The Deflector Extended Project licence (E59/1657) comprises a single exploration licence of 5 blocks, about 15km2, which was granted on the 12 July 2011, for a period of five years. On the 30 September 2016, the licence was renewed for a second, five year term, to the 11 July 2021, with no reduction in area. This is the only tenement held by MinRex in the Gullewa area.
The lease is in the Cagacaroon Hills area at Gullewa, in the Yalgoo Mineral Field, about 370km north of Perth, 40km southwest of Yalgoo and 160km east of Geraldton (Figure 1).
Access from Perth is via the sealed Morawa to Yalgoo road (83km from Morawa) and then turning east into the tenement on old pastoral station and mineral exploration tracks (a further 12km to the lease).
Since construction of the new Deflector Mine at Gullewa, in 2016, the most direct access to E59/1657 is from the northwest by track or from the north along a track following the west bank of the Salt River.
The Deflector Extended Project licence (E59/1657) lies in the Gullewa Greenstone Belt, of the Murchison Province of the Archean Yilgarn Craton of Western Australia. The Murchison Province comprises Archean supracrustal greenstones of the Murchison Supergroup which are intruded by plutonic granitoid rocks, which are also dominantly Archean in age. Bedrock in the Province has been affected by deep weathering in the Cenozoic and outcrop in the Gullewa Belt is poor and all past and present geological and exploration programs have been hampered by the lack of exposure (Figure 2).
Gold was discovered at Gullewa in 1894 and historic production occurred in the region from 1897 to 1942. During this period a reported total of 36,000 ounces of gold was produced from a total of 24,000 tonnes of ore at an overall recovered grade of 46.3 g/t Au. Modern mining commenced in 1994 and by 2003 the processing of 530,000 tonnes of ore at a grade of 2.6g/t Au had resulted in the production of some 39,000 ounces of gold, mainly from open cut mining but with a small underground component. Mining re-commenced in 2016 with the opening of the Deflector Mine, as an underground copper-gold operation, with production to date estimated at about 110,000 ounces of gold, greater than the previous historic production.
The geology of the 15% of the licence area that outcrops is a typical Archean greenstone sequence of meta-basalt, with some high-Mg basalt horizons, ultramafic rocks, some gabbroic zones, thin cherty metasediment horizons, meta-sedimentary shale bands, aplite dykes and quartz veins; with intrusive granitoids occurring locally. There is extensive outcrop in the basaltic greenstone area, which also forms the topographic high of the Cagacaroon Hills. Small areas of granitic outcrop are more scattered and occupy lower relief topography, especially to the north of the Cagacaroon Hills. A large, magnetic granitoid dome (the Gearless Well Intrusion) is interpreted to occur, at depth, in the south of the tenement, based on the airborne magnetic geophysics over the area. Geophysics also indicates that a major north-south dextral shear zone – the Salt River Shear – passes through the south-eastern corner of E59/1657.
MinRex has been actively exploring the licence (E59/1657) since 2011. Work has sought to use surface sampling, geological mapping and existing geophysics to hone in to buried mineralized structures and favourable settings for mineralization, to allow subsequent drilling to be efficiently utilized. The tenement is thought to contain the northeast-trending extensions, under cover, of both the Golden Stream and the Deflector Mines.
In the period 2013-2018, MinRex has completed seven geological mapping and surface sampling exploration programs over the Project area. All parts of the lease have been examined, observations made of the geology, geomorphology, soil types and rock outcrops and a total of 534 surface rock (including float and scree) samples, 341 soil samples and 187 auger drill samples been collected. This work returned anomalous gold values (up to 2.89g/t Au), copper (up to 1,060ppm Cu), lead (up to 10,300ppm Pb) and nickel (up to 592ppm Ni). An initial geological map was drawn in 2013 and this was subsequently updated in 2016 and 2017; all of this work has been designed with geological input and completed under close geological supervision, and with regard to past work and available geological and geophysical databases (Figure 3).
The 1,062 samples collected to date indicate a number of anomalous areas, suitable for further examination and sampling. In particular a number of anomalous assay values (up to 2.89ppm Au) have been returned in the past year, and a number of these cluster in a distinct scree-covered area, adjacent to mafic meta-basalt and an interpreted fault zone, with scattered sub-crops of shaly metasediments, near the central corner of the lease. To date two main anomalous zones have been defined by this surface sampling and geological mapping. These are summarised in the map below (Figure 4).
Planning is now underway for the next field sampling program, which will aim to collect additional rock and scree samples within the three defined anomalous zones, especially focussing on the newly defined Corner Creek zone, where several scree sample assay values exceed 0.1ppm Au. These samples were of float material, in an area of mafic scree and patchy meta-sedimentary shale outcrop, with the sampled rocks comprising quartz vein and goethite, possibly after sulphide minerals, which is a similar composition to the gold ore previously mined at the Golden Stream mine and currently being mined at the Deflector Mine. A detailed examination of this area will be made in the next field program to determine the origin of these anomalous float samples.