Study on the ore-forming mechanism of the Wutubulake iron deposit in the southern of Altay, Xinjiang

The medium sized Wutubulake iron deposit is hosted in the metamorphosed volcaniclastic-sedimentary sequence of the Upper Silurian-Lower Devonian Kangbutiebao Formation,the orebodies occur as stratoids or lenses, which are surrounded by the skarn minerals. Homogenization temperature of fluid inclusions in early skarn stage vary from 256 to 534 degrees C, salinity range from 11.90% to > 73.96% NaCleqv,density range from 0.56 to 0.96g/cm(3), all of these showed that the ore-forming fluid in early skarn stage are high-middle temperature, high-middle salinity and high-middle density, which is belong to NaCl-H2O system; Homogenization temperature of fluid inclusions in retrograde alteration stage vary from 188 to 313 degrees C, salinity range from 12.30% to 39.76% NaCleqv,density range from 0.83 to 1.05g/cm(3), which have the characteristic of middle temperature, middle-low salinity and high-middle density, also belong to NaCl-H2O system. In quartz-sulfide-carbonate stage,the ore-forming fluid is NaCl-H2O-CO2 +/- CH4 or N-2 type fluid. Homogenization temperature of fluid inclusions in this stage vary from 162 to 320 degrees C, salinity range from 2.90% to 15.57% NaCleqv, density range from 0.70 to 1.02g/cm(3). The oxygen and hydrogen isotopic data of garnet suggest that the ore-forming fluid in early skarn stage is mainly derived from magmatic water, but the oxygen and hydrogen isotopic characteristic of quartz and calcite imply that the ore-forming fluid in quartz-sulfide-carbonate stage is derived from mixing of magmatic water and low temperature and salinity meteoric water. The carbon and oxygen isotopic data of calcite suggest that the carbon in the fluid is mainly derived from the deep-seated magma,and the sulfide isotopic data show that the characteristic magma sulfur. We hold that the ore-forming mechanism is closely related to the retrogressive metamorphism of the skarn minerals,which might have resulted from the Early Triassic magmatic hydrothermal interaction with volcanic of the Upper Silurian-Lower Devonian Kangbutiebao Formation.