Summary:
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 Archean 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 Deflector mineralisation is hosted in six main vein sets, referred to as the Western, Central, DaVinci, Contact, Southwest, and the newly defined Spanish Galleon Lodes.
Ongoing work at Deflector Southwest indicates that it is likely the continuous strike extension of the Western domain. The main lodes are narrow, sub-parallel, fault-hosted, quartz-sulphide veins within a thick sequence of high-Mg 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. Spanish Galleon mineralisation is to the west of the Deflector system and is hosted within a coarse dolerite unit as massive sulphide veins and thinner stockwork style veinlets. The host dolerite is bound to the east by basalt, sediment and ultramafic units, and to the west with a footwall sediment unit followed by further ultramafics. The metamorphic grade is defined as lower greenschist facies.
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.
Dimensions
The Deflector resource extents are approximately 1,600m along strike, 430m across strike and 630m below surface. These extents host approximately 157 known mineralised zones (mineralised domains). The mineralised zones typically vary between 0.3 to 1m in width.
The Spanish Galleon resource extents are approximately 400m along strike, 200m across strike and 200m below surface. These extents host approximately 5 known mineralised zones (mineralised domains). The mineralised zones typically vary between 0.3 to 5m in width.