THE GEOCHEMICAL CHARACTERISTICS AND MINEROGENIC MODEL FOR THE AMO HYPOTHERMAL TIN DEPOSIT IN XIMENG COUNTY, YUNNAN PROVINCE

Through studies on the element geochemistry, alteration of country rocks, ore-forming fluids and isotope geochemistry of the Amo tin deposit in the metamorphic rocks of the Upper Proterozoic Ximeng Group, the authors consider that the concentration of the B-F-Li-Rb-Cs-Sn association is related to acidic magmatism in the study area. The Fe- Mg- Li tourmaline in the ore is the replaced product of the country rocks by hypothermal fluid. The delta-O-18 values of mineral separates are +2.01-+13.16 parts per thousand and their delta-S-34 values, +2.6-+7.2 parts per thousand. The ore- forming materials were derived from hydrothermal fluid of granitic magma. For the mineralization, the temperature is 450-degrees-350-degrees-C, the pressure, 450-1000 x 10(5) Pa, and the age, Himalayan (21.5 Ma). According to the geochemical characteristics, a minerogenic model is established: the deposit is a hypothermal cassiterite-quartz vein type tin deposit controlled by the hidden Himalayan granites.