Exploration of an area located 50 km south-southwest of Keith aimed to test the potential of known Cambrian siliceous volcanic rocks for hosting massive base metal sulphide deposits plus possible disseminated and skarn-related precious metals,...
Exploration of an area located 50 km south-southwest of Keith aimed to test the potential of known Cambrian siliceous volcanic rocks for hosting massive base metal sulphide deposits plus possible disseminated and skarn-related precious metals, following an exploration model put forward on the basis of the rocks' supposed petrological and geochemical similarities with the Mount Read Volcanics of western Tasmania. Early work consisted of an interpretation of regional magnetic data, scout geological mapping and geochemical grab sampling of sparse basement outcrops, and the acquisition and interpretation of ground magnetic, gravity and TEM surveys intended to firm up drillable targets. No useful TEM results were obtained. The north-south volcanic belt crossing the licence area was interpreted to be demagnetised over a strike length of about 25 km. Within it the licensee discerned three small linear magnetic highs 1-2 km long with maximum amplitudes of 400 nT. These appeared to be conformable with the volcanic strata, and it was inferred that they might arise from pyrrhotite-bearing skarn or from massive sulphide deposits. Difficulties ensued with securing a drilling contractor and with finding a joint venture partner to help bear the cost of drill testing the chosen magnetic anomalies. Consequently, no work took place during the period July 2004 until June 2007. On 30/5/2007 an option agreement was signed by the licensee with Uranium Exploration Australia, who undertook to fund drilling activities over two years in order to earn a 50% interest in the tenement. However, the agreement was allowed by that company to lapse on 13/2/2008 without its requirements being fully exercised. The main field activity carried out under EL 3013 was the completion of a single vertical rotary mud - HQ/NQ diamond drillhole 336.1 m deep at the Clover Ridge magnetic/gravity anomaly during the week of 5-11/6/2007. After passing through 53.8 m thickness of Cenozoic cover rocks, the hole stayed within a tholeiitic dolerite intrusion for the remainder of its length. The mafic rocks recovered in the drill core show chlorite, epidote and carbonate alteration and veining plus the effects of contact metamorphism, but their sulphide content is minor and the core sample assay results were not encouraging. Petrographic work suggested that the magnetite which produces the Clover Ridge magnetic anomaly predates contact metamorphism, and is therefore not related to skarn mineralisation. Hence, if the magnetite in the dolerite is not related to contact metamorphism, it is likely that the dyke post-dates regional hydrothermal alteration which destroyed magnetite, an observation based on the airborne magnetic data. Any volcanogenic massive sulphide (VMS) deposits in the area would then be contemporaneous with the regional alteration, and thus pre-date the dyke. It was concluded, therefore, that drillhole 07CR001 had done little to elucidate the potential of EL 3013 for VMS mineralisation. Given the presence of magnetic dykes in the area, it now seemed to the licensee that ongoing use of magnetic data as the primary exploration tool would not be reliable. Electrical geophysics might also struggle, as any zinc-rich ores would be poor conductors. But better results might be achieved using gravity, given that VMS deposits have very high specific gravities. It was suggested that any future gravity survey should concentrate on the 20 km long demagnetised zone in the southern half of the licence area, since this demagnetisation may have been caused by sulphur-rich fluids which had converted magnetite to pyrite (and in this process may also have deposited valuable metals).
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