Characterization of primary geochemical haloes for gold exploration at the Huanxiangwa gold deposit, China

摘要

Recognition of primary geochemical haloes is one of the most important tools for exploring undiscovered mineral resources. This tool is being routinely applied in exploration programs at the Huanxiangwa gold deposit, Xiong'er Mountains, China. Sampling of unweathered rock for multi-element analysis has been undertaken in all completed and ongoing exploration and development work, including drilling and galleries. Samples have been analyzed for 12 elements (Au, Ag, Pb, Zn, Cu, Mo, As, Sb, Bi, Co, Ni and Ba) from unaltered andesites, altered andesites, altered rocks and mineralized altered rocks. To identify multi-element geochemical associations that can be used to recognize enrichment zones, the lithogeochemical datasets were subjected to centered log-ratio transformation to address the closure problem with compositional data, and the log-ratio transformed datasets were subjected to principal components analysis. Results of analyses show that, in the Huanxiangwa deposit, gold mineralization is characterized by a Au±Ag±Cu association, base-metal mineralization by a Zn-Pb-Ag-Cu±As±Sb±Mo association, supra- and/or near-ore primary haloes in mineralized altered rocks by an As±Sb±Bi±Ag±Au±Pb association, sub-ore primary haloes in altered andesites and altered rocks around gold mineralization by a Mo-Bi±Sb±Ba±Zn±Ag association, and the host andesites by a Ni-Co-Ba association. Analyses of axial and longitudinal primary haloes indicate that gold mineralization is overprinted base-metal mineralization in the western and deeper parts of the Huanxiangwa deposit. Modified enrichment indices for Au and linear Au productivity values also indicate extension of gold mineralization with base-metal overprint beneath the western parts of the deposit. Based on this, an exploration target zone extending ca. 200 m below the known ore body was delineated, in which the presence of gold mineralization has been successfully verified by drilling. This study concludes that characterization of primary geochemical haloes associated with known deposits, coupled with analysis of linear element productivities, facilitates vectoring toward ore. Characterization of primary haloes associated with known deposits using lithogeochemical data would benefit highly from applications of log-ratio transformations developed for compositional data analysis.