| Daheishan molybdenum deposit is located in Yongji County, Jilin Province,belongs to the southeast Jilin Variscan orogenic belt. Regional stratigraphicdevelopment is complete，but stratigraphic distribution is discontinuous due to the latetectonic magmatic activity, from old to new, there are strata of Paleozoic Cambrian,Ordovician, Carboniferous, Permian, and Mesozoic Triassic, Jurassic, Cretaceous andCenozoic.In the view of tectonic framework, Daheishan belongs to Late Paleozoic-EarlyMesozoic Ancient Pacific belt and Mesozoic-Cenozoic Circum-Pacific tectonic belt.Daheishan has experienced occurrence and development of orogeny from earlyPaleozoic to late Paleozoic. After that, a large area of crust began to rise, then largescale transqression ended. Folding orogenesis did not occur immediately, transitionalstage of transformation happened from late Permian to early Triassic, thicktransitional sedimentary formation had been deposited. Terrestrial clastic rock was themainly sedimentary formation in late Permian. In the lower part, clastic rockformation of marine or sea-land interbedding facies was interbeded. In the upper part,it was volcanic formation of intermediate–intermediate-acidic. Sedimentaryformation in early Triassic was terrestrial clastic rock. Long-term evolution andcomplexity of the process of the geological structure belonged to category ofpaleo-asiatic tectonic domain. Late Triassic the region entered into a new continentalmargin active belt, in another word, the period of development of the coast of the geological history of the pacific tectonic domain. The structural frame had undergonefundamental changes. Tectonic stress field changes from N-S compression to NW,NWW, thus showing the structural features of the NE, NEE.The intrusive rocks of mining area included fine-grained granite, K-feldspargranite porphyry, granodiorite, dioriterocks and quartz diorite, these rocks were outputof batholith and stock. There are aslo wall-like, vein-like output mafic-ultramaficrocks, porphyry and granite porphyry in the mining area. The ore-bearing rock is acomposite pluton, flat oval-shaped, north-east to the8km long,3.5km wide.Acorrding intrusive order, rocks can divided into Changgangling ridge biotitegranodiorite, Quancuoluo biotite granodiortte, granodiorite porphyry and felsophyrictexture granodiorite porphyry.The ore of Daheishan molybdenum deposit strike along north-east, and extendedin a dirtction in space (mainly in the vertical direction), the other two direction werenot developed, but the cross-section was not small, surface showing approximateround, so orebody was shape of a huge mine tube.Daheishan molybdenum deposit was veinlet-like filling cracks or joints in therock, or produced in the quartz veins on both sides; or disseminated more evenlywithin the granodiorite; some molybdenite star-shaped coarse crystals was dispersedin the edges of the slightly altered lots and the ore body. The main ore minerals werepyrite and molybdenite, and minor minerals were sphalerite, chalcopyrite, tetrahedrite,scheelite and so on. Ore structure are crystal structure, metasomatic structure andsolid solution separation and compression structure. The crystal structure andmetasomatic structures constituted the main structure of the ore. The construct type ofthe ore mainly were vein and veinlet disseminate, the second was disseminatedconstruct. The alteration of wall rocks were K-feldspar, biotite, silicification,sericitizaton.The study of Daheishan molybdenum deposit fluid inclusions system acquiresimportant metallogenic physicochemical parameters: fluid inclusions mainly werecontaining daughter-mineral three-phase and gas-liquid two-phase inclusions.。The liquid ratio of two-phase gas-liquid inclusions was4%-80%, an average of37%; thesize of inclusions was4-16μm, mostly was in6-12μm, and inclusions was in theform of oval, circular, quadrilateral, irregular triangle. Such inclusions develop inmineralization stage and late mineralization stage; gas-liquid ratio of containingdaughter-mineral inclusions is from20%to35%, an average of26%. The size was8-12μm, with three-phase of liquid, gas and daughter minerals. Temperature andsalinity range of different types of inclusions vary greatly, the temperature of variousstages of fluid inclusions in quartz veins was196.5℃~440.5℃, and salinity rangedfrom2.56wt%~49.92wt%. Deposit formation depth was about1.2～2.8km. Themain ore-forming fluids are magmatic fluids with meteoric water mixed in late stage.Analytical studies on the isotope geochemistry (including H, O and S isotopes)show that the ore-forming fluids were magmatic water. Minerals were frommulti-source of the mantle and upper crust. The source of the ore-forming fluids in theore-forming process is not entirely magmatic water which is the main source, but withmeteor water mixed.Daheishan molybdenum deposit is the only stock-type molybdenum mine in theNortheast China, with typical characteristics of porphyry deposit, but also has its ownunique: metallogenic rock is of calc-alkaline granitic rock series, formed incontinental compressional margin, while that of alkaline and alkaline calcic series forthe stockwork molybdenum deposits in western United States (such as the famousClimax Molybdenum Mine), formed in a back-arc extensional tectonic background.Differ from stockwork deposits associated with plutonic intrusions(such as theHuojihe, Lumin, etc.), the metallogenic rocks in Daheishan molybdenum mine arestock-like. The genetic type is considered to be the stock-type molybdenum mine withmetallogenic rock of calc-alkaline series, and the metallogenic model has beenestablished. |
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