Vertical variations and dispersion of elements in arid desertregolith: a case study from the Jinwozi gold deposit,northwestern China

Abstract

Desert terrains in northern China are covered by widespread regolith sediments which mask geochemical signals from ore bodies and are major obstacles to mineral exploration. There is a critical need to study the vertical distribution of elements in the regolith, and to determine potential mechanisms for transferring elements from the ore body upwards through regolith cover to the surface, and to establish appropriate sampling media and analytical methods. The Jinwozi gold deposit, which is covered by four to several tens of metres of regolith sediment, was selected for this study. Samples were taken from different regolith horizons in two vertical profiles over the deposit. Gold and associated elements showed crescent-shaped distribution patterns in the vertical profile, i.e. elements tend to be enriched in lower and upper parts of the profile over the ore body. Enrichment of elements in weathered rocks is derived from the ore body, whereas enrichment at or near surface is due to adsorption by clays or oxide coatings. For gold, the greatest contrast between anomalous and background concentration is in the fine fraction of soils, and the Au anomalies are located directly over the ore body. Gold appears to migrate vertically to the surface to be trapped in clays and oxide coatings to produce superimposed anomalies in the regolith near or at the surface. Fine fraction samples (−120 mesh; 125 μm) from clay-rich horizons or selective leaching of elements adsorbed on clays or oxide coatings are effective for locating buried deposits.