Study On The Mineralization Processes And Metallogenic Model Of Epithermal-porphyry Copper-polymetallic Mineralization System In The Central And Eastern Of Great Xing’an Range, China

The central-eastern of Great Xing’an Range is one of important epithermal-porphyry Cu(Mo)-Pb-Zn ore concentrating area in China. Mineral exploration in this area has discovered Budunhuakongqueshan, Lianhuashan and Naoniushan middle-scale and Jubao small-scale epithermal copper deposits, Budunhuajinjiling middle-scale porphyry Cu deposit, Changchunling middle-scale epithermal Ag-Pb-Zn deposit and Mengentaolegai large epithermal Pb-Zn-Ag deposit since seventies of the last century. Chinese and foreign scholars have paied great attention and done many research on mineralization geological processes and resource potential problem of the copper-polymetallic deposits of this area. With further exploration and research on mining area, ore field, ore district(zone) recently, mineral exploration has discovered small-scale porphyry Cu deposit in Naoniushan ore field, epithermal Ag-Pb-Zn in Budunhua ore field, Chentaitun small-scale porphyry Cu deposit in Lianhushan ore field and Houliujiu large porphyry Cu-Mo deposit in Longjiang County northern of the metallogenic belt(Tuquan-Longjiang County), which made this area really to be an ore concentrating area or metallogenic belt that mainly developed epithermal copper deposits, and associated with epithermal Pb-Zn deposits, Ag deposits and porphyry Cu-Mo deposits. There can be divided into five important ore field from south to north, which are Budunhua epithermal Cu(Pb-Zn-Ag)- porphyry Cu(Mo) ore field, Mengentaolegai Pb-Zn-Ag ore field, Naoniushan epithermal Cu(Pb-Zn-Ag)- porphyry Cu(Mo) ore field, Lianhuashan epithermal Cu(Pb-Zn-Ag)- porphyry Cu(Mo) ore field and Houliujiu porphyry Cu(Mo) ore field, which makes this area to be a good natural laboratory in that exploring metallogenic theory of the epithermal-porphyry copper polymetallic mineralization system and founding metallogenetic geological model. Therefore, based on the studies of previous researchers and regional metallogenic background as a precondition, this study focuses on the ore field, geological characteristics, fluid inclusion, geochemistry, and geochronology of epithermal Copper deposits, associated with epithermal Ag-Pb-Zn deposits and porphyry Cu(Mo) deposits in the Lianhuashan, Naoniushan and Budunhua ore flield. And we have achieved results as follow.1. The study of typical ore field and geological characteristics of the deposit found that there are widespread developed different size of epithermal copper deposit, epithermal Ag-Pb-Zn deposit and porphyry Cu(Mo) deposit(body) in the ore field. The Lianhuashan ore field developed medium-scale epithermal copper deposit, medium-scale epithermal Ag-Pb-Zn deposit and small-scale porphyry Cu(Mo) deposit. The Naoniushan ore field is mainly developed epithermal copper deposit, associated with epithermal Ag-Pb-Zn ore body and small-scale veinlet-disseminated type porphyry Cu/Mo ore body or small-scale deposit. Budunhua ore field developed medium-scale epithermal copper deposit, porphyry type Cu(Mo) deposit and epithermal Ag-Pb-Zn ore body. Every ore field constitutes epithermal-porphyry copper polymetallic mineralization system on the whole.2. Different deposit has different ore body type in the epithermal-porphyry copper polymetallic mineralization system. The porphyry Cu(Mo) deposit is mainly developed small-scale veinlet-disseminated type ore body. The epithermal copper deposit are mainly developed veined and small-scale veinlet-disseminated type ore body, and associated with explosion breccia type ore body in Naoniushan ore field. And the epithermal Ag-Pb-Zn deposit mainly developed veined and net vein ore body. The type of ore body showed small-scale veinlet-disseminated type to small-scale veinlet-disseminated type plus vein type or explosion breccia type to vein type from porphyry Cu(Mo) deposit to epithermal copper deposit to epithermal Ag-Pb-Zn deposit.The wall-rock alteration of the epithermal-porphyry copper polymetallic mineralization system in study area is mainly potassic-biotitization, phyllic, propylitization, silicification and carbonation. The porphyry Cu(Mo) ore bodies are mainly host in potassic-biotitization zone and phyllic zone. The epithermal vein copper ore bodies are mainly host in phyllic zone and propylitization zone. The epithermal Ag-Pb-Zn mineralization is mainly host in propylitization zone and carbonation zone.There are widespread developed magnetites in the early stage of the epithermal-porphyry copper polymetallic mineralization system in study area. And the Lianhuashan ore field developed a small amount of primary hematite, which infer a stronger initial oxidizing environment. The formation order of the metallic minerals of the mineralization system is(hematite) plus magnetite plus molybdenite plus arsenopyrite plus pyrite to pyrrhotite plus chalcopyrite plus pyrite to sphalerite plus galena plus chalcopyrite to pyrargyrite.3. The study of fluid inclusion show that(1) the homogeneous temperature of the fluid inclusions from epithermal copper deposit in the Lianhuashan ore field are 460~316℃, 401~186℃, 279~178℃ and 198~123℃ from early stage to late stage. And the salinities of fluid inclusions are 4.32~52% Na Cl equiv, 1.9~44.5% Na Cl equiv, 0.87~4.48% Na Cl equiv and 0.53~2.73% Na Cl equiv, respectively;(2) the homogeneous temperature of the fluid inclusions from epithermal copper ore bodies in the Naoniushan ore field are 405~260℃, 407~183℃ and 183~109℃, respectively. And the salinities of fluid inclusions are 3.05~43.83% Na Cl equiv, 0.35~46.56% Na Cl equiv and 0.71~3.69% Na Cl equiv, respectively. The homogeneous temperature of the fluid inclusions from epithermal Pb-Zn ore bodies is 368~170℃, with the salinities of fluid inclusions is 0.35~8.67% Na Cl equiv;(3) the homogeneous temperature of the fluid inclusions from porphyry copper deposit in the Budunhua ore field are 576~301℃, 501~237℃ and 312~150℃, respectively. And the salinities of fluid inclusions are 13.22~53.81% Na Cl equiv, 6.87~48.84% Na Cl equiv and 2.56~11.36% Na Cl equiv, respectively. The homogeneous temperature of the fluid inclusions from epithermal copper deposit in the Budunhua ore field are 562~241℃, 425~175℃ and 225~138℃, respectively. And the salinities of fluid inclusions are 8.81~57.19% Na Cl equiv, 4.32~38% Na Cl equiv and 0.87~5.7 NaCl equiv, respectively.The study of Raman component analysis of the fluid inclusions and H-O isotope of quartz further reveals that the primary ore-forming fluid of the epithermal-porphyry mineralization system derived from exsolved fluid of residual magma, which is high temperature, high oxygen and high salinity H2O-CO2-CH4-Na Cl fluid system, and mixing meteoric water or paleo-rainwater during elements unloading. The metallogenic mechanism of the early stage small-scale veinlet-disseminated type Cu(Mo) mineralization is boiling, which is boiling and mixing in epithermal copper deposit. And the mineralization of the epithermal vein Ag-Pb-Zn deposit is mainly controlled by ore-forming fluid mixing with meteoric water.4. The study of chronology in each ore field revealed that(1) the quartz andesite and granodiorite porphyry in Lianhuashan ore field formed at 242.1±1.8Ma and 246.1±7.6Ma, that is early-middle Triassic;(2) the andesite porphyry, granodiorite porphyry and quartz porphyry in Naoniushan ore field formed at 143±4.2 Ma, 141.2±0.74 Ma and 162.8±1.6 Ma. And the mineralization of Cu(Mo) occurred at 134.3±0.8 Ma, that is early stage of the early Cretaceous, which indicate that the mineralization of Cu(Mo) occurred after the emplacement of granodiorite porphyry.(3) dacite porphyry, plagioclase porphyry, biotite granodiorite porphyry, granite porphyry and diorite formed at 157±2.3 Ma, 151.1±1.1 Ma, 151.7±1.3 Ma, 140.1±1.3 Ma and 127.1±1.7 Ma. And the mineralization of Cu(Mo) occurred at 150±2.2 Ma(Wu, 2013), that is late Jurassic, which indicate that the mineralization of Cu(Mo) occurred after the emplacement of plagioclase porphyry and biotite granodiorite porphyry.Combined field geological survey, diagenetic and metallogenic geochronology and characteristics of zircon trace elements show that Indosinian magmatic rocks exposed in in Lianhuashan ore field doesn’t have the attribute of metallogenic geological body, which may has the same metallogenic geological body with the Naoniushan ore field, which is granodiorite porphyry of early stage of the early Cretaceous. The metallogenic geological bodies of Budunhua ore field is plagioclase porphyry and biotite granodiorite porphyry series.5. The studies of petrology, element geochemistry, isotope geochemistry and geochronology of magmatic rock closely related to mineralization show that(1) the late Jurassic magmatic rock closely related to mineralization in Budunhua ore field formed by crystallization differentiation from initial magma. The initial magma formed by partial melting of 70~80% neonatal basaltic lower crust uniformly mixing with 20~30% ancient lower crustal component, and it was subjected to a certain extent of crustal contamination during rising evolution;(2) the late Jurassic magmatic rock closely related to mineralization in Naoniushan ore field has high Si O2, high Al2O3, high Sr、low Y, meta-potassium, low Mg O, Cr, Co and Ni, which is adakitic magmas formed by partial melting of thickening lower crust. The wall rocks is mainly andesitic of Manitu group, which has lower Mg#, Cr and Ni and is different from contemporaneous adakitic High-Mg andesite, formed by partial melting of contemporaneous shallow parts of neonatal lower crust.Combined with the result of S-Pb, Re-Os isotopic of the ore mineral, the Budunhua deposit has been concentrated in ore-formation by the hasal-intruded of basaltic magma and well-mixed source region of the lower crust, then partial melting of magma carry the minerals rising to the shallow crust; The formation of the Lianhuashan deposit and Naoniushan deposit are mainly due to the partial melting of the neonatal-thickening lower crust leading to the metallogenic material being activated from the neonatal lower crust, and union dye part of the lower crust material, then concentrated in ore-formation.6. Combing regional evolution setting of tectonic, the geological process of diagenesis and metallognesis in the research area can be summarized:(1) Late Jurassic, subduction slab for Mongolian-Okhotsk breakoff, and material from asthenosphere upwelling lead to initial intermediate-acidic magmas of the Budnhua ore-field, which formed by partial melting of 70~80% neonatal basaltic magma and existed 20~30% ancient lower crustal component and ore-bearing fluid formed epithermal-porphyry Cu polymetallic metallogenic system of the Budunhua ore field during the process of the ore bearing fluid rising.(2) Early period of Early Cretaceous, coincided with the stage of the squeezing action weakened of paleo-pacific to Eurasian continent and after the closure orogeny, Mongolia-Okhots Ocean is transfer from compression to extension, regional lithospheric extension caused the massive upwelling of asthenosphere material and provided heat to cause the partial melting to the neonatal basaltic thickened lower crust, formed the adakitic intermediate-acidic magmas which have a high oxygen fugacity ?(O2), rich in mineral and fluid with garnet, pyroxene, rutile, ilmenite and other minerals as the residual phase. In the extensional environment, adakitic intermediate-acidic magmas rising to the shallow crust occurred ore fluid exsolution formed ore-bearing fluid, then during the process of the ore bearing fluid rising up, it formed the epithermal-porphyry Cu polymetallic metallogenic system of the Naoniushan(Lianhuashan) ore-field.