Stannoidite and cubanite from Askot polymetallic sulphide ores, Kumaun Lesser Himalaya, India

Results of mineral, chemical and XRD investigations on stannoidite and cubanite from Askot sulphide deposit, Kumaun Himalaya are presented here. Stannoidite occurs as myrmekitic intergrowth and cubanite as exsolved lamellae in chalcopyrite. Chemical composition of this tin-bearing sulphide closely matches that of stannoidite, hitherto unreported from the Himalayan sulphides. Stannoidite and cubanite from Askot are non-stoichiometric. An average of 1.13 wt% Zn is present in stannoidite, whereas the zinc content of cubanite is very low. Cu/(Cu + Fe) ratio of about 0.326 in cubanite indicates iron enrichment. These sulphides were formed from cooling of high-temperature hydrothermal solution, possibly with higher sulphur fugacity.