Exploration Licence 2340 “Hedley Hill” is located adjacent to the northeast extremity of Lake Torrens. During the 80’s and 90’s exploration of the Lake Torrens district has had the prime objective of the discovery of an "Olympic Dam" style deposit...
Exploration Licence 2340 “Hedley Hill” is located adjacent to the northeast extremity of Lake Torrens. During the 80’s and 90’s exploration of the Lake Torrens district has had the prime objective of the discovery of an "Olympic Dam" style deposit with prospectivity guided by identifying similar signature magnetic and gravity anomalies. Previous exploration over the tenement area has been limited to broad spaced airborne magnetics and seismic refraction survey and basin drilling completed by ETSA. East of the Torrens Hinge Zone (THZ), which lies along the eastern margin of Lake Torrens, is the Neoproterozoic sedimentary succession of the Adelaidean trough. Poorly exposed north of the dune system, the succession is gently folded, exposing Wilpena Group bedrocks in the northeast and at the western extremity. The area is currently being explored for Olympic Dam style polymetallic deposits along with Adelaidean stratabound mineralisation. The progressive investigation of the Elizabeth geochemical anomaly at Mount Gunson by Stuart Metals has stimulated further scrutiny of the Stuart Shelf and geological margins. The area held under licence has no basement intersecting drill-holes, save one stratigraphic hole, WWD 1, just outside the southeast corner of EL 2339 (concurrently held by Tasman Resources to the south of EL 2340). The Tasman Resources search is twofold: the more easily exploitable high-grade stratiform base metal deposits in the Neoproterozoic sedimentary sequences; and the company making deeper buried "Olympic Dam" magnetite bodies found in the Mesoproterozoic age basement. With the stratiform type mineralisation, the favourable host units are believed to be the thin-bedded dolomites and laminated siltstones of the Amberoona, Nuccaleena and Wonoka Formations. Dolomites of the lower Tapley Hill member units would also be investigated, albeit as a deeper target. During licence year 1 to 24th May 1998, Tasman Resources NL initial prospecting was to relocate a malachite enriched outcrop discovered in the early 1970's in the vicinity of Airport Claypan-West Dam. Although the outcrop has so far been elusive, copper and zinc(?) mineral detritus was discovered on the shoreline o f a two-kilometre playa identified as Airport Claypan. This mineral occurrence is co-incident with the flexure o f a near thirty-kilometre weak magnetic anomaly. The broader exploration model was to identify magnetic anomalies, define the positions on the ground and undertake broad-spaced reconnaissance geochemical traverses. In this case, the analytical method selected was MMI partial leach. Soil samples were collected from 2 m long trenches from a depth of 15 cm and sieved to minus 40-mesh size fraction. Samples were analysed at AMDEL utilising the companies proprietary MMI Deepleach method. A total of 1207 samples were collected across 3 main target areas: Airport Claypan, West Mount and Lake Arthur. Multiple zones of weakly anomalous copper, zinc and gold were recorded. During licence year 2 to 24th May 1999, work included further reconnaissance MMI traverses (2598), follow-up verification sampling and infill geochemical surveys of one copper and two of precious metal anomalies. Enhancement of the airborne magnetics from the 1993 SAEI survey C1, which covered the area to the north, has indicated several linear, low amplitude magnetic anomalies. It is probable that these features are related to units within the Wilpena Group of the out-cropping Adelaidean strata. The features are nearer to the surface (<200 m) than the broad high amplitude polar magnetic anomalies that have previously been the objective of earlier exploration to find Olympic Dam-type basement mineralisation. Over the 2-year period, MMI surveys of Tasman Resources have identified significant geochemical trends, grouped as three extended zones. The anomalous zones are spaced at about fifteen kilometres apart and trend NNW in a curvilinear alignment. Interestingly, all of the geochemical anomalies so far detected, although non-continuous, appear to be along strike to the shallow-source magnetic horizons. Two narrow 700 m long copper-PGE (Palladium) anomalies at Airport Claypan are attributed to a siliceous laminated siltstone unit of possibly the Bunyeroo Fm; the dual Mirrabuckinna traverses indicate a 4 km long copper-zinc anomaly above 20 m blanket of Cretaceous Bulldog Shale; and at West Mount, the discontinuous 650 m long dual quartz-vein copper showings. Sparse MMI sampling at Apollo (Northeast Magnetic Feature) returned a 1300 m by 100 m silver (gold)-zinc anomaly in the south. The silver-gold anomalous zone is coincident with a prominent siliceous thin-bedded sandy siltstone succession of the Brachina Fm and is adjacent to a weakly magnetic horizon; and, southeast of Airport Claypan and 20 km SSW of Apollo, the adjacent Manser and Payne traverses returned a similar gold-silver-zinc coincident anomaly, describing an inclusive area of 2 km x 200 m. At Airport Claypan, traced within fine grained sedimentary rocks, an arcuate 2 km palladium anomaly is indicated beneath the claypan; and, from within a broad weak Nickel anomaly, a 200 m wide palladium interval is detected at both the Dog Fence and Mirrabuckinna traverses. Coincident with the southern margin of the copper anomaly at Airport Claypan, and, from the traverses Armstrong to Big Flat, this insufficiently sampled MMI zinc-silver anomaly has an interrupted extent of 16 km, coincidentally parallel with the Porter Hill magnetic horizon identified on the adjoining tenement to the north, EL 2543. During licence year 3 to 25th May 2000, Tasman acquired low altitude geophysical data, surface sampling along 148 line-km utilising MMI techniques and the provision of depth modelling of magnetic and detailed shallow interpretation of the Wilpena Group geology, as yet incomplete. Magnetic sheets for the area were acquired through the completion of the AGSO managed Flinders Ranges airborne geographical survey, flown on a 200 m line spacing at an altitude of 60 m. Modelling of the First Vertical Derivative, completed by A. Bontenakel, displayed three parallel structures aligned north-westerly passing through the tenement. Wo have been sampled previously with interesting results and the third will need to be followed up. The soil sampling was completed in two field programs directed towards extending existing sample lines, testing new targets identified from the newly processed magnetic data, and gridding/close sampling to confirm proposed drill targets. A total of 1480 soil samples but only result from the first 740 were available at the time of reporting. Tasman believe that the results from this reporting period to be compromised due to very high rainfall in the area and the potential metal ion dissipation in the soil as a result. Tasman has commissioned Archimedes Consulting Pty Ltd to further process the magnetic data collected by AGSO.
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