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Higginsville Gold Field - Trident, Chalice, Poseidon South, Graveyard, Mitchell, Challenge-Swordsman |
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Western Australia, WA, Australia |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Higginsville Gold Field is located ~120 km south of Kalgoorlie, in the Kalgoorlie Terrane of the Eastern Goldfields Superterrane in the Yilgarn Craton, Western Australia. It encompasses alluvial gold accumulations and a cluster of small to medium sized lode gold deposits that include the recent Trident, Chalice, Two Boys and Poseidon South hard rock deposits, the Graveyard, Mitchell and Challenge Swordsman palaeochannel placer deposits and the small historic Fairplay, Sons of Erin and Eundynie mines. These deposits and occurrences are distributed over an area of ~12 x 8 km.
In addition to these deposits, the Higginsville Carbon-in-Pulp gold processing plant treats ore (in 2019) from the small Brigette and Sophia open pits in the Lake Cowan Gold Field <10 km to the NE and from the larger Mt Henry cluster Mt Henry, Selene and North Scotia deposits ~70 km to the south in the Noresman area. The latter is to replace the declining reserves of the Trident deposit.
The Higginsville Gold Field, is located between the Norseman deposits to the south, and the Saint Ives cluster to the north. The supracrustal succession within the district comprises a lower mafic-ultramafic sequence overlain by felsic volcanic and volcaniclastic rocks deposited between 2700 and 2690 Ma and at <2680 Ma respectively. These are equivalent to the Kambalda and Kalgoorlie sequences respectively that are defined in the Kalgoorlie and Saint Ives gold fields. The mafic-ultramafic suite comprises fault-bounded, thrust repeated NNW trending mafic-ultramafic and sedimentary packages developed over a width of up to 5 km (McEwan, 2001). These rocks have been metamorphosed to upper greenschist to middle amphibolite facies and are principally high magnesium basalt, minor komatiite units and interflow clastic sedimentary rocks intruded by dolerite and gabbro. The overlying felsic suite is composed of sedimentary rocks to the east and includes felsic metasedimentary, felsic volcaniclastic rocks and carbonaceous shales (Buerger et al., 2010). This supracrustal sequence is intruded, or bounded, by numerous granitoid bodies, which were emplace during two major periods of magmatism at 2690 to 2685 Ma and 2665 to 2660 Ma and by minor intrusive activity at 2630 to 2600 Ma. See the Yilgarn overview record for more detail of the regional setting.
The Chalice gold deposit is hosted by an interlayered mafic-ultramafic rock sequence of tholeiitic and komatiitic basalts, flanked to the west and east by granitic bodies, and locally intruded by four generations of monzogranite dykes, within a middle to upper amphibolite facies metamorphic domain.
Two stages of gold mineralisation have been identified on the basis of crosscutting relationships, formed under broadly syn-peak to post-peak metamorphic conditions respectively.
The orogenic lode-type Main stage gold mineralisation, which represents 95% of the resource, accompanied D2 deformation and comprises S1 foliation-parallel, quartz-albite-diopside-titanite-garnet-gold veins and wall-rock replacement, both of which occur within locally developed asymmetric folds in mafic amphibolite.
Second stage magamtic event gold mineralisation, is associated in time with a second-generation, post-Main stage, monzogranite dyke that crosscuts the folds and comprises disseminated gold within the dyke as well as S1 foliation-discordant quartz-gold, quartz-diopside-gold, actinolite-gold, and molybdenite-tellurobismuthite-gold veins.
Gold is in textural equilibrium with hydrothermal alteration assemblages in both of the mineralisation stages and also with primary igneous phases (quartz and feldspar) in the monzogranite dyke in the Second stage ore. Geologically constrained geochronologic data suggest that the two stages are independent gold events separated by up to 20 m.y.
The quoted resource at Chalice in 2003 was 4 Mt @ 4.9 g/t Au (Bucci et al., 2004).
The Trident gold deposit was discovered in late 2004 and is 200 m NNE of the mined out Poseidon South open pit. It was developed as an underground mine that commenced operations in 2007. The deposit comprises a series of NNE trending, shallowly north plunging ore zones designated the East Vein, Poseidon, Eastern Zone, Western Zone, EOS, Athena, Apollo, Helios and Artemis.
The deposit is primarily hosted within a thick, multiply deformed, weakly differentiated gabbro with subordinate mafic and ultramafic lithologies bounded by sedimentary packages to the west and east. Shearing and faulted contacts are common, and the constituent units have been structurally repeated by east over west thrust faulting. The bulk of the mineralisation is hosted within the large, zoned Poseidon Gabbro and a metasomatically altered basalt in the south of the deposit. The Poseidon Gabbro is a thick sill that is weakly differentiated (Newman et al., 2005) and strikes north-south, dips 60°E. It is >500 m thick and 2.5 km long. The gabbro is divided into five zones, with Zone 3 considered the most favourable for mineralisation. Zone 3 is characterised by tabular sub-euhedral feldspar and stubby amphibole crystals, and is basically a quartz granophyre that is conducive to brittle fracturing and gold deposition. This Zone 3 gabbro is the primary host to the large wallrock-hosted mineralised systems with the Western Zone and Apollo forming near the gradational basal contact
of Zone 3, whilst the Eastern Zone is located near the contact with the overlying Zone 4 (Stokes et al., 2011).
To the south, the gabbro is underlain by a sheared actinolite-chlorite mafic unit, known as the Eastern Mafic, that at depth grades into a coarse acicular actinolite-bearing high MgO basalt that is interpreted to be the protolith to the sheared rock. The intrusive gabbro body is overlain by a high MgO basalt
that although not as coarse, exhibits the same variable acicular actinolite growth as the basalt unit underlying the Poseidon Gabbro (Brown, 2005). Both of these basalts are interpreted to be equivalents of the Paringa Basalt at Kalgoorlie and Kambalda and predate the gabbro intrusion.
Overlying the basalts, a thrust juxtaposed sedimentary succession of interbedded shales, siltstones and volcaniclastics is considered part of the regionally extensive Black Flag Beds. The sheared contact is locally known as the Poseidon Thrust and is considered prospective for gold mineralisation. The stratigraphy is cross-cut and offset by a large subvertical structure, locally known as the Athena Shear. To the west of the shear, the offset Poseidon Gabbro is underlain by a tectonically emplaced, talc-rich ultramafic unit, interpreted to be an altered komatiite analogous to the Kambalda Komatiite (2708±7 Ma; Nelson, 1997). The faulted eastern contact of this ultramafic unit is a host to lode-style gold deposits (Stokes et al., 2011).
Overall, the Trident Deposit plunges at ~20° to the north over an interval of >1700 m. The mineralisation can be divided into two main styles (Stokes et al., 2011);
i). Large wallrock-hosted ore zones comprising sigmoidal quartz tensional vein arrays of various attitudes with associated metasomatic (primarily silica-albite) wall rock alteration (Western Zone, Eastern Zone and Apollo), hosted exclusively within the Poseidon Gabbro. These orebodies are primarily within steeply east dipping shear zones. Gold is free milling but microscopic and occurs in both arsenopyrite-quartz tensional vein arrays and the surrounding sulphide bearing alteration zones. Rare coarse gold is almost exclusively associated with the quartz tensional vein arrays. The high grade alteration assemblage is defined by intense silica and albite, although the highest grades occur where arsenopyrite is also evident. The Western Zone, Eastern Zone and Apollo make up approximately 80% of the in situ resource tonnes and 60% of the contained metal (Stokes et al., 2011).
ii). Thin, lode-style, nuggety laminated quartz veins (Athena and Artemis) that formed primarily at sheared lithological contacts between the various mafic and ultramafic lithologies. Athena is a quartz lode style ore system characterised by narrow (0.5 to 3 m wide) shear zone controlled, laminated quartz veins and associated variable host rock mineralisation that extends up to 5 m into the wallrock. Native gold is erratically distributed, spatially associated with laminated sulphide bearing domains as well as in late stage micro-fractures. The common mineral assemblage comprises quartz–arsenopyrite-pyrrhotite-galena-gold, with galena having a very close spatial association with higher grade zones. Pyrite and chalcopyrite have also been recognised. Wall rock alteration is composed of chlorite ±biotite but is relatively weak and proximal to the ore zone. Athena and Artemis collectively account for 20% of the in situ resource tonnes and 40% of the contained metal (Stokes et al., 2011).
The total Mineral Resource at the feasibility stage for Trident in May 2006 was 4.5 Mt @ 4.6 g/t Au, amounting to 20.7 t of contained gold;
The pre-depletion Mineral Resource inventory in January 2010 was 7.1 Mt @ 5.1 g/t Au, for 36.2 t of contained gold.
Production from 2007 to 2010 was 1.89 Mt @ 4.2 g/t Au for 7.9 t of contained Au (Buerger et al., 2010).
The Two Boys gold deposit is masked by an ~50 m thick lateritic weathering profile and is hosted by a sequence of high-Mg basalt, gabbro and minor sedimentary rocks. This sequence includes the Fairplay quartz gabbro, which cuts the SW corner of the deposit area. A NW strike and
subvertical dip have been interpreted from drill intersections of a narrow intercalated metasedimentary unit. High-Mg basalt predominates, varying in texture from a fine grained, variolitic rock to a doleritic granophyre, with the strongest gold mineralisation developed within the granophyric phases. The sequence is cut by a low angle shear/thrust zone, the Two Boys shear zone which strikes east-west with an overall dip of ~27 to 30° NNE. The shear hosts the Two Boys gold deposit, which occurs as lenses of quartz-vein reef of variable width and extent with sheared, altered and mineralised selvages. A second significant reef structure 100 m to the north strikes NNW with a shallow easterly dip and contains alteration and subeconomic gold mineralisation. Whilst the mineralised shear and the associated quartz veining, wall rock alteration and gold mineralisation are laterally persistent throughout the lease area, higher grade gold mineralisation is confined to two main areas in the east and west of the deposit area. Adjacent to the mineralised shear zone, the host high-magnesium
basalt is intensely foliated over several metres into the wall rock, and is characterised by intense biotite-chlorite-carbonate-sericite-pyrite alteration. Mineralisation occurs in quartz veins and sheared selvages and is often visible as coarse free gold grains up to several mm in diameter. Carbonate, arsenopyrite and pyrite are important accessories to the gold. Carbonate, occurring as coarse-grained intergrowths with quartz and as irregularly distributed disseminations of fine grained masses are widely distributed throughout the altered zone. Euhedral arsenopyrite occurs as crystals up to several millimetres across, whilst fine grained euhedral pyrite has a much wider distribution, spread throughout the alteration zone. Minor discrete crystals of scheelite within quartz veins, is also frequently associated with the mineralisation.
Mineral Resources and Ore Reserves were as follows at June 1996 (Shedden, 1998):
Inferred + Indicated Resource - 0.570 Mt @ and uncut grade of 9.2 g/t Au for 5.25 t of contained gold;
Proved + Probable Reserve - 0.230 000 t @ 12.29 g/t Au after a top cut of 80.0 g/t Au and a 4 g/t Au lower cutoff.
Mine development commenced in January 1997.
Mitchell, Graveyard, Challenge-Swordsman Palaeochannels, which are each 4 to 6 km long, and host placer gold mineralisation. These channels were discovered in the late 1990s. Gold mineralisation occurs in Tertiary sand, grit and conglomerates at the base of the palaeochannels. A typical regolith profile within the mineralised palaeochannels comprises, from the top (Lintern, 2004):
0 to 2 m. Dense red, calcareous clays with abundant dark red to black ferruginous granules, some in lenses, with some gypsum. Calcrete occurs within the top 1 to 2 m as nodules, pisoliths, concretions and as coatings on clay particles;
2 to 6 m. Red, non-calcareous clay with some grey mottling;
6 to 12 m. Multi-coloured clay with abundant ferruginous nodules and some pisoliths;
12 to 18 m. Red and khaki puggy clay becoming paler with depth - some ferruginous nodules;
18 to 34 m. Cream to white, silty, sandy clay;
34 to 40 m. Sandy clay with carbonaceous (including fossil wood) and sulphidic material; and
40 to 80 m. Clay saprolite consisting of variably coloured clays with quartz and rock fragments. Fresh rock occurs at a variable depth, generally >80 m.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2011.
Record last updated: 27/8/2019
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.
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Selected References:
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Bucci L A, Hagemann S G, Groves D I and Standing J G 2002 - The Archean Chalice gold deposit: a record of complex, multistage, high-temperature hydrothermal activity and gold mineralisation associated with granitic rocks in the Yilgarn Craton, Western Australia: in Ore Geology Reviews v19 pp 23-67
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Bucci LA, McNaughton N, Fletcher IR, Groves DI, Kositcin N, Stein HJ and Hagemann SG 2004 - Timing and Duration of High-Temperature Gold Mineralization and Spatially Associated Granitoid Magmatism at Chalice, Yilgarn Craton, Western Australia: in Econ. Geol. v99 pp 1123-1144
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Lintern, M.J., 2004 - Higginsville palaeochannel gold deposits, Kambalda, Western Australia: in CRC LEME online, http://crcleme.org.au/RegExpOre/Higginsville.pdf 3p.
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Stokes, C.F., Buerger, R.J. and Turner, B.J., 2011 - An Evolving Understanding of the Controls of the Trident Gold Deposit – Higginsville, Western Australia: in Eighth International Mining Geology Conference, Queenstown New Zealand, 22-24 August, 2011, The AusIMM, Melbourne Proceedings, pp. 191-210.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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