A small licence area located on the Flinders Ranges piedmont plain south-east of Lake Torrens was taken up by Jim Allender to investigate the IOCG potential of a discrete regional gravity anomaly which he had identified from data in the public...
A small licence area located on the Flinders Ranges piedmont plain south-east of Lake Torrens was taken up by Jim Allender to investigate the IOCG potential of a discrete regional gravity anomaly which he had identified from data in the public domain, and which comprised a single station reading made in the 1980s on the BMR's four-mile national gravity grid. Following the licensee's initial review of relevant geological and geophysical information, he was approached by Salisbury Resources who wished to acquire equity in the tenement, and suitable entry terms were negotiated. Salisbury's reprocessing of the gravity data in the area of the Merna Mora anomaly revealed that it potentially could cover 7 km x 15 km as a NE-SW elongate +5 mGal feature straddling the Torrens Hinge Zone. It was decided that additional gravity data would be needed in order to select a drilling target. After some delays, a detailed gravity survey of 269 stations read at 1 km x 1 km and 1 km x 500 m intervals was acquired during July 2009, with specialist assistance being obtained from consultant geophysicist David McInnes regarding preparation of 3D models of the pre- and post survey gravity data. The preliminary models indicated that both shallow and deep dense source rocks existed, down to 800 m depth, with multiple subsidiary highs apparent on an overall 8 mGal amplitude regional anomaly. Consequently, an initial four test drillsites were pegged during July 2011, after land acess and environmental protection permits had been obtained. A SAMREF records database desktop study undertaken by Salisbury late in 2011 came across mention of an in-depth structural interpretation of the bedrock in the tenement vicinity which had already been done by a previous explorer during 1996-1997, as part of a search for possible diamondiferous kimberlite. Unfortunately, perusing those interpretation findings downgraded the IOCG prospectivity of the majority of the licence area, since they placed the source of the gravity features within basal Adelaidean or younger strata that occupy a local synform structure partly offset at its southern end by a minor north-west trending fault. Salisbury therefore asked Montana GIS to do additional 3-D modelling of both gravity and magnetic data to check this interpretation, but in so doing the consultant could find no associated IOCG-type magnetic signatures located within 1 km of the deep gravity source, which obviously now made it appear much less attractive. It was decided to switch exploration emphasis onto delineating possible epithermal copper-gold targets which could have developed within the structurally complicated western "transitional domain" of the Torrens Hinge Zone, in part a narrow strip along the western margin of EL 3630 where basement rocks might lie closer to the surface. A small bullseye aeromagnetic feature, T10-K32, noted in 1997 EL progress reports written by diamond explorer Desertstone but not drill tested, was chosen by Salisbury as a possible economically accessible high priority drill target. It was thought that it could represent an intensely magnetic basic intrusion present within Wooltana Volcanics - equivalent rocks now buried under ~200-250 m thickness of Recent cover sediments. Such a fertile host would have been subject to deep crustal hydrothermal flows, as it lies within a dilational break along the major Arden-Ediacara Fault Zone. During May-June 2012 the JV undertook the drilling of a single vertical exploratory hole to TD 327.3 m, to test the above T10-K32 magnetic anomaly at a site located near the western licence boundary of the subject renewed EL 4859, and ~350 m to the north of Etowie Creek. Drillhole ET1 was precollared using rotary mud drilling methods for 207 m through the Tertiary sediments (clays, silts, sands and lignitic mud) of the Torrens Basin, and then was switched to NQ/HQ diamond coring in the Adelaidean bedrock. The Adelaidean sequence was penetrated at 206.9 m depth, and consisted of chaotic diapiric breccias composed of siltstone, claystone, shale, sandstone and carbonate-rich clasts within a carbonate matrix. From a depth of 304.6 m, an amygdaloidal albite-tremolite-actinolite-leucoxene-hematite basalt breccia was encountered that was considered to be stratigraphically equivalent to the Wooltana Volcanics. No economic mineralisation was intersected. However, minor anomalous copper values were recorded over two depth intervals, 263.5-269.5 m and 309.8-315.9 m. The best drill core sample assay result was 0.27% Cu from the interval 292.1-292.9 m, which was accompanied by an anomalous gold value of 19 ppb Au; this came from sericite and quartz-rich breccia clasts in a carbonate-rich (mostly dolomite) matrix. No further activities ensued on the licence before a decision was made to surrender tenure.
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