The Round Mountain and Borealis mines, Nevada, are in Teriary volcanic host rocks. The Picacho mine, California, is in Precambrian schists and gneisses. Geologic setting is characterised by extension, rifting and the presence of grabens, which may or may not contain volcanic and sedimentary rocks. Basin-Range fault structures commonly control ore locations. Near surface breccias of tectonic and hydrothermal origin are host to gold mineralisation.
Alteration zoning with high level silicification and argillization are typical lithocaps.
As, Sb, Hg, W, Ba, Tl are geochemically associated with gold and may form halos. Dick Neilsen is a consultant, based in Colorado, USA and specialising in new project generation. He is well known for his work in porphyry copper deposits and more recently in gold and silver. Dick lived in Australia, in the early 1970's, at which time he was Research Geologist for Kennecott.