Genesis of the Jurassic Dongfengbeishan porphyry Mo deposit in Eastern Yanbian, NE China inferred from molybdenite Re–Os and zircon U–Pb ages, and whole-rock elemental and zircon Hf isotopic compositions
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Molybdenite
Fractional crystallization (geology)
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The recently discovered Dongbulage Mo-polymetallic deposit is located in the southern part of the Great Xing’an Range, northeast China. Mineralization is closely related to the emplacement of Middle–Late Jurassic granitoids. In order to understand the petrogenetic link between mineralization and host granitoids, this study presents new zircon U–Pb ages, bulk-rock geochemistry, and molybdenite Re–Os ages for the Dongbulage deposits. LA-ICP-MS zircon U–Pb dating of the monzogranite and syenogranite intrusions yielded two weighted mean 206Pb/238U ages: of 164 ± 2 Ma and 165 ± 3 Ma, respectively. The subvolcanic rocks (red porphyritic granite and rhyolite) yielded a time interval between 161 ± 2 and 162 ± 3 Ma. In addition, molybdenite from the Dongbulage deposit gave a Re–Os isochron age of 162.6 ± 1.5 Ma, which was interpreted as the age of the mineralization. The new geochronology has established the close temporal and genetic relationships between the mineralization event and the emplacement of the Middle–Late Jurassic granitoids. Bulk-rock geochemistry shows that the Dongbulage granitoids are characterized by high SiO2, K2O, and A/CNK [Al2O3/(CaO + Na2O + K2O)(molar ratio)] values, and low TiO2, CaO, and MgO values, indicating a metaluminous to peraluminous, high-K calc-alkaline affinity. The granitoids also featured enrichments of large ion lithophile elements and light rare earth elements (LREE), and a relative depletion of high field strength elements (HFSE), along with an increasing negative δEu anomaly. The high differentiation index (DI), ranging from 81.75 to 94.76, and obvious fractionation between LREE and HREE, indicate that the Dongbulage granitoids are highly fractionated, metaluminous–peraluminous, and high-K calc-alkaline I-type granites. Combined with the regional geology, the Dongbulage granitoids may have formed during post-orogenic extension that followed the Mongol–Okhotsk Ocean closure coeval with subduction of the paleo-Pacific plate.
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The Xingjiashan molybdenum-tungsten deposit,located in the intersection between North China block and Yangtze block,is a large-scale skarn-type deposit in the North Fushan ore field.It belongs to the regional multi-metal metallogenetic series related to the Early Yanshanian granitoid magmatic actions.In this study,in order to restrict the timing of mineralization,direct Re-Os isotopic dating on molybdenites collected from the skarn ore in the Xingjiashan molybdenum-tungsten deposit have been carried out.The results of Re-Os isotopic dating show that the Re-Os model ages range from 156.91±1.78Ma to 160.70±1.66Ma,with an average of 158.91±1.91Ma,and give an isochron age of 158.70±2.06Ma.Combined with the zircon SHRIMP U-Pb age of 158.53±0.79Ma of the Early Yanshanian granite,it is suggested that the mineralization of the regional molybdenum-tungsten is temporally and genetically related to the granite in the area,and the large-scale re-melting granitoid magma might provided the major metallogenetic materials and hydrotherm.Based on the results of Re-Os isotopic dating presented in this study and available isotopic data published in previous studies,we suggest that the mineralization in the Jiaodong Peninsula since Mesozoic could be divided into four mainly phases:the first is the copper-molybdenum multi-metal mineralization phase at ca.165~155Ma;the second is the gold mineralization phase at ca.137~110Ma;the third is the copper-molybdenum-lead-zinc multiple metal mineralization phase at ca.120~110Ma;and the fourth is the gold-silver-lead-zinc multi-metal mineralization phase at ca.100~75Ma.They are respectively responding to the multiphase granitoid magmatic actions during Early-Late Yanshanian.
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Located in the East Qinling molybdenum belt of Shaanxi Province,the Shijiawan ore deposit is a large porphyry deposit.Mineralization of the deposit consists of quartz-molybdenite veinlets and stockworks which occur in altered granite porphyry and wall rocks.Hydrothermal alteration is composed of potash feldspathization,silicification and sericitization.Direct Re-Os dating of molybdenites collected from different ores in the Shijiawan deposit was carried out to better understand the age of mineralization.The results show that molybdenite samples yield 187Re-187Os model ages ranging from 143.1±2.1 Ma to 145.1±2.2 Ma,with the average of 144.0±1.1 Ma(MSWD=0.91),and give an isochron age of 145.4±2.1 Ma(MSWD=0.83).These ages are close to the zircon U-Pb ages of Shijiawan feldspar-granite porphyry(141.4±0.6 Ma),indicating that mineralization occurred in Late Jurassic-Early Cretaceous period.In combination with the evidence from S isotope,Re content and chemical characteristics of the related pluton,the authors hold that the ore-forming materials were mainly derived from the crust,with the addition of a little mantle material.
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Hongshan Cu-polymetallic deposite,which has long been considered as an Indosinian skarn-type Cu-polymetallic deposit,is located in Zhongdian arc,south of Yidun arc,northwest Yunnan,China.Recent researches show that there is late Yanshan Epoch porphyry Cu-Mo mineralization in Hongshan deposit area too.In this paper,late Yanshan Epoch granite porphyry in Hongshan deposit area was found for the first time.LA-ICP-MS zircon U-Pb dating of the granite porphyry yields crystallization age of 81.1±0.5 Ma,which is very close to a previously reported molybdenite Re-Os isochron age of porphyry Cu-Mo mineralization(77±2Ma).It means that there is a consistent spatial-temporal relationship between the granite porphyry and the porphyry Cu-Mo mineralization.The age of the late Yanshan Epoch magmatism(81.1±0.5 Ma) in the Hongshan Cu-polymetallic deposit is consistent with the peak period(around 80Ma) of the granites magmatism under post-orogenic extensional environment in Yidun arc.So it is suggested that there is not only Indosinian skarn-type Cu-polymetallic mineralization in Hongshan area,which is closely related to the subduction of oceanic crust,but also the late Yanshan Epoch porphyry Cu-Mo mineralization under post-orogenic extensional environment.
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The Yanqian tungsten deposit is located in east section of Nanling region,the conjunction of the E-W striking Nanling tectonic belt and the NNE Circum Pacific Ocean tectonic belt.The primary mineralization types include skarn type scheelite deposit and wolframite-quartz vein deposit.The orebodies occur in the inner and the outer contact zone of the Early Yanshanian granite.Based on the studies of regional geology and deposit geology,the LA-ICP-MS zircon U-Pb and molybdenite Re-Os isochron dating have been carried out to accurately determine the ages of the granite pluton and the mineralized quartz vein within the pluton.The zircon U-Pb age of mineralized pluton is(160.6±0.72)Ma.The Re-Os isotopic age of molybdenite within mineralized quartz vein is(159.2±2.3)Ma.The isotopic dating results show that petrogenic age of the granite is similar with that of the mineralized quartz vein,which means that the magmatism and mineralization occurred in the same period.According to the previous research data,it was considered that the magmatism and mineralization during 160~150Ma in the Nanling region primarily developed within the mid-east section,and might be caused by the large-scale lithosphere extension.The Yanqian tungsten deposit belongs to the same sub-metallogenic series as some famous deposits in the eastern Nanling region,such as Pangushan,Huameiao and Shizhuyuan,with great exploration potential in the depth.The exploration targets in Yanqian area should primarily be aimed at skarn type and quartz vein type tungsten-polymetallic deposits in the inner contact.
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The Longmala and Mengya'a deposits are two representative skarn Pb–Zn deposits of the Nyainqêntanglha Pb–Zn–(Cu–Mo–Ag) polymetallic belt in the Gangdese region, Tibet, China. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the mineralization-related biotite monzogranite from the Longmala deposit yielded a weighted mean age of 55.7 Ma, which can be interpreted as the emplacement age of the pluton. Re–Os dating of three molybdenite samples from the Longmala deposit yielded model ages of 51.8–54.3 Ma, with a weighted mean age of 53.3 Ma, which is interpreted as the mineralization age of the deposit and overlaps the age of the causative intrusion. The Re–Os dating of four molybdenite samples from the Mengya'a deposit yielded model ages of 60.4–65.8 Ma, with a weighted mean age of 63.6 Ma, which represents the mineralization age of this deposit. Our new precise age data for these two deposits are consistent with the existing ages of ca. 65–51 Ma for other skarn polymetallic deposits in the Nyainqêntanglha metallogenic belt. In addition, these new age data, combined with existing information on the geological evolution history of the Lhasa terrane, indicate that the belt of skarn deposits is closely related to initial collision between India and the Asian continents.
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This study reports U-Pb isotopic geochronology and geochemistry of the Zhuxiling granite pluton exposed in the northeast area of the middle-lower Yangtze area of SE China.The Zhuxiling granites have high SiO2-and K2O-contents and low MgO-content,enriched in large ion lithosphere elements of K,Rb,Ba and Sr,low Sr/Y ratios,depleted in high field strength elements of Nb,Ta,Zr and Ti,significantly positive Pb-anomalies which showed a crust source.The Zr/Hf ratios of these granites(between 21.5and26.7)were dramatically lower than that of the crust(35.5in average).It is speculated that the fractional crystallization of zircon may cause the decrease of Zr/Hf ratios in the melt.Analytical results of the zircon U-Pb dating yield an age of 140.5±1.3Ma,138.7±1.6Ma and 142.4±1.6Ma for the formation time of granites.TheeHf(t)values of zircon ranges from 2.3to-4.76with only a few positive value.Taken the background of the study area and the SE China into consideration,we propose that the formation of Zhuxiling pluton may be related to slab rollback.
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New ReOs molybdenite and UPb zircon dates from deposits of the Tombstone Gold Belt provide direct timing constraints for sulphide mineralization and crystallization of spatially associated plutons. At Clear Creek ReOs molybdenite dates (93.6 ± 0.3 to 92.4 ± 0.4 Ma) are in excellent agreement with the host intrusion UPb zircon age (92.3 ± 0.3 Ma). Consequently we propose the nominally younger existing 40 Ar/ 39 Ar hydrothermal mica ages (91.7 ± 0.4 and 90.0 ± 0.3 Ma) for Clear Creek are a result of slow cooling. At Dublin Gulch, the ReOs molybdenite date (93.2 ± 0.3 Ma) for a late stage vein is nominally younger than the host intrusion UPb zircon age (94.0 ± 0.3 Ma), in agreement with the deposits paragenesis. The UPb zircon date (92.1 ± 0.2 Ma) for the Mactung pluton, which lies adjacent to the W-skarn, has a younger age than the ReOs molybdenite dates (97.5 ± 0.5 Ma). Fluid inclusion geochemical data for ore-fluid indicate a magmatic origin for the W-skarn. However, the UPb and ReOs age data suggest that the exposed Mactung stock is not the source of ore-fluid for the W-skarn and that the progenitor pluton for ore-fluid is unknown. The robust age constraints obtained for mineralization and magmatism in this study are in accord with the hypothesis that these deposits are intrusion-related ore systems. The results are also in agreement with previous studies demonstrating that the ReOs molybdenite chronometer can provide accurate and precise dates for the timing of metallic mineralization with rigorous sampling protocol.
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Longjiaoshan Cu-W deposit is a strata-bound skarn deposit in southeastern Hubei!Province.In this paper,the authors carry out detail geochronological study by using LA-ICP-MS zircon U-Pb and molybdenite Re-Os analyses.The results indicate that the granodioriteporphyries in the Longjiaoshan orefield were emplaced in 144±1Ma,and mineralization occurred in 144.7±2.9Ma,suggesting that diagenesis and mineralization were broadly coeval and occurred in Early Cretaceous.This means that the mineralization was closely related to the evolution of granodiorite porphyries.The Longjiaoshan-Fujiashan granodiorite porphyries are high-K calc-alkaline,and show adakite-like geochemical characteristics,such as high Al2O3(14.99%~16.16%),Sr(751×10-6~1382×10-6)contents and Sr/Y(65~99),La/Yb(40~48)ratios,as well as low Y(12×10-6~15×10-6),Yb(0.93×10-6~1.23×10-6)contents.(87Sr/86Sr)i andeNd(t)value of the whole rock is 0.70603and-5.1,respectively,and zirconeHf(t)values range from-0.5to-4.8.Geochemical,Sr-Nd isotopic of the whole rock and zircon Hf isotopic characteristics consistently indicate that the Longjiaoshan-Fujiashan granodiorite porphyries were mainly derived from partial melting of enriched lithospheric mantle,and possibly followed by fractional crystallization of mafic minerals in the course of the diagenesis.Moreover,compared with the Tongshankou granodiorite porphyry,the Longjiaoshan-Fujiashan granodoirite porphyry has lower oxygen fugacity,which likely resulted in their difference of mineralization type(Cu-Mo mineralization predominated in the former,however,Cu-W mineralization predominated in the latter).
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Tin, tungsten, and rare metals are key strategic metals and are regarded as having potentially relationship with highly evolved granites. However, excessive U accumulation with magmatic evolution, complex melt-fluid interaction, and late hydrothermal alteration make it difficult to obtain accurate age information from the highly evolved granitic system. The Xianghualing deposit, located in southern Hunan Province, China, is a giant Sn-Nb-Ta-polymetallic deposit with various types of mineralization spatially associated with the Laiziling and Jianfengling highly evolved granite plutons, and is an ideal target to investigate the magmatic-hydrothermal process of highly evolved magmas and related Sn-Nb-Ta-polymetallic mineralization. Previous studies have reported a relatively wide range of intrusion ages and multi-stage mineralization ranging from Triassic to Cretaceous. However, the timing and genetic link between magma emplacement and Sn-Nb-Ta-polymetallic mineralization remain controversial. Here we employ multiple dating methods, including SHRIMP zircon U-Pb analysis, LA-ICP-MS zircon and monazite U-Pb analysis, and molybdenite Re-Os dating analysis with a view to obtain a precise geochronological framework of the Xianghualing deposit. The SHRIMP zircon U-Pb data from the Laiziling protolithonite granite yielded a weighted 206Pb/238U age of 156.4 ± 1.5 Ma, whereas the LA-ICP-MS monazite U-Pb age for the Laiziling albite granite and the greisenized granite show 207Pb-corrected lower intercept 206Pb/238U ages of 155.5 ± 0.7 and 155.3 ± 0.5 Ma, respectively, which represent the emplacement ages of the Laiziling granite stock. Compared with the scattered SHRIMP and LA-ICP-MS zircon U-Pb age, monazite from the albite granite and greisenized granite yields more precise age information. Our study shows that monazite can be used as a robust tool for dating highly evolved granites. Molybdenite from the Laiziling pegmatite yields a Re-Os isochron age of 157.8 ± 4.2 Ma, which is consistent with the emplacement age of the Laiziling pluton. This result, integrated with previously reported metallogenic age, suggests a temporal and genetic link between the Laiziling granite and Sn-Nb-Ta polymetallic mineralization. Although multi-stage Sn-W metallogenic events have been identified in Nanling Region, it is suggested that the Xianghualing Sn-Nb-Ta mineralization formed during the Late Jurassic within a short duration coeval with the regional large-scale W-Sn mineralization at 160–150 Ma.
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