The Walford Creek Prospect ? an exploration overview

Abstract

alford Creek is a Zn, Pb, Cu, Ag prospect located in northwest Queensland at 17° 48¢S, 138° 17¢E. Both stratiform mineralisation and stratabound breccia style mineralisation are present but not in sufficient quantity to make the deposit economic. The base-metal occurrences are closely associated with a much larger body of stratiform massive pyrite. This massive pyrite body has a shallow southerly dip, a strike length of six kilometres, and a typical width of 1500 m. The classic geological setting and similar geophysical signature to some economic deposits make it a useful case history. The mineralisation is hosted by the mid-Proterozoic Mt Les Siltstone on the northern margin of the Lawn Hill Platform. It lies immediately to the south of the Fish River Fault, under thin alluvial cover. The prospect was originally targeted by Western Mining Corporation on conceptual geological grounds, with the aid of government geological mapping. Until recently the prospect was thought to have no surface expression, and exploration has been primarily advanced by the use of electromagnetic techniques. The stratiform mineralisation is intimately associated with a series of three gently dipping and vertically stacked synsedimentary massive pyrite horizons. It comprises an overprinting diagenetic impregnation of coarse-grained sphalerite and galena. The stratabound breccia mineralisation is hosted by a series of dolomite talus breccias adjacent to the Fish River Fault. It is a later, discordant style of mineralisation consisting of sphalerite, galena and chalcopyrite. The coincident-loop TEM method has been the primary geophysical exploration tool. The host shale package to the mineralisation is not graphitic, and the TEM results have successfully mapped the extent and gross geometry of the upper pyrite lens. Gravity has been shown to be a useful exploration aid at both the regional and prospect scales. Airborne magnetic surveys have successfully mapped the main basin structure controlling the mineralisation. Airborne TEM and a large fixed-loop survey have been tested over a part of the mineralized system.