Au-Se Paragenesis in Cambrian Stratabound Gold Deposits,Western Qinling Mountains,China

Cambrian stratabound gold deposits in the western Qinling Mountains are hosted in a siliceous formation composed of black chert and carbonaceous slate. Studies have shown that Se is sufficiently high in abundance either in wall rocks or in gold ores as to reach economic grade. Locally, some independent Se ore bodies (Se >500 ppm) can be delineated. In gold ores, Se is present mainly as separate minerals, or as isomorphous solutions in sulfides. In addition, Se is positively correlated with Au. What is more important is that in the gold ores, native gold is commonly intimately inter-grown with selenium minerals. On the basis of this unique phenomenon, the authors hypothesize that gold and selenium may be transported by Au-S-Se or Au-Se complexes. The co-enrichment of Au and Se is attributed mainly to the boiling of ore fluids and their mixing with shallow-seated oxygen-bearing water.