Bangong-Nujiang Metallogenic Belt Research Articles

Major types, spatio-temporal distribution, and metallogenesis of magmatism-related polymetallic deposits in the Bangonghu–Nujiang metallogenic belt, Tibet

The Bangong–Nujiang metallogenic belt (BNMB) is one of the vital metallogenic belts in the Tibetan Plateau. At present, the metallogenic regularity on the scale of the whole metallogenic belt is still poorly understood. In this contribution, the geological, geochronological, geochemical, and isotopic data of 87 magmatism-related polymetallic deposits in the BNMB have been systematically collected to summarize the metallogenesis of polymetallic deposits in this belt. Our research shows that different segments of the BNMB have distinct metallogenic differences. The western, central, and eastern segments of the BNMB are characterized by the development of abundant Cu–Au, Fe–Cu–Cr–Ni, and W–Pb–Zn deposits, respectively. These various types of magmatism-related polymetallic deposits in the BNMB were formed between 188 Ma and 76 Ma, and the mineralization has two peak periods of 125–110 Ma and 90–75 Ma. The spatio-temporal variation of different types of magmatism-related polymetallic deposits in the BNMB is likely to be constrained by the lithospheric architecture and deep geodynamic processes. The elemental and Sr–Nd–Hf–S–Pb isotopic results indicate that various kinds of mineralization are closely related to relevant magmatism. The Cu–Au mineralization is related to dominantly mantle-derived, highly-oxidized, and less-evolved granitic intrusions; the Pb–Zn–W mineralization is genetically associated with dominantly ancient middle–upper crust-derived, relatively reduced, and highly-evolved granitic intrusions; the characteristics of the ore-causative intrusions related to Fe–Cu–Mo polymetallic mineralization are between those of the above two end members. In combination with previous studies, we propose a comprehensive model that includes four stages (>145 Ma, ∼145–125 Ma, ∼125–105 Ma, and ∼105–74 Ma) to illustrate the Jurassic–Cretaceous tectonic–magmatic–metallogenic evolution history in the whole BNMB.

Strongly Peraluminous Highly Fractionated I-Type Granite from Bangong–Nujiang Metallogenic Belt, Tibet: Implications for Continental Evolution and Evaluation of Economic Potentiality

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma’s evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits.

Metallogeny in the Bangong–Nujiang belt, central Tibet, China: A review

The Bangong–Nujiang metallogenic belt consists of scattered Tethyan oceanic blocks, mainly distributed underneath the margins of the Qiangtang and Lhasa terranes in central Tibet. A new world-class metallogenic belt has been reported in this region recently, based on the geological mapping and ore deposit prospecting over the last two decades. It currently comprises inferred resources of 30 Mt Cu and 500 t Au, together with several Cr–Ni, Fe, and W (Mo) resources, forming a significant potential area for future mineral exploration. These metals are mainly hosted in porphyry copper, skarn copper, skarn iron, orogenic gold, quartz-vein tungsten, and ophitic chromite deposits. The mineral deposits in the Bangong–Nujiang metallogenic belt have been widely recognized in different localities, including the southern edge of the southern Qiangtang block, part of the north Lhasa block, and even part of the central Lhasa block, indicating they were formed in variable geological settings, from the initial opening, subduction, and collision to the extension of the Bangong–Nujiang Ocean. Specifically, five major tectonic events contributed to mineralization, including the stage 1 (240–165 Ma) initial opening of the Bangong–Nujiang Ocean, stage 2 (165–145 Ma) oceanic subduction, stage 3 (145–100 Ma) close of the ocean, stage 4 (100–65 Ma) continent–continent collisional orogenesis, and stage 5 (65–0 Ma) post-orogenesis. At stage 1, Cr–Ni deposits were formed during the initial opening of the ocean; porphyry–epithermal Cu (Au), skarn Fe, and minor orogenic Au deposits were formed at stage 2 and stage 3; a younger pulse of a few porphyry–skarn Cu ± Mo and orogenic Au deposits were formed during stage 4; finally, W(Mo) deposits were generated in stage 5. In general, porphyry Cu systems, orogenic Au, and skarn Cu polymetallic deposits that occurred in the subduction and post-collision settings related W(Mo) deposits have the most potential for future exploration. An in-depth investigation of several scientific problems, such as addressing the tectonic setting, magmatism, and metallogeny of this region and genetic linkage of these deposit preservations to plateau uplift, is essential for the future success of exploration in the Bangong–Nujiang metallogenic belt.

Age and compositions of garnet in a magnesian skarn Au-Cu deposit, Tibet, implications for ore-fluid evolution

Compared to calcareous skarn Au-Cu deposits, magnesian skarn (Mg-skarn) Au-Cu deposits are scarce; hence the early evolution of the ore-fluids to late mineralization for the kinds of deposits has been inadequately investigated. Located at the southern margin of the Bangong-Nujiang metallogenic belt, the Galale Au-Cu deposit contains 32.59 tonnes of gold (average grade 2.04 g/t) and 105,600 tonnes of copper (average grade 0.66 %). The orebodies are hosted in an Mg-skarn with associated minerals, including olivine, pyroxene, garnet, and serpentine, which developed in the contact zone between the granodiorite and dolomite of the Jiega Formation. However, the genetic relationship between the Mg-skarn, granodioritic magma, and Au-Cu mineralization remains unclear. The contribution of early stage ore-forming fluids to late Au-Cu mineralization is still vague. In this study, we present the major and trace element compositions, and U–Pb isotope data for garnets obtained from the Galale deposit. We used the data to define the timing, nature, and evolution of early ore-forming fluid and described the genesis of the deposit. The color, at macro- and micro-scales, and chemical composition of the garnets can be used to divide them into two categories, namely early Al-rich Grt-I type garnets, and late stage Fe-rich Grt-II type garnets. In practice, Grt-I (And29.5∼56.1Gro41.3∼68.0Pra1.6∼2.8) and Grt-II (And96.7∼99.9Gro0∼2.7Pra0.1∼0.7) are grossular-andradite solid solution system garnets. Based on the chondrite-normalized REE patterns, Grt-I can be further divided into two sub-classes: Grt-I-1 domain in the core, enriched in HREEs and U, and Grt-I-2 material in the rim, relatively depleted in HREEs. Grt-II is enriched in LREEs and depleted in HREEs. Eu anomalies are slightly negative for the Grt-I-1 domain, weakly positive for the Grt-I-2 domain, and strongly negative for the Grt-II type garnets. The variations in texture and composition in garnets indicated that the formation of Grt-I garnets occurred during diffusive metasomatism in a relatively closed system, in a moderately oxidized ore-forming fluid setting. The formation of Grt-II occurred in a strongly oxidized setting during advective metasomatism in an open system. The enrichment of REE and U in Grt-I garnets was mainly controlled by a “menzerite” type substitution mechanism, partially explaining the strong positive correlation between Mg and REE concentrations. In the Grt-II type garnets, enrichment may also have been co-controlled by coupling substitution and adsorption. In situ U–Pb dating of garnet shows that Grt-I-1 and Grt-I-2 material has isotopic ages of 92 ± 2 Ma (2σ, MSWD = 0.85) and 91 ± 2 Ma (2σ, MSWD = 0.96), respectively. The results were consistent with the previous ages obtained from the granodiorite and Molybdenite using Re–Os isotopic dating within error. This indicates that magma, skarn alteration, and mineralization were spatially and temporally related. In addition, it indicates that the Galale deposit is a typical Mg-skarn Au-Cu deposit. In the earliest stages of deposit development, ore-forming fluids with a high oxygen fugacity (fO2) have inherited their characteristics from the magma. The crystallization of many magnetites during the oxide stage has decreased oxygen fugacity in the metallogenetic system. This has resulted in a relatively low fO2 fluid for Au-Cu precipitation. The study demonstrates that the ore-fluid fO2 plays a vital role in metal migration, hence Au-Cu mineralization in Mg-skarn deposits.

Post-subdution evolution of the Northern Lhasa Terrane, Tibet: Constraints from geochemical anomalies, chronology and petrogeochemistry

Bangong-Nujiang collisional zone (BNCZ) is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt, which plays an important role in evaluating the formation and uplift mechanism of plateau. The northern and central Lhasa Terrane composed the southern part of the BNCZ. Since ore deposits can be used as markers of geodynamic evolution, the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization, and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane. The authors find Early Cretaceous magma mainly resulted in Cu, Mo mineralization, Late Cretaceous magma mainly resulted in Cu, Mo, and W mineralization in the studying area. The results suggest a southward subduction, slab rolling back and break-off, and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.© 2022 China Geology Editorial Office.

The first intra-oceanic island-arc porphyry Cu (Au) deposit in the western Bangong-Nujiang suture zone: Evidence from the Saidengnan Cu (Au) deposit

The Saidengnan deposit, located in the Bangong-Nujiang suture zone, is proposed to be the first intra-oceanic island-arc porphyry Cu (Au) deposit in the Bangong-Nujiang metallogenic belt. The Cu (Au) mineralization is hosted in the quartz diorite porphyry as fine grained disseminated form. Zircon U-Pb ages of the ore-forming quartz diorite porphyry and the post-mineralization granodiorite are 118.1–118.8 Ma and 116.2 Ma, respectively, suggesting that mineralization occurred in the Early Cretaceous. The S isotopes (δ34S = −3.8 to −1.5) of ore sulfides and H-O isotopes (δD = −99‰ to −89.9‰, δ18OH2O = 4.9–9.4‰) of ore-bearing quartz veins indicate that the ore-forming fluids was sourced from the ore-forming intrusion. All intrusive rocks are enriched in light REE and LILE (Rb, K) and depleted in HFSE (Ni, Ta, Ti), similar with the island-arc magmas. Whole rock (87Sr/86Sr)i values (0.7040–0.7056), εNd(t) values (−0.35 to 1.94), and significantly positive zircon εHf(t) values (7.37–11.38) and young TDM2 of zircon Hf (455–705 Ma) indicate that the Saidengnan intrusive rocks are dominantly derived from mantle wedge metasomatized by subducted fluids and sediments. This is different from the Duolong continental arc magmas formed by crust-mantle mixing. Combined with stratigraphic data published, we propose that the Saidengnan porphyry Cu (Au) deposit should be formed in the intra-oceanic island-arc setting caused by the oceanic-oceanic subduction of the Bangong-Nujiang Ocean.

Sulphate supergene minerals: An intuitive indicator for deep deposit in plateau regions

The world‐class Rongna Cu(Au) deposit, located in the Duolong mining district, is the first epithermal‐porphyry deposit along the Bangong–Nujiang metallogenic belt. The acidic spring developed in the centre of the Rongna Deposit and its basin has a high amount of heavy metals. Therefore, metal elements (Cu, Pb, Zn, Cd, As, Cr and Hg), pH, SO42− of the Rongna River and the composition of its supergene minerals are studied to discuss the environmental influence and provide a theoretical basis for the comprehensive utilization and environmental management of the Rongna Deposit. The result shows that there are eight kinds of supergene minerals: natrojarosite, hexahydrite, tamarugite, anhydrite, pickeringite, bloedite, gypsum and naujakasite, among which, naujakasite is discovered for the first time in China. The material sources of these sulphate minerals and acidic water are from the sulphate in the ores that experience the leaching process and oxidation. The spring is severely acidified, whose pH values are 2.70–3.08, the single pollution index of Cr, Cd, Pb, Hg and As are less than 1, but the index of Cu and Zn exceed the Class III National Water Standard by about twice, showing a mild pollution, its comprehensive pollution index values 0.8 ~ (<2.5), showing good quality. The pH of Rongna River water values are 7.70–7.92, the single pollution index is less than 1, indicating no pollution, and the comprehensive pollution index is less than 0.8, indicating good quality. However, considering the vulnerable ecological environment in Tibet, the acidic spring still needs manual intervention. An open‐air reservoir can be built upstream of the acidic spring, and the pollutants can precipitate by natural evaporation and then be recycled.

Post-subdution evolution of the Northern Lhasa Terrane, Tibet: Constraints from geochemical anomalies, chronology and petrogeochemistry

Bangong-Nujiang collisional zone (BNCZ) is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt, which plays an important role in evaluating the formation and uplift mechanism of plateau. The northern and central Lhasa Terrane composed the southern part of the BNCZ. Since ore deposits can be used as markers of geodynamic evolution, the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization, and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane. The authors find Early Cretaceous magma mainly resulted in Cu, Mo mineralization, Late Cretaceous magma mainly resulted in Cu, Mo, and W mineralization in the studying area. The results suggest a southward subduction, slab rolling back and break-off, and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.© 2022 China Geology Editorial Office.

Timing and origin of the Shesuo skarn Cu-polymetallic deposit in the northern Lhasa subterrane, central Tibet: Implications for Early Cretaceous Cu(Mo) metallogenesis in the Bangong-Nujiang metallogenic belt

The Bangong-Nujiang metallogenic belt is a newly discovered copper-polymetallic belt in the Tethyan domain. To date, the Shesuo skarn Cu-polymetallic deposit is the only productive Early Cretaceous Cu deposit in the middle segment of this belt. We conducted zircon U-Pb and molybdenite Re-Os dating of this deposit, and the results show that the Shesuo skarn Cu-polymetallic deposit formed at 117–112 Ma. Within the mining area, granodiorites and monzogranites are the main metallogenic granitic bodies. The petrogeochemical features imply that the granodiorites and monzogranites were derived from the partial melting of juvenile lower crust resulting from mantle-derived magmatic underplating, with the additional involvement of ancient crust in the magma chamber, whereas the monzogranites experienced significant fractional crystallization. The δ34S values of sulfide ores suggest that they were mainly sourced from the magma and slightly contaminated by surrounding strata. The Pb isotope compositions of sulfides and Re contents of molybdenite indicate that the metals were derived from the juvenile lower crust, with a small fraction from ancient crustal materials. Our study suggests that the generation of the Shesuo deposit was most likely triggered by slab breakoff during the southward subduction of the Bangong-Nujiang Ocean lithosphere. The Shesuo and Xiongmei deposits have low zircon Ce4+/Ce3+ and EuN/Eu* ratios and low whole-rock average V/Sc, Sr/Y and (EuN/Eu*)/YbN ratios. We propose that these values are due to the input of reduced components, leading to the generation of metallogenic magmas with relatively low magmatic oxidation states and water contents and rendering the magmas infertile for later porphyry-skarn Cu formation in the Xiongmei area.

Geology, fluid inclusions, 40Ar/39Ar geochronology and H-O-S-Pb isotopes of the Galale Cu[sbnd]Au deposit, Northwestern Tibet, China

The Galale CuAu skarn deposit is located on the southern margin of the Bangong-Nujiang metallogenic belt, Tibet, and the CuAu mineralization is related to the Late Cretaceous granodiorite. The orebodies occurring as stratiform, lenticular and vein types are hosted within the skarn along the contact between the granodiorite and dolomitic marble or calcitic marble of the Jiega Formation. At least four hydrothermal alteration stages of the deposit have been recognized: prograde magnesian and calcic skarn stage (Stage 1), retrograde skarn stage (Stage 2), hydrosilicate alteration stage (Stage 3), and phyllic alteration stage (Stage 4).Fluid inclusions from skarn rocks and quartz veins are indicative of multiple fluid events. The prograde skarn was formed from a medium-salinity, hot (466–518 °C), high pressure (>1000 bar) homogenous magmatic-hydrothermal fluid, under its possible direct separation from crystallizing magma. The subsequent retrograde skarn was formed from a slightly lower temperatures (370–460 °C) and lower pressure (~800 bar) homogenous magmatic-hydrothermal fluid that could be supplied by crystallizing magma. Sharp drop of pressure (from 800 bar to 300 bar) and significant decrease of temperatures (low to 300 °C) may be related to fracturing and increase of porosity during alteration of skarns, and caused the fluid boiling in hydrosilicate alteration stage. The fluid from the latest phyllic alteration stage is characterized by dominant meteoric water and more lower temperatures (low to 178 °C). Decrease of fluid temperatures and pressures, fluid boiling and changes of redox regime are considered the crucial mechanisms for controlling the precipitation of the ores.The δ34S values of the sulfides range from −4.4 to 6, primarily from −0.9 to 1.7, that suggest a magmatic source. The sulfides yield narrow ranges of 206Pb/204Pb ratios (18.141–18.871) and 207Pb/204Pb ratios (15.588–15.701) and a wide range of 208Pb/204Pb ratios (38.359–39.008), indicating a mixed crust-mantle ore-forming metal source. The 40Ar39Ar plateau age of phlogopite from the chalcopyrite-bearing phlogopite tremolite skarn (Stage III) is 87.5 ± 0.6 Ma, which is consistent with the crystallization age of the Late Cretaceous granodiorite. Consequently, taking the data together suggests that the Galale CuAu deposit is a typical oxidized CuAu skarn deposit related to the Late Cretaceous magmatic-hydrothermal systems.

Alteration mineralogical and geochemical features of the Rongna deposit in Duolong mining district of Tibet and their deep prospecting significances

位于西藏多龙矿集区的荣那铜金矿床是班公湖-怒江成矿带首例斑岩型-浅成低温热液型矿床，它的发现对于班公湖-怒江成矿带找矿模型的构建以及资源潜力评估有着重要意义。本文以荣那矿床ZK3204岩芯钻孔为研究对象，针对其蚀变矿物，运用短波红外光谱测试技术，并结合金属矿物组合以及黄铁矿LA-ICP-MS原位微量元素特征，以期查明其矿床成因，并为深部资源勘查提供理论依据。短波红外光谱测试显示出ZK3204钻孔蚀变矿物垂向分带组合为：高岭石+（地开石）→高岭石+伊利石→高岭石+（地开石+石膏）→高岭石+绢云母+伊利石→高岭石+伊利石+（叶腊石）+（地开石），金属矿物也从Cu-S体系逐渐转变为Cu-Fe-S体系。通过黄铁矿LA-ICP-MS原位微量元素分析发现，黄铁矿可分为四类，分别对应荣那矿床四个成矿阶段：（1）Py I：Co、Ni、Cu、Ag、Au含量较低，Co/Ni显示为沉积成因，代表成岩期黄铁矿；（2）Py Ⅱ：Co、Ni含量较低，Cu、Ag、Au含量较高，Co/Ni显示为沉积成因，代表第一期斑岩型矿床成矿期黄铁矿；（3）Py Ⅲ：Co含量较低，Ni、Cu、Ag、Au含量较高，Co/Ni显示为沉积成因，代表第二期斑岩型矿床成矿期黄铁矿；（4）Py Ⅳ：Cu、Ag、Au含量较低，Co、Ni含量较高，Co/Ni显示为热液成因，代表浅成低温热液矿床成矿期黄铁矿。风化作用也是荣那矿床重要地质过程，贯穿于各成矿阶段，反映为早白垩世班公湖-怒江洋盆向北俯冲消减大背景下的多龙矿集区隆升事件，导致矿床被大量剥蚀，也使黄铁矿显示沉积成因。荣那矿床目前仍有较大找矿潜力，在钻孔深部（815m以下），黄铁矿Cu、Ag、Au含量，钻孔中Cu、Pb、Zn、Cr、Hg等含量，绢云母、伊利石含量以及铜金矿的矿石品位均有向下升高的趋势，说明在ZK3204钻孔下部仍有巨大的找矿潜力，可作为未来深部资源探测的重点对象。;The Rongna Cu-Au deposit, located within the Duolong mining district, is the first discovered epithermal porphyry deposit in the Bangong-Nujiang metallogenic belt, and it is of great importance to built the prospecting model and to assess the resource potential along this belt. The alteration assemblages and ore minerals and pyrite's LA-ICP-MS trace element features of ZK3204 drilling are studied to determine the genesis of deposit, and to provide theoretical foundation for deep resource exploration in this area. It is found that alteration minerals identified by shortwave infrared techniques exhibits vertical zoning of kaolinite+(dickite)→kaolinite+illite→kaolinite+(dickite+gypsum)→kaolinite+sericite+illite→kaolinite+illite+(pyrophyllite)+(dickite), and Cu-S systematic metallic minerals gradually become Cu-Fe-S systematic metallic minerals. The LA-ICP-MS trace element analyses of these pyrites demonstrates four mineralization stages in the Rongna deposit, which are corresponding to four types of pyrites, respectively, namely: (1) Py I, regarded as the product of diagenetic stage, containing low value of Co, Ni, Cu, Ag, Au, and Co/Ni is interpreted as sedimentary in origin; (2) Py Ⅱ, regarded as the product of porphyry deposit stage I, containing low value of Co, Ni, and rich in Cu, Ag, Au, and Co/Ni is interpreted as sedimentary in origin; (3) Py Ⅲ, regarded as the product of porphyry deposit stage Ⅱ, containing low value of Co, and rich in Ni, Cu, Ag, Au, and Co/Ni is interpreted as sedimentary in origin; and (4) Py Ⅳ, regarded as the product of epithermal deposit stage, containing low value of Cu, Ag, Au, and rich in Co, Ni, and Co/Ni is referred to be the result of hydrothermal activities. Weathering is also an important geological process in the Rongna mineralization stages, which is leaded by the uplifting of the Duolong mining district area generated by northward subduction of the Bangong-Nujiang oceanic crust at Early Cretaceous, eroding some part of ore body, and making pyrites shown as sedimentary ones in origin. The Rongna deposit also shows great resource potential and prospecting under the bottom of drilling (below 815m) since contents of Cu, Pb, Zn in pyrites, and contents of Cu, Pb, Zn, Cr, Hg, sericite and illite of the drilling cores all have trends to extend to the under part, showing there is still a large prospecting potential of porphyry deposit under ZK3204 drilling, which could be an important target for deep resource exploration in the future.

Ore genesis of the Late Cretaceous Larong porphyry W-Mo deposit, eastern Tibet: Evidence from in-situ trace elemental and S-Pb isotopic compositions

The Late Cretaceous (ca. 92 Ma) Larong porphyry W-Mo deposit (39.44 Mt WO3 @ 0.1541%), a newly discovered deposit in the easternmost Bangong-Nujiang metallogenic belt (BNMB), is located in eastern Tibet. The W-Mo mineralization occurs as veins and stock-works hosted in monzogranite porphyry, granodiorite porphyry and surrounding quartz schist, and can be divided into two main paragenetic stages: the W-mineralization stage (Stage I) consists of various K-feldspar-quartz-scheelite veins and the quartz-sulfide stage (Stage II) is dominated by molybdenite and pyrite, of which the latter can be further subdivided into three sub-stages. Here, we present LA-ICPMS in-situ trace elements and S-Pb isotopes of sulfides from the Larong deposit, in order to constrain the sources of ore-forming elements and the processes of mineralization. Our study shows that pyrite is rich in Co and As, molybdenite is rich in W, Pb and Bi, and chalcopyrite has high Sn contents. These results are consistent with the mineralization characteristics of the Larong deposit, where the main metallogenic elements are W and Mo, accompanied by Bi, Sn and Cu. Overall, sulfides from the Larong deposit have calculated δ34SVCDT values ranging from 0.25‰ to 6.37‰, suggesting a predominantly magmatic origin for sulfur. From Stage II-1, to Stage II-2, to Stage II-3, the average δ34SVCDT values of pyrite change from 0.33‰, to 1.88‰, to 5.34‰, showing a progressive and gradual change in redox and temperature conditions. Molybdenite has high Pb isotopic ratios (208Pb/204Pb = 39.356–39.908, 207Pb/204Pb = 15.747–15.928, 206Pb/204Pb = 18.843–20.120) but low Re contents, and pyrite has low Ni contents, implying that the ore-forming materials were mainly derived from the crust. We propose that the W-Mo mineralization is genetically related to the Late Cretaceous monzogranite porphyry, with the mineralization of W and Mo occurring as a result of decreases in temperature and oxygen fugacity of the ore-forming fluid exsolved from the magma. In combination with previous studies, our study led to the identification of three W-dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the BNMB.

Zircon U-Pb-Hf isotopes and mineral chemistry of Early Cretaceous granodiorite in the Lunggar iron deposit in central Lhasa, Tibet Y, China

The Lunggar iron deposit belongs to the Bangong-Nujiang metallogenic belt and is located in central Lhasa on the Tibetan Plateau. In the Lunggar deposit, iron mineralization formed in the skarnization contact zone between the Early Cretaceous granodiorite and the late Permian Xiala Formation limestone. In this study, we achieved detailed zircon U-Pb-Hf isotopes and mineral chemistry for the Early Cretaceous granodiorite. Zircon U-Pb dating results indicate that the Early Cretaceous granodiorite emplaced at ca. 119 Ma. Based on the trace elements in zircons and the mineral chemical composition of amphibole and biotite, the Early Cretaceous granodiorite was believed to form under condition of high temperature (>700 °C), low pressure (100–400 MPa), and relatively high oxygen fugacity (lg/O2)(−13.6 to −13.9) and H2O content (4%–8%). Zircon trace elements, Hf isotope and biotite chemistry collectively reveal that significant juvenile mantle-derived magmas contributed to the source of the granodiorite. The relatively high log/O2 and shallow magma chamber are beneficial for skarn iron mineralization, implying remarkable potential for further prospecting in the Lunggar iron deposit.

Geochronology and petrogenesis of the Xiongmei Cu-bearing granodiorite porphyry in North Lhasa subterrane, central Tibet: Implication for the evolution of Bangong-Nujiang metallogenic belt

Bangong-Nujiang metallogenic belt is a recently recognized post-subduction porphyry-skarn Cu polymetallic metallogenic belt in Tibet. The Xiongmei Cu-bearing granodiorite porphyry was newly found in the middle segment of this belt. In this study, we combined zircon U-Pb ages, Hf isotopic, REEs data, whole-rock Sr-Nd isotopic data, and whole-rock geochemical data to constrain the geochronology, petrogenesis and metallogenic features of the Xiongmei Cu-bearing granodiorite porphyry. Zircon U-Pb and whole rock Rb-Sr isochronal age show Xiongmei Cu-bearing granodiorite porphyry formed during 110–105 Ma. The zircon Hf isotope together with whole rock Sr-Nd isotopic features and high Mg# value (39–59), relatively high Cr (10.9–35.5 ppm) and Ni (10–224 ppm), indicating a melt deriving from mixing between mantle material and an ancient crustal source. The possibility of crustal addition in the magma is further supported by varied Eu anomalies (0.5–1.5), Sr anomalies (0.6–1.9) and high Al2O3 contents (15.50–17.25 wt%). Geochemical composition including K2O contents (0.52–4.72 wt%) and K2O/Na2O ratios (0.2–5.5), and the linear relations between LOI, Cu, Rb and Sr contents indicated that the magma sourced from melting of an amphibolite source, and further suggesting that the juvenile crust derived from an enriched lithospheric mantle. The ratios between incompatible elements together with the absence of Ce anomaly suggested the contribution of fluids from subducted oceanic crust rather than melt. The negative Eu and Sr anomaly features together with relatively high HREEs and Y contents, low (La/Yb)N and Sr/Y ratios are interpreted as low pressure partial melting. Combination with the regional geologic background, we adopted a slab break-off model to explains the diverse contemporaneous magmatic rocks recognized in the North Lhasa subterrane including that of the Xiongmei Cu-bearing granodiorite porphyry.

Magmatism and metallogenic mechanism of the Ga’erqiong and Galale Cu-Au deposits in the west central Lhasa subterrane, Tibet: Constraints from geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes

The Ga’erqiong-Galale ore district in the Bangong-Nujiang metallogenic belt hosts two large skarn Cu-Au deposits, associated with voluminous Late Cretaceous volcanism and plutonism. In this study, we present new zircon U-Pb age and Hf isotopic data, whole-rock geochemical and Sr-Nd-Pb isotopic data to constrain the geodynamic mechanisms of Late Cretaceous magmatism and metallogenesis within the Ga’erqiong-Galale ore district. The intrusive rocks in the district include diorite, quartz diorite, granodiorite, granite, and dioritic porphyrite. Zircon U-Pb analyses suggest those rocks mainly emplaced at early Late Cretaceous (84–95 Ma), which coincide with the ore-forming age of Ga’erqiong and Galale deposits (87 and 88 Ma, respectively). Geochemically, the granodiorite and dioritic porphyrite are metaluminous with depletion of Nb, Ta, and Ti and characterized by high MgO (2.68–4.16 wt%), Mg# (55–87), Sr (414–616 ppm), Sr/Y (30–56), Cr (22.5–105.0 ppm), and Ni (26.6–59.7 ppm), low Y (10.6–14.0 ppm), and heavy rare earth elements (HREE), showing geochemical signatures of high Mg# adakitic rocks. Four dioritic porphyrite and three granodiorite samples exhibit homologous Sr-Nd-Pb isotope compositions and have positive whole rock εNd(t) values of +1.1 to +3.0, (87Sr/86Sr)i values of 0.7045–0.7048, (206Pb/204Pb)t ratios of 18.42–18.73, (207Pb/204Pb)t ratios of 15.58–15.63, and (208Pb/204Pb)t ratios of 38.54–38.88. Besides, 116 analyses from the Ga’erqiong-Galale adakitic rocks give positive zircon εHf(t) values (+4.3 to +12.1). The geochemical and isotopic data indicate that the early Late Cretaceous high Mg# adakitic rocks in the Ga’erqiong-Galale ore district originated from the delaminated juvenile lower mafic crust that has been modified by the previously subduction. Partial melting of previously subduction modified, delaminated juvenile lower crust not only formed the hydrous adakitic melts in highly oxidation state, but also provided the ore metals (e.g., Cu, Au, Mo) for the subsequent mineralization. Such melts reacted with surrounding mantle peridotite to elevate the contents of metallic elements again. Then the melts experienced varying degrees of fractional crystallization process in the shallow magma chamber to form the dioritic and granodioritic magmas. Those magmas emplaced into the limestone of Duo’ai and Jiega Formation to form the Ga’erqiong and Galale skarn Cu-Au deposits, respectively. Field observation, together with geochronological and geochemical data, indicate that the early Late Cretaceous mineralization events in the northern and central Lhasa subterranes took place in a transition tectonic setting from collisional orogeny to extension and the input of subduction modified juvenile crust play an important role in the Late Cretaceous ore-forming events.

Geological and geochemical characteristics of the Jiaoxi deposit in the western Bangong-Nujiang metallogenic belt, Tibet

Geological and geochemical characteristics of the Jiaoxi deposit in the western Bangong-Nujiang metallogenic belt, Tibet

Main collisional mineralization of Bangong-Nujiang metallogenic belt, Tibet: Geochronological, geochemical and isotopic evidence from Rongga molybdenum deposit

荣嘎钼矿是新近在班公湖-怒江成矿带发现并证实的首例斑岩型钼矿床。为了查明班公湖-怒江成矿带主碰撞期的成岩成矿作用，探讨荣嘎钼矿的富Mo机制，对该矿床进行岩石地球化学以及同位素年代学的研究。本次研究获得荣嘎含矿二长花岗斑岩的锆石SHRIMP 206Pb/238U加权平均年龄为99.8±1.9Ma（MSWD=2.0），属晚白垩世早期。7件辉钼矿样品的模式年龄较为一致，介于98.0±1.6Ma~101.8±1.7Ma之间，加权平均年龄为99.7±1.1Ma。荣嘎含矿二长花岗斑岩样品主量元素表现为富硅（SiO2=72.83%~75.49%）、富碱（Na2O+K2O=8.12%~8.55%）、过铝质（A/CNK=1.08~1.13）的高钾钙碱性系列岩石。样品明显富集Rb、K、Th、U等元素，中等亏损Nb、Ta，强烈亏损Ba、Sr、P、Ti等元素，具中等程度的负Eu异常（δEu=0.53~0.63），稀土元素配分曲线呈轻稀土相对较陡，重稀土较为平坦的右倾型。荣嘎含矿二长花岗斑岩样品的（87Sr/86Sr）i值为0.7042~0.7055，eNd（t）值介于0.03~0.68之间，锆石eHf（t）值介于+12.4~+17.9之间，两阶段模式年龄tDM2较为年轻（31~314Ma）。基于以上同位素以及岩石地球化学特征研究，荣嘎含矿二长花岗斑岩很可能是幔源岩浆诱发了富Mo洋底沉积物的熔融并与壳源熔体混合形成母岩浆，再经历结晶分异作用而形成。结合本文以及区域上的研究资料，荣嘎钼矿可能形成于拉萨地块与南羌塘地块碰撞的大地构造背景，富Mo大洋沉积物熔体的加入及随后的结晶分异是荣嘎含矿岩浆中金属Mo富集的主要原因。班公湖-怒江成矿带南缘侏罗-白垩纪海相地层分布的地区，可能为勘查钼矿床的有利靶区，应重点评价晚白垩世早期高分异中酸性岩体的含矿性。

Tectonic Control, Reconstruction and Preservation of the Tiegelongnan Porphyry and Epithermal Overprinting Cu (Au) Deposit, Central Tibet, China

The newly discovered Tiegelongnan Cu (Au) deposit is a giant porphyry deposit overprinted by a high-sulfidation epithermal deposit in the western part of the Bangong–Nujiang metallogenic belt, Duolong district, central Tibet. It is mainly controlled by the tectonic movement of the Bangong–Nujiang Oceanic Plate (post-subduction extension). After the closure of the Bangong–Nujiang Ocean, porphyry intrusions emplaced at around 121 Ma in the Tiegelongnan area, which might be the result of continental crust thickening and the collision of Qiangtang and Lhasa terranes, based on the crustal radiogenic isotopic signature. Epithermal overprinting on porphyry alteration and mineralization is characterized by veins and fracture filling, and replacement textures between two episodes of alteration and sulfide minerals. Alunite and kaolinite replaced sericite, accompanied with covellite, digenite, enargite, and tennantite replacing chalcopyrite and bornite. This may result from extension after the Qiangtang–Lhasa collision from 116 to 112 Ma, according to the reopened quartz veins filled with later epithermal alteration minerals and sulfides. The Tiegelongnan deposit was preserved by the volcanism at ~110 Ma with volcanic rocks covering on the top before the orebody being fully weathered and eroded. The Tiegelongnan deposit was then probably partly dislocated to further west and deeper level by later structures. The widespread post-mineral volcanic rocks may conceal and preserve some unexposed deposits in this area. Thus, there is a great potential to explore porphyry and epithermal deposit in the Duolong district, and also in the entire Bangong–Nujiang metallogenic belt.

Early Cretaceous diorites in the Kenbale Cu mineralization occurrence, Tibet, China, and its geological significance

The Kenbale Cu mineralization occurrence related to the diorite is a newly discovered Cu mineralization event in the Bangong-Nujiang metallogenic belt, Tibet, China. The Cu mineralization is hosted in the contact between the monzogranite or biotite quartz diorite and the fine-grained diorite, which is the mineralization related intrusion. In order to constrain the Kenbale mineralization age, petrogenesis and tectonic setting, we conducted LA-ICP-MS zircon U-Pb dating and Hf isotopic analyses of the biotite quartz diorite and fine-grained diorite and also the whole-rock geochemical study of the biotite quartz diorite. Zircon UPb dating show that weighted mean 206Pb/238U ages of the biotite quartz diorite and fine-grained diorite are 123.5 ± 1.9 Ma (MSWD = 2.3, n = 16) and 118.9 ± 1.3 Ma (MSWD = 2.5, n = 18), respectively. The biotite quartz diorite is a high-K calc-alkaline I-type magma rock and was controlled mainly by partial melting process during the magma formation and evolution. This intrusion is characterized by positive eHf(t) values (2.6 to 5.8) and old Hf crustal model ages (813 to 1016 Ma), indicating that the magma was sourced from partial melting of the Mesoproterozoic to Neoproterozoic juvenile crust of the northern Lhasa Terrane. Compared with the biotite quartz diorite, the mineralization associated fine-grained diorite has much higher zircon eHf(t) values (8.2 to 11.4) and younger Hf crustal model ages (450 to 650 Ma). These characteristics are similar with those of the coeval magmatic rocks induced by slab break-off of the southward subducted Bangong-Nujiang Ocean. The geochronology and geochemical results show that the Kenbale Cu mineralization was controlled by the slab break-off of the southward subducted Bangong-Nujiang Ocean.

A Miocene tungsten mineralization and its implications in the western Bangong-Nujiang metallogenic belt: Constraints from U-Pb, Ar-Ar, and Re-Os geochronology of the Jiaoxi tungsten deposit, Tibet, China

The Jiaoxi quartz-vein type wolframite deposit is the first tungsten mineralization discovered in the western part of the Bangong-Nujiang metallogenic belt, which is well-known for the porphyry-epithermal-skarn Cu-Au mineralization. The Jiaoxi deposit is associated with a porphyritic monzogranite that intrudes sandstone and shale in the Shiquanhe ophiolite mélange. The ages of the magmatism and mineralization in the deposit are here constrained by the dates obtained from the porphyritic monzogranite, hydrothermal muscovite and molybdenite. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating of two porphyritic monzogranite samples yields weighted mean 206Pb/238U coincident age of 14 ± 1 Ma. Two samples of hydrothermal muscovite from wolframite-bearing quartz veins yield plateau 40Ar/39Ar ages of 13.4 ± 0.1 and 13.3 ± 0.1 Ma, respectively. Re-Os model ages of five molybdenite samples range from 11.4 ± 0.2 to 11.8 ± 0.2 Ma, with a weighted mean model age of 11.6 ± 0.2 Ma. These dates indicate that the tungsten mineralization at Jiaoxi was formed during the Middle Miocene. This Miocene tungsten mineralization is significantly different from the Early and Late Cretaceous Cu-Au mineralization in the western part of the Bangong-Nujiang metallogenic belt. Our dating results show that there is a Middle Miocene tungsten mineralization in the western part of the Bangong-Nujiang metallogenic belt. The tectonic setting for the tungsten mineralization is here interpreted to be the regional extension associated with the India-Asia continental collision. The discovery of the Jiaoxi deposit has important significance on regional tungsten prospecting.