Basal Umberatana Group glacial tillitic sedimentary sequences and upper Burra Group interglacial arenaceous sediments were explored for possible economic stratabound gold mineralisation in an area located about 10-40 km north-west of Burra. In...
Basal Umberatana Group glacial tillitic sedimentary sequences and upper Burra Group interglacial arenaceous sediments were explored for possible economic stratabound gold mineralisation in an area located about 10-40 km north-west of Burra. In the main the search emphasis was for hydrothermal gold in quartz veins associated with stratal dilational zones developed near the hinges of regional anticlinal folds and inferred related thrust faults. 17 rock chip samples taken from the historic Canny and Doherty prospect returned gold values ranging from 172 ppb up to 4.24 g/t Au. The most anomalous samples comprised vuggy quartz removed from 10 cm wide veins within sandstone of the upper Wilyerpa Formation. Anomalous copper was also identified within the quartz vein material found on the mine dumps, with assayed grab samples returning up to 9.37% Cu; this high copper content was attributed to the observed copper carbonate minerals malachite and azurite, present as fracture coatings and minor blebs. Anomalous gold was also identified in streams draining the Canny and Doherty prospect. During orientation stream sediment sampling (18 samples), a gold dispersion train was mapped to extend 1.5 km from the old workings: however, it could not be identified at points 2 km downstream within the same catchment. Consequently, it was decided that future stream sediment sampling of this locality and nearby areas, if carried out at a density of 1.5-2 samples per square km, would be adequate to detect any significant detrital gold mineralisation. The AAS and BLEG stream sample assay method results were compared, and it was seen that BLEG sampling returned higher anomalous results; however, the correlation was poor, with a correlation coefficient of only 0.39. The BLEG method returned a greater statistical contrast compared to the background, with anomalous results being four times the mean, compared with anomalous AAS results which returned only twice the mean. A structural geological interpretation of available airborne magnetic data, gravity and Shuttle Radar Topographic Mapping (SRTM) elevation datasets was completed to identify favorable lithological and structural targets. Four such targets were found, being principally fold and thrust complexes lying either along strike from the Burra mine or on regional anticlinal and synclinal fold axes running parallel to that host structure. Other features of interest were arcuate flexures cross-cut by later northwest-trending significant lineaments. An inferred north-south aligned major thrust fault was also mapped, underlying a linear topographic low which parallels synclinal folds that cross into the subject licence from the company's adjoining EL 3989 to the south. The recommended follow-up programme of additional detailed stream sediment sampling, rock chip sampling and ground-based geophysical profiling of the better geochemical and structural targets, was not commenced before a decision was made to surrender tenure.
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