The Colquiri Tin Deposit: a Contribution to Its Genesis

The paragenesis of a representative vein in a deeply situated part of Colquiri tin mine (Bolivia) was investigated in detail. The mineral content consists of sulphides (about 80 wt.% pyrrhotite, sphalerite, pyrite and marcasite as main components), cassiterite and gangue minerals. The occurrence of topaz, chalcopyrrhotite and traces of teallite is remarkable. Deposition of the minerals took place during three periods. Topaz is formed possibly katathermaEy. The kata to mesothermal cassiterite exhibits small grain size and a columnar and needlelike habit. Using experimental sulphide data, the formation temperatures of the primary sulphides were determined to be 300°–400°C. No paragenetic relations to subvolcanic tin mineral assemblages could be observed. Indications of hydrothermal regenerative processes (“hybrid” formations) were not found.