Qingyan Tang - Academia.edu (original) (raw)

Papers by Qingyan Tang

Research paper thumbnail of The origin of volatiles in the Emeishan large igneous province, China: Constraints from chemical and C–He–Ar isotopic compositions of volatiles in picrites and basalts

Geological Journal

The Emeishan large igneous province (LIP) consists of Permian flood basalts and coeval intrusive ... more The Emeishan large igneous province (LIP) consists of Permian flood basalts and coeval intrusive rocks with compositions varying from mafic–ultramafic rocks to syenites and granites. The volatiles in the Emeishan LIP are dominated by H2O with high H2, indicating that the plume‐derived magma was generated under a reduced condition. Picrite has minor contents of H2S without detectable SO2, and the basalt samples show no detectable H2S and SO2, indicating that the basaltic magma may have undergone sulphur‐saturation during magma evolution. The δ13C values of CO2 and CH4 in picrites and basalts are between the values of mantle and crustal organic carbon. This, together with the distribution patterns among CH4 homologue, indicates contribution of recycled sediments to the Emeishan mantle‐derived magma. The 3He/4He ratios of volatiles extracted from olivine and pyroxene phenocrysts of picrites vary from 0.01 to 0.66 Ra, and those from pyroxene separates of olivine websterite samples in th...

Research paper thumbnail of Origin of highly variable and unusually low δ7Li in mineral separates from ultramafic intrusive rocks in a convergent tectonic setting in the Tibetan plateau

Research paper thumbnail of The chemical and carbon isotopic compositions of volatiles in Cenozoic high-potassic basalts in western Qinling, China and their mantle geodynamic implications

Acta Petrologica Sinica, 2012

India-Asia continental plate subduction and collision lead to widespread Cenozoic potassic-ultrap... more India-Asia continental plate subduction and collision lead to widespread Cenozoic potassic-ultrapotassic magmatism in the Tibet which provides a valuable indicator of the composition and nature of the deep mantle beneath the Tibet. The Cenozoic mantle xenolith bearing high-potassic basalts (7.1 similar to 23Ma) distributed in western Qinling, western China are a window to probe the mantle composition and geodynamics beneath north-eastern margin of Tibet Plateau. The chemical and carbon isotopic compositions of volatiles in olivine(Olv) and plagioclase (P1) phenocrysts and matrix (Mtx) of Cenozoic high-potassic basalts in western Qinling have been determined by stepwise heating mass spectrometer to reveal volatile sources and geodynamic implications under the system of continental plate subduction and collision. The results showed that the volatiles in high-potassic basalts were released by stage at temperature intervals of 200 similar to 400 degrees C, 400 similar to 800 degrees C a...

Research paper thumbnail of Sr-Nd-Hf-O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide ore deposits in the Emeishan large igneous province

Geochimica et Cosmochimica Acta, 2021

O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide... more O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide ore deposits in the Emeishan large igneous province, Geochimica et Cosmochimica Acta (2020), doi:

Research paper thumbnail of The origin of Permian Pobei ultramafic complex in the northeastern Tarim craton, western China: Evidences from chemical and C-He-Ne-Ar isotopic compositions of volatiles

Chemical Geology, 2017

The large Pobei Permian layered mafic-ultramafic complex in the northeastern margin of Tarim crat... more The large Pobei Permian layered mafic-ultramafic complex in the northeastern margin of Tarim craton, western China is related temporally and spatially to adjacent Tarim Large Igneous Province (LIP), and hosts Ni-Cu sulfide mineralization. The chemical composition, carbon and noble gas isotopic compositions of volatiles in olivine, pyroxene and plagioclase minerals of the Pobei complex have been measured to reveal the composition and origin of magmatic volatiles, mantle information and dynamic settings. The magmatic volatiles in the Pobei complex are composed of dominant H 2 O (av. 3284.3 mm 3 •STP/g, STP = standard temperature and pressure), H 2 (449.1) and CO 2 (449.4), indicated a H 2 O-rich reduced magmatic condition. The δ 13 C values of CH 4 , C 2 H 6 , C 3 H 8 and C 4 H 10 show normal or (partial) reversal distribution pattern with carbon number. The δ 13 C values of CO 2 and CH 4 range among mantle, crust (methane oxidation) and thermogenic origins. The 3 He/ 4 He (1.13 to 6.15 Ra) and 40 Ar/ 36 Ar (326.4 to 1004.3) ratios are plotted on a trend of the mantle plume to atmosphere. The high 20 Ne/ 22 Ne and low 21 Ne/ 22 Ne ratios fall along the mass fractionation line. The volatile compositions indicated that the Pobei mafic-ultramafic complex could be originated from the staged partial melting of heterogeneous H 2 O-rich mantle sources triggered by a mantle plume, the air and crust components from subducted altered oceanic crust have been added into the Pobei magma.

Research paper thumbnail of Molecular and carbon isotopic variation in 3.5 years shale gas production from Longmaxi Formation in Sichuan Basin, China

Marine and Petroleum Geology, 2017

A time series of produced shale gas samples from Lower Silurian Longmaxi Formation (Fm.) were col... more A time series of produced shale gas samples from Lower Silurian Longmaxi Formation (Fm.) were collected from six production wells during 3.5 years production period from the Weiyuan and Changning shale gas pilots in Sichuan basin, China. The molecular compositions and carbon isotopes of CH 4 , C 2 H 6 , C 3 H 8 and CO 2 , and the hydrogen isotope of methane were analyzed for these samples by an integrated method of gas chromatography combined with mass spectrometry. The results showed that the produced shale gases are dominated by CH 4 (90.1e99.3%) with minor C 2 H 6 (0.3e0.8%) and non-hydrocarbon gases, and have low wetness (0.3e0.8%). The non-hydrocarbon gases are mainly CO 2 and N 2 , and trace amount of He. The Longmaxi shale gases display completed reversal pattern of carbon isotopic compositions with carbon number (i.e., d 13 C 1 > d 13 C 2 > d 13 C 3) except for Wells W201 and W201-H1 with normal patterns between C 2 H 6 and C 3 H 8 (i.e., d 13 C 2 < d 13 C 3), and it is a mixture of oil cracking gas and kerogen cracking gas at high-over level of thermal maturity. Some CO 2 (d 13 C CO2 ranging from À2.5 to À6.0‰) is mainly derived from the decomposition of carbonate minerals. CH 4 concentration and the carbon isotopes of methane and ethane during 3.5 years shale gas production from year 2012 to 2016 displayed small fluctuations, which possibly suggested that gas supply from shale matrix to fracture network after hydraulic fracturing is abundant. The Weiyuan shale gases show larger decrease of CH 4 content than the Changning shale gases, indicated more adequate supply in the Changning area. The difference in d 13 C 1 values between horizontal and vertical wells on the same drilling site in the Weiyuan pilot indicated that the vertical heterogeneity of Lower Silurian Longmaxi shale plays an important role to shale gas production. Interestingly, the shale gases in the Weiyuan pilot display much lighter d 13 C 1 (À34.46 to À36.82‰) and d 13 C 2 (À37.59 to À41.89‰) values than those (d 13 C 1 ¼ À27.18eÀ27.27‰, d 13 C 2 ¼ À33.70eÀ34.14‰) in the Changning pilot. The difference in carbon isotopic compositions in Weiyuan and Changning pilots mainly attributes to mixing between varied proportion of oil cracking gas and kerogen cracking gas because of the regional heterogeneity of the Longmaxi marine shale, in particular amount of residual oil retained in organic matter rich shale. The isotopic difference between Weiyuan and Changning shale gases doesn't disappear in the period about 3.5 years of shale gas development, which further suggests the regional heterogeneity of retained residual oil exists in the Longmaxi Fm. marine shale.

Research paper thumbnail of Noble gas isotopic variations and geological implication of Longmaxi shale gas in Sichuan Basin, China

Marine and Petroleum Geology, 2017

The large difference in carbon isotopic compositions of shale gases from the Lower Silurian Longm... more The large difference in carbon isotopic compositions of shale gases from the Lower Silurian Longmaxi Formation marine organic-rich shales between Changning and Weiyuan areas in Sichuan Basin, China is a still debate issue. In this study, 30 produced shale gas samples were collected during 3 years production period and analyzed for noble gas (He, Ne and Ar) abundances and isotopic compositions to reveal the origin and variation causes of shale gases. The results show that the Longmaxi shale gases show low 3 He/ 4 He and 20 Ne/ 22 Ne, and varied but high 21 Ne/ 22 Ne and 40 Ar/ 36 Ar ratios. The Weiyuan shale gases are characterized by low 3 He/ 4 He, high 40 Ar/ 36 Ar ratios and varied 4 He and 40 Ar abundances, and a large increase in 40 Ar contents and a slight decrease in 40 Ar/ 36 Ar ratios display during 3 years shale gas production period from Jan. 2014 to Jun. 2016. Whereas the Changning shale gases are characterized by low and varied 3 He/ 4 He ratios and high 4 He and 40 Ar abundances, and small fluctuations in 40 Ar contents and 40 Ar/ 36 Ar ratios exhibit during 3 years production period. In addition, the shale gases produced from horizontal wells in the Weiyuan area possessed higher 40 Ar and 40 Ar/ 36 Ar ratio than that those from vertical wells at same well site. The noble gas isotopic compositions and variation of Longmaxi shale gases suggested that they are originated mainly from crust, air saturated fluid (ASF) and radiogenic accumulation. The variation of 40 Ar and 4 He contents during shale gas production mainly reflects the degree of shale gas source supply from mineral matrix to fracture network, and the greater increases in 40 Ar and 4 He contents with production time show less abundant shale gas supply. Therefore, the increase trend of 40 Ar contents with shale gas production time in the Weiyuan area during 3 years production period possibly suggests less adequate shale gas supply. In contrast, the uniform or nearly constant of 40 Ar content through production time in the Changing area indicates abundant supply of shale gas sources from mineral matrix, resulting in less production decline. Variation in 4 He and 40 Ar contents through shale gas production time could be sensitive indicators of abundant or depleted shale gas source supply.

Research paper thumbnail of The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes

Chemical Geology, 2017

The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW Chi... more The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Chemge(2017),

Research paper thumbnail of Neoproterozoic subduction-related basaltic magmatism in the northern margin of the Tarim Craton: Implications for Rodinia reconstruction

Precambrian Research, 2016

Abstract A single mantle plume model for the Neoproterozoic mafic-ultramafic intrusive rocks (760... more Abstract A single mantle plume model for the Neoproterozoic mafic-ultramafic intrusive rocks (760–820 Ma) in the northern rim of the Tarim Craton (Kuluketage, Xinjiang, China) is not supported by the protracted nature of magma emplacement that does not show a hot spot track, and whole-rock trace element compositions that clearly show arc signatures. New and previous zircon U-Pb age data reveal an age difference of up to 11 myr for a single mafic-ultramafic intrusive complex and an age difference of up to 32 myr for two mafic-ultramafic intrusive complexes separated by only ∼10 km. Such age differences are more than 2–5 times the analytical uncertainties. No major faults are present between the two intrusive complexes with different ages so their original distance is still well preserved. In addition, the age change of the mafic-ultramafic intrusive rocks in the region occurs in different directions. The temporal-spatial distribution of these rocks can be well explained by subduction-related magmatism that can last for a very long period of time at the same location. The protracted Neoproterozoic mafic-ultramafic intrusive rocks in the Kuluketage district are all characterized by moderate light rare earth element enrichments, pronounced negative Nb-Ta anomalies and low eNd(t) values (1 to −11) coupled with elevated initial 87Sr/86Sr ratios (0.706–0.71), which are consistent with the products of arc basalts contaminated with crustal materials. The results from this study support the notion that the northern margin of the Tarim Craton was part of the Neoproterozoic Circum-Rodinia Subduction System.

Research paper thumbnail of Neoproterozoic Magmatism in the Northern Margin of the Tarim Craton: Implications for Rodinia Reconstruction

Acta Geologica Sinica - English Edition, 2016

Research paper thumbnail of The molecular and carbon isotopic constrains on origin and storage of Longmaxi Formation shale gas in Changning area, Sichuan Basin, China

Interpretation, 2015

We have developed a vacuum-crushing method for the extraction of gases stored in shale for the de... more We have developed a vacuum-crushing method for the extraction of gases stored in shale for the determination of gas yield, chemical composition, and carbon isotopic composition by online gas-chromatography and mass spectrometry. Analysis of the evacuation and parallel experiments showed low standard deviation and good reproducibility. This approach significantly improved the detection limits for trace-gas analysis in shale and measured multiple nonhydrocarbon gas components in a single run. We analyzed the chemical and carbon isotopic compositions of the gases released by one-step vacuum crushing from nineteen samples of organic-rich Longmaxi Formation (Fm.) shale in Changning outcrop, Sichuan Basin, China, and we studied the main controls on gas chemistry of retained gas in the Longmaxi Shale. The results showed that the crushed gas is high in [Formula: see text] and [Formula: see text] but low in [Formula: see text]. The crushed gas has obviously lower [Formula: see text] ratios t...

Research paper thumbnail of Carbon Isotope Reversals of Changning-Weiyuan Region Shale Gas, Sichuan Basin

Acta Geologica Sinica - English Edition, 2015

Research paper thumbnail of U–Pb age and Hf isotopes of zircon from basaltic andesite and geochemical fingerprinting of the associated picrites in the Emeishan large igneous province, SW China

Mineralogy and Petrology, 2014

Research paper thumbnail of The Ore-forming Conditions of the Zhubu Magmatic Ni-Cu-PGE Deposit, Emeishan Large Igneous Province, SW China: Constraints from Hf-Sr-Nd-C Isotopic Compositions and Volatile Chemical Compositions

Acta Geologica Sinica - English Edition, 2014

The Zhubu magmatic Ni-Cu-PGE deposit is hosted in a small mafic-ultramafic intrusion which belong... more The Zhubu magmatic Ni-Cu-PGE deposit is hosted in a small mafic-ultramafic intrusion which belongs to the Permian Emeishan large igneous province (ELIP) in SW China and northern Vietnam. Most of the mafic-ultramafic intrusions in the ELIP host world-class magmatic Fe-Ti-V oxide deposits; only a few of them host magmatic Ni-Cu-PGE sulfide deposits including the Zhubu deposit. A better understanding of fundamental controls on sulfide mineralization in the Zhubu intrusion is important in mineral exploration.

Research paper thumbnail of Detrital zircon constraint on the timing of amalgamation between Alxa and Ordos, with exploration implications for Jinchuan-type Ni–Cu ore deposit in China

Precambrian Research, 2014

Abstract The Jinchuan Ni–Cu deposit, which is the largest single magmatic sulfide ore deposit in ... more Abstract The Jinchuan Ni–Cu deposit, which is the largest single magmatic sulfide ore deposit in the world, is hosted by a mafic-ultramafic intrusion in the Alxa block, northwestern China. The timing of amalgamation between the Alxa block and the adjacent Ordos block, which is important for Precambrian reconstruction of North China Craton and the search for another Jinchuan-type ore deposit, is contentious. The age distribution patterns of detrital zircon crystals with Precambrian ages from the Devonian and older sedimentary rocks of the Alxa and Ordos blocks are similar. This supports the traditional view that the Alxa and Ordos blocks were amalgamated in the Paleoproterozoic along the 1.95 Ga Khondalite Belt, long before the emplacement of the ∼830 Ma Jinchuan intrusion. The U–Pb–Lu–Hf isotope data of comagmatic zircon crystals from the Jinchuan intrusion, together with its whole-rock Sm–Nd isotopes and trace element compositions given previously by other researchers, indicate that the Jinchuan ore-bearing intrusion is the product of continental rift-related basaltic magmatism which took place during the early stage of Rodinia breakup. Based on these observations, we conclude that in addition to the Alxa block, the adjacent regions in the North China Craton such as the Ordos basin, the Khondalite belt and the Yinshan terrane are most promising for new discoveries of Jinchuan-type Ni–Cu ore deposits.

Research paper thumbnail of The Origin of Ni-Cu-PGE Sulfide Mineralization in the Margin of the Zhubu Mafic-Ultramafic Intrusion in the Emeishan Large Igneous Province, Southwestern China

Economic Geology, 2013

The Zhubu magmatic Ni-Cu-PGE sulfide deposit is hosted in a mafic-ultramafic intrusion which is p... more The Zhubu magmatic Ni-Cu-PGE sulfide deposit is hosted in a mafic-ultramafic intrusion which is part of the Emeishan large igneous province in southwest China. The Zhubu intrusion is composed of a layered sequence (750 × 400 × 600 m) with subhorizontal modal layering and a subvertical marginal zone of <40 m across. The marginal zone is composed of lherzolite and olivine websterite with minor gabbroic rocks. The layered sequence is composed of lherzolite, websterite, gabbro, and gabbrodiorite from the base to the top. The Zhubu intrusion can be explained by two stages of formation, an early conduit stage for the marginal zone and a late in situ differentiation stage for the layered sequence. Most important Ni-Cu-PGE mineralization in the intrusion occurs as disseminated sulfides within the marginal zone. Olivine crystals from the marginal zone contain 81 to 84 mol % Fo and 1,600 to 1,900 ppm Ni. The rims of zoned olivine phenocrysts in the Emeishan picrites have similar Fo contents but significantly higher Ni contents (2,300−2,600 ppm). The olivine data indicate that the parental magma of the Zhubu ultramafic rocks is similar to the transporting magma of the Emeishan picrites in MgO/FeO ratios but depleted in Ni due to sulfide segregation before olivine crystallization. The initial concentrations of PGE in the Zhubu magma, estimated from bulk sulfide compositions, are 7 ppb Pd, 9.3 ppb Pt, and 0.8 ppb Ir, similar to the values in the Emeishan picrites. Like the Emeishan picrites, the Zhubu intrusive rocks are characterized by light REE enrichments. Negative Nb anomalies relative to Th and Ta, which are rare in the Emeishan picrites, are present in the Zhubu samples. The (87 Sr/ 86 Sr)i and εNd values of the Zhubu intrusive rocks vary from 0.709591 to 0.710692 and from-2 to-3, respectively. The trace element and isotope compositions indicate that the Zhubu magma was contaminated by crustal materials, supporting the interpretation that sulfide saturation in the magma was triggered by crustal contamination. The area where the lower part of the conduit may have been brought up by faulting should be the focus of future exploration at Zhubu.

Research paper thumbnail of PGE and Isotope (Hf-Sr-Nd-Pb) Constraints on the Origin of the Huangshandong Magmatic Ni-Cu Sulfide Deposit in the Central Asian Orogenic Belt, Northwestern China

Economic Geology, 2013

Many magmatic Ni-Cu sulfide deposits have been found to be associated with Permian basaltic magma... more Many magmatic Ni-Cu sulfide deposits have been found to be associated with Permian basaltic magmatism in the Central Asian orogenic belt, Xinjiang, China. The style of basaltic magmatism and the origin of associated Ni-Cu sulfide deposits in the region are highly debated. The Huangshandong mafic-ultramafic intrusion is at the center of the debate mainly because it hosts the largest magmatic Ni-Cu sulfide deposit in the region. In this paper we report integrated petrological and geochemical data for the Huangshandong Ni-Cu sulfide deposit. The host intrusion consists of a massive gabbronorite unit and a layered sequence, which is composed of two to three ultramafic layers overlain by gabbroic rocks with visible modal layering. Important sulfide mineralization in the intrusion is associated with the ultramafic rocks and massive gabbronorite. The ultramafic rocks and massive gabbronorite are characterized by moderate enrichments in light rare earth elements (LREE), pronounced negative Nb-Ta anomalies relative to Th and La, positive εNd (t = 274 Ma) values (6.6−8.3), low initial 87 Sr/ 86 Sr ratios (0.7031−0.7038), low initial 206 Pb/ 204 Pb ratios (17.7−18), and positive εHf values of zircon (14−17). These data are consistent with mixing between a depleted mantle-derived magma and a granitic melt formed by partial melting of a juvenile arc crust as a result of mafic magma underplating. Olivine crystals enclosed in large clinopyroxene and plagioclase crystals from the ultramafic rocks have Fo contents up to 83 mol %. The contents of Ni in the olivine crystals decrease rapidly with Fo contents, indicating sulfide segregation from magma during olivine crystallization. Numerical modeling using bulk sulfide compositions and constraints from olivine-liquid relationships reveals that the parental magma of the intrusion was significantly depleted in PGE and contained <7 wt % MgO. Depletion of PGE in the magma can be explained by previous sulfide segregation possibly due to magma mixing in a staging chamber. Fractional crystallization and addition of external sulfides from juvenile arc crust appear to have played a critical role in triggering the second event of sulfide segregation to form the deposit. We believe that the Huangshandong sulfide ore-bearing intrusion formed by basaltic magmatism related to postsubduction delamination and asthenosphere upwelling instead of a deep-seated mantle plume.

Research paper thumbnail of Noble gas isotopic constraints on the origin and evolution of the Jinchuan Ni–Cu–(PGE) sulfide ore-bearing ultramafic intrusion, Western China

Research paper thumbnail of Association of Mg-rich Olivine with Magnetite as a Result of Brucite Marble Assimilation by Basaltic Magma in the Emeishan Large Igneous Province, SW China

Journal of Petrology, 2017

An unusual feature of the magmatic Fe-Ti oxide deposits associated with layered intrusions in the... more An unusual feature of the magmatic Fe-Ti oxide deposits associated with layered intrusions in the Permian Emeishan large igneous province (LIP) in SW China is the association of the mineralization with olivine that is significantly more Mg-rich than those that occur elsewhere. A working hypothesis for the production of Mg-rich olivine is that significant assimilation of carbonate occurred during the formation of the Fe-Ti oxide deposits in the Emeishan LIP. This study provides several lines of supporting evidence from a coeval picritic dyke in the footwall of the Panzhihua layered intrusion at Zhujiabaobao. Country rocks to the Zhujiabaobao picritic dyke are brucite marbles. Olivine phenocrysts in the dyke have Fo contents varying from 79 to 91 mol %. The most Mg-rich olivine phenocrysts (Fo89-91) are present in the margins of the dyke and contain undissolved calcite. Olivine phenocrysts in the marginal sample show reversed zoning in Fo content and contain 2020% lower Ni than those with similar Fo contents in the coeval picrites emplaced in the nearby area. Olivine-hosted oxide inclusions in this sample are exclusively Cr-magnetite (calculated atomic Fe 3þ /Cr 3þ > 1) instead of chromite or Cr-spinel (calculated atomic Fe 3þ /Cr 3þ < 1) that characterizes the coeval picrites. Within the dyke olivine phenocrysts with different ranges of Fo content (Fo89-91 versus Fo78-83) have similar Mn contents but different Ni contents. The most Mg-rich olivine phenocrysts have Ni contents that are 20-30% less than those for the more Fe-rich olivine phenocrysts. Diopside crystals associated with the most Mg-rich olivine phenocrysts contain higher Fe 2 O 3 /FeO than those associated with the more Fe-rich olivine phenocrysts. The dyke samples with different olivine compositions have similar e Nd values (1Á4-2) but contrasting Sr isotope compositions. The sample with the most Mg-rich olivine (Fo89-90) has the highest initial 87 Sr/ 86 Sr ratio (0Á7054), whereas samples with more Fe-rich olivine (Fo78-83) have lower initial 87 Sr/ 86 Sr ratios (0Á7046-0Á7049). The results of mixing calculations indicate that up to 2025 wt % assimilation of brucite marble by basaltic magma with a composition similar to that of the average of the coeval high-Ti basalts can readily explain the observed mineralogical and isotopic variations within the dyke. The results from the dyke show that carbonate assimilation by basaltic magma is an efficient way to produce the association of magnetite with olivine that is anomalously rich in magnesium.

Research paper thumbnail of Mineralogy and Geochemistry of Pyrite and Arsenopyrite from the Zaozigou Gold Deposit in West Qinling Orogenic Belt, Central China: Implications for Ore Genesis

Resource Geology, 2019

The Zaozigou gold deposit lies in the West Qinling orogenic belt, Gansu Province, China. It is on... more The Zaozigou gold deposit lies in the West Qinling orogenic belt, Gansu Province, China. It is one of the largest gold deposits, and the orebodies are hosted in fine-grained slates intercalated with limestone of the Middle-Triassic Gulangdi Formation and varied dykes. The gold orebodies are strictly controlled by the NE-, NW-, and SN-trending tensional and shearing faults with high dipping angle. The mineralogy and geochemistry of pyrite and arsenopyrite are measured by electron microprobe. Pyrite has up to 0.12 wt.% Au, and arsenopyrite contains up to 0.17 wt.% Au. The antithetic correlation between S and As indicates the substitution of As for S in pyrite, and arsenic occurs in anionic As 1− state in the pyrite structure under the reduced conditions. Pyrite has relatively high Co (~364-2248 ppm) but relatively low Ni (~109-497 ppm) contents, with Co/Ni ratios ranging from~1.63 to 10.50, indicating that the deposit originated from a volcanogenic fluid and remobilized by hydrothermal fluid. Au in arsenopyrite occurs as cationic Au in solid solution, whereas Au in pyrite is in solid solution and metal nanoparticles (Au 0). The texture characteristics and trace element geochemistry among cores, transition zones, and rims of pyrites demonstrate that there are at least four pulses of fluid participating in the generation of pyrite in the deposit. The calculated formation temperatures of the Zaozigou deposit vary from 148 C to 304 C, with an average temperature of 213 C based on Au contents in pyrite. The Pb isotopic compositions of pyrite samples suggest that the metallogenic materials of the Zaozigou deposit were derived from the mantle and upper crust. All the characteristics above lead us to draw the conclusion that the Zaozigou gold deposit is classified as an epithermal deposit.

Research paper thumbnail of The origin of volatiles in the Emeishan large igneous province, China: Constraints from chemical and C–He–Ar isotopic compositions of volatiles in picrites and basalts

Geological Journal

The Emeishan large igneous province (LIP) consists of Permian flood basalts and coeval intrusive ... more The Emeishan large igneous province (LIP) consists of Permian flood basalts and coeval intrusive rocks with compositions varying from mafic–ultramafic rocks to syenites and granites. The volatiles in the Emeishan LIP are dominated by H2O with high H2, indicating that the plume‐derived magma was generated under a reduced condition. Picrite has minor contents of H2S without detectable SO2, and the basalt samples show no detectable H2S and SO2, indicating that the basaltic magma may have undergone sulphur‐saturation during magma evolution. The δ13C values of CO2 and CH4 in picrites and basalts are between the values of mantle and crustal organic carbon. This, together with the distribution patterns among CH4 homologue, indicates contribution of recycled sediments to the Emeishan mantle‐derived magma. The 3He/4He ratios of volatiles extracted from olivine and pyroxene phenocrysts of picrites vary from 0.01 to 0.66 Ra, and those from pyroxene separates of olivine websterite samples in th...

Research paper thumbnail of Origin of highly variable and unusually low δ7Li in mineral separates from ultramafic intrusive rocks in a convergent tectonic setting in the Tibetan plateau

Research paper thumbnail of The chemical and carbon isotopic compositions of volatiles in Cenozoic high-potassic basalts in western Qinling, China and their mantle geodynamic implications

Acta Petrologica Sinica, 2012

India-Asia continental plate subduction and collision lead to widespread Cenozoic potassic-ultrap... more India-Asia continental plate subduction and collision lead to widespread Cenozoic potassic-ultrapotassic magmatism in the Tibet which provides a valuable indicator of the composition and nature of the deep mantle beneath the Tibet. The Cenozoic mantle xenolith bearing high-potassic basalts (7.1 similar to 23Ma) distributed in western Qinling, western China are a window to probe the mantle composition and geodynamics beneath north-eastern margin of Tibet Plateau. The chemical and carbon isotopic compositions of volatiles in olivine(Olv) and plagioclase (P1) phenocrysts and matrix (Mtx) of Cenozoic high-potassic basalts in western Qinling have been determined by stepwise heating mass spectrometer to reveal volatile sources and geodynamic implications under the system of continental plate subduction and collision. The results showed that the volatiles in high-potassic basalts were released by stage at temperature intervals of 200 similar to 400 degrees C, 400 similar to 800 degrees C a...

Research paper thumbnail of Sr-Nd-Hf-O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide ore deposits in the Emeishan large igneous province

Geochimica et Cosmochimica Acta, 2021

O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide... more O isotope constraints on crustal contamination and mantle source variation of three Fe-Ti-V oxide ore deposits in the Emeishan large igneous province, Geochimica et Cosmochimica Acta (2020), doi:

Research paper thumbnail of The origin of Permian Pobei ultramafic complex in the northeastern Tarim craton, western China: Evidences from chemical and C-He-Ne-Ar isotopic compositions of volatiles

Chemical Geology, 2017

The large Pobei Permian layered mafic-ultramafic complex in the northeastern margin of Tarim crat... more The large Pobei Permian layered mafic-ultramafic complex in the northeastern margin of Tarim craton, western China is related temporally and spatially to adjacent Tarim Large Igneous Province (LIP), and hosts Ni-Cu sulfide mineralization. The chemical composition, carbon and noble gas isotopic compositions of volatiles in olivine, pyroxene and plagioclase minerals of the Pobei complex have been measured to reveal the composition and origin of magmatic volatiles, mantle information and dynamic settings. The magmatic volatiles in the Pobei complex are composed of dominant H 2 O (av. 3284.3 mm 3 •STP/g, STP = standard temperature and pressure), H 2 (449.1) and CO 2 (449.4), indicated a H 2 O-rich reduced magmatic condition. The δ 13 C values of CH 4 , C 2 H 6 , C 3 H 8 and C 4 H 10 show normal or (partial) reversal distribution pattern with carbon number. The δ 13 C values of CO 2 and CH 4 range among mantle, crust (methane oxidation) and thermogenic origins. The 3 He/ 4 He (1.13 to 6.15 Ra) and 40 Ar/ 36 Ar (326.4 to 1004.3) ratios are plotted on a trend of the mantle plume to atmosphere. The high 20 Ne/ 22 Ne and low 21 Ne/ 22 Ne ratios fall along the mass fractionation line. The volatile compositions indicated that the Pobei mafic-ultramafic complex could be originated from the staged partial melting of heterogeneous H 2 O-rich mantle sources triggered by a mantle plume, the air and crust components from subducted altered oceanic crust have been added into the Pobei magma.

Research paper thumbnail of Molecular and carbon isotopic variation in 3.5 years shale gas production from Longmaxi Formation in Sichuan Basin, China

Marine and Petroleum Geology, 2017

A time series of produced shale gas samples from Lower Silurian Longmaxi Formation (Fm.) were col... more A time series of produced shale gas samples from Lower Silurian Longmaxi Formation (Fm.) were collected from six production wells during 3.5 years production period from the Weiyuan and Changning shale gas pilots in Sichuan basin, China. The molecular compositions and carbon isotopes of CH 4 , C 2 H 6 , C 3 H 8 and CO 2 , and the hydrogen isotope of methane were analyzed for these samples by an integrated method of gas chromatography combined with mass spectrometry. The results showed that the produced shale gases are dominated by CH 4 (90.1e99.3%) with minor C 2 H 6 (0.3e0.8%) and non-hydrocarbon gases, and have low wetness (0.3e0.8%). The non-hydrocarbon gases are mainly CO 2 and N 2 , and trace amount of He. The Longmaxi shale gases display completed reversal pattern of carbon isotopic compositions with carbon number (i.e., d 13 C 1 > d 13 C 2 > d 13 C 3) except for Wells W201 and W201-H1 with normal patterns between C 2 H 6 and C 3 H 8 (i.e., d 13 C 2 < d 13 C 3), and it is a mixture of oil cracking gas and kerogen cracking gas at high-over level of thermal maturity. Some CO 2 (d 13 C CO2 ranging from À2.5 to À6.0‰) is mainly derived from the decomposition of carbonate minerals. CH 4 concentration and the carbon isotopes of methane and ethane during 3.5 years shale gas production from year 2012 to 2016 displayed small fluctuations, which possibly suggested that gas supply from shale matrix to fracture network after hydraulic fracturing is abundant. The Weiyuan shale gases show larger decrease of CH 4 content than the Changning shale gases, indicated more adequate supply in the Changning area. The difference in d 13 C 1 values between horizontal and vertical wells on the same drilling site in the Weiyuan pilot indicated that the vertical heterogeneity of Lower Silurian Longmaxi shale plays an important role to shale gas production. Interestingly, the shale gases in the Weiyuan pilot display much lighter d 13 C 1 (À34.46 to À36.82‰) and d 13 C 2 (À37.59 to À41.89‰) values than those (d 13 C 1 ¼ À27.18eÀ27.27‰, d 13 C 2 ¼ À33.70eÀ34.14‰) in the Changning pilot. The difference in carbon isotopic compositions in Weiyuan and Changning pilots mainly attributes to mixing between varied proportion of oil cracking gas and kerogen cracking gas because of the regional heterogeneity of the Longmaxi marine shale, in particular amount of residual oil retained in organic matter rich shale. The isotopic difference between Weiyuan and Changning shale gases doesn't disappear in the period about 3.5 years of shale gas development, which further suggests the regional heterogeneity of retained residual oil exists in the Longmaxi Fm. marine shale.

Research paper thumbnail of Noble gas isotopic variations and geological implication of Longmaxi shale gas in Sichuan Basin, China

Marine and Petroleum Geology, 2017

The large difference in carbon isotopic compositions of shale gases from the Lower Silurian Longm... more The large difference in carbon isotopic compositions of shale gases from the Lower Silurian Longmaxi Formation marine organic-rich shales between Changning and Weiyuan areas in Sichuan Basin, China is a still debate issue. In this study, 30 produced shale gas samples were collected during 3 years production period and analyzed for noble gas (He, Ne and Ar) abundances and isotopic compositions to reveal the origin and variation causes of shale gases. The results show that the Longmaxi shale gases show low 3 He/ 4 He and 20 Ne/ 22 Ne, and varied but high 21 Ne/ 22 Ne and 40 Ar/ 36 Ar ratios. The Weiyuan shale gases are characterized by low 3 He/ 4 He, high 40 Ar/ 36 Ar ratios and varied 4 He and 40 Ar abundances, and a large increase in 40 Ar contents and a slight decrease in 40 Ar/ 36 Ar ratios display during 3 years shale gas production period from Jan. 2014 to Jun. 2016. Whereas the Changning shale gases are characterized by low and varied 3 He/ 4 He ratios and high 4 He and 40 Ar abundances, and small fluctuations in 40 Ar contents and 40 Ar/ 36 Ar ratios exhibit during 3 years production period. In addition, the shale gases produced from horizontal wells in the Weiyuan area possessed higher 40 Ar and 40 Ar/ 36 Ar ratio than that those from vertical wells at same well site. The noble gas isotopic compositions and variation of Longmaxi shale gases suggested that they are originated mainly from crust, air saturated fluid (ASF) and radiogenic accumulation. The variation of 40 Ar and 4 He contents during shale gas production mainly reflects the degree of shale gas source supply from mineral matrix to fracture network, and the greater increases in 40 Ar and 4 He contents with production time show less abundant shale gas supply. Therefore, the increase trend of 40 Ar contents with shale gas production time in the Weiyuan area during 3 years production period possibly suggests less adequate shale gas supply. In contrast, the uniform or nearly constant of 40 Ar content through production time in the Changing area indicates abundant supply of shale gas sources from mineral matrix, resulting in less production decline. Variation in 4 He and 40 Ar contents through shale gas production time could be sensitive indicators of abundant or depleted shale gas source supply.

Research paper thumbnail of The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes

Chemical Geology, 2017

The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW Chi... more The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Chemge(2017),

Research paper thumbnail of Neoproterozoic subduction-related basaltic magmatism in the northern margin of the Tarim Craton: Implications for Rodinia reconstruction

Precambrian Research, 2016

Abstract A single mantle plume model for the Neoproterozoic mafic-ultramafic intrusive rocks (760... more Abstract A single mantle plume model for the Neoproterozoic mafic-ultramafic intrusive rocks (760–820 Ma) in the northern rim of the Tarim Craton (Kuluketage, Xinjiang, China) is not supported by the protracted nature of magma emplacement that does not show a hot spot track, and whole-rock trace element compositions that clearly show arc signatures. New and previous zircon U-Pb age data reveal an age difference of up to 11 myr for a single mafic-ultramafic intrusive complex and an age difference of up to 32 myr for two mafic-ultramafic intrusive complexes separated by only ∼10 km. Such age differences are more than 2–5 times the analytical uncertainties. No major faults are present between the two intrusive complexes with different ages so their original distance is still well preserved. In addition, the age change of the mafic-ultramafic intrusive rocks in the region occurs in different directions. The temporal-spatial distribution of these rocks can be well explained by subduction-related magmatism that can last for a very long period of time at the same location. The protracted Neoproterozoic mafic-ultramafic intrusive rocks in the Kuluketage district are all characterized by moderate light rare earth element enrichments, pronounced negative Nb-Ta anomalies and low eNd(t) values (1 to −11) coupled with elevated initial 87Sr/86Sr ratios (0.706–0.71), which are consistent with the products of arc basalts contaminated with crustal materials. The results from this study support the notion that the northern margin of the Tarim Craton was part of the Neoproterozoic Circum-Rodinia Subduction System.

Research paper thumbnail of Neoproterozoic Magmatism in the Northern Margin of the Tarim Craton: Implications for Rodinia Reconstruction

Acta Geologica Sinica - English Edition, 2016

Research paper thumbnail of The molecular and carbon isotopic constrains on origin and storage of Longmaxi Formation shale gas in Changning area, Sichuan Basin, China

Interpretation, 2015

We have developed a vacuum-crushing method for the extraction of gases stored in shale for the de... more We have developed a vacuum-crushing method for the extraction of gases stored in shale for the determination of gas yield, chemical composition, and carbon isotopic composition by online gas-chromatography and mass spectrometry. Analysis of the evacuation and parallel experiments showed low standard deviation and good reproducibility. This approach significantly improved the detection limits for trace-gas analysis in shale and measured multiple nonhydrocarbon gas components in a single run. We analyzed the chemical and carbon isotopic compositions of the gases released by one-step vacuum crushing from nineteen samples of organic-rich Longmaxi Formation (Fm.) shale in Changning outcrop, Sichuan Basin, China, and we studied the main controls on gas chemistry of retained gas in the Longmaxi Shale. The results showed that the crushed gas is high in [Formula: see text] and [Formula: see text] but low in [Formula: see text]. The crushed gas has obviously lower [Formula: see text] ratios t...

Research paper thumbnail of Carbon Isotope Reversals of Changning-Weiyuan Region Shale Gas, Sichuan Basin

Acta Geologica Sinica - English Edition, 2015

Research paper thumbnail of U–Pb age and Hf isotopes of zircon from basaltic andesite and geochemical fingerprinting of the associated picrites in the Emeishan large igneous province, SW China

Mineralogy and Petrology, 2014

Research paper thumbnail of The Ore-forming Conditions of the Zhubu Magmatic Ni-Cu-PGE Deposit, Emeishan Large Igneous Province, SW China: Constraints from Hf-Sr-Nd-C Isotopic Compositions and Volatile Chemical Compositions

Acta Geologica Sinica - English Edition, 2014

The Zhubu magmatic Ni-Cu-PGE deposit is hosted in a small mafic-ultramafic intrusion which belong... more The Zhubu magmatic Ni-Cu-PGE deposit is hosted in a small mafic-ultramafic intrusion which belongs to the Permian Emeishan large igneous province (ELIP) in SW China and northern Vietnam. Most of the mafic-ultramafic intrusions in the ELIP host world-class magmatic Fe-Ti-V oxide deposits; only a few of them host magmatic Ni-Cu-PGE sulfide deposits including the Zhubu deposit. A better understanding of fundamental controls on sulfide mineralization in the Zhubu intrusion is important in mineral exploration.

Research paper thumbnail of Detrital zircon constraint on the timing of amalgamation between Alxa and Ordos, with exploration implications for Jinchuan-type Ni–Cu ore deposit in China

Precambrian Research, 2014

Abstract The Jinchuan Ni–Cu deposit, which is the largest single magmatic sulfide ore deposit in ... more Abstract The Jinchuan Ni–Cu deposit, which is the largest single magmatic sulfide ore deposit in the world, is hosted by a mafic-ultramafic intrusion in the Alxa block, northwestern China. The timing of amalgamation between the Alxa block and the adjacent Ordos block, which is important for Precambrian reconstruction of North China Craton and the search for another Jinchuan-type ore deposit, is contentious. The age distribution patterns of detrital zircon crystals with Precambrian ages from the Devonian and older sedimentary rocks of the Alxa and Ordos blocks are similar. This supports the traditional view that the Alxa and Ordos blocks were amalgamated in the Paleoproterozoic along the 1.95 Ga Khondalite Belt, long before the emplacement of the ∼830 Ma Jinchuan intrusion. The U–Pb–Lu–Hf isotope data of comagmatic zircon crystals from the Jinchuan intrusion, together with its whole-rock Sm–Nd isotopes and trace element compositions given previously by other researchers, indicate that the Jinchuan ore-bearing intrusion is the product of continental rift-related basaltic magmatism which took place during the early stage of Rodinia breakup. Based on these observations, we conclude that in addition to the Alxa block, the adjacent regions in the North China Craton such as the Ordos basin, the Khondalite belt and the Yinshan terrane are most promising for new discoveries of Jinchuan-type Ni–Cu ore deposits.

Research paper thumbnail of The Origin of Ni-Cu-PGE Sulfide Mineralization in the Margin of the Zhubu Mafic-Ultramafic Intrusion in the Emeishan Large Igneous Province, Southwestern China

Economic Geology, 2013

The Zhubu magmatic Ni-Cu-PGE sulfide deposit is hosted in a mafic-ultramafic intrusion which is p... more The Zhubu magmatic Ni-Cu-PGE sulfide deposit is hosted in a mafic-ultramafic intrusion which is part of the Emeishan large igneous province in southwest China. The Zhubu intrusion is composed of a layered sequence (750 × 400 × 600 m) with subhorizontal modal layering and a subvertical marginal zone of <40 m across. The marginal zone is composed of lherzolite and olivine websterite with minor gabbroic rocks. The layered sequence is composed of lherzolite, websterite, gabbro, and gabbrodiorite from the base to the top. The Zhubu intrusion can be explained by two stages of formation, an early conduit stage for the marginal zone and a late in situ differentiation stage for the layered sequence. Most important Ni-Cu-PGE mineralization in the intrusion occurs as disseminated sulfides within the marginal zone. Olivine crystals from the marginal zone contain 81 to 84 mol % Fo and 1,600 to 1,900 ppm Ni. The rims of zoned olivine phenocrysts in the Emeishan picrites have similar Fo contents but significantly higher Ni contents (2,300−2,600 ppm). The olivine data indicate that the parental magma of the Zhubu ultramafic rocks is similar to the transporting magma of the Emeishan picrites in MgO/FeO ratios but depleted in Ni due to sulfide segregation before olivine crystallization. The initial concentrations of PGE in the Zhubu magma, estimated from bulk sulfide compositions, are 7 ppb Pd, 9.3 ppb Pt, and 0.8 ppb Ir, similar to the values in the Emeishan picrites. Like the Emeishan picrites, the Zhubu intrusive rocks are characterized by light REE enrichments. Negative Nb anomalies relative to Th and Ta, which are rare in the Emeishan picrites, are present in the Zhubu samples. The (87 Sr/ 86 Sr)i and εNd values of the Zhubu intrusive rocks vary from 0.709591 to 0.710692 and from-2 to-3, respectively. The trace element and isotope compositions indicate that the Zhubu magma was contaminated by crustal materials, supporting the interpretation that sulfide saturation in the magma was triggered by crustal contamination. The area where the lower part of the conduit may have been brought up by faulting should be the focus of future exploration at Zhubu.

Research paper thumbnail of PGE and Isotope (Hf-Sr-Nd-Pb) Constraints on the Origin of the Huangshandong Magmatic Ni-Cu Sulfide Deposit in the Central Asian Orogenic Belt, Northwestern China

Economic Geology, 2013

Many magmatic Ni-Cu sulfide deposits have been found to be associated with Permian basaltic magma... more Many magmatic Ni-Cu sulfide deposits have been found to be associated with Permian basaltic magmatism in the Central Asian orogenic belt, Xinjiang, China. The style of basaltic magmatism and the origin of associated Ni-Cu sulfide deposits in the region are highly debated. The Huangshandong mafic-ultramafic intrusion is at the center of the debate mainly because it hosts the largest magmatic Ni-Cu sulfide deposit in the region. In this paper we report integrated petrological and geochemical data for the Huangshandong Ni-Cu sulfide deposit. The host intrusion consists of a massive gabbronorite unit and a layered sequence, which is composed of two to three ultramafic layers overlain by gabbroic rocks with visible modal layering. Important sulfide mineralization in the intrusion is associated with the ultramafic rocks and massive gabbronorite. The ultramafic rocks and massive gabbronorite are characterized by moderate enrichments in light rare earth elements (LREE), pronounced negative Nb-Ta anomalies relative to Th and La, positive εNd (t = 274 Ma) values (6.6−8.3), low initial 87 Sr/ 86 Sr ratios (0.7031−0.7038), low initial 206 Pb/ 204 Pb ratios (17.7−18), and positive εHf values of zircon (14−17). These data are consistent with mixing between a depleted mantle-derived magma and a granitic melt formed by partial melting of a juvenile arc crust as a result of mafic magma underplating. Olivine crystals enclosed in large clinopyroxene and plagioclase crystals from the ultramafic rocks have Fo contents up to 83 mol %. The contents of Ni in the olivine crystals decrease rapidly with Fo contents, indicating sulfide segregation from magma during olivine crystallization. Numerical modeling using bulk sulfide compositions and constraints from olivine-liquid relationships reveals that the parental magma of the intrusion was significantly depleted in PGE and contained <7 wt % MgO. Depletion of PGE in the magma can be explained by previous sulfide segregation possibly due to magma mixing in a staging chamber. Fractional crystallization and addition of external sulfides from juvenile arc crust appear to have played a critical role in triggering the second event of sulfide segregation to form the deposit. We believe that the Huangshandong sulfide ore-bearing intrusion formed by basaltic magmatism related to postsubduction delamination and asthenosphere upwelling instead of a deep-seated mantle plume.

Research paper thumbnail of Noble gas isotopic constraints on the origin and evolution of the Jinchuan Ni–Cu–(PGE) sulfide ore-bearing ultramafic intrusion, Western China

Research paper thumbnail of Association of Mg-rich Olivine with Magnetite as a Result of Brucite Marble Assimilation by Basaltic Magma in the Emeishan Large Igneous Province, SW China

Journal of Petrology, 2017

An unusual feature of the magmatic Fe-Ti oxide deposits associated with layered intrusions in the... more An unusual feature of the magmatic Fe-Ti oxide deposits associated with layered intrusions in the Permian Emeishan large igneous province (LIP) in SW China is the association of the mineralization with olivine that is significantly more Mg-rich than those that occur elsewhere. A working hypothesis for the production of Mg-rich olivine is that significant assimilation of carbonate occurred during the formation of the Fe-Ti oxide deposits in the Emeishan LIP. This study provides several lines of supporting evidence from a coeval picritic dyke in the footwall of the Panzhihua layered intrusion at Zhujiabaobao. Country rocks to the Zhujiabaobao picritic dyke are brucite marbles. Olivine phenocrysts in the dyke have Fo contents varying from 79 to 91 mol %. The most Mg-rich olivine phenocrysts (Fo89-91) are present in the margins of the dyke and contain undissolved calcite. Olivine phenocrysts in the marginal sample show reversed zoning in Fo content and contain 2020% lower Ni than those with similar Fo contents in the coeval picrites emplaced in the nearby area. Olivine-hosted oxide inclusions in this sample are exclusively Cr-magnetite (calculated atomic Fe 3þ /Cr 3þ > 1) instead of chromite or Cr-spinel (calculated atomic Fe 3þ /Cr 3þ < 1) that characterizes the coeval picrites. Within the dyke olivine phenocrysts with different ranges of Fo content (Fo89-91 versus Fo78-83) have similar Mn contents but different Ni contents. The most Mg-rich olivine phenocrysts have Ni contents that are 20-30% less than those for the more Fe-rich olivine phenocrysts. Diopside crystals associated with the most Mg-rich olivine phenocrysts contain higher Fe 2 O 3 /FeO than those associated with the more Fe-rich olivine phenocrysts. The dyke samples with different olivine compositions have similar e Nd values (1Á4-2) but contrasting Sr isotope compositions. The sample with the most Mg-rich olivine (Fo89-90) has the highest initial 87 Sr/ 86 Sr ratio (0Á7054), whereas samples with more Fe-rich olivine (Fo78-83) have lower initial 87 Sr/ 86 Sr ratios (0Á7046-0Á7049). The results of mixing calculations indicate that up to 2025 wt % assimilation of brucite marble by basaltic magma with a composition similar to that of the average of the coeval high-Ti basalts can readily explain the observed mineralogical and isotopic variations within the dyke. The results from the dyke show that carbonate assimilation by basaltic magma is an efficient way to produce the association of magnetite with olivine that is anomalously rich in magnesium.

Research paper thumbnail of Mineralogy and Geochemistry of Pyrite and Arsenopyrite from the Zaozigou Gold Deposit in West Qinling Orogenic Belt, Central China: Implications for Ore Genesis

Resource Geology, 2019

The Zaozigou gold deposit lies in the West Qinling orogenic belt, Gansu Province, China. It is on... more The Zaozigou gold deposit lies in the West Qinling orogenic belt, Gansu Province, China. It is one of the largest gold deposits, and the orebodies are hosted in fine-grained slates intercalated with limestone of the Middle-Triassic Gulangdi Formation and varied dykes. The gold orebodies are strictly controlled by the NE-, NW-, and SN-trending tensional and shearing faults with high dipping angle. The mineralogy and geochemistry of pyrite and arsenopyrite are measured by electron microprobe. Pyrite has up to 0.12 wt.% Au, and arsenopyrite contains up to 0.17 wt.% Au. The antithetic correlation between S and As indicates the substitution of As for S in pyrite, and arsenic occurs in anionic As 1− state in the pyrite structure under the reduced conditions. Pyrite has relatively high Co (~364-2248 ppm) but relatively low Ni (~109-497 ppm) contents, with Co/Ni ratios ranging from~1.63 to 10.50, indicating that the deposit originated from a volcanogenic fluid and remobilized by hydrothermal fluid. Au in arsenopyrite occurs as cationic Au in solid solution, whereas Au in pyrite is in solid solution and metal nanoparticles (Au 0). The texture characteristics and trace element geochemistry among cores, transition zones, and rims of pyrites demonstrate that there are at least four pulses of fluid participating in the generation of pyrite in the deposit. The calculated formation temperatures of the Zaozigou deposit vary from 148 C to 304 C, with an average temperature of 213 C based on Au contents in pyrite. The Pb isotopic compositions of pyrite samples suggest that the metallogenic materials of the Zaozigou deposit were derived from the mantle and upper crust. All the characteristics above lead us to draw the conclusion that the Zaozigou gold deposit is classified as an epithermal deposit.