ARTICLE

The Transfiguration continental red-bed Cu–Pb–Zn–Agdeposit, Quebec Appalachians, Canada

Alexandre Raphael Cabral & Georges Beaudoin &

Bruce E. Taylor

Received: 26 March 2008 /Accepted: 22 October 2008 /Published online: 29 November 2008# Springer-Verlag 2008

Abstract The Transfiguration Cu–Pb–Zn–Ag deposit,enclosed within reduced grey sandstone, is associated withcontinental red beds of the Lower Silurian RobitailleFormation in the Quebec Appalachians, Canada. TheRobitaille Formation rests unconformably on foliatedCambro-Ordovician rocks. The unconformity is locally cutby barite veins. The basal unit of the Robitaille Formationcomprises green wacke and pebble conglomerate, whichlocally contain calcite nodules. The latter have micro-structures characteristic of alpha-type calcretes, such as“floating” fabrics, calcite-filled fractures (crystallaria) andcircumgranular cracks. Massive, grey sandstone overliesthe basal green wacke and pebble conglomerate unit, whichis overlain, in turn, by red, fine-grained sandstone.Mineralisation occurred underneath the red sandstone unit,chiefly in the grey sandstone unit, as disseminated andveinlet sulphides. Chalcopyrite, the most abundant Cusulphide, replaced early pyrite. Calcrete, disseminatedcarbonate and vein carbonate have stable isotope ratiosvarying from −7.5‰ to −1.1‰ δ13C and from 14.7‰ to21.3‰ δ18O. The negative δ13C values indicate the

oxidation of organic matter in a continental environment.Sulphur isotope ratios for pyrite, chalcopyrite and galenavary from −19‰ to 25‰ δ34S, as measured on mineralconcentrates by a conventional SO2 technique. Laser-assisted microanalyses (by fluorination) of S isotopes inpyrite show an analogous range in δ34S values, from −21‰to 25‰. Negative and positive δ34S values are compatiblewith bacterial sulphate reduction (BSR) in systems openand closed with respect to sulphate. We interpret similarlyhigh δ34S values for sulphide concentrates (25.1‰) and forvein barite (26.2‰) to result from rapid and completethermochemical reduction of pore-water sulphate. Twoearly to late diagenetic stages of mineralisation best explainthe origin of the Transfiguration deposit. The first stage wascharacterised by the ponding of groundwater over theTaconian unconformity, recorded by calcrete and earlypyrite formation via BSR in grey sandstone. Early pyritecontains up to 2 wt.% Pb, which is consistent with Pbfixation by sulphate-reducing bacteria. The second stage(II) is defined by the replacement of early pyrite bychalcopyrite, as well as by sulphide precipitation via eitherBSR or thermochemical sulphate reduction (TSR) in greysandstone. This event resulted from the synsedimentaryfault-controlled percolation and mixing of (1) an oxidising,sulphate-bearing cupriferous fluid migrating per descensumfrom the red-bed sequence and (2) a hydrocarbon-bearingfluid migrating per ascensum from the Cambro-Ordovicianbasement. Mixing between the two fluids led to sulphatereduction, causing Cu sulphide precipitation. The positivecorrelation between Cu and Fe3+/Fe2+ bulk rock valuessuggests that Fe acted as a redox agent during sulphatereduction. Stage II diagenetic fluid migration is tentativelyattributed to the Late Silurian Salinic extensional event.

Keywords Copper . Continental red beds . Calcrete .

Stable isotopes . Quebec . Canada

Miner Deposita (2009) 44:285–301DOI 10.1007/s00126-008-0217-z

Editorial handling: D. Lentz.

A. R. Cabral :G. BeaudoinDépartement de Géologie et de Génie Géologique,Université Laval,Québec, QC, Canada G1K 7P4

B. E. TaylorGeological Survey of Canada,601 Booth Street,Ottawa, ON, Canada K1A 0E8

Present address:A. R. Cabral (*)Department of Geology, Exploration Geology, Rhodes University,P.O. Box 94, Grahamstown 6140, South Africae-mail: A.Cabral@ru.ac.zae-mail: cabral70tricolor@yahoo.com.br

Introduction

Sediment-hosted, stratiform cupriferous deposits accountfor approximately 23% of the world’s Cu productionand known reserves and are important sources of Agand Co, as well as by-product Au, U, Pt and Pd insome cases (Kirkham 1989; Brown 1992; Hitzman et al.2005). For instance, the Neoproterozoic Copper Belt incentral Africa hosts several world-class Cu–Co deposits

with reserves totalling 140 Mt Cu and 6 Mt Co (Cailteuxet al. 2005).

Two types of sediment-hosted, stratiform Cu depositscan be broadly distinguished (e.g. Kirkham 1989; Hitzmanet al. 2005): (1) the Kupferschiefer type, which consists ofdeposits hosted by carbonaceous sedimentary rocks thatwere formed in shallow marine or lacustrine environ-ments, and (2) the red-bed type in which cupriferousmineralisation develops in grey clastic rock occurrences

Fig. 2 The depositional envi-ronments during the Silurian forthe Lake Témiscouata region(modified from Bourque et al.1995). At the Transfigurationdeposit, rocks of the RobitailleFormation rest directly on theCambro-Ordovician basement(cf. Fig. 4)

Fig. 1 Regional geological map of the Gaspé Appalachians (modified from Malo 2004) showing the location of the Transfiguration deposit

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within continental successions that are dominated by redbeds, typically at the interface between red and greyclastic units. Copper sulphide deposition is generallyinterpreted to be caused by interaction between anoxidising, low-temperature Cu-bearing fluid and a reduced(grey) rock unit that contains pyrite (e.g. Kirkham 1995;Brown 2005; Hitzman et al. 2005), but processesinvolving fluid mixing have also been proposed (Suttonand Maynard 2005).

The Transfiguration deposit (Fig. 1) was initiallyregarded as a galena-cemented sandstone deposit (Schrijverand Beaudoin 1987), but further exploration indicated adominance of vein and disseminated Cu mineralisation inassociation with continental red beds. The Transfigurationdeposit is now considered to be a red-bed type, sediment-hosted Cu deposit. Although other sediment-hosted Cudeposits are known in the Quebec Appalachians, andsedimentary-diagenetic and epigenetic models have been

Fig. 3 a Geological map of the Transfiguration deposit, based on acompilation of diamond drill holes, exploration trenches and outcropgeology and on a 3D model constructed with gOcad (Bédard,unpublished). Location of faults (at surface) and interpretation of

their displacement are derived from diamond drill core description andthe 3D geological reconstruction. b Geological section (A–A′) of abarren zone (modified after Bergeron 1999, unpublished). c Geolog-ical section (B–B′) of a mineralised zone

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proposed (Gauthier et al. 1994), their petrogenesis is notwell constrained. In this paper, we describe the geology,geochemistry and petrography of the Cu–Pb–Zn–Agdeposit at Transfiguration and propose a new diageneticmodel involving fluid mixing during the Late SilurianSalinic extensional event (Bourque 2001; Malo 2001).

Geological setting

The Transfiguration deposit is located in the Gaspé Belt,which is the largest remnant basin of Middle Palaeozoicrocks in the Canadian Appalachians (e.g. Bourque et al.1995; Malo 2004). The Gaspé Belt is an Upper Ordovicianto Middle Devonian tectono-stratigraphic assemblage thatunconformably rests on, or is in fault contact with, pre-Taconian rocks of both the Humber (e.g. Trinité Group)and Dunnage zones (e.g, Williams 1979; Malo 2004)(Fig. 1). The Taconian basement in the Transfigurationarea comprises Cambro-Ordovician pelitic rocks andminor calcareous rocks of the Trinité Group, conformablyoverlain by arenaceous rocks of the Québec Supergroup(Goutier 1989).

Following the Taconian Orogeny, the Siluro-DevonianGaspé Belt successor basin recorded a marine regression(shallowing phase I in Fig. 2) that can be recognised by theupward transition from deep-water turbidites to shallow-water sediments (Cabano Group), followed by sub-aeriallava flows and volcaniclastic gravels (Pointe-aux-Trembles)and capped by terrestrial red beds of the RobitailleFormation (Bourque et al. 1995, 2001). The red beds arethe lower terrigenous assemblage of the ChaleursGroup. The Transfiguration deposit is hosted by rocksof the Llandoverian Robitaille Formation which rests onthe Taconian unconformity. Marine platform limestonesof the Sayabec Formation, the middle carbonate assem-blage of the Chaleurs Group, overlie the RobitailleFormation. The late Llandoverian to late WenlockianSayabec limestones evolve laterally into peritidal mudflats and deeper water nodular marls (Lavoie et al.1992). The Sayabec Formation corresponds to a period ofhigher relative sea level than during continental depositionof the Robitaille Formation. The Sayabec platform endedwith a late Wenlockian transgression and an associatedinflux of deep-water, fine-grained siliciclastic sediments ofthe Saint-Léon Formation (Fig. 2). Subsequent to thistransgression, Late Silurian extension (the Salinic Distur-bance) resulted in synsedimentary faulting that wasconcomitant with the sub-aerial erosion of uplifted blocks(Bourque 2001; Malo 2001). The Middle DevonianAcadian Orogeny deformed the Gaspé Belt assemblage,overprinting older deformation features related to theSalinic Disturbance.

Geology of the Transfiguration deposit

The local geology is known from exploration trenches anddiamond drill holes. Sandstones of the Robitaille Formationfound in open NE-trending folds are truncated by a NNW-striking dextral fault and W- to NW-verging reverse faults(Fig. 3a). The NNW-striking dextral fault displaces both theopen folds and the reverse faults. Evidence of any normalfaulting was likely obliterated by fault inversion during theAcadian Orogeny. Diamond drill holes have revealedchanges in the thickness of laterally continuous, but slightlydisplaced, units (Fig. 3b) best explained by synsedimentarynormal faulting. The local stratigraphic succession com-prises, from bottom to top (Fig. 4), (a) sheared slate of theCambro-Ordovician Taconian basement (Trinité Group), (b)green to grey sandstones with calcrete nodules, (c) polymictconglomerate with minor calcrete nodules, (d) grey sand-stone and (e) red sandstone and siltstone.

The nodular calcrete unit is predominantly green,subordinately grey and hosted by pebbly sandstone andchloritic quartz wacke. The calcrete nodules are irregular inshape, vary in width from a few millimetres to about 5 cmand consist of micritic and sparry calcite with micro-structures typical of alpha-type calcretes (sensu Wright1990). The microstructures include calcite-filled fractures(crystallaria), “floating” grains (Fig. 5a) and calcite-filledcircumgranular cracks (Fig. 5b). The calcrete noduleslocally have barite in crystallaria (Fig. 5a), authigenic albite(Fig. 5c) and replacement pyrite (Fig. 5d) with or without

Fig. 4 Simplified stratigraphic section through the Transfigurationdeposit

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traces of galena and sphalerite. “Floating” grains of detritalquartz commonly exhibit evidence of reaction (Fig. 5e) andsome grains are replaced by calcite (Fig. 5f).

The polymict conglomerate contains clasts of quartz,quartzite, sandstone and siltstone in a sericitic matrix. Theclasts are irregularly cemented by carbonate close to thecontact with the subjacent nodular calcrete unit. Fragmentsof calcrete nodules also occur in the polymict conglomer-ate, particularly in its lower portion, but in situ calcretenodules are occasionally found within the arenaceousmatrix of this conglomerate. These observations suggestan early diagenetic origin for the calcrete, which initiatedprior to deposition of the polymict conglomerate, andcontinued after.

The grey and superjacent red sandstones are composedof quartz arenite, sub-litharenite and quartz wacke withfine- to medium-grained, moderately to poorly sorteddetrital quartz and minor feldspar. The contact between

the red and the grey sandstone units is irregular, withoxidised zones that are either rimmed by a green alterationhalo within grey sandstone (Fig. 6a) or that envelop pocketsof grey sandstone remnants within otherwise thoroughlyoxidised rock (Fig. 6b). In grey sandstone, intergranularillite is ubiquitous, as well as disseminated pyrite foundinterstitial to detrital grains in amounts varying from traceto a few modal percents. Displacement calcite growth isobserved to have taken place in grey sandstone (Fig. 7a). Inmineralised intervals of grey sandstone, feldspar and quartzare replaced by ankerite with some chalcopyrite and rareauthigenic albite (Fig. 7b,c).

Sample material and analytical techniques

Electron microprobe analyses of sulphide (Table 1) andcarbonate (Table 2) minerals were performed at the

Fig. 5 Photomicrographs ofstained thin sections showingcalcrete alpha fabrics (plane-polarised transmitted light, unlessotherwise indicated). a Calcite-filled fractures (crystallaria) withbarite (Ba). b Crystallaria withcircumgranular cracks (arrows)in micritic fabric of “floating”grains (white, mainly quartz).c Albite (Ab) in calcrete nodule.d Idiomorphic pyrite (Py) withinclusions of corroded quartz(Qz), replacing a groundmass ofunsupported (“floating”) grains(reflected light). e Etched mar-gins (arrows) of detrital quartz ina “floating” fabric. f Completereplacement of detrital quartz bycoarse-grained calcite. Thedashed line separates two calcitecrystals and the arrow points torelic quartz (white)

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Laboratoire de Microanalyse, Université Laval, Canada,using a Cameca SX100 electron microprobe in wavelength-dispersion mode, under 15 kV and 20 nA (standards inparentheses): (1) for sulphide minerals: FeKα (haematite),SKα (pyrite), ZnKα (Zn), CuKα (chalcopyrite), CoKβ(skutterudite), PbMβ (galena), AgLα (Au80Ag20), AsLαand SeLα (Se90As10); (2) for carbonate minerals: FeKα(haematite), MnKα (ilmenite), CaKα and MgKα (diopside).

Bulk rock chemical analyses of drill core samples(Table 3) were carried out at Activation Laboratories,Lancaster, Canada. Magnesium, Al, P, S, K, Ca, Ti, V,Mn, Zn and Mo were analysed by inductively coupledplasma spectrometry (ICP). The ICP technique was usedon an acid solution resulting from a four-acid digestion(hydrochloric, nitric, perchloric and hydrofluoric acids).Gold, Pt and Pd were determined by fire assay plusinductively coupled plasma–mass spectrometry (ICP-MS). Ferrous iron was obtained by titration, with Fe3+

contents being derived from the difference between totalFe by instrumental neutron activation analysis (INAA) andFe2+. All other elements in Table 3 were analysed byINAA.

Sulphide, sulphate and carbonate were manually con-centrated under a binocular microscope. Sulphur, C and Oisotope compositions (Table 4) were determined at the G.G.Hatch Isotope Laboratory, University of Ottawa, using (1) aconventional SO2 technique performed on a VarioEL IIIelemental analyser and a DeltaPlus mass spectrometer withan analytical precision of ±0.2‰ δ34S; and (2) continuousflow extraction (after reaction with 0.1 mL H3PO4)measured on a Delta XP and a Gas Bench II with ananalytical precision of ±0.1‰ δ13C and δ18O. Pyrite andchalcopyrite S isotope compositions were also measured byfluorination with the micro in situ laser extraction system(MILES) at the Geological Survey of Canada, Ottawa(Beaudoin and Taylor 1994; Taylor 2004). Laser-induced

reaction pits varied in diameter from 240 to 500 μm,slightly larger than typical.

Mineralisation

The Transfiguration deposit contains disseminated andveinlet sulphides confined to the grey sandstone andconglomerate, which rest between the underlying Taconianunconformity and the overlying red sandstone unit (Figs. 3cand 4). The contact between the nodular calcrete in greensandstone and the basement is sometimes marked by (1)

Fig. 6 a Green alteration halo about a centre of red sandstone in greysandstone. Drill core 97–11, 8.70 m. b Red alteration obliterated greysandstone bedding (arrows). Drill core 97–10, 18.2 m

Fig. 7 Photomicrographs of grey sandstone (transmitted light withcrossed polars). a Displacement calcite in detrital quartz (arrows). bFeldspar destruction (centre) and disseminated chalcopyrite (Cpy) inankerite (Ank) cement between corroded detrital quartz (whitearrows). c Etched detrital quartz (arrows) with albite (Ab) andchalcopyrite (Cpy) in ankerite cement

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breccias and calcite veins with minor disseminated pyrite,as well by (2) fault-related barite veins with disseminatedsphalerite in green and grey sandstones. Mineralisation canbe along bedding for some 2 km, attaining 13.9 m inthickness, with 0.4% Cu and 5.3 g/t Ag (Hupé 2001). Someintervals are particularly rich in Pb, Zn and Ag (e.g. 3.4 mat 0.25% Cu, 3.0% Pb, 2.0% Zn, 18.2 g/t Ag; Hupé 2001).Such mineralised zones tend to thin away from faults(Fig. 3c).

Ore petrography and mineral chemistry

Pyrite and minor marcasite were the earliest formedsulphides. Pyrite is disseminated as euhedral crystals,from 50 to 300 μm across, in grey sandstone. Innodular calcrete, pyrite forms isolated xenomorphicaggregates, up to about 500 μm across, which enclosedetrital quartz. Chalcopyrite replaced and overgrewpyrite in grey sandstone (Fig. 8a) in places. This early

Table 1 Selected electron microprobe analyses of sulphide minerals

1 2 3 4 5 6 7 8 9 10

wt.%Cu 34.84 34.63 34.92 48.17 44.51 50.90 73.30 55.98 61.34 <0.17Fe 30.88 30.52 30.16 14.17 13.36 14.55 2.45 13.51 11.55 16.34Pb 0.25 0.28 0.24 0.51 0.26 0.30 0.21 0.25 0.30 4.03Zn <0.23 <0.23 <0.23 <0.23 <0.23 <0.23 <0.23 <0.23 <0.23 41.82Ag <0.03 0.07 0.05 4.06 10.80 0.42 0.31 0.60 0.34 0.04As <0.05 <0.05 <0.05 0.07 <0.05 <0.05 <0.05 <0.05 <0.05 0.07S 34.60 34.40 34.35 31.48 30.19 33.41 23.04 29.93 27.04 37.39Total 100.56 99.90 99.72 98.46 99.12 99.58 99.31 100.27 100.57 99.69afpuCu 1.005 1.006 1.016 2.981 2.826 3.039 7.811 4.697 5.734 –Fe 1.014 1.009 0.999 0.998 0.965 0.988 0.297 1.290 1.229 0.276Pb 0.002 0.002 0.002 0.010 0.005 0.005 0.007 0.006 0.009 0.018Zn – – – – – – – – – 0.604Ag – 0.001 0.001 0.148 0.404 0.015 0.019 0.030 0.019 0.000As – – – 0.004 – – – – – 0.001S 1.979 1.981 1.982 3.860 3.799 3.953 4.866 4.977 5.010 1.101Total 4 4 4 8 8 8 13 11 12 2

Compositions were first reported in wt.% and then recast as atom per formula unit (apfu)1–3 chalcopyrite, 4–6 idaite, 7 geerite, 8 empirical Cu4:7; Fe1:3ð ÞΣ6:0S5:0, 9 empirical Cu5:7;Fe1:2ð ÞΣ6:9S5:0, 10 sphalerite

Table 2 Selected electron microprobe analyses of carbonate minerals

1 2 3 4 5 6 7 8 9 10 11 12

wt.%CaCO3 55.16 54.06 52.71 52.93 52.26 51.87 55.43 58.10 56.14 55.28 92.72 92.55MgCO3 27.57 32.41 30.64 34.40 27.13 24.76 32.56 34.49 32.67 31.05 2.02 2.42FeCO3 16.16 11.54 14.58 10.89 19.58 22.29 8.80 3.71 7.96 10.37 2.50 3.58MnCO3 1.15 2.33 2.45 2.12 1.45 0.72 2.75 3.08 2.42 2.71 1.83 2.17Total 100.04 100.33 100.38 100.33 100.41 99.65 99.54 99.37 99.19 99.41 99.07 100.71apfuCa 1.073 1.035 1.015 1.008 1.018 1.026 1.065 1.107 1.081 1.069 0.938 0.922Mg 0.636 0.736 0.701 0.778 0.627 0.581 0.743 0.780 0.746 0.712 0.024 0.029Fe 0.271 0.191 0.243 0.179 0.330 0.381 0.146 0.061 0.132 0.173 0.022 0.031Mn 0.020 0.039 0.041 0.035 0.025 0.012 0.046 0.051 0.041 0.046 0.016 0.019Total 2 2 2 2 2 2 2 2 2 2 1 1Mg/Fe 2.3 3.9 2.9 4.3 1.9 1.5 5.1 12.8 5.7 4.1 – –

Compositions were first reported in wt.% and then recast as atom per formula unit (apfu). According to Deer et al. (1992), Mg/Fe ≤4 correspondsto ankerite, whereas Mg/Fe >4 defines ferroan dolomite1–6 chalcopyrite-bearing carbonate cement in mineralised grey sandstone, 7–10 carbonate cement in barren grey sandstone, 11–12 displacementcalcite in barren grey sandstone

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Table 3 Bulk rock chemical analyses of selected samples

Column 1 2 3 4 5 6 7 8 9Sample no. 850 807 850 819 850 821 850 826 850 827 850 828 850 830 850 831 850 832Drill hole 98-04 98-68 96-15 96-03 96-03 96-03 96-04A 96-04A 96-10From (m) 25.05 37.95 3.97 46.17 49.70 51.05 12.00 15.90 6.06To (m) 25.37 38.50 4.25 46.49 50.00 51.50 12.26 16.21 6.40

(wt.%)Na 0.55 0.50 0.49 0.37 0.34 0.76 0.52 1.12 1.58Mg 0.31 0.40 0.06 0.49 0.26 0.18 0.22 0.69 0.65Al 1.18 1.19 1.02 0.90 0.61 1.54 1.07 2.15 2.90P 0.015 0.027 0.023 0.012 0.008 0.022 0.018 0.019 0.034S 0.451 2.047 2.759 7.873 0.626 0.774 5.283 3.019 1.736K 0.39 0.29 0.27 0.29 0.10 0.51 0.27 0.36 1.58Ca 0.61 1.43 0.77 4.81 6.69 0.28 4.46 1.60 0.98Ti 0.09 0.06 0.08 0.06 0.03 0.09 0.06 0.21 0.30Fe2+ 0.31 0.72 0.30 1.98 0.73 0.59 2.40 2.38 0.72Fe3+ 0.23 0.94 1.48 3.31 0 0.16 0.83 0 0.93(ppb)Pd <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5Re 2 137 337 45 <1 8 20 2 301Ir <5 <5 <5 <5 <5 <5 <5 <5 <5Pt <0.5 1.0 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5Au 3 11 5 7 5 6 4 12 6(ppm)Li 10.7 12.5 12.7 8.4 10.4 10.6 15.7 26.9 16.0Be 0.3 0.2 <0.1 0.2 <0.1 0.2 0.2 0.3 1.0Sc 1.5 1.2 1.2 1.3 1.1 1.4 1.0 2.5 6.2V 15 20 14 9 7 19 9 20 50Cr 55 48 45 47 26 91 50 78 111Mn 148 318 103 1,012 775 48 815 291 277Co 5.5 11.9 3.7 23.7 4.1 1.5 25.9 23.1 25.0Ni 7.8 7.4 3.8 13.4 6.8 5.8 16.9 13.8 18.2Cu 2,260 1.37b 2.44b 738 179 6,400 1,200 66.4 1.52b

Zn 23 27 19 3,055 16 24 12,010 9,275 66Gaa 4.0 2.4 2.1 2.7 1.2 3.6 3.0 5.8 9.8Ge <0.1 <0.1 0.2 <0.1 <0.1 <0.1 <0.1 <0.1 0.1As 6.6 18.3 6.7 36.5 6.8 5.1 72.8 142 33.1Se 0.6 0.8 0.5 1.0 0.8 1.0 1.3 1.0 1.0Br <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5Rb 10.7 8.6 7.1 8.8 3.2 13.3 7.7 10.4 39.1Sr 85.8 33.3 33.1 81.4 439 43.6 102 52.1 105Y 5.7 12.7 7.2 19.6 14.7 6.4 14.0 13.1 12.8Zra 39 42 48 42 13 51 36 145 216Nb 1.8 1.4 1.6 1.5 0.7 1.7 1.6 4.4 6.6Mo 2 144 5 62 3 4 43 4 13Ag 0.42 1.01 226 4.07 <0.05 2.08 9.82 2.27 10.3Cd <0.1 <0.1 <0.1 9.0 <0.1 0.2 45.6 35.0 <0.1In <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1Sna <1 <1 <1 <1 <1 <1 <1 <1 <1Sb 0.1 1.0 0.5 1.2 0.2 0.1 1.5 0.2 0.7Te 0.1 <0.1 <0.1 <0.1 0.9 <0.1 0.1 <0.1 <0.1Cs 4.18 3.97 3.95 4.18 3.78 4.39 4.03 3.95 4.75Ba 790 150 <50 230 180 200 72 150 2,200La 6.4 7.9 6.2 9.3 3.7 6.8 8.4 7.4 14.1Ce 13 15 13 16 8 14 16 15 27Pra 1.8 2.5 2.1 2.9 1.6 2.1 3.1 2.6 3.3Nda 7.1 10.6 8.7 12.1 8.9 8.2 13.3 11.3 12.7Sma 1.4 2.3 1.8 2.6 4.0 1.5 3.0 2.5 2.4Eua 0.34 0.57 0.40 0.72 1.66 0.33 1.70 0.64 0.53Gda 1.4 2.5 1.7 3.2 3.8 1.5 3.1 2.7 2.4Tba 0.2 0.4 0.3 0.5 0.5 0.2 0.4 0.4 0.4Dya 1.1 2.1 1.4 2.7 2.8 1.2 2.4 2.3 2.2Hoa 0.2 0.5 0.3 0.6 0.6 0.3 0.5 0.5 0.6Era 0.6 1.2 0.7 1.5 1.3 0.7 1.3 1.4 1.6Tma 0.1 0.2 0.1 0.2 0.2 0.1 0.2 0.2 0.3Yb 0.7 1.1 0.7 0.9 1.0 0.8 0.9 1.2 2.0Lu 0.12 0.17 0.14 0.15 0.14 0.15 0.15 0.24 0.35Hf 3 2 3 2 1 3 2 8 12Ta <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 1.2W <1 <1 <1 <1 <1 <1 <1 <1 <1Hg <1 <1 <1 <1 <1 <1 <1 <1 <1Tl 0.17 0.70 0.11 3.02 0.50 0.13 0.78 1.02 0.48Pb 24.9 859 44.4 3,680 58.5 3.8 683 1,760 14.3Bi <0.02 0.97 0.43 <0.02 <0.02 <0.02 0.16 <0.02 <0.02Th 1.6 1.3 1.4 1.2 0.7 1.9 1.3 2.8 4.3U 0.6 1.1 0.7 0.6 0.3 0.9 0.7 1.1 5.2

All samples except those indicated by Sq (Squatec property) are from TransfigurationaElements may not be total due to the inability to completely dissolve very resistant mineralsbCu and Pb assay values %; Ba assays in columns 10 and 141–9 grey sandstone, 10–13 polymict conglomerate, 14–15 cover–basement contact with hydrothermal breccia (14) and calcrete (15), 16 red polymict conglomerate, 17–19 greenpolymict conglomerate, 20 red polymict conglomerate

292 Miner Deposita (2009) 44:285–301

10 11 12 13 14 15 16 17 18 19 20850 833 850 837 850 839 850 840 850 841 850 842 850 843A 850 843B 850 845 850 848 850 85096-10 96-22 97-03 97-03 97-03 98-09 Sq/98-01 Sq/98-01 Sq/98-07 Sq/98-12 Sq/98-1325.17 23.03 27.80 28.00 30.82 29.45 9.25 9.35 3.20 13.68 25.2925.45 23.30 28.00 28.30 31.19 30.00 9.35 9.45 3.40 13.86 25.60

(wt.%)0.26 0.30 0.44 0.24 0.08 0.23 0.70 0.49 0.62 0.67 1.060.35 0.85 0.43 0.60 0.35 1.35 2.05 4.85 0.58 1.43 1.100.84 1.63 1.25 1.46 0.34 3.12 2.79 2.43 1.86 2.03 2.590.019 0.060 0.017 0.025 0.009 0.033 0.076 0.021 0.043 0.050 0.0551.347 2.688 1.322 3.297 4.244 1.702 0.033 0.010 10.102 1.060 0.0770.41 0.90 0.56 0.87 0.15 2.08 1.01 0.80 0.71 0.52 0.981.45 1.91 0.82 1.57 12.62 4.99 1.07 6.11 0.11 0.87 0.600.06 0.12 0.09 0.11 0.03 0.25 0.20 0.19 0.17 0.19 0.260.73 1.89 0.80 1.97 2.54 2.30 1.41 1.87 2.54 1.59 1.130.49 0.11 0.48 0.36 0.59 0 0.76 0.34 5.56 0 0.01

(ppb)<0.5 <0.5 <0.5 <0.5 <0.5 0.6 <0.5 <0.5 7.1 <0.5 <0.5408 371 501 374 10 30 <1 <1 150 <1 <1<5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <50.7 0.6 0.6 0.7 <0.5 0.7 <0.5 <0.5 5.5 <0.5 <0.57 5 5 5 4 3 13 4 29 5 5

(ppm)10.1 9.5 10.9 9.5 2.4 22.0 39.7 46.9 19.6 32.4 29.90.2 0.5 0.3 0.5 <0.1 1.2 0.6 0.8 0.4 0.5 0.61.1 2.7 2.1 2.6 0.7 5.6 3.9 5.3 2.9 2.3 3.4

44 33 20 31 13 58 35 30 25 25 3347 46 54 51 23 95 29 72 24 42 51258 533 205 392 2,234 844 446 1,601 131 605 24330.4 71.4 112 99.6 9.4 36.1 9.6 10.5 673 14.2 9.610.4 21.0 31.8 24.1 9.6 48.0 21.6 21.8 42.0 15.2 16.2

5,100 1,100 6,760 1,580 12.3 169 5.0 10.8 2.32b 857 53448 232 31 159 10,997 81 44 29 30 31 332.6 5.5 3.8 4.8 1.3 10.7 9.1 7.4 5.9 5.5 6.5

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 0.1 <0.1 <0.115.1 38.7 14.1 52.3 10.5 21.9 2.7 4.8 513 12.2 8.20.6 1.4 0.7 1.1 1.5 1.0 0.8 0.8 1.1 0.7 0.4

<0.5 <0.5 <0.5 <0.5 <0.5 <0.5 0.7 1.2 <0.5 <0.5 <0.512.6 28.9 16.6 27.6 6.3 70.6 35.3 29.2 22.9 17.3 22.4343 97.6 129 71.3 552 108 81.9 112 51.4 139 7224.8 13.7 6.4 9.1 9.5 15.1 15.6 27.7 11.4 30.3 12.0

24 65 54 50 17 105 90 131 86 95 1361.4 3.4 2.0 3.0 0.9 6.8 5.8 5.3 5.1 5.3 6.38 51 33 42 26 1 <1 <1 68 9 9

16.0 12.2 9.04 14.4 4.79 0.96 <0.05 <0.05 9.02 <0.05 <0.050.2 1.9 0.1 1.4 55.2 0.3 <0.1 <0.1 0.5 <0.1 <0.1

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1<1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <10.3 1.5 0.8 1.5 0.7 0.9 0.3 0.4 0.2 0.3 0.4

<0.1 <0.1 <0.1 <0.1 0.9 0.6 0.4 1.6 0.1 0.2 0.34.42 4.76 4.74 4.88 4.26 10.7 7.56 8.05 4.92 4.71 4.77

13,481 1,300 3,500 4,600 156,520 300 990 240 3,900 300 3505.3 11.2 6.8 11.2 7.6 17.1 16.9 15.9 13.1 14.1 16.19 22 15 21 13 36 37 40 21 31 351.5 3.8 2.2 2.8 2.0 5.7 5.7 6.2 2.0 4.9 4.46.0 16.6 8.7 11.8 8.2 21.4 22.4 27.2 10.8 20.0 17.31.3 3.6 1.6 2.3 1.7 4.3 5.0 7.3 2.5 4.6 3.30.41 0.83 0.34 0.45 0.45 0.93 1.03 1.96 0.52 1.08 0.661.4 3.8 1.5 2.1 1.8 3.9 4.5 7.2 2.4 5.3 3.10.2 0.5 0.2 0.3 0.2 0.5 0.6 1.0 0.4 0.9 0.41.0 2.7 1.3 1.8 1.3 3.0 3.1 5.6 2.2 5.5 2.40.2 0.6 0.3 0.4 0.3 0.6 0.6 1.0 0.5 1.1 0.50.5 1.4 0.8 0.9 0.6 1.6 1.6 2.6 1.3 2.9 1.4

<0.1 0.2 0.1 0.1 <0.1 0.2 0.2 0.4 0.2 0.4 0.20.5 1.1 0.8 0.9 0.5 1.5 1.5 2.5 1.1 2.7 2.40.09 0.18 0.12 0.15 0.08 0.23 0.27 0.45 0.17 0.43 0.393 4 4 3 2 4 5 8 5 5 9

<0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5<1 <1 <1 <1 <1 1 <1 1 <1 <1 <1<1 <1 <1 <1 1 <1 <1 <1 <1 <1 <12.17 3.80 1.05 4.47 1.50 2.23 0.17 0.11 2.17 1.81 0.11

80.7 3.20b 204 3.58b 874 59.3 3.4 1.7 771 20.6 6.8<0.02 <0.02 <0.02 0.02 <0.02 <0.02 <0.02 <0.02 0.07 <0.02 <0.021.1 2.2 1.7 1.9 <0.2 4.3 3.2 3.9 2.7 2.5 3.74.9 2.2 2.9 1.9 1.2 1.9 1.1 1.1 5.0 1.2 1.3

Table 3 (continued)

Miner Deposita (2009) 44:285–301 293

Table 4 Isotopic compositions of carbonates, sulphides and barite

Sampleδ34SV-CDT(‰)

δ13CVPDB

(‰)δ18OSMOW

(‰)

850 809 calcrete −4.6 18.1py crystals in calcrete 6.9a

5.9a

7.4a

8.7a

9.7a

850 810 vein calcite (white) in slate (basement) −2.3 18.1vein calcite (slightly pink) in slate (basement) −1.6 21.3

850 811 calcrete −2.4 18.0vein calcite −2.6 18.6

850 819 cpy in grey sandstone 19.1py crystals replaced by cpy 13.7a

13.8a

13.2a

4.9a

24.8a

850 825 calcrete −4.1 18.3850 826 cpy in grey sandstone 25.1850 827 vein calcite in grey sandstone −4.4 17.8850 828 cpy in grey sandstone 15.3850 829 calcrete −3.9 18.3

py crystals in calcrete 17.2a

22.5a

22.6a

23.2a

21.4a

850 830 vein calcite in grey sandstone −4.8 18.5py in grey sandstone 2.8sph in grey sandstone 1.1

850 831 sph in grey sandstone 12.3850 832 carbonate in grey sandstone −6.8 17.6

veinlet cpy in grey sandstone −1.2veinlet cpy in grey sandstone 14.9a

10.1a

7.8a

7.0a

6.4a

5.9a

850 833 py in polymict conglomerate −15.4850 835 cpy in grey sandstone −19.4850 837 gn in polymict conglomerate −15.3

plumbiferous py in polymict conglomerate −15.9−20.4a

−17.9a

−20.2a

−20.8a

−18.5a

−20.2a

850 839 veinlet cpy in polymict conglomerate −15.2py in polymict conglomerate −18.6

850 840 carbonate in polymict conglomerate −2.6 20.1gn in polymict conglomerate −15.7

850 841 vein barite between calcrete and basement 26.2850 842 calcrete −6.0 17.5850 843† vein calcite in green polymict conglomerate −7.5 20.7

vein dolomite in red polymict conglomerate −1.9 14.7850 845† cpy in green polymict conglomerate −12.7

py+marcasite in green polymict conglomerate −8.8850 846† vein calcite in slate −1.1 16.5

vein calcite (slightly pink) in slate −1.5 19.6

a Laser-assisted microanalyses† Samples from Squatec, a property contiguous to TransfigurationAbbreviations: py, pyrite; cpy, chalcopyrite; gn, galena; sph, sphalerite

294 Miner Deposita (2009) 44:285–301

pyrite is commonly plumbiferous, with Pb-rich cores andPb-poor rims discernible only under high-gain backscat-tered electron (BSE) imaging (Fig. 9a). The Pb content inpyrite is as high as 2.2 wt.% and co-varies with Fe(Fig. 9b). Occasionally, marcasite may dominate the Fesulphides as isolated crystals and aggregates, both partial-ly inverted to pyrite. Secondary pyrite from marcasite isporous, and the pores appear to be filled by galena and acupriferous phase, possibly chalcopyrite. Marcasite hasinclusions of, and is cut by, sphalerite containing up to16 wt.% Fe.

Chalcopyrite is interstitial to detrital quartz and occurs asdisseminations and irregular septal mottles (Fig. 8b). Itcoexists with pyrite and albite in <2 mm-wide veinlets(Fig. 8c). Vein albite hosts tiny, <5 μm long, hydrocarbon-bearing fluid inclusions. Euhedral crystals of Ti oxide arefound in chalcopyrite-cemented interstices.

Galena occurs as inclusions in authigenic albite (Fig. 8d)and as blebs <5 μm across in nodular calcrete-hosted,xenomorphic pyrite aggregates. Galena blebs can also beobserved within Pb-poor outer zones of plumbiferouspyrite. Late galena veinlets cut plumbiferous pyrite.

The major argentiferous phase is idaite, containing asmuch as 11 wt.% Ag (Fig. 10, Table 1). Idaite presentsitself in tabular crystals and composite aggregates withchalcopyrite in interstices between detrital grains. Othersulphides that are associated with chalcopyrite, probablythrough replacement, are compositionally close to (Cu,Fe)6S5 and (Cu,Fe)7S5 (Table 1). There is a Cu-rich, Ag-

Fig. 8 Photomicrographs ofsulphide minerals in grey sand-stone. a Chalcopyrite (Cpy)overprints early pyrite (Py)—reflected light. b Irregular septalmottles of chalcopyrite (black)cementing detrital quartz—plane-polarised transmittedlight. c Veinlet chalcopyrite(Cpy) intergrown with pyrite(Py) and albite (Ab)—reflectedlight. d Galena (PbS, white)included within a grain ofauthigenic albite (Ab)—reflectedlight

Fig. 9 a High-gain BSE image of plumbiferous pyrite showing Pb-poor (dark grey) and Pb-rich (light grey) growth bands. Numbers referto electron microprobe analyses in b. b Plot of wt.% Fe vs. wt.% Pb ofmicroscopic domains located in a

Miner Deposita (2009) 44:285–301 295

bearing phase that is similar in composition to geerite, atthe margin of idaite. The idaite of Fig. 10 is surrounded bya narrow rim of argentiferous, geerite-like phase.

Carbonate minerals

Ferroan dolomite and calcite are the predominant carbon-ate minerals in barren grey sandstone. In these greysandstones, calcite is typically found as fracture infillswithin detrital quartz (Fig. 7a). Ankerite is preferentiallyassociated with disseminated chalcopyrite and occurs ininterstices of detrital grains. It corrodes detrital feldsparand quartz (Fig. 7b,c). Following Deer at al. (1992), theterm ankerite is applied to material with Mg/Fe ≤4(Table 2).

Bulk rock composition

Bulk rock chemical analyses are presented in Table 3.Significant positive correlations of Al vs. Ti (Spearman’srank correlation coefficient, rs=0.96), Al vs. Nb (rs=0.96)and Al vs. other elements (K, Li, Be, Sc, V, Rb, La, Ce, Yb,Hf and Th with rs>0.70) denote the composition of detritalaluminous components. Although the presence of authi-genic Ti oxide implies some relative Ti mobility during

diagenesis, the Al vs. Ti correlation suggests that Ti did notleave the system. Manganese and Ca show a positivecorrelation (rs=0.90), confirming that the bulk rockdistribution of Mn is controlled by carbonate minerals(Table 2).

Copper and Pb have assay values as much as 2.4% and3.6%, respectively, in some samples. Copper correlates with

Fig. 10 a Reflected-lightphotomicrograph of interstitialchalcopyrite (Cpy) and idaite.X-ray mapping for Cu (b), Fe(c) and Ag (d) in idaite

Fig. 11 Plot of wt.% Cu vs. Fe3+/Fe2+ ratio in bulk rock chemicalanalyses primarily from the Transfiguration deposit (Table 3)

296 Miner Deposita (2009) 44:285–301

Fe3+/Fe2+ (rs=0.68; cf. Fig. 11). The contact between thebasement and the overlying calcrete is typically the locus ofZn–Cd-bearing (about 1% Zn, 55 ppm Cd) barite veins(about 16% Ba, total). Silver and Re values reach up to226 ppm and 501 ppb, respectively. Gold abundances varyfrom 3 to 29 ppb. The contents of Au, Pt and Pd arecomparable with those from the cupriferous shale of thePolish Kupferschiefer (20 ppb Au, <5 ppb Pt, 4 ppb Pd), inwhich higher contents of Au, Pt and Pd occur in a Cu-poor,oxidised facies (Piestrzyński and Sawlowicz 1999).

Stable isotope geochemistry

Results for stable isotope analyses of carbonate aggregates,sulphide minerals and barite are given in Table 4. Dissem-inated and vein carbonates have δ13C values in the rangefrom −7.5‰ to −1.1‰ and δ18O values from 14.7‰ to21.3‰, whereas values for bulk rock calcrete calcite varyfrom −6.0‰ to −2.4‰ δ13C and from 17.5‰ to 18.3‰δ18O (Table 4, Fig. 12). Sulphur isotope ratios of sulphideconcentrates display a wide distribution, from −19.4‰ to25.1‰, which is apparently bimodal with modes at about−18‰ and 12‰ (Fig. 13). δ34S values for individualgrains have a similar distribution, between −20.8‰ and24.8‰. The highest δ34S value (25.1‰) for sulphide isclose to that of vein barite (26.2‰). δ34S values forplumbiferous pyrite fall between −20.8‰ and −17.9‰(Fig. 14a,b), again, similar to analyses of mineral concen-trates (δ34S=−15.9‰; Table 4; analysed by the SO2

technique). Concentrates of chalcopyrite intergrown withalbite (Fig. 8c), which hosts hydrocarbon-bearing fluidinclusions, have low δ34S values (−15.2‰ and −1.2‰),whereas MILES δ34S values for the veinlet shown inFig. 14c are 5.9‰ and 14.9‰ (Table 4).

Individual grains of calcrete-hosted pyrite have δ34Svalues varying from 5.9‰ to 23.2‰ (Fig. 14d,e; Table 4).This large range of values was also found for pyrite partlyreplaced and overgrown by chalcopyrite (Fig. 14f). Pyritegrains have δ34S values extending from 4.9‰ to 24.8‰(Table 4).

Discussion

Alpha fabrics indicative of desiccation and expansivegrowth by evaporation, such as exhibited by barite- andcalcite-filled fractures (Fig. 5a,b), commonly characterisegroundwater calcretes that form in semi-arid and arid areas(e.g. Wright and Tucker 1991; Nash and McLaren 2003).Such alpha fabrics occur in the nodular calcrete layer,which rests directly on the Taconian unconformity. Thenodular calcrete layer is, therefore, probably the result ofpalaeogroundwater seepage and ponding over the Taconianunconformity in an evaporative environment. The largerange in δ34S values for calcrete-hosted pyrite (5.9‰ to23.2‰; Figs. 13 and 14d,e) suggests that the nodule-forming environment acted as a closed system with respectto sulphate, such that the bacterially mediated S isotopecomposition of the later-formed pyrite produced a δ34S

Fig. 13 Histogram of δ34S values of sulphides and barite chiefly fromthe Transfiguration deposit (Table 4). Note the bimodal distribution(see text)

Fig. 12 δ13C vs. δ18O plot of vein and disseminated carbonates andcalcrete bulk rock (Table 4)

Miner Deposita (2009) 44:285–301 297

distribution distinctively skewed towards positive values(Ohmoto and Felder 1987; Machel et al. 1995). Bulk rockcalcrete calcite has δ13C values similar to those reported forphreatic calcrete hardpans, for example, in the Carbonifer-ous Maritimes Basin of eastern Canada (Jutras et al. 2007).An organic origin for the calcrete C is suggested by thelight C isotope composition of the calcrete calcite (Table 4),compatible with degradation of terrestrial organic matter(e.g. Irwin et al. 1977).

Whereas the calcrete nodules may represent a systemthat was closed to sulphate, the grey sandstone unit containsdisseminated early pyrite with S isotope compositionssuggestive of a system open to sulphate. The negativeδ34S values of the early-formed plumbiferous pyrite founddisseminated in grey sandstone are in a range typical foropen-system BSR (Marowsky 1969; Ohmoto and Felder1987; Lerouge et al. 2005; McGowan et al. 2006). Theexistence of Pb in pyrite (Fig. 9) is consistent with Pb

removal by sulphate-reducing bacteria in brines (e.g.Massadeh et al. 2005) and its subsequent incorporationinto pyrite. Reduction of the basal, calcrete-bearing bedsmust have occurred deep below the water table, after burialbelow the overlying red beds (Fig. 15a,b).

Disseminated and veinlet sulphides that post-datedearly pyrite exhibit a wide δ34S distribution, fromnegative to positive values (Fig. 13). The highest δ34Svalue for disseminated chalcopyrite (25.1‰) is similar tothat of vein barite (26.2‰), suggesting that TSR was atwork (e.g. Machel et al. 1995; Hoefs 1997; McGowanet al. 2006).

The bulk S isotope composition of chalcopyrite–albiteveinlets (−15.2‰ and −1.2‰ δ34S) distinctly differs fromthat obtained by the in situ technique (between 5.9‰ and14.9‰ δ34S). Such a difference may reasonably beexplained in at least two ways: (1) a difference in scale ofsampling, bulk sampling would obscure microscopic δ34S

Fig. 14 Reflected-lightphotomicrographs showing thelocation and δ34S values of insitu analyses of sulphide miner-als by laser-assisted fluorination(Table 4). Craters produced bylaser have sizes betweenapproximately 240 and 500 μmin diameter. Circles representlocations and approximate sizeof analytical domains. a Cratersin aggregates of plumbiferouspyrite (white) in grey pebblysandstone (dark grey). b Crystalof plumbiferous pyrite (Py) priorto analysis at the site indicatedin a. c Vein chalcopyrite (Cpy)and albite (Ab) in grey sand-stone. d, e Replacement pyrite(Py, white) in calcrete.f Chalcopyrite (Cpy)overprinting early pyrite (Py)in grey sandstone. Thismicroanalysis combined pyriteand chalcopyrite

298 Miner Deposita (2009) 44:285–301

variations (e.g. McKibben and Eldridge 1995; McConvilleet al. 2000); and (2) contamination by pyrite, which occursas sparsely distributed, fine-grained inclusions in the albite-associated chalcopyrite. Alternatively, and rather unlikely,the fO2 and pH of ore-forming fluids during sulphidedeposition varied in the different chalcopyrite–albite vein-lets sampled by the two methods (e.g. Ohmoto 1972).

Mineralisation was located in reduced units only,without any obvious connection with redox boundaries,rather than along the redox boundary between the red andthe grey sandstone units. Metal precipitation was, therefore,probably controlled by factors other than abrupt redox

changes, insofar as they can be inferred from the hostlithologies. In this respect, the occurrence of mineralised,barite-bearing fault veins at the basal contact with Cambro-Ordovician rocks is relevant because precipitation of highlysoluble Ba from Ba-rich solutions requires oxidation ofreduced S species to sulphate, or a mixing between areduced Ba-bearing solution and a sulphate-containingsolution (Blount 1977). Sulphide to sulphate oxidationneeds either to be balanced by reduction of anothercompound, the mineralogical evidence for which has notbeen found at the Transfiguration deposit, or to have anoxidising solution introduced into the system. If we acceptthe hypothesis that metals were leached by sulphate-bearing, oxidising groundwater from the overlying red-bedsequence (Brown 2003, 2005), then, by analogy with theLisbon Valley Cu deposit (Hitzman et al. 2005), acupriferous fluid could have been channelled downwardby normal faults to percolate laterally through the perme-able, reduced grey sandstone.

After deposition of the Robitaille and Sayabec for-mations, possibly during Ludlowian times (Fig. 15c),synsedimentary faulting related to the Salinic Disturbancetriggered the release of hydrocarbon-bearing fluids origi-nating from the Cambro-Ordovician basement into lower-most Silurian rocks (Kirkwood et al. 2001; Lavoie andMorin 2004). At the Transfiguration deposit, infiltration ofhydrocarbons is recorded by fluid inclusions in albiteintergrown with chalcopyrite in veinlets. The hydrocarbon-bearing fluid likely carried Ba and heavy S, whereas fluiddescending from the red sandstone unit was oxidising andcupriferous. Interaction between a red-bed-derived cuprif-erous solution and a hydrocarbon-bearing basinal fluid fromthe underlying Cambro-Ordovician rocks would accountfor: (1) replacement of pre-existing pyrite by isotopicallyheavier chalcopyrite (Figs. 8a and 14f); (2) precipitation ofsulphide by fluid mixing and redox reactions with Fe as aredox agent; and (3) the positive correlation between Cuand Fe3+/Fe2+ ratio (Fig. 11). A similar model of fluidmixing-induced sulphide precipitation and barite precipi-tation has recently been proposed for Konkola North,Zambian Copper Belt (Sutton and Maynard 2005).

Conclusions

The red-bed type Transfiguration Cu deposit formed inresponse to fluid mixing in the following stages: (1) basalnodular calcrete developed over the Taconian unconformi-ty; (2) early pyrite formed in the superjacent grey sandstoneby Pb-fixating BSR; (3) synsedimentary normal faultingtook place during the Salinic Disturbance, creating path-ways for both the descent of a sulphate-bearing, metallif-erous fluid from the red-bed unit and the ascent of a

Fig. 15 The model illustrates the formation of the Cu–Pb–Zn–Agmineralisation of the Transfiguration deposit. Arrows indicate fluidmigration paths. Suggested stages in the mineralising process include:a ponding of groundwater on the Cambro-Ordovician basement (C-O)and calcrete development with pyrite, formed by BSR, below thewater table. b Erosion of early calcrete and incorporation withinpolymict conglomerate, which evolved upward into poorly sorted greysands and red sands. Reddening of the latter occurred duringprolonged exposure to the vadose groundwater of an arid or semi-arid environment. c Faulting related to the Salinic Disturbancetriggered leakage of hydrocarbon-bearing fluid from the basement,concomitant with a downward influx of cupriferous groundwater fromthe overlying red beds. Sulphides, chiefly via TSR, were deposited byreaction with early (BSR) pyrite and by the mixing between areducing, hydrocarbon-bearing basement fluid and an oxidising,metalliferous groundwater

Miner Deposita (2009) 44:285–301 299

reducing fluid from the Cambro-Ordovician basement; and(4) the oxidising fluid reacted with pre-existing, diagenetic(BSR) pyrite and mixed with the reducing, Ba-containingfluid, resulting in the deposition of Cu, Pb and Znsulphides, as well as barite.

Acknowledgements This work was supported by a postdoctoralfellowship funded by the Diversification de l’Exploration Minérale auQuébec (Divex) research network. Ressources Appalaches, particular-ly Alain Hupé, and SOQUEM granted access to drill cores andinternal reports. Marc Choquette (Université Laval) diligently assistedus in use of the electron microprobe. Michel Malo (INRS-ETE) sharedhis geological knowledge of the Quebec Appalachians and madeavailable the map of Fig. 1. Karine Bédard integrated the geologicalinformation in a gOcad 3D model and constructed the geological mapof the deposit used in this paper. ARC acknowledges MiguelTupinambá for discussions. Thoughtful comments by Dave Lentzand an anonymous referee, together with a very perceptive review byPierre Jutras, greatly improved the manuscript. Bernd Lehmann isthanked for his careful editorial handling.

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