| The northern Great Xing’an and Lesser Xing’an Ranges are located in eastern segment of the Central Asian Orogenic Belt (CAOB), which is surrounded by the Siberian plate in the north, the North China plate in the south, and the Pacific plate in the east. Since Phanerozoic, this area has experienced the evolution of the Paleo-Asian Ocean, the Mongolia-Okhotsk Ocean, and the Western Pacific Ocean, resulting in a complicated geologic structure. Because of the widespread forest cover and the lengthy ice period, the geologic characteristics of this district hasn’t been well studied. Since the 1990 s’systematic geological prospecting work, a large number of important endogenous metal deposits have been discovered, especially the large scale porphyry Cu, Mo deposits. Based on the latest exploration achievements in this area, this paper mainly dissects the geologic feature, ore-forming fluids, stable isotopes, mineralization age and the genesis of the porphyry Cu, Mo deposits, and the zircon U-Pb geochronology, petrogeochemistry and the Sr-Nd-Hf isotopic characteristics of the ore-related granitoids. Along with the preexisting research data, the temporal-spatial distribution discipline and the geodynamic background of the porphyry Cu, Mo deposits have been discussed, providing theoretical foundation for the next-step metallogenic prediction and the selection of the ore-prospecting target area.The northern Great Xing’an and Lesser Xing’an Ranges can be divided into the Erguna, Xing’an and Songnen Blocks from north to south. The Erguna Block has been stable since the Early Paleozoic, subsequently the Xing’an Block accreted with it along the Tayuan-Xiguitu belt. During the end stage of the Early Paleozoic, the Songnen Block accreted with them along the Hegenshan-Heihe Fault. The strata of the study area are complete and dominated by the Paleozoic and Mesozoic strata. The Precambrian and Cambrian strata are mainly composed of epimetamorphic rocks. The Ordovician to Permian strata are dominated by clastic and carbonate rocks. The Jurassic and Cretaceous strata dominantly consist of volcanic and volcanic clastic rocks. The granites are mainly I type and A type, they were mainly formed during the Mesozoic, followed by the Late Paleozoic. The WE trending faults are overlain by the NE-NNE trending faults, the former was constrained by the Paleo-Asian tectonic system, while the later was resulted from the Paleo-Pacific tectonic system.The orebodies in the Duobaoshan Cu deposit are hosted within the granodiorite. The orebodies are veined, lenticular or lenticular. The wall rock alteration display a linear distribution. The ore-forming process can be divided into four phases:quartz-potassium feldspar'quartz-molybdenite'quartz-chalcopyrite'quartz-carbonate. The homogenization temperature of the ore-forming fluid in the second phase generally range from 240 to 320℃, the salinity vary from unsaturated to supersaturated, and the δD and δOH2O values range from -81.2%o to -74.2%o and 4.3‰ to 4.8‰, respectively, implying its magmatic origin. The homogenization temperature of the ore-forming fluid in the third phase is mainly 140 to 180℃, the salinity is 1.4 to 14.7 wt% NaCl eqv, with the δD and δOH2O values of -88%o to -82.3%o and -2.3%o to -2%o, respectively, suggesting the origination from mixture of magmatic and meteoric water. The δ34 S value of the sulfides range from -0.76‰ to 1.1‰, indicating a magmatic source of sulfur. The molybdenite Re-Os isotopic model ages range from 473.8 Ma to 481.3 Ma. The zircon U-Pb ages of the granodiorite, granite porphyry, and two-mica monzogranite are 480.4 ± 2.8 Ma,478.9 ± 3.6 Ma, and 232.3 ± 2.5 Ma, respectively. All of them belong to the high-K calc-alkaline series, and are metaluminous to weakly peraluminous. They are enriched in large ion lithophile element (LILE, Rb, Ba, Th、U, and Pb), and depleted in high field-strength element (HFSE, Nb、Ta、P、Ti). The Sr-Nd-Hf isotopes indicate that the magma is originated from partial melting of the juvenile crustal materials which is sourced from depleted mantle.The orebodies of the Tongshan deposit are hosted in the Duobaoshan Formation. The orebodies are mainly veined, and the alterations are planar. Four phases of mineralization have been recognized:quartz-potassium feldspar' quartz-epidote-chalcopyrite' quartz-polymetallic sulfide'quartz-calcite-ankerite. The homogenization temperatures, the δD and δOH2O values of the ore-forming fluids in the first phase are 220 to 260℃ and 300 to 360℃,-95.7‰, and 5‰, respectively. While that of the second phase are 180 to 260℃,-98.5‰ to-93.2‰, and 2.6‰ to 3.2‰, respectively. The homogenization temperatures of the ore-forming fluid in the third phase decrease to 120 to 160℃, the δD and δOH2O values are -99.7‰, and -4‰, respectively. It suggests a evolution from magmatic water to meteoric water. Both the sulfur (δ34S=-2.6%o～-1.1‰) and lead isotopes (206Pb/204Pb= 17.682～17.798,207Pb/204Pb= 15.471-15.495,208Pb/204Pb= 37.395～37.52) indicate a magmatic origin for the ore-forming materials. No mineralization is observed in the outcropping granodiorite of the Tongshan district, which yields a crystallization age of 214.3 ± 2.6 Ma and indicate no relation to the metallogenesis. The ore-forming granitoid is actually the concealed granodiorite, which may be connected with the granodiorite in the Duobaoshan district in deep.The upper part of the Chalukou Mo polymetallic deposit is dominated by Pb-Zn orebodies, while the lower part is dominated by Mo orebodies. The Pb-Zn orebodies are hosted within the propylitic zone as veins or lenticles, and the Mo orebodies occur in the potassium and quartz sericitization zones as vaults. The ore-forming process has experienced four phases:quartz-potassium feldspar' quartz-molybdenite' quartz-polymetallic sulfide'fluorite-quartz-calcite. The peak homogenization temperature of the ore-forming fluid in the first phase range from 380 to 440 ℃, and the salinity concentrate from 48 to 60 wt% NaCl eqv and from 6 to 16 wt% NaCl eqv. The peak homogenization temperature and salinity of the second phase fluids are from 300 to 400 ℃, and from 4 to 12 wt% NaCl eqv. That of the third and fourth phases range from 260 to 300 ℃,3 to 5 wt% NaCl eqv, and from 160 to 260 ℃,0 to 5 wt% NaCl eqv, respectively. The ore-forming fluids gradually evolve from high oxygen fugacity and CO2 content in the early phase to low oxygen fugacity and CO2 content in the late phases. The low 5D values (-144.5%o～-117.3%o) of the ore-forming fluids may have resulted from degasification of the primary magma. The sulfur (δ34S= 1.8‰～2.9‰) and lead isotopes (206Pb/204Pb= 18.311～ 18.356,207Pb/204Pb= 15.536～15.573,208Pb/204Pb= 38.115～38.229) of the sulfides indicate their magmatic origin. The molybdenite Re-Os isochron age is 144.7 ± 2.6 Ma, which is in accordance with the crystallization age of the ore-bearing granite porphyry (148.2 ±1.6 Ma). The Caledonian granite porphyry, which is intruded by the ore-bearing granite porphyry, yields LA-ICPMS zircon U-Pb age of 464.9 ± 2.8 Ma. The Yanshanian biotite monzogranite, quartz monzonitic porphyry and rhyolite in the Chalukou district display crystallization ages of 163.0 ± 0.9 Ma,135.3±1.6 Ma, and 135.1±1.2 Ma, respectively, indicating that the rhyolite erupted after the ore-forming process. These granites generally belong to the high-K calc-alkaline to shoshonite series, and are metaluminous to weakly peraluminous. They are enriched in LILEs (Ba, Th, U, and Pb) and depleted in HFSEs (Nb, P, and Ti). It can be concluded from the Sr-Nd-Hf isotopes that the quartz monzonitic porphyry is originated from depleted mantle, the Caledonian granite porphyry originates from partial melting of the ancient crustal materials, and the biotite monzogranite and rhyolite are sourced from mixture of the crustal and mantle materials.The orebodies os the Luming Mo deposit are hosted in the monzogranite, and the molybdenites occur as veinlets or quartz-molybdenite veins. Four major alteration zones can be established approximately from the monzogranite outward:quartz-K-feldspar alteration' quartz-pyrite-biotite alteration'sericitization'propylitization. The ore-forming process can be divided into four phases:quartz-potassium feldspar'quartz-molybdenite'quartz-pyrite' quartz-calcite. The homogenization temperature and salinity of the ore-forming fluids in the first phase are from 320 to 400℃, and from 3.7 to 12.8 wt% NaCl eqv. The 8D and δOH2O values are from -89.1‰ to -85.7‰, and from 6.3%o to 7.4%o, respectively. The homogenization temperature, salinity,δD and δOH2O values of the second phase fluids are from 300 to 340℃,1.7 to 8.3 wt% NaCl eqv,-84.6‰ to -80.4‰, and 2.4%o to 3.6‰, respectively. The homogenization temperature and salinity of the third phase fluids range from 220 to 260℃, and 3.1 to 7.3 wt% NaCl eqv, respectively. The δD values are from -80‰ to -79.1‰, and δOH2O value is 0.4‰. It is suggested that the ore-forming fluids are dominated by magmatic water, and the meteoric water gradually contribute a larger part as the fluides evolve. The molybdenite Re-Os isochron age is 177.9 ± 2.6 Ma, which is in agreement with the crystallization age of the ore-bearing monzogranite (180.7 ± 1.6 Ma). The monzogranite is weakly peraluminous, and belongs to the shoshonite series. It is enriched in LILEs (Rb, Th, U, and Pb) and depleted in Ba, Nb, Ta, P, and Ti. The Sr-Nd-Hf isotopes suggest that the monzogranite is originated from mixture of the crustal and mantle materials. The Luming Mo deposit and the adjacent Xulaojiugou Pb-Zn deposit share the same mineralization age and similar features of the ore-forming granitoid, they form a porphyry Mo-skarn Pb-Zn metallogenic series.Based on the study of the typical ore deposits, combined with the preexisting research data, the main mineralogenetic epochs of the porphyry Cu, Mo deposits are established. It is suggested that the porphyry Cu deposits mainly formed during 510 ～ 470 Ma and-180 Ma, the former is represented by the Duobaoshan and Tongshan deposits, and the later is represented by the Wulugetushan Cu(Mo) deposit. The porphyry Mo deposit generally formed during～180 Ma and 150～130 Ma, the former is represented by the Luming, Huojihe, Taipingchuan, and Cuiling deposits, while the later is represented by the Chalukou, Taipinggou, and Xing’a deposits. The porphyry Cu, Mo metallogeny in the study area is polycyclic and inherited. The ore-forming elements evolves from Cu in 510 to 470 Ma, through Mo(Cu) in about 180 Ma, to Mo during 150 to 130 Ma.According to the positions of the explored ore deposits, the spatial distribution regularities of the porphyry Cu, Mo deposits have been summarized. The Erguna Block is dominated by porphyry Cu(Au) and Cu(Mo) mineralization, the northern Xing’an Block is characterized by widespread porphyry Cu and Mo metallogenesis, and the Lesser Xing’an Range contains mainly porphyry Mo deposits. The mineralizations range from porphyry Cu(Au, Mo), through porphyry Cu and Mo, to porphyry Mo from northwest to southeast in the study area.Considering the tectonic evolution history of the study area, the geodynamic background of the magmatism and mineralization in the porphyry Cu, Mo deposits have been discussed. During the evolution of the Paleo-Asian Ocean, circumscribed magmatism have taken place in the northern Great Xing’an and Lesser Xing’an Ranges, while the large-scale Duobaoshan and Tongshan deposits have formed. The evolution of the Mongolia-Okhotsk Ocean has limited effects on the study area, it may have resulted in the middle Jurassic magmatism and porphyry Cu, Mo mineralization in the northernmost Great Xing’an Range (the Erguna district), such as the Taipingchuan and Wunugetushan Cu(Mo) deposit. The large scale magmatism and porphyry Mo mineralization in the study area may be attributed to the evolution of the Paleo-Pacific Ocean, including the Jurassic magmatism and mineralization in the northern Xing’an Block and the Lesser Xing’an Range, and the Early Cretaceous volcanic magma activities with combined porphyry Mo polymetallic and volcanic hydrothermal gold metallogeny in the Great Xing’an Range.According to the comparison of the porphyry Cu and porphyry Mo deposits, their metallogenic depth is generally lesser than 3 km. Most of them has experienced four phases of mineralization:quartz-potassium feldspar'quartz-chalcopyrite (and/or molybdenite)' quartz-polymetallic sulfide' quartz-calcite (-fluorite). The ore-forming materials are both originated from magma. The porphyry Cu and Mo deposits have similar wall rock alteration type and zoning, and they share same characteristics of ore-forming fluids, which evolve gradually from magmatic water to meteoric water. However, the porphyry Cu and porphyry Mo deposits also display differences on their metallogenic age, spatial distribution and the ore-forming granitoids. The ore-forming granitoids of the porphyry Cu deposits are mainly intermediate-acidic, metaluminous to peraluminous, high-K calc-alkaline series mantle-sourced I type granites, with diagenetic temperature between 650 and 750℃. Whereas the ore-forming granitoids of the porphyry Mo deposits are generally acidic, metaluminous to peraluminous, high-K calc-alkaline to shoshonite series I type or S type granites, which are sourced from mixture of crustal and mantle materials and have diagenetic temperatures of 750 to 800℃.Finally, this paper discusses the prospecting target of the porphyry Cu and Mo deposits based on the temporal-spatial distribution discipline of the deposits and the development of magmatic rocks. It is proposed that the prospecting of porphyry Cu deposits should focus on the Duobaoshan-Daxintun, Yichun-Yanshou, Heihe-Nenjiang and Erguna districts, while the porphyry Mo deposits have prospecting prospects in the Xingnong-Hanjiayuanzi area of the northern Xing’ an Block and the Tieli and Xunke areas of the Lesser Xing’ an Range. |
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