The Gangcha gold deposit was discovered in 2011 in the Xiahe-Hezuo region, West Qinling Orogen, China. Five types of pyrite have been identified in the ore according to the detailed mineral paragenetic studies. Geoche...The Gangcha gold deposit was discovered in 2011 in the Xiahe-Hezuo region, West Qinling Orogen, China. Five types of pyrite have been identified in the ore according to the detailed mineral paragenetic studies. Geochemical data are presented for type I pyrite （pyl） rim-core zonation and for the different types of pyrite based on in-situ laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） and electron probe microanalysis （EPMA）. The results show that pyrites are characterized with heterogeneous Au concentrations, which indicate that Au occurs mainly as micro- or nano-particle native inclusions. Time-resolved depth profiles demonstrate that As, Co and Ni occur as solid solutions in pyrite, whereas Cu, Pb, Zn and Ag occur mainly as inclusions. Trace element concentrations differ between rims and cores in pyl, and the differences also exist within different pyrite types. These differences indicate complex chemical evolution of the ore-forming fluids, and the overall geology, geochronology, and stable isotope and pyrite data suggest that the ore-forming fluids were closely linked to magmatic activity during the Triassic Period in West Qinling orogenic belt.展开更多
The extensive Changba-Lijiagou Pb-Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite-calcite-quartz schi...The extensive Changba-Lijiagou Pb-Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite-calcite-quartz schist of the Middle Devonian Anjiacha Formation, and are structurally controlled by the fault and anticline. The ore-forming process can be divided into three main stages, based on field geological features and mineral assemblages. The mineral assemblages of hydrothermal stage I are pale-yellow coarse grain, low Fe sphalerite, pyrite with pits, barite and biotite. The mineral assemblages of hydrothermal stage II are black-brown cryptocrystalline, high Fe shalerite, pyrite without pits, marcasite or arsenopyrite replace the pyrite with pits, K-feldspar. The features of hydrothermal stage III are calcite-quartz-sulfide vein cutting the laminated, banded ore body. Forty-two sulfur isotope analyses, twenty-five lead isotope analyses and nineteen carbon and oxygen isotope analyses were determined on sphalerite, pyrite, galena and calcite. The δ34 S values of stage I(20.3 to 29.0‰) are consistent with the δ34 S of sulfate(barite) in the stratum. Combined with geological feature, inclusion characteristics and EPMA data, we propose that TSR has played a key role in the formation of the sulfides in stage I. The δ34 S values of stage II sphalerite and pyrite(15.1 to 23.0‰) are between sulfides in the host rock, magmatic sulfur and the sulfate(barite) in the stratum. This result suggests that multiple S reservoirs were the sources for S2-in stage II. The δ34 S values of stage III(13.1 to 22‰) combined with the structure of the geological and mineral features suggest a magmatic hydrothermal origin of the mineralization. The lead isotope compositions of the sulfides have 206 Pb/204 Pb ranging from 17.9480 to 17.9782, 207 Pb/204 Pb ranging from 15.611 to 15.622, and 208 Pb/204 Pb ranging from 38.1368 to 38.1691 in the three ore-forming stages. The narrow and symmetric distributions of the lead isotope values reflect homogenization of granite and mantle sources before the Pb-Zn mineralization. The δ13 CPDB and δ18 OSMOW values of stage I range from-0.1 to 2.4‰ and from 18.8 to 21.7‰. The values and inclusion data indicate that the source of fluids in stage I was the dissolution of marine carbonate. The δ13 CPDB and δ18 OSMOW values of stage II range from-4 to 1‰ and from 12.3 to 20.3‰, suggesting multiple C-O reservoirs in the Changba deposit and the addition of mantle-source fluid to the system. The values in stage III are-3.1‰ and 19.7‰, respectively. We infer that the process of mineralization involved evaporitic salt and sedimentary organic-bearing units interacting through thermochemical sulfate reduction through the isotopic, mineralogy and inclusion evidences. Subsequently, the geology feature, mineral assemblages, EPMA data and isotopic values support the conclusion that the ore-forming hydrothermal fluids were mixed with magmatic hydrothermal fluids and forming the massive dark sphalerite, then yielding the calcite-quartz-sulfide vein ore type at the last stage. The genesis of this ore deposit was epigenetic rather than the previously-proposed sedimentary-exhalative(SEDEX) type.展开更多
The West Qinling Orogen(WQO) in Central China Orogenic Belt contains numerous metasedimentary rock-hosted gold deposits(>2000 t Au), which mainly formed during two pulses: one previously recognized in the Late Tria...The West Qinling Orogen(WQO) in Central China Orogenic Belt contains numerous metasedimentary rock-hosted gold deposits(>2000 t Au), which mainly formed during two pulses: one previously recognized in the Late Triassic to Early Jurassic(T3 - J1) and one only recently identified in the Late Jurassic to Early Cretaceous(J3 - K1). Few studies have focused on the origin and geotectonic setting of the J3 - K1 gold deposits.Textural relationships, LA-ICP-MS trace element and sulfur isotope compositions of pyrites in hydrothermally altered T3 dykes within the J3 - K1 Daqiao deposit were used to constrain relative timing relationships between mineralization and pyrite growth in the dykes, and to characterize the source of ore fluid. These results are integrated with an overview of the regional geodynamic setting, to advance understanding of the tectonic driver for J3 - K1 hydrothermal gold systems. Pyrite in breccia-and dykehosted gold ores at Daqiao have similar chemical and isotopic compositions and are considered to be representative of J3 - K1 gold deposits in WQO. Co/Ni and sulfur isotope ratios suggest that ore fluids were derived from underlying Paleozoic Ni-and Se-rich carbonaceous sedimentary rocks. The geochemical data do not support the involvement of magmatic fluids. However, in the EQO(East Qinling Orogen), J3 - K1 deposits are genetically related to magmatism. Gold mineralization in WQO is contemporaneous with magmatic deposits in the EQO and both are mainly controlled by NE-and EWtrending structures produced by changes in plate motion of the Paleo-Pacific plate as it was subducted beneath the Eurasian continent. We therefore infer that the J3 - K1 structural regime facilitated the ascent of magma in the EQO and metamorphic fluids in the WQO with consequent differences in the character of contemporaneous ore deposits. If this is correct, then the far-field effects of subduction along the eastern margin of NE Asia extended 1000's of km into the continental interior.展开更多
Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovi...Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. WeaMy peraluminous granite porphyry （A/ CNK=1.10-1.15） is enriched in LREE, depleted in HREE with Nb-Ta-Ti anomalies, and displays subduction-related geochemistry. Quartz porphyry is strongly peraluminous （A/CNK=1.64-2.81） with highly evolved components, characterized by lower TiO2, REE contents, Mg#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and CI. LA- ICP-MS zircon U-Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, εHf（t） values of Triassic magmatic zircons from the granite and quartz porphyries are -14.2 to -9.1 （with an exception of ＋4.1） and -10.8 to -8.6 respectively, indicating a crustal-dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc-related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east.展开更多
The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian ...The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman’s plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ34S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.展开更多
The West Qingling Orogen is endowed with more than 1100 t gold resources and with 50 gold deposits,ranking it the third-largest gold province in China.The Jianchaling giant gold deposit with 52 t gold reserve is a typ...The West Qingling Orogen is endowed with more than 1100 t gold resources and with 50 gold deposits,ranking it the third-largest gold province in China.The Jianchaling giant gold deposit with 52 t gold reserve is a typical orogenic gold deposit in West Qinling Orogen.The deposit lacks accurate and direct metallogenic age.Five pyrite samples collected from the quartz-polymetallic veins yielded Re–Os isochron age of 206.3±2.7 Ma and an initial187 Os/188 Os ratio of 0.1154±0.0016(MSWD=0.54).The pyrites were analyzed by the electron microprobe(EMPA),and the results show that the iron content ranges from 45.1 to 47.8 wt.%,the sulfur content ranges from 52.0 to 53.5 wt.%,and the gold content varies from0.022 to 0.035%.The higher gold content means that gold is closely related to pyrite,which is a gold-bearing mineral.Moreover,the age is very close to the previous fuchsite40 Ar/39 Ar isotopic ages of 199–194 Ma,which indicates that the gold mineralization at Jianchaling has begun in the Late Triassic(206 Ma),and continued into the Early Jurassic.Through summary and comparison,it is found that the gold metallogenic age of the southern ore belt of the Mian-Lue Suture belt in the West Qinling is younger than that of the northern ore belt,suggesting that the gold deposits in the southern ore belt such as Jianchaling were formed in the transitional period from oceanic subduction to continental collision.展开更多
As the main content of terrestrial ecosystem study,vegetation coverage change has gained extensive attention in the process of global climate change and sustainable development recently.Based on MODIS NDVI data from J...As the main content of terrestrial ecosystem study,vegetation coverage change has gained extensive attention in the process of global climate change and sustainable development recently.Based on MODIS NDVI data from June to October during 2000-2010,taking Longnan City as a case area,this paper develops the calculation method of vegetation coverage(VC) by using Pixel Dichotomy model and analyzes the spatial-temporal variation of vegetation coverage in the West Qinling region by using simple linear regression and standard deviation method.The results show that vegetation coverage remains stable and is significantly correlated with temperature and precipitation during the decade.The vegetation coverage of 90% of study area shows stability with small annual variation and also is consistent with the spatial distribution of forest land;the vegetation coverage in the remaining study areas shows a growing trend with significant variation and also is consistent with the spatial distribution of farmland and grassland,especially in Huicheng Basin,Xili Basin and adret slope of Bailongjiang River Valley,indicating that Project about the Conversion of Degraded Farmland into Forest has made a great contribution to vegetation coverage increase.This paper proves the effect of ecology construction in the West Qinling region since the late 20 th century.All the findings also provide references for local ecological environment construction and sustainable development.展开更多
The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision oroge...The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.展开更多
The West Qinling orogen in central China,formed from continental collision between the North China and Yangtze cratons in the Late Triassic,hosts numerous gold deposits with a total Au endowment of about 2000 t.Most d...The West Qinling orogen in central China,formed from continental collision between the North China and Yangtze cratons in the Late Triassic,hosts numerous gold deposits with a total Au endowment of about 2000 t.Most deposits were emplaced at ca.250-195 Ma and are genetically associated with the Triassic orogenesis.Here in situ U-Pb titanite dating with laser ablation inductively coupled plasma mass spectrometry indicates the Ma’anqiao gold deposit in the northern portion of this orogen has a distinctive age and under a contrasting tectonic regime.This structurally controlled gold deposit is hosted in Late Ordovician to Early Silurian sub-greenschist facies metasedimentary rocks.The gold mineralization is hosted in quartz-pyritepyrrhotite veins and pyrite-pyrrhotite disseminations in hydrothermally altered rocks,which are crosscut by K-feldspar-calcitechlorite±pyrite veins.Titanite,present both in the disseminated sulfide ores and later veins,was used for in situ U-Pb dating.Titanite from three disseminated sulfide ore samples with Th and U averaging 27.46 and 39.31 ppm(1 ppm=1μg g^(-1)),respectively,yielded lower-intercept ages of 121.1±3.1 to 120.7±3.5 Ma(2σ)in the Tera-Wasserburg diagram.Titanite from three later vein samples with much lower Th and U concentrations averaging 2.74 and 16.21 ppm,respectively,yielded overlapping ages of 120.8±3.2 to 120.3±5.8 Ma(2σ).These new titanite U-Pb ages tightly constrain the formation of the Ma’anqiao gold deposit at ca.121-120 Ma and,when combined with independent geological data,indicate it is not related to the Triassic Qinling orogeny.Rather,its formation is attributed to lithospheric thinning and destruction of the North China craton during the Late Jurassic to Early Cretaceous which has generated numerous gold deposits along the southern margin of this craton.This catastrophic event caused extensive magmatism in large areas of the North Qinling terrane and northern edge of the West Qinling orogen immediately to the south of the North China craton.The heat flux and elevated geothermal gradients associated with this magmatism could have induced prograde metamorphism of the Paleozoic sedimentary infrastructure in and beneath these areas with the derived fluids ascending along pre-existing crustal-scale regional structures to form the Ma’anqiao gold deposit.We suggest that areas in the North Qinling terrane that have been affected by the Late Mesozoic magmatism are potential targets for future exploration of the decratonization-related gold deposits.Additionally,this study highlights the use of titanite U-Pb dating as a robust geochronometer for metasedimentary rock-hosted gold deposits in Phanerozoic orogens,which has previously not been utilized.展开更多
The mafic-ultramafic assemblages,which thrustthrust into the Wushan-Tangzang boundary fault as some blocks and outcropped in the Yuanyangzhen,Lijiahe,Lubangou and Gaojiahe area,consist mainly of meta-peridotites,gabbr...The mafic-ultramafic assemblages,which thrustthrust into the Wushan-Tangzang boundary fault as some blocks and outcropped in the Yuanyangzhen,Lijiahe,Lubangou and Gaojiahe area,consist mainly of meta-peridotites,gabbros and basalts.The meta-peridotites are characterized by high SiO_(2) and MgO contents,lowΣREE,as well as their chondrite-normalized rare earth element patterns show some similarities to that of middle oceanic meta-peridotite.The basalts from the Yuanyangzhen,Lijiahe and Lubangou area are characterized by relatively high TiO_(2) content,low Al_(2)O_(3) content and Na_(2)O>>K_(2)O.Above all,it is the slight enrichment or flat REE distribution patterns and the unfractionated in HFS elements in the primitive-normalized trace elements distribution patterns that indicate these basalts are similar to that of the typical E-MORB.In comparison,the basalts from the Gaojiahe section are featured by depletion in Nb and Ta contents and enrichment in Th content which show that these were derived from an island-arc setting.From studies of the regional geology,petrology,geochemistry,geo-chronology and all above evidence,it can be suggested that the mafic-ultramafic rocks from the Wushan area are mainly dismembered E-MORB type ophiolite,which represent the fragments of the lithosphere of the Early-Paleozoic Qinling ocean.It is preferred that these rocks were formed in an initial mid-ocean ridge setting during the beginning stage of the oceanic basin spreading.This ophiolite together with the Gaojiahe island-arc basalts shows that there exists an ophiolitic mélange along the Wushan-Tangzang boundary fault,and marks the suture zone after the closure of the Qinling ocean in early Paleozoic.展开更多
The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains, which show significant geological differences after the Indo...The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains, which show significant geological differences after the Indosinian orogeny. The Fengxian-Taibai fault zone and the Meso-Cenozoic Huicheng Basin, situated at the boundary of the East and West Qinling, provide a natural laboratory for tectonic analysis and sedimentological study of intracontinental tectonic evolution of the Qin- ling Orogenic Belt. In order to explain the dynamic development of the Huicheng Basin and elucidate its post-orogenic tecton- ic evolution at the junction of the East and West Qinling, we studied the geometry and kinematics of fault zones between the blocks of West Qinling, as well as the sedimentary fill history of the Huicheng Basin. First, we found that after the collisional orogeny in the Late Triassic, post-orogenic extensional collapse occurred in the Early and Middle Jurassic within the Qinling Orogenic Belt, resulting in a series of rift basins. Second, in the Late Jurassic and Early Cretaceous, a NE-SW compressive stress field caused large-scale sinistral strike-slip faults in the Qinling Orogenic Belt, causing intracontinental escape tectonics at the junction of the East and West Qinling, including eastward finite escape of the East Qinling micro-plate and southwest lateral escape of the Bikou Terrane. Meanwhile, the strike-slip-related Early Cretaceous sedimentary basin was formed with a fight-order echelon arrangement in sinistral shear zones along the southern margin of the Huicheng fault. Overall during the Mesozoic, the Huicheng Basin and surrounding areas experienced four tectonic evolutionary stages, including extensional rift basin development in the Early and Middle Jurassic, intense compressive uplift in the Late Jurassic, formation of a strike-slip extensional basin in the Early Cretaceous, and compressive uplift in the Late Cretaceous.展开更多
In the northern West Qinling orogen(WQO), granulite-facies metamorphic rocks are recognized within the Qinling Complex. These rocks are composed of amphibole-bearing two-pyroxene granulite and garnet-sillimanite gneis...In the northern West Qinling orogen(WQO), granulite-facies metamorphic rocks are recognized within the Qinling Complex. These rocks are composed of amphibole-bearing two-pyroxene granulite and garnet-sillimanite gneiss with widespread migmatitization. We investigate three granulite-facies samples and one leucosome sample from the Qinling Complex, which are suitable for U-Pb analyses of zircon and monazite. SHRIMP and LA-ICPMS U-Pb age dating of zircon and monazite from two pelitic granulites provides weighted mean ages of 430±4 Ma(MSWD=0.88) and 433±4 Ma(MSWD=0.27), respectively.Based on the petrographic characteristics and zircon CL imagery, we postulated a ca. 430 Ma metamorphic timing for the pelitic granulites. LA-ICPMS zircon U-Pb data from an amphibole two-pyroxene granulite sample reports two weighted mean age groups:424±3 Ma(MSWD=0.45) and 402±3 Ma(MSWD=1.4), which were interpreted as granulite-facies metamorphic and retrograde ages, respectively. LA-ICPMS U-Pb dating of zircons from the leucosome sample yields a weighted mean age of 426±2 Ma(MSWD=0.3), which is interpreted as the crystallization age of the leucosome. These data indicate that the West QOB experienced early Paleozoic granulite-facies metamorphism and anatexis similar to the East QOB. However, it remains unclear whether the early Paleozoic granulite facies metamorphism resulted from an arc setting created by the northward subduction of the Shangdan ocean or from a continental collisional orogenic event.展开更多
The quantitative classification of granite and their metallogenetic relations have never been discussed.The Q-system clustering analysis and discriminant analysis methods were alternately used to quantitatively analyz...The quantitative classification of granite and their metallogenetic relations have never been discussed.The Q-system clustering analysis and discriminant analysis methods were alternately used to quantitatively analyze the 11 oxide data in granite samples from the West Qinling area of Gansu Province,and then to construct the quantitative classification series models of granite(oxide).The granites samples are divided into three categories and eight subcategories.The classification of granites is biased toward prospecting.According to the spatial correlation between eight types of granites and copper deposits,lead and zinc deposits,gold deposits,etc.(within 3 km of the intrusion)in the West Qinling area in Gansu Province,the“metallogenic related intrusions”are sought,and the prospecting target areas are defined.Furthermore,they provide reliable basis for regional geological prospecting.展开更多
基金The National Natural Science Foundation of China (41072070) provided financial support for this study
文摘The Gangcha gold deposit was discovered in 2011 in the Xiahe-Hezuo region, West Qinling Orogen, China. Five types of pyrite have been identified in the ore according to the detailed mineral paragenetic studies. Geochemical data are presented for type I pyrite （pyl） rim-core zonation and for the different types of pyrite based on in-situ laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） and electron probe microanalysis （EPMA）. The results show that pyrites are characterized with heterogeneous Au concentrations, which indicate that Au occurs mainly as micro- or nano-particle native inclusions. Time-resolved depth profiles demonstrate that As, Co and Ni occur as solid solutions in pyrite, whereas Cu, Pb, Zn and Ag occur mainly as inclusions. Trace element concentrations differ between rims and cores in pyl, and the differences also exist within different pyrite types. These differences indicate complex chemical evolution of the ore-forming fluids, and the overall geology, geochronology, and stable isotope and pyrite data suggest that the ore-forming fluids were closely linked to magmatic activity during the Triassic Period in West Qinling orogenic belt.
基金supported and funded by the Special Research Funding for Public Benefit sponsored by MLR(Grant No.200911007-21)the Fundamental Research Funds for the Central Public Welfare Research Institutes(Grant No.K1612 and K1607)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.300102279401)the Geological Survey Project(Grant No.N1916)and(Grant No.DD20190368)。
文摘The extensive Changba-Lijiagou Pb-Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite-calcite-quartz schist of the Middle Devonian Anjiacha Formation, and are structurally controlled by the fault and anticline. The ore-forming process can be divided into three main stages, based on field geological features and mineral assemblages. The mineral assemblages of hydrothermal stage I are pale-yellow coarse grain, low Fe sphalerite, pyrite with pits, barite and biotite. The mineral assemblages of hydrothermal stage II are black-brown cryptocrystalline, high Fe shalerite, pyrite without pits, marcasite or arsenopyrite replace the pyrite with pits, K-feldspar. The features of hydrothermal stage III are calcite-quartz-sulfide vein cutting the laminated, banded ore body. Forty-two sulfur isotope analyses, twenty-five lead isotope analyses and nineteen carbon and oxygen isotope analyses were determined on sphalerite, pyrite, galena and calcite. The δ34 S values of stage I(20.3 to 29.0‰) are consistent with the δ34 S of sulfate(barite) in the stratum. Combined with geological feature, inclusion characteristics and EPMA data, we propose that TSR has played a key role in the formation of the sulfides in stage I. The δ34 S values of stage II sphalerite and pyrite(15.1 to 23.0‰) are between sulfides in the host rock, magmatic sulfur and the sulfate(barite) in the stratum. This result suggests that multiple S reservoirs were the sources for S2-in stage II. The δ34 S values of stage III(13.1 to 22‰) combined with the structure of the geological and mineral features suggest a magmatic hydrothermal origin of the mineralization. The lead isotope compositions of the sulfides have 206 Pb/204 Pb ranging from 17.9480 to 17.9782, 207 Pb/204 Pb ranging from 15.611 to 15.622, and 208 Pb/204 Pb ranging from 38.1368 to 38.1691 in the three ore-forming stages. The narrow and symmetric distributions of the lead isotope values reflect homogenization of granite and mantle sources before the Pb-Zn mineralization. The δ13 CPDB and δ18 OSMOW values of stage I range from-0.1 to 2.4‰ and from 18.8 to 21.7‰. The values and inclusion data indicate that the source of fluids in stage I was the dissolution of marine carbonate. The δ13 CPDB and δ18 OSMOW values of stage II range from-4 to 1‰ and from 12.3 to 20.3‰, suggesting multiple C-O reservoirs in the Changba deposit and the addition of mantle-source fluid to the system. The values in stage III are-3.1‰ and 19.7‰, respectively. We infer that the process of mineralization involved evaporitic salt and sedimentary organic-bearing units interacting through thermochemical sulfate reduction through the isotopic, mineralogy and inclusion evidences. Subsequently, the geology feature, mineral assemblages, EPMA data and isotopic values support the conclusion that the ore-forming hydrothermal fluids were mixed with magmatic hydrothermal fluids and forming the massive dark sphalerite, then yielding the calcite-quartz-sulfide vein ore type at the last stage. The genesis of this ore deposit was epigenetic rather than the previously-proposed sedimentary-exhalative(SEDEX) type.
基金financially supported by the National Natural Science Foundation of China (Grant No. 41325007) the GPMR State Key Laboratory (grant MSFGPMR03)+1 种基金the China Geological Survey (Grant No. 1212011120570)National Demonstration Center for Experimental Mineral Exploration Education at China University of Geosciences (Wuhan)
文摘The West Qinling Orogen(WQO) in Central China Orogenic Belt contains numerous metasedimentary rock-hosted gold deposits(>2000 t Au), which mainly formed during two pulses: one previously recognized in the Late Triassic to Early Jurassic(T3 - J1) and one only recently identified in the Late Jurassic to Early Cretaceous(J3 - K1). Few studies have focused on the origin and geotectonic setting of the J3 - K1 gold deposits.Textural relationships, LA-ICP-MS trace element and sulfur isotope compositions of pyrites in hydrothermally altered T3 dykes within the J3 - K1 Daqiao deposit were used to constrain relative timing relationships between mineralization and pyrite growth in the dykes, and to characterize the source of ore fluid. These results are integrated with an overview of the regional geodynamic setting, to advance understanding of the tectonic driver for J3 - K1 hydrothermal gold systems. Pyrite in breccia-and dykehosted gold ores at Daqiao have similar chemical and isotopic compositions and are considered to be representative of J3 - K1 gold deposits in WQO. Co/Ni and sulfur isotope ratios suggest that ore fluids were derived from underlying Paleozoic Ni-and Se-rich carbonaceous sedimentary rocks. The geochemical data do not support the involvement of magmatic fluids. However, in the EQO(East Qinling Orogen), J3 - K1 deposits are genetically related to magmatism. Gold mineralization in WQO is contemporaneous with magmatic deposits in the EQO and both are mainly controlled by NE-and EWtrending structures produced by changes in plate motion of the Paleo-Pacific plate as it was subducted beneath the Eurasian continent. We therefore infer that the J3 - K1 structural regime facilitated the ascent of magma in the EQO and metamorphic fluids in the WQO with consequent differences in the character of contemporaneous ore deposits. If this is correct, then the far-field effects of subduction along the eastern margin of NE Asia extended 1000's of km into the continental interior.
基金financially supported by the National Natural Science Foundation of China (41372207)China Geological Survey (12120115069401, DD20160201-04, DD20160022-02, and DD20160101)the China Scholarship Councilprogram (201408110143)
文摘Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. WeaMy peraluminous granite porphyry （A/ CNK=1.10-1.15） is enriched in LREE, depleted in HREE with Nb-Ta-Ti anomalies, and displays subduction-related geochemistry. Quartz porphyry is strongly peraluminous （A/CNK=1.64-2.81） with highly evolved components, characterized by lower TiO2, REE contents, Mg#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and CI. LA- ICP-MS zircon U-Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, εHf（t） values of Triassic magmatic zircons from the granite and quartz porphyries are -14.2 to -9.1 （with an exception of ＋4.1） and -10.8 to -8.6 respectively, indicating a crustal-dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc-related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east.
基金jointly provided by the National Natural Science Foundation of China (Grant Nos. 41421002, 41730426, 41272092, and 41030423)MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest UniversityNorthwest University Graduate Innovation and Creativity Fund (YZZ17190)
文摘The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman’s plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ34S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.
基金financially supported by the National Natural Science Foundation (No. 41403032)the National Crisis Mine Prospecting Foundation (No. 20089934)+1 种基金the discipline construction project of Guangzhou City University of Technology (No. 60-CQ190025)supported by the Exploration Team 711 of Northwest Mining and Geology Group Co., Ltd
文摘The West Qingling Orogen is endowed with more than 1100 t gold resources and with 50 gold deposits,ranking it the third-largest gold province in China.The Jianchaling giant gold deposit with 52 t gold reserve is a typical orogenic gold deposit in West Qinling Orogen.The deposit lacks accurate and direct metallogenic age.Five pyrite samples collected from the quartz-polymetallic veins yielded Re–Os isochron age of 206.3±2.7 Ma and an initial187 Os/188 Os ratio of 0.1154±0.0016(MSWD=0.54).The pyrites were analyzed by the electron microprobe(EMPA),and the results show that the iron content ranges from 45.1 to 47.8 wt.%,the sulfur content ranges from 52.0 to 53.5 wt.%,and the gold content varies from0.022 to 0.035%.The higher gold content means that gold is closely related to pyrite,which is a gold-bearing mineral.Moreover,the age is very close to the previous fuchsite40 Ar/39 Ar isotopic ages of 199–194 Ma,which indicates that the gold mineralization at Jianchaling has begun in the Late Triassic(206 Ma),and continued into the Early Jurassic.Through summary and comparison,it is found that the gold metallogenic age of the southern ore belt of the Mian-Lue Suture belt in the West Qinling is younger than that of the northern ore belt,suggesting that the gold deposits in the southern ore belt such as Jianchaling were formed in the transitional period from oceanic subduction to continental collision.
基金Supported by National Natural Science Foundation of China(41171109)Key Research Program of the Chinese Academy of Sciences(KZZD-EW-06)
文摘As the main content of terrestrial ecosystem study,vegetation coverage change has gained extensive attention in the process of global climate change and sustainable development recently.Based on MODIS NDVI data from June to October during 2000-2010,taking Longnan City as a case area,this paper develops the calculation method of vegetation coverage(VC) by using Pixel Dichotomy model and analyzes the spatial-temporal variation of vegetation coverage in the West Qinling region by using simple linear regression and standard deviation method.The results show that vegetation coverage remains stable and is significantly correlated with temperature and precipitation during the decade.The vegetation coverage of 90% of study area shows stability with small annual variation and also is consistent with the spatial distribution of forest land;the vegetation coverage in the remaining study areas shows a growing trend with significant variation and also is consistent with the spatial distribution of farmland and grassland,especially in Huicheng Basin,Xili Basin and adret slope of Bailongjiang River Valley,indicating that Project about the Conversion of Degraded Farmland into Forest has made a great contribution to vegetation coverage increase.This paper proves the effect of ecology construction in the West Qinling region since the late 20 th century.All the findings also provide references for local ecological environment construction and sustainable development.
基金supported financially by the National Nature Sciences Foundation of China(Nos.41872235,42172236,41872233,42072267,41802234,41602229 and 41502191)China Scholarship Council(No.201806565026)+3 种基金Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2019JM-312,2019JQ-090 and 2019JQ-209)China Geological Survey(Nos.12120114041201 and DD2016007901)China Postdoctoral Science Foundation(No.2016M592726)the Fundamental Research Funds for the Central Universities of China(Nos.300102270202,300103120009,202110710062,300103183081,300104282717,300102279204 and 201810710233).
文摘The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.
基金financially supported by the National Natural Science Foundation of China(Grant No.42130814)。
文摘The West Qinling orogen in central China,formed from continental collision between the North China and Yangtze cratons in the Late Triassic,hosts numerous gold deposits with a total Au endowment of about 2000 t.Most deposits were emplaced at ca.250-195 Ma and are genetically associated with the Triassic orogenesis.Here in situ U-Pb titanite dating with laser ablation inductively coupled plasma mass spectrometry indicates the Ma’anqiao gold deposit in the northern portion of this orogen has a distinctive age and under a contrasting tectonic regime.This structurally controlled gold deposit is hosted in Late Ordovician to Early Silurian sub-greenschist facies metasedimentary rocks.The gold mineralization is hosted in quartz-pyritepyrrhotite veins and pyrite-pyrrhotite disseminations in hydrothermally altered rocks,which are crosscut by K-feldspar-calcitechlorite±pyrite veins.Titanite,present both in the disseminated sulfide ores and later veins,was used for in situ U-Pb dating.Titanite from three disseminated sulfide ore samples with Th and U averaging 27.46 and 39.31 ppm(1 ppm=1μg g^(-1)),respectively,yielded lower-intercept ages of 121.1±3.1 to 120.7±3.5 Ma(2σ)in the Tera-Wasserburg diagram.Titanite from three later vein samples with much lower Th and U concentrations averaging 2.74 and 16.21 ppm,respectively,yielded overlapping ages of 120.8±3.2 to 120.3±5.8 Ma(2σ).These new titanite U-Pb ages tightly constrain the formation of the Ma’anqiao gold deposit at ca.121-120 Ma and,when combined with independent geological data,indicate it is not related to the Triassic Qinling orogeny.Rather,its formation is attributed to lithospheric thinning and destruction of the North China craton during the Late Jurassic to Early Cretaceous which has generated numerous gold deposits along the southern margin of this craton.This catastrophic event caused extensive magmatism in large areas of the North Qinling terrane and northern edge of the West Qinling orogen immediately to the south of the North China craton.The heat flux and elevated geothermal gradients associated with this magmatism could have induced prograde metamorphism of the Paleozoic sedimentary infrastructure in and beneath these areas with the derived fluids ascending along pre-existing crustal-scale regional structures to form the Ma’anqiao gold deposit.We suggest that areas in the North Qinling terrane that have been affected by the Late Mesozoic magmatism are potential targets for future exploration of the decratonization-related gold deposits.Additionally,this study highlights the use of titanite U-Pb dating as a robust geochronometer for metasedimentary rock-hosted gold deposits in Phanerozoic orogens,which has previously not been utilized.
基金Supported by the National Natural Science Foundation of China(Grant Nos.40472115 and 40234041)
文摘The mafic-ultramafic assemblages,which thrustthrust into the Wushan-Tangzang boundary fault as some blocks and outcropped in the Yuanyangzhen,Lijiahe,Lubangou and Gaojiahe area,consist mainly of meta-peridotites,gabbros and basalts.The meta-peridotites are characterized by high SiO_(2) and MgO contents,lowΣREE,as well as their chondrite-normalized rare earth element patterns show some similarities to that of middle oceanic meta-peridotite.The basalts from the Yuanyangzhen,Lijiahe and Lubangou area are characterized by relatively high TiO_(2) content,low Al_(2)O_(3) content and Na_(2)O>>K_(2)O.Above all,it is the slight enrichment or flat REE distribution patterns and the unfractionated in HFS elements in the primitive-normalized trace elements distribution patterns that indicate these basalts are similar to that of the typical E-MORB.In comparison,the basalts from the Gaojiahe section are featured by depletion in Nb and Ta contents and enrichment in Th content which show that these were derived from an island-arc setting.From studies of the regional geology,petrology,geochemistry,geo-chronology and all above evidence,it can be suggested that the mafic-ultramafic rocks from the Wushan area are mainly dismembered E-MORB type ophiolite,which represent the fragments of the lithosphere of the Early-Paleozoic Qinling ocean.It is preferred that these rocks were formed in an initial mid-ocean ridge setting during the beginning stage of the oceanic basin spreading.This ophiolite together with the Gaojiahe island-arc basalts shows that there exists an ophiolitic mélange along the Wushan-Tangzang boundary fault,and marks the suture zone after the closure of the Qinling ocean in early Paleozoic.
基金supported by National Natural Science Foundation of China(Grant Nos.40802051&41190074)MOST Special Fund from the State Key Laboratory of Continental DynamicsNorthwest University
文摘The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains, which show significant geological differences after the Indosinian orogeny. The Fengxian-Taibai fault zone and the Meso-Cenozoic Huicheng Basin, situated at the boundary of the East and West Qinling, provide a natural laboratory for tectonic analysis and sedimentological study of intracontinental tectonic evolution of the Qin- ling Orogenic Belt. In order to explain the dynamic development of the Huicheng Basin and elucidate its post-orogenic tecton- ic evolution at the junction of the East and West Qinling, we studied the geometry and kinematics of fault zones between the blocks of West Qinling, as well as the sedimentary fill history of the Huicheng Basin. First, we found that after the collisional orogeny in the Late Triassic, post-orogenic extensional collapse occurred in the Early and Middle Jurassic within the Qinling Orogenic Belt, resulting in a series of rift basins. Second, in the Late Jurassic and Early Cretaceous, a NE-SW compressive stress field caused large-scale sinistral strike-slip faults in the Qinling Orogenic Belt, causing intracontinental escape tectonics at the junction of the East and West Qinling, including eastward finite escape of the East Qinling micro-plate and southwest lateral escape of the Bikou Terrane. Meanwhile, the strike-slip-related Early Cretaceous sedimentary basin was formed with a fight-order echelon arrangement in sinistral shear zones along the southern margin of the Huicheng fault. Overall during the Mesozoic, the Huicheng Basin and surrounding areas experienced four tectonic evolutionary stages, including extensional rift basin development in the Early and Middle Jurassic, intense compressive uplift in the Late Jurassic, formation of a strike-slip extensional basin in the Early Cretaceous, and compressive uplift in the Late Cretaceous.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41630207, 41572180)the China Geological Survey Project (Grant No. 12120115027001)
文摘In the northern West Qinling orogen(WQO), granulite-facies metamorphic rocks are recognized within the Qinling Complex. These rocks are composed of amphibole-bearing two-pyroxene granulite and garnet-sillimanite gneiss with widespread migmatitization. We investigate three granulite-facies samples and one leucosome sample from the Qinling Complex, which are suitable for U-Pb analyses of zircon and monazite. SHRIMP and LA-ICPMS U-Pb age dating of zircon and monazite from two pelitic granulites provides weighted mean ages of 430±4 Ma(MSWD=0.88) and 433±4 Ma(MSWD=0.27), respectively.Based on the petrographic characteristics and zircon CL imagery, we postulated a ca. 430 Ma metamorphic timing for the pelitic granulites. LA-ICPMS zircon U-Pb data from an amphibole two-pyroxene granulite sample reports two weighted mean age groups:424±3 Ma(MSWD=0.45) and 402±3 Ma(MSWD=1.4), which were interpreted as granulite-facies metamorphic and retrograde ages, respectively. LA-ICPMS U-Pb dating of zircons from the leucosome sample yields a weighted mean age of 426±2 Ma(MSWD=0.3), which is interpreted as the crystallization age of the leucosome. These data indicate that the West QOB experienced early Paleozoic granulite-facies metamorphism and anatexis similar to the East QOB. However, it remains unclear whether the early Paleozoic granulite facies metamorphism resulted from an arc setting created by the northward subduction of the Shangdan ocean or from a continental collisional orogenic event.
基金This work was supported by Mineral Resources Compensation Project of Gansu Province(2017D18)Basic Geological Survey Project of Gansu Province(20151616).
文摘The quantitative classification of granite and their metallogenetic relations have never been discussed.The Q-system clustering analysis and discriminant analysis methods were alternately used to quantitatively analyze the 11 oxide data in granite samples from the West Qinling area of Gansu Province,and then to construct the quantitative classification series models of granite(oxide).The granites samples are divided into three categories and eight subcategories.The classification of granites is biased toward prospecting.According to the spatial correlation between eight types of granites and copper deposits,lead and zinc deposits,gold deposits,etc.(within 3 km of the intrusion)in the West Qinling area in Gansu Province,the“metallogenic related intrusions”are sought,and the prospecting target areas are defined.Furthermore,they provide reliable basis for regional geological prospecting.
