| Southern Great Xing’an Range is located in the central and western Songnen Terrane of the Xingmeng Orogenic Belt. Songliao Basin is in the East bounded by the Nenjiang fault, Xing’an block is in the North bounded by the Erlianhot-Hegenshan fault, Liaoyuan block is in the south bounded by the Wenduermiao-Xilamulun fault, respectively. Formation in this area belongs to the Dashizhai and Linxi area of the Saihantala-Ulanhot subregion from the Junggar-Xing’an region. The regional stratigraphy includes Proterozoic, Paleozoic, Mesozoic and Cenozoic. Proterozoic strata contain lower Proterozoic Baoyintu group biotite plagioclase gneiss and upper Proterozoic Ailigemiao group sericite quartz schist, Baoyintu group biotite plagioclase gneiss is the outcropped oldest stratigraphy, located in the Xilinhaote district. Paleozoic strata contain shallow marine sedimentary rocks of Silurian Xingshuwa group, shallow marine carbonate-clastic sedimentary rocks of Carboniferous Benbatu group and Amushan group, and Permian strata, Permian strata are widespread in the studied area, consisting of lower Permian Dashizhai group intermediate-acidic volcanic rocks, lower Permian huanggangliang group carbonate rocks and upper Permian Linxi group freshwater sedimentary rocks. Mesozoic strata include Jurassic Xinmin group, Manketouebo group, Manitu group and baiyingaolao group of volcanic and volcaniclastic rocks, Cenozoic strata are mainly Quaternary alluvial.The studied area is located in the southern Great Xing’an Range metallogenic belt, namely eastern part of Central Asian Orogenic Belt (also known as Xingmeng Orogenic Belt), which is one of the world’s largest granite province and the metal metallogenic zones in northern China. In recent decades, many metal deposits related with the Mesozoic magmatic rocks occurred, such as Dajing, Huanggang, Baiyinnuoer, Bairendaba, Weilasituo, Bianjiadayuan and other large-medium sized hydrothermal deposit, which are showing good exploration potential. It still does not seem very disproportionate compared with its excellent metallogenic condition and huge exploration potential. Thus, to study metallogenic dynamics background, mineralization and metallogenic regularity is a key issue need to be addressed to achieve prospecting breakthrough. In this paper, the magmatic rocks associated with the mineralization in the northern Chifeng region of Inner Mongolia were analyzed using chronology and geochemistry methods to discuss magmatism period time and petrogenesis, and on this basis, Baiyinnuoer lead-Zinc deposits, Dajing tin polymetallic deposit, Huanggang tin-iron polymetallic deposits, Bianjiadayuan lead-Zinc-silver and Bairendaba-Weilasituo silver polymetallic deposits from the southern Great Xing’an Range were analyzed on the genesis of mineral deposit and constructed the metallogenic series of the southern Great Xing’an Range polymetallic ore. Some recognition is as follows:1 regional magmatic evolutionSouthern Great Xing’an Range is located in the eastern part of Central Asian Orogenic Belt, also known as the Xingmeng orogenic belt. It is formed by continuous collision and combination among multiple plates during Paleozoic, and experienced complicated tectonic evolution stages during Mesozoic, which can be divided into the following three stages:(1) Post-orogenic extension stage during Paleo-Asian Ocean closure (234-245Ma), some early-middle Triassic intrusive rocks occurred, such as Baiyinnuoer intrusion (244.51 ±0.9 Ma), Aoergai intrusion (245.4±1.8 Ma) and Lianhuashan intrusion (236.8～237.9 Ma). The rock types of these intrusions are granodiorite, plagioclase granite porphyry, etc., showing the feature of high strontium I-type granite, magma was originated from partial melting of the juvenile crust from the depleted mantle during Neoproterozoic-Early Paleozoic. (2) Tectonic regime transformation stage (154～175.5Ma), some middle-late Jurassic intrusive rocks occurred, such as Dajing intrusion (168.4～175.5Ma) and Budunhua intrusion (151.95±0.75Ma). The rock types of these intrusions are felsite porphyry, andesitic porphyrite, tonalite porphyry, etc., showing the feature of low strontium I-type granite; magma was originated from partial melting of the juvenile crust from the depleted mantle during Neoproterozoic, and contaminated by little ancient crustal material during ascent. (3) Intra-plate extension stage (126-145Ma), a large amount of late Jurassic early Cretaceous intrusive rocks occurred, such as Huanggang intrusion (145.3±1.6Ma), Bianjiadayuan intrusion (143.3±1.8Ma), Aolunhua intrusion (134-135Ma), Banlashan intrusion (132.1～133.5Ma) and Yangchang intrusion (132-138Ma). The rock types of these intrusions are K-feldspar granite, plagioclase granite, monzonitic granite, granite porphyry, granodiorite, etc., showing the feature of within plate A-type granite, magma was originated from partial melting of the juvenile crust, and contaminated by 20% to 30% ancient crustal material during ascent.2 Study on the typical deposits and new understanding of the ore genesis(1) Baiyinnuoer lead-zinc deposit is a typical skarn deposit, skarn and orebodies mainly occur within the contact zone between the indosinian granodiorite, diorite porphyrite and Permian marble, the zone The north and south ore belts are mainly controlled by the NE trending anticline fold, NE and EW trending faults are the major rock-controlling and ore-controlling structures, morphology of ore body are mainly layered, plate, supine and vein shape, etc. Ore minerals are mainly sphalerite, galena. Fluid inclusion studies indicate that fluid activities in the mineralization process can be divided into three stages, that is skarn stage, quartz sulfide stage and carbonate stage.(2) Dajing deposit is the biggest tin-polymetallic hydrothermal vein-type deposit in the North of China. The ore body is mainly hosted in different units of the Upper Permian, Linxi Formation, or middle Jurassic subvolcanic rocks (felsite porphyry, andesitic porphyrite). NE trending faults (such as F1 and F2) are the main leading ore structure, NW or NWW trending faults are the main hosting ore structures, the morphology of ore body are mainly irregular vein or vein type, the main ore minerals are chalcopyrite, cassiterite, sphalerite and galena, etc. Fluid inclusion studies indicate that there are three stages in this area, which is Ⅰ stage (Cassiterite-Arsenopyrite-Quartz stage); Ⅱ stage (copper-iron sulfide stage); Ⅲ stage (lead-Zinc-silver sulfide stage). The main metallogenic mechanism is fluid mixing, which means that the fluid ofⅠstage is magmatic, and Ⅱ, Ⅲ stage have mixed with meteoric waters.(3) The Huanggang iron-tin deposit is a typical skarn deposit. Skarns and iron orebodies occur along the contact between granite plutons and the lower Permian Huanggangliang Formation marble or Dashizhai Formation andesite. The orebodies occur as lenses and layered, controlled by the NE spreading faults. Their occurrence and morphology are controlled by the top of the intrusion. The ore minerals are magnetite, cassiterite, sphalerite, chalcopyrite, galena and some molybdenite. There are three stages of hydrothermal activity, i.e., skarn, iron-tin oxide and quartz sulfide stages, in the skarn stage, Based on the fluid inclusion and isotope studies, the fluid evolution of the Huanggang deposit can be described as follows:in the skarn stage, fluids separated directly from silicate melts at relatively high temperatures(-500 ℃) and lithostatic pressures (-500 bar, a closed system). These hypersaline brines yield δ18Oh2O and δD values similar to those of silicate melt (7.4 to 9.1%o and-73 to-96%o, respectively), due to their equilibrium at high temperatures. As the temperature decreased, residual fluids from the skarn stage cooled faster upon ascent. Boiling may have occurred at these relatively low temperatures (400-500 ℃), giving rise to fluid inclusions during the oxide stage with a variable but continuous sequence of low salinities. Consequently, these fluids yield lower δ18OH2O values and δD values (3.8 to 4.9%o and-100 to-116%o, respectively). Subsequently, a transition took place from the closed system of the oxide stage (lithostatic conditions) to the open system of the sulfide stage (hydrostatic conditions), accompanied by cooling from-350 ℃ to 160 ℃. This transition resulted in the mixing of the early, hot, hypersaline brines withmeteoric water, boiling of the fluids (160-250 ℃), and subsequent copper and zinc deposition; thus, the fluids yield the lowest 518OH2O values and moderate δD values (-1.6 to-2.8%o and-101 to-104%o, respectively). The oxygen isotope values of the magnetite suggest that the fluid is of magmatic origin. The sulfur isotope values of the sulfides suggest that the sulfur is also of magmatic origin. The lead isotope compositions of the ore suggest that the ore forming fluid is related with the K-feldspar granite.(4) Bianjiadayuan silver polymetallic deposit is controlled by the fault and cryptoexplosive breccia, the orebodies occur as veins, Yanshanian plagiogranite is closely related with the mineralization. The main ore minerals are galena, sphalerite, chalcopyrite, pyrite, arsenopyrite, argentite, freibergite, the wall rock alteration (carbonation, sericitization) are well developed. Fluid inclusions indicate that the deposit was formed in the medium temperature environment.(5) The Bairendaba-Weilasituo deposits are the two of the largest hydrothermal vein-type silver deposits at the Southern Great Xing’an Range, this paper studied the fluid inclusions from wolframite, light sphalerite, quartz and fluorite and the sulfur isotope of sulfides. Results show that in the Bairendaba deposit, the homogenization temperatures and salinities decrease gradually from Ⅰ to Ⅲ stage. But in the Weilasituo deposit, the fluid from 1 to Ⅱ stage have the features of higher temperature and salinity. The Ⅲ stage has immiscible fluid, which are medium temperature and salinity fluid, and the higher temperature and lower salinity. The fluid of the IV stage have the features of lower temperature and salinity. The gas phase compositions of the fluid inclusion show that ore-forming fluids are CO2-H2O-NaCl system in the two deposits. In the Bairendaba deposit, the temperature and salinity decreased from Ⅰ to Ⅲ stage and H-O isotopes show that the earlier stage fluid is magmatic and the later stage fluid is meteoric water. In the Weilasituo deposit, H-O isotopes and fluid compositions (CH4/C2H6 vary from 39.271 to 101.438 mol%) show that the fluid is magmatic. Sulfur isotopes demonstrated the sulfur is from the deep source in Bairendaba-Weilasituo deposit. In all, metallogenic mechanism of the Bairendaba deposit is the fluid mixing with the different origin, metallogenic mechanism of the Weilasituo deposit is cooling and fluid immiscibility.3 Establishment of metallogenic series and studies on regional metallogenic regularityIn the Mesozoic, the southern great Xing’an Range has experienced post-orogenic extension stage after the Paleo-Asian Ocean closure (234.9～245.4Ma), tectonic regime transformation stage from the collision to extension (151～179Ma), intra-plate extension stage (129～148Ma). In the tectonic setting of three stages, the lead-zinc skarn deposit and copper-silver porphyry deposit were formed in the post-orogenic extensional stage, which were related with granodiorite and plagioclase granite porphyry, respectively. The tin-copper-lead-zinc-silver hydrothermal deposits were formed in the tectonic regime transformation stage, which were related with felsite porphyry, andesitic porphyrite and other subvolcanic rocks. The tin-iron skarn deposit and lead-zinc hydrothermal vein-type deposit were formed in the intra-plate extension stage, which were related with K-feldspar granite and granite, respectively. Based on the studies of the metallogenic geological conditions, geological factors and typical deposits (Baiyinnuoer lead-zinc deposit, Dajing tin-copper polymetallic deposit, Huanggang tin-iron deposit and Bianjiadayuan lead-zinc deposit), we establish three metallogenic series, such as (1) Pb-Zn-Cu-Ag mineralization subseries related with I-type granite in post-orogenic extension stage. (2) Sn-Cu-Pb-Zn-Ag metallogenic subseries related with I-type subvolcanic rocks in tectonic regime transformation stage. (3) Sn-Fe-Pb-Zn-Ag-Cu metallogenic subseries related with A-type granite in the intra-plate extension stage.Based on the geological evidence and geochemical information according to the metallogenic prospect, the southern Great Xing’an Range has been divided into three metallogenic prospective areas, namely, (1) central district of southern Great Xing’an Range Pb-Zn-Cu-Ag mineralization prospect area. (2) northern district of southern Great Xing’an Range Cu-Ag-Pb-Zn mineralization prospect area, (3) southern district of southern Great Xing’an Range Sn-Pb-Zn-Ag-Fe mineralization prospect area. |
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