Evaluation of mercury pathfinder techniques: Base metal and uranium deposits

Abstract

The applicability of Hg as a pathfinder for base metal mineralization has been investigated in an Australian case-history-based study. The principal objectives of the project were: (a) to compare the behaviour of Hg with that of the target elements in the secondary environment with reference to the intensity and extent of the anomalies around outcropping base metal mineralization under varying conditions of climate and geomorphology; (b) to determine whether vapour-generated Hg anomalies can be detected in surface media over buried and blind mineralization, and if so under what geological, geomorphic and climatic conditions; (c) to define the most appropriate sampling media and methods for use in Hg surveys; (d) to develop appropriate techniques for the determination of Hg in geological samples. Some twenty-nine case history studies have been completed within this project, covering a range of styles of mineralization and commodities and where possible under varying secondary regimes. The data from these studies, together with laboratory and theoretical considerations, have led to the following conclusions regarding the geochemistry of Hg and its possible role in exploration for base metals: (a) Hg is present in sufficient concentration in many styles of mineralization to be a potential pathfinder; metamorphism does not necessarily lead to serious loss of the element. (b) Hg tends to give ‘residual’ anomalies with little observable secondary dispersion. Situations have been defined where the element is a valid pathfinder. However, in general exploration Hg has no advantages over the target elements, Cu, Pb and Zn. (c) Hg may, under certain conditions, indicate buried mineralization. (d) The use of gas-phase sampling is appropriate only in quite specific circumstances; soil is almost always the preferred sample medium. (e) Hg determination can be made at or below background levels in a routine manner if certain requirements are observed. The remaining question, that of blind mineralization, is in need of further testing since most study areas showed a geochemical expression.