The Study On Mineralization Processes And Ore Genesis Of Yanghuidongzi Hydrothermal Copper Deposit In Heilongjiang Province

Dongning Yanghuidongzi copper deposit, eastern Heilongjiang Province, is located in northeast Taipingling uplift of northern part of Xingkai-Yanbian magmatic-tectonic zone. Yanghuidongzi copper deposit discovered in 1980 s, which is hosted in granodioritic porphyry and breccia zone of the inner contact zone between granodioritic porphyry and Triassic metamorphic rocks of Huangsong Group. It always has been a big controversy on mineralization and ore genesis. This paper through systematic studies of diagenesis and mineralization Age, geochemistry, fluid inclusions and isotopic geochemistry and suggests the Yanghuidongzi copper deposit belongs to the porphyry copper type.Intrusive rocks strongly occurred in this area, which are granodiorite and granodioritic porphyry of Late Indo-Chinese to epoch-Early Yanshanian and lamprophyre, etc. Structures of mining areas are mianly Yanwangdian duplex anticline and Northeast trend fracture, and the ore-bearing granodioritic porphyry bodies are located in the intersections of both. The Yanghuidongzi copper deposit are consisted of 16 orebodies, which are mainly hosted in granodioritic porphyry and breccia zone of the inner contact zone between granodioritic porphyry and Triassic metamorphic rocks of Huangsong Group, Yanwangdian formation, which are mainly lenticular and vein in shape. The ore minerals are mainly chalcopyrite, pyrite and pyrrhotite, secondly arsenopyrite, molybdenite, sphalerite and galena etc; gangue minerals are mainly consisted of quartz, sericite, chlcorite, calcite, etc. The detail studies of geological features of ore deposit geology and petrography indicate that the wall-rock alteration is IV m ainly biotitization, sericitization, silicification, chloritization, epidotization and carbonation etc and the alteration zoning from the lithosome to wall rock is potassium silicate zone, phyllic zone and propylitization zone, respectively. The mineralization process can be classified into four stages:(Ⅰ) quartz-pyrite-arsenopyrite stage;(Ⅱ) quartz-pyrrhotite-molybdenite stage;(Ⅲ) quartz-polymetallic sulphides stage; and(Ⅳ) quartz-carbonate stage.Zircon LA-ICP-MS U-Pb dating of granodiorite and ore-hosting granodioritic porphyry are 193.5±1.6Ma(n=16, MSWD=2.7) and 196.2±1.7Ma(n=22, MSWD=3.9), which reveals that they formed in early of the Early Jurassic. The muscovite age of 40Ar/39 Ar of chalcopyrite phyllic altered rock from mining is 195.0±1.3Ma, which is correspond with the granodioritic porphyry and represents the formation age of Yanghuidongzi copper deposit. Element geochemical characteristics reflect that granodiorite belongs to high-K calc-alkaline series, charactered by enrichment of large ion lithophile element(such as Ba, Rb, K, Sr), relatively depletion of high field strength elements(Zr, Hf, Yb, Y) and notable depletion of Nb, Ta, P and Ti, which are correspond with the Taipingling granite rock; granodioritic porphyry is characterized by high Al2O3(15.43% ~ 17.19%), high Na2O(1.91% ~ 3.60%), low Mg O(0.92% ~ 0.97%), δEu=0.95~1.11, high Sr(114.7~521.0ppm) and low Y(4.5~9.3 ppm), which has the similar geochemical characteristic of adakite formed in partial melting of subducted oceanic crust. Combined with Sr-Nd isotopic of Taipingling granite and Hf isotopic of zircons, indicating the granodiorite magma was derived from the overriding mantle wedge modified by oceanic fluid and mixed with a certain proportion of Proterozoic crustal material during ascending and evolution, while the granodiorite porphyry magma was derived from partial melting of subducted oceanic crust and mixed with crustal material during ascending and evolution. Comparative studies suggest the diagenesis and mineralization of the Yanghuidongzi copper deposit occurred in early of the Early Jurassic, formed in the extrusional environment under the subduction of Paleo-Pacific plate.The fluid inclusions in Yanghuidongzi copper deposit are mainly liquid-rich inclusion(WL-type), vapor-rich inclusion(WV-type), pure liquid inclusion(L-type), pure vapor inclusion(V-type) and daughter-minerals bearing three-phase inclusion(S-type). The Ⅰstage quartz contains WL-type fluid inclusions; The Ⅱ stage quartz contains WL-type and very small S-type fluid inclusions; The Ⅲ stage quartz contains WL-type, WV-type, L-type, V-type and S-type fluid inclusions, which output in isolation or in group; The Ⅳ stage quartz contains WL-type and L-type fluid inclusions. The homogeneous temperature of the fluid inclusions from Ⅰ toⅣ stage are 380~417℃, 304~368℃, 171~310℃ and 116~189℃, respectively, which are correspond with the four mineralization stages. The w(Na Cleq)of fluid inclusions from Ⅰ and Ⅱ stage are 4.63%~14.5% and 5.09%~14.63%; The w(Na Cleq) of fluid inclusions from Ⅲ stage could be divided into two groups: 1.73%~10.37% and 13.44%~15.35%; The w(Na Cleq)of Ⅳ stage is 0.87%~9.08%. Laser Raman spectroscopic analysis indicate that the gas components of fluid inclusions in the early stage is dominated by H2 O and little CO2; while the gas components of fluid inclusions from the main mineralizing stage is dominated by H2 O and little CH4; which from late stage is only H2 O, suggesting that the ore-forming process evolved from salt-water system containing CO2 to salt-water system containing CH4 gradually with temperature decreasing. The study on H-O isotope of quartz from phenocrysts of granodioritic porphyry and from sulfide quartz veins of every ore-forming stage and Pb isotope of sulfides show that the primary ore-forming fluid mainly derived from granodioritic magma or may be the product of exsolved fluid and ore material was origin in deep magma. The mineralization process experienced the emplacement for granitoid magmas, fluid exsolution and the formation of ore bearing fluid, ore-fluid boiling and the mixing of ore-forming fluid and meteoric water, which formed pyritization dominated altered rock, sulfide quartz vein of dominated-copper and quartz-carbonate vein in succession. Comparative studies suggest the Yanghuidongzi copper deposit belongs to the porphyry copper type.