Epithermal gold deposits are typical precious metal deposits related to volcanic and subvolcanic magmatism.Due to the lack of direct geological and petrographic evidences,the origin of the ore-forming fluid is deduced...Epithermal gold deposits are typical precious metal deposits related to volcanic and subvolcanic magmatism.Due to the lack of direct geological and petrographic evidences,the origin of the ore-forming fluid is deduced from the spatial diagenesis-mineralization relationship,chronological data,physicochemical characteristics of mineral fluid inclusions,mineral or rock elements and isotopic geochemical characteristics.By objectively examining this scientific problem via a geological field survey and petrographic analysis of the Gaosongshan epithermal gold deposit,we recently discovered and verified the following points:(1) Pyrite-bearing spherical quartz aggregates (PSQA) occur in the rhyolitic porphyry;(2) the mineralization is structurally dominated by WNW- and ENE-trending systems and occurs mostly in hydrothermal breccias and pyrite-quartz veins,and the ore types are mainly hematite-crusted quartz,hydrothermal breccia,massive pyrite-quartz,etc.;(3) the alteration types consist of prevalent silicification,sericitization,propylitization and carbonation,with local adularization and illitization.The ore minerals are mainly pyrite,primary hematite,native gold,and electrum,with lesser amounts of chalcopyrite,magnetite,sphalerite,and galena,indicating a characteristic epithermal low-sulfidation deposit.The ore-forming fluid may have been primarily derived from magmatic fluid exsolved from a crystallizing rhyolitic porphyry magma.Further zircon U-Pb geochronology,fluid inclusion,physicochemical and isotopic geochemical analyses revealed that (1) rhyolitic porphyry magmatism occurred at 104.6 ± 1.0 Ma,whereas the crystallization of the PSQA occurred at 100.8 ± 2.1 Ma;(2) the hydrothermal fluid of the pre-ore stage was an exsolved CO2-bearing H2O-NaCl magmatic fluid that produced inclusions mainly composed of pure vapor (PV),vapor-rich (WV) and liquid-rich (WL) inclusions with a small number of melt-(M) and solid-bearing (S) inclusions;mineralization-stage quartz contains WL and rare PV,WV and pure liquid (PL) inclusions characterized by the H2O-NaCl system with low formation temperatures and low salinities;(3) the characteristics of hydrogen,oxygen,sulfur,and lead isotopes and those of rare earth elements (REEs) provide insight into the affinity between PSQA and orebodies resulting from juvenile crust or enriched mantle.Combined with previous research on the mineralogenetic epoch (99.32 ± 0.01 Ma),we further confirm that the mineralization of the deposit occurred in the late Early Cretaceous,which coincides with the extension of the continental margin induced by subduction of the Pacific Plate beneath the Eurasian Plate.The formation of the ore deposit was proceeded by a series of magmatic and hydrothermal events,including melting of enriched juvenile crust,upwelling,the eruption and emplacement of the rhyolitic magma,the exsolution and accumulation of magmatic hydrothermal fluid,decompression,the cooling and immiscibility/boiling of the fluid,and mixing of the magmatic fluid with meteoric water,in association with water-rock interaction.展开更多
The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone t...The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.展开更多
A great amount of alkali-feldspar and alkaline granites have been found around Nenjiang, Northwest Lesser Xing’an Ranges, but their forming ages have been a controversial subject due to the lack of reliable geologica...A great amount of alkali-feldspar and alkaline granites have been found around Nenjiang, Northwest Lesser Xing’an Ranges, but their forming ages have been a controversial subject due to the lack of reliable geological and isotopic geochronological evidence. The zircon U-Pb isotopic dating results conducted in this note indicate that these granites emplaced at 260-290 Ma, coeval with the late stage of Late Paleozoic. Studies of mineralogy, petrology andgeochemistry show that they are post-orogenic A-type granites, and consist of the northeastern extension of huge belt of Late Paleozoic A-type granite along North Xinjiang-Southeast Mongolia-Central Inner Mongolia. Therefore, we can determine that the Suolunshan-Hegenshan-Zhalaite collisional suture zone extends northeastward to Heihe with the collision age of Carboniferous.展开更多
The formation time of the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range , NE China, remains controversial owing to the lake of the precise dating data. This article reports zircon U-Pb ages for the le...The formation time of the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range , NE China, remains controversial owing to the lake of the precise dating data. This article reports zircon U-Pb ages for the leptynite and gneissic granitoids from the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range. The aim is to constrain the formation time and prove- nance of Fengshuigouhe Group. Field observation indicates that the Fengshuigouhe Group consists of a suit of metamorphic rocks （leptynite） and gneissic granitoids intruding the leptynite, and that both of them are cut by late granitic pegmatite. Zircons from two leptynites are euhedral-subhedral in shape and display oscillatory zoning in CL （cathodeluminescence） images. These detrital zircons give weighted mean ages of 255, 291,321,361, 469, and 520 Ma. The youngest age of them is interpreted to maximum deposi- tional age of the protoliths of these leptynites. Zircons from gneissic granites are euhedral and subhedral in shape and exhibit typical oscillatory zoning in CL images. The dating results indicate that the gneissic granites were formed in the Early Jurassic （185~2 Ma）. Zircons from the late granitic pegmatite are sub- hedral in shape and exhibit two types in CL images： structureless and oscillatory zoning. The former gives a weighted mean age of 143~1 Ma, considered to represent the timing of crystallization of the pegmatite, the latter yield several groups of ages： 178, 273, 319, 482, 611, and 788 Ma, representing the crystallization age of inherited or captured zircons entrained by the pegmatite. Taken together, we conclude that the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range formed between Late Paleozoic （255Ma） to Early Mesozoic （185 Ma）, rather than Neoproterozoic as previously believed, and that the sediments in the Fengshuigouhe Group were sourced directly from geological bodies in the study area and adjacent regions. KEY WORDS： the Lesser Xing＇an Range, Fengshuigouhe Group, formation time, leptynite, zircon U-Pb geochronology.展开更多
Located in the eastern portion of the Xing'an-Mongolian Orogenic Belt (XMOB), the Xinkailing-Kele complex has previously been considered to be Precambrian metamorphic rocks, mainly according to its relatively high...Located in the eastern portion of the Xing'an-Mongolian Orogenic Belt (XMOB), the Xinkailing-Kele complex has previously been considered to be Precambrian metamorphic rocks, mainly according to its relatively high metamorphic grade. Our filed observation, however, revealed that the complex is composed mainly of metamorphic rocks (Kele complex), tectono-schists (“Xinkailing Group”),and granitoids (Xinkailing granitic complex). Dating on these rocks using advanced SHRIMP zircon U-Pb technique indicates that: (1) Biotite-plagioclase gneiss from the Kele complex has a protolith age of 337±7Ma (2σ) and a metamorphic age of 216±3Ma (2σ); (2) the tectono-schist of the “Xinkailing Group” gave a magmatic age of 292±6Ma (2σ), indicative of felsic volcanic protolith of the schist formed in Late Paleozoic time; and (3) the Menluhedingzi and Lengchuan granites of the Xinkailing granitic complex were emplaced at167±4 (20σ) and 164±4Ma (2σ), respectively. These results suggest that the Xinkailing-Kele complex is not Precambrian metamorphic rocks and the so-called Precambrian “Nenji-ang Block” does essentially not exist. In combination with regional geological data, we propose that the Kele metamorphic complex is likely related to a collisional tectonism that took place in Triassic lime, as indicted by its metamorphic age of 216±3Ma. The Xinkailing granitic complex was emplaced along the collisional zone during Mid-Jurassic time，likely in a post-orogenic or anorogenic setting.展开更多
基金financially supported by the National Key Research and Development Program of China (Grant No.2017YFC0601306)the National Natural Science Foundation of China (Grant No.41390444)+1 种基金the Program of the China Geological Survey(Grant No.DD20160344)supported by Team 707, Heilongjiang Bureau of Geological Exploration for Nonferrous Metals
文摘Epithermal gold deposits are typical precious metal deposits related to volcanic and subvolcanic magmatism.Due to the lack of direct geological and petrographic evidences,the origin of the ore-forming fluid is deduced from the spatial diagenesis-mineralization relationship,chronological data,physicochemical characteristics of mineral fluid inclusions,mineral or rock elements and isotopic geochemical characteristics.By objectively examining this scientific problem via a geological field survey and petrographic analysis of the Gaosongshan epithermal gold deposit,we recently discovered and verified the following points:(1) Pyrite-bearing spherical quartz aggregates (PSQA) occur in the rhyolitic porphyry;(2) the mineralization is structurally dominated by WNW- and ENE-trending systems and occurs mostly in hydrothermal breccias and pyrite-quartz veins,and the ore types are mainly hematite-crusted quartz,hydrothermal breccia,massive pyrite-quartz,etc.;(3) the alteration types consist of prevalent silicification,sericitization,propylitization and carbonation,with local adularization and illitization.The ore minerals are mainly pyrite,primary hematite,native gold,and electrum,with lesser amounts of chalcopyrite,magnetite,sphalerite,and galena,indicating a characteristic epithermal low-sulfidation deposit.The ore-forming fluid may have been primarily derived from magmatic fluid exsolved from a crystallizing rhyolitic porphyry magma.Further zircon U-Pb geochronology,fluid inclusion,physicochemical and isotopic geochemical analyses revealed that (1) rhyolitic porphyry magmatism occurred at 104.6 ± 1.0 Ma,whereas the crystallization of the PSQA occurred at 100.8 ± 2.1 Ma;(2) the hydrothermal fluid of the pre-ore stage was an exsolved CO2-bearing H2O-NaCl magmatic fluid that produced inclusions mainly composed of pure vapor (PV),vapor-rich (WV) and liquid-rich (WL) inclusions with a small number of melt-(M) and solid-bearing (S) inclusions;mineralization-stage quartz contains WL and rare PV,WV and pure liquid (PL) inclusions characterized by the H2O-NaCl system with low formation temperatures and low salinities;(3) the characteristics of hydrogen,oxygen,sulfur,and lead isotopes and those of rare earth elements (REEs) provide insight into the affinity between PSQA and orebodies resulting from juvenile crust or enriched mantle.Combined with previous research on the mineralogenetic epoch (99.32 ± 0.01 Ma),we further confirm that the mineralization of the deposit occurred in the late Early Cretaceous,which coincides with the extension of the continental margin induced by subduction of the Pacific Plate beneath the Eurasian Plate.The formation of the ore deposit was proceeded by a series of magmatic and hydrothermal events,including melting of enriched juvenile crust,upwelling,the eruption and emplacement of the rhyolitic magma,the exsolution and accumulation of magmatic hydrothermal fluid,decompression,the cooling and immiscibility/boiling of the fluid,and mixing of the magmatic fluid with meteoric water,in association with water-rock interaction.
文摘The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.
基金the National Natural Science Foundation of China (Grant No. 49872031)the Excellent Young Teachers and Doctor's Disciplines Foundation of the Ministry of Education of China (Grant No. 9518701).
文摘A great amount of alkali-feldspar and alkaline granites have been found around Nenjiang, Northwest Lesser Xing’an Ranges, but their forming ages have been a controversial subject due to the lack of reliable geological and isotopic geochronological evidence. The zircon U-Pb isotopic dating results conducted in this note indicate that these granites emplaced at 260-290 Ma, coeval with the late stage of Late Paleozoic. Studies of mineralogy, petrology andgeochemistry show that they are post-orogenic A-type granites, and consist of the northeastern extension of huge belt of Late Paleozoic A-type granite along North Xinjiang-Southeast Mongolia-Central Inner Mongolia. Therefore, we can determine that the Suolunshan-Hegenshan-Zhalaite collisional suture zone extends northeastward to Heihe with the collision age of Carboniferous.
基金supported by the National Natural Science Foundation of China(No.41072038)China Geological Survey(No.1212010070301)the Opening Foundation of the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan
文摘The formation time of the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range , NE China, remains controversial owing to the lake of the precise dating data. This article reports zircon U-Pb ages for the leptynite and gneissic granitoids from the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range. The aim is to constrain the formation time and prove- nance of Fengshuigouhe Group. Field observation indicates that the Fengshuigouhe Group consists of a suit of metamorphic rocks （leptynite） and gneissic granitoids intruding the leptynite, and that both of them are cut by late granitic pegmatite. Zircons from two leptynites are euhedral-subhedral in shape and display oscillatory zoning in CL （cathodeluminescence） images. These detrital zircons give weighted mean ages of 255, 291,321,361, 469, and 520 Ma. The youngest age of them is interpreted to maximum deposi- tional age of the protoliths of these leptynites. Zircons from gneissic granites are euhedral and subhedral in shape and exhibit typical oscillatory zoning in CL images. The dating results indicate that the gneissic granites were formed in the Early Jurassic （185~2 Ma）. Zircons from the late granitic pegmatite are sub- hedral in shape and exhibit two types in CL images： structureless and oscillatory zoning. The former gives a weighted mean age of 143~1 Ma, considered to represent the timing of crystallization of the pegmatite, the latter yield several groups of ages： 178, 273, 319, 482, 611, and 788 Ma, representing the crystallization age of inherited or captured zircons entrained by the pegmatite. Taken together, we conclude that the Fengshuigouhe Group in the northwestern Lesser Xing＇an Range formed between Late Paleozoic （255Ma） to Early Mesozoic （185 Ma）, rather than Neoproterozoic as previously believed, and that the sediments in the Fengshuigouhe Group were sourced directly from geological bodies in the study area and adjacent regions. KEY WORDS： the Lesser Xing＇an Range, Fengshuigouhe Group, formation time, leptynite, zircon U-Pb geochronology.
文摘Located in the eastern portion of the Xing'an-Mongolian Orogenic Belt (XMOB), the Xinkailing-Kele complex has previously been considered to be Precambrian metamorphic rocks, mainly according to its relatively high metamorphic grade. Our filed observation, however, revealed that the complex is composed mainly of metamorphic rocks (Kele complex), tectono-schists (“Xinkailing Group”),and granitoids (Xinkailing granitic complex). Dating on these rocks using advanced SHRIMP zircon U-Pb technique indicates that: (1) Biotite-plagioclase gneiss from the Kele complex has a protolith age of 337±7Ma (2σ) and a metamorphic age of 216±3Ma (2σ); (2) the tectono-schist of the “Xinkailing Group” gave a magmatic age of 292±6Ma (2σ), indicative of felsic volcanic protolith of the schist formed in Late Paleozoic time; and (3) the Menluhedingzi and Lengchuan granites of the Xinkailing granitic complex were emplaced at167±4 (20σ) and 164±4Ma (2σ), respectively. These results suggest that the Xinkailing-Kele complex is not Precambrian metamorphic rocks and the so-called Precambrian “Nenji-ang Block” does essentially not exist. In combination with regional geological data, we propose that the Kele metamorphic complex is likely related to a collisional tectonism that took place in Triassic lime, as indicted by its metamorphic age of 216±3Ma. The Xinkailing granitic complex was emplaced along the collisional zone during Mid-Jurassic time，likely in a post-orogenic or anorogenic setting.
