Geophysical exploration for base metals in the carbonates for the Buchan Rift, eastern Victoria

Abstract

"Base metal mineralisation occurs in the carbonates of the Buchan Rift in eastern Victoria. Lead mineralisation was first found on the banks of Back Creek in the late 1860s. Several small mines were sporadically worked from 1872 until the mid 1900s. About 350 tonnes of lead and copper ore was produced in this time, but not all of it was smelted and production is generally poorly reported. The mineralisation has similarities to the Irish Style deposits. Galena with minor pyrite, sphalerite and chalcopyrite occurs as veins and lenses and also as disseminated grains. The mineralisation is locally stratabound in both dolomitised and undolomitised limestone. The volcanics underlying the carbonates also have disseminated lead and zinc mineralisation and it is probable that the mineralisation in the carbonates was mobilised from the underlying volcanics. Modern exploration from 1966 targeted a large exploitable lead-zinc-silver orebody. Soil geochemistry and induced polarization surveys were carried out in the area, with wide line spacings, but did not resolve an orebody. A zinc soil anomaly and coincident low resistivity <100 W m) and high frequency effect (5%) corresponded with an intersection of 3.5 m @ 1.63% zinc in a drillhole at 44 m depth. The best drilling intersections were 0.6 m @ 40.56% lead and 1.5 m @ 7.52% lead, 9.97% zinc, 190 ppm silver. A spontaneous potential survey was also carried out and the high results (not specified) were reported to coincide with drillholes which had intersected lead and zinc mineralisation. Regional magnetic and radiometric surveys do not directly detect the mineralisation, but are useful for geological mapping."