δEu Values Research Articles

The effect of hydrothermal fluids on Ordovician carbonate rocks, southern Ordos Basin, China

Hydrothermal processes have an important influence on the spatial distribution and formation of carbonate reservoirs, and play a critical role in certain deep reservoirs where hydrothermal fluid-rock interaction may result in permeability creation due to carbonate dissolution or permeability destruction due to the deposition of cementing minerals. This study analyzed certain hydrothermal indicator minerals (quartz, celestite, multi-stage calcareous fillings) in carbonate rocks from the Ordovician Majiagou Formation, southern Ordos Basin, China. The petrological and geochemical characteristics of these indicator minerals imply that the Majiagou Formation was affected by two metasomatic events related to the Hercynian–Indosinian and Yanshanian orogenies and linked to magmatic-hydrothermal fluids derived from basaltic melts. Most of the δCe and δEu values obtained from matrix dolomite samples were lower than one, but U/Th and V/C ratios showed positive anomalies. The δ13C and δ18O values of the matrix dolomite were concentrated between −12.8‰ and −6.0‰, whereas δ13C showed a bipolar distribution at the same depth. Elemental geochemistry results showed that the Ordovician carbonate rocks were subjected to freshwater leaching followed by evaporation and widespread hydrothermal dissolution successively. As a result of the multi-episodic hydrothermal activity that affected the southern Ordos Basin and the path of migration channel, a parental magmatic-hydrothermal fluid (fluid 1) that had been generated during the underplating of the southern North China Craton by Mesozoic alkaline basalt melts, separated into two types of fluids with different chemical properties: an acidic, hydrocarbon-bearing fluid (fluid 2a) mixed with Cambrian oil and gas and a weakly to moderately alkaline brine (fluid 2b), not in contact with hydrocarbons. Both fluids 2a and 2b then interacted with the Ordovician carbonate rocks with fluid 2a having undergone hydrothermal sulfate reduction with SO42- in the layers in which gypsum was developed, and convection of fluid 2a having resulted in brine formation. The reaction products of H2S and CO2 together with organic acid co-dissolved carbonate minerals in the Ordovician strata played a major role in the formation of a high porosity reservoir. Conversely, owing to the progressive reduction of temperature and solubility during fluid ascent, fluid 2b precipitated quartz-calcite fillings in the residual pore spaces, resulting in the localized destruction of the original reservoir permeability. In summary, this study analyzed the petrological and geochemical characteristics of 60 carbonate rock drill core samples, established the likely formation mechanism of fluids 2a and 2b, and determined the effects of these hydrothermal fluids on the Ordovician Majiagou Formation carbonate reservoir.

Halogens and trace elements of apatite from Late Mesozoic and Cenozoic porphyry Cu-Mo-Au deposits in SE Tibet, China: Constraints on magmatic fertility and granitoid petrogenesis

Abstract Tethyan orogenesis and Indian–Eurasia collision facilitate the development of abundant Late Mesozoic and Cenozoic porphyries and associated Cu ± Mo ± Au deposits in the SE Tibetan plateau. Typical deposits including Beiya with the largest Au reserve of 350 t, Tongchanggou with the largest Mo reserve of 142.5 Mt and Pulang with the largest Cu reserve of 804 Mt were mostly concerned by economic geologists. Porphyries occurred in these three typical deposits were classified as Au-fertile (Wandongshan monzogranite porphyry in Beiya), Mo-fertile (granodiorite porphyry in Tongchanggou), Cu-fertile (quartz monzogranite porphyry in Pulang) and ore-barren (Baliancun biotite monzogranite porphyry in Beiya) systems. In this study, apatite geochemistry from four porphyry systems with distinctive metal endowments was investigated to further constrain magmatic fertility indicators and granitoid petrogenesis. All the studied apatite grains belong to magmatic fluorapatite and are generally wrapped within plagioclase and biotite phenocrysts, suggesting that apatite occurs as early-crystallization phase during crystal fractionation. Apatite grains with porous texture, irregular patchy zoning and secondary rare earth mineral inclusions were eliminated to make the minimal effect of hydrothermal alteration. The F and Cl contents in melt are also estimated based on analyzed F–Cl contents and corresponding F–Cl partition coefficients between apatite and melt under different P–T conditions in this study. Apatite from the Wandongshan (WDS) Au-fertile monzogranite porphyry (MP) has the highest Sr content (average of 1530 ppm) and (F/Cl)melt ratios (44 to 125), indicating that the WDS MP experienced the highest degree of melt fractionation. Additionally, the WDS Au-fertile porphyry is more oxidized than ore-barren, Mo-fertile and Cu-fertile porphyries, evidenced by its highest apatite δEu (0.56–0.83) and lowest δCe (0.98–1.05) values. Rare earth elements (REEs), Y and Sr in apatite were found to be most effective for discriminating magma types. All the apatite grains from typical Late Mesozoic and Cenozoic porphyries in SE Tibet show relatively high Sr/Y (0.5–23.6) and δEu (0.41–0.83) values, pointing to an adakitic affinity of apatite-bearing rock, which is consistent with the whole-rock geochemistry. These porphyries formed under distinctive tectonic settings show distinguishable Clmelt and (F/Cl)melt ratios. The Pulang Cu-fertile quartz monzonite porphyry formed under a subduction setting has relatively high Clmelt contents of 100–1000 ppm and low (F/Cl)melt ratios of 2–22, suggesting derivation of the parental magma from a metasomatized hydrous mantle wedge. Whereas, the WDS Au-fertile MP and Bailiancun ore-barren biotite monzonite porphyry generated under intracontinental setting show low Clmelt contents of 23–180 ppm and variable (F/Cl)melt ratios of 12–125, because F-bearing minerals were decomposing at greater depths under higher pressures during the collision.

Magmatic expression of tectonic transition from oceanic subduction to continental collision: Insights from the Middle Triassic rhyolites of the North Qiangtang Block

The tectonic transition from subduction to collision is a fundamental process during orogenesis, yet the magmatic expression of this transition and related deep geodynamic processes remain unclear. This study focuses on a newly identified volcanic belt within the Moyun–Zaduo–Sulu area of the North Qiangtang Block and presents new zircon U-Pb data that indicate that this belt formed during the Middle Triassic (247–241 Ma), a time characterized by a regional transition from subduction to collisional tectonism. The volcanic belt is located to the south of a Permian to Early Triassic arc and is dominated by high-K calc-alkaline and peraluminous rhyolites. These rhyolites have low Mg#, Nb/Ta, and δEu values, contain low contents of Sr, have high Rb/Sr and whole-rock εNd(t) values, and show positive zircon εHf(t) values, all of which suggest that they formed from magmas generated by the dehydration melting of juvenile crustal material. The migration of Middle Triassic volcanism in this region was most likely caused by rollback of the subducting Longmucuo–Shuanghu Tethyan oceanic slab. Combining our new data with previously published results of numerical modeling of subduction–collisional processes and regional data from north-central Tibet yields insights into the magmatic expressions and related deep geodynamics of the transition from oceanic subduction to continental collision. This combination of data also suggests that variations in oxygen fugacity can be used as a proxy for the discrimination of magmatism related to subduction, the transition from subduction to collision, and collisional tectonism.

Origin and evolution of ore-forming fluids of the Larong W-(Mo) deposit, eastern Tibet: Constraints from fluid inclusions, H-O isotopes, and scheelite geochemistry

The Larong porphyry W-(Mo) deposit, formed in the main collisional orogenic stage of Lhasa and Qiangtang terranes, is the first-discovered giant W-(Mo) deposit in the Leiwuqi-Zogang metallogenic belt, Sanjiang region. The W-Mo mineralization occurs as veins and stock-works mainly hosted in the granodiorite porphyry, monzogranite porphyry, biotite granite porphyry, and surrounding schist. Four types of fluid inclusions (FIs) including PC-type (pure vapor CO2), C-type (CO2-H2O), W-type (aqueous two-phase) and L-type (pure liquid H2O) FIs have been identified from Stage I quartz-scheelite ± alkaline feldspar veins, Stage II (including three sub-stages) quartz-molybdenite ± pyrite ± chalcopyrite veins, and Stage III quartz ± calcite ± pyrite veins. The total homogenization temperatures of FIs vary widely (187–437 °C) with multiple peaks, indicating multistage fluid activities. The ore-forming fluids of the main mineralization stages are characterized by CO2 enrichment, high-medium temperature (~270–440 °C), and medium–low salinity (2.4–14.4 wt% NaCl equiv.). The homogenization temperature of W-type inclusions is obviously higher than that of C-type inclusions, and the salinity is relatively lower, implying multiple immiscibility of fluids with continuous escape of CO2. H-O isotopic compositions suggest that the primary ore-forming fluids dominantly originated from magma water. Mo concentrations and δEu values in scheelite indicate a decreasing trend of redox state of ore fluids. From Stage I to Stage II to Stage III, the relatively higher-temperature, CO2-rich, and oxidized fluids gradually evolved into relatively lower-temperature, CO2-poor, and reduced fluids. Here we propose that the decrease of temperature and oxygen fugacity and increase of S2- activity and PH values of the ore fluids caused by continuous fluid-rock interaction and loss of CO2 could account for the successive mineralization of W and Mo at the Larong deposit.

Petrogenesis of early Cretaceous granitoids in the southern Great Xing’an Range, NE China: Constraints from the Haliheiba pluton

Early Cretaceous granitoids are widespread in the southern Great Xing’an Range. However, the petrogenesis of these rocks is poorly understood. We therefore present field investigations, petrological observations, zircon U–Pb ages, whole-rock geochemistry and Hf isotope compositions for the Haliheiba pluton. The pluton comprises fine-grained biotite granite, medium- to coarse-grained biotite granite and porphyritic biotite granite, and mafic microgranular enclaves (MMEs) are unevenly distributed within the host granites. Zircon LA-ICP-MS U–Pb dating yields emplacement ages of ∼139 Ma for the three units. The host granites are characterized by high SiO2 contents (73.16–76.55 wt%) and alkali concentrations (7.92–8.62 wt%), enrichment in light rare earth elements (LREEs), Rb, U, Th, K, and Pb, depletion in heavy rare earth elements (HREEs), Sr, Ba, Ti, and P, and intensely negative Eu anomalies with δEu values from 0.14 to 0.47. The zircons in the host granites yield positive εHf(t) values of +5.0 to +11.2 and fairly young Hf model ages of 408 Ma to 731 Ma. These results indicate that the host granites have high-K calc-alkaline, metaluminous to weakly peraluminous A-type affinity and were mainly derived from partial melting of juvenile crustal materials originated from the depleted mantle, and fractional crystallization was involved in magma evolution. The MMEs have SiO2 contents of 63.45–64.14 wt% and have higher MgO, CaO, tFe2O3 and TiO2 contents than the host granites. The MMEs are enriched in LREEs relative to HREEs with slightly negative Eu anomalies (δEu values of 0.77–0.79) and are slightly enriched in Rb, U, Th, K, Sr, Pb and strongly to slightly depleted in Nb, Ta, Ti and P. These results, together with field investigations and petrological observations, indicate that crust-mantle magma mixing played an important role during the petrogenesis. Furthermore, the MMEs were intermediate members after magma mixing between mafic end-member magmas derived from lithospheric mantle and felsic end-member magmas derived from juvenile crustal materials. Combined with regional geology, our results suggest that a substantial crustal accretion in the southern Great Xing’an Range that occurred during the Neoproterozoic–Carboniferous, and the formation of the Early Cretaceous granitoids in this region was closely related to the lithospheric delamination triggered by the subduction of the Paleo-Pacific Ocean beneath Eurasia.

The Late Mesozoic granodiorite and polymetallic mineralization in southern Anhui Province, China: A perspective from apatite geochemistry

The region of southern Anhui Province (SAP) is one of Late Mesozoic magmatic belts and copper-molybdenum-gold-tungsten polymetallic ore districts in China, but the relationship of polymetallic mineralization and related granodiorite remains unclear. Previous studies indicate that apatite can be an indicator for magmatic evolution and mineral exploration. In this study, apatites from the SAP ore-bearing granodiorites were investigated using observations from the electron microscope, electron probe microanalysis (EPMA), laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS). The studied apatite samples identified as fluorapatite, show high F (2.69–4.13 wt.%) and low Cl contents (mainly<0.2 wt.%). These apatites also have high La/Y (0.41–4.69) and δEu (0.13–0.70) values, and low (Sm/Nd)N values (0.34–0.81), indicating that the SAP magma was derived from mafic I-type melt. The REE patterns, negative Eu anomalies, the negative δEu and δCe correlation, and high logfO2 values (−10.5 to −13.8) of apatites studied, further indicate that the SAP granodiorites had originated from mantle-derived magmas mixing with the lower crustal components in high oxygen fugacity environment. The results indicate that the Sr/Y and δEu values of apatite can be a good indicator to distinguish adakitic rocks from non-adakitic rocks. Moreover, the δEu value and Cl content in apatite can be effectively used to discriminate the unmineralized rocks and ore deposit types.

Origin of the Xiaohekou skarn copper deposit and related granitoids in the Zha-Shan ore cluster area, South Qinling, China

The Xiaohekou copper deposit is one of the few typical skarn-type, commercial deposits in the Zha-Shan ore cluster area in the eastern part of South Qinling. The ore-related granitoids in the Xiaohekou mining district include a number of small plutons of granodiorite porphyry and granite porphyry, as well as numerous dykes. They are characterized by relatively low SiO2 (65.9–73.3 wt%) and MgO (0.26–1.72 wt%) contents, variable Mg# (29.4–64.0) values, high K2O (3.11–5.75 wt%) content and negligible δEu (1.00–1.15) values. The samples also exhibit depletion in Cr, Ni, Nb, Ta, and Ti content, and high Sr/Y (46.6–64.7) and La/Yb (17.0–25.0) ratios. These features are similar to those of high-K calc-alkaline adakite-like magma formed by partial melting of thickened lower crust in continental collision zones or intracontinental settings. The majority of the samples have TDM2(Hf) of 1.5–1.2 Ga, corresponding to weakly negative εHf(t) values (−4.75 to −0.13) typical of crustal material, but more than one quarter have TDM1(Hf) of 0.80–0.71 Ga, corresponding to positive εHf(t) values of +0.07 to +2.45, indicating that the granitoids resulted from partial melting of Mesoproterozoic lower crustal rocks with significant input from enriched lithospheric mantle-derived magmas. Zircons from the Xiaohekou granitoids have ΔFMQ values concentrated around −0.62 to +5.54, most of which show the magma fO2 of FMQ to HM, in accordance with the widespread occurrence of magnetite, hematite and specularite in the Xiaohekou skarn system, which is an indicator of relatively high fO2 for a magmatic–hydrothermal system. The granitoids exhibit similar or even higher Ce4+/Ce3+ (average of 452) and Eu/Eu* (average of 0.72) values in comparison with those of fertile Cu deposits worldwide, indicating that the Xiaohekou granitoids may possess the potential to form a large magmatic–hydrothermal Cu deposit. Zircons of the granitoids show obvious positive correlations between oxidation indices (Ce and Eu anomalies, Ce4+/Ce3+ ratios, and ΔFMQ values) and εHf(t) values, implying the involvement of an oxidized mantle component which might have caused the fO2 elevation and played an important role in the formation of Cu deposits. The zircon U–Pb ages (141.3 ± 1.3 and 138.1 ± 2.0 Ma) of the Xiaohekou ore-related granitoids obtained in this study are similar to the zircon U–Pb and molybdenite Re–Os ages yielded from porphyry Mo mineralization at the Chigou and Lengshuigou deposits in the Zha-Shan ore district, indicating that they are possibly part of a single tectonic, magmatic, and metallogenic event in the Yanshan orogeny. The ore-related granitoids in the Xiaohekou area were formed in a post-collisional compression–extension transition regime during the Early Cretaceous Qinling intracontinental orogeny. The orogeny can be attributed to the far-field effect of a switch from pre-Mesozoic Tethyan tectonics to Late Mesozoic Pacific tectonics. This triggered a stress field transition from N–S to E–W trending and from intracontinental subduction thickening to large-scale lithospheric delamination and thinning.

Influence of volcanic and hydrothermal activity on organic matter enrichment in the Upper Triassic Yanchang Formation, southern Ordos Basin, Central China

Abstract Based on the field investigation of oil shales in the southern Ordos Basin, detailed observations, and systematic sample analyses of core samples from a well that penetrated an oil shale, the influence of volcanic and hydrothermal activity on the Chang 8–Chang 7 members of the Yanchang Formation on organic matter (OM) enrichment was geochemically and petrologically analyzed. According to maceral analyses and rock pyrolysis, the kerogen types of the samples in the study area are widely distributed. Those of the oil shale with the highest OM abundance are mostly type II-I, and are immature or in a stage of low-maturity. Six layers of tuff and tuffaceous mudstone were identified by core observation and element characteristics; they are characterized by higher total rare earth element (∑REE) and δCe values and Th contents, and lower (La/Yb)N and δEu values. Mineral assemblages of anhydrite–pyrite–marcasite and relevant diagrams of the elemental geochemistry confirmed the existence of hydrothermal deposits. The high Yn/Hon and U/Th ratios and total sulfur (TS) contents indicate that the Chang 7 Member experienced four episodes of intense hydrothermal activity. Early in the Chang 73 Member, volcanic ash and hydrothermal fluids brought in a large amount of nutrients, which not only increased primary productivity, but also increased the salinity of the water column, enhanced anoxia in the sedimentary environment of the lake bottom, promoted the preservation of OM, and finally formed the oil shale layer with the richest OM. However, the strong volcanic eruption in the late Chang 73 Member led to changes in the regional climate, causing it to dry and become colder and resulting in a decrease of primary productivity. Earthquakes triggered by volcanism resulted in turbidite deposits, which destroyed the preservation and diluted the enrichment of OM. This study reveals in detail the influence of volcanic and hydrothermal activity on OM enrichment during the evolution of the basin, and thereby deepens our theoretical understanding of OM enrichment.

Factors controlling the geochemical differences between two types of rhyolites in the middle Okinawa Trough

The origin of the felsic volcanic rocks in the Okinawa Trough (OT) remains uncertain. In the middle Okinawa Trough (MOT), two types of rhyolites (type 1 and type 2 rhyolites) have been recognized. Research on the diverse volcanic rocks should be prioritized to determine the magmatic origins of these rocks. Consequently, in this article, the geochemical differences and controlling factors for these two types of MOT rhyolites are systematically discussed. Type 2 rhyolites have higher Dy/Yb and Nb/Ta ratios than type 1 rhyolites, implying that the former might be influenced by a greater contribution of amphibole. Quantitative models suggest that type 1 rhyolites could have formed via the remelting of andesites when amphiboles remain in the source, whereas type 2 rhyolites could have formed without residual amphiboles. These two distinct melting models effectively explain most discrepancies between the major and trace element compositions of type 1 and 2 rhyolites. Additionally, the lower Mg# and δEu values of type 2 rhyolites are partly caused by significant magmatic differentiation. Quasi-linear correlations between some major oxides, trace element ratios and Sr-Nd isotopic ratios for type 2 rhyolites suggest that these rhyolites might have been contaminated by crustal rocks or melts with compositions similar to those of the Kueishantao (KST) andesites or the Middle Miocene upper crustal rocks of SW Japan. Therefore, isotopically enriched crustal materials likely remain in the OT crust.

Characterization of ore-forming fluids in the Tamusu sandstone-type uranium deposit, Bayingobi Basin, China: Constraints from trace elements, fluid inclusions and C–O–S isotopes

The Tamusu deposit is a large sandstone-type uranium deposit discovered in recent years in the Bayingobi basin, Inner Mongolia. Hydrothermal activity was recorded by veins in this deposit, but its relationship with uranium mineralization has not been clarified. In this study, petrographic observations, chemical composition of U minerals, whole rock geochemistry, fluid inclusions and C–O–S stable isotope studies of sandstone and veins were integrated to characterize the mineralizing fluids and mineralization conditions. We found uranium minerals generally co-exist with pyrite occurring in interstitial pores or on detrital grains in sandstone. The main ore mineral is pitchblende, and minor ore minerals include brannerite and coffinite. Pitchblende coexists with subhedral pyrite, whereas brannerite and coffinite coexist with cubic pyrite and calcite. Calcite also occurs in veins together with gypsum. Fluid inclusions from calcite and gypsum in the veins have homogenization temperatures ranging from 124 °C to 326 °C, with salinities of 5.7–17.2 wt% NaCl equivalent. The C–O and S isotopes of the vein minerals suggest that the hydrothermal fluids were derived from circulated formation water. Trace element analysis shows that the U-bearing sandstone is commonly enriched in V, Re and Mo, while the high-grade uranium ores are further enriched in Zn, Co, Ni and Cu. The REE patterns and δEu values in the high-grade U-bearing sandstone are similar to those in the veins, which are characterized by high LREE and low δEu, suggesting that the high-grade U-bearing sandstone is related to hydrothermal activity. The mineral assemblages, temperatures, trace elements and isotopes indicate that the Tamusu deposit was affected by two distinct types of fluids: supergene diagenetic alkaline oxidizing fluids and acidic reducing hydrothermal fluids. The oxidizing fluids started to be involved after the deposition of the ore-hosting upper Bayingobi Formation, forming a large amount of low-grade U-bearing ores. The hydrothermal fluids occurred in association with the eruption of basalt in the overlying Suhongtu Formation. The involvement of hydrothermal fluids changed the pH and Eh conditions, superimposed and reformed the low-grade uranium ores, forming high-grade uranium ores, and finally fixed the position of the uranium orebodies. Therefore, the Tamusu deposit experienced four main stages: (i) sedimentary and early diagenetic uranium concentration, (ii) oxidation and ore-forming stage, (iii) hydrothermal alteration and superimposed mineralization, and (iv) post-ore stage.

Geochemical attributes of magmatic apatite in the Kukaazi granite from western Kunlun orogenic belt, NW China: Implications for granite petrogenesis and Pb-Zn (-Cu-W) mineralization

Apatite is a significant accessory mineral which is ubiquitous in Kukaazi granitic bodies and provides vital geological information concerning petrogenetic as well as metallogenic attributes. Particularly, igneous apatite is important to delineate nature of parental magma and its characteristics. Here we present new EPMA and LA-ICP-MS data on magmatic apatite of Kukaazi pluton to explore its potential in petrogenesis as well as mineralization and this deposit is widely exposed in western Kunlun, NW China. Our results reveal that the apatite can be characterized as fluorapatite and it reflects the parental magma characteristics of Kukaazi granite. The apatite exhibits high fluorine content, right inclined distribution pattern with enrichment of light rare earth elements (LREEs), a prominent moderate negative Eu anomaly and this anomaly is possibly resulting from plagioclase crystallization prior to apatite. The negative correlation and variation of δCe and δEu together with the moderate negative Eu anomaly suggests that the parental magma of Kukaazi granite have moderate oxidizing nature. The apatite also reveals Kukaazi pluton with adakitic affinity containing higher Sr/Y and Eu/Eu* ratios. This implies that the fluorapatite can be robust tool for distinguishing the adakite plutons and may preserve original Sr/Y and Eu/Eu* ratios as a result of no influence of hydrothermal alteration. Our results also indicate that apatite Cl/F ratio is a potential indicator to track the content of magmatic volatiles and pointer for mineralization. It is inferred that Cl/F ratio in the parental magma of Kukaazi pluton is low, attributable to source control and discrepancy in the Cl/F values can be ascribed to variability of degassing. Halogen data indicates low Cl, fairly high F and low Cl/F ratios which implies that the parental magma of Kukaazi granite is produced in consequence of partial melting of lower crust material. The negative correlation of F and Cl suggests crystallization of Kukaazi apatite from hydrous parental magma. Besides, apatite Eu/Eu* vs. Cl content is significant as proxy record to discriminate mineralized rock from unmineralized. Based on Eu/Eu* vs. Cl plot, we propose that the Kukaazi granite is mineralized. Furthermore, variation and positive correlation between F/Cl ratios and F contents, increase in fluorine concentration, (La/Yb) N and δEu possibly support process of magmatic differentiation. Based on apatite geochemistry, we identified two types of ore deposits specifically Mo-W and Cu deposit in Kukaazi area. In comparison, the apatite of Mo-W deposit is distinguished by slightly higher fluorine and Y, lesser Sr and δEu values however, copper deposits are characterized by higher Sr, δEu values and lesser F, Y. These elements of apatite are prime prolific indicators and proxies for distinguishing fertile granite from barren one. Thus, in view of these findings, we confirm that apatite is a potential pointer of petrogenesis, metallogenesis, mineralization and ore varieties.

Geochronology, Petrogeochemistry, and Tectonic Setting of Cretaceous Granitoids in the Zanzongcuo Zone, Northern Tibet, China

Magmatic rock plays a key role in controlling tectonics. By determining the chronology, petrogenesis and tectonic significance of newly discovered granite porphyry and granite units, this study documents the Bangong-Nujiang Neo-Tethys ocean evolution and the tectonic environment of the Zanzongcuo zone. Based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of zircons, the ages of the granite porphyry and the granite are 113.74 ± 0.68 and 79.58 ± 0.83 Ma, respectively. Thus, these intrusive rocks formed at different times in the Cretaceous. The two studied intrusive bodies are I-type granitoids with peraluminous characteristics. The granite porphyry and the granite belong to the medium- to high-K calc-alkaline and low-K calc-alkaline series, respectively. These rocks are enriched in large ion lithophile elements (LILEs, e.g., Rb, U, and Th) and light rare earth elements (LREEs) but depleted in high field strength elements (HFSEs, e.g., Nb, Ta, and Ti). The granite porphyry and the granite have δEu values of 0.69–0.82 and 0.6–0.73, respectively, and have moderately negative Eu anomalies. The granite porphyry formed in a subduction-related structural environment and represents an arc-type granite. The granite formed in a collisional tectonic environment and represents a granite that formed in a within plate setting. The geochronologic and tectonic characteristics of these two intrusive rocks indicate that the Zanzongcuo zone experienced a series of tectonic events in the Cretaceous, including oceanic crust subduction in the late Early Cretaceous, continent-continent collision, and intraplate compression in the late Late Cretaceous. Furthermore, the Bangong-Nujiang Neo-Tethys ocean closed in the late Early Cretaceous.

Genesis of the Panjia Wu‐Cu‐Mo deposit: Evidence from the geochemistry and geochronology of the Datongkeng pluton, northeast South China Block

The Panjia polymetallic deposit, located in the northwestern region of Zhejiang Province, is a newly discovered medium‐ to large‐sized W–Mo–Cu ore deposit belonging to the northern part of the Qinzhou Bay–Hangzhou Bay metallogenic belt. Through investigation in the field and under the microscope, the hydrothermal activity of this deposit can be divided into four stages: pre‐ore stage, silicate oxidation stage, quartz sulfide stage, and post‐ore stage. The Datongkeng pluton, outcroping in Panjia deposit, is one S‐type intrusive rock and characterised by concentrations of SiO2, K2O and Na2O ranging from 67.03 to 71.09%, 3.03 to 4.89%, and 0.24 to 3.37%, respectively. The major elements display peraluminous, high‐K, calc‐alkaline features. Their A/CNK(A/CNK = n (Al2O3)/ [n (CaO) + n (Na2O) + n(K2O)]) ratios, δEu values, and δCe values vary from 0.93 to 1.98, 0.45 to 0.91, and 0.93 to 1.07, respectively. These rocks are enriched in light rare earth elements (all record values of (La/Yb)N &lt;10, except for one) whereas are depleted in Sr, Ba, Nb, P, Eu, and Ti. The end‐member study of the Pb and S isotopes shows that the mantle material plays an important role in the ore‐forming. Zircon U–Pb dating indicates that the second part of the multiperiod magmatism (154–150 Ma) of Datongkeng pluton is the relevant crystallisation age, and the study of metallogenic stage manifests that the molybdenite is formed at the third stage of the mineralisation sequence considered as the main period of mineralisation, subsequent to the mineralogenetic epoch of scheelite. The petrogenesis is related to the materials in the crust and a small amount of materials in the mantle. While the low degree of mantle source and the Proterozoic basement contribute to the Mo, Cu ore‐forming materials. Finally, two types of metallogenic assemblage are formed, including the W‐Mo polymetallic deposit in the Datongkeng pluton and the W‐Cu‐Pb‐Zn‐Ag polymetallic deposit in the veins in the Lantian Formation.

Petrogenesis of the Dasuji porphyry Mo deposit at the northern margin of North China Craton: Constrains from geochronology, geochemistry and isotopes characteristics

The Dasuji porphyry Mo deposit is located at the northern margin of North China Craton. Mo mineralization occurs mainly within the intrusions of alkali feldspar granite, granite porphyry, and quartz porphyry, which yield weighted mean 206Pb/238U ages (2σ) of 227.6 ± 1.5, 225.7 ± 1.5, and 224.3 ± 1.8 Ma, respectively. These ages are indistinguishable to the molybdenite ReOs isochron age of 223.9 ± 1.5 Ma (2σ). The Dasuji granites show the petrological, mineralogical, geochemical, and geotectonic characteristics of A-type granites. They exhibit low negative εNd(t) values (−16.7 to −12.6) with corresponding TDM2 (Nd) ages of 1705–2000 Ma, variable but mainly negative εHf(t) values (mostly −21.0 to −7.9) with corresponding TDM2 (Hf) ages of 1715–2728 Ma, and Pb isotopic compositions indicating that the primary magmas were dominantly derived from partial melting of ancient lower crust. In chondrite- and mantle-normalized trace element diagrams, all the granitic rocks show negative anomalies in Ba, Sr, and Eu, and a positive anomaly in Pb. The ratios of LREE/HREE, and (La/Yb)N and δEu values decrease from the alkali feldspar granite to the granite porphyry and quartz porphyry. These data are attributed to fractional crystallization processes. Fractionation of feldspar, biotite, and possibly K-feldspar produced the variations in major elements and Rb, Sr and Ba, and the distribution of REE are controlled mainly by fractionation of zircon, allanite, minor apatite, and possibly a small quantity of monazite. Together with the regional geology, the data infer that the Dasuji porphyry Mo deposit formed in a post-collision extensional setting during the Late Triassic.

Characteristics of genetic mineralogy of pyrite and quartz and their indicating significance in the Gaosongshan Gold Deposit, Heilongjiang Province, NE China

The Gaosongshan epithermal gold deposit in Heilongjiang, Northeast China, is hosted by the Lower Cretaceous intermediate-basic volcanic rocks. Three auriferous quartz veins including eleven gold orebodies were all discovered in tectonoclastic zones. Genetic mineralogy study including the thermoelectricity, rare earth elements and trace elements of pyrite and rare earth elements of quartz were carried out. Thermoelectric conductive type of pyrite is mainly N-P type. Calculating the thermoelectric parameters XNP and denudation percentage γ of pyrites from orebodies 1-I, 2-II and 2-IV, suggests that gold orebodies are all eroded to their middle-lower parts. The variable range of Co concentrations (51.3-264.0ppm) and Ni concentrations (68.9-258.0ppm) and Co: Ni ratio (0.31-1.90), together with relatively small Sr/Ba ratio in ore-bearing pyrites (0.11-0.50), supports a hydrothermal origin of mineralization at Gaosongshan gold deposit. Compared with volcanic rocks, the chondrite-normalized REE patterns of ore-bearing pyrites and quartz are all LREE enriched with similar ΣLREE/ΣHREE ratio ranging from 7.37-13.68 in ore-bearing pyrites, 4.74-15.37 in ore-bearing quartz and no Ce anomalies. δEu values in ore-bearing pyrites and quartz are 0.65-1.66 (average=0.93) and 0.66-1.62 (average=1.03), respectively. δEu values of volcanic rocks are 0.86­1.07 (average 0.94), suggesting no obvious negative Eu anomalies. Similar REE characteristics of ore-bearing pyrites and quartz and volcanic rocks, together with previous oxygen and hydrogen isotope studies of quartz, suggest that the ore-forming fluids of the Gaosongshan gold deposit were mainly magmatic origin which was associated with andesitic magma and was partly mixed with atmospheric water. Comparing trace elements characteristics of ore-bearing pyrites with volcanic rocks, together with previous S isotopic studies, it is concluded that the ore-forming materials were derived from the surrounding rocks. Slight changes of Y/Ho (23.80­27.28), Zr/Hf (35.41­47.83), Nb/Ta (10.96­18.52) in ore-bearing pyrites indicate that the ore-forming fluid system is relatively stable during the ore-forming process.

In-situ LA-ICP-MS trace element analyses of scheelite and wolframite: Constraints on the genesis of veinlet-disseminated and vein-type tungsten deposits, South China

Veinlet-disseminated and vein-type tungsten deposits are important tungsten resources in South China and show remarkable diversity in dominant tungsten minerals. To better understand their genesis, scheelite from the Shimensi veinlet-disseminated deposit and wolframite from the Xihuashan and Piaotang vein-type deposits were selected to conduct in-situ laser ablation-inductively coupled plasma-mass spectrometry trace element analyses.The Shimensi tungsten mineralization occurs in intensively altered granitic rocks and is characterized by scheelite. Two generations of scheelite in a single grain can be identified by cathodoluminescence (CL) imaging. The early scheelite (dark domains in CL images) is characterized by nearly flat chondrite-normalized REE (REEN) patterns with significantly negative Eu anomalies, whereas the late one (bright domains in CL images) shows light rare earth element (LREE)-enriched REEN patterns and obviously positive Eu anomalies. The former has higher REE, Na, Nb and Ta and lower Sr contents than the latter. The Xihuashan and Piaotang wolframite-quartz veins are developed in greisenized granite (type I) and metasedimentary rocks (type II). Both types of wolframite show LREE-depleted patterns, but type I exhibits strongly negative Eu anomalies and type II positive Eu anomalies. Type I contains higher REE, Nb and Ta concentrations, and lower FeO/MnO ratios than type II.Variations of Eu anomalies and trace element compositions in both scheelite and wolframite can be used to decipher the origin and processes of tungsten mineralization. Both the early scheelite and wolframite (type I) display significantly negative Eu anomalies and have high REE, Nb and Ta contents, suggesting that the initial ore-forming fluids were of magmatic origin. Precipitation of tungsten minerals and alteration would effectively modify the composition of ore-forming fluids. Deposition of the early tungsten minerals would lower REE, Nb and Ta in the mineralizing fluids, leading to depletion of these elements in the late ones. Although both the type I and II wolframite have different REE contents and Eu anomalies, they show similar left-dipped REEN patterns, implying that compositional variation of fluids is likely driven by crystallization of wolframite during the processes of fluid evolution. In contrast, the elevated LREE/HREE (heavy rare earth element) ratios, δEu (EuN/EuN∗) values and Sr abundances in the late scheelite are possibly caused by the decomposition of plagioclase and K-feldspar. Alteration plays an important role in the formation of veinlet-disseminated scheelite deposits. It can be concluded that vein-type wolframite mineralization is mainly formed by filling and that veinlet-disseminated scheelite mineralization is associated with metasomatism.

Garnet and scheelite as indicators of multi-stage tungsten mineralization in the Huangshaping deposit, southern Hunan province, China

The Huangshaping W–Mo–Pb–Zn deposit in southern Hunan province, south China, contains multiple generations of garnet and scheelite in skarn and sulfide–carbonate altered rocks. Optical characteristics and chondrite-normalized rare earth element (REEN) patterns obtained by in situ laser ablation–inductively coupled plasma–mass spectrometry analysis were used to distinguish different generations of garnet and scheelite. These data show a clear correspondence of garnet REEN patterns to major element zonation, with HREEs (e.g., Gd–Lu) being depleted overall. Coarse-grained garnets in the Huangshaping deposit have extreme HREE depletions and significant LREE (e.g., La–Eu) enrichment, particularly for Ce, Pr, and Nd. This indicates that REEs in these garnets are the result of coupled substitutions: [Ca2+]VIII− 1[REE3+]VIII+1 and [Fe2+]IV +1[Al3+]IV − 1. Medium-grained garnets have REEN patterns showing significant LREE enrichment and depleted HREEs, with high Sn contents. This suggests that substitution of REEs in these garnets occurs as [Ca2+]VIII−1[REE3+]VIII+1[Sn4+]IV−1[Al3+]IV+1. The fact that medium-grained garnets have high Sn contents indicates mineralizing fluids were oxidizing, which is consistent with significant positive Eu anomalies. However, hump-shaped REEN patterns for garnet rims suggest substitution by: [Ca2+]VIII−2[Na+]VIII+1[REE3+]VIII+1, where Nd–Tb are preferentially incorporated into the garnet lattice over other REEs.Group-1a scheelite has black cores in cathodoluminescence images, and REEN patterns showing extreme LREE enrichment and HREE depletion. Group-1b scheelite has cores with fine oscillatory zoning and enriched LREEs with depleted HREEs, similar to the REEN patterns of Group-2a scheelite that occur as rims with bright CL surrounding both Group-1a and 1b scheelite. The substitution mechanism for REEs in these three types of scheelite is: [Ca2+]VIII−3[ ]VIII+1[REE3+]VIII+2, with [ ] being a Ca site vacancy. The influence of REE speciation in the hydrothermal fluid dominates the REEN patterns of these types of scheelite. However, for Group-2b bright rims of scheelite, REEs are incorporated as: [Ca2+]VIII−2[Na+]VIII+1[REE3+]VIII+1, similar to the garnet rims. Finally, scheelite Mo contents and δEu values that decrease from Group-1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids.Ratios of Y/Ho and Mo contents that decrease from Group-1a and 1b to Group-2a and 2b scheelites are similar to those in porphyry-related skarn W (Mo) and quartz vein Au–W deposits, respectively. Our studies also suggest that all these scheelites in this deposit formed from magmatic fluids. At the Huangshaping deposit, medium-grained garnets associated with Group-1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism, as indicated by their complementary Y/Ho ratios. Paragentically younger scheelite, particularly Group-2b, may have formed from dilute magmatic fluids that underwent large-scale hydrothermal circulation. The characteristics of Group-1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic Huangshaping deposit.

In situ major-, trace-elements and Sr-Nd isotopic compositions of apatite from the Luming porphyry Mo deposit, NE China: Constraints on the petrogenetic-metallogenic features

Apatite is an important accessory mineral in granitic rocks and can record important petrogenetic-metallogenic information. In particular, magmatic apatite can provide information on the volatile composition and magma source of the ore-forming rocks in porphyry deposits. This work focuses on magmatic apatite within the ore-forming intrusion of the Luming super-large porphyry Mo deposit. We use electron probe micro-analyzer (EPMA) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analytical methods to analyze the major- and trace-element and Sr-Nd isotopic compositions of the apatite. The results show that the apatite grains are magmatic apatite, classified as fluorapatite. The trace-element patterns of the apatites feature clearly negative Sr, Ba, and Zr anomalies and Ba, Nb, Sr, Zr and Eu depletions that are more distinct than those in the granite porphyry and monzogranite in the Luming deposit. The apatites exhibit slight LREE enrichment and distinctly negative Eu anomalies. The positive Eu/Eu∗ (δEu)-Ga correlation and the strongly negative Eu anomaly indicate that the magma of this granite porphyry may have been in a relatively reductive state. The apatites also indicate that the granite porphyry is a non-adakitic rock, which is consistent with the whole-rock geochemical characteristics. Furthermore, the apatites feature low Sr contents and δEu values and high F/Cl ratios, similar to the characteristics of typical Mo deposits. The 87Rb/86Sr and 87Sr/86Sr ratios of the apatites are 0.012811–0.037958 and 0.710897–0.714423, respectively. The (87Sr/86Sr)i (ISr) values are 0.710865–0.721183. The 147Sm/144Nd and 143Nd/144Nd ratios are 0.132166–0.225171 and 0.512520–0.512681, respectively. The εNd(t) values are −1.78–0.21, and the two-stage Nd model ages are 949–1065 Ma. The approximately positive εNd(t) values and young Nd model ages of the apatite are similar to those of the ore-forming rocks in Early Jurassic Mo deposits in NE China, indicating that these rocks shared the same magma source, which originated from the partial melting of juvenile crust.

Geochronology, geochemistry, and zircon Hf isotopes of the Mo‐bearing granitoids in the eastern Jilin‐Heilongjiang provinces, NE China: Petrogenesis and tectonic implications

In order to investigate their precise geochronological framework, petrogenesis, and tectonic implications, whole‐rock major and trace elements, together with zircon U–Pb and Hf isotope data, are reported for the Mo‐bearing granitoids from the eastern Jilin‐Heilongjiang provinces in the eastern segment of the Central Asian Orogenic Belt. Zircon U–Pb dating by LA–ICP–MS yields crystallization ages for the Liushengdian monzogranite porphyry (252.2 ± 1.6 Ma), the Luming monzogranite porphyry (197.1 ± 1.6 Ma), and the Baoshan granodiorite (164.4 ± 1.9 Ma) and quartz diorite (165.2 ± 1.7 Ma), respectively. This zircon U–Pb data, combined with previous ages, indicate that the eastern Jilin‐Heilongjiang provinces is dominated by 2 stages of ore‐related granitic magmatism and associated Mo mineralization, that is, Late Permian (259–252 Ma) and Early‐Middle Jurassic (200–165 Ma). Geochemically, these Mo‐bearing granitoids have high SiO2 (60.78–74.67 wt.%) and K2O (2.85–6.23 wt.%), low MgO (0.17–2.85 wt.%) and CaO (0.66–4.38 wt.%) contents, with A/NCK and δEu values of 0.87–1.08 and 0.19–1.07, respectively; we infer that they belong to high‐K calc‐alkaline series and are metaluminous to peraluminous in nature. They are characterized by enrichment in large ion lithophile elements and light rare earth elements, and weak depletion in high field strength elements and heavy rare earth elements, consistent with the geochemical signatures of subduction‐related genesis. In addition, in situ Hf isotopic analyses of zircons from 4 dated samples reveal that they have εHf(t) values of −0.4 to +10.3, with 2‐stage model ages varying from 551 to 1,261 Ma, indicating that they probably originated from the partial melting of a dominantly Mesoproterozoic–Neoproterozoic crustal source. On the basis of the geochemical data and regional geological investigations, we propose that the formation of the Late Permian Mo‐bearing granite was related to the subduction of the Paleo‐Asian Ocean plate, whereas the generation of the Early‐Middle Jurassic Mo‐bearing granitoids was associated with the subduction of the Paleo‐Pacific Plate beneath the Eurasian continent.

S-type granite from the Gongpoquan arc in the Beishan Orogenic Collage, southern Altaids: Implications for the tectonic transition

Voluminous Paleozoic intrusions occur in the Beishan Orogenic Collage (BOC) and their genesis and tectonic background are important to reconstruct the accretion-collision processes in the southernmost Altaids. Paleozoic is an important period for arc development in the BOC, where the Gongpoquan and Huaniushan arcs are located. There are two pulses of magmatism in the Huaniushan and Gongpoquan arcs, i.e., the ca. 470–423Ma I-type and ca. 424–395MaS- and A-type granitoids. In this study, we focus on two peraluminous granitic plutons in the Gongpoquan arc, i.e., the Baitoushan muscovite granite and Haergen two-mica granite, aiming at unraveling their petrogenesis and tectonic background. Zircon LA-ICP-MS U-Pb dating yields emplacement ages of ca. 409–395Ma and ca. 409Ma for the Baitoushan and Haergen plutons, respectively. Both the granitic plutons are strongly peraluminous with A/CNK ratios of 1.10–1.20, indicative of S-type affinities. The rocks are characterized by high SiO2 and K2O contents with high CaO/Na2O ratios. Moreover, the rocks possess low MgO contents, Rb/Sr and Rb/Ba ratios, together with their relatively high initial 87Sr/86Sr ratios (0.7139–0.7152) and less radiogenic εNd(t) values (−3.15 to −5.17), implying a clay-poor and plagioclase-rich crustal source.Compared with earlier pulse of arc-related magmatism (ca. 470–423Ma), the latter pulse of magmatism (ca. 424–395Ma) consists mainly of “normal granite” characterized by higher SiO2 (>66%) and K2O contents, weaker fractionated REE patterns and lower δEu values, and gabbroic to dioritic intrusions are only sporadic. Moreover, the granitoids of the latter pulse show variable but more crust-like Sr-Nd isotopic compositions ((87Sr/86Sr)0=0.7038–0.7327; εNd(t)=−6.70 to +0.33) than the earlier ones ((87Sr/86Sr)0=0.7024–0.7080; εNd(t)=−2.56 to +8.86), indicating that the Early Devonian (ca. 424–395Ma) experienced extensive crustal melting with minor involvement of mantle materials. Considering Early Devonian geological evidence, the transition from I- to S- and A-type magmatism probably reflects the Early Devonian amalgamation between the Gongpoquan and Huaniushan arcs, which caused not only regional unconformity and strong deformation-metamorphism, but also extensive melting of the accreted crustal materials in the BOC.