The subject licence is one of four located to the east and south-east of the Olympic Dam deposit, on which greenfields exploration for economic IOCG-U mineralisation is being carried out by Western Mining in joint venture with the Power and...
The subject licence is one of four located to the east and south-east of the Olympic Dam deposit, on which greenfields exploration for economic IOCG-U mineralisation is being carried out by Western Mining in joint venture with the Power and Nuclear Fuels Corp. of Japan. Interest in the Island Dam tenement, which was formerly held by WMC but was relinquished in mid-1986, had been rekindled by the recent re-interpretation of past exploration data in the light of new geophysical survey results obtained on nearby parts of the Stuart Shelf. Consequently, during November-December 1995, WMC acquired a semi-regional gravity survey in the region east of Andamooka, totalling 969 stations read on a 500 m x500 m grid surveyed with GPS across the northern end of Andamooka Island and over the adjacent mainland portion of Andamooka Station, coverage which was designed to replace the old BMR 1 km x 1 km gravity data that had originally been used to define the Island Dam and Burden Hill prospects. Only about 22% of this new survey coverage (215 stations) was located within EL 2138 and on Andamooka Island, however, at this time it was planned that further detailed gravity surveying would shortly be done on the licence to confirm an anomaly located under Lake Torrens just to the north of the island (designated as Lifesaver prospect). Accordingly, the access track and causeway leading onto the island were upgraded by WMC, and a Declaration of Environmental Factors was prepared for this proposed survey, which was later approved by Mines and Energy SA on 28/4/1997. During mid-December 1996, WMC performed downhole geophysical logging in two still accessible previously completed diamond drillholes (IDD5 and IDD7) at Island Dam prospect on its adjoining EL 2208, running TEM and IP wireline tools to obtain petrophysical information for refining its geophysical models. The Australian High Court's Wik Native Title decision made in December 1996 created much land access uncertainty for WMC with regard to the Lake Torrens region, as five different aboriginal groups made title claims there which served to complicate and delay the company's negotiations for obtaining heritage clearances to allow ground-based activities to proceed. In order to meet licence commitments for the subject tenement, WMC had planned to drill two exploratory holes, percussion precollared to about 250 m depth and then diamond cored for another 200 m or so, to test gravity high targets that had been modelled within the Lifesaver prospect, once the holes' siting could be optimised after interpreting required additional detailed gravity coverage as mentioned above. However, because of the unforeseen delayed access, no field work could take place on EL 2138 during all of 1997 and for part of 1998. To occupy the interim situation until legal rights were resolved, WMC undertook a fresh regional geology interpretation and prospect prioritisation across all four exploration licence areas forming the Stuart Shelf Joint Venture Project: most of this conceptual work was concentrated on EL 2208, by far the largest tenement which contained the majority of historically identified prospects. After agreement was eventually reached with the aboriginal custodians for conducting brief, low-impact ground work such as gravity surveys on the project acreage, WMC was able to proceed to acquire the detailed gravity survey at Lifesaver prospect during June 1998. However, the intended full coverage of 100 stations on a 500 m x 250 m grid could not be completed then because the surface of the lake was too wet and muddy to carry the survey vehicles. Only 28 stations could be read, mainly at 250 m intervals along two north-south traverses spaced 500 m apart. A later attempt was made in September 1998 to continue the survey on foot, but for lack of weight-bearing support this too had to be aborted. Modelling of the Lifesaver gravity data suggested to WMC that a 3 mGal residual gravity high coincides with a ring-shaped magnetic anomaly exhibiting an obliquely stacked array of sources (?caldera strata) at around 500 m depth. The rocks at the caldera southern rim appeared to be denser/more prospective. Due to still not being able to obtain aboriginal heritage protection clearances for the small drilling programme proposed to take place on EL 2138, WMC could not carry out any further field work during the two-year period 1999 through 2000. Towards the end of 2000 the licence tenure came up for renewal, which was applied for and was granted.
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