An area centred ~100 km south-east of Tarcoola is being explored for possible economic buried Carrapateena or Prominent Hill style IOCG and polymetallic skarn style mineralisation which may be associated with zones of elevated relief seen in...
An area centred ~100 km south-east of Tarcoola is being explored for possible economic buried Carrapateena or Prominent Hill style IOCG and polymetallic skarn style mineralisation which may be associated with zones of elevated relief seen in existing aeromagnetic data, and also for possible buried Streltsovska caldera style epigenetic volcanic-hosted primary uranium deposits. Initially, a ground magnetic survey was conducted for the licensee during August 2011 along 16 north-south traverses totalling 70.4 line km. These traverses were spaced 200 m apart, with magnetic data read along them at 1 second time intervals in a streamed bi-directional mode. The survey data delineated an area of strong magnetic relief which is aligned parallel to the inferred margin of an intrusive Hiltaba granite pluton. This strongly magnetic area had not been tested by previous explorers' drilling because their holes had been sited on gravity highs, where there is a significantly lower magnetic response. Historical rock chip sampling data from the area indicated that possible granite hornfels or skarn style base metal-silver anomalism may occur to the north-east of the magnetic trend, while significant nickel, cobalt and copper anomalism is associated with a magnetic mafic intrusion lying to the north-west. During the second licence year, Renaissance Uranium ('Renaissance') continued with its ground magnetic profiling of selected aeromagnetic anomalies, and also acquired a detailed ground gravity survey of 536 new stations on three separate regular 200 m x 200 m grids during July 2012. Quantitative assessment of the gravity data confirmed significant excess mass consistent with IOCGU-style mineralisation over the Border and Kokatha anomalies. Detailed magnetic coverage consisted of 19 survey lines for a total of 21.7 km at Border and 4 survey lines for a total of 9.6 km at Kokatha. The ground magnetic data delineated an area of strong magnetic relief interpreted to run parallel to the inferred margin of the intrusive Hiltaba granites. Other work done by Renaissance at this time involved exploring for anomalous bedrock silver geochemistry in extensive areas of inferred Lower Gawler Range Volcanics. Silver prospect areas were identified through a program of wide-spaced (300 m interval) soil sampling followed up with 100 m-spaced infill sampling. The program collected 395 samples which were submitted for multi-element laboratory assaying. Two zones of interest were defined at Kokatha and Freshwater, with a peak soil silver value of 970 ppb Ag returned amongst multiple assay results with values significantly above background silver levels. The Kokatha silver prospect was seen to have a spatial association with major structures interpreted from aeromagnetic data: nearby historic outcrop rock chip sampling had reported anomalous silver. The Freshwater anomaly lies adjacent to an magnetic high. Both of these geochemical anomalies were tested by drilling 5 angled RC percussion holes totalling 630 m, but no significant silver mineralisation was detected. However, copper mineralisation associated with IOCGU-style alteration of the bedrock was encountered at Kokatha prospect within the anomalous magnetic and gravity footprint. Hole 12RGDRC06 intersected an interval with 0.1% Cu, 52 ppb Au and 500 ppm Pb from 138-140 m depth, near the bottom of the hole. A detailed petrological examination of two drill cuttings samples taken from this level in holes 12RGDRC04 and 12RGDRC06 identified microplaty specular hematite coating bornite and chalcocite grains, that suggested the effect of oxidising fluids similar to those involved in forming known IOCG deposits. Other encouraging 2013 drilling results were the elevated silver reported in Freshwater prospect drill sample assays, and some elevated nickel values returned from within a high chromium ultramafic sequence at Border prospect. During the third licence year, Renaissance undertook rock chip sampling on four traverses crossing Gabbro Hill, a low rising large mafic outcrop located ~12 km north-west of Kokatha Homestead, being a place from which historic explorer Ascarco had previously reported nickel assay results of up to 6000 ppm Ni associated with geochemically anomalous base metals. Several sample sites from the north-eastern ends of Renaissance's central two traverses, i.e. situated on that side of the hill, returned moderately anomalous nickel values (>70 ppm) over an area of about 200 m x 300 m. Exploration of the Kokatha prospect was continued via the acquisition of a dipole-dipole IP survey consisting of two 100 m long north-south lines. On the eastern line an apparent resistivity anomaly was detected that appeared to be associated with anomalies in both the gravity and magnetic data. This resistivity anomaly was subsequently targeted with one RC drillhole (13RGDRC010) which formed part of an RC drilling program, of two inclined holes for 420 m, completed during May-June 2013. The results of both holes were of interest and were believed to warrant more drilling. The first hole, 13RGDRC010, was taken to a total depth of 300 m, the available capacity of the rig with the amount of drill rods then available, but the resisitive Kokatha target zone was not reached. This hole drilled through a sequence of variably weathered and altered basalts. Multi-element assaying of 5 metre composite drill cuttings samples returned elevated rare earth element values in the upper 220 m, plus elevated copper and nickel from the lower portion of the hole. The second hole, 13RGDRC011, targeted the bedrock source for a cluster of +50 ppb Ag-in-soil results disclosed at the Freshwater prospect, where there is a coincident small but discrete magnetic anomaly that it was thought might represent a small basaltic plug. This hole encountered variably weathered basalt (GRV) to about 97 m hole depth, and then remained within rhyodacite to the bottom of the hole at 120 m. Elevated cerium and lanthanum were detected in assayed 2 metre composite drill cuttings samples from the upper portion of the hole. No on-ground exploration of the licence area took place over the ensuing four years of tenure, before that was allowed to lapse during February 2018, although Renaissance declared that it had hoped to further investigate the potential for epithermal silver mineralisation associated with the Gawler Range Volcanics and for nickel mineralisation associated with eastern extensions to the ultramafic Harris Greenstone Belt.
More +