Metallogenic Model Of Epithermal And Low-sulfidation Gold Deposit, Yanbian Area

Yanbian area is located in the east of Xing'an-Mongolia orogen,and it controled by the North China plate,Xingkai block and Jiamusi block. This area is one of the most important epithermal gold-copper deposits in east China continental margin ore-forming belts.Wufeng,wuxingshan golden deposit and Ciweigou golden deposit are typical epithermal deposits in this area.The ore body of the Wufeng,wuxingshan deposit can be divided into two types: Vein ore is mainly found in the Wufeng ore-section. In Wuxingshan ore-section, we found many disseminated stockwork orebodies. In Wufeng mine, the narrow-long single vein and composite vein have clear boundaries with the surrounding rock. There have no chalcedony-like quartz veins in Wuxingshan mine. It is thin and short disseminated stockwork, which have no significant boundaries with the wall rock.Accordding to these characteristics of above , the two mines are the same in the cause. But the mineralization depth, temperature and -geological conditions are different. ,Wufeng mine is on the space above, and Wuxingshan mine is in the lower part. From veinlets disseminated to vein-like ore body, is linked to the causes and the overall space. Wall rock hydrothermal alteration of the deposit superimposed with a multi-phase meeting. The wall alteration have the zoning caused characteristic on space. Take the veins as the center , it can be divided into three zones. The inter zone which dominated by dominated strong silicification and adularia, the middle zone which mainly have sericitization and silicification, and the outer zone which dominated by chloritization. The chief structure of the ore is granular structure, and followed by account structure, interstitial structure, crushing structure. Dense massive structure is the main structure of the ore, in addition to construction and brecciated structure. Deposits can be divided into four mineralization stages: the massive-quartz stage, chalcedony quartz vein-like stage, calcite-quartz vein stage and calcite phase stage. The chalcedony quartz vein-like stage and the calcite-quartz vein stage is the main mineralization stages.The Ciweigou golden deposit contains three gold-bearing calcite-quartz veins. On the basis of the sequence generated veins, mineral composition, texture and structure, as well as differences in chemical composition, the three veins can be divided into seven tupes, namely quartz adularia vein, rough - giant grain of calcite veins, quartz veins in fine-grained calcite, fine-grained quartz veins, coarse-grained calcite and chalcedony veins - microcrystalline quartz vein. Wall-rock alteration strictly control by the faults, which showing zonal distribution in the veins on both sides. The strength of the alter ralated to the type and size of veins. Which is near the vein are strong, and stay away from those weak. Altered rocks and veins have clear boundaries, and with the fresh rock was gradually transition relations. Respectively, silicide,albitization,kaolinization and pyritization alteration zone, carbonation and sericitization alteration zone, as well as propylitation alteration zone. The main ore texture is shape, since the shape of granular structure, in addition to the residual textyre , the crystal texture, the emulsion drops texture, the unequigranular mosaic texture. The structure of the ore are massive structure, vein structure and sparsely disseminated structure and so on. Ore-forming hydrothermal stage of the deposit can be divided into five ore-forming stage: ice-feldspar - quartz vein stage, coarse-grained - calcite veins stage, fine-grained quartz-calcite stage, with polymetallic calcite-quartz vein stage, including dolomite, opal, barite and calcite stage.The fluid inclusions of the wufeng,wuxingshan and Ciweigou golden deposit, which are almost have the type of aqueous-biphase. The gas- liquid was 10%-30%, and there only few could reach 35%. In the aspect of homogenization temperature, the Wufeng mine is 130～310°C, the Wuxingshan mine is 160～330°C, and the Ciweigou deposit is 10～250°C. All of them are same with the temperature 100～320°C which belong to the epithermal deposit.ω(NaCl)% of the inclusions in wufeng mine are between 0.88～1.4%; Wuxingshan mine are between 4.38～12.39%; Ciweigou deposit are mainly concentrated between 1.57～3.23%; the two deposits are relatively low salinity, only a few of the more than 12%. Calculated and combined according to the situation of the exploitation of mineral deposits, the depth of mineralization below 1km, and generally in the vicinity of 0.10～0.65km, it is clear that belong to the range of epizonal. Both the ore-forming fluid system of the Wufeng-wuxingshan gold deposit and Ciweigou gold deposit ore-forming fluid system are typical epithermal systems. Accrodding to the research on the stable isotope of the ore, the origin of the metallogenic material is telated to the volcanic eruptions. By the precise Ar-Ar method, the age of the calcite-quartz vein in Wufeng,wuxingshan deposit is 123±7Ma. The mineralization age of this deposit may in the Early Cretaceous. Ciweigou gold deposit business in the Tuntianying Group volcanic rocks, the ore-forming age should be in the Late Jurassic-Early Cretaceous.Mesozoic volcanic rocks developped in the Yanbian area. The formation of the epithermal deposits have close relation with the Mesozoic volcanic rocks in time,space and genesis.Wufeng,wuxingshan gold deposit produced in the volcanic rocks of the Jingouling group and the contact zone of the volcanic with the intrusive rocks. The host rock of the Ciweigou golden deposit is the volcanic rocks of the Tuntianying grop. Through the research on the geologocal and geochemical characteristics and the formation age of the two volcanic rock groups,it can be known that the magmatic source region shoule be the mantle wedge which replaced by the subductive fluid. The tectonic background of the formation of the volcanic rocks is the active continental margin environment. And so do the deposits.Both the Wufeng,wuxingshan gold deposit and the Ciweigou gold deposit are typical, epithermal and low-sulfidation gold deposits. Combination of the regional tectonic setting, we can inform that in Mesozoic period, the Yanbian region get into the interaction phase stage of the Pacific plate and the Paleo-Asian continental plates. It belonged to marginal-pacific tetonic system. The magmatic activity is very strong in this peried. And so do the tetonic activity. The fracture which formed before was inheritted or reformed. Then a series fault depression and fault basins which have different size and properies were formed. Late Jurassic to Early Cretaceous period, Izanagi plate give very stong subduction and collision to the Asian plate. Because of this, it formed and actived faults which have eastwest trend, northeast trend and southnorth trend. And this destroyed the equilibrium system of the mantel rock. Along the fault, the magma intruded upward and produced two set of valcanic rocks– Tuntianying group and Jingouling group, as well as a series of sub-valcanics. In the later stage of the volcanic-magmatic acivities, the heat flow which caused by mantle-derived origin gone up to the shallow crust along the fissures of the sub-valcanics and the regional faults. Then it recirculating flow with the meteoric water. The ore-forming fluid which have more meteoric water and less magmatic water was formed. The ore-forming fluid transport upward along the fault zone and the valcanic apparatus. At the intersection part of fault which was superficial, metallogenic material enriched and sedimented, so the deposit was formed.