The Study On Mineralization Mechanism Of The Wutubulake Iron Deposit In The Southern Of Altay, Xinjiang

The polymetallic mineralization belt of South Altay is an important metallogenetic belt in Xinjiang, China. The iron deposits are mainly located in the Kelan and Maizi volcaniclastic-sedimentary basin. The medium-sized Wutubulake iron deposit is located in the Maizi basin, its geological characteristics is similar to other deposits, is the typical one of this kind of deposits. The host rocks is biotite granulite, striped hornblende granulite, leptite, amphibolite and marble lense, which is belong to the metamorphosed volcaniclastic-sedimentary sequence of the Upper Silurian-Lower Devonian Kangbutiebao Formation. The ore bodies is hosted in skarns, which occurs as stratoids or lenses, and granite is existed in district. Based on collecting predecessors material and detailed field survey of geological background, focused on the study of geological characteristics, skarn minerals assemble, fluid inclusion, stable isotope, the age of diagenetic and metallogenetic, mineralization mechanism, achieving the summaries as follows.(1) The orebodies which occur as stratoids or lenses is hosted in the metamorphosed volcaniclastic-sedimentary sequence of the Upper Silurian-Lower Devonian Kangbutiebao Formation, surrounding by the skarns minerals. Ore minerals are mainly magnetite, with minor pyrite, pyrrhotite, chalcopyriteand molybdentite etc. Gangue minerals are mainly garnet, chinopyoxene, actinolite, epitote, chlorite, with minor biotite, feldspar, quartz, calcite etc.(2) Filed evidence and petrographic observation indicate two periods of metallogensis, including skarns period and supergene oxidation period. Skarns period is also devide into three stages, including early stage, retrogressive metamorphism stage, quartz-sulfide-carbonate stage.(3) The analytical results of electron microprobe show that the end member of garnet is mainly andradite-almandite, the composition of pyroxene is mainly diopside and the composition of amphibole is mainly ferrotschermakite, all of them show the characteristics of calcic skarn. Magnetite is belong to magmatic hydrothermal type, which is closely related to the skarns.(4) The ore-forming fluids in early stage of skarn period is high-middle temperature, high-middle salinity and high-middle density, which is belong to NaCl-H2O system; The ore-forming fluids in retrogressive metamorphism stage of skarn period is middle temperature, middle-low salinity and high-middle density, which is belong to NaCl-H2O system; The ore-forming fluids in quartz-sulfide-carbonate stage of skarn period is dominantly NaCl-H2O type fulid, locally mixed with CO2-H2O type fluid.(5) The ore-forming fluids in early and retrogressive metamorphism stage of skarn period are mainly derived from magmatic water, while the ore-forming fluids in quartz-sulfide-carbonate stage of skarn period is derived from mixing of magmatic water and meteoric water. The sulfide and rare earth element data of rocks and ores suggest that the ore-forming materials is mainly derived from the amphibolite, which is belong to the metamorphosed volcaniclastic-sedimentary sequence of the Upper Silurian-Lower Devonian Kangbutiebao Formation.(6) Based the Re-Os model ages of molybdentite in magnetite ore rang from 243.6±4.1 Ma to 244.2±4.2 Ma, we concluded that the mineralization age is in the Early Triassic, while have pioneered the the Triassic Mineralization in Altay.(7) LA-ICP-MS U-Pb zircon dating on the tonalite and biotite tonalite in the district, yielded concordant ages of 385.6±2.3 Ma and 387.7±2.1 Ma, indicates that the two plutons were formed at the beginning of the Middle Devonian in continental arc at active extensional continental margin setting, which is earlier than the mineralization age.(8) The Wutubulake iron deposit is belong to skarn type, and the mineralization mechanism is Triassic magmatic hydrothermal interacting with metamorphic volcanic, the formation of magnetite is related to the retrogressive metamorphism of the skarns.