| The Luotuoshan deposit located in west Henan province in Luanchuan polymetallic ore accumulated area, it is a middle polymetallic pyrite deposit. Previous studies focused on the porphyry-skarn-type molybdenum(tungsten) deposit, hydrothermal vein-type silver-lead-zinc deposit, while the research on skarn polymetallic sulfide deposits are relatively less. Based on field investigation, petrography, electron microprobe analysis of minerals, fluid inclusions microthermometry and laser Raman analysis, metal sulfides Rb-Sr isotopic dating analysis, stability isotope analysis, this paper has got a preliminary understanding for the geological characteristics, the nature and evolution of fluids, metallogenic epoch, the mineralization enrichment mechanism and the genesis of mineral deposit, which achieved the following results and understanding:(1)The Luotuoshan polymetallic sulfur pyrite ore bodies occured in the skarn zones of Sanchuan group, with bedded, lenticular based. Ore minerals mainly includes pyrrhotite, pyrite, marmatite and less chalcopyrite, scheelite. The gangue minerals mainly includes diopside, calcium and iron garnet, quartz, tremolite, fluorite and less actinolite, K-feldspar,beryl and a small amount of epidote, chlorite, calcite, sericite and so on. Wall rock alteration are mainly skarn, silicification, potassic, calcite, phyllic. Mineralization stages can be divided into skarn stage, retrograde alteration stage, early sulfide stage,late sulfide stage and carbonatation stage.(2) Luotuoshan polymetallic sulfur pyrite deposit mainly developed two-phase inclusions of gas and liquid, three-phase inclusions which contains CO2 and multiphase inclusions containing intron crystal. Inclusions temperature is 260 ~> 600 ℃, salinity is 3.15 to 39.60 percent, metallogenic system pressure is 35~70MPa, depth is 1.3~2.8Km. Forming fluids evolved from high temperature, high salinity to high temperatures, low salinity. In general they belonged to H2O-NaCl ± CO2 system.(3) The isotope isochron age of metal sulfide Rb-Sr is 137.3 ± 2.6Ma, which means Luotuoshan deposit was formed in the Early Cretaceous, and was the same structure- magmatic- fluid activity product as Nannihu rock andmolybdenum deposit, Lengshuibeigou pb-zn deposit, which have got a minerogenetic series(4) δ18OH2O of ore fluids is 2.4 ~ 10.7 ‰ and δDH2O value is-106.7 ~-82 ‰, shown ore-forming fluids in early stage were mainly magmatic water and in late stage, there were atmospheric precipitation mixed in. δ34S value of flash zinc, pyrrhotite and galena were 1.4 ~ 3.0 ‰, shown that the source of S may come from the deep. Sr isotopes showed mineralize material came from crust-mantle contamination.(5) During the late Jurassic to the early Cretaceous epoch, the tectonic regime transition occurred in eastern China, the primary SN stress field switchs to EW direction. in the southern margin of the North China Craton, the asthenosphere was upwelling and the lower crust was partial melting, which formed the ore magma. The magma rised along the weak tectonic belt and formed Nannihu granite-porphyry and molybdenum deposit. In the late period of magmatic evolution, the fluid went through the further evolution and migration, high-temperature magmatic water-based fluid formed the skarn type sulfur polymetallic deposit in the outer contact zone of the porphyry and the vein type zinc deposit in the fault zone. |
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