Indium Mineralization in a Sn-Poor Skarn Deposit: A Case Study of the Qibaoshan Deposit, South China

Indium (In) is commonly hosted in Sn-rich deposits but rarely reported in Sn-poor deposits. However, an In-rich and Sn-poor skarn deposit, the Qibaoshan Cu-Zn-Pb deposit, has been identified in south China. Geochemical analyses were undertaken on 23 samples representing the following mineral assemblages: sphalerite-pyrite, pyrite-chalcopyrite, pyrite-sphalerite-galena-chalcopyrite, pyrite, magnetite-pyrite, and magnetite. The results show that In is richest in the sphalerite-pyrite ores, with concentrations of 28.9–203.0 ppm (average 122.8 ppm) and 1000 In/Zn values of 2.7–10.9 (average 7.0). Other ore types in the Qibaoshan deposit are In poor, whereas all are Sn poor (10 to 150 ppm), with most samples having Sn concentrations of ≤70 ppm. Indium is mainly hosted by sphalerite, as inferred from the strong correlation between In and Zn, and weak correlation between In and Sn. Mineral paragenetic relationships indicate sphalerite formed from late quartz-sulfide stage of mineralization processes. Indium in the Qibaoshan deposit is richer in vein-type orebodies than in lenticular-type orebodies occurring at contact zones between carbonate and quartz porphyry, or in carbonate xenoliths. Igneous intrusions that were Sn poor and emplaced at shallow depths formed the In-rich orebodies of the Qibaoshan deposit.