The Metallogenesis Study Of The Cuihongshan Fe-polymetallic Deposit In Heilongjiang Province, NE China

Located in the north segment of the Lesser Xing’an range, NE China, the Cuihongshan Fe-polymetallic deposit is a giant skarn type deposit. It is discovered in Heilongjiang Province, NE China, which yields proven resources of 68.35 Mt Fe, 0.09 Mt Mo,0.12 Mt W, and 0.51 Mt Zn, with some dispersed elements, such as gaining resources of Se 252Mt, In 341Mt, Cd 2936Mt. On the basis of precious studies, for instance the studies of the deposit geological, geochemical characteristics, I obtain the main advance achievements as followings.(1) Four main stages of mineralization have been identified, ranging from early skarn phase,through late skarn phase to the stage of sulfides. And the composition of the rocks, ores and the occurance of the dispersed elements, Se, In, Cd, have been authenticated. More than forty minerals have been discovered in the deposit. The metal minerals mainly comprise magnetite, molybdenite, scheelite, sphalerite, galena, pyrite, chalcopyrite and pyrrhotite with minor cassiterite, arsenopyrite. The main nonmetallic minerals consist of garnet, diopside, phlogopite, fluorite, chlorite, Plagio-clase, quartz calcite, dolomite, epidote, tremolite, serpentine etc. And the dispersed elements, Se, In, Cd, mainly occur in the ore of copper-lead-zinc sulfide, with entering the metal sulfide through isomorphism. Among them, Se mainly occurs in galena and molybdenite, however, In and Cd mainly entering sphalerite.(2) The lead-zinc ore and monzogranite have similar geochemical characteristics, with obviously higher than the marble and skarn of the deposit, such as, REE and trace elements characteristics. The contents of REE and trace elements in lead-zinc is somewhere between monzogranite and the marble, indicating the inheritance relationship between the ore and wall rocks, with the major contributions of monzogrnite. The sulfur isotope, lead isotope and rhenium-osmium isotope characteristics suggest that the sulfur, lead and Re come from the mixture of mantle and crust.(3) The biotite granite, monzogranite and granite-porphyry yield zircon U-Pb ages of 496±1.5Ma, (199.0±3.1)～(193.0±1)Ma and (173.0±1.0) Ma, Re-Os dating of molybdenites yielded the isochron ages of 205.1±1.9 Ma and 204.0±3.9 Ma from Cuihongshan and Cuizhong ore spot respectively, which is consistent with the zircon diagenetic age of (199.0±3.1) Ma from the monzogranite, indicating that the monzogranite has a close relationship with the mineralization of Cuihongshan deposit.(4) According to zircon Hf isotope analyses, the biotite granite has εHf(t) value of-4.7 to 0.0 with Hf modal age from 1463Ma-1764Ma. which suggests that the magma source mainly should derive from Mesoproterozoic crustal materials. Both the granite porphyry and monzogranite have εHf(t) values from -4.7 to 10.1, and with Hf modal age mainly from781Ma to 1184Ma,showing that their sources are mainly from the new crust with the mixture of some depleted mantle resouces, indicating that the crust in the Songnen Block was extracted from the mantle two times during the Meso-Neoproterozoic.(5) Combining with mesozoic regional dynamics background, I can conclude that, at the late Indo Chinese epoch, the Lesser Xing’an range-Zhangguangcai range district was in an extensional tectonic background, and the upwelling of asthenospheric mantle induced partial melting of crust, forming deep magma chamber, which migrated along the fracture zone and emplacing to Qianshan formation and middle Caledonian biotite granite. And the geochemical reaction between magama-hydrthor-mal solutions and wall rocks induced a series of alteration, mineralization, and the extraction of some ore-forming minerals. with the mixture of atmospheric water, the ore bearing hydrothermal temperature, salinity, temperature, pressure decreased gradually. During the further evolution process, the change of redox conditions resulted in the precipitation of the metallogenic materials along the skarn contact zones between monzogranite and stratum and forming the ore bodies. On the basis of the study of regional metallogenesis, I insist that many contemporary skarn type deposits and porphyry deposits in the Lesser Xing’an range-Zhangguangcai range district, are likely to be deposits of the same mineralization system. The magmatic hydrothermal system evolves tending to different components and takes place geological action with different wall rocks, resulting in forming different stype of deposit, ie., the magma-hydrothermal solution sytem intruded in porphyry body, in favor for forming porphyry type deposits, such as Huojihe, Luming, Cui Ling deposits, and emplaced in the carbonate rock or shale, leading to the formation of skarn deposits, such as Cuihongshan, Daxilin, Xiaoxilin, Yibeihe, Xiangshuihe and Erguxishan skarn deposit.