Development of geochemical exploration technique for epithermal gold deposits

摘要

Geochemical exploration technique using oxygen isotope geochemistry has been conducted by Ministry of International Trade and Industry (Mm, 1999) with entrustment to Metal Mining Agency of Japan since 1994. Intention of this paper is to introduce the main results of the studies for epithermal Au deposits of the Koryu, Okuzu, Kushikino and Iwato mines.In addition to oxygen isotope compositions, we introduced the following indexes to evaluate the degree of hydrother-mal alteration.K_2O~# = (K_2O) /(CaO+ K_2O +MgO+ Na_2O) (wt percent)T/A = log 10 (Total)/(CaO+MgO+ Na_2O ){ (wt percent)K_2O~# express the degree of K_2O enrichment in low sulfidation system, and T/A express the degree of hydrothermal leaching in both low and high sulfidation systems. Different alteration patterns between low and high sulfidation systems can be successfully distinguished using K_2O~# and T/A values and Au contents.In the Koryu area, the combined indicator of oxygen isotopic compositions, Ag contents and T/A values is more useful for focusing the mineralized area than a single indicator.