Characteristics Of Intermediate-acid Small Intrusive Bodies And Metallogenic System Of Molybdenum-polymetallic Deposits In Mesozoic In Dabie Mountain, Henan Province

Dabieshan area of Henan province located in the northern foot of Western Dabie orogenic belt, the structural evolution and magma intrusions are complicated at this region, especially of theYanshanian intrusive rocks. There are many intermediate-acid small intrusive bodies among Yanshanian intrusive rocks and they are usually closed related to Molybdenum-polymetallic mineralization.Mesozoic intermediate-acid small intrusive bodies of Dabieshan area mainly distributed along deep-seated faults and controlled by groups of faults with orientations of NWW and NNE. Most of small intrusive bodies are stocks or dikes, and each of the dimension is less than 1km2 ; they are mostly granite-porphyry,porphyritic-granite,monzogranite,a small amouts of them are quartz diorite or diorite; the chemical characters are high content of SiO2,K2O and low content of Mg and CaO, on the SiO2-K2O diagram all the samples fall in the field of high-K calc-alkalic series and shoshonite series. The magma of small intrusive bodies come from partial melting of lower crustal, and intruded in shallow crustal, they belonged to deep-hypabyssal Granites.Small intrusive bodies are closely related with the molybdenum-polymetallic deposits in space and genesis. Most molybdenum-polymetallic deposits situated in or around small intrusive bodies; small intrusive bodies which had high abundance of ore-forming elements are source rocks of metallogenesis. The main types of molybdenum-polymetallic deposits in Dabieshan area include porphyry-type Mo deposits, skarn deposit, vein-type deposits and breccia pipe-type deposits, they had the similar ore-forming environments and metallogenetic processes, they can be defined as a unitized porphyry-type molybdenum-polymetallic metallogenic system.Characters of S istopic compositions, Pb istopic compositions, contents of Re in molybdenite and characters of REE reveals that ore-forming materials of molybdenum-polymetallic deposits in Dabieshan area came from lower crustal.Re-Os model ages of molybdenite at Mushan porphyry-type Mo deposit and Doupo Mo ore spot are 155.7±5.1Ma and 140.5±8.2Ma, respectively. Combined with others isotopic ages, it's considered that the metallogenetic ages of molybdenum-polymetallic deposits can be devided into two groups: the earlier group is 155.7±5.1 Ma～140.5±8.2 Ma and later 122.1±2.4～113.1±7.9 Ma, and the metallogenetic scale of the later group is larger, so it's the main metallizing stage. The metallogenetic age is later than it is in Eastern Qinling porphyry-type Mo metallogenic belt.Rock-and ore-forming ages reveal that the geodynamicas setting of magma activities and molybdenum-polymetallic metallogenesis was transition of the regional structural stress field from compressional to extensional and large scale lithospheric delamination at late Jurassic to early Cretaceous.Molybdenum-polymetallic deposits in Dabie mountain are reformed by uplift of weathering, but mainly preserved well, this area is potential for ore prospecting.