Saint Ives (St Ives) - Argo, Invincible, Junction, Revenge, Victory, Cave Rock, Intrepide, Hunt, Orchin, Apollo, Diana, Athena, Hamlet, Delta, Agamemnon, Minotaur, Mars, Belleisle, Grinder, Leviathon, Defiance, Conquerer, Repulse, Britannia-Sirius
Western Australia, WA, Australia
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The St Ives Gold Field comprises a cluster of more >60 deposits distributed over a broad ~35 km long, NNW-SSE orieneted corridor, ~60 to ~100 km SSE of Kalgoorlie and ~600 km ENE of Perth (#Location: 31° 19' 13"S, 121° 44' 21"E).
The main mines and related deposits include Junction, Argo (including Argo, Apollo, Diana, Athena and Hamlet), Victory (including Leviathon, Victory, Defiance, Conquerer, East Repulse, Sirius-Britannia), Revenge (including Revenge, West Revenge, W45, W66, Delta, Agamemnon, NKR, Minotaur, Mars, Belleisle and Grinder) and Invincible (including, Invincible and Invincible South), each of which have endowments of >60 t of gold, whilst Cave Rock, Intrepide (Intrepide, Formidable, Redoubtable, Beta-Hunt and Temeraire) and Orchin (Orchin, North Orchin, Pinnace, Lifeboat and Thunderer) each contained >15 t of Au. These deposits and complexes are distributed over an interval of 40 km. Other mines, either within these complexes or in between include Clifton (Clifton, Blue Lode and Ives Reward), Hunt/Red Hill, Bahama, Santa Ana, Idough/West Idough, Incredible, Orion, Bellerophon and Nelsons Fleet.
Gold was first discovered in the Saint Ives Goldfield in 1897 following the Coolgardie and Kalgoorlie gold rushes, initially at Red Hill, Victory, Orchin and Delta Island, and subsequently at Ives Reward in 1919. Mining ceased in the goldfield during the 1930s, with a total cumulative production of 1.25 t of gold. The Kambalda nickel deposits were discovered in 1966, with the first gossan being only a few hundred metres from the historic Red Hill gold mine. During the exploration and mining of these deposits, sporadic rich patches of gold mineralisation were intersected in the Lunnon, Hunt and Fisher nickel mines. In 1979, the Hunt gold deposit was found beneath the Hunt nickel orebody and in 1980 Victory was discovered. These were followed soon after by Defiance, Orchin, Orion, Britannia and Sirius in the Victory area, Junction to the south and Revenge to the north. Discoveries after 1988 have included Intrepide, Cave Rocks, Delta South, Argo, Apollo, Britannia, Sirius, Thunderer, Lifeboat, Redoutable and Santa Ana-Bahama, as well as major extensions to most of the known orebodies.
The St Ives deposits lie within the NNW-SSE elongated Kalgoorlie Terrane, the westernmost segment of the Eastern Goldfields Superterrane, within the Archaean Yilgarn Craton of Western Australia. The deposits are located proximal to the trace of the NNW trending axis of the gently south-plunging Kambalda Anticline which is bounded to the east and west by the major, similarly NNW-SSE trending Boulder-Lefroy and Zuleika shear zones respectively.
For detail of the regional setting and geology of the Kalgoorlie Terrane and Yilgarn Craton, and the distribution of mineralisation, see the Yilgarn Craton overview record.
The corridor within which these deposits lie extends for ~35 km from the southern end of the Kambalda structural dome in the north, to the Junction mine in the south. A major second order structure, the Playa Shear which follows this axis for >10 km also controls mineralisation. This latter structure splays from the regional NNW trending Boulder-Lefroy Shear Zone that lies along the eastern margin of the Anticline. The New Celebration cluster of gold deposit occurs within a similar domal segment of the Kambalda Anticline some 30 km to the NNW, while the Kambalda komatiite hosted nickel-sulphide deposits are distributed around the flanks of the Kambalda Dome which lies between the two gold complexes in the same regional structure.
The stratigraphy within the Saint Ives Gold Field may be summarised as follows, from the base (after Blewett et al., 2010):
• Lunnon Basalt, deposited between 2720 and 2710 Ma, comprising >1750 m of abundant massive and pillow basalt with lesser monomictic basalt breccia and rare interflow sedimentary units. The basalts are subaqueous tholeitiic lavas with rare subvolcanic intrusions of ponded lava succession (Gresham and Loftus-Hills, 1981; Squire et al., 1998). It has lower MgO rich and upper less MgO rich members separated by an interflow sediment (Redman and Keays, 1985) and has a uniform mantle source (Morris, 1993).
• Kambalda Komatiite, deposited at 2709±4 Ma (Claoué-Long et al., 1988), comprising from ~100 to >1200 m of internally zoned ultramafic lava sheets, each of <100 m thickness, separated by sulphidic sedimentary units which include high-Mg flows of the Silver Lake Member which host Ni-sulphide mineralisation, and lower-MgO flows of the Tripod Hill Member (Gresham and Loftus-Hills, 1981). The upper komatiite lavas are more differentiated and contain less-abundant interflow units. The Kambalda Komatiite conformably overlies Lunnon Basalt. The Tripod Hill Member predominates to the south of the Kambalda Dome where the Saint Ives gold deposits occur, whilst the Silver Lake Member is mostly well developed in the northern half of the dome and to its north hosting the main Kambalda nickel deposits.
• Devon Consols Basalt, deposited at 2693±30 Ma, and comprises up to 150m of pillowed and massive high-MgO basalt with abundant varioles. There is commonly gradational contacts from pillow to massive basalt to dolerite internally within the unit, but sharp and occasionally gradational boundaries with the underlying Tripod Hill Member. It is divided into high-Si low-Mg and low-Si high-Mg basalts (Redman and Keays, 1985) and is interpreted to have been generated from a crustally contaminated komatiitic melt (Compston et al., 1986; Claoué-Long et al., 1988; Lesher and Arndt, 1995).
• Kapai Slate, deposited after 2692±4 Ma (detrital zircons; Claoué-Long et al., 1988), as a <10m thick black sulphidic mudstone with minor felsic volcaniclastic rock fragments. It is interpreted to represent a combination of tuffaceous debris from distal felsic volcanic eruptions and minor chemical deposition from silica-rich exhalations that separate the Paringa and Devon Consols Basalts. Interflow sedimentary rocks similar in appearance are found in both units, complicating identification of the boundary between the two basalts.
• Paringa Basalt, deposited at 2690±5 Ma (Clout, 1991), comprising 500 to 1500 m of massive and variolitic pillow lavas, lesser doleritic units and rare monomictic hyaloclastite basalt breccia. The contacts between pillow basalt, massive basalt and dolerite are commonly gradational. It has lower a Ti/Zr ratio than the Devon Consols Basalt, interpreted to indicate up to 25% crustal contamination in its melt (Lesher and Arndt, 1995).
• Black Flag Group, which was deposited after 2690 Ma and is locally >2000m thick, subdivided into 5 different lithofacies, which are summarised below (after Squire et al., 2007), but not in stratigraphic order:
Plagioclase-rich granule breccia or gritstone, composed of massive to graded beds that are <5 m thick and are rich in feldspar crystal fragments, minor felsic volcanic lithic fragments and rare quartz;
Volcanic sandstone and siltstone, moderately well-sorted beds that are >5m thick, composed of massive and graded volcanic sandstone and siltstone with gradational lower contact with the gritstone;
Black Mudstone beds that generally as tops to siltstone units;
Mafic cobble breccia that are internally massive, and generally >15 m thick units dominated by subangular clasts of aphyric basalt with lesser
well-rounded rhyolitic clasts up to 15 cm across;
Felsic cobble conglomerate, made up of massive and graded beds up to 10 m thick containing subrounded <25 cm diameter clasts of moderately
A thick extrusive metabasalt, the Athena Basalt, is found in the lowermost parts of the Black Flag Group, in the St Ives Goldfields and has been mapped in some instances with the upper Paringa Basalt. Another thick volcaniclastic unit, the Black Flag Andesite, higher in the sequence comprises a reworked quartzo-feldspathic sandstone with interbedded conglomerates and forms a prominent band along the Speedway Shear Zone.
Although his formation is regionally subdivided into an early and late succession, only the Early Merougil Formation is represented at Saint Ives, occurring as the:
• Merougil Creek Beds, deposited after 2665 Ma, comprising a >2500 m thick sub-aerial quartz-rich succession subdivided into a lower conglomerate-rich package and an upper sandstone rich unit (Bader, 1994; Krapez et al., 2000). The conglomerate is polymictic, whilst the overlying sandstones are dominated by well sorted quartz-rich facies that range from massive graded, planar bedded to trough cross-bedded varieties. This sequence disconformably overlies mudstone-rich units of the Black Flag Group (Hand, 1998)
• Intrusions. As at Kalgoorlie, the Kambalda and Kalgoorlie sequences are intruded by dolerite sills, including the differentiated up to 300 m thick, 2693±50 Ma Defiance Dolerite which was injected at the base of the Paringa Basalt, and the 2680±8 Ma Junction and 500 m thick equivalent Condensor dolerites within the lower Black Flag Group which are considered to be a correlative of the Golden Mile Dolerite at Kalgoorlie. Similar to the latter, the Junction Dolerite has been differentiated into 4 zones, from basal pyroxenite; to plagioclase-pyroxene-bearing gabbro; to the most evolved granophyric zone; and the upper coarse grained, magnetite-rich granophyric plagioclase-pyroxene gabbro. Where the dolerite sill is mineralised, the uppermost of these zones is the favoured host. In contrast, the Defiance Dolerite has a more uniform composition of a high-Mg basalt.
Deposition of the Kambalda and Kalgoorlie sequences took place during D1 pulsed ENE-WSW extension from 2720 to 2670 Ma, accompanied by growth faults, initial updoming of the Kambalda Anticline, and intrusion of the Kambalda Granodiorite. The pulsed extension is reflected by internal hiatuses and unconformities within these sequences.
This was followed by regional ENE-WSW contraction during D2 from 2665 to 2660 Ma which resulted in termination of volcanism, amplification of the Kambalda Anticline and inversion of D1 growth faults.
D3, from 2660 to 2655 Ma, renewed regional ENE-WSW extension with deposition of the clastic Merougil Basin, intrusion of NW-trending porphyry dykes and formation of granitic metamorphic core complex domes.
D4a ENE-WSW contraction, from 2655 to 2650 Ma, resulting in upright folding and intense NNW foliation, as well as extensive thrusting which inverted the Merougil Basin and further amplified the Kambalda Anticline;
D4b WNW-ESE contraction at 2650 Ma, produced sinistral transpressive strike-slip shearing along pre-existing NNW trending faults parallel to the Kambalda Anticline, and thrusting on crosscutting faults perpendicular or at a high angle to the anticline axis. This phase coincided with the major gold mineralising event, particularly in jogs produced by transpression of irregularities on the NW to NNW aligned faults such as the regional Boulder-Lefroy, Zuleika and Playa faults;
D5 NE-SW contraction, from 2650 to 2625 Ma, produced dextral strike-slip transpression along pre-existing NNE trending faults and dextral transtension on brittle north-south to NNW faults in the St Ives Gold Field, where it was accompanied by minor gold mineralisation;
D6, which is regionally at ∼2600 Ma, has not been recognised in the district; and
D7 after 2400 Ma, was responsible for minor contraction and intrusion of early Palaeoproterozoic mafic dykes.
The regional NNW trending Kambalda Anticline influenced the emplacement of magmatism with a number of granite domes being buried at depth beneath the greenstone stratigraphy carapace of the structure. It also focussed gold mineralising fluids into its domed core and bounding shears, whilst deformation was partitioned across the limbs and crest of the structure.
Deposits of the St Ives Gold Field
Primary structurally controlled gold deposits are hosted in all stratigraphic units at St Ives, including the Devons Consuls Basalt, Kapai Slate, Paringa Basalt, Lunnon Basalt, Kambalda Komatiite and Black Flag Group, as well as the Condenser, Junction and Defiance dolerites and felsic and syenite dykes.
Individual Deposits and Deposit Clusters may be summarised as follows:
Junction is one of the largest single lode deposits in the Kambalda-Saint Ives Goldfield. It is located towards the southern extremity of the St Ives line of deposits, and is principally hosted within the quartz and magnetite-rich granophyric zone of the Junction Dolerire. Mineralisation is associated with quartz veining and breccia zones, with the highest grades localised on the contact between dolerite and the NNW striking and ENE dipping, strongly biotite-pyrite and biotite-pyrrhotite altered Junction N25 shear zone. Discontinuous and less well developed mineralisation extends outward into the surrounding equigranular dolerite. The Junction Dolerite is gently folded about a NW-trending axis, with the high grade zone following the granophyric zone from gently plunging in the axial crest near surface, to steeply NW as it follows the favourable lithology down the northern limb. The mineralisation changes from pyrite-dominant near surface to predominantly pyrrhotite at depth. Other less significant structures are also evident, including the moderately mineralised, sub-parallel N75 structure, ~400 m to the east. Cumulative production to 2017 was 9.6 Mt @ 6.6 g/t Au, for 63 t of contained gold from one underground mine and one open pit (Oxenburgh et al., 2017).
The principal deposits of the Argo cluster include Argo, Apollo, Diana, Athena and Hamlet. These deposits lie within a kilometre scale fault/fracture network, principally composed of north-striking, steep to moderately east and west dipping dextral reverse shear zones. These structures form links between NW-trending splays from the major regional Boulder-Lefroy Fault zone that is to the east (Oxenburgh et al., 2017).
Argo is located within the Condensor Dolerite, and comprises an interconnected network of 5 to 15 m thick shear zones that are moderately west-dipping, and are linked by shallow north-dipping subsidiary shears. Mineralisation occurs within 2 to 5 m thick zones of quartz-carbonate fault fill veining, extension veins and hydraulic breccia. These zones are fringed by a 1 to 2 m wide proximal alteration assemblage of dominantly albite-carbonate-biotite-pyrrhotite-pyrite, passing out to a distal envelope of chlorite-biotite that extends for up to 10 m from the quartz-carbonate lodes. The shallow-dipping segments of the main shear zone contain thick and voluminous high grade breccias up to 15 m wide, while steeper dipping segments of the same structure appear to be more ductile with lesser veining and alteration. The shallowly dipping segments are commonly coincident with the intersection between shallowly north-dipping faults and the footwall of the main shear zones, forming high grade plunging shoots. The highest grade and most continuous of these shoots occur within the granophyric and magnetite-rich sections of the Condensor Dolerite (Oxenburgh et al., 2017).
Athena and Hamlet are ~1000 m apart, hosted by the Upper Paringa Basalt, occurring within 10 to 30 m wide, north-striking, moderately east dipping shear zones. As at Argo, mineralisation accompanies quartz-albite shear parallel, extensional and breccia veins with 1 to 2 m wide selvages of proximal albite-biotite-actinolite-pyrite pyrrhotite alteration and distal assemblages of chlorite-biotite-carbonate that persit for up to 15 m from the central vein. Gold grades are proportional to the vein density and proximal alteration intensity, with mineralisation being primarily controlled by the intersection between the iron-rich Upper Paringa Basalt and Athena and Hamlet shear zones in the respective deposits. Higher grade, thick and continuos development of mineralisation are localised by strike and dip changes of the basalt and shear zones. Orientaion changes within the shear zones is often infuenced by pre-mineral felsic porphyry dykes. Within the high MgO Lower Paringa Basalt to the north, the shear zones become wider and less focussed and mineralisation becomes weaker and discontinuous. Shallow, north dipping shear zones are also mineralised for up to 40 m beyond where they intersect the main Athena and Hamlet shears, but rapidly wane at greater distances to become weak to barren chlorite altered shears. Zones of supergene mineralisation up to 300 m long, 1 to 2 m thick and 60 m wide are present within the saprolite zone at both deposits. Total production + reserves from the Argo cluster of >5 active mines (in 2017) had totalled 17.7 Mt @ 4.5 g/t Au for ~80 t of gold to 2017 (Oxenburgh et al., 2017).
The Victory Complex comprises at least 14 mines exploiting a number of lodes related to a major jog in the sinistral-reverse, northwest trending Playa Shear Zone. The Leviathon Pit has amalgamated the earlier Victory, Defiance, Conqueror and East Repulse open pit and underground operations (Oxenburgh et al., 2017).
At Defiance, mineralisation is controlled by shallow dipping dilatant thrusts within the footwall of the steeper Repulse Shear Zone cutting Defiance Dolerite and Paringa Basalt. An envelope of quartz rich veins and dilational breccia occurs within a cross-cutting extensional array of quartz veins that is up to 5 m wide. Wall rock alteration composed of intense albite-carbonate-pyrite is found immediately adjacent to the lodes (Oxenburgh et al., 2017).
At Conqueror, a laterally extensive array of anastomosing quartz veins represents the down dip extension of the Defiance Shear Zone (Oxenburgh et al., 2017).
At Repulse, mineralisation is associated with a thin, <1 m thick, cataclasite band that has undergone intense albite-carbonate alteration and extends into the hanging wall of the Repulse Shear via a network of <5 mm carbonate-quartz veinlets and albite replacement alteration following zones of pre-existing weakness. It is generally restricted to those parts of the shear that dip more shallowly than 45°. At East Repulse, mineralisation accompanies an anastomosing quartz-carbonate breccia above a sub-horizontal ramp that is sub-parallel to a footwall felsic porphyry dyke swarm. The breccia veins are surrounded by pervasive albite-carbonate alteration with substantial amounts of euhedral pyrite. Very strongly albite-carbonate-pyrite altered rafts of Kapai Slate with quartz veining are enclosed within the Repulse Shear Zone. Where mineralised, the Kapai Slate always exhibits pyrite replacement of earlier magnetite that has, in turn, replaced primary sedimentary pyrite (Oxenburgh et al., 2017).
Sirius and Britannia, which are in the hanging wall of the Repulse Shear Zone, comprise mineralised quartz-carbonate breccia with albite-biotite-pyrite alteration overprinting earlier ductile fabrics. Britannia contains very high grade mineralisation that includes intense, coarse pyrite alteration surrounding a deformed felsic porphyry.
The Victory group of deposits had a total known endowment in 2017 of ~112 t of gold (Oxenburgh et al., 2017).
Mineralisation in the Orchin area occurs as a series of deposits developed within a strike interval of 2.2 km, from Orchin in the south to Thunderer in the north, related to the east dipping, north-south striking Orchin A2 reverse shear zone. The high grade shoots correspond to the intersection of the A2 Shear Zone and the SW-dipping Kapai Slate. This intersection forms shallow plunging, elongate arrays of quartz veins accompanied by albite alteration and replacement of magnetite by pyrite. Mineralisation also occurs in chloritic shear zones, fault filling veins and pyrite alteration in the Defiance Dolerite and Paringa Basalt. Total production to 2017 amounted to 5 Mt @ 2.9 g/t Au, for 14.5 t of gold (Oxenburgh et al., 2017).
This group of at least 21 mines exploits deposits that include Revenge, West Revenge, Delta, Agamemnon, NRK, W45, W66, Minotaur, Mars, Belleisle and Grinder. Gold mineralisation within these deposits is associated with a complex shear zone and quartz vein system dominantly within mafic host rocks, including the Kambalda Komatiite, Devon Consols Basalt, Kapai Slate, Defiance Dolerite, Paringa Basalt and felsic-intermediate porphyries. With the exception of Belleisle and Grinder, which are hosted within the Playa Shear Zone, all are controlled by an array north-south striking reverse shear zones. These shears are located between the major NW trending Playa and Delta shear zones to the east and west respectively. Individual shears are typically 100 to 200 m apart and dip at 30 to 60°E, shallowing with depth, with a listric relationship to the domal W66 shear, suggesting an extensional core complex setting. The stratigraphic sequence dips gently to the NE. Intersections between shear zones and more favourable units (e.g., the Kapai Slate) frequently determine the location of high grade shoots, and the development of dilatant zones based on chemical and competency characterisics respectively. Intermediate porphyry sills and dykes are predominantly barren to low grade, and frequently disrupt the continuity of grade. Mineralisation occurs as central shear and/or breccia veins, with accompanying extensional veins up to 30 cm thick that may persist for up to 10 m from the central shear veining. Halos of pale brown to cream albite-carbonate-pyrite that are up to 1 to 2 m wide and envelope the vein arrays and contrast with the dark green country rock. This grades out into chlorite alteration with lesser biotite and dolomite that persists for up to 10 m into the surrounding host units (Oxenburgh et al., 2017).
At the main Revenge deposit, the outer chlorite zone extends from 10 to 30 m from the centre of the shear zones, and predominantly comprises chlorite with lesser amounts of biotite and dolomite. As the shear zone is approached the chlorite is replaced by biotite, carbonate and minor albite, pyrite and magnetite, which are strongly aligned with the shear fabric. The inner albite rich zones are commonly adjacent to the quartz veins. Two shear zone directions are recognised in the Revenge deposit:
i). East dipping shear zones - which trend NNW to NNE and dip at 40 to 45°E with gold grades of 4 to 5 g/t, associated with quartz veins and albite-pyrite rich altered wall rocks. These structures are mainly hosted by the Defiance Dolerite in the eastern part of the mine, while lodes to the west are hosted by the Devon Consols Basalt. The most important of these, the N01-S01 shear, is 1 to 12 m thick and has a continuous strike length of ~900 m. The next most significant, the N22 Shear has a strike length of ~400 m and varies in width from 1 to 8 m, hosted by Paringa Basalt and felsic porphyry. These shears host complex quartz vein systems, comprising shear- and extensional-veins. The former are 5 to 70 cm thick and 10 to 100 m in strike length, and commonly occupy the centre of the shear zones. The extensional veins are north- to NE-trending and dip at 5 to 25°E. They vary from 1 to 30 cm in thickness, and extend for up to 20 m from the centre of the shear zones, commonly cutting the shear veins with visible albite-carbonate-pyrite alteration halos.
ii). West dipping shear zone, which trend north to ENE and dip at 10 to 15°WNW and is 200 to 300 m below surface. It is principally hosted by the Devon Consols Basalt but extends eastward into the Kapai Slate and intermediate porphyry which has intruded the base of the latter. To the NW the shear passes into the Kambalda Komatiite, where it thickens with lower gold grades of only ~1 g/t compared to the average of 3.5 g/t for the structure. The shear zone is characterised by a subhorizontal undulating fabric with a large brecciated zone in the centre of the structure, filled by 0.5 to 5 m thick quartz veins. Geometrical and kinematic indicators suggest the structure is a D3 thrust zone with a displacement of ~70 m , representing an ESE–WNW subhorizontal shortening and subvertical extension at the time of formation. The vein system in this shear zone is dominated by quartz with subordinate carbonate and albite. Shear veins are well developed and typically occupy the core of the shear zone. Individual shear veins have dimensions of ~50 to 100 m along both dip and strike, whilst thick breccia veins commonly occur as large dilational jogs on the releasing side of the curved shear surfaces. Extension veins have prominent albite alteration haloes, but are less well developed than in the east-dipping shear zones and range from 1 to 20 cm in thickness, with strike lengths that vary in strike from 5 to 040° and dip 10 to 30°E. Disseminated gold is mainly associated with altered wall
rock, especially in the albite-biotite-dolomite zones, whilst visible gold up to 10 µm in diameter is common in pyrite-rich quartz veins. Pyrite is the best mineralogical indicator of high gold in both the disseminations and veins, as gold is commonly present as inclusions in pyrite or coats and infiltrates pyrite grains along fractures. (Nguyen et al., 1998).
Many of the Revenge deposits have an associated broad 1 to 5 m thick, sub-horizontal supergene horizon within the saprolite profile, carrying >1 g/t Au that extends for as much as 80 m laterally from the deposit. Total cumulative production to 2017 has been 33 Mt @ 2.4 g/t Au for ~79 t of gold (Oxenburgh et al., 2017).
This line of deposits includes Intrepide, Formidable, Redoubtable and Temeraire which are associated with intrusives into the Kambalda Komatiite along the crest of the Kambalda Dome/Anticline. The Intrepide deposit comprises a quartz vein stockwork with an associated strong zone of albite alteration with 2 to 5% pyrite. It occurs within a west dipping mylonite, immediately to the west of the Playa Shear Zone. Mineralisation at Redoubtable, Formidable and Temeraire comprises parallel, sub-vertical envelopes of quartz-vein stockworks hosted by felsic porphyry dykes. Narrow, 1 to 2 m wide high grade zones are hosted by zones of ductile deformation within the surrounding Tripod Hill Member of the Kambalda Komatiite along the immediate contact with the porphyry. Associated alteration comprises biotite-pyrite in the Tripod Hill Member and albite-pyrite accompanying the stockwork zone in the brittle felsic porphyries. Total production fom the cluster to the end of 2016 was 10 Mt @ 2 g/t Au for ~20 t of gold (Oxenburgh et al., 2017).
The Intrepide Cluster includes the Beta-Hunt mine which hosts both nickel and gold resources in adjacent discrete mineralised zones. The mining tenements (as of 2019) on which the Beta Hunt Mine is located are held by Gold Fields Limited. The Royal Nickel Corporation owned Salt Lake Mining Pty Ltd operates the Beta Hunt Mine by virtue of a sub-lease agreement with Gold Fields Limited. Nickel mineralisation is mainly hosted by talc-carbonate and serpentine altered ultramafic rocks of the Kambalda Komatiite and typically comprises pyrrhotite-pentlandite-pyrite±chalcopyrite. Gold mineralisation predominantly occurs mainly within the Lunnon Basalt in the footwall to the nickel-bearing ultramafics, and is characterised by intense albite, carbonate and chlorite alteration, with a halo of biotite/pyrite. Beta Hunt Gold Mineral Resources comprise Measured+Indicated resources of 10.104 Mt @ 2.9 g/t Au plus Inferred resources of 4.109 Mt @ 3.1 g/t Au for a cumulative total of ~42 t of gold. The deposit has yielded bonanza grade zones of coarse massive gold veining within broader quartz veins (Oxenburgh et al., 2017).
Invincible Lode - one of the gold bearing lodes within the Invincible deposit. Visible gold is circled in red. Fine pyrite cubes are evident in the darker bands. Image by Mike Porter, 2019, of drill core at St Ives.
The Invincible deposits are hosted by mudstone and fine siltstone at the top of the Black Flag Group within the NNW trending Speedway Shear Zone on the western limb of the Kambalda Anticline. These siltstone and mudstone hosts are underlain by the Morgan Island Shear Zone which separates them from an underlying quartzofeldspathic sandstone unit interpreted to represent a reworked andesite. In turn, the hosts immediately underlie clastic sedimentary rocks of the Merougil Formation, below the Merougil Shear Zone. Together these two bounding structures, which dip at ~70° WSW, constitute the multistrand Speedway Shear Zone. Mineralisation is predominantly hosted in the mudstone and comprises bedding-parallel, shear-hosted, laminated to brecciated quartz veins accompanied by intense albite alteration, pyrite and free gold. NNW dipping extension veins up to 20 cm thick extend for as much as 10 m into the footwall andesitic volcanosedimentary rocks containing hematite alteration and free gold. Other alteration associated with the mineralisation includes carbonate (dolomite and ankerite), actinolite, biotite, chlorite, sericite and pyrrhotite. The main deposit comprises three 20 to 30°S plunging shoots. Invincible South, which is 500 m to the SSW across a fault zone has a similar mineralisation and structural orientation. Invincible and Invincible South had produced 4.412 Mt @ 2.85 g/t Au to 2017, containing ~12.6 t of gold contributing to an endowment of >37 t (Oxenburgh et al., 2017).
Santa Ana and Bahama
This small cluster is located 2 to 3 km to the west of the main Intrepide line of deposits on the western limb of the Kambalda Anticline, adjacent to the NE-SW trending Alpha Island Fault, which also cuts the Invincible deposits to the SW. Mineralisation occurs as quartz vein arrays and breccia lodes within sub-parallel, 1 to 5 m thick shear zones on the flanks of a large trondhjemite intrusion. Lode mineralisation is only found in steep shear zones within the Paringa Basalt, with shallower vein arrays occurring in the footwall of the shear zone within the trondhjemite. The total production form the deposit cluster was 3.2 Mt @ 2.5 g/t Au for 8 t of gold (Oxenburgh et al., 2017).
The Cave Rocks deposit is located ~5 km west of Kambalda, adjacent to the Zuleika Shear Zone, and is principally hosted by the Condensor Dolerite. The typical Kambalda–St Ives stratigraphic succession is structurally disrupted, with widely disparate units fault juxtaposed. Ultramafic rocks of the Kambalda Komatiite are exposed to the west, faulted against an intrusion that is compositionally similar to the Condenser Dolerite. Packages of alternating 10 to 100 m thick, subvertical units of sedimentary rock, black shale, chert and wacke, correlated with the Black Flag Group interleaved with dolerite, occur to the east. These rocks have been subjected to mid-amphibolite facies metamorphism, which is generally higher grade than is seen in the main St Ives deposits to the east.
The mineralisation is composed of two subvertical, probably en echelon orebodies known as the East and West lodes which are subvertical, 2 to 10 m thick lenses with a gentle southerly plunge within a 5 to 50 m wide chlorite-rich shear. The central core of this shear contains quartz veins with biotite altered wall rocks with the addition of albite in the high grade zones. The ore mineralogy is similar to that at Argo, with pyrrhotite and some euhedral arsenopyrite (Watchorn, 1998). Production from Cave Rocks to 2017 has amounted to 0.584 Mt @ 3.32 g/t Au in open cut, and 3.792 Mt @ 3.96 g/t Au for a total combined 17 t of gold (Oxenburgh et al., 2017).
The Incredible deposit is located to the west of the Speedway Shear Zone, on the eastern limb of the Merougil Syncline. It is hosted at the unconformable contact between the Merougil Formation and the underlying Black Flag Group, ~5 km WSW of the Argo deposit. The principal hosts are polymictic conglomerate and sandstone of the Merougil Formation, and upper Black Flag turbiditic facies. The fabric within the latter suggest a lack of deformation, while in contrast, flattening of clasts and a NNW dipping cleavage within the matrix of the conglomerate imply deformation of the Merougil Formation. Mineralisation occurs in association with a dominant set of laminated quartz veins which dip to the SW. These veins have visible gold, but little accompanying pervasive wall rock alteration, other than inconsistent phengite developed within 5 cm of the veins. Two other vein sets carry visible gold, one parallel to bedding and the other which follows the foliation (Oxenburgh et al., 2017).
In summary, the lode gold deposits of the gold field are hosted by almost all of the units of both the Kambalda and Kalgoorlie sequences, from the Lunnon Basalt to the Merougil Conglomerate, particularly the Lunnon Basalt, Tripod Hill Komatiite, Devon Consols Basalt, Kapai Slate, Defiance Dolerite, Paringa Basalt, and the Condensor and Junction Dolerites within the Black Flag Group. The deposits are composed of 0.5 to 20 m wide, structurally controlled quartz veins, breccias, stockworks, mylonites and disseminations with geometry and alteration asemblages influenced by the host rock competence and chemistry.
Gold mineralisation is localised within low-displacement reverse shear zones up to 1 km long with maximum displacement of up to a few hundred metres. Many of the mineralised shears are local structures, adjacent to larger NNW-trending regional shear zones, such as the Playa Shear Zone, to which they are interpretted to be related. The Playa Shear Zone extends for an interval of 10 to 15 km south of the Kambalda Dome, and is considered to be a second order structure, a splay which converges southwards with the major regional composite Boulder-Lefroy Shear Zone to its NE. The Boulder-Lefroy Shear Zone is composed of three segments connected via a series of soft linkages or accommodation zones. The St Ives, New Celebration and Kalgoorlie gold deposits all occur in the footwall of these fault segments (e.g., Blewett et al., 2010).
Ore is contained within 2 to 10 m wide thrust/shear zones trending north to NNW. Gold deposits are also associated with stockworks and vein arrays that have been developed in brittle host rocks, such as the Kapai Slates and the felsic to intermediate lithologies, in breccia zones and central, quartz rich and mylonitic parts of shear zones which are invariably only minor structures. They are also associated with post-peak metamorphic faults and thrusts which post date felsic dyking and are also splays from the nearby regionally extensive Boulder-Lefroy Fault.
Alteration zonation associated with mineralisation comprises a core development of albite-ankerite/dolomite-quartz-pyrite, with gold being associated with the pyrite; enclosed by a biotite zone; passing in turn into a chloritic halo and then the regional greenschist metamorphic assemblage.
In addition to the lode gold deposits, mineralisation is also present as supergene concentrations which comprise broad zones of flat-lying gold mineralisation in weathered Archaean and overlying Cenozoic sediments; and as palaeoplacer deposits hosted by palaeochannels in the unconsolidated Cenozoic cover that overlies the Archaean basement.
Palaeoplacer deposits are developed within the ~140 km network of meandering, dendritic, Eocene fluvial palaeo-channels developed within the district. These palaeochannels overlie and are incised into saprolitic profile developed within the Archaean basement, comprising, from the base:
• Pidinga Formation - which comprises a basal palaeochannel sequence that is typically composed of clay dominant sediments containing 10 to 20% sand and gravel. These are overlain by marine clays that are typically 15 to 40 m thick with intermittent and discontinuous intercalated lignite beds;
• Princess Royal spongolite, composed of >50% siliceous sponge spicules with silt, clay, sand and glauconitic sandstone which overlie the palaeochannel sediments and lap onto the saprolitic basement;
Oligocene to Miocene
• Revenge Formation - fine grained, oxidised, ferruginous, non-marine sandy clays with marginal ferricrete facies;
• Aeolian calcareous dunes - calcareous sandy loams and pisolitic gravel.
The Palaeochannel gold deposits are focussed in sand and gravel bearing clays at the base of broad incised channels, generally from north of Argo to Intrepide. Deposits mined comprise quartz gravel and clay-rich gravel in channels that vary from 60 m deep and 200 m wide, as at Neptune, Thunderer (near Orchin) and Argo, to steep sided tributaries that are ~20 deep and 40 m wide, as at Africa.
Two styles of gold mineralisation are recognised: i). basal sands and gravel hosted in palaeochannels which are typically of higher grade; and ii). oxide mineralisation, which is more extensive, representing oxidised hypogene mineralisation, occurring within saprolite below channel. Mineralisation is typically 1 to 2 m thick, although rare accumulations of up to 5 m thick are locally important. Production from the key palaeochannel deposits of Neptune and Africa totalled 0.819 Mt @ 3.32 g/t Au for 2.7 t of gold.
Reserves, Resources and Production
The complex of more than 60 deposits has been historically operated by WMC Resources Gold Division until 2001, before being purchased by the Gold Fields Group.
The endowment of individual deposits and clusters are included within the descriptions above.
To June 1997, the total production at St Ives had totalled:
15.6 Mt @ 4.2 g/t Au underground, and 14.3 Mt @ 2.8 g/t Au open pit for 105 t of contained Au
The total resource in December 1999 was:
23.5 Mt @ 6.4 g/t Au underground and 33.9 Mt @ 2.5 g/t Au open-cut for 235 t of contained Au.
At December 31 2006 the reserves and resources were quoted at (Gold Fields, 2008):
proved + probable reserve - 27.74 Mt @ 2.7 g/t Au,
measured + indicated + inferred resource - 56.6 Mt @ 2.9 g/t Au.
In 2007, production was 0.1336 Mt @ 5.28 g/t Au (underground) and 3.928 Mt @ 2.23 g/t Au (open pit), with a waste to ore ratio of 6.38.
Total production from all deposits to the end of 2016 was 136.385 Mt @ 3.0 g/t Au for 409 t of contained Au;
Total Measured+Indicated+Inferred Mineral Resources at 31 December, 2016 were 30.126 Mt @ 3.4 g/t Au for 102 t of gold (Oxenburgh et al., 2017).
Remaining JORC compliant Ore Reserves and Mineral Resources as at 31 December, 2018 were (Gold Fields Annual Report, 2018):
Proved + Probable Ore Reserves - 19.1 Mt @ 2.84 g/t Au for 54.25 t of contained Au;
Measured Mineral Resource - 2.154 Mt @ 3.58 g/t Au for 7.7 t of contained Au;
Indicated Mineral Resource - 19.815 Mt @ 4.13 g/t Au for 81.8 t of contained Au;
Inferred Mineral Resource - 7.779 Mt @ 3.58 g/t Au for 27.8 t of contained Au;
TOTAL Mineral Resource - 29.747 Mt @ 3.68 g/t Au for 122.2 t of contained Au.
NOTE: Mineral Resources are Inclusive of Ore Reserves.
In 2018, production was 0.911 Mt @ 4.1 g/t Au (underground) and 3.396 Mt @ 2.7 g/t Au (open pit), with a waste to ore ratio of 5.1.
The most recent source geological information used to prepare this summary was dated: 2017.
Record last updated: 5/10/2019
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Anonymous 1996 - The WMC Group: in Extracts form WMC 1996 Annual Report pp 1, 24-26, 36-37|
Anonymous 1998 - Saint Ives (WMC): in Register of Australian Mining 1997/98 p 162|
Bath A B, Walshe J L, Cloutier J, Verrall M, Cleverley J S, Pownceby M I, Macrae C M, Wilson N C, Tunjic J, Nortje G S and Robinson P, 2013 - Biotite and Apatite as Tools for Tracking Pathways of Oxidized Fluids in the Archean East Repulse Gold Deposit, Australia: in Econ. Geol. v.108 pp. 667-690|
Blewett, R.S., Squire, R., Miller, J.M., Henson, P.A. and Champion, D.C., 2010 - Architecture and geodynamic evolution of the St Ives Goldfield, eastern Yilgarn Craton, Western Australia: in Precambrian Research v.183, pp. 275-291.|
Cox S F, Ruming K, 2004 - The St Ives mesothermal gold system, Western Australia - a case of golden aftershocks?: in J. of Structural Geology v26 pp 1109-1125|
Evans, K., 2010 - A test of the viability of fluid-wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the Kambalda-St. Ives goldfield, Western Australia: in Mineralium Deposita v.45 pp. 207-213|
Gregory, D.D., Large, R.R., Bath, A.B., Steadman, J.A., Wu, S., Danyushevsky, L., Bull, S.W., Holden, P. and Ireland, T.R., 2016 - Trace Element Content of Pyrite from the Kapai Slate, St. Ives Gold District, Western Australia: in Econ. Geol. v.111, pp. 1297-1320.|
Kriewaldt M 1998 - Nelsons Fleet gold deposit, St Ives: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 239-242|
McGoldrick, K.L., Squire, R.J., Cas, R.A.F., Briggs, M., Tunjic, J., Allen, C.M., Campbell, I.H. and Hayman, P.C., 2013 - The largest Au deposits in the St Ives Goldfield (Yilgarn Craton, Western Australia) may be located in a major Neoarchean volcano-sedimentary depo-centre: in Mineralium Deposita v.48, pp. 861-881.|
Miller, J.M., Blewett, R.S., Tunjic, J. and Connors, K., 2010 - The role of early formed structures on the development of the world class St Ives Goldfield, Yilgarn, WA: in Precambrian Research v.183, pp. 292-315.|
Mueller, A.G., Hagemann, S.G. and McNaughton, N.J., 2020 - Neoarchean orogenic, magmatic and hydrothermal events in the Kalgoorlie-Kambalda area, Western Australia: constraints on gold mineralization in the Boulder Lefroy-Golden Mile fault system: in Mineralium Deposita v.55, pp. 633-663.|
Neall F B, Phillips G N 1987 - Fluid-wall rock interaction in an Archean hydrothermal Gold deposit: A thermodynamic model for the Hunt mine, Kambalda: in Econ. Geol. v82 pp 1679-1694|
Neumayr P, Walshe J, Hagemann S, Petersen K, Roache A, Frikken P, Horn L and Halley S, 2008 - Oxidized and reduced mineral assemblages in greenstone belt rocks of the St. Ives gold camp, Western Australia: vectors to high-grade ore bodies in Archaean gold deposits?: in Mineralium Deposita v43 pp 363-371|
Nguyen P T, Donaldson J S, Ellery S G 1998 - Revenge gold deposit, Kambalda: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 233-238|
Oxenburgh, S.K., Falconer, M., Doutch, D., Edmonds, O., Foley, A. and Jane, M., 2017 - Kambalda-St Ives Goldfield: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy, Mono 32, pp. 215-222.|
Palin J M, Xu Y 2000 - Gilt by association? Origins of Pyritic Gold ores in the Victory mesothermal Gold deposit, Western Australia: in Econ. Geol. v95 pp 1627-1634|
Roberts D E, Elias M 1990 - Gold deposits of the Kambalda-St Ives region: in Hughes FE (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 479-491|
Watchorn R B 1998 - Kambalda-St Ives gold deposits: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 243-254|
Weinberg R F, Van der Borgh P, Bateman R J and Groves D I, 2005 - Kinematic History of the Boulder-Lefroy Shear Zone System and Controls on Associated Gold Mineralization, Yilgarn Craton, Western Australia : in Econ. Geol. v100 pp 1407-1426|
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