Southern Goldfields Operations is 100% owned by Westgold and includes the Beta Hunt, Higginsville processing plant, underground and open pit mining operations including the Lake Cowan and Two Boys deposits.
On August 1, 2024, Westgold Resources Limited and Karora agreed to combine in a merger pursuant to which Westgold acquired 100% of the issued and outstanding common shares of Karora. The Westgold name was retained as the name for the merged company.
Summary:
Cases assume processing the entire Southern Goldfields Ore Reserve. Southern Goldfields portfolio includes the Higginsville and Beta Hunt operations.
Higginsville operation
The gold deposits at Higginsville are consistent with the greenstone-hosted quartz-carbonate vein (mesothermal) gold deposit model.
Higginsville Gold Operations can be subdivided into seven major geological domains: Trident Line-of-Lode; Chalice; Lake Cowan; Southern Palaeochannels; Mt Henry; Polar Bear Group; and Spargos Project Area.
Trident Line-of-Lode
The majority of mineralisation projects along the Trident Line-of-Lode are hosted within the Poseidon Gabbro and high-MgO dyke complexes in the south. The Poseidon Gabbro is a thick, weakly-differentiated gabbroic sill, which strikes north-south and dips 60° to the east, is over 500 m thick and 2.5 km long.
The mineralisation is hosted within or marginal to quartz veining and is structurally and lithologically controlled. Veins occur on and adjacent to the thrust contact and may be up to 3 m in width and lie preferentially in the basalt host. Alteration consists of silica flooding which has obscured older textures; locally intense biotite alteration within the basalts closely associated with the silicification and arsenopyrite alteration is common and locally intensified with the quartz veining and silica-biotite alteration. Laterisation and erosion have resulted in supergene enrichment within the transitional layer following downward surface water leaching of the upper saprolite.
Chalice
The dominant unit that hosts gold mineralisation is a fine grained, weak to strongly foliated amphibole-plagioclase amphibolite, with a typically lepidoblastic (mineralogically aligned and banded) texture. It is west-dipping and generally steep, approximately 60° to 75°. It is typically more competent than the ultramafic unit. The amphibolite is of basaltic derivation, with alteration and the metamorphic grade generally increasing markedly towards the main mineralisation zone.
Lake Cowan
The area is interpreted to have undergone intense intraformational folding and transposition, and has a metamorphic grade estimated to be upper greenschist facies with local hornfelsing proximal to the Binneringie dyke.
The majority of mineralisation at the Lake Cowan Mining Centre is hosted within an enclave of Archaean material surrounded by the Binneringie dyke.
Southern Palaeochannels
Throughout the Higginsville Gold Operations, a significant proportion of gold deposits are hosted by sediments within the Southern Palaeochannel network. Mineralised zones comprise both placer gold, normally near the base of the channel-fill sequences, and chemicallyprecipitated secondary gold within the channel-fill materials and underlying saprolite. These gold concentrations commonly overlie, or are adjacent to, primary mineralised zones within Archaean bedrock.
The Cowan palaeodrainage system that includes the Challenge/Swordsman and Mitchell palaeochannels comprises up to 100 m of Cainozoic sediment overlying Precambrian basement.
Two main palaeochannel systems exist at Higginsville:
• Mitchell palaeochannel system includes the existing pits of Graveyard North, Graveyard, Aphrodities and Mitchell. Mitchell 3 and 4 remain unmined and are located to the south of the existing Mitchell pit.
• Challenge/Swordsman palaeochannel system includes the existing pits of Bullseye, Venus, Jupiter, Saturn, Neptune and Pluto. The areas of Mars (south of the Venus Pit) and the southern extension of Pluto remain in situ (unmined). Both palaeochannel systems get deeper towards the south (which suggest the flow direction of the ancient rivers) and flow into Lake Cowan.
Mt Henry
The Archean rocks in the Norseman area have historically been classified into a series of formations.
Units of the Penneshaw Formation host the gold mineralisation at Everlasting and Mildura prospects.
The Woolyeenyer Formation hosts the Norseman style quartz reef gold mineralisation, as well as the Abbotshall gold deposit which is hosted in a regionally extensive porphyry/siliceous sedimentary unit of the Woolyeenyer Formation. The Woolyeenyer Formation is unconformably overlain by the Mount Kirk Formation.
Polar Bear Group
Lake Cowan covers most of the project area with a 1 m to 3 m thick layer of gypferrous mud and clay with a poorly developed halite crust. The deeper channels within the lake contain thick sequences of transported clays, with intercalated lignite beds from 1 m to 20 m, which overlie laterally extensive fossiliferous sandstone, locally known as the Norseman Formation of probable Eocene age. Locally running sands and gravels are present at the base of the channels, which can be in excess of 90 m thick. Some of these channels are mineralised with gold and have been mined historically, including the Challenge-Swordsman palaeochannel on the Eundynie Peninsula. The entire project area is intruded by numerous Proterozoic dolerite dykes.
Spargos Project Area
Gold mineralisation at Spargos Reward is hosted by a coarse-grained pyrite-arsenopyrite lode in quartz-sericite schists, between strongly biotitic altered greywacke to the east and quartzsericite-fuchsite-pyrite altered felsic tuff to the west. Gold mineralisation is associated with very little quartz veining which is atypical for many deposits in region. Sporadic lower-grade gold mineralisation (1–2 g/t Au) occurs within the footwall tuffs.
Beta Hunt operation
Gold Mineralization
Gold mineralization is focused about the Kambalda Anticline and controlled by northwest trending, steep, west dipping shear zones associated with re-activated normal faults that previously controlled the komatiitic channel flow and associated nickel sulphide deposition. Gold mineralization is interpreted as a D3 extensional event associated with porphyry intrusives, the source of magmatic hydrothermal fluids carrying the gold.
Mineralization is hosted dominantly in Lunnon Basalt (below the ultramafic contact) with minor amounts associated with specific porphyry intrusives. Not all porphyries are mineralized; some are intruded post-mineralization. The basalt (and porphyries) are preferred mineralization hosts as a result of their susceptibility to hydraulic fracturing to form quartz veining, with the migrating ore fluids causing wall-rock alteration.
Gold mineralization occurs in broad, steeply dipping, north-northwest striking quartz vein systems within biotite-albite-pyrite altered shear zones hosted by the Lunnon Basalt. Veining is dominated by shear parallel and extensional vein styles. In the Hunt Block, mineralized shears are represented by the A Zone, Western Flanks and Fletcher zones. The interpreted offset to the Western Flanks is represented by the Larkin shear zone to the south of the AIF in the Beta Block.
The East Alpha shear zone is interpreted by analogy to the known mineralized quartz vein systems.
Nikel Mineralization
The nickel deposits on the Beta Hunt sub-lease are examples of the Kambalda style komatiitehosted nickel sulphide deposits. The characteristics of the Western Flanks and A Zone gold lodes at Beta Hunt are consistent with the greenstone-hosted quartz-carbonate vein (mesothermal) gold deposit model.
Nickel mineralization is hosted mainly by talc-carbonate and serpentine altered ultramafic rocks (Kambalda Komatiite) that overlie the Lunnon Basalt. The primary sulphide minerals are typically pyrrhotite > pentlandite > pyrite with trace chalcopyrite.