Summary:
The Deflector Region Operation is comprised the Deflector and Rothsay underground mines.
Deflector
The Deflector deposit is a gold-copper mineral system located within the Gullewa Greenstone Belt of the Yilgarn Craton, Western Australia. The stratigraphic sequence at Gullewa comprises a lower group of ultramafic and mafic greenstones with minor local BIF units, overlain by intermediate and felsic volcanic rocks, with an upper association of clastic sediments, including shale, sandstone, conglomerate and turbidites. Three distinct lithological domains – northern, southern and eastern have been identified.
The Gullewa Goldfield and the Deflector deposit occur in the northern domain, which is dominated by high-magnesium basalts and contains a distinct package of tholeiitic basalt and BIF, which is the preferred host for much of the known mineralisation. A thin sequence of turbidites and black shales is present in drilling southeast of the Deflector trend, where the rocks young to the southeast towards the Gearless Well Trachyandesite.
The Deflector deposit lies beneath a broad drainage system, comprising sheetwash, and a braided channel deposit that transports alluvium from the northwest through the project area towards the Salt River. Beneath the cover sequence, the Deflector deposit is hosted by a monotonous sequence of pillowed, variolithic, high-magnesium basalts that have been intruded by dacitic porphyry, dolerite and dolerite – lamprophyre dykes typically oriented 45° towards 240°) and exlithic stock. Underlying the northwestern side of Deflector is a large area of metabasalt that has a thickness of at least 300 m, strikes 045° and dips steeply to the southeast. The metabasalt is in contact with a sedimentary unit dominated by siltstone on the southeastern side of the deposit.
The high-magnesium metabasalt is generally black, fine grained, extremely hard and lacks any obvious cleavage. A needle-like texture that is similar to spinifex textures in komatiites is observed in approximately half of the basalt units and the others have poorly developed pillows.
The heterogeneous nature of the sedimentary sequence makes rock identification difficult. Siltstone is interpreted to be the major rock type in the sedimentary zone, which is mostly black and graphitic; however, it can be locally pale brown or grey. There is an absence of cleavage or fissile bedding. The sedimentary sequence is cut by quartz feldspar porphyries and dark grey to black, intermediate biotite lamprophyres.
A major sinistral reverse fault in the north end of the mine, called the Shredder Fault, offsets the ore lodes by approximately 35 m and is itself intruded by dacitic porphyry.
The mineralisation type is classified as a hybrid Archaean orogenic gold-copper type within the Gullewa greenstone sequence. The deposit comprises a series of en echelon veins hosted within a flexure in the greenstone stratigraphy. Locally, the mineralisation is hosted in five main vein sets, the Western, Central, Da Vinci, Contact and Deflector South West lodes.
Ongoing work at the Deflector South West lode indicates that it is likely the continuous strike extension of Western domain. The main lodes are narrow, subparallel, fault-hosted, quartz-sulfide veins within a thick sequence of high-magnesium basalt intruded by a series of dacitic, dolerite and lamprophyric dykes. The mafic sequence is bound in the east by a volcaniclastic unit, and in the west by an ultramafic unit. The metamorphic grade is defined as lower greenschist facies. Mineralisation occurs as quartz, carbonate, chalcopyrite and pyrite veins and associated breccias with visible gold observed in both oxide and fresh mineralisation. Mineralisation is strongly associated with ‘spinifex’ basalt, but also occurs along the footwall ultramafic contact to the basaltic package, and also along the sedimentary hanging wall contact.
Chalcopyrite is the only significant copper-bearing mineral in the primary unweathered mineralised areas of the lodes, with pyrite also occurring. The oxidised zone contains the copper minerals malachite and chrysocolla, with native copper being common in the lower parts of the zone and closely correlated with cuprite.
The Deflector resource extents are approximately 1,600 m along strike, 430 m across strike and 630 m below surface. These extents host approximately 100 known mineralised zones (mineralised domains). The mineralised zones are typically 0.3–5 m wide.
Rothsay
The Rothsay gold mine is located within the Warriedar Greenstone Belt, an Archaean sequence of mafic, ultramafic, metavolcanic and sedimentary rocks folded in an anticlinal formation which plunges and strikes to the north-northwest with steeply dipping limbs.
The five main lodes within Deflector (Western, Central, Da Vinci, Contact and Deflector South West) are tabular sheets of gold-copper mineralisation, all striking northeast with a moderate variation in thickness and occurring parallel to the enclosing strata. All lodes are narrow, subparallel, fault-hosted, quartz sulfide veins.
The Rothsay gold mine is located within the Warriedar Greenstone Belt, an Archaean sequence of mafic, ultramafic, metavolcanic and sedimentary rocks folded in an anticlinal formation which plunges and strikes to the north-northwest with steeply dipping limbs. The deposit is hosted in three discrete areas and within five individual shear zones. Woodley Shear (formerly A Shear), Woodley East and associated hanging wall shears (formerly H Shear) occur to the east of the main Woodley Lode. Orient Shear (formerly B Shear) and Clyde and Clyde East shears (formerly C and D shears) occur in a second area further west and Miners Shear (formerly E Shear) occurs as an isolated shear in the northwest.
The Woodley Shear is located at the contact between serpentinised peridotite and a porphyritic pyroxenite. The serpentinite forms the hanging wall unit. A sequence of mafic volcanic and sub-volcanic sills forms the hanging wall to the serpentinite. The Woodley Shear is characterised by several generations of quartz veining with adjacent tremolite alteration. The early quartz phase is typically blue-black due to the partial replacement of alumina by chromium oxide. The shear zone is typically 2–5 m thick, and mineralisation does not typically occur outside the shear zone. The main gold mineralisation is associated with shear-hosted quartz veins of blue and white quartz up to 3 m thick. The footwall porphyritic dolerite is relatively unaltered, while the hanging wall serpentinite is strongly foliated and has been subject to intense, though patchy, tremolite alteration.
The Rothsay resource extents are 1,500 m strike, 300 m across strike and 400 m below surface and the resource is open at depth. These extents host approximately 17 interpreted ore lodes. The lodes are 0.1–2 m wide.