Dispersion of gold and other metals by trees, gravels and soils near Boddington Gold Deposit, Western Australia

• Published in: Journal of geochemical exploration 2017-10, Vol.181, p.10-21
• Main Authors: Lintern, Melvyn J., Anand, Ravi R.
• Format: Article
• Language: English
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2017.06.016

South west Western Australia is host to some of the world's largest mineral deposits including bauxite, Ta and Au. The giant Boddington Gold Mine exploits one such deposit and is located in forested areas south east of Perth. Exploration for Au in this area has concentrated on sampling surficial Fe-rich lateritic residuum and its degradation products and was how Boddington was originally discovered; it has a multi-element signature. Despite its location in forest there has been little biogeochemistry undertaken in this area or consideration of whether trees (including eucalypts) are agents of dispersion of metals in this terrain. Eucalyptus trees have been shown to be responsible for forming anomalies above gold deposits in semi-arid areas of Australia and the location of Boddington in a humid environment provided an important comparison in which to investigate this possibility. The Golden Triangle Au prospect near Boddington Gold Deposit is located on the flank of a small lateritic hill. Limited shallow drilling has identified sub-economic mineralisation with some metre composite cuttings grading >1ppm Au. A selection of different trees and shrubs, organic soil and ferruginous pisoliths were collected over a surface traverse of 800m at 50m intervals from across the prospect. Samples were analysed for major elements, Au and several pathfinder metals. Additional foliage samples were collected from the same trees over mineralisation and background to test for sample heterogeneity. Golden Triangle vegetation samples were generally anomalous in Au and pathfinder elements (e.g. Ag, Bi, W and Sn). For example, Banksia and Macrozamia had elemental anomalies in Bi and Ag located directly above or down slope of mineralisation although for Eucalyptus the anomaly over mineralisation itself was poorly defined. Topsoil containing organic matter overlying the ferruginous pisoliths was particularly anomalous in Au (mean of 47ppb against of background of