The Murninnie Cu-Bi-Au deposit and mine environs, located approximately 40 km south-west of Whyalla, have not been seriously explored in more than 50 years due to quarantining of the deposit under Private Mine title. The lode-style deposit is...
The Murninnie Cu-Bi-Au deposit and mine environs, located approximately 40 km south-west of Whyalla, have not been seriously explored in more than 50 years due to quarantining of the deposit under Private Mine title. The lode-style deposit is exposed over 450 m of strike and was originally developed to more than 50 m depth about 100 years ago, having produced over 1,000 tonnes of high grade secondary copper ore (~10% Cu, with or without per cent values of bismuth). During August 2006 Australasia Gold acquired a 45% interest in the project (Private Mine and surrounding EL) from the existing syndicate of private owners, and in July 2007 the company completed a formal agreement with them to acquire a 90% interest in the two tenements. Over this period Australasia Gold has acted as project manager and operator. The Murninnie deposit is emerging as a potential variant of the IOCGU class of Cu-Au-U deposits identified as occurring in proximity to Hiltaba Suite granite intrusions throughout the Olympic Domain of the Gawler Craton. The mineralisation at the deposit, and occasional outcropping copper showings along 4 km of strike extension, are associated with haematitic and other alteration that is consistent with alteration styles associated with IOCGU deposits elsewhere. New geochemistry work has confirmed the continuity of a 4 km line of strike of anomalous gold and copper in soils to the north and south of the Murninnie mine. A Bouguer gravity anomaly identified in an area of high magnetic intensity, at the edges of an area surveyed by PNC Exploration 20 years ago, also needed follow-up. A partly PACE-subsidised drilling programme was proposed in late 2006 to test the depth extensions of the Murninnie deposit, the strike extensions of the mineralising system defined by the soil geochemical anomaly, and to examine the source of the gravity anomaly. It was hoped that successful characterisation of this mineralisation would have the potential to reinvigorate exploration for IOCGU-styles of mineralisation in the southern part of the Olympic Domain of the Gawler Craton, encompassing eastern Eyre Peninsula and northern Yorke Peninsula. After approval was gained early in 2007 for A PACE Initiative Year 4 drilling subsidy grant, Australasia Gold carried out shallow aircore drilling (80 holes for a total of 1572 m) during March-April 2007 to test the bedrock beneath the copper-gold soil anomaly. Five traverses of overlapping, angled holes were drilled both to the north and south of the historic mine workings. One traverse included 3 holes which probed beneath an outcrop of haematitic breccia located at "The Scratchings". Resulting analyses of 4 metre composited drill cuttings did not yield geochemical values worthy of immediate follow-up, but the observed trace element associations did suggest that mineralising fluids had passed through the gneissic bedrock. In May 2007 five partly PACE-funded diamond drillholes totalling 1140 m (590 m cored) were put down at Murninnie. Two were planned to investigate two discrete gravity anomalies delineated by a recent gravity survey done in EL 3542. The other three diamond holes were intended to look for possible deeper extensions to the Murninnie mine lodes. The first two, vertical diamond holes were both drilled to depths below the interpreted source of each gravity anomaly, but neither encountered rocks of sufficient density to explain the anomalies. Lithologies encountered were predominantly granitic gneiss, made up of interlayered dark mafic schist and paler coloured granitic/pegmatitic gneiss. The rock is weakly to moderately chlorite-altered throughout, with sporadic zones of weak haematite and epidote alteration. There are minor zones of trace pyrite and chalcopyrite, mostly observed on fracture surfaces. The haematite concentrations are accompanied by relatively elevated levels of copper, gold, silver, uranium, rare earth elements (cerium, lanthanum and yttrium), zircon, tungsten and titanium. Whilst the levels of these elements are considered to be geochemically only mildly anomalous, they are elevated compared to values for rock that contains no haematite alteration. The geochemical associations observed with the haematite alteration are encouraging, and support the belief that the gravity anomalies could still be related to a nearby body of iron oxide - associated copper-gold mineralisation. Further gravity work is envisaged to assist in refining the interpretation of possible sources of the anomalies, ahead of further drilling to locate their source. The inclined diamond drilling beneath the mine workings intersected the target of sheared and faulted granitic rocks at between 80 and 150 metres vertical depth. An earlier run IP survey had disclosed a chargeability anomaly there which it was hoped would be due to sulphides, but instead only widespread disseminated, finely crystalline graphite was found. Trace amounts of copper carbonates were observed forming fracture coatings, with traces of pyrite and chalcopyrite within the fractures. The best return from core sample assaying was 1 m @ 0.9% Cu, in hole MDD3.
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