On Kalgoorlie (Australia), Timmins Porcupine (Canada), and factors in intense gold mineralisation

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1 Ore Geology Reviews 32 (2007) On Kalgoorlie (Australia), Timmins Porcupine (Canada), and factors in intense gold mineralisation Roger Bateman a, Frank P. Bierlein b, a 6/187 Bagot Rd, Subiaco, WA, 6008, Australia b Tectonics Special Research Centre and Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia Received 17 January 2006; accepted 8 August 2006 Available online 13 December 2006 Abstract The Golden Mile gold deposits of Kalgoorlie (Eastern Goldfields Province, Yilgarn craton, Australia: 46 Moz Au) and the gold deposits in the Timmins Porcupine camp (southern Abitibi Province, Superior craton, Canada: 63.7 Moz Au) are Earth's two biggest Archaean lode gold camps. While similarities at the camp scale are dominant, they differ in that the Golden Mile is a compact camp of one major deposit with two nearby, subordinate deposits separated by less than 10 km along strike, whereas Timmins Porcupine consists of a relatively large camp with 30 important mines distributed over 20 km strike length. Seismic data show a detachment fault at the base of the supracrustal rocks at Kalgoorlie at between 5 and 9 km, but none is identified in the Timmins Porcupine camp. Map-scale patterns, ages and lithologies are superficially similar. The gabbros in Kalgoorlie and conglomerates in Timmins Porcupine are distinctive rock types, but served similar competence contrast functions. Late-orogenic sediments are an important host at Timmins Porcupine for competence contrast reasons, but are apparently absent in the Golden Mile area. Gold deposit formation in both camps is of the same age ( 2.67 Ga), with a long duration of mineralisation. Porphyries, albitites and lamprophyres are characteristic features, but played no major genetic role. Both camps have early elements of mineralisation that have an epithermal character in Cu Au W V 3+ and fo 2, and both camps lie in belts locally characterised by the abundance of telluride minerals. However, none of these characteristics seem to be necessary or sufficient for intense gold mineralisation. Syn-mineralisation transpressive deformation in both camps involved the imbrication of thrust slices, followed by strike slip movement along a major crust-scale fault with a dilatational curve in its trend in the centre of both camps. The various deposits in each of the two camps were formed from immediately before to just after strike slip deformation, and opening of late-orogenic sedimentary basins. Both areas are characterised by an early episode of intense thrust faulting. Extensive, intersecting fracture arrays likely developed as thrusting gave way to strike slip faulting. These arrays may have enabled access to fertile source rock and also served as fluid conduits throughout deformation. Moreover, both terranes are characterised by a relatively short pre-mineralisation crustal history, thin(ned) subcontinental lithospheric mantle, and input of juvenile, mantle-derived material. The pre-mineralisation crustal history and evolution of the host terranes thus may have been the most important single factor in the formation of giant orogenic gold deposits at Kalgoorlie and Timmins Porcupine Elsevier B.V. All rights reserved. Keywords: Thrusting; Transpression; Kalgoorlie; Timmins; Abitibi; Yilgarn; Gold Corresponding author. Tel.: ; fax: address: fbierlein@tsrc.uwa.edu.au (F.P. Bierlein) /$ - see front matter 2006 Elsevier B.V. All rights reserved. doi: /j.oregeorev

2 188 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Introduction The two outstanding orogenic lode gold camps in Earth's Archaean greenstone belts are Kalgoorlie and Timmins Porcupine (Witwatersrand excluded). The relatively compact Kalgoorlie deposits, having produced 46 million ounces of gold (Moz Au) to date, consist of one major deposit (the Fimiston lodes) with two nearby subordinate deposits (Mt Charlotte, Mt Percy) spread over less than 10 km of strike in the Eastern Goldfields Province (Yilgarn craton, Western Australia). In contrast, the approximately 30 deposits (63.7 Moz Au) in the Timmins Porcupine camp (southern Abitibi Province, Superior craton, Ontario) are dispersed over more than 20 km of strike. These two exceptionally well-endowed gold camps lie within intensely mineralised provinces that contain a significant number of other camps and deposits that are very similar in many respects, particularly in structures and lithologies at the sub-regional scale. However, the Kalgoorlie and Timmins Porcupine camps are unique within their respective greenstone belts not only in scale but also in their diversity of geological style, relative timing of mineralisation, metal suites, geochemical associations, styles of vein formation, and in details of deformation, faults and folds. The unique nature of these two camps inevitably prompts a set of questions: Why are the Eastern Goldfields and southern Abitibi greenstone granite provinces so enriched at the scale of a thousand kilometres? What is it about the Kalgoorlie and Timmins Porcupine camps, on the scale of tens of kilometres, that made them so well endowed? What factors account for the longevity of mineralisation in these two camps (Bateman et al., 2001b, 2005)? Is the longevity of gold deposit formation in these two camps sufficient to explain their extraordinary size? Were the processes operating in these two camps nearunique among Archaean camps, or common processes merely operating over a longer period of time than elsewhere, and/or more intensely? In the latter case, why did these processes operate for so long? And what can these camps tell us about giant orogenic gold deposition processes? Via a comparison of potentially necessary or sufficient parameters that operate at a range of scales, and assessment of the importance of each of these parameters, this study attempts to shed light on some of the above questions. A resolution of these issues ultimately leads to tools and methodologies for use in the search for concealed deposits and camps of this magnitude in other, more data-deficient, Archaean greenstone belts of the world. The present work does not repeat all the data and ideas on the geology and mineralisation of these camps that are readily available elsewhere (Bateman et al., 2001b, 2005). Seismic data are also published in greater detail elsewhere (Owen et al., 2001; Goleby et al., 2002; Snyder et al., in preparation). These principal sources also present extensive reference lists to other work and ideas relating to these two camps. 2. Geological nature of the two camps and provinces The Abitibi Subprovince, which includes the Timmins gold camp, is composed of nine chronostratigraphic assemblages (Ayer et al., 2002b, 2005), ranging in age from 2750 Ma to 2665 Ma. The seven oldest consist of various combinations of ultramafic and mafic volcanic rocks, felsic volcanic and volcaniclastic rocks, and BIF, whereas the two youngest assemblages are sedimentary units. Unconformities or disconformities separate these assemblages. A comparable, yet not identical sequence is recognised in the Kalgoorlie camp, Eastern Goldfields: the Kambalda (from 2715 Ma), Spargoville ( Ma), Kalgoorlie ( Ma), and Kurrawang sequences (b 2655 Ma) (Krapez et al., 2000). In the Eastern Goldfields, no substrate to the Kambalda Sequence is recognised. However, zircon xenocrysts record pre-existing rocks as old as 3570 Ma down to 2730 Ma (Krapez et al., 2000), hinting that the Abitibi assemblage concept may be applicable in the Eastern Goldfields to older rocks. A great deal of details of the geology are discussed below, as part of the comparison and contrast of these two camps, and will not also be given under this heading. Full details of recent data and interpretations, and sources of earlier data and ideas, are given elsewhere (Piroschco and Kettles, 1991; Burrows et al., 1993; Phillips et al., 1996; Owen et al., 2001; Bateman and Hagemann, 2004; Bateman et al., 2005; Snyder et al., in preparation). Geological maps of the two camps show great similarities (Fig. 1), and this is the most obvious basis for drawing a comparison between the two camps. Development of stratigraphic sequences (Table 1) in the two areas commenced at much the same time ( 2705 Ma). In Kalgoorlie, subsequent volcanism, sedimentation and intrusion were spread over 65 million years, whereas in Timmins Porcupine it occurred over 35 million years, in both cases culminating with the intrusion of lamprophyres and albitites, respectively, and final Archaean deformation (Table 1 and Fig. 2). In both areas, early extensional deformation was followed by thrusting and shortening, and transpression (Swager, 1997). The transpressive deformation in both areas consisted of regional folding, shortening and foliation development together with regional-scale left lateral strike slip faulting along the most important

3 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Fig. 1. Geological maps, at the same scale, of (A) Timmins Porcupine gold camp in the Abitibi Province of Ontario; and (B) the Kalgoorlie gold camp in the Eastern Goldfields of Western Australia. Red dots in inset maps show locations within Ontario and Western Australia, respectively.

4 Table 1 Summary tabulation of stratigraphy, lithology, geochronology, gold mineralisation and deformation in the Kalgoorlie and Timmins Porcupine gold camps (Campbell and Hill, 1988; Claoue-Long et al., 1988; Kent and McDougall, 1995; Nelson, 1997; Woods, 1997; Yeats et al., 1999; Krapez et al., 2000; Bateman et al., 2001a; Ayer et al., 2002a, 2005; Bateman et al., 2005; McNaughton et al., 2005) 190 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007)

5 Rows with dashed lower lines mark correlatable events: otherwise, no precise equivalence between entries on the same line for the two camps should be assumed. R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007)

6 192 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Fig. 2. Schematic chronostratigraphic sequence for the Kalgoorlie gold camp and the Timmins Porcupine gold camp, as per the data summarised in Table 1. shear zones of the provinces. These linear shear zones in both provinces can be traced laterally for hundreds of kilometres, and have been controlling structures in gold mineralisation. In Kalgoorlie this incorporated antithetic D3 D4 right-lateral faulting. In Timmins Porcupine en-echelon synthetic left lateral movement and D3 folding was followed by D4 right-lateral strike slip movement and D5 intense constrictional or prolate strain. Localised igneous activity (Mikucki and Robert, 2003; Thompson, 2004) has generated biotite-bearing contact metamorphic aureoles. Regional metamorphic grade in both areas is greenschist facies, with local transition to biotite grade present as results of alteration associated with gold mineralisation. Gold mineralisation styles in the two camps are distinct. Syn-D1 Fimiston-style mineralisation at Kalgoorlie is characterised by breccia lodes and open-cavity infill in fracture networks with pyrite gold telluride mineralisation, and ankerite sericite alteration (Gauthier et al., 2004). The syn-d2 Oroya shoot within the Golden Mile deposits comprises microbrecciation and green leader with vanadium-rich green mica and other vanadium-bearing minerals (e.g. roscoelite, nolanite) in a single 1500-m-long ore shoot. In contrast, the syn-d4 Mt Charlotte deposit consists of sheeted quartz veins formed in a oblique-slip fault system, and is similar to other syn-d4 tectonic quartz vein-style mineralisation that characterises much of the Eastern Goldfields Province. Over 90% of Kalgoorlie gold occurs in Fimiston lodes. These lodes cannot be dated relative to Kurrawang Merougil late-tectonic sedimentation because there is none within the Golden Mile, but compilation of absolute and relative dates (Bateman and Hagemann, 2004) shows the that mineralisation began before the onset of these syn-d3 sediments and continued after their deposition (Table 1 and Fig. 2). Gold deposition in the Timmins Porcupine camp also spanned a long period of time, commencing with ankerite veining formed prior to Timiskaming

7 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) sedimentation (prior to 2674 Ma). Cu Au Ag Mo porphyry-style mineralisation in the McIntyre deposit postdated Timiskaming sedimentation, as shown by the fact that this mineralisation postdates albitite dykes that intruded Timiskaming assemblage sedimentary rocks. However, only about 20% of the total gold at Timmins was produced from McIntyre (Robert, 2004). The bulk of Timmins Porcupine gold mineralisation is younger than 2674 Ma, and consists largely of vein arrays formed in an oblique-shortening environment, evolving through ankerite quartz+tourmaline quartz veins in the Hollinger mine. Molybdenite has been dated at the Dome mine (2672±7 Ma) and McIntyre mine (2670±10 Ma) by the Re Os radiometric method (Bateman et al., 2005). The D4 mineralisation at Pamour has been dated at around 2660 Ma (Ayer et al., 2005) byu Pb on deformed and undeformed rock units. Youngest deposits include Pamour, which consists of extensional vein arrays formed during local reverse faulting that was part of the overall D4 transpressive left-lateral strike slip movement (Aitken, 1990). Albite alteration was intense, whereas sericite was subordinate. Several such deposits (Broulan, Hoyle, Hallnor, Buffalo Ankerite, Aunor) occur within Timiskaming assemblage rocks, and comprise a significant gold resource in excess of 20 Moz Au (Ontario Ministry of Northern Development and Mines, 2005). In summary, Kalgoorlie is a compact camp of less than 10 km strike extent, with few yet large deposits, and with the great bulk of the gold deposited early in its history. Timmins consists of around 30 deposits over 30 km of strike, with early ankerite veins contributing relatively little gold, and the bulk of the gold being deposited in D3 and D4, the later stages of orogenesis. Both camps had an early phase (with variable gold content) that had a strong epizonal character (Bateman and Hagemann, 2004), relatively oxidising fluids with high Te contents and breccia and open-cavity textures at Kalgoorlie, and a Cu Au Ag Mo association at the McIntyre mine. Both camps have a protracted history that resulted in mineralisation styles of diverse character. 3. Assessment of the role of some of the important features of Kalgoorlie and Timmins Porcupine In this section, a number of facets of these two deposits are examined that have been described (Phillips et al., 1996) as being potentially important in the generation of both camps. In each subsection, these criteria will be evaluated in terms of whether they are necessary and/or sufficient for the formation of deposits containing more than 50 Moz of gold Gold mineralisation and progress of crustal evolution Both camps occur within the upper portion of the volcanic sedimentary assemblages in their respective cratons (Myers, 1995; Ayer et al., 2002b), at the culmination of a history of crustal generation and growth in the late Archaean (Condie, 2000). In the Abitibi Province, the youngest assemblages are the two sedimentary assemblages, and major orogenic gold concentrations are nowhere far from these rocks. In the Yilgarn craton, the precision of the geochronological database is not yet adequate to subdivide the rocks into chronostratigraphic assemblages as in the Abitibi Province, but the Kalgoorlie greenstone belt is evidently among the youngest of greenstones in the craton (Nelson, 1997). Komatiites in the Kalgoorlie and the Timmins Porcupine camps are mostly of the Al-undepleted type (Bateman et al., 2001a; Sproule et al., 2002). This composition probably represents a diminishing involvement of garnet (through processes such as decreasing depth of magma generation, increasing fraction of shallow-generated magmas) in a plume ascending through time in both areas. Orogenesis and final basin infill was also accompanied by extraordinary gold deposition in both camps and both terranes. This localisation of gold in assemblages and structures formed at the end of late Archaean crustal growth cannot be interpreted in simple terms. The development of plate tectonic processes in the Late Archaean is likely to have been a significant factor in the appearance of Earth's first giant orogenic gold deposits at that time. As plumedominated tectonics of the Early to Mid-Archaean gave way to accretion subduction processes, shear zones with a non-linear geometry that would have resulted from the plume-driven tectonics were supplanted by deep-seated andlinearfracturesystems(groves et al., 2005; Bierlein et al., 2006). These linear shear zones, in turn, were able to provide the means for the efficient transport, and focusing, of ore-bearing fluids (Eisenlohr et al., 1989; Neumayr et al., 2000; Groves et al., 2005). In addition, source rocks of this age may have been generated with a gold fertility that had not previously been attained, perhaps through the evolution of mantle plumes and subcontinental lithospheric mantle, as evidenced by changing komatiite chemistry and petrogenesis (Bateman et al., 2001a). The exact formation age of the host rocks within this late Archaean episode of crustal formation appears to be relatively unimportant: the Tisdale assemblage was formed during this period of crustal growth, whereas

8 194 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) the youngest mafic volcanic assemblage, the Blake River assemblage, is not well mineralised. The Blake River assemblage is extensively exposed in the zone between the Porcupine Destor and Cadillac Larder Lake Shear Zones, where only minor concentrations of gold have been found (Ayer et al., 2005). In contrast, it is apparent that gold in both camps was primarily deposited along second-order structures adjacent to long-lived first-order structures that remained active during late cratonising deformation (Eisenlohr et al., 1989; Neumayr et al., 2000; Goldfarb et al., 2001), such as the Boulder Lefroy Fault and Zuleika Shear Zone in the Eastern Goldfields, and Porcupine Destor and Cadillac Larder Lake Shear Zones in the Abitibi Province. Thus, orogenesis late during crustal growth was not necessarily a period of exceptional gold availability, but it was a period when the gold that was available was being taken up in solution, focussed into conduits, and deposited within small volumes of rock to form economic concentrations of metals. These foci were actively deforming at greenschist facies grade while gold solubility greatly declined with decreasing pressure and rapid changes in fo 2,pH and f S(Reed, 1997; Mikucki, 1998). During protracted periods of deformation, fluid conduits and veins were repeatedly opened to allow fluid transport and metal deposition. Proximity to second-order faults is a broadly necessary condition for major gold deposits, but it is clearly not sufficient. Proximity to first-order structures is a necessary condition for the late sedimentary basins: basins and gold deposits are both dependent on these structural corridors Camp and regional stratigraphic column The stratigraphic columns for the two camps are summarised in Table 1 and shown in Fig. 2. Both camps are hosted within Archaean greenstone belts wherein tholeiitic basalts overlie early komatiite flows. Basalts in Kalgoorlie yielded U Pb ages of 2708±8 Ma (Nelson, 1997), and at Timmins mafic volcanic rocks have been dated by the same method at 2703 Ma (Ayer et al., 2002b). While the Kalgoorlie basalts show some crustal contamination (Bateman et al., 2001a), the Tisdale assemblage basalts in Timmins are nearly pristine mantle-derived magmas with only local contamination (Smith et al., 1987; Sproule et al., 2002; Ayer et al., 2005). The Kalgoorlie area is characterised by a number of thick and laterally extensive tholeiitic gabbro and peridotite sills (Table 1), whereas no significant sill is known in the Timmins area. Tholeiitic rocks are a typical component of the bigger Archaean gold camps (Robert et al., 2005). Overlying the Kalgoorlie mafic volcanic rocks are medium- to coarse-grained volcaniclastic rocks of the Spargoville formation ( 2690 Ma) and Black Flag Beds, dated at Ma (Nelson, 1997; Krapez et al., 2000). In Timmins, felsic volcaniclastic rocks of the Krist formation are overlain by fine- to medium-grained turbiditic sedimentary rocks, and these together constitute the Porcupine assemblage, dated at Ma (Ayer et al., 2005). There is an angular unconformity at the base of these sequences in each camp (Krapez et al., 2000; Ayer et al., 2005). In neither camp are these units a significant host to gold, although these rocks do host gold elsewhere in the Eastern Goldfields. In both camps, the volcaniclastic rocks are the same age and composition as coeval, yet volumetrically minor, calc alkaline quartz feldspar porphyry dykes. Lamprophyres constitute a very minor and slightly younger intrusive suite, dated by U Pb at 2642 Ma in Kalgoorlie (McNaughton et al., 2005), and at 2675 Ma in Timmins (Ayer et al., 2005). Other than these two dyke phases, no major plutonism has been recognised in the immediate vicinity of either camp. Overlying the Porcupine assemblage in Timmins is the Timiskaming assemblage consisting of conglomerates and sandstones of alluvial fan, fluvial and deltaic origin, and dated at Ma (Ayer et al., 2005). These deposits are a major exploration target in Timmins, as they are a common host-rock to ore in the area. Similar rocks are known from the Eastern Goldfields dated at b2655 Ma (Krapez et al., 2000), in the Kurrawang syncline northwest of Kalgoorlie (host to the b10,000 oz Au Kurrawang gold deposit) and in the Merougil beds south of Kalgoorlie (no known gold), but none are known near Kalgoorlie. In both areas, the late tectonic sediments form elongate basins immediately adjacent to the largest shear zones of the greenstone belts, and are the last suite of Archaean rocks to have formed. In neither case can it be said whether these rocks are the erosional remnants of much more extensive basins, or not. Thus, the two camps have very similar stratigraphic columns, and very similar ages. Elsewhere in both provinces, the same stratigraphies host important gold deposits and camps that do not attain the scale of Kalgoorlie or Timmins Porcupine. The major difference in the columns of the two camps resides in very important host rocks for these camps layered gabbro sills, and late orogenic sediments absent in Kalgoorlie and present in Timmins Porcupine and are discussed in detail below. No aspect of the stratigraphic columns can be considered necessary and sufficient for the formation of these gold camps.

9 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Ultramafic rocks A common feature of most productive belts is the presence of ultramafic komatiite lavas (Groves et al., 2005), and Al-undepleted type (Bateman et al., 2001a; Sproule et al., 2002) komatiitic lavas are present in the lower parts of stratigraphic sections at both Kalgoorlie and Timmins. Ultramafic lavas are known from some of the other Abitibi assemblages, yet not all ultramaficbearing assemblages have important gold deposits. In both the Kalgoorlie and Timmins Porcupine gold camps, intrusive peridotite sills are minor constituents in the stratigraphic column, although not common hosts to mineralisation. The Norseman Wiluna belt is distinguished by the abundance of ultramafic rocks. The reasons for this are not clear: the komatiitic rocks may serve as a direct source of gold or as an intermediate step in a multi-stage enrichment process (Bierlein et al., 2006). They may have a rheological function, such as the quartz feldspar dykes within less competent komatiites at Mt Percy near Kalgoorlie (Johnston et al., 1990). In Timmins, the Delnite Aunor Buffalo Ankerite deposits occur in relatively competent basalts intercalated with komatiitic rocks (Pressacco, 1999). A suggestion of a more direct role for ultramafic rocks comes from PGE data from the Williamstown layered peridotite, 5 km north of the Fimiston gold lodes. When normalised to chondrite, these rocks are depleted in gold relative to Pt and Pd, in contrast to the Golden Mile gabbro (Bateman et al., 2001a). Since these peridotites are in close proximity to a major deposit, the possibility is that they were a source of at least some gold. In summary, the presence of komatiites was possibly a broadly necessary yet not a sufficient factor in gold mineralisation Layered gabbros Layered gabbro sills are distinctive of Kalgoorlie, but notably absent within the Timmins Porcupine camp. The Golden Mile tholeiitic gabbro sill (Bateman et al., 2001a) played an important role in mineralisation in that the granophyric Unit 8 represents a strong rheological contrast with adjacent chlorite-rich units, and this rheology contrast was key to Mt Charlotte-style gold mineralisation (Clark, 1980). High Fe contents or Fe/Mg ratios have also been implicated (Groves and Phillips, 1987). On the other hand, Unit 7 of the Golden Mile gabbro at Mt Charlotte is the most iron-rich unit in this deposit, yet contains only minor mineralisation. The important factor for gold grades at Mt Charlotte is quartz content of the host rock units (Bateman et al., 2001a). In the geochemical evolution of fractionating tholeiitic magmas, quartz content reaches a maximum around the stage where Fe contents and Fe/Mg ratios also reach their maximum. In the Abitibi Province, there are a number of gabbro sills that are similar in composition and in age to the tholeiitic basalts of the Tisdale assemblage (Ayer et al., 2005). The Hollinger Au-quartz vein system is concentrated in basalt flows distinctive for their pillows, variolites and interflow sediments, and these features probably provided the same rheological contrast (Burrows et al., 1993). Thus, a rheological contrast between host rocks is a very important factor in gold mineralisation, but many rock types can supply this contrast. Fractionated gabbros serve this purpose very well, albeit not exclusively well. The absence of such gabbro sills in the immediate vicinity of the deposits in the Timmins Porcupine camp was no impediment to mineralisation, implying that gabbro sills were neither necessary nor sufficient factors in mineralisation Porphyries, albitites, lamprophyres In Kalgoorlie, the dykes and Fimiston gold were likely introduced very close in time (Bateman and Hagemann, 2004), and some hornblende porphyry dykes were interpreted as post-dating the Fimiston lodes (Gauthier et al., 2004). The dykes are extremely small in volume, and it is very difficult to make a case that there is any genetic relationship. No major plutonic body is known for tens of kilometres laterally, and none are identified at depth in seismic or gravity data. In Timmins Porcupine (Bateman et al., 2005), the quartz albite porphyry dykes provide relative and absolute age constraints on mineralisation: the younger albitite dykes are exceedingly rare, they are mineralised, and are at least million years younger than the porphyry dykes. Lamprophyres are also present in small volumes in each camp, but differ significantly in absolute age (McNaughton et al., 2005; Ayer et al., 2005), but possibly not so much in their ages relative to other components of the local stratigraphy, since geochronology in the Eastern Goldfields Province indicates that lamprophyres postdate the Kurrawang Merougil sedimentary rocks (McNaughton et al., 2001). In both camps, the lamprophyres and albitites are altered and predate the latest phases of mineralisation. The volumetrically very minor porphyry and other dykes had no genetic role (Mason and Melnik, 1986; Ayer et al., 2005) and cannot account for the size of the Kalgoorlie and Timmins Porcupine gold deposits. While there is a distinctive epizonal character in both Fimiston Oroya in Kalgoorlie (Te f O 2 V 3+ ) and

10 196 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) McIntyre (Cu Au Ag Mo) in Timmins, there is no important igneous body identified in either camp to which this epithermal character can be attributed. Aside from providing the rheological contrast that many rocks can provide, the porphyry and other dykes were neither necessary nor sufficient factors in mineralisation Cu Au Ag Mo Te W V high fo 2 alteration and mineralisation Both of these camps show a distinctive alteration geochemistry. In Kalgoorlie, 30% of early Fimiston gold (locally 80%) resides in calaverite (AuTe 2 ), petzite (Ag 3 AuTe 2 ), with coloradoite (HgTe) and altaite (PbTe) also present. Hematite, magnetite, sulphates and V minerals such as roscoelitic mica are also present, and these minerals imply a relatively oxidising fluid when compared to ore-bearing fluids in orogenic gold systems elsewhere (Bateman et al., 2001b). Sulphur isotope compositions of pyrite from laser ablation micro-analysis show a very large range, from 10 to δ 34 S, which has been interpreted to be the result of fluid mixing and phase separation (Hagemann et al., 1999). Temperatures of ore formation are estimated at b 350 C for Fimiston and Oroya (Bateman and Hagemann, 2004). The δ 18 O fluid composition has been estimated at 6.5± 2.0 (Golding et al., 1988) interpreted by these authors as indicating a metamorphic fluid source. Radiogenic crustal Os isotope compositions of pyrite (Lambert et al., 1998) suggest a crustal origin for Os. According to these authors, Au behaves geochemically similar to the PGEs as a group, and therefore, may also be crustal in origin in the Kalgoorlie deposits. Deposits and mines in the Norseman Wiluna belt commonly contain trace amounts of tellurides (Hagemann and Cassidy, 2001) in such deposits as Norseman, Victory Revenge, and Mt Mulgine (W, Mo, Cu; Oliver, 2005), Bronzewing and Jundee Nimary (Te minerals), Fig. 3. (A) Simplified geological map of the Timmins area (Abitibi Province) showing location of seismic reflection profiles shown in B and C (modified from Snyder et al., in preparation). (B) Seismic reflection interpretations (this study) of the Crawchest section. (C) Seismic reflection interpretations (this study) of the Shillington section. Thrust and extension deformation are interpreted; assemblages crossed by the profiles are indicated. Note that there is no obvious detachment fault at the base of the supracrustal sequence, as there is in sections from the Yilgarn craton (e.g., Goleby et al., 1993). Also note different vertical scales for the two interpreted sections.

11 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Agnew Lawlers, Tarmoola and Sunrise Cleo (Te minerals, molybdenite; Brown et al., 2002). Tower Hill, which was interpreted by Witt (2001) as having formed structurally early in the Sons of Gwalia area, contains Mo and Bi minerals but no tellurides. Traces of tellurides (not Au-bearing) occur in D2 microveins at Kanowna Belle (Davis et al., 2000). The Karonie deposit in the eastern Yilgarn craton also contains a suite of tellurides (Pigott and Green, 1990). In contrast, the Bardoc Tectonic Zone, north of Kalgoorlie, is devoid of tellurides (Morey et al., 2005). At Cleo (Brown et al., 2002) and Mt Mulgine (Oliver, 2005), early gold styles were overprinted by orogenic gold. Elsewhere in the Yilgarn craton, the intrusion-related Boddington deposit (south-western Yilgarn craton) contains minor Ag Bi tellurides (Symons et al., 1990; Allibone et al., 1998; McCuaig et al., 2003). In the Ma Southern Cross Province west of the Eastern Goldfields, the Nevoria amphibolite-grade gold deposit hosted in Archaean iron formation contains a suite of Bi tellurides (Mueller, 1997). In the Timmins Porcupine camp, Dome contains altaite, melonite (NiTe), hessite (Ag 2 Te) (Couture et al., 1994; Couture and Robert, 1997; Robert and Poulsen, 1997). The Cu Au Ag Mo deposit at McIntyre is classically regarded as porphyry-style ore (Mason and Melnik, 1986), and contains minor hematite, anhydrite, petzite and hessite. It predates main-stage Au-quartz in Hollinger (Timmins). Sulphur isotope compositions for Hollinger McIntyre, from bulk samples, show a narrow range from 0.7 to +7.0 δ 34 S, with a peak at +3.0± 1.3 (Wood et al., 1986). These authors also reported ore-forming fluid temperatures at Hollinger McIntyre of b305 C. δ 18 O fluid composition of 4.7±0.5 were interpreted to indicate an oxidising magmatic fluid source (Wood et al., 1986). Elsewhere in the Abitibi, Hemlo has high contents of molybdenite, altaite, melonite, coloradoite, and V 3+ roscoelitic mica (Tomkins et al., 2004). The Macassa mine in Kirkland Lake (post 2677 Ma) contains altaite, calaverite, molybdenite, hematite and sulphates (Robert and Poulsen, 1997). Bousquet and Doyon contain hematite alteration and a Au Cu Te association, and are likely early-formed deposits with a VHMS-style origin (Dubé et al., 2003). Horne is an auriferous VHMS deposit in 2700 Ma host rocks with Te and synvolcanic gold (Robert and Poulsen, 1997). The deformed Campbell A.W. White deposit (Au Ag+ Mo, Cu, W) predates a 2714 Ma dyke (Robert and Poulsen, 1997). Malartic has a Au Cu Te W association and biotite K feldspar hematite alteration, and porphyry-type model has been put forward (Robert and Poulsen, 1997). Throughout these two highly mineralised provinces, there are diverse Te mineral suites, diverse timings of mineralisation where some deposits have components with a relatively early age, and some deposits have a VHMSstyle Au metal-alteration character. A diverse metal association is commonly found in the larger Archaean gold camps (Robert et al., 2005). The Au Te± Mo ± Cu association is not restricted to major deposits or to the bestmineralised greenstone belts, and so cannot represent a unique guide to major orogenic gold mineralisation. However, there appears to be a tendency for deposits with an epizonal component to begin formation relatively early in the history of mineralisation, and perhaps this early input promotes the subsequent formation of a major deposit. A diversity of fluid sources, some epizonal, is a broad necessity for formation of the largest gold camps Timings and durations of mineralisation phases One very apparent feature of both the Kalgoorlie and Timmins Porcupine camps is that their formation spans a relatively long period of time, perhaps 40 million years (Bateman and Hagemann, 2004; Bateman et al., 2005). However, these two camps differ in several aspects regarding their temporal evolution: the bulk of gold was deposited in Kalgoorlie in the early stages of mineralisation before strike slip movement, whereas in Timmins Porcupine most of the gold was relatively late, deposited during strike slip. In each province, there is a range in relative age for other deposits (Davis et al., 2000; Witt, 2001; Bateman and Hagemann, 2004; Bateman et al., 2005). Kalgoorlie and Timmins Porcupine appear to be unique in the time span of their gold mineralisation. Clearly, one way to generate an exceptionally large deposit is to have efficient gold-deposition processes operating over an exceptionally long period of time. Earth's larger gold camps are generally characterised by multiple styles of mineralisation with multiple timings for the ore and deposit types (Robert et al., 2005). A variant view is that the factors that gave rise to this long duration of mineralisation may also be responsible for making available an exceptionally large quantity of gold, or of fluid capable of picking up and depositing such large quantities of gold. Therefore, long duration of mineralisation is a broad necessity for formation of the largest gold camps The 3D nature of mineralised shear zones in seismic reflection profiles Major, laterally continuous shear zones are very closely related to both of these very big gold camps: the

12 198 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Boulder Lefroy Fault in Kalgoorlie, and the Porcupine Destor Shear Zone in Timmins. Seismic reflection profiles in the northern Yilgarn craton (Goleby et al., 2002, 2004) indicate that shear zones which penetrate the entire crust, such as the Laverton and Keith Kilkenny shear zones, are commonly spatially related to major gold camps. Closer to Kalgoorlie, the picture appears different (Swager et al., 1997; Goleby et al., 2000). The first-order Ida Fault Shear Zone penetrates through the upper and middle crust, and is anomalously low in gold. The first-order Boorara Shear Zone is also equally low in gold-bearing structures, but is offset along the regional-scale detachment fault at the base of the supracrustal volcanic sedimentary sequences, above the middle crust at a depth of 5 10 km. Pre-D2 extensional opening of Kurrawang-style late-orogenic basins took place along this detachment (Swager et al., 1997). The Boulder Lefroy Fault, above which the Kalgoorlie camp lies, is not crustal-scale, and instead is listric at the base of the supracrustal rocks and merges with this detachment fault. The Zuleika Shear Zone is an important gold-bearing structure, and it, too, is listric at a relatively shallow depth. Recent seismic profiling work in the Timmins Porcupine area (Snyder et al., in preparation) has provided new information on the structure of the middle upper crust in the vicinity of gold deposits in this region. No basal detachment fault is as clearly apparent (Fig. 3) inthe Abitibi (Calvert and Ludden, 1999) as in the Eastern Goldfields. The Porcupine Destor Shear Zone may be listric and appears to flatten out at depth, but the data do not allow for definite identification of this fault below a depth of 5 km (Fig. 3). In Lithoprobe data (Calvert and Ludden, 1999), both the Porcupine Destor and Cadillac Larder Lake Shear Zones are shown as upper-crust-scale faults, whereas first-order, crust-penetrating shear zones do not appear to be gold-enriched. Good knowledge of the vertical geometry of major shear zones related to gold mineralisation is the weakest part of our overall understanding of gold mineralisation. The depth extent of gold-related shear zones is likely to be important. If there were a consistent pattern (e.g. if all gold-bearing shears were listric at the base of the supracrustal sequence), then this may indicate the crustal level essential fluid constituents are sourced from either the gold or other components that assist in the sequestration and transport of the gold. However, major shears zones that are listric at relatively shallow depths are not characteristic of all important gold camps, and crustalscale shear zones can be associated with both goldbearing and gold-barren belts. The Rice Lake Pickle Lake gold belt (Superior Province, Uchi Subprovince, including Red Lake mine) is not evidently associated with any major, continuous shear zone (Robert et al., 2005). Crust-penetrating shears are generally given a major role in forming crust-scale fluid circulation paths in major gold provinces. However, the major shear zones adjacent to the Kalgoorlie and Timmins Porcupine camps (the Boulder Lefroy Fault and the Porcupine Destor Shear Zone) are upper-crust-scale deformation zones. Crustal-scale shear zones therefore are deemed not necessary for the biggest gold camps, nor are they sufficient factors Late-orogenic conglomerates and turbidites Conglomerate sandstone turbidite deposits unconformably overlie both the volcanic sequences and the Black Flag (in Kalgoorlie) and Porcupine (in Timmins Porcupine) sedimentary rocks. In the Eastern Goldfields, the Kurrawang and Merougil beds are younger than 2655 Ma (Krapez et al., 2000). In Timmins Porcupine, the Timiskaming assemblage is younger than Ma (Ayer et al., 2005). No sedimentary rocks of the Kurrawang age group are known at Kalgoorlie, although it is possible that they have been misidentified as Black Flag Beds (drill core is generally the only source of reliable data over large areas). The Merougil Beds may have formerly extended as far north along the Boulder Lefroy Fault as Kalgoorlie, prior to erosion. The bulk of Kalgoorlie gold in Fimiston lodes are crosscut by D2 faults (Bateman and Hagemann, 2004) and hence predate Merougil Kurrawang sedimentation. Mt Charlotte at Kalgoorlie is a major deposit similar in timing to many Eastern Goldfields Province gold deposits (Groves et al., 1995), and postdated Kurrawang and Merougil sedimentation. Wallaby near Laverton (Salier et al., 2004) and the Kurrawang deposit at Kundana (northwest of Kalgoorlie) in the Eastern Goldfields Province occur within these lateorogenic sedimentary basins. Thus, gold deposition at Kalgoorlie spanned the formation of late-tectonic basins. Similarly, relatively minor gold in ankerite veins at Timmins Porcupine predated Timiskaming assemblage deposition (Bateman et al., 2005). Hollinger mine gold postdated albitite dykes, and hence postdated Timiskaming sediments. Deposits such as Pamour (Aitken, 1990) and parts of Dome (Pressacco, 1999) are hosted in Timiskaming assemblage rocks, and contain approximately 15% of all gold in Timmins Porcupine. The function played by the sedimentary rocks at a local scale is rather unclear, although competence contrast between conglomerate, the major host to gold (Aitken, 1990), and other more argillaceous rock types is likely at Pamour. There is a common occurrence of this sedimentary rock-over-volcanic rock unconformity in major camps (Robert et al., 2005). It may be that younger deposits

13 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Fig. 4. Schematic block diagram to illustrate the geometries of fractures and conduits generated during transpressive orogenesis, with fracture arrays induced by both thrust (A) and strike slip (B) movement. hosted in 2705 Ma basalts in both Kalgoorlie and Timmins Porcupine formed immediately below the unconformity. Low permeability rocks may have served as a seal, maintaining fluid pressure below (e.g., at Kanowna Belle; Trofimovs et al., 2006). In the Yilgarn craton of Western Australia, both the original and even the current extent of these sediments may be underestimated, and hence the potential for these deposits has been inadequately explored. At a more regional scale, extensional deformation appears to be an important factor (e.g., Davis and Maidens, 2003). Mineralisation spanned extension in both camps, although with variable proportions of the gold predating basin opening. In both the Eastern Goldfields and the Abitibi Province, gold camps are strung along the major shear zones that are related to lateorogenic (Timiskaming-style) sedimentary basins. These basins opened at Kalgoorlie by syn-d2 extension (Swager, 1997) or syn-d3 strike slip (Bateman et al., 2005). Late-orogenic basins provided important host rocks, possibly for rheological-competence reasons, as in the case of gabbro sills at Kalgoorlie. While the sediments

14 200 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) themselves were neither a necessary nor a sufficient factor in mineralisation, the tectonics and basin-opening deformation may represent an important factor. The importance of tectonic evolution is discussed in more detail in the following section Transpressional deformation Both the Kalgoorlie and Timmins Porcupine districts are characterised by an early history of major thrusting, folding and shortening, culminating in late transpressional left lateral strike slip (Bateman and Hagemann, 2004; Bateman et al., 2005). Both areas are characterised by a curvature in the trend of the dominant shear zone (Boulder Lefroy Fault and Porcupine Destor Shear Zone, respectively). Important thrusting perpendicular to these shear zones (Golden Mile Fault and Fifth Avenue Fault, respectively) is one of the outstanding parallels between the two camps, and is a main factor in the broad similarity of the structural pattern of the two areas (Fig. 1). In Kalgoorlie, mineralisation started with D1 local thrusting, before the D2 extensional opening of Kurrawang-type basins (Swager, 1997; Blewett et al., 2004). In Timmins the earliest mineralisation predated D3 opening of the Timiskaming basin, and was associated with D2 thrusting (Bateman et al., 2001b, 2005). Both areas experienced both left-lateral and right-lateral strike slip, but the two camps differ in the details of this transpressional deformation. At Kalgoorlie, left lateral slip occurred on secondary shear zones, whereas coeval rightlateral slip occurred as antithetic shear on tertiary faults. In Timmins Porcupine, right-lateral slip succeeded leftlateral shear along the Porcupine Destor Shear Zone. Strike slip deformation in an anticlockwise curve in the major fault trace opened up the Timmins sedimentary basin. In the Eastern Goldfields, these sediments were deposited within post-d1 extensional basins (Swager, 1989), prior to D2 shortening deformation. Although mineralisation in both camps spanned the formation of the late-orogenic basins, the mineralisation in the two camps cannot be explained in terms of transtensional basin opening, since the timing and kinematics of the opening the basins were different in each province. The D2 deformation was evidently diachronous in the Eastern Goldfields (Blewett et al., 2004), advancing from east to west (i.e. towards the older part of the craton) over at least 20 million years. Available data on timing and duration of deformation in the Abitibi Province and Superior craton are insufficient to make a comparison. The importance of this point is that if deformation is prolonged, structures are repeatedly reactivated as subsequent stages of deformation sweep through zones recently deformed in earlier phases of D2 (Bierlein et al., 2004). An even more important factor might be that mineralisation in both camps spanned the period from early thrusting to later strike slip faulting. Both Kalgoorlie and Timmins Porcupine are characterised by particularly well-developed early thrust stacks. This kinematic history may have formed a network of both shallowly plunging and steeply inclined fractures and conduits that were repeatedly opened during progressive deformation, and available for the transport of auriferous fluids. During thrusting, fractures would form with variable dips and with strikes perpendicular to the direction of movement (Fig. 4A). Where fractures of parallel strike and variable dip intersect, linear damage zones will form that can act as conduits, and will lie parallel to subhorizontal Y and will gape parallel to vertical Z. During later strike slip, Y and Z will swap orientations to generate vertical conduit arrays in a similar manner. Together, the resultant intersecting network of fractures would have tapped a large volume of source rock, as potentially necessary for ore formation. There would also be the potential for focussing and converging of fluid pathways into a single channel, or a very few channels, that would feed the future deposit (Fig. 4B). Both Kalgoorlie and Timmins Porcupine occur very near anticlockwise bends in the trend of the adjacent major shear zones (Boulder Lefroy Fault and Porcupine Destor Shear Zone, respectively). These curves in the shear zones trends may have been important in localising a single concentration of the steep fracture set to form the vertical conduit. The precise form of individual openings would depend on local geometries and kinematics, but the arrays may have taken these broad orientations. Thus, evidence of early thrusting followed by strike slip movement may imply an intersecting array of fractures. The detailed geometry, and curvature in the trend, of the first-order upper-crustal-scale shear zone may have been a cause of this locally intense early thrusting. Well-developed early thrusting within these first-order shear zones thus may have been a major and necessary factor in the formation of the largest gold camps. 4. Synthesis: the factors in the scale of the Kalgoorlie and Timmins Porcupine mineralisation 4.1. Factors of lesser importance Many of the similarities and differences between the two areas outlined above are of secondary importance

15 R. Bateman, F.P. Bierlein / Ore Geology Reviews 32 (2007) Table 2 A comparison of the most salient characteristics of the Kalgoorlie and Timmins Porcupine gold camps, and a summary evaluation of the importance of these features in their formation Characteristic Kalgoorlie Timmins Porcupine Role Least important factor Sulphur isotopes Layered gabbros Porphyries, albitites, lamprophyres Late-orogenic marine, fluvial sediments Very wide range at Fimiston on scale from zoned grains to lodes 10 to δ 34 S Common rock type, major host of Au Minor in volume, broadly synchronous with Au Not present/identified within the Kalgoorlie gold camp Narrow range of 3.0±1.4 δ 34 S in bulk samples. Similar to many Archaean gold deposits Uncommon rock type, minor host of Au Minor in volume. Albitites broadly synchronous with Au Locally an important host to Au Range of values an indicator of local precipitation processes Serve important rheological role where present (other rock types may serve the same role) No genetic role Serve important rheological role (other rock types may serve the same role) Age of stratigraphy Ma to b2679 Ma 2703 Ma to b2655 Ma Largely coincidental: volcanic rocks erupted along same structures that transmitted auriferous fluids Ultramafic rocks Stage of cratonisation 3D structure Transpression Timing of Au Komatiites, intrusive peridotites present, Au depleted in normalised PGE Au plot Around the end of Archaean crust formation; prior to major, final deformation Mineralised structures listric to major detachment at base of supracrustal rocks Overall left-lateral strike slip with right-lateral antithetic faulting. Diachronous D2 Protracted Au: D2 ( 2670 Ma) and D4 ( 2625 Ma) Basin opening, Basins opened prior to deposition of late major D2 shortening orogenic sediments Tellurides Abundant at Fimiston, common in other parts of Eastern Goldfields Komatiites, intrusive peridotites present At the end of Archaean crust formation; prior to major, final deformation Mineralised structures listric to base of supracrustal rocks; no detachment recognized at base of supracrustal rocks Overall left-lateral strike slip and en-echelon folding; subsequent left-lateral strike slip and constriction Protracted Au: pre-d3 (pre 2679 Ma); Dome 2670 Ma ; to D4 ( 2660 Ma) Basins opened during D3 strike slip Ultramafic rocks may be a source of Au Au deposited during the later stages of Archaean crust formation, deformation and cratonisation Depth extents of major faults controls the sources of fluid components and their conduits Mineralisation in each camp spanned transpression. Diachronous deformation allows time for fluid flow, mineralisation Long duration and diverse sources of mineralisation promotes large ore body Extension implicit in basin opening also conducive to mineralisation Minor amounts present, widespread elsewhere in Abitibi Province Te possibly has an important role in chemistry of Au-bearing fluids Epithermal-style fluids Mixed seawater hydrothermal water, oxidising fluid (anhydrite, hematite, V +3 ), tellurides Early Cu Au Ag Mo McIntyre deposit, hematite, anhydrite Early contribution from possible epithermal/ igneous source common in Eastern Goldfields and Abitibi provinces Early thrusting Very well developed stacked thrust sheets formed early during transpression Very well developed stacked thrust sheets formed early during transpression Perhaps necessary role in developing extensive array of interconnecting fractures and fluid conduits Most important factor Entries are arranged in general order of importance in the formation of the biggest gold deposits, with the least important at the top of the table. (Table 2). A rheological role was played by layered gabbros (and to a minor extent porphyry dykes within komatiites) in Kalgoorlie, and pillowed basalts and Timiskaming conglomerates in Timmins Porcupine. The timing of albitites in Timmins (absent in Kalgoorlie) and quartz porphyry dykes show they played no important role in fluid source. Some deposit components have a distinctively igneous character, and these formed relatively early in their camp. Although telluride minerals may occur in deposits regardless of age or size, these Tebearing phases seem broadly to characterise both of the two well-endowed provinces. In each case, the largest camps (Kalgoorlie and Timmins Porcupine) commenced formation early in the structural history. In contrast, the