Indium Mineralization in Copper-Tin Stratiform Skarn Ores at the Saishitang-Rilonggou Ore Field, Qinghai, Northwest China

摘要

The Saishitang-Rilonggou Ore Field (SROF), which includes the Saishitang, Tongyugou, and Rilonggou ore deposits as well as other scattered occurrences, is located in the Elashan region in Qinghai Province, and is a significant Cu-Sn ore field in NW China. These ores are hosted in stratiform skarn deposits with the main metals being Cu and Sn, as well as Zn, Pb, Au, Ag, and trace elements (e.g. Ga, Ge, Se, and In). Bulk-rock geochemical analyses of 50 ore samples from the three deposits show that In contents in the Saishitang deposit range from 0.03 to 39ppm (average 12.7ppm, n=19), with 1000 In/Zn values that vary from >0.01 to 29.83 (average 4.29). Indium contents in the Tongyugou deposit vary from 7.51 to 131ppm (average 28.37ppm, n=13), with 1000 In/Zn values from 0.74 to 48 (average 17.55). Finally, indium contents in the Rilonggou deposit vary from 0.73 to 120ppm (average 36.15ppm, n=18), with 1000 In/Zn values from 0.33 to 47 (average 8.52). Indium is hosted mainly in sphalerite, while some other In-bearing minerals (e.g., roquesite, stannoidite, and stannite) are present locally within the ore field. Roquesite, which replace or fill bornite, occurs in bornite-rich ores in the Saishitang deposit. This is the first reported Chinese locality of roquesite. Based on previously reported Zn resources, a total of 136 tons of In is calculated to be hosted in the SROF, with 30, 66, and 40 tons of In attributed to the Saishitang, Tongyugou, and Rilonggou deposits, respectively. The differences in indium contents among the deposits and their respective geological histories and characteristics suggest that the origin of indium relates to volcanogenic metallogenesis in an early Permian volcano-sedimentary basin. Based on the evaluation of In resources, future mining operations should include the recovery of indium in the Tongyugou and Rilonggou deposits.