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Location: 65 km SE from Coolgardie, Western Australia, Australia
PO Box 359KambaldaWestern Australia, Australia6831
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Deposit typeThere are several styles of gold mineralisation at St Ives. Individual deposits and targets may contain more than one of the following styles: • Lode mineralisation: Archaean orogenic lode mineralisation typically consisting of 0.5m – 20m-wide mesothermal vein complexes that may also have hydraulic breccias and/or mylonites. Mineralisation is typically discontinuous with short-range predictability; • Supergene mineralisation: Broad zones of flat-lying gold mineralisation in weathered Archaean and overlying tertiary sediments; • Palaeoplacer mineralisation: Placer deposits hosted by palaeochannels in the unconsolidated tertiary sediments that overlie the Archaean basement.GeologySt Ives lies within the Norseman-Wiluna Greenstone Belt of the Yilgarn Craton. The deposit area features a sequence of mafic and ultramafic volcanics, felsic intrusives, and sedimentary rocks. Gold is primarily hosted in structurally controlled quartz-carbonate breccia veins, shear zones, and disseminated sulphide-bearing alteration halos. Mineralisation styles include orogenic lode systems associated with major shear corridors, with Invincible hosted in a folded package of sediments and volcanics along the Playa Fault system.Mineralisation There are four main styles of gold mineralisation at St Ives. Individual deposits may contain more than one style depending on the local structural and lithological conditions:• Lode mineralisation: typically consists of a 0.5 cm to 50 cm wide cataclasite core surrounded by 0.1 cm to 3.0 m of foliated cataclasite. • Quartz vein stockworks: irregular bodies of closely spaced and regularly oriented quartz veins. • Composite style: variably developed quartz vein stockwork mineralisation localised in and around lode shear zones. • Supergene: broad zones of flat-lying gold mineralisation hosted in deeply weathered Archean and overlying Tertiary rocks.The current major production centres at St Ives are the Invincible deposits, the Neptune paleochannel and underlying lodes and the Hamlet deposit.Invincible Invincible is situated on Lake Lefroy, approximately 8 km northwest of the Lefroy process plant. The Invincible camp is dominated by a 2 km long open pit mined between 2014 and 2019, with mineralisation extending a further 1.9 km to the south of the pit (Invincible South) and >800 m depth (Invincible Deeps).There are three major lithofacies identified at the Invincible Camp:• The Black Flags Andesite (BFA): This unit forms the footwall sequence at Invincible and consists of volcanic quartz-rich sandstone with lenses of polymictic sub-rounded to sub angular pebble to cobble conglomerate. • The Black Flags Mudstone (BFM): Is the main unit to the host mineralisation at Invincible and is comprised of fissile massive to laminated grey mudstone, planar laminated to thinly interbedded siltstone with graded beds and massive to diffusely laminated medium interbedded siltstone. The BFM is approximately 110 m thick at depth and narrows to around 50 m near the surface. • The Merougil Group (MER): This unit form the tops of the Invincible sequence (hangingwall) and comprises medium to coarse grained quartz-rich sandstones, pebble to boulder polymictic conglomerates and very rare siltstone to mudstone.There are two main styles of mineralisation within the Invincible Camp: (Type 1) BFM hosted shear veins and breccias, with albite-pyrite alteration, directly related to the high-grade mineralisation and (Type 2) Footwall BFA hosted extensional veins and stockwork veining alteration selvages of medium to strong hematite ± albite ±sericite alteration. Veins range in width from a few centimetres to two meters with visible gold is common in these veins.Two prominent shear zones are associated with the Invincible deposit: the Merougil shear and the Morgan Island shear. These structures exploit the both the hangingwall and footwall contacts and are not themselves mineralised but are thought to be conduits for the mineralisation.Neptune The Neptune deposit consists of three main mineralisation styles: paleochannel, supergene and fresh lode material with the deposit located beneath Lake Lefroy with post mineralisation sedimentary cover to depths of 30 m to 60 m.The majority of mineralisation mined at Neptune comes from paleochannel gold deposited within a main east-west channel, minor tributaries and paleo-slope sheetwash as free gold nuggets and gold entrained in quartz that is post Archean in age. Supergene mineralisation is derived from a combination of gold mobilised from the underlying fresh lode structures and from overlying paleochannel material.Archean lode structures within the Neptune Open Pit include the more significant N01 structure trend roughly northsouth and generally dip moderately to the east and have been mined in the Stage 5 Pit at Neptune. In Stage 7 Neptune mineralised structures dip away to the west at a shallow trend with a north-south strike. Lodes are characterised by a pyrite + quartz + carbonate + gold assemblage. Host rocks vary with mineralisation at Neptune encountered in the lower Kambalda sequence geology (Defiance Dolerite, Devon Consols Basalt, Kapai Slate and various intrusives).Hamlet North The Hamlet North deposit is located to the north of the historically mined Hamlet deposit and was discovered in 2018. It is a ~150 m in strike and 5-10 m wide orebody with a down plunge extent of >750 m located on the Hamlet Shear. The Hamlet Shear is a north-south trending reverse slip shear zone. Mineralisation occurs within the Defiance Dolerite Unit 4, a granophyric unit within the Defiance Dolerite. Gold mineralisation is associated with a biotite alteration halo hosting quartz-albite and quartz-carbonate veins. The high-grade zone comprises breccia zones (pods) and vein or stockwork vein arrays. The shallow to moderate dipping veins a widely spaced, generally discontinuous and form part of the halo mineralisation. A series of felsic and intermediate intrusive units occur within Hamlet North, although these are not volumetrically significant in the ore zone.
