| Yanbian-Dongning area is located in the eastern part of Mongolia orogenic belt, adjacent to Jiamusi massifs in the north and North China plate in the South and Khanka massifs in the northeast. The region has undergone the evolution of the Ancient Asian Ocean, Xing'an-Mongorian orogenic process, superposition of Mesozoic subduction of palaeo-Pacific plate and Cenozoic supercrustal faulting. Owing to multi-stage tectonic-magmatism, the study area became one of important Au-Cu-dominated polymetallic mineral producing area in China, and the geologists world-wide have paid much attation to the area for a long period. This paper chooses typical epithermal Au-Cu deposits of Late Mesozoic in the area to further reveal the metallogenic regularity and ore-searching direction. The study, including deposit geology, geochemistry, metallogenic epoch of typical deposits and the geology, geochemistry, isotope and chronology of intermediate-acid igneous associated with the ore, was systemically carried out. The following important developments are obtained.The study on deposit geology indicates that:the orebodies in porphyry type No.18 of Jinchang, Nongping and porphyry-like type Xiaoxinancha Au-Cu deposit are characterized by veinlike and veinlet-dissemination, Those in epithermal high sulfidation deposits (HSD) belong to breccia pipe type and alteration type. The five deposits are all controlled by linear fractures and secondary fracture, and the orebody occurred in breccia pipe and secondary fracture. The porphyry type and HSD type deposit are all divided into four mineralization stage, the first stage for the porphyry type and HSD type deposit are potassic alteration and pyritized phyllite, respectively, the other three stages are quartz-pyrite±chalcopyrite±molybdenite stage, polymetallic sulfide stage, quartz-calcite stage in sequence, whereas Xiaoxinancha can be divided five stages, the first and the end stages are the same to that of the porphyry type deposit, theⅡ-Ⅳstages are disseminated sulfide and alteration rocks stage, sulfide veins stage, pure sulfide stage, in turn. Hydrothermal alteration in five studied deposits are widespread, including argillic alteration, silicification, kaolinization, sericitization, as well as potassic alteration, biotitization and tourmalinization in porphyry type and porphyry-like Au-Cu deposit.Four type fluid inclusions are recognized in HSD deposit, including aqueous inclusion, vapor-rich inclusion, polyphase inclusion and liquid-rich inclusion, the discovered daughter minerals are halite, sylvite, anhydrite, barite, as well as opaque mineral such as hematite, chalcopyrite; the total homogenization temperatures and the salinity of early mineralizing fluids are in the ranges of 90-530℃and 62.38±wt%(NaCl) for Duhuangling, in the ranges of 140-560℃and 60.03-64.49 wt%(NaCl) for Jiusangou,120℃-600℃and 35.66-65.85 wt%(NaCl) for No.0 in Jinchang deposit, and the mineralization depth of the HSD is mainly less 1.5km. The porphyry type deposit in study area have the same fluid inclusion type to HSD, as well as melt inclusion; the range in the salinity of early mineralizing fluids and total homogenization temperatures varies from 31.75-69.82 wt%(NaCl) and 230℃-600℃for No.18, those of Nongping are in the ranges from 170 to 490℃for total homogenization temperature and 2.89 wt%(NaCl)±for the salinity of early mineralizing fluids. In Xiaoxinancha, Hydrate and calcite daughter minerals are also discoveried, except for the same fluid inclusion type to the porphyry type; the total homogenization temperatures are in the ranges of 150℃-500℃for the North mine,150℃-390℃for the South mine,90℃-530℃for the granitic complex associated with the minerazition, and the salinity of early mineralizing fluids is in range from 9.45～20.15 wt%(NaCl), that is consistent with the salinity of the granitic complex (10.49-15.55 wt% NaCl), and the North mine began the mineralization at the depth of 4 km, the main mineralization depth is less 2 km. The salinity in the main mineralizing stage of study deposits all show low- and high-range two regions. The result of Laser raman mainly gives the gas composition of H2O, CO2, CH4, as well as N2 in Xiaoxinancha, Jinchang and Duhuanling. Calculatedδ18O values of H2O in the fluid in equilibrium with quartz and calcite are, respectively,+0.048 to +6.125%o for the South mine, -0.09 to +3.78%o for the North mine in Xiaoxinancha, and +4.1 to +7.14%o for No.0 in Jinchang (SMOW). TheδDH2O of inclusion fluids is -46 to -99.5%o,-38 to -82.5%o, and -73 to -86.62‰, respectively. The result indicated together that early mineralizing fluids of the five deposit are characterized by high temperature, high oxidation, mantle-derived and CO2-bearing, but high salinity for Jinchang, Duhuangling and Jiusangou whereas low salinity for Xiaoxinnach and Nongping. The fluids of three type deposit both experienced boiling; mixing with meteoric water at 450-400℃and 30 Mpa is precondition and fluid boiling at 350-200℃,15-5Mpa is the main mechanism of high sulfidation deposit; fluid boiling is the main mechanism for No.18 of Jinchang and Nongping, and the boiling condition is 450-300℃,35-10Mpa and 350-300℃,20-10Mpa, respectively; and fluid boiling at 370-400℃and 20 Mpa is the prerequisite of the mineralization in Xiaoxinancha, subsequently replacement and crystallization of mixed fluids with young crustal fluid at 15Mpa is the main mechanism of ore precipitation for the North mine whereas filling in fissures with the change of temperature and pressure at 400-200℃and 20-5 Mpa formed sulfide-quartz veins of the South mine, local immiscibility caused by adding of meteoric water at 5Mpa is responsible for middle and late mineralization in North and South mine. The main geochemical characteristics of the intermediate-acid igneous rocks associated with the mineralization are SiO2≥53%, high Al content (Al2O3≥17%), rich in LILE and LREE, and depleted in HREE; the initial Nd and Sr isotopic compositions of the igneous rocks in Jinchang, Jiusangou and Xiaoxinancha are in the ranges of 0.70414-0.70487 for (87Sr/86Sr)i, 0.51258-0.51264 for INd, and 1.56-2.88 forεNd(t); the Pb isotopic ratios of those range from 18.3481 to 18.4682 for 206Pb/204Pb, from 15.5438 to 15.6198 for 207Pb/204Pb, and from 38.2316 to 38.4177 for 208Pb/204Pb. The geochemistry together with petrochemistry is suggested that the igneous rocks are exhibit calc-alkaline and adakite signatures, and the product of the interaction betweem slightly depleted mantle and subducted fluids and melts.LA-ICP-MS U-Pb dating analysis for zircon grains in the igneous rocks together with 40Ar/39Ar laser probe of dating single quartz particle in sulfide veins indicate that the metallogenic epoch is 107±6 Ma for Duhuangling, the upper limit of metallogenic epoch is 110±1.1Ma for Jinchang,109.8±2.2Ma for Jiusangou,102.1±2.2Ma for Xiaoxinancha, 96.9±1.4Ma for Nongping; they are mainly focused on two stages, one is 110Ma, and the other is 100Ma, both related with the subduction of Izanagi Plate.Based with magmatic genesis, chronology of the intermediate-acid igneous rocks, and the fluid evolution, the dynamic setting and ore-forming process are summarized as following. As a result of Izanagi Plate NNW-trend subduction beneath paleo-Asian continent at 110Ma, mantle wedge contaminated and mixed with dehydration fluids and melts from the subducted oceanic crust, in the process, metal elements such as Cu, Au carried by the magma were gradually unloaded in the magma chamber to form supercritical ore-bearing fluid reservoir. With the crystallization of magma, the critical fluid boiled separating out lower-salinity vapor and hypersaline fluid in magma chamber; As the extension of the lithospheric mantle, the pre-produced magma and the ore-bearing fluids rose along the fractures, the former emplaced at shallow crust to form intermediate-acid igneous rocks, whereas the boiled hypersaline fluid took place "second boiling" and subsequently mixing with meteoric water by crystallization and filling to form No.18 veinlet-dissemination in Jinchang, the hypersaline fluid by condensed out from the lower-salinity vapor in magma chamber, fristly mixed with meteoric water and then "second boiling" in Duhuangling, Jiusangou and No.0 of Jinchang, respectively, which formed breccia pipe type (Cu-) Au orebody. When Izanagi Plate transformed to NW-trend subduction at 100Ma, adakitic magma and low and moderate salinity supercritical fluid generated as the above process in Nongping and Xiaoxinancha rose along the fractures, Nongping Au-Cu deposit was formed as the same way as No.18 of Jinchang. High temperature vapor from boiling was mixed with young crustal fluid, and the mixed fluids metasomatized wall rocks to form veinlet-dissemination orebody in the North mine, with the change of temperature and pressure, moderate temperature mineralizing fluids from boiling formed the South mine sulfide-quartz veins by filling, at middle and late ore-forming stage, local immiscibility was caused by adding of meteoric water, therefore, ore-rich fluids generated in the South mine deposited pure sulfide and breccia, high temperature vapor-like fluids generated in North mine in fissure formed melnicovite-dominated sulfide-quartz veins by filling, as such, the adakitic magma emplaced at shallow crust during the precipation of mineralizing fluids, hence, three types hydrothermal Au-Cu deposits of Late Mesozoic in Yanbian-Dongning area were formed by the similar dynamic setting but different fluids evolving process at the two stage.
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