Indium concentration in zinc ores in plutonic and volcanic environments:examples at the Dulong and Dachang mines, South China

摘要

Two largest indium ore deposits of 5,000 tons In class in China, Dulong and Dachang mines, were studied geochemically. The Dulong deposits have 1000In/Zn value of 4.1 in the average, which is similar to 2.6 of the Changpo-Tongkeng orebody and 3.1 of the Longtaoshan orebody of the Dachang mine. Yet the Dulong ores are depleted in silver and antimony, and enriched in tungsten among the ore metals, while the Dachang ores are rich in silver and antimony similarly to the Toyoha ores occurring in the volcanogenic Green Tuff belt in Japan. Concentration of indium in sphalerites is homogeneous in the Dulong ores but is strongly banded in the Toyoha ores. It is suggested that the Dulong ore deposits were formed in a plutonic environment related to S-type ilmenite-series granite, while the Dachang deposits were formed at shallower level, related to subvolcanic intrusions. A volcanogenic environment is necessary to concentrate indium in tin-polymetallic ore deposits.