A very small (35 square km) area located ~35 km west-northwest of Olary and covering part of the Weekeroo Inlier is being explored for possible buried epigenetic stratiform Broken Hill type Pb-Zn-Ag and VHMS (volcanic hosted massive sulphide)...
A very small (35 square km) area located ~35 km west-northwest of Olary and covering part of the Weekeroo Inlier is being explored for possible buried epigenetic stratiform Broken Hill type Pb-Zn-Ag and VHMS (volcanic hosted massive sulphide) style mineralisation, which may have formed in prospective Palaeoproterozoic volcanogenic metasedimentary units which are unusual for the region around Weekeroo. During the first licence year, SAEX initially undertook a review and evaluation of the available results of previous company exploration and SA Government surveys which had been done in the subject area. Following this, the licensee and joint venture partner Marathon Resources acquired an airborne EM (RepTEM) survey of 263.8 line km in November 2013, targeting potential sulphide mineralisation in a sequence of tightly folded rocks hosting a highly prospective meta-exhalite target zone with anomalous Zn, Pb, Ag, Cu, Co, and Au. The AEM data were read from two separate grids with NW-SE and NNE-SSW flight line orientations that covered all formerly mapped strike extensions of the target zone, representing an area of 26 square km that lies on both EL 5306 and SAEX's adjoining larger EL 4520. Helicopter-borne instrument passes were made along 122 flight lines spaced 100 m apart, using a 30 m mean sensor elevation above the ground surface. A logistics report for the REPTEM survey, along with a flight line plot and processed imagery of conductivity plans and section, are presented herein. A significant late time conductivity anomaly was identified at Creagh Dhubh, with an interpreted source depth of ~250 m, but unfortunately Marathon chose not to drill it, and as a result withdrew from the project. A geological reconnaissance visit was made to the AEM anomaly position in January 2014 in the company of consultant Colin Conor. He concluded that the anomaly was drill-worthy, but that ground EM or ground magnetic survey should be done before selecting exactly where to drill. He also recommended that the REPTEM survey data be reinterpreted with a focus on defining weaker EM features within or adjacent to the prospective volcanogenic sequence, that may represent disseminated sulphides rather than massive sulphide bodies. His advice was based on the presence nearby of favourable host rocks of the Willyama Supergroup, including mafic volcanics and manganiferous exhalites, similar to the rocks associated with Broken Hill lodes. There was also some surficial geochemical evidence to support the exploration model, because earlier rock chip geochemical sampling of outcrop (Leyh, 2009) had returned peak values of 1200 ppm Zn, 500 ppm Cu, 10 g/t Ag, 235 ppm Ni, 250 ppm Co, 180 ppm As and 11.2% Mn, plus up to 0.29 g/t Au. During licence Years 2 through 4, no work was done. A 25% reduction of the tenement area was effected on 15/8/2017. During licence Year 5, following the purchase of the subject licence by Petratherm, that company undertook a review of Marathon's AEM data. This work, which was commissioned from geophysical consultant Kelvin Blundell, found that the previously modelled conductor at depth beneath a thin conductive cover was more likely an artefact caused by an unrealistic decay (elevated noise) in channels 13-16 (Blundell, 2018). It was opined that the REPTEM system which was used in the Marathon survey is a low-power / high-noise system compared with many other helicopter-borne TEM systems, and thus is not an ideal system to use for resolving bedrock conductors at depth. Consequently, Petratherm thought that this historic target warranted further ground EM surveying, to determine if a buried bedrock conductor can been found within the exhalite unit which is exposed at Creagh Dhubh. To otherwise inform its ongoing exploration of both project licences, Petratherm reviewed available historical company exploration and government data, inspected and assayed stored historic drill cores, reprocessed available geophysical data, and undertook field reconnaissance visits and grab rock chip geochemical sampling, especially of pegmatite bodies (53 samples collected) which are numerous and extensive across the Walparta Inlier. They returned no geochemical anomalism. They all appear to be coeval with late stages of regional high grade metamorphism and deformation, and hence share a uniform rock chemistry. They are coarse, plagioclase dominant, and in some instances include coarse white mica. During the regional pegmatite sampling programme a new, gossanous haematite-quartz dominant possible exhalite horizon was found on EL 5306 which was named the Two Wolf’s prospect. The exposed horizon extends for ~400 m on an approximate W-E trend, albeit with several faulted offsets. This stratabound unit, between 5 and 10 m thick, lies immediately above the prominent meta-granite of the Basso Suite and at the base of a meta-pelite sequence. Its western edge is Mn rich and also highly anomalous in Ba and REE elements. During licence Year 6, on renewed EL 6250 Whey Whey Creek, Petratherm undertook further evaluation of historic mineralised prospects, but did no field data acquisition. Eventually, at the end of Year 7, Petratherm decided that the subject area did not hold any known mineral occurrences of perceived sufficient size or likely grade improvement potential to warrant ongoing work. Therefore it allowed tenure to lapse.