Assessment of soil parameters and pathfinder elements for gold exploration in a mining-disturbed granitic terrain, Southeast New South Wales, Australia

Geochemical exploration for gold in historic or mature goldfields can be complicated by mining-related surface disturbance, including alluvial workings, reef mining and ore processing, as well as from other related anthropogenic activities such as land clearing and farming. The Braidwood region in southeast New South Wales is such an area, having been extensively worked for alluvial gold from the first gold rush of 1851 to the period of large scale mechanical dredging, which ended in 1914. Total gold production was 1.25 million ozs, making this the 6th largest alluvial goldfield in Australia (Middleton 1970). Major disturbance was along the rivers, creeks and alluvial flats, but also extended to adjacent slopes, which were commonly worked by ground sluicing or ‘surfacing’ and to areas of reef mining. Modern gold exploration in the area is focussed on locating primary bedrock gold deposits within the Braidwood Granodiorite, the major host unit to the known deposits, such as Dargues Reef, near Majors Creek. These intrusion-related gold deposits appear to be the source for the extensive alluvial gold concentrations and have a primary geochemical association of Au-Cu-Pb-Bi-Te-Sb with As and Fe in pyrite (McQueen & Perkins 1995). Geochemical exploration using shallow 10-15 cm A horizon) soil sampling has had limited success, even in areas away from major disturbance from historic alluvial mining (e.g. Duncan 1984). The aim of this study was to make a detailed assessment of the soils in the area, particularly around Majors Creek, and to determine the most appropriate soil fraction, horizon and components to sample and the most useful suite of elements, for improved geochemical exploration.