Archean Karari gold deposit, Eastern Goldfields Province, Western Australia: a monzoniteassociated disseminated gold deposit

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1 Australian Journal of Earth Sciences ISSN: (Print) (Online) Journal homepage: Archean Karari gold deposit, Eastern Goldfields Province, Western Australia: a monzoniteassociated disseminated gold deposit W. K. Witt, D. R. Mason & D. P. Hammond To cite this article: W. K. Witt, D. R. Mason & D. P. Hammond (2009) Archean Karari gold deposit, Eastern Goldfields Province, Western Australia: a monzonite-associated disseminated gold deposit, Australian Journal of Earth Sciences, 56:8, , DOI: / To link to this article: Published online: 30 Oct Submit your article to this journal Article views: 489 View related articles Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at

2 Australian Journal of Earth Sciences (2009) 56, ( ) Archean Karari gold deposit, Eastern Goldfields Province, Western Australia: a monzonite-associated disseminated gold deposit W. K. WITT 1 *, D. R. MASON 2 AND D. P. HAMMOND 3 1 The Walter Witt Experience, 4/10 Field Street, Mt Lawley, WA 6050, Australia. 2 Mason Geoscience, Greenhill, SA 5140, Australia. 3 De Grey Mining Ltd, Suite 4, 100 Hay Street, Subiaco, WA 6008, Australia. The Karari gold deposit is situated in the Carosue sedimentary basin, 110 km northeast of Kalgoorlie, in the Archean Eastern Goldfields Superterrane of Western Australia. The Carosue basin is a late-tectonic accumulation of volcaniclastic sedimentary rocks that unconformably overlies a deformed granite greenstone association. The sedimentary basin is intruded by numerous plutons and dykes of monzonite, lamprophyre and syenite and is cut by a swarm of post-intrusion faults with north south orientations. Gold mineralisation at Karari occurs in a fault-bound zone of volcaniclastic sedimentary rocks that are intruded by monzonite porphyry and lamprophyre dykes. The hangingwall of the central mineralised zone is formed by the eastern intrusive complex, a porphyritic monzonite unit intruded by numerous dykes of monzonite porphyry, syenite porphyry and lamprophyre. The eastern intrusive complex is characterised by widespread potassic alteration and contains minor low-grade copper mineralisation. In the Karari pit, gold is associated with W and As, whereas Ag, Bi, Cu, Mo, Pb, Te and Zn form spatially distinct anomalous zones in the eastern intrusive complex and associated bounding faults. The central mineralised zone is interpreted as a downfaulted, higher-level exposure of the magmatic system represented by the eastern intrusive complex. Gold lodes are steep tabular zones of sodic alteration within a more extensive area of potassic alteration. Sodic alteration zones contain numerous veins and veinlets, which contain a variety of assemblages, several of which are mutually overprinting. Hematite occurs as a dusting in fine-grained albite and carbonate in the sodic alteration zones but is interpreted as a later (post-gold) event. Modelling using Hch software suggests that potassic alteration and low-grade copper mineralisation were caused by a high-temperature, saline fluid, probably derived from magmas of the eastern intrusive complex. The sodic alteration assemblage at Karari could not be duplicated but the results of other workers show that sodic alteration could have formed by reaction of quartzo-feldspathic rocks with a mesothermal, lowsalinity H 2 O CO 2 fluid. The data and observations described in this paper do not permit an unequivocal distinction between orogenic and orthomagmatic models for the gold mineralisation. KEY WORDS: Archean, gold, hydrothermal alteration, Karari, mesothermal, modelling, monzonite, Yilgarn Craton. INTRODUCTION The Carosue Dam gold camp is located 110 km northeast of Kalgoorlie, in the Eastern Goldfields Superterrane of the Archean Yilgarn Craton (Figure 1). Most deposits in the camp (Karari, Whirling Dervish, Luvironza, Monty s Dam) represent a style of mineralisation that is different from the typical orogenic-gold deposits of the Yilgarn Craton (Groves et al. 1998; Witt & Vanderhor 1998), but show some similarities to disseminated deposits associated with syenitic intrusions in the Abitibi greenstone belt of Canada (Robert 2001). Distinctive features of the Carosue Dam deposits, which stand in contrast to typical orogenic-gold deposits are: (i) the association with quartz-poor alkaline intrusions; (ii) the diverse range of vein and veinlet assemblages; (iii) the low gold content of quartz veins; and (iv) the association, at the deposit scale, with anomalous levels of elements such as Ag, Bi, Cu, Mo, Pb, Te and Zn. Other gold deposits in the Eastern Goldfields Superterrane with some similarities to the Carosue Dam deposits include Wallaby [213 t (7.1 Moz) Au: Maidens 2002; Salier et al. 2004; Miller et al. 2007], Bull Terrier, Butcher Well and Tin Dog Flats [no production, 1.5 t (0.05 Moz) Au, and no production, respectively: Roberts et al. 2004] and Jupiter [3 t (0.1 Moz) Au: Duuring et al. 2000; Salier et al. 2005]. All of these deposits are located close to or east of the Kilkenny Yilgangi Fault (Figure 1). Witt & Hammond (2008) also drew attention to the similarity of Karari and similar deposits in the Carosue basin, to younger alkalic intrusion-related deposits such as those in the Lachlan Fold Belt, New South Wales. *Corresponding author and present address: Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia (wittww@iinet.net.au). ISSN print/issn online Ó 2009 Geological Society of Australia DOI: /

3 1062 W. K. Witt et al. Figure 1 Geological setting of the Carosue Dam gold camp. Other mining centres in the Pig Well Yilgangi basin are shown, as are other deposits associated with quartz-poor intrusions and hematitic sodic alteration (BT, Bull Terrier; BW, Butcher Well; J, Jupiter; T, Tin Dog Flats; W, Wallaby). Labelled granite intrusions are Relief Monzogranite (RL) and Galvalley Monzogranite (GV). Inset shows location of Carosue Dam (CD) in the Yilgarn Craton. Estimated gold production from the Carosue Dam camp, at June 2004, was *15 t (*0.5 Moz), including 8 t (0.27 Moz) from Karari, and a small (but undocumented) proportion from outlying operations at Safari Bore. Production from Carosue Dam ceased in The geology of the northern (Stage 1) Karari pit was the subject of an Honours thesis by Michael (2001). This paper describes the basic geological features and geochemistry of the Karari deposit as a representative example of the disseminated deposits associated with quartz-poor intrusions at Carosue Dam, and discusses possible genetic models. District-scale geological relationships at Carosue Dam are described by Witt & Hammond (2008).

4 Karari gold deposit, WA 1063 During 2003, the Karari openpit was mapped and 96 whole-rock samples were collected from the pit floor and walls, and from selected drillcores (KRGT0005, PDRC000009A, PDRC000016, PDRC and PDRC ). These samples were analysed by X-ray fluorescence at UltraTrace Laboratories, Western Australia, for major components, and the following trace elements were analysed by ICP techniques following a mixed acid digestion: Ag, As, Ba, Bi, Cr, Cs, Cu, Mo, Pb, Rb, Sb, Te, Th, V, W, Zn, Zr. Total carbon, expressed as CO 2, was determined by the total combustion method. In addition, 206 grade-control samples taken from the 265 metre R.L. of the southern (Stage 3) Karari pit (and previously analysed for gold) were analysed for As, Sb, Te, Bi, W, Mo, Cu, Zn, Pb and Ag to investigate geochemical associations and the distribution of mineralisation within the deposit. Thin-sections were prepared from selected samples from the openpit and cores. Reaction with 10% HCl solution was used to determine carbonate species at Karari. Sluggish reaction indicates the presence of dolomite or ankerite but the term dolomite is used here to denote a carbonate containing essential iron and/or magnesium. The origin of the alteration assemblages observed at Karari was investigated using Hch software (Shvarov & Bastrakov 1999) to model the interaction of intermediate composition host-rocks with a variety of hydrothermal fluids. The results of these experiments are used to assist in the interpretation of the geological history of the gold deposit and the controls on mineralisation. REGIONAL GEOLOGICAL SETTING Although exposure of bedrock is poor, the Carosue Dam camp is interpreted to lie within the Pig Well Yilgangi basin (Figure 1), one of several late-stage syntectonic basins, which unconformably overlie deformed mafic to felsic volcanic greenstone belts in the Eastern Goldfields Superterrane (Swager 1997; Krapez et al. 2000; Kositcin et al. 2008). At Carosue Dam, this sedimentary basin is locally referred to as the Carosue basin, and comprises a monotonous sequence of metamorphosed quartz-lithic sandstone with minor siltstone and grit. Lithic clasts are dominated by aphanitic and porphyritic felsic to intermediate rocks, with minor granite. The volcaniclastic sedimentary sequence is intruded by numerous quartz-poor igneous intrusions, including biotite pyroxenite, syenite, monzonite, monzonite porphyry and lamprophyre (Witt & Hammond 2008). Geochronological data indicate a depositional age of Ma for the metasediments (Kositcin et al. 2008). This is close to a SHRIMP U Pb in zircon age of * Ma for a monzodiorite dyke that intrudes the Yilgangi basin at Yilgangi, north of Carosue Dam (Nelson 1997). Kositcin et al. (2008) considered that the dated zircons in some intrusions of the Eastern Goldfields Superterrane, including the sample dated by Nelson (1997), may be xenocrystic in origin and therefore not recording the age of intrusion. Blewett et al. (2004) showed that east west regional shortening in the Eastern Goldfields Superterrane caused folding of the underlying greenstone sequence (D 2a ) prior to formation of the late-stage basins, but continued or resumed following deposition of the latestage sedimentary sequence (D 2b ). The Carosue basin sedimentary rocks and intrusions, and the underlying greenstones, are cut by a swarm of north south faults that are associated with dextral offset of tens to a few hundred metres. These faults are particularly common in the Carosue Dam area and probably formed during D 3 of Blewett et al. (2004), equivalent to D 4 of Swager (1997). The Karari gold deposit is located within the central part of a district-scale (430 km63 km) geochemically zoned alteration system described in more detail by Witt & Hammond (2008). The central part of this system is broadly coincident with the igneous intrusions and comprises sodic and potassic alteration (described below). These alteration domains are characterised by relatively low strain. The central alteration zone is enveloped by a zone of muscovite alteration in which muscovite defines a prominent tectonic fabric. The outermost zone of this hydrothermal system is characterised by chlorite but chlorite also occurs in the north south faults that cut the central domains of the alteration system. GEOLOGY OF THE KARARI GOLD DEPOSIT The Karari mine sequence can be subdivided into three lithostructural domains, separated by the north- to north-northwest-trending Footwall and Hanging Wall Faults (Figures 2, 3). Footwall sedimentary sequence The footwall sedimentary sequence comprises metamorphosed fine- to coarse-grained sandstone and siltstone, with interbedded chloritic shale. The metasedimentary rocks are dominated by detrital quartz with subordinate feldspar and phyllosilicate minerals, and up to 1% pyrite. Muscovite and chlorite define a foliation that wraps individual clastic grains. The rocks are considered to display an unaltered metamorphic assemblage, apart from the intense chlorite carbonate alteration that occurs within several metres of the Footwall Fault. Cross-bedding and graded bedding are relatively common, in contrast to the feldspar-rich volcaniclastic sediments of the central mineralised zone, but the sediments are folded, and no consistent direction of younging could be established. Central mineralised zone All economic gold mineralisation occurs in the central mineralised zone, between the Hanging Wall and Footwall Faults. The central mineralised zone is dominated by metamorphosed volcaniclastic sedimentary rocks, which belong to the Carosue basin. The metasedimentary rocks are intruded by dykes of monzonite porphyry and lamprophyre. The volcaniclastic sedimentary rocks are dominated by angular to rounded, quartz-poor, intermediate to felsic lithic fragments with lesser quartz and feldspar

5 1064 W. K. Witt et al. Figure 2 Geology of the Karari pit. The northern third of the pit is referred to as the Stage 1 pit and the southern two thirds is referred to as the Stage 3 pit. Note that internal contacts between alteration domains (see Figure 3) are shown for reference but not separately patterned. Mineralised zones are: FWL, Footwall Lode; CL, Central Lode; HWL, Hanging Wall Lode; NWL, Northwest Lode; K1L, K1 Lode. mineral clasts and generally less than 10% phyllosilicates (biotite, muscovite or chlorite, depending on the alteration facies). Graded bedding and low-angle crossbedding have been observed locally and indicate younging to the west (i.e. the beds are overturned). Lithic clasts are generally less than 5 mm in length, and the metasediments are moderately well sorted, although rare, isolated clasts up to several centimetres across have been observed in volcaniclastic sandstone. A welldeveloped foliation, defined by the preferred orientation of phyllosilicate minerals, sweeps around lithic and mineral clasts but the clasts themselves are generally not strongly flattened. The geological setting, comprising igneous dykes within a sedimentary succession, and the porphyritic textures of the dykes, suggests a relatively shallow crustal level for the central mineralised zone, compared with the eastern intrusive complex. Lamprophyre and monzonite porphyry dykes are similar to those in the eastern intrusive complex but the monzonite porphyry dykes are more strongly altered in the central mineralised zone (see below). Eastern intrusive complex To the east of the Hanging Wall Fault, the eastern intrusive complex is dominated by coarse-grained monzonite and porphyritic monzonite. These monzonitic rocks are intruded by numerous dykes of monzonite porphyry, syenite porphyry and lamprophyre. Tectonic strain in the eastern intrusive complex is weak and igneous textures are widely preserved.

6 Karari gold deposit, WA 1065 Porphyritic monzonite contains phenocrysts of plagioclase (mainly), amphibole, biotite and clinopyroxene. Monzonite porphyry dykes are mineralogically similar to the porphyritic monzonite but contain phenocrysts of plagioclase (+K-feldspar) in a fine-grained, feldspar-rich groundmass. Syenite porphyry dykes contain elongate K-feldspar phenocrysts set in a medium-grained groundmass and have a trachytic texture. Lamprophyre dykes contain hexagonal phenocrysts of biotite in a groundmass that varies from biotite-rich to feldspar-rich. Faults The Hanging Wall Fault and the Footwall Fault are two of several faults that cut the Karari mine sequence (Figure 2). Exposures in the pit and intersections in drillcore indicate that these structures are brittle ductile faults, several metres to 51 m wide. The faults are characterised by intense fracturing and cataclasis with locally superimposed ductile strain, which produces an anastomosing fabric that wraps angular rock fragments. They are associated with several metres of chloritic alteration where wall-rocks are cut by a ramifying network of chloritic fractures and contain disseminated calcite. Most faults dip moderately to steeply east but an exception is the Youngfella s Other Fault, which dips about 708W. The Hanging Wall Fault and Footwall Fault converge in the north of the Karari pit (Figure 2). Although poor exposure prevents mapping of the faults beyond the limits of the Karari pit, the Footwall Fault, the Youngfella Fault and Youngfella s Other Fault are interpreted as members of the district-wide north south fault swarm. Sigmoidal tails on clastic grains and S C fabrics provide evidence for reverse movement throughout the Karari pit. Flat to gently dipping quartz veins in the Hanging Wall Lode and locally elsewhere in the pit also imply vertical extension. Reverse movement was followed by strike-slip displacements on relatively brittle structures that partly coincided with the earlier reverse faults. Dextral movement across the Youngfella Fault has offset the Hanging Wall Fault and the central mineralised zone (Figure 2), effectively dividing the Karari deposit into northern (Stage 1 pit) and southern (Stage 3 pit) sections. The Youngfella Fault terminates a lamprophyre dyke and the K1 and Northwest Lodes, in the Stage 1 pit (Figure 3). The Resurrection Fault formed during a later period of reactivation, linking the southern segment of the Hanging Wall Fault with the northern part of the Footwall Fault. Hydrothermal alteration, lamprophyres and veins Several alteration facies are recognised in the Karari pit (Figure 3). Gold is most closely associated with zones of sodic alteration. SODIC ALTERATION ZONES Sodic alteration zones (albite dolomite rutile pyrite) show a general spatial association with monzonite porphyry dykes in the central mineralised zone but extend into the volcaniclastic country rock (Figures 2, 3). Progressive replacement relationships at transitions with potassic alteration zones indicate that the potassic alteration assemblage is overprinted by sodic alteration. Sodic alteration zones are typically a metre to several metres wide and tens to hundreds of metres in strike length. They are deep-pink to brick-red in colour and are dominated by sodic plagioclase (An 8 13, determined optically) with subordinate to minor dolomite and up to 10% pyrite, and accessory rutile. Variable amounts of microcline K-feldspar (up to about 30%) occur in some samples, as thin veinlets, alteration halos to veinlets and patchy alteration. Traces of galena and chalcopyrite are quite common. Magnetite is unstable in the sodic alteration assemblage but may be present in relict patches of potassic alteration. The red colour of sodic alteration zones is caused by dusty inclusions of hematite in albite and dolomite. Dolomite (+pyrite) hosts much of the iron and most of the magnesium in the albitised rocks, thus resulting in a bleaching of dark minerals. The albitised rocks are massive to only weakly foliated but albitisation is texturally destructive making distinction between porphyry and volcaniclastic precursors difficult. Nevertheless, euhedral white feldspar phenocrysts, mostly 52 mm, are generally preserved in porphyry dykes and bedding is locally preserved in volcaniclastic sedimentary rocks. Examples of rocks affected by sodic alteration are shown in Figure 4. POTASSIC ALTERATION ZONES Potassic alteration in the central mineralised zone defines broad domains that surround sodic alteration zones (Figure 3). Clastic sedimentary textures in volcaniclastic sedimentary rocks are generally well preserved in potassic alteration zones. The potassic alteration assemblage in volcaniclastic rocks is plagioclase biotite quartz (+calcite). The composition of the plagioclase in samples from the potassic alteration facies, determined optically, is in the range oligoclase to andesine (mostly An 30 to An 36 ). The dominant phyllosilicate mineral is (brown or green) biotite and this mineral hosts the bulk of the iron and magnesium in the rock. Minor pyrite, magnetite and chalcopyrite are locally present but these rarely constitute more than 1% of the rock. Potassic alteration is pervasive throughout the eastern intrusive complex. The typical potassic alteration assemblage is plagioclase þ K-feldspar þ green or brown biotite + magnetite, pyrite, chalcopyrite. A weak dusting of hematite is locally present. Much of the biotite, especially that in the lamprophyres, may be primary but igneous amphibole and (in some cases) pyroxene are altered to biotite, and discontinuous biotite + magnetite, pyrite, chalcopyrite veinlets are common. These features indicate the widespread presence of hydrothermal biotite. Fibrous, blue-green tremolite occurs along fractures and in small veins within the monzonitic rocks. These veinlets are larger than the thin, discontinuous veinlets of biotite and appear to at least partly pre-date potassic

7 1066 W. K. Witt et al. Figure 3 Map showing alteration facies in the Karari pit. Mineralised sodic alteration zones marked as in Figure 2. alteration. Fibrous, blue-green tremolite also forms feathery terminations on igneous hornblende. Variable amounts of carbonate (calcite) are present locally in potassic alteration zones in the central mineralised zone and the eastern intrusive complex but is practically absent in some samples. Because of its irregular occurrence, calcite is not viewed as an integral part of the potassic alteration assemblage, but may have been introduced during the later chloritic hydrothermal event (see below). TRANSITIONAL ZONES BETWEEN POTASSIC AND SODIC ALTERATION Transitions between potassic and sodic alteration zones in the central mineralised zone are commonly banded. Bedding-controlled albitisation of the potassic assemblage produces alternating bands of relict, black potassic alteration with 1 10% magnetite and pink to red bands of sodic alteration (Figure 5). The banded nature of the transitional zones indicates that bedding was an important local factor in controlling the passage of hydrothermal fluids responsible for sodic alteration. However, observations of sodic alteration halos around veins and veinlets in the pit and in drillcore (Figure 4b) indicate that albitisation is related to brittle fracture at the larger scale. MUSCOVITE ALTERATION ZONES Muscovite alteration zones (plagioclase muscovite quartz + pyrite) are extensive in the Carosue Dam

8 Karari gold deposit, WA 1067 Figure 4 Sodicalterationinvolcaniclastic sedimentary rocks, Karari. (a) Volcaniclastic sedimentary rock with sodic alteration. The rock is cut by dolomitic and biotitic fracture networks, which in turn are cut by late calcite veinlets (scale bar is *1 cm long). (b) Fracture-controlled sodic alteration (pale grey) cuts potassic alteration (dark grey) in volcaniclastic sedimentary rock (scale bar is 5 cm long). district, mostly in zones surrounding potassic alteration zones (Witt & Hammond 2008), but they also have a restricted distribution in the Karari pit. Some of these zones are in direct contact with sodic alteration zones indicating that they are not consistently distal with respect to potassic alteration, as appears the case at a district scale. The main muscovite alteration zone at Karari is in the Stage 3 pit, between the Hanging Wall and Central Lodes (Figure 3), where potassic alteration is incompletely overprinted by muscovite alteration. Other, smaller domains of more complete muscovite alteration have been identified on the western contact of the lamprophyre dyke in the Stage 3 pit and within the Hanging Wall Lode (not shown in Figure 3). Where muscovite alteration is complete, muscovite is the only phyllosilicate mineral, replacing biotite of the potassic alteration assemblage. Minor calcite may be present but is not an integral component of muscovite alteration. Although mass-balance calculations have not been carried out, depletion of Fe and Mg in this facies is inferred, since there is no major Fe Mg mineral phase. The preferred orientation of muscovite defines a strong foliation in the volcaniclastic sedimentary rocks, which wraps lithic and mineral clasts. Trace to minor magnetite, pyrite and tourmaline are common. Muscovite alteration is generally barren of gold, even though minor amounts of pyrite may be present. CHLORITIC ALTERATION Chloritic alteration (plagioclase chlorite calcite) is concentrated along the Hanging Wall Fault and especially the Footwall Fault. In the Karari deposit, chloritic alteration is the latest alteration event, overprinting

9 1068 W. K. Witt et al. Figure 5. Transition between sodic and potassic alteration zones. (a) Banded transition in left-hand core from potassic alteration (dark grey, above) to sodic alteration (mid grey, below) in volcaniclastic sandstone. Note the large hematitised lithic clast in lower (sodic) part of core. Pale-grey core on right is more intensely albitised volcaniclastic sandstone. (b) Schematic diagram illustrating mineralogical variation, and interpreted changes in sulfur and oxygen fugacity across a transition from sodic to potassic alteration (left) to sodic alteration (right). potassic alteration and sodic alteration facies adjacent to faults. Chlorite is the only phyllosilicate mineral and contains most of the Fe and Mg in assemblages where chlorite alteration has gone to completion. It is generally accompanied by calcite, as disseminations, aggregates, veinlets and porphyroblasts up to about 5 mm across. The chloritised rocks may contain up to several percent pyrite and magnetite, depending on the precursor alteration assemblage, but more generally these minerals account for 51% of chloritic alteration assemblages. Although albitic lithic clasts may be present, hematite is generally absent from chloritic assemblages suggesting that hematite was unstable with respect to the relatively reducing fluids responsible for chloritic alteration. CHLORITE MAGNETITE ALTERATION Chlorite magnetite alteration has been noted as small domains, up to several metres wide, within the largest muscovite alteration zone in the Karari Stage 3 pit. These relicts contain several percent of bedding-controlled magnetite with chlorite, in bands that alternate with muscovite-rich bands. Although contact relationships are ambiguous, this magnetite-rich assemblage is interpreted as a probable relict of early Fe metasomatism that has been overprinted by later hydrothermal events. Textural evidence indicates that rocks hosting chlorite magnetite alteration are not significantly different to those that host potassic and chloritic alteration. DISTAL HEMATITIC ALTERATION Within the potassic and muscovite alteration zones, lithic clasts (predominantly fine-grained feldspar) in the volcaniclastic sediments are commonly pink to red indicating weak hematite dusting. Despite this, feldspar crystal fragments in the same rocks are white. The reason for this enigma is not known but it is clear that fine-grained feldspathic lithic clasts are more susceptible to hematite alteration than coarser-grained feldspar crystal fragments (Figure 6a). In the same way, it is also noted that white feldspar phenocrysts in monzonite porphyry intrusions occur within a red, hematitic albite matrix, again suggesting selective hematitisation of fine-grained feldspars (Figure 6b). District-scale logging of bottom-of-hole samples suggests that the distal hematitic alteration is very extensive (several kilometres wide). The presence of hematite-altered lithic clasts in volcaniclastic sedimentary rocks could be used to suggest that hematitic alteration pre-dated sedimentation. However, logging of diamond core has identified several small-scale instances where selective reddening of lithic clasts occurs adjacent to veinlets with sodic alteration halos (Figures 6b, 7e) and hematitisation is interpreted to post-date sedimentation and intrusion of monzonite porphyry dykes.

10 Karari gold deposit, WA 1069 LAMPROPHYRE DYKES Lamprophyres display local zones of weak hematitisation (Figures 2, 3). Hematitic alteration zones are characterised by a pink groundmass but hexagonal biotite phenocrysts are well preserved in most of these zones. Where alteration is stronger, ferromagnesian phenocrysts are selectively replaced by carbonate minerals. Magnetite and pyrite generally comprise 51% of these assemblages. Lamprophyre dykes appear to have intruded within or adjacent to sodic alteration zones and cut the sodic alteration zones and the monzonite porphyries. This is especially evident in the Stage 1 pit but the Footwall Lode in the Stage 3 pit is also terminated by a lamprophyre dyke (Figures 2, 3). The lamprophyre dykes contain only low-grade gold mineralisation, locally at dyke margins, and are believed to largely or completely post-date gold mineralisation. The weak mineralisation (50.2 g/t Au) on some contacts is interpreted to be due to remobilisation or digestion of gold from adjacent lodes, or minor overlap between mineralisation and lamprophyre emplacement. VEINS Eight vein types, defined in Table 1, have been recognised in pit exposures and core. Some examples Figure 6 Distal expression of sodic alteration, Karari. (a) Coexisting hematitic lithic clasts (pale grey, LC) and white feldspar crystal fragments (XF) in volcaniclastic sedimentary rocks, potassic alteration zone, Stage 3 pit, Karari. (b) Pervasive hematitisation selvage (pale grey) around carbonate vein and biotite stringer in potassic alteration zone, Stage 3 pit, Karari. A lithic clast (SH) beyond the selvage has been selectively hematitised. Note porphyry clast (P) in which the groundmass is hematitic and the phenocrysts (white) are unaltered.

11 1070 W. K. Witt et al. of the variety of veins encountered at Karari are shown in Figure 7. Veins are most abundant in zones of sodic alteration, where several different mineralogically defined sets of veinlets and stringers comprise a complex stockwork. Cross-cutting relationships are obscured by possible self-healing of fracture veinlets where they intersect quartz-rich veins and veinlets, hindering recognition of a vein paragenesis. However, mutually cross-cutting relationships between most vein types have been observed and there appears to be broad overlap in the timing of most vein types, with the exception of late calcite veins, which consistently overprint all other veins. Biotite-rich veinlets and stringers are locally abundant in zones of sodic alteration in the volcaniclastic sedimentary rocks, but are absent or a minor component in the monzonite porphyry dykes. The veinlets are dominated by biotite, although biotite is altered to chlorite where the host-rock has been overprinted by chloritic alteration. Minor calcite and/or pyrite may also be present, particularly in thicker veinlets, some of which are zoned from a calcite core to biotiterich margins. Magnetite and chalcopyrite have been observed in some biotite-rich veinlets. At the margins of sodic alteration zones, biotite-rich veinlets have sodic alteration halos that overprint potassic alteration (Figure 7d). Locally, the biotiterich veinlets pass transitionally into breccia zones, up to several centimetres wide, with biotite-dominant infill. Massive to laminated grey quartz pyrite veins and veinlets (Figure 7a) are uncommon but there is a good correlation between their presence and high gold grades (44 ppm Au). Furthermore, the only siting of visible gold was adjacent to a quartz pyrite veinlet (Figure 8). Pyrite forms up to several percent of the veins and may occur as very fine-grained disseminations or as lamellae. Quartz in these veins has a fine-grained, grey, cherty appearance. Pyrite-rich veinlets and stringers are locally common in zones of strong sodic alteration, normally accompanied by abundant (45%) disseminated pyrite. Pyrite is the major component of these veinlets but petrographic observations indicate that some also contain significant K-feldspar (microcline), carbonate and/or biotite. Pyrite microcline veinlets are particularly common in samples collected from the Hanging Wall Lode (exposed in the floor of the Stage 3 Karari pit), where they cut sodic-altered, brecciated monzonite porphyry. Quartz carbonate veins contain minor biotite, chlorite, pyrite and, less commonly, minor albite or microcline. They contain more than 10% carbonate (calcite or dolomite) in addition to quartz. Carbonate minerals are generally concentrated at the margins of these veins and there appears to be a continuum between them and the buck quartz veins. As with quartz veins (below), thin selvages of hematitic alteration are common but the association is not consistent. Some veins of this type cut sodic/potassic alteration banding in transition zones and therefore post-date sodic and potassic alteration. Buck white quartz-dominant veins are relatively common, especially in zones of sodic alteration, but locally extend a short distance into the adjacent potassic alteration zone. The Hanging Wall Lode hosts a prominent ladder system of subhorizontal quartz veins exposed in the south wall of the Stage 3 pit (Figure 9). Intersections of buck quartz veins in oriented core confirm the gentle east and west dips of many veins, but others with steep south and steep west dips have also been recognised. Table 1 Definitions of veins and stringers recognised at Karari. Vein type (dominant minerals) Other minerals (in variable but mostly minor amounts) Texture Abundance Size Comments Late carbonate (calcite) Quartz, chlorite, biotite, dolomite Massive Common 55 mm Calcite-rich veinlets, stringers and fracture-veinlets Quartz Carbonate Massive to zoned Common Variable Buck white quartz veins; carbonate absent or minor (510%) Quartz carbonate Chlorite, biotite, pyrite Massive to zoned Common Variable Massive to zoned quartz carbonate veins + chlorite, biotite; quartz: carbonate between 1:10 and 10:1; +minor albite, K-feldspar Pyrite Carbonate, biotite, microcline Stringers Moderately common 55 mm Pyrite-rich stringers Quartz pyrite Carbonate Massive to laminated Biotite Magnetite Calcite, magnetite, pyrite, chalcopyrite Quartz, carbonate, pyrite Moderately common 55 mm Laminated pyritic, grey, cherty quartz veins, carbonate generally minor to absent; pyrite fine-grained to dusty. Generally auriferous Stringers Common 55 mm Veinlets and stringers; biotite altered to chlorite where overprinted by chloritic alteration Stringers Rare 55 mm Veinlets and stringers of magnetite; minor but variable quartz, carbonate, pyrite

12 Karari gold deposit, WA 1071 Figure 7 Veins and vein relationships, Karari. (a) Laminated quartz dolomite chlorite very fine-grained pyrite breccia vein (Qp) in volcaniclastic sedimentary unit with sodic alteration. Both the Qp vein and other, quartz dolomite biotite veins (Qc) to right of the Qp vein are cut by late calcite dolomite veins (Lc). The section with the Qp vein assayed þ 6 ppm Au. (b) Quartz breccia vein (Q) in volcaniclastic sedimentary unit with sodic alteration. The Q vein is cut by quartz carbonate chlorite veins (Qc). (c) Polished slab from zone of strong sodic alteration. Early quartz carbonate K-feldspar veins (Qck) are cut by quartz veins (Q). A later biotite-rich stringer (B) has refractured the Q vein. A still later calcite veinlet (Lc) cuts all veins obliquely. (d) Sodic alteration (Na) around biotite-rich veinlet (B) in volcaniclastic sandstone. The biotite-rich vein is cut by quartz carbonate chlorite veins (Qc) that cut and are deformed by a foliation defined by biotite. There is no sodic alteration adjacent to the Qc veins. (e) Thin quartz carbonate veinlets (Qc) parallel to and oblique to a foliation defined by biotite in volcaniclastic sediment with potassic alteration. Narrow halos of sodic alteration occur in the upper row of core, beyond which lithic clasts are selectively hematitised (SH). Carbonate-rich veinlets and stringers are predominantly calcite but may contain minor chlorite or pyrite. In sodic alteration zones, some carbonate veinlets contain dolomite as well as calcite. Calcite veins are the latest event, overprinting all other vein types and are interpreted to post-date gold mineralisation (Figure 7a, c, e).

13 1072 W. K. Witt et al. Figure 8 Sketch of polished core showing geological context of coarse, visible gold. GOLD MINERALISATION Economic gold ore is mostly confined to sodic alteration zones and is more consistently ore grade in volcaniclastic sedimentary host rocks than in monzonite porphyry. Figure 3 highlights a number of lodes, defined by sodic alteration, most of which strike between north and northwest. The Footwall Lode is coincident with sodic alteration within a thin monzonite porphyry dyke and the adjacent volcaniclastic sedimentary rocks, in the southwestern sector of the pit. The Footwall Lode is terminated to the north by a lamprophyre intrusion and the Footwall Fault. The Central Lode lies near the eastern margin of the lamprophyre intrusion, and is coincident with a zone of sodic alteration within volcaniclastic sedimentary rocks. The Hanging Wall Lode lies within volcaniclastic sedimentary rocks, directly below the Hanging Wall Fault and is associated with sodic alteration and monzonite porphyry dykes. The Northwest Lode is a localised concentration of gold associated with a zone of sodic alteration in volcaniclastic sedimentary rocks adjacent to the Resurrection Fault. This lode lies near the western contact of a lamprophyre intrusion. The K1 Lode in the Stage 1 pit coincides with a broad zone of sodic alteration centred on a thin monzonite porphyry dyke but extends into the enveloping volcaniclastic sedimentary country rock. Quartz-dominant veins, prominent in many sodic alteration zones, were selectively sampled to determine their significance for gold mineralisation. The results show that many of these veins are barren and that, in most cases, samples with a large proportion of quartz veins contain less gold than those of altered wall-rock in which quartz veins are absent or only a minor component (Table 2). It is concluded that quartz veins are non-auriferous or, at best, weakly auriferous. This does not necessarily mean that all quartz veins were deposited from barren fluids, because gold may have been preferentially deposited in wall-rocks as a result of reaction with Fe-bearing minerals. However, at least some quartz veins (e.g. V with 510 ppb Au) are unlikely to have been deposited from the ore fluid, as are quartz veins that cut sodic/potassic alteration banding in transition zones. A single observation of visible gold was located in a white quartz vein but adjacent to a thin, grey quartzpyrite vein with abundant very fine-grained pyrite (Figure 8). Although visible gold has not been observed in other grey, sulfide-rich quartz veins, the presence of these veins correlates with some of the higher-grade drill intercepts (Figure 7a; V in Table 2). There is a broad correlation between gold grade and the abundance of pyrite, as fine-grained disseminations and irregular veinlets and stringers. Native gold is observed as microscopic inclusions in disseminated and veinlet pyrite in albite-rich rocks. Minor galena and chalcopyrite are present in some high-grade samples.

14 Karari gold deposit, WA 1073 Figure 9 Subhorizontal quartz veins in the Hanging Wall Lode, Stage 3 pit, Karari. (a) Looking southeast in Stage 3 pit, Karari; eastdipping Hanging Wall Fault separates the eastern intrusive complex from the Hanging Wall Lode (pale grey) in the central mineralised zone. (b) Close-up of Hanging Wall Lode in (a), showing the subhorizontal quartz veins (arrowed) in the Hanging Wall Lode.

15 1074 W. K. Witt et al. Table 2 Selective analyses of quartz and quartz pyrite veins and altered wall-rock containing few or no quartz veins. Sample a Location Lode Description Gold (ppb) V South wall, Stage 3 pit, Hanging Wall Volcaniclastic sedimentary m RL, point rock; sodic alteration; no quartz veins V South wall, Stage 3 pit, Hanging Wall Quartz veins extracted from above material m RL, point V South wall, Stage 3 pit, Footwall Monzonite porphyry; sodic m RL, point alteration; no quartz veins V South wall, Stage 3 pit, Footwall Quartz veins extracted from above material m RL, point V m RL, Stage 3 pit Gently east-dipping lode Volcaniclastic sedimentary rock; sodic 973 alteration; no quartz veins V m RL, Stage 3 pit Gently east-dipping lode Volcaniclastic sedimentary rock; sodic 1490 alteration; overprinted by thin zones of non-hematitic?dolomite albite alteration; no quartz veins V m RL, Stage 3 pit Gently east-dipping lode Volcaniclastic sedimentary rock; pale grey, 245 non-hematitic dolomite albite alteration; larger quartz veins removed; minor fluorite on fractures V m RL, Stage 3 pit Gently east-dipping lode Monzonite porphyry; pale grey, 554 non-hematitic dolomite albite alteration; larger quartz veins removed V m RL, Stage 3 pit Gently east-dipping lode Buck white quartz coarse pyrite veins 10 V m RL, Stage 3 pit Gently east-dipping lode Quartz veins in monzonite porphyry 476 with sodic alteration V m RL, Stage 3 pit Gently east-dipping lode Monzonite porphyry; sodic alteration; 106 no quartz veins V m RL, Stage 3 pit Gently east-dipping lode Quartz veins in volcaniclastic sedimentary 772 rock with sodic alteration V m RL, Stage 3 pit Gently east-dipping lode Volcaniclastic sedimentary rock with sodic 3160 alteration; no quartz veins V PDCD000034, m Footwall Lode Volcaniclastic sedimentary rock with sodic 2560 alteration; 20% quartz veins V PDCD000034, m Footwall Lode Volcaniclastic sedimentary rock with sodic 5487 alteration; 2% quartz veins V PDCD000034, m Footwall Lode Volcaniclastic sedimentary rock with sodic 114 alteration; 450% quartz veins V PDCD000034, m Footwall Lode Volcaniclastic sedimentary rock with sodic 914 alteration; 55% quartz veins V PDCD000034, m Central Lode Laminated quartz pyrite vein V PDCD000034, m Central Lode Volcaniclastic sedimentary rock with sodic alteration; no quartz veins a Samples with little or no vein quartz are shown in bold. Although flat-lying structures could not be recognised in the walls of the Karari pit, drillhole analytical data suggest the presence of linking structures between the steep albitic lodes described above (Gerteisen et al. 2002). A linking structure may be exposed in the floor of the Karari pit, where the Central and Hanging Wall Lodes appear to broaden into a gently east-dipping surface (Figure 3). Samples taken from this location are brecciated monzonite porphyry with strong sodic alteration and high modal pyrite content. Gold is also present in a shallowly dipping brittle fault zone, which was poorly exposed in the pit floor during a brief visit to the Karari openpit, after the bulk of this study was completed. This grey to yellow (non-hematitic), brecciated zone is composed of ankerite albite pyrite. Clasts with hematitic sodic alteration in the fault breccia suggest that this structure postdated the steeper zones of sodic alteration and gold mineralisation described above. Copper mineralisation Two core samples from a hole designed to intersect the Hanging Wall Lode illustrate the presence of minor low-grade copper mineralisation in the eastern intrusive complex. The samples, which contain 602 ppm Cu and 1080 ppm Cu, were taken from a 37.5 m interval characterised by alternating intervals of lamprophyre and porphyritic monzonite. While only two copper analyses are available from the 37.5 m interval, the core was sampled continuously for gold, returning a composite grade of *0.11 ppm Au.

16 Karari gold deposit, WA 1075 The monzonite in this interval is intensely fractured and locally brecciated. Both the lamprophyre and the monzonite contain phenocrysts of pyroxene and amphibole which, in the monzonite, are replaced by secondary green biotite. Copper mineralisation appears to be confined to the monzonite. Pyrite is relatively scarce but chalcopyrite occurs in irregular, discontinuous veinlets of quartz albite microcline and as spatially related disseminations. The mineralised veins are oriented at a high angle to a weak foliation defined by secondary biotite. Fibrous amphibole is commonly developed in these veins, oriented roughly perpendicular to the vein walls suggesting incremental growth of the amphibole during repeated fracturing and progressive vein growth. The chalcopyrite-bearing veinlets are cut by secondary green biotite veinlets and fractures, which commonly contain magnetite but no sulfides. Geochemistry of grade-control samples Figure 10b shows the distribution of gold in the Stage 3 pit, using the complete grade-control drilling sample set (4500 samples) from the 265 m RL. A subset of 206 of these samples was analysed for As, Sb, Te, Bi, W, Mo, Cu, Zn, Pb and Ag, in addition to gold. These data were gridded and selected examples are shown in Figure 10c f. Each figure is referenced to a simplified geological interpretation map of the 265 m level (Figure 10a), based on an extrapolation from the walls of the pit at the same RL, and taking into account known and estimated dips of various units and structures. The elements can be assigned to two groups, based on their distribution. Most of the base-metals and the elements Ag, Bi, Cu, Mo, Pb, Te and Zn have very similar spatial distributions, with the main zones of anomalism coincident with the Hanging Wall Fault and the Youngfella Fault, and adjacent intrusive rocks of the eastern intrusive complex (Figure 10e, f). These elements do not display any association with the Central or Footwall Lodes and are associated with the margins rather than the centres of the Hanging Wall and Northwest Lodes. The spatial distributions of arsenic and tungsten (Figure 10c, d) are different to those of Ag, Bi, Cu, Mo, Pb, Te and Zn. Unlike these elements, arsenic and tungsten display a general spatial association with the Footwall and Hanging Wall Lodes. THERMODYNAMIC MODELLING OF KARARI ALTERATION ASSEMBLAGES Method Thermodynamic modelling was used to clarify possible conditions of formation, especially fluid composition and temperature, of Karari alteration assemblages. Models are based on HydroChemistry software (abbreviated as HCh: Shvarov & Bastrakov 1999), which adopts the approach of minimisation of Gibbs free energies of system components at equilibrium. A total load pressure of 150 MPa was assigned to all models, given the inferred shallow crustal environment of the deposit. Temperature varies from model to model, in the range C. Methods and assumptions used for the modelling are given in Table 3 and Appendix 1. The choice of a starting rock composition is problematic owing to the pervasive alteration of the volcaniclastic sedimentary rocks at Karari. Biotite, chlorite and muscovite in these rocks are all considered the products of hydrothermal alteration. It seems likely that the bulk composition of the average Carosue basin sediment would reflect the composition of the underlying greenstones, which are the probable source of the sediments. The underlying greenstones are dominated by basalt, andesite and felsic volcaniclastic rocks. Therefore, an intermediate bulk composition is proposed for the average unaltered Carosue basin sedimentary rock. This conclusion is supported by a plot of TiO 2 vs Zr Table 3 Compositions of starting rock composition and model fluids used for thermodynamic modelling. Average Karari volcaniclastic sediment a Magmatic fluid b Metamorphic fluid c SiO 2 (%) TiO 2 (%) 0.88 Al 2 O 3 (%) Fe (%) 2.21 FeO (%) 4.10 MnO (%) MgO (%) 4.29 CaO (%) 7.10 Na 2 O (%) 3.50 K 2 O (%) 1.13 P 2 O 5 (%) LOI (%) H 2 O (%) CO 2 (%) H 2 S (%) SO 2 (%) 0.64 NaCl (%) KCl (%) CaCl 2 (%) Total Au (ppm) Fe (ppm) Cu (ppm) Pb (ppm) Zn (ppm) a Surrogate for average Karari volcaniclastic sediment (Welcome Well andesite) normalised to 100%. Separate FeO and Fe 2 O 3 calculated from assumed FeO/FeO þ Fe 2 O 3 ¼ 0.65 (Le Maitre 1976). b Magmatic fluid: X CO2 ¼ 0, total S ¼ 0.1 mol with SO 2 / SO 2 þ H 2 S ¼ 1, NaCl þ KCl ¼ 50%, KCl/NaCl ¼ 5/1. Metal abundances are assumed diluted to 10% of those given in Ulrich et al. (1999). Other modifications of this fluid are noted in the text. c Metamorphic fluid: X CO2 ¼ 0.15, total S ¼ 0.01 mol with SO 2 / SO 2 þ H 2 S ¼ 0, NaCl þ KCl ¼ 3%. Values from Witt et al. (1997) and McCuaig & Kerrich (1998). Total sulfur at different temperatures from Mikucki (1998). Modifications of this fluid are noted in the text.

17 1076 W. K. Witt et al. Figure 10 Geology and geochemistry of the 265 m RL, Stage 3 pit, Karari. Geological symbols in Figure 10a as for Figure 2. The highs (H) and lows (L) for the elements are: gold H, 5 20ppm, L, ppb; arsenic H, ppm, L, 52.5 ppm; tungsten H, ppm, L, 50.5 ppm; copper H, ppm, L, 510 ppm; molybdenum H, ppm, L, 50.5 ppm.

18 Karari gold deposit, WA 1077 (Witt & Hammond 2008), in which Carosue basin metasedimentary rocks overlap the field of andesite defined by a regional study of northeast Yilgarn rock samples (Hallberg 1985). It is also noted that Carosue basin sediments are less felsic (lower Zr) than the associated amphibole-bearing monzodiorite intrusions (Witt & Hammond 2008). Because an analysis of unaltered Carosue basin sedimentary rock was not available, an andesite from the Welcome Well complex, 160 km north-northwest of Karari, was chosen as the starting rock composition. Model fluids investigated were: (i) a high-temperature, saline fluid of orthomagmatic origin; and (ii) a mesothermal, low-salinity H 2 O CO 2 fluid, consistent with the composition of metamorphic fluid. Modelling the potassic alteration assemblage The potassic alteration assemblage was most closely approximated by reaction of average Karari volcaniclastic sediment with a hydrothermal fluid of inferred magmatic origin. In the absence of an independent estimate of temperature of formation, models were run for a wide range of temperatures (T ¼ C). Calculated alteration assemblages in the temperature range C are plagioclase þ biotite þ minor magnetite þ anhydrite þ trace rutile þ chalcopyrite (Figure 11a). This assemblage is comparable with the observed potassic alteration assemblage, except for the high calculated magnetite and anhydrite (not shown in Figure 11a), which are attributed to an overestimation of Fe and oxidation state [SO 2 /(SO 2 þ H 2 S) ¼ 1] in the model fluid. Outside this temperature range, actinolite (not an essential component of the potassic assemblage at Karari) becomes excessively abundant. Chlorite and gold, both of which are predicted at lower temperatures, are absent in the potassic assemblage. The model predicts minor amounts of chalcopyrite, consistent with observation. Both sphalerite and galena are absent from the calculated assemblages, and only minor pyrite persists, again consistent with observations. The effect of variable fluid/rock ratio was studied over the range F/R ¼ 1/ to /1, at T ¼ 5508C and P ¼ 150 MPa. The dominance of plagioclase and biotite, and the absence of muscovite, in the observed potassic alteration assemblages at Karari suggest that potassic alteration took place at low to moderate F/R ratios (1:1 to 10:1). The absence of sphalerite, galena and microcline supports the proposal that the high-temperature fluid responsible for potassic alteration at Karari was highly saline, as these minerals appear at lower salinities under the model temperature and fluid/rock ratio. Attempts to reproduce the potassic alteration assemblage by reaction of average Karari volcaniclastic sediment with the model metamorphic fluid were unsuccessful at all temperatures between 300 and 5008C. These models produced excessive muscovite and chlorite, neither of which are a critical component of potassic alteration assemblages at Karari. Models using a metamorphic fluid also produced excessive dolomite and/or calcite at temperatures below 4008C. Modelling the sodic alteration assemblage The sodic alteration assemblage was most closely approximated by reaction of average Karari volcaniclastic sediment with a metamorphic hydrothermal fluid at a temperature of 3508C. The estimated temperature is constrained by the presence of dolomite/ankerite as the principal carbonate phase, the presence of albitic plagioclase, and the lack of biotite. The sodic alteration assemblage at Karari is most closely replicated at F/R between 1/1 and 10/1, where the calculated assemblage is albite þ quartz þ dolomite þ chlorite þ muscovite þ minor pyrite þ hematite þ trace rutile þ native gold + trace chalcopyrite, sphalerite, galena (Figure 11b). The presence of about 10% each of chlorite and muscovite in the model assemblage is problematic since these minerals are negligible in the observed sodic alteration assemblage at Karari. They remain at similar abundances for all reasonable F/R ratios using a model metamorphic fluid. All attempts to duplicate the sodic alteration assemblage using a model magmatic fluid failed because biotite or chlorite remained stable across a wide range of temperatures and fluid rock ratios, dolomitic carbonate was not produced, and plagioclase compositions were too calcic. Overestimation of muscovite and chlorite may indicate some modification of the model starting rock composition is required. For example, Bohlke (1989) showed how the bulk composition of a rock exposed to a metamorphic fluid can affect the relative stability of albite and muscovite. If the unaltered host-rock at Karari had a higher Al/(Mg þ Fe þ Cr) ratio than the andesite from Welcome Well, albite may have been stabilised over muscovite. The presence of accessory base-metal sulfides in the Karari sodic alteration zones suggests that fluid total salt content was relatively low as increasing total salinity beyond NaCl þ KCl 4 6% results in suppression of sphalerite and galena. K-feldspar is present locally in and around veinlets within the sodic alteration zones but the timing of the fluid responsible for K-feldspar is uncertain. These observations appear to require the influx of a fluid with higher KCl/ (KCl þ NaCl) than that responsible for typical sodic alteration zones. DISCUSSION Structural evolution of the Karari deposit Michael (2001) reconstructed the geology of the Karari deposit by accounting for dextral movement on the Youngfella Fault (Figure 12a, b), followed by dextral reactivation of the southern section of the Hanging Wall Fault (creating the newly formed Resurrection Fault: Figure 12c). The stepwise reconstruction in Figure 12 shows that, prior to strike-slip movements, the Hanging Wall Fault was a continuous structure, and the southern and central lamprophyres were a single unit, as were the Hanging Wall and K1 Lodes. Dextral movements on faults in the Karari pit, most of which are equated with

19 1078 W. K. Witt et al. Figure 11 Results of Hch modelling of potassic and sodic alteration assemblages at Karari. (a) Model CDNC011 showing variations in mineral abundance with temperature for average Karari volcaniclastic sediment (andesite) equilibrated with a saline magmatic brine [F/R ¼ 1; SO 2 /(SO 2 þ H 2 S) ¼ 1]. (b) Model CDAM0340 showing variation in mineral abundance with F/R for andesite equilibrated with a low-salinity H 2 O CO 2 (metamorphic) fluid at a temperature of 3508C. the north south fault swarm at Carosue Dam, are probably equivalent to D 3 in the regional deformation history of the Eastern Goldfields Superterrane (Blewett et al. 2004). Evidence for earlier reverse movement on the Hanging Wall Fault is consistent with the different levels of erosion described above, probably during D 2b of Blewett et al. (2004). Gold lodes and post-gold lamprophyre dykes are terminated and offset by dextral strike-slip faults, and the mineralisation event may have been earlier or coeval with reverse movement on the Hanging Wall Fault. Late reactivation of the southern section of the Youngfella Fault and the northern portion of the Resurrection Fault formed the Footwall Fault (Figure 12d). Late reverse movement on the Footwall Fault juxtaposed the central mineralised zone against the footwall sedimentary sequence. Figure 13 summarises the interpreted igneous, hydrothermal and structural history of the Carosue Dam belt and the Karari deposit, based on the observations described above.

20 Karari gold deposit, WA 1079 Figure 12 Structural reconstruction of the Karari deposit from lode formation until the present. FWL, Footwall lode; HWL, Hanging Wall Lode; K1L, K1 Lode; NWL, Northwest Lode. Early high-temperature alteration in the eastern intrusive complex The potassic alteration assemblage was successfully modelled by reacting a high-temperature (45308C) saline magmatic fluid with an intermediate igneous rock at low to moderate fluid:rock ratios. Secondary green biotite and associated magnetite attest to oxidising conditions during potassic alteration. Potassic assemblages in the eastern intrusive complex commonly contain minor disseminated chalcopyrite, with local concentrations of 40.1% Cu. Chalcopyrite occurs in quartz plagioclase microcline amphibole veinlets, implying formation at relatively

21 1080 W. K. Witt et al. Figure 13 Interpreted paragenetic history of the Karari gold deposit in the context of the history of the Carosue basin, referenced to the regional deformation history of Blewett et al. (2004).