1988 Volume 38 Issue 211 Pages 419-435
Various kinds of tin-bearing minerals, such as cassiterite, stannite, kesterite, franckeite, hocartite, teallite, cylindrite, rhodostannite, canfieldite, incaite and potosiite occur from polymetallic deposits in Eastern Cordillera of Bolivian Andes. These deposits, called Bolivian type polymetallic deposits, were formed by xenothermal mineralization related to Miocene igneous activities. The mineralization stages are generally divided into six as follows: I: quartz-tourmaline, II: quartz, III: quartz-pyrite, IV: sulfide, V: sulfosalt and VI: sulfate-phosphate stages. Cassiterite principally occurs in the quartz-tourmaline (I), quartz (II) and quartz-pyrite (III) veins. Stannite and kesterite appear in the sulfide (IV) and sulfosalt (V) veins. Meanwhile, tin-bearing sulfosalt minerals, such as franckeite, hocartite, teallite, cylindrite, rhodostannite and canfieldite are found commonly in the sulfosalt (V) vein in small amount. Homogenization temperature and NaCl equivalent concentration of fluid inclusions in quartz at each stage of the mineralization are I: 260° to 510° and 18.5 to 55.4 wt%, II: 250° to 405°C and 23.4 to 26.0 wt%, III: 250° to 400°C and 4.4 to 19.7 wt%, IV: 230° to 350°C and 1.5 to 10.6 wt%, and V: 190° to 300°C and 0.4 to 5.4 wt%, respectively. The homogenization temperatures, salinities and sulfur fugacities at each stage decrease as a whole with progressing the mineralization stages. Sulfur fugacity values at the III, IV and V stages are 10-13 to 10-7 atm., 10-15 to 10-9 atm., and 10-16 to 10-19 atm., respectively.
