干旱区生态环境知识资源中心

This study concerns the implementation of the most suitable geochemical prospecting methodology to explore for gold deposits in the Andean Altiplano, Bolivia. The main gold ore deposits in this area are associated with the ’saddle reef antimony-gold type’ in low-grade metamorphic Ordovician-Silurian siliciclastic rocks, placer gold deposits of Miocene age and epithermal gold deposits related to acid volcanic rocks of Tertiary age. An orientation biogeochemical survey was carried out over these deposits by analysing a common plant (Thola shrub) for Au, Sb and pathfinder elements. Thola is widespread and abundant in this semi-arid highland terrain and includes different families such as Compositae (Baccharis incarum/B. tola) and Solanaceae (Fabiana densa) with deep roots (>5 m) that are able to penetrate allochthonous rocks (acid tuffs) and mineralized zones. This orientation survey shows strong anomalies in gold and antimony over saddle reef antimony-gold deposits and anomalies over placer gold deposits where the bottom of the placer is exposed. High concentrations of Au and pathfinder elements were obtained in transects across acid volcanic rocks in the vicinity of abandoned mines. The Thola shrub therefore has the potential to be an excellent exploration medium throughout an area of 140 000 km(2) in the Bolivian Altiplano.