Lithogeochemical and mineralogical indicators of Andean precious-metal and polymetallic vein mineralization

Abstract

Proximal and distal lithogeochemical alteration patterns associated with precious-metal and polyTnetallic vein mineralization in the Andes of Bolivia and Peru are delineated both by sulphophile elements such as Ag, As, Pb, S, Sb, Sn and Zn, and also by hydrothermal alteration indicators such as Ca0/Mg0, K20/Na20, Rb/K and Rb/Sr. In some cases, single-element, ratio and normalized data additive plots permit the detection of a vein at a distance of more than 100 m even when the visible alteration extends for less than 10 m. Asymmetric hanging-wall-footwall halos in both volcanic and sedimentary rocks provide a useful supra-ore/sub-ore indicator for inclined veins. The K20/Na20 ratio appears to be the most reliable lithogeochemical guide to ore-related hydrotherrnal alteration.