Study Of The Metallogenesis In Diantan Fe-polymetallic Deposit, Yunnan Province

Diantan Fe-polymetallic deposit which is one of representative skarn deposits inthe southern Bowo-Tengchong polymetallic belt is located in the southern Sanjiangmatellogenic belt. The deposit is related to the Early Cretaceous granite along theouter contact zone between granite and Carboniferous Kongshuhe Group and PermianDadongchang Group, controlled by magmatic rock, structure and strata. Themorphology and distribution of orebodies are mainly controlled by the NS-trendingfault.The morphology orebodies is irregularly lenticular in the plane, and stratiform,vein, lenticular and wedged in the section. Iron ore is massive, disseminated, bandingand granular blastic texture. The metallic minerals in ores are mainly composed ofmagnetite, hematite secondly, associated with marmatite, pyrite, gelenite and so on.The nonmetallic minerals are mainly chondrodite, diopside, forsterite, phlogopite anda few calcites.The contact zone between magmatic rocks and carbonate formation presentsobvious zonation in the plane and section. The skarns develop generally, includingcalcium skarn and magnesium skarn, the former are mainly garnet and vesuvianiteskarn, the latter are diopside, chondrodite, phlogopite skarm. Electron microprobeanalysis shows the end member of garnet is mainly andradite, followed by grossular;pyroxene is given priority to diopside. The wall-rock alteration includes silicification,potassic alteration, serpentinization, carbonatization and chloritization, in addition tohornfels, skarnization.Granitoids in the Diantan orefield are mainly monzonitic granite, it exhibits thefeatures of high potassic and peraluminous S type granite, rich in silicon andaluminum, poor in iron and magnesium. The granite zircon U-Pb dating shows, theU-Pb harmonic age of rock body is121.5±1.0Ma,120.79±0.83Ma, MSWD=1.5. Itbelongs to Early Cretaceous. The metallogenic age is slightly latter than granitediagenetic age, and it belongs early Cretaceous mineralization in Sanjiang area.The range of δ18O of magnetite varies from-2.1‰to1.9‰, mean value is-0.36‰. According to the oxygen isotope fractionation equations of magnetite-water system, calculate the δ18O of H2O of ore-forming fluid varies from3.15‰to8.06‰.It indicates that the ore-forming fluid is mainly derived from magmatic water. Therange of δ34S of sulfide ore varies from1.08‰to4.5‰, mean value is3.25‰, peakvalue is4.0‰to4.5‰. The δ34S spread around the zero line, shows sulfur comesfrom magma.Diantan Fe-polymetallic deposit belongs to early Cretaceous mineralization inSanjiang area. In the early Cretaceous, a large number of Donghe terrain graniteintruded upward along the NS-trending fault, contact with Carboniferous KongshuheGroup stratum and Permian Dadongchang Group stratum, then formed skarm typedeposit. On the basis of the metallogenic genesis, a metallogenic model wasestablished.