriogenic H₂S. The main ore stage involved rapid precipitation of sulfides driven by mixing between these brines and higher temperature, metal-bearing (Zn, Pb, Fe, Cd) fluids derived from a basement-equilibrated fluid reservoir. Some elements (Cu, As, Co, Ni) may have been released during alteration of the footwall red sandstones. Fluid flow was focused both within damage zones associated with the main Lisheen extensional fault array and northwest-trending fractures in its hanging wall. Ore formation ceased due to exhaustion of the brine reservoir or blocking of the brine flow path. Late ore-stage sulfides precipitated from higher temperature hydrothermal fluids in hydraulic fractures and breccias as the system became sealed. This ore-forming process is consistent with geologic and geochemical evidence from the other economic deposits of the Irish ore field.

	APPENDIX

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 

	Acknowledgments

December 31, 2002; September 16, 2004

	Footnotes

 
^* Present address: TLC Ventures Corporation, Suite 285–200 Granville Street, Vancouver, British Columbia, Canada V6C 1S4.

December 31, 2002; September 16, 2004

	References

Top Abstract Introduction Geologic Setting Geology of the Lisheen... Methodology Ore Mineralogy and Paragenesis Sulfur and Lead Isotopes Discussion Model for Mineralization Conclusions APPENDIX References

 

Anderson, I.K., Andrew, C.J., Ashton, J.H., Boyce, A.J., Caulfield, J.B.D., Fallick, A.E., and Russell, M.J., 1989, A sulphur isotopic reconnaissance study of mineralization in the lower Palaeozoic strata of Ireland and the Southern Uplands of Scotland: Implications for Zn-Pb-Ba mineralization in the Lower Carboniferous of Ireland: Journal of the Geological Society [London] , v. 146, p.715 –720.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Anderson, I.K., Ashton, J.H., Boyce, A.J., Fallick, A.E., and Russell, M.J.,1998 , Ore depositional processes in the Navan Zn + Pb deposit, Ireland: Economic Geology, v. 93, p. 535–563.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Andrew, C.J., 1993, Mineralization in the Irish Midlands, in Pattrick, R.A.D., and Polya, D.A., eds., Mineralization in the British Isles: London, Chapman and Hall, p. 208–269.

Ashton, J.H., Black, A., Geraghty, J., Holdstock, M., and Hyland, E., 1992, The geological setting and metal distribution patterns of the Zn-Pb-Fe mineralization in the Navan Boulder Conglomerate, in Bowden, A.A., Earls, G., O’Connor, P.G., and Pyne, J.F., eds., The Irish minerals industry 1980–1990:Dublin, Irish Association for Economic Geology , p. 171–210.

Blakeman, R., Ashton, J.H., Boyce, A.J., Fallick, A.E., and Russell, M.J.,2002 , Timing of interplay between hydrothermal and surface fluids in the Navan Zn + Pb orebody, Ireland: Evidence from metal distribution trends, mineral textures, and ³⁴S analyses: Economic Geology, v.97 , p. 73–91.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Boast, A.M., Coleman, M.L., and Halls, C., 1981, Textural and stable isotope evidence for the genesis of the Tynagh base metal deposit, Ireland: Economic Geology, v. 76, p. 27–55.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Boyce, A.J., 1990, Sedimentation, exhalation and sulphur isotope geochemistry of the Silvermines Zn + Pb + Ba deposits, County Tipperary, Ireland: Unpublished Ph.D thesis, Glasgow, Scotland, University of Strathclyde, 354 p.

Boyce, A.J., Anderton, R., and Russell, M.J., 1983, Rapid subsidence and Early Carboniferous mineralisation in Ireland: Transactions of the Institution of Mining and Metallurgy, v. 92, p. 55–66.

Boyce, A.J., Fallick, A.E., Fetcher, T.J., Russell, M.J., and Ashton, J.H.,1994 , Detailed sulphur isotope studies of lower Paleozoic-hosted pyrite below the giant Navan Zn + Pb mine, Ireland: Evidence of mass transport of crustal S to a sediment-hosted deposit: Mineralogical Magazine, v. 58A, p. 109–110.

Canfield, D.E., 2001, Isotope fractionation by natural populations of sulfate-reducing bacteria: Geochimica et Cosmochimica Acta, v. 65, p. 1117–1124.[CrossRef][Web of Science][GeoRef]

Canfield, D.E., and Thamdrup, B., 1994, The production of ³⁴S-depleted sulfide during bacterial disproportionation of elemental sulfur: Science, v.266 , p. 1973–1975.[Abstract/Free Full Text][CrossRef][Web of Science][Medline]

Carboni, V., Walsh, J.J., Stewart, D.R.A., and Güven, J.F., 2003, Timing and geometry of normal faults and associated structures at the Lisheen Zn/Pb deposit, Ireland—investigating their role in the transport and trapping of:Society for Geology Applied to Mineral Deposits Meeting, 7^th biennial, Athens, Greece, Proceedings , p. 665–668.

Caulfield, J.B.D., LeHuray, A.P., and Rye, D.M., 1986, A review of lead and sulphur isotope investigations of Irish sediment-hosted base metal deposits, with new data from Keel, Ballinalack, Moyvoughly and Tatestown deposits, in Andrew, C.J., Crowe, R.W.A., Finlay, S., Pennell, W.M., and Pyne, J., eds., Geology and genesis of mineral deposits in Ireland: Dublin, Irish Association for Economic Geology, p. 591–616.

Claypool, C.E., Holser, W.T., Sakai, I.R., and Zak, I., 1980, The age curves for sulfur and oxygen isotopes in marine sulfate and their mutual interpretation: Chemical Geology, v. 28, p. 199–260.[CrossRef][Web of Science][GeoRef]

Coleman, M.L., and Moore, M.P., 1978, Direct reduction of sulphates to sulphur dioxide for isotopic analysis: Analytical Chemistry, v. 28, p. 199–260.

Coomer, P.G., and Robinson, B.W., 1976, Sulphur and sulphate-oxygen isotopes and the origin of the Silvermines deposits, Ireland: Mineralium Deposita, v. 11, p. 155–169.[Web of Science][GeoRef]

Craig, H., 1957, Isotopic standards for carbon and oxygen and correction factors for mass-spectrometric analysis of carbon dioxide: Geochimica et Cosmochimica Acta, v. 12, p. 133–149.[CrossRef][Web of Science][GeoRef]

Cruise, M.D., 2000, Iron oxide and associated base metal mineralization in the Central Midlands basin, Ireland: Unpublished Ph.D thesis, Dublin, Trinity College, 651 p.

Cruise, M.D., Boyce, A.J., and Fallick, A.E., 1999, Iron oxide alteration associated with the carbonate-hosted Tynagh and Crinkill base-metal deposits, Ireland: Evidence of the involvement of dissolved atmospheric oxygen, in Stanley, C.J. et al., eds., Mineral deposits: Processes to processing:Rotterdam, Balkema , v. 2, p. 833–836.

Czamanske, G.K., 1974, The FeS content of sphalerite along the chalcopyrite-pyrite-bornite sulfur fugacity buffer: Economic Geology, v. 69, p.1328 –1334.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Dixon, P.R., LeHuray, A.P., and Rye, D.M., 1990, Basement geology and tectonic evolution of Ireland as deduced from Pb isotopes: Journal of the Geological Society [London] , v. 147, p. 121–132.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Doyle, E., Bowden, A.A., Jones, G.V., and Stanley, G.A., 1992, The geology of the Galmoy deposits, in Bowden, A.A., Earls, G., O’Connor, P.G., and Pyne, J.F., eds., The Irish minerals industry 1980–1990: Dublin, Irish Association for Economic Geology, p. 211–225.

Earls, G., 1994, The Lisheen Zn-Pb deposit: Mining Magazine, July 1994, p. 6–8.

Elmes, J.D., Fusciardi, L.P., and Guven, J.F., 2000, Geology of the Lisheen zinc/lead deposit: first impressions, in Europe’s major base metal deposits [abs.]: Dublin, Irish Association for Economic Geology, Abstracts Volume, 3 p.

Everett, C.E., 1999, Tracing ancient fluid flow pathways: A study of the Lower Carboniferous base metal ore field in Ireland: Unpublished Ph.D thesis, New Haven, CT, Yale University, 354 p.

Everett, C.E., and Wilkinson, J.J., 2000, What makes an orebody? A comparison of fluid inclusion and sulfur isotope data from prospects and deposits in the Irish Zn-Pb ore field [abs]: Geological Society of America Abstracts with Programs, v. 32, no. 7, p. A-282.

Everett C.E., Wilkinson, J.J., and Rye, D.M., 1999a, Fracture-controlled fluid flow in the lower Palaeozoic basement rocks of Ireland: Implications for the genesis of Irish-type Zn-Pb deposits: Geological Society of London Special Publications, v. 155, p. 247–276.

Everett, C.E., Wilkinson, J.J., Boyce, A.J., Ellam, R.M., Fallick, A.E., and Gleeson, S.A., 1999b, The genesis of Irish-type Zn-Pb deposits: Characterisation and origin of the principal ore fluid, in Stanley, C.J. et al., eds., Mineral deposits: Processes to processing: Rotterdam, Balkema, v. 2, p. 845–848.

Everett, C.E., Wilkinson, J.J., Boyce, A.J., and Gleeson, S.A., 2001, The role of bittern brines and fluid mixing in the genesis of the Navan Zn-Pb deposit, Ireland [abs]: Geological Society of America Abstracts with Programs, v. 33, no. 7.

Everett, C.E., Rye, D.M., and Ellam, R.M., 2003, Source or sink? An assessment of the role of the Old Red Sandstone in the genesis of the Irish Zn-Pb deposits: Economic Geology, v. 98, p. 31–50.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Eyre, S.L., 1998, Geochemistry of dolomitization and Zn-Pb mineralization in the Rathdowney trend, Ireland: Unpublished Ph.D thesis, University of London,414 p.

Eyre, S.L., Wilkinson, J.J., Stanley, C.J., and Boyce, A.J., 1996, Geochemistry of dolomitization and zinc-lead mineralization in the Rathdowney trend, Ireland [abs.]: Geological Society of America Abstracts with Programs, v.28 , p. A210–A211.

Fallick, A.E., Ashton, J.H., Boyce, A.J., Ellam, R.M., and Russell, M.J.,2001 , Bacteria were responsible for the magnitude of the world-class hydrothermal base-metal orebody at Navan, Ireland: Economic Geology, v. 96, p.883 –888.

Fusciardi, L.P., Guven, J.F., Stewart, D.R.A., Carboni, V., and Walshe, J.J.,2003 , The geology and genesis of the Lisheen Zn-Pb deposit, Co. Tipperary, Ireland, in Kelly, J.G., Andrew, C.J., Ashton, J.H., Boland, M.B., Earls, G., Fusciardi, L., and Stanley, G., eds., Europe’s major base metal deposits:Dublin, Irish Association for Economic Geology , p. 455–481.

Gleeson, S.A., Banks, D.A., Everett, C.E., Wilkinson, J.J., Samson I. M., and Boyce, A.J., 1999, Origin of mineralising fluids in Irish type deposits: Constraints from halogens, in Stanley, C.J. et al., eds., Mineral deposits: Processes to processing: Rotterdam, Balkema, v. 2, p. 857–860.

Goldhaber, M.B., and Kaplan, I.R., 1975, Controls and consequences of sulfate reduction in recent marine sediments: Soil Science, v. 119, p. 42–55.[Web of Science][GeoRef]

Graham, R.A.F., 1970, The Mogul base metal deposits, Co. Tipperary, Ireland:Unpublished Ph.D. thesis, London, ON, University of Western Ontario , 235 p.

Gregg, J.M., Shelton, K.L., Johnson, A.W., Somerville, I.D., and Wright, W.R., 2001, Dolomitization of the Waulsortian Limestone (Lower Carboniferous) in the Irish Midlands: Sedimentology, v. 48, p. 745–766.[CrossRef][Web of Science][GeoRef]

Greig, J.A., Baadsgard, H., Cumming, G.L., Folinsbee, R.E., Krouse, H.R., Ohmoto, H., Sasaki, A., and Smejkal, V., 1971, Lead and sulfur isotopes of the Irish base metal mines in Carboniferous carbonate host rocks: Tokyo, Society of the Mining Geologists of Japan Special Issue 2, p. 84–92.

Hitzman, M.W., 1995, Mineralization in the Irish Zn-Pb-(Ba-Ag) orefield:Society of Economic Geologists Guidebook Series , v. 21, p. 25–61.

Hitzman, M.W., and Beaty, D.W., 1996, The Irish Zn-Pb-(Ba) orefield: Society of Economic Geologists Special Publication, v. 4, p. 112–143.

Hitzman, M.W., and Large, D.E., 1986, A review and classification of the Irish carbonate-hosted base metal deposits, in Andrew, C.J., Crowe, R.W.A., Finlay, S., Pennell, W.M., and Pyne, J., eds., Geology and genesis of mineral deposits in Ireland: Dublin, Irish Association for Economic Geology, p.217 –238.

Hitzman, M.W., O’Connor, P.G., Shearley, E., Schaffalitzky, C., Beatty, D.W., Allan, J.R., and Thompson, T., 1992, Discovery and geology of the Lisheen Zn-Pb-Ag prospect, Rathdowney trend, Ireland, in Bowden, A.A., Earls, G., O’Connor, P.G., and Pyne, J.F., eds., The Irish minerals industry 1980–1990:Dublin, Irish Association for Economic Geology , p. 227–246.

Hitzman, M.W., Allan, J.R., and Beaty, D.W., 1998, Regional dolomitization of the Waulsortian Limestone in southeastern Ireland: Evidence of large-scale fluid flow driven by the Hercynian orogeny: Geology, v. 26, p. 547–550.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Hitzman, M.W., Redmond, P.B., and Beaty, D.W., 2002, The carbonate-hosted Lisheen Zn-Pb-Ag deposit, County Tipperary, Ireland: Economic Geology, v. 97, p.1627 –1655.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Honjo, H., and Sawada, Y., 1982, Quantitative measurements on the morphology of NH₄Br dendritic crystal growth in a capillary: Journal of Crystal Growth, v. 58, p. 297–303.[CrossRef]

Jørgensen, B.B., Isaksen, M.F., and Jannasch, H.W., 1999, Bacterial sulfate reduction above 100°C in deep-sea hydrothermal vent sediments: Science, v. 258, p. 1756–1757.

Lee, M.J., 2002, Origin and Zn-Pb mineralization of dolomite breccias in the Irish Midlands: Unpublished Ph.D thesis, University of London, 256 p.

Lee, M.J., and Wilkinson, J.J., 2002, Cementation, hydrothermal alteration, and Zn-Pb mineralization of carbonate breccias in the Irish Midlands: Textural evidence from the Cooleen zone, near Silvermines, County Tipperary: Economic Geology, v. 97, p. 653–662.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Lee, M.J., Wilkinson, J.J., and Earls, G., 2001, Textural and cathodoluminescence evidence for the origin of black dolomite matrix breccias in the Irish Zn-Pb ore field, in Piestrzñski, A. et al., eds., Mineral deposits at the beginning of the 21st century: Lisse, Swets and Zeitlinger, p.161 –164.

Lowther, J.M., Balding, A.B., Dunphy, S., and McEvoy, F.M., 1999, The Galmoy mine: Some geological aspects of development from 1995 to 1999, in Stanley, C.J. et al., eds., Mineral deposits: Processes to processing: Rotterdam, Balkema, v. 2, p. 881–884.

Lowther, J.M., Balding, A.B., McEvoy, F.M., Dunphy, S, MacEoin, P.M., and Bowden, A.A., 2003, The Galmoy zinc-lead orebodies: Structure and metal distribution—clues to the genesis of the deposit, in Kelly, J.G., Andrew, C.J., Ashton, J.H., Boland, M.B., Earls, G., Fusciardi, L., and Stanley, G., eds., Europe’s major base metal deposits: Dublin, Irish Association for Economic Geology, p. 437–454.

Mallon, A.J., 1997, Petrological and mineralogical characteristics of the Old Red Sandstone facies rocks beneath base metal deposits as a guide to the setting of mineralisation in the Irish Midlands: Unpublished Ph.D. thesis, Ireland, University College Cork, 636 p.

O’Keeffe, W.G., 1986, Age and postulated source rocks for mineralization in central Ireland as indicated by lead isotopes, in Andrew, C.J., Crowe, R.W.A., Finlay, S., Pennell, W.M., and Pyne, J., eds., Geology and genesis of mineral deposits in Ireland: Dublin, Irish Association for Economic Geology, p.617 –624.

Philcox, M.E., 1983, Lower Carboniferous stratigraphy of the Irish Midlands:Dublin, Irish Association for Economic Geology , 89 p.

Phillips, W.E.A., and Sevastopulo, G.D., 1986, The stratigraphic and structural setting of Irish mineral deposits, in Andrew, C.J., Crowe, R.W.A., Finlay, S., Pennell, W.M., and Pyne, J., eds., Geology and genesis of mineral deposits in Ireland: Dublin, Irish Association for Economic Geology, p.1 –30.

Reed, C.P., and Wallace, M.W., 2003, Cementation, hydrothermal alteration, and Zn-Pb mineralization of carbonate breccias in the Irish Midlands—a discussion: Economic Geology, v. 98, 191–193.

Rhoden, N.H., 1960, Mineralogy of the Silvermines district, Co. Tipperary, Eire: Mineralogical Magazine, v. 32, p. 128–139.

Rhodes, D., Lantos, E.A., Lantos, J.A., Webb, R.J., and Owens, D.C., 1984, Pine Point orebodies and their relationship to the stratigraphy, structure, dolomitization, and karstification of the Middle Devonian barrier complex:Economic Geology , v. 79, p. 991–1055.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Robinson, B.W., and Kusakabe, M., 1975, Quantitative preparation of sulfur dioxide, for ³⁴S/³²S analyses, from sulfides by combustion with cuprous oxide: Analytical Chemistry, v. 47, p. 1179–1181.[CrossRef]

Roedder, E., 1968, The noncolloidal origin of "colloform" textures in sphalerite ores: Economic Geology, v. 63, p. 451–471.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Sáez, R., Pascual, E., Toscano, M., and Almodóvar, G.R., 1999, The Iberian type of volcano-sedimentary massive sulphide deposits: Mineralium Deposita, v.34 , p. 549–570.[CrossRef][Web of Science][GeoRef]

Sakai, H., 1968, Isotopic properties of sulfur compounds in hydrothermal processes: Geochemical Journal (Japan) , v. 2, p. 29–49.

Samson, I.M., and Russell, M.J., 1987, Genesis of the Silvermines zinc-lead-barite deposit Ireland: Fluid inclusion and stable isotope evidence:Economic Geology , v. 82, p. 371–394.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Sangster, D.F., Savard, M.M., and Kontak, D.J., 1998, A genetic model for mineralization of lower Windsor (Visean) carbonate rocks of Nova Scotia, Canada:Economic Geology , v. 93, p. 932–952.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Sevastopulo, G.D., and Redmond, P., 1999, Age of mineralization of carbonate-hosted, base metal deposits in the Rathdowney trend, Ireland:Geological Society of London Special Publication , v. 155, p. 303–311.

Shearley, E., Redmond, P., Goodman, R., and King, M., 1995, A guide to the Lisheen Zn-Pb deposit: Society of Economic Geologists Guidebook Series, v. 21, p. 123–137.

Shearley, E., Redmond, P., King, M., and Goodman, R., 1996, Geological controls on mineralization and dolomitization of the Lisheen Zn-Pb-Ag deposit, Co. Tipperary, Ireland: Geological Society of London Special Publications, v.107 , p. 23–33.

Sheridan, D.J.R., 1977, The hydrocarbons and mineralization proved in the Carboniferous strata of deep boreholes in Ireland, in Garrard, P., ed., Proceedings of the forum on oil and ore in sediments: London, Department of Geology, Imperial College, p. 113–146.

Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotopic evolution by a two-stage model: Earth and Planetary Science Letters, v.26 , p. 207–221.[CrossRef][Web of Science][GeoRef]

Stetter, K.O., 1999, Extremophiles and their adaptation to hot environments:FEBS (Federation of European Biochemical Societies) Letters , v. 452, p. 22–25.

Sverjensky, D.A., 1981, The origin of a Mississippi Valley-type deposit in the Viburnum Trend, Southeast Missouri: Economic Geology, v. 76, p. 1848–1872.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Swart, P.K., Wortmann, U.G., Mitterer, R.M., Malone, M.J., Smart, P.L., Feary, D.A., and Hine, A.C., 2000, Hydrogen sulfide-rich hydrates and saline fluids in the continental margin of South Australia: Geology, v. 28, p. 1039–1042.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Taylor, S., 1984, Structural and paleotopographic controls of lead-zinc mineralization in the Silvermines orebodies, Republic of Ireland: Economic Geology, v. 79, p. 529–548.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Tucker, M.E., and Wright, V.P., 1990, Carbonate sedimentology: Oxford, Blackwell Science, 482 p.

Velasco, F., Sanchez-Espana, J., Boyce, A.J., Fallick, A.E., Sáez, R., and Almodovar, G.R., 1998, A new sulphur isotopic study of some Iberian pyrite belt deposits: Evidence of a textural control on sulphur isotope composition:Mineralium Deposita , v. 34, p. 4–18.[CrossRef][Web of Science][GeoRef]

Wilkinson, J.J., 2003, On diagenesis, dolomitisation and mineralisation in the Irish Zn-Pb orefield: Mineralium Deposita, v. 38, p. 968–983.[CrossRef][Web of Science][GeoRef]

Wilkinson, J.J., and Earls, G., 2000, A high temperature hydrothermal origin for black dolomite matrix breccias in the Irish Zn-Pb ore field: Mineralogical Magazine, v. 64, p. 1077–1096.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]

Wilkinson, J.J., Boyce, A.J., Everett, C.E., and Lee, M.J., 2003, Timing and depth of mineralization in the Irish Zn-Pb ore field, in Kelly, J.G., Andrew, C.J., Ashton, J.H., Boland, M.B., Earls, G., Fusciardi, L., and Stanley, G., eds., Europe’s major base metal deposits: Dublin, Irish Association for Economic Geology, p. 483–497.

Wright, W.R., Somerville, I.D., Gregg, J.M., Shelton, K.L., and Johnson, A.W., 1999, Dolomite CL and ¹⁸O, ¹³C data from Irish Midlands and Dublin basin, Carboniferous, in Stanley, C.J. et al., eds., Mineral deposits: Processes to processing: Rotterdam, Balkema, v. 2, p. 913–917.

Wright, W.R., Johnson, A.W., Shelton, K.L., and Gregg, J.M., 2000, Fluid migration and rock interactions during dolomitisation of the Dinantian Irish Midlands and Dublin basin: Journal of Geochemical Exploration, v. 69–70, 159–164.

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