Summary:
Regionally, the Dalgaranga project lies in the Archean aged Dalgaranga Greenstone Belt in the Murchison Province of Western Australia.
At the Gilbey’s deposit, most gold mineralisation is associated with shears situated within biotite-sericite-carbonate pyrite altered schists with quartz-carbonate veining within a porphyry-shale-mafic (dolerite, gabbro, basalt) rock package (Gilbey’s Main Porphyry Zone and Sly Fox). The Gilbey’s Main Porphyry Zone trends north – south and dips moderately-to-steeply to the west on local grid while Sly Fox trends east – west and dips steeply to the north. These two trends define the orientation of the limbs of an anticlinal structure, with a highly disrupted area being evident in the hinge zone.
At the Sly Fox deposit gold mineralisation occurs in quartz veined and silica, pyrite, biotite altered schists.
The Plymouth deposit lies between Gilbey’s and Sly Fox within the hinge zone of anticlinal structure – mineralisation at Plymouth is related to quartz veins and silica, pyrite, biotite altered schists.
At Hendricks and Vickers gold mineralisation occurs in quartz-pyrite veined and altered zones hosted in basalts.
The Never Never deposit at Gilbey’s North appears to be an intersection between a significant mineralised structure and the mine sequence – the lode plunges moderately to the west and is characterised by strong quartz – sericite – fucite alteration, with fine to very fine pyrite sulphide mineralisation.
Lesser amounts of mineralisation outside of the porphyry-shale-mafic zones are associated with highly discontinuous structures in the footwall and hangingwall of the sheared porphyry-shale-mafic lithologies.
The primary style of mineralisation at Never Never is a high-grade thickened zone located on the hangingwall of the northwest-striking shale unit. The Never Never Lode strikes west-south-west (MGA grid) and is noticeably different in geometry, grade tenor and alteration to other mineralisation styles at Dalgaranga. In unweathered material, the Never Never mineralisation is associated with highly silicified, sericite altered and mylonitic textured volcaniclastic unit with a fine-grained pyrite present.
The secondary style of mineralisation is analogous to the mineralisation styles present in the Gilbey’s Main deposit, where mineralisation is understood to be structurally controlled, and where silicification and the presence of sulphides typically accompany mineralisation. Gascoyne postulate the Never Never mineralisation is a high-grade feeder to the Gilbey’s system, with other feeder zones noted in grade control drilling within the main Gilbey’s Pit.
Dimensions
Mineralised domains at Gilbey’s North extend over a 375 m local grid north–south strike length. Lode thicknesses are highly variable and range from 1 m to 20 m thick in the local grid north–south striking domains, and up to 50 m thick in the Never Never ‘mineralised thickened zone’ (domains 1030, 1230, 1080 and 1280). Mineralisation exists from surface and currently extends 240 m to a lower limit of 185 mRL at its deepest.
The Gilbey’s Mineral Resource has an overall local grid north-south strike length of approximately 2,000m. The overall mineralised width of Gilbey’s varies but for the majority is approximately 800m wide. The elevation extent of Gilbey’s is from -100mRL to 450mRL (i.e., to roughly 550m below surface).
The Plymouth Mineral Resource has an overall local grid north-south strike length of pproximately 350m. The average mineralised width is approximately 150m. The elevation extent of Plymouth is from 250mRL to 450mRL (i.e., to roughly 200m below surface).
The Sly Fox Mineral Resource has an overall local grid east-west strike length of approximately 600m. The average mineralised width is approximately 150m. The elevation extent of Sly Fox is from 250mRL to 450mRL (i.e., to roughly 200m below surface).
Never Never Lode System is a thickened plunging shoot extending 500m from surface to 450m vertically below the surface. The shoot is orientated west, trending west-southwest at depth striking approximately 150m to 90m with lode thickness ranging from 15m to 50m thick in the northern and central portion, thinning towards the southern flank to approximately 4-5m. Never Never remains open at depth. The Gilbey’s North orientated domains extend 200m northeast-southwest with variable thickness ranging from 1m to 10m. Mineralisation has been defined 175m below surface and remains open at depth.