What is Down Plunge of the Dobroyde Hill High-Sulphidation Epithermal Deposit, near Junee, NSW? An Emerging Carbonate-Base-Metal-Gold Epithermal System

Abstract

Discovered by Getty Oil in 1983, the outcropping Dobroyde Hill 77k Oz gold high-sulphidation epithermal prospect is now known to transition into a carbonate base-metal epithermal gold system down plunge. The project is 50km north of Wagga Wagga and 10km north of Junee which is the far southern toe of the Junee-Narromine Volcanic Belt. It is hosted within a 4km long package of middle Ordovician andesitic to basaltic sub-marine volcanic rocks and early Silurian plagioclase and hornblende phyric shoshonitic andesite sub-marine breccias (Crawford 2014, 2017). Revival of the prospect was driven by field mapping armed with a TerraSpec Halo, ground magnetics and 3D IP and magnetic inversions (by Chris Moore, Moore Geophysics). This lead to the recognition of a 3m x 2km surficial dickite ± pyrophyllite ± kaolinite ± illite ± silica ± pyrite alteration in shoshonitic andesite breccias. Follow up drilling which targeted a zone 700m down plunge of the Dobroyde Hill resource was completed in partnership with the NSW Government through the New Frontiers cooperative drill funding scheme. This hole, NDD005, intersected a far larger system than expected, with 280m of intense dickite + pyrophyllite + kaolinite + pyrite ± illite ± silica alteration then 200m of unmistakable carbonate-base-metal-gold epithermal style alteration as presented in Corbett & Leach (1998). Evolution Mining’s giant Cowal Gold Mine (~8M Oz Resource) 120km north of Dobroyde is also characterised as carbonate-base-metal-gold epithermal. Both mineralising styles show a genetic link by overprinting relationships and both having associated broad low-grade gold and silver mineralisation with individual 1m intervals to 9.5g/t gold. NDD005 is interpreted to have stepped over the top of the main epithermal gold zone, hence the target remains open to further exploration. Additionally, this 700m down plunge gap between the new and historic drilling is completely untested and if mineralised could extend the strike length of the deposit to one kilometre.