| Dongan gold deposit is located in the northern section of Xiaoxing'anling, lying between the Songnen block and Jiamusi block, and belonging to Caledonian orogenic belt of Yichun-Yanshou section. Affected by the subduction of the Pacific during Mesozoic period, it is at the active zone of continental margin which is a stretching geodynamic environment, and the effect of extensional rift is great. From early Jurassic to early Cretaceous, with the happening of intense Yanshan movement, together with large-scale Fault activity,a series of NE, NW, and SN trending fault are produced and Wudi River basin is formed. Ku'erbin fault is important for the formation of rock and ore deposits.The research is started from the regional geological setting and geological features of Dong'an gold deposit. In this article,detailed studies on isotope geochemistry, physical and chemical conditions, and geochemical characteristics of volcanic rocks are made. According to the contrast of epithermal gold deposits between home and abroad, we have summarised temporal and spatial characteristics, alteration characteristics, tectonic setting, and the material sources and mechanism of mineralization of the deposit.Strata exposed in the ore deposit include:medium-acid volcanic lava and pyroclastic rocks of Guanghua group (K1gn) of lower Cretaceous, glutenite of Sun Wu group(N1-2S) of middle- Upper Tertiary, basalt of the Big Bear Hill group of the lower Pleistocene of Quaternary, glutenite of Leshan group(Q2l) of Middle Pleistocene, and flood alluvial soil of Holocene(Q42).Fault is the main structure of the deposit. Kuerbin fault is located in the northwest of the deposit,trending 60°, inclined to SE. It resulted in the formation of SN, NNE, NNW, NW-trending faults, and the shallow intrusion of complex rocks in late Yanshan period and formation of volcanic apparatus. SN and NW-trending faults are the main faults in the area which controlled the formation of volcanic rock and ore deposit, and it belongs to the secondary faults of Kuerbin. Under the control of the fault, fine-grained alkali feldspar granite of the Yanshanianc and granite porphyry were formed. In the volcanic apparatus, the ore favorable position is volcanic channel, especially the explosive breccia pipe. EW-trending faults are post- mineralization fault,which damaged the ore body and have a character of dextral shift.Magmatic activities are strong and have a characteristic of multi-phase,multi-stage. It can be divided into three stages,which are Caledonian, Indosinian,and Yanshanian. The intrusive rocks of middle Caledonian and Late Indosinian are mainly base rock, and only a small part of them are rock stocks. During the late Yanshan, The intrusive rocks mainly are stock rocks or dikes, which are often contemporary with medium-acidic explosive rocks. The main wall rock of Dong'an gold deposit mainly are coarse and fine-grained alkali feldspar granite, rhyolite, dacite volcanic rocks of Yanshanian.Seven gold ore body groups and 58 rock ore bodies are found, of which No.5 is the largest, and ore bodies occur in quartz veins.Ore body is mainly controlled by SN, NNW, and NW-trending faults. Ore minerals mainly are pyrite, arsenopyrite, galena, and chalcopyrite. Ore texture is mainly xenomorphic granular structure. Ore structures mainly are breccia, disseminated, vein and stockwork. Wall rock alteration include silicification, chlorite, sericite, adularia, fluorite and so on, of which silicification and adularia are close to the mineralization.The deposit is formed by the superposition of multi-stage mineralization. Which can be devided into hydrothermal period and hypergene period. Hydrothermal period can be further divided into three stages, namely:pyrite-quartz stage,multi-Metal sulfide phase, and chalcedony-fluorite phase. Hypergene period mainly formed limonite, illite, muscovite and kaolinite and so on.According to systematic study of fluid inclusions of Dong'an gold deposit, fluid inclusions are mainly two-phase inclusions including gas and liquid, and the latter one is more. The salinity is low, the peak of which is 0.7～1.6% NaCl. The peak of density concentrated at 0.72-0.84g/cmJ, and the homogenization temperature is at around 150～200℃. The fluid belongs to a low temperature,low salinity, low density fluid. The main mineralization pressure is 10-12MPa, depth of which is 1.0～1.2km. It is a typical environment for low sulfide epithermal deposit to form.Hydrogen and oxygen isotope geochemistry analysis showed that the ore-forming fluid is a mixture of atmosphere water and magmatic water, and is mainly atmosphere water. The magmatic water of upward migration extracted ore forming materials from the base rocks, with the join of the atmosphere water, and then transferred into ore fluids, and in the end Au precipitated.Geochemical analysis of volcanic rocks showed that the rock type are rhyolite, dacite rhyolite-dacite, and trachyte, which is a peraluminous acidic volcanic rocks. Rare earth distribution pattern showed enrichment in LREE but flat in HREE.In the trace element spider diagram, the samples generally rich in highly incompatible elements such us Rb, Th, but lack of Nb, Ta, Sr, which reflect the geochemical characteristics of arc volcanic rocks.Diagrams for discriminating tectonic settings show that the volcanic rock was formed in a transferred environment, which is syn-collision, arc volcanic to post-collision. In the end, the formation of volcano of Dong'an may be of very complex, possibly arc volcanic to post collision orogeny setting, which is the transition from compression to expansion.
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