A Study On The Genesis Of The Giant Donggou Porphyry Mo Deposit, Henan Province

The relationship between magmatic activities and mineralization is one of the“hot spots”studied by the international economic geologists. In this thesis, we primarily summarize regional research about molybdenum metallogenic belt in the East Qinling-Dabie orogenic belt. According, we studied Donggou porphyry molybdenum deposit (DGPMD) which is a giant deposit and Taishaniao batholith on the basis of the theory of transmagmatic fluid metallogenesis, and found that DGPMD is a typical example of transmagmatic fluid metallogenesis.Molybdenum deposits in the East Qinling-Dabie region are mainly related to small porphyry. According to the location of ore bodies and their relationships with the porphyry, the deposits can be divided into eight types as Shanggusi type, Tangjiaping type, Donggou type, Leimengou type, Huilongsi type, Shandongdian type, qianechong type and Huangchengshan type. The potential mineralized capacity of small rock body is proportional to the degree of complexity of the body edges. The time-scale of mineralization is generally 0.5 ~ 4Ma.DGPMD(0.69Mt) is located in the east end of the east Qinling molybdenum metallogenic belt. The main mineralized types are disseminated and veinlet-disseminated. Ore body exists in Donggou granite porphyry and Xiong’er Group Jidanping formation volcanic rocks. In the mining area, the structure is simple, one syncline between two anticlines, and DGPMD is located in northeast flank of syncline. The main tectonic deformation is fracture, which EW, NW and NE three directions. Taishanmiao batholith, Donggou granite porphyry and a variety of dikes distribute in this region. Previous studies suggested Taishanmiao batholith is parent rock of Donggou porphyry and DGPMD.Based on mass balance calculation, three-dimensional geometry of rock body, geology, petrology, mineralogy and geochemistry studies, we find Taishanmiao batholith and Donggou porphyry are similar in geochemical characteristics suggesting they have similar source regions and are not related to magma evolution.Both Taishanmiao batholith and Donggou porphyry are metaluminous to weakly peraluminou A-type granite, which have low Sr and high Yb, indicating the source region should be in the feldspar stability region without garnet and the residual mineral phases are plagioclase + hornblende + pyroxene, which is equivalent to low pressure granulite facies or high-pressure amphibolite facies. The magma might form between 30 and 50 km in lower crust. Fluid inclusions and S, Pb isotopes of ore from DGPMD indicate that the Ore-forming fluid was derived maily from the deep crust and have characteristics of mixed materials from both crust and mantle.Accordingly, magmatic system and ore-forming fluid system of DGPMD can be considered as two independent geological systems. Ore-forming fluid was mainly derived from Ore-bearing fluid pool which gathered in lithospheric detachment zones of different layer in orogenic belts. The lithospheric delamination causes the rapid uprising of melt and fluid and ore-mineral precipitation. The melt-fluid acsent activates the pre-existing tectonic fissures and also damage some wall rocks. Ore-forming materials precipitated in tectonic fissures as the decoupling of melt and fluid systems and only a little fluid was trapped in porphyry.