Western Gangdese Research Articles

Geological, Geochemical, and Mineralogical Constraints on the Genesis of the Polymetallic Pb-Zn-Rich Nuocang Skarn Deposit, Western Gangdese, Tibet

The Nuocang Pb-Zn deposit is a newly discovered polymetallic skarn deposit in the southern Lhasa subterrane, western Gangdese, Tibet. The skarn occurs at the contact between the limestone of Angjie Formation and the Linzizong volcanic rocks of Dianzhong Formation (LDF), and the subvolcanic granite porphyry intruding those formations; the contact metasomatic skarn is well zoned mineralogically and texturally, as well as geochemically. The skarn minerals predominantly consist of an anhydrous to hydrous calc-silicate sequence pyroxene–garnet–epidote. The endoskarn mainly consists of an assemblage of pyroxene, garnet, ilvaite, epidote, and quartz, whereas the exoskarn is characterized proximal to distally, by decreasing garnet, and increasing pyroxene, ilvaite, epidote, chlorite, muscovite, quartz, calcite, galena, and sphalerite. Geochemical analyses suggest that the limestone provided the Ca for all the skarn minerals and the magmatic volatiles were the main source for Si (except the skarnified hornfels/sandstone, and muscovite-epidote-garnet-pyroxene skarn possibly from the host sandstones), with Fe and Mn and other mineralizing components. During the hydrothermal alteration, the garnet-pyroxene skarn and pyroxene-rich skarn gained Si, Fe, Mn, Pb, Zn, and Sn, but lost Ca, Mg, K, P, Rb, Sr, and Ba. However, the skarnified hornfels/sandstone, and muscovite-epidote-garnet-pyroxene skarn gained Fe, Ca, Mn, Sr, Zr, Hf, Th, and Cu, but lost Si, Mg, K, Na, P, Rb, Ba, and Li. The REEs in the skarn were sourced from magmatic fluids during the prograde stage. Skarn mineral assemblages and geochemistry indicate the skarn in the Nuocang deposit were formed in a disequilibrated geochemical system by infiltrative metasomatism of magmatic fluids. During the prograde stage, garnet I (And97.6Gro1.6) firstly formed, and then a part of them incrementally turned into garnet II (And64.4Gro33.8) and III (And70.22Gro29.1). The subsequent substitution of Fe for Al in the garnet II and III indicates the oxygen fugacity of the fluid became more reduced, then resulted in formation of significant pyroxene. However, the anisotropic garnet IV (And38.5Gro59.8) usually replaced the pyroxene. In the retrograde stage, the temperature decreased and oxygen fugacity increased, but hydrolysis increased with epidote, ilvaite, chlorite I, and muscovite forming with magnetite. The continuing decreasing temperature and mixing with meteoric water lead to Cu, Pb, and Zn saturation as sulfides. After the sulfides deposition, the continued mixing with large amounts of cold meteoric water would decrease its temperature, and increase its pH value (neutralizing), promoting the deposition of significant amounts of calcite and chlorite II. The geological, mineralogical, and geochemical characteristics of Nuocang skarn, suggest that the Nuocang deposit is of a Pb-Zn polymetallic type. Compared to the other typical skarn-epithermal deposits in the Linzizong volcanic area, it indicates that the Nuocang deposit may have the exploration potential for both skarn and epithermal styles of mineralization.

Ages and petrogenesis of the late Triassic andesitic rocks at the Luerma porphyry Cu deposit, western Gangdese, and implications for regional metallogeny

The Tibetan Plateau is one of the most significant Cu poly-metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry Cu mineralization. This study investigates a new occurrence of Cu mineralization-related andesitic porphyries in the western domain of the Gangdese magmatic belt and assesses its petrologic, zircon U-Pb geochronology, whole-rock chemistry, and Sr-Nd-Hf-Pb isotope data. Zircon U-Pb dating of three ore-related porphyries yields crystallization ages of 212–211 Ma. These ages are consistent with previous molybdenite Re-Os dating, indicating a late Triassic magmatic and Cu mineralization event in the western Gangdese magmatic belt. Nb, Ta, and Ti depletion, Th and LREE enrichment, and high La/Yb and Th/Yb ratios in addition to high U/Yb ratios from zircons suggest that the magma was generated in an active continental arc setting. The porphyries have radiogenic isotopic compositions with (87Sr/86Sr)i 0.70431–0.70473, εNd(t) +1.1 to +3.8, (207Pb/204Pb)i 15.601–15.622, and (208Pb/204Pb)i 38.450–38.693, as well as high positive zircon εHf(t) values from +6.2 to +10.6 (mean value 8.3), corresponding to model ages (TDM) ranging from 509 Ma to 819 Ma (mean 646 Ma). This suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment-derived melts during the subduction of the Neo-Tethys Ocean. The mineralization-related porphyries contain amphibole and epidote, as well as high whole-rock Fe2O3/FeO and zircon Ce4+/Ce3+ ratios, suggesting hydrous and highly oxidized parent magmas. Considering the existing Cu mineralization and highly oxidized magma of the well-preserved Triassic andesitic igneous rocks in the western Gangdese belt, the subduction-related continental arc magma system is favorable for subduction-related porphyry Cu deposits. The existence of Luerma porphyry mineralization demonstrates that there are at least five generations of porphyry Cu-(Mo-Au) mineralization in the Gangdese magmatic belt, which advances the timeframe of porphyry mineralization to the late Triassic.

Zircon U-Pb, Molybdenite Re-Os and Quartz Vein Rb-Sr Geochronology of the Luobuzhen Au-Ag and Hongshan Cu Deposits, Tibet, China: Implications for the Oligocene-Miocene Porphyry–Epithermal Metallogenic System

The Gangdese metallogenic belt in Tibet is an important copper and iron polymetallic, metallogenic belt in western China. The Luobuzhen epithermal Au-Ag and Hongshan porphyry Cu deposits, as two new discovery deposits in the last few years, are located in the western Gangdese metallogenic belt. In this paper, we present quartz vein Rb-Sr isochron, zircon U-Pb and molybdenite Re-Os ages for a better understanding of the minerallogenetic epoch of the deposits. Geochronological data show that the Rb-Sr isochron age of a quartz vein in a Luobuzhen Au-Ag deposit is 21.1 ± 1.8 Ma (MSWD (mean standard weighted deviation) = 0.19), zircon U-Pb ages from diorite and granodiorite porphyry in Hongshan Cu deposit are 50.0 ± 0.4 Ma (MSWD = 0.94) and 23.7 ± 0.1 Ma (MSWD = 0.73), respectively, and a Re-Os isochron age of molybdenite in Hongshan Cu deposit is 23.0 ± 2.0 Ma (MSWD = 0.014). These data suggest that the Luobuzhen epithermal Au-Ag and Hongshan porphyry Cu deposits formed at ca. 23–21 Ma, which were controlled by the same magmatic hydrothermal events. Formation of both the Luobuzhen and Hongshan deposits were obviously earlier than the Miocene porphyry metallogenetic events in the Gangdese porphyry copper belt.

Sulphur and lead isotopic compositions of the Pb–Zn polymetallic deposits in the Linzizong volcanic area, Gangdese belt, Tibet: Implications for variation characteristics of ore‐forming material sources and exploration targeting

Relatively little attention has been given to variations in ore‐forming metal sources of Pb–Zn polymetallic deposits hosted in or near the Linzizong volcanic rocks from the eastern to western Gangdese belt. Based on the S and Pb isotopic data of typical Pb–Zn polymetallic deposits from the eastern to western Gangdese, the ore‐forming sources are discerned. The δ34SV‐CDT values of the typical Pb–Zn polymetallic deposits in the Gangdese metallogenic belt have a relatively large range of −11.6‰ to 6.0‰, different from those of the porphyry Cu ± Mo ± Au deposits (mainly vary from −2.0‰ to 1.0‰) in the Gangdese metallogenic belt, indicating that the sulphur in the ore‐forming fluid of Pb–Zn polymetallic deposits was dominantly of magmatic origin, but also influenced by strata nearby. The Nuocang and Beina deposits in the western Gangdese have a predominantly upper crustal source of Pb (average values: 207Pb/204Pb = 15.705, 208Pb/204Pb = 39.102), while the Narusongduo and Dexin deposits in the central Gangdese and the Leqingla and Xingaguo deposits in the eastern Gangdese are characterized by a mixed source in which Pb was derived from both the subducted slab and the ancient Lhasa basement. From the eastern to western Gangdese, Pb isotopic data show a gradually increasing scale of crustal materials from the Lhasa terrane basement. Combined with the geochemical data of the ore‐related intrusions and Linzizong volcanic rocks from the six deposits, or nearby, we proposed that the heterogeneity of Lhasa terrane crust resulted in more ancient Lhasa basement components contributing to ore‐forming sources from the eastern to western Gangdese. Moreover, relatively higher contents of Au, Ag elements could be identified in the Linzizong volcanic rocks of the western Gangdese than those of in the central and eastern Gangdese. Therefore, in addition to finding the cryptoexplosive breccia, epithermal, skarn, hydrothermal vein‐type Pb–Zn polymetallic deposits, there is exploration potential for epithermal Au–Ag deposits associated with the Linzizong volcanic rocks, western Gangdese.

Age and genesis of the Pusangguo skarn Cu-dominated polymetallic deposit, Gangdese metallogenic belt, Tibet

The Pusangguo skarn Cu-polymetallic deposit is a newly discovered deposit in the western Gangdese porphyry copper belt (GPCB). The orebodies are hosted along the contact between limestone of the Early Cretaceous Takena Formation and a biotite granodiorite intrusion. The mineralization is associated with the biotite granodiorite intrusion and is divided into four-stages: (1) a prograde skarn stage; (2) a pre-ore retrograde skarn stage; (3) a quartz-sulfides stage; and (4) a post-ore carbonate stage. These skarns have the characteristics of both calcareous and manganese skarns. The mineral compositions of the garnets and pyroxenes indicate that the ore-forming environment gradually evolved from a high-temperature, oxidative and alkaline environment into a low-temperature and reductive environment. The sulfur and lead isotopic compositions of the ore sulfides suggest a magmatic source for the sulfur and a crust-dominated source for the ore-forming metals. The hydrogen and oxygen isotopic compositions of the quartz and garnets in the ores indicate that the ore-forming fluids may have originated from a mixture of magmatic and meteoric fluids. The geochronological data show that both the magmatism (14.8 ± 0.4 Ma) and mineralization (13.2 ± 0.7 Ma) occurred during the Miocene in a post-collisional tectonic setting. The ore-forming biotite granodiorite is a high-K calc-alkaline I-type granite and has an adakitic geochemical affinity similar to the Gangdese Miocene adakites, which were generated from thickened lower crust in a post-collisional tectonic setting. The low positive εHf(t) values (0 to +2.6), young two-stage Hf model zircon ages, and whole-rock geochemical and lead isotopic compositions indicate that the magma of the ore-related biotite granodiorite may have originated from the thickened lower crust in the Lhasa terrane.

The newly-discovered Late Cretaceous igneous rocks in the Nuocang district: Products of ancient crust melting trigged by Neo–Tethyan slab rollback in the western Gangdese

The newly discovered polymetallic Nuocang Pb-Zn skarn deposit is located in the southern Lhasa subterrane, western Gangdese, Tibet. The orebodies occur primarily at the contact zone between the Angjie Formation and the Linzizong volcanic rocks of Dianzhong Formation (LDF) that are dominated by basaltic andesitic tuff and rhyolite. Zircon U–Pb dating for two granite porphyries yield ages of 72.4 ± 0.2 Ma and 73.4 ± 0.9 Ma, which are different from the ages (~69–60 Ma) of the LDF in the eastern Gangdese. The basaltic andesite tuff at Nuocang exhibits enrichment of MgO, TiO2, LILE, and LREE, with a relative depletion of SiO2, K2O, HFSE, and HREE, low Sr/Y ratios (32.9–38.0), and weak negative Eu anomalies (mean 0.86). They have 87Sr/86Sr(i) from 0.70695 to 0.70807 and εNd(t) values between −4.3 and −5.9. These features are similar to the Linzizong volcanic rocks of Dianzhong Formation in the Linzhou basin, indicating that they were associated with partial melting of mantle wedge mixing with 25–35% ancient Lhasa terrane basement. The rhyolite and granite porphyry show high SiO2 and K2O, and low Sr/Y ratio (1.2–9.9), enrichment of LILE and LREE and strong depletion of the HFSEs. They have pronounced negative Eu anomalies (mean 0.46), and εHf (t) values of the granite porphyry zircons range from −22.0 to −6.0. All these features suggest that they are the product of anatexis of ancient crustal materials heated by mantle-derived magma, the latter derived from Neo-Tethyan slab dehydration mechanisms. Combined with the previous geochronological and geochemical data, we proposed that the Nuocang district of western Gangdese in the southern Lhasa subterrane contains an ancient block, and the igneous rocks here were triggered by the Neo-Tethyan slab rollback starting at ~82 Ma. The western Gangdese contains more ancient continental crustal materials and Late Cretaceous–Eocene Linzizong volcanic rocks and coeval intrusions than in the eastern Gangdese. Thus the western Gangdese block displays greater potential for deposits associated with Late Cretaceous-Eocene magmatism including porphyry Mo, polymetallic skarn (W-Sn-Mo-Pb-Zn-Ag), base and precious metal epithermal (Pb-Zn-Ag-Au), cryptoexplosive breccia (Pb-Zn-Ag), and hydrothermal vein Pb-Zn-Ag deposits.

Land submerged to carbonate platform by conodonts: paleoenvironment reconstruction of the western Gangdese in Tibet during Triassic

Land submerged to carbonate platform by conodonts: paleoenvironment reconstruction of the western Gangdese in Tibet during Triassic

Geology, fluid inclusion and isotope constraints on ore genesis of the post-collisional Dabu porphyry Cu–Mo deposit, southern Tibet

The Dabu Cu-Mo porphyry deposit is situated in the southern part of the Lhasa terrane within the post-collisional Gangdese porphyry copper belt (GPCB). It is one of several deposits that include the Qulong and Zhunuo porphyry deposits. The processes responsible for ore formation in the Dabu deposit can be divided into three stages of veining: stage I, quartz–K-feldspar (biotite)±chalcopyrite±pyrite, stage II, quartz–molybdenite±pyrite±chalcopyrite, and stage III, quartz–pyrite±molybdenite. Three types of fluid inclusions (FIs) are present: liquid-rich two-phase (L-type), vapor-rich two-phase (V-type), and solid bearing multi-phase (S-type) inclusions. The homogenization temperatures for the FIs from stages I to III are in the ranges of 272–475°C, 244–486°C, and 299–399°C, and their salinities vary from 2.1 to 49.1, 1.1 to 55.8, and 2.9 to 18.0wt% NaCl equiv., respectively. The coexistence of S-type, V-type and L-type FIs in quartz of stage I and II with similar homogenization temperatures but contrasting salinities, indicate that fluid boiling is the major factor controlling metal precipitation in the Dabu deposit. The ore-forming fluids of this deposit are characterized by high temperature and high salinity, and they belong to a H2O–NaCl magmatic–hydrothermal system. The H–O–S–Pb isotopic compositions indicate that the ore metals and fluids came primarily from a magmatic source linked to Miocene intrusions characterized by high Sr/Y ratios, similar to other porphyry deposits in the GPCB. The fluids forming the Dabu deposit were rich in Na and Cl, derived from metamorphic dehydration of subducted oceanic slab through which NaCl-brine or seawater had percolated. The inheritance of ancient subduction-associated arc chemistry, without shallow level crustal assimilation and/or input of the meteoric water, was responsible for the generation of fertile magma, as well as CO2-poor and halite-bearing FIs associated with post-collisional porphyry deposits. The estimated mineralization depths of Qulong, Dabu and Zhunuo deposits are 1.6–4.3km, 0.5–3.4km and 0.2–3.0km, respectively, displaying a gradual decrease from eastern to western Gangdese. Deep ore-forming processes accounted for the generation of giant-sized Qulong deposit, because the exsolution of aqueous fluids with large fraction of water and chlorine in deep or high pressure systems can extract more copper from melts than those formed in shallow systems. However, the formation of small-sized Dabu deposit can be explained by a single magmatic event without additional replenishment of S, metal, or thermal energy. In addition, the ore-forming conditions of porphyry Cu–Mo deposits in GPCB are comparable to those of porphyry Cu±Au±Mo deposits formed in oceanic subduction-related continental or island arcs, but differ from those of porphyry Mo deposit formed in the Dabie-Qinling collisional orogens. The depth of formation of the mineralization and features of primary magma source are two major controls on the metal types and ore-fluid compositions of these porphyry deposits.

Genesis of Luobuzhen Pb–Zn veins: Implications for porphyry Cu systems and exploration targeting at Luobuzhen-Dongshibu in western Gangdese belt, southern Tibet

Porphyry systems are known to form in magmatic arc environment and commonly include porphyry Cu, epithermal Pb–Zn–Au–Ag, skarn polymetallic mineralization, etc. The systems are rarely reported in collisional zones, such as the Gangdese belt in southern Tibet where many postcollisional porphyry copper deposits occurred. In addition, other types of mineral systems are rarely present except porphyry copper mineralization in the Gangdese belt. In this study, we present Pb–Zn-bearing quartz veins at Luobuzhen in the western Gangdese belt. The Luobuzhen Pb–Zn veins cross-cut dacite of the Linzizong Group with zircon U–Pb age of 50.1±0.2Ma and monzogranite with zircon U–Pb age of 17.1±0.1Ma. Ore minerals include sphalerite, galena, chalcopyrite, and pyrite; gangue minerals are quartz with minor chlorite and sericite. Primary fluid inclusions of quartz are liquid-rich, aqueous, and two-phase inclusions. The homogenization temperatures of these primary inclusions are moderate to high (267–400°C), and salinities range from 8.9 to 18.4wt.% NaCl equiv. Quartz has δ18OSMOW values of 6.2–9.3‰, while sulfides have δ34SV-CDT values of −5.1‰ to 0.1‰, 206Pb/204Pb of 18.722–18.849, 207Pb/204Pb of 15.640–15.785, and 208Pb/204Pb of 39.068–39.560. These data suggest that magmatic fluids with contribution from meteoric water, magmatic sulfur, and lead derived from upper crust and metasomatized mantle by Indian continental materials would be critical for the Luobuzhen base metal mineralization.The Dongshibu area, located at ∼2km east of the Luobuzhen, is characterized by high concentrations of Cu (up to 1450ppm) and Mo (up to 130ppm) of stream sediments, which is quite different from high concentrations in Pb, Zn, Ag, and Au shown in the Luobuzhen area. In addition, porphyry copper mineralization-related alteration and veins/veinlets occur in the Miocene monzogranite at Dongshibu. The monzogranite is characterized by high Sr/Y ratios, which are also shown on ore-forming intrusions in the Gangdese postcollisional porphyry copper deposits, and shows similar zircon Hf isotopes to the ore-related high Sr/Y intrusions from the Zhunuo porphyry copper deposit which is located ∼20km northeast of the Luobuzhen-Dongshibu. A comprehensive analysis allows us to infer that the base metal veins at Luobuzhen are components of a porphyry Cu system with porphyry Cu mineralization likely present at Dongshibu and epithermal Au–Ag veins possibly occurring at Luobuzhen, which are indicative of the existence of porphyry copper systems in collisional zones. The potential porphyry Cu mineralization and epithermal Au–Ag veins should be targeted in future exploration at Luobuzhen-Dongshibu.

Eocene magmatic processes and crustal thickening in southern Tibet: Insights from strongly fractionated ca. 43 Ma granites in the western Gangdese Batholith

This study reports zircon U–Pb age and Hf isotope, whole-rock major and trace element, and Sr–Nd–Pb–Hf isotope data for the Dajia pluton, western Gangdese Batholith, in southern Tibet. These data indicate that the pluton consists of moderately (Group 1) and strongly (Group 2) fractionated granites that were emplaced synchronously at ca. 43Ma. Group 1 samples have SiO2 contents of 69–72wt.% and vary in terms of the differentiation index (DI=84–93). These rocks are depleted in Ba, Nb, Sr, P, and Ti, with moderate negative Eu anomalies, and display low heavy rare earth elements (HREEs) and Y abundances. Group 2 samples are characterized by high SiO2 (75–78wt.%) and DI (95–97); significantly negative Eu anomalies; marked concave-upward middle REE (Gd–Ho) patterns; and Ba, Sr, P, and Ti anomalies that are significantly more negative than those of Group 1 samples. Group 1 samples have whole-rock εNd(t) (−5.9 to −6.0), εHf(t) (−4.0 to −4.5), and zircon εHf(t) (−6.0 to +5.8) values identical to those of Group 2 samples [εNd(t)=−5.7 to −6.7, εHf(t)=−3.5 to −2.9, and zircon εHf(t)=−2.0 to +4.2], as well as similar initial Pb isotopic compositions. These data indicate that the two groups were derived from a common source region with garnet as a residual mineral phase. Group 1 samples were most likely derived from partial melting of garnet-bearing amphibolite (rather than eclogite) within the juvenile southern Lhasa crust and mixed with the enriched components from the subducting ancient Indian continental crust and/or the ancient central Lhasa basement. Group 2 samples are interpreted as the products of extensive fractional crystallization (plagioclase, K-feldspar, biotite, apatite, allanite, titanite, monazite, and ilmenite) of the melts represented by Group 1 samples. Low HREEs and Y abundances of the Dajia pluton, together with the presence of strongly fractionated granites (Group 2) identified for the first time in the Gangdese Batholith, indicate that the crust beneath the Dajia region had already been thickened by ca. 43Ma. High whole-rock zircon saturation temperatures (815°C–869°C) of Group 1 samples and the other ca. 43Ma coeval magmatism documented both in the Gangdese Batholith and in the Tethyan Himalaya can be best interpreted as the final consequences of the magmatic responses to the Neo-Tethyan oceanic slab breakoff.

Zircon U–Pb age and Sr–Nd–Hf–O isotope geochemistry of the Paleocene–Eocene igneous rocks in western Gangdese: Evidence for the timing of Neo-Tethyan slab breakoff

Northward Neo-Tethyan oceanic lithosphere subduction beneath southern Tibet in the Mesozoic–Early Cenozoic produced continental arc magmas in the ~1600km-long Gangdese belt. The most voluminous magmatism occurred in the Paleocene–Eocene, and is characterized by extensive I-type calc-alkaline to high-K calc-alkaline Linzizong volcanic rocks, and coeval plutons. These rocks have been extensively studied in the eastern Gangdese belt (east of ∼89°E), but few data exist from the western Gangdese belt. New data for eleven samples of these rocks, combined with existing data from the literature, show that they are similar to the eastern Gangdese belt rocks, with relative depletions in Nb, Ta, P, and Ti, and enrichments in Rb, Ba, Th, U, K, Pb, Zr, and Hf on a primitive mantle-normalized trace element diagrams, typical of continental arc-related igneous rocks. However, compared to the east, western Gangdese igneous rocks range to higher K2O contents (up to 6.1wt.%), higher (87Sr/86Sr)i ratios (up to 0.7151), and lower εNdi values (down to −8.1), suggesting that an evolved crustal source was involved in arc magmatism.The Gangdese arc magmatism lasted to ~80Ma, and has a gap or quiescent period afterwards. Starting at ~69Ma, the arc magmatism initiated and shifted southward from ~30.5°N to ~29.5°N in southern Tibet with an abrupt change of India-Asia convergence rate. The magmas through the whole Gangdese belt at ~69–53Ma are characterized by intermediate εNdi values (−0.6 to +4.0), positive εHfi values (+3.8 to +7.1), intermediate δ18O values (+5.0‰ to +6.5‰), and low Th/Y and La/Yb ratios (<20). These magmas were likely derived from the mantle with crustal contamination by MASH process in response to Neo-Tethyan slab rollback as proposed by previous studies.The Sr–Nd–Hf–O isotopic compositions of Linzizong volcanic rocks and coeval intrusions are relatively homogeneous during ~69–53Ma, but show a wide range at ~53–50Ma. Zircon temperature values from these rocks are distinctively high during the latter period and whole rock Th/Y and La/Yb ratios increased significantly after ~50Ma. We suggest that the high temperature and heterogeneous geochemistry of these magmas at ~53–50Ma reflect Neo-Tethyan slab breakoff during India-Asia collision, which triggered asthenospheric mantle upwelling. Mantle derived magmas resulted in extensive heating, induced crustal melting, and generated magmas with variable isotopic compositions. Tibetan crust was significantly thickened after ~50Ma.

Mineral Resources Potential Assessment and Optimization of Skarn‐type Iron Ore Prospecting Target Area in Western Gangdese Magmatic Arc, Tibet

Acta Geologica Sinica - English EditionVolume 88, Issue s2 p. 1283-1284 Meeting Abstracts Mineral Resources Potential Assessment and Optimization of Skarn-type Iron Ore Prospecting Target Area in Western Gangdese Magmatic Arc, Tibet Hao SONG, Corresponding Author Hao SONG Chengdu University of Technology, Chengdu 610059 Sichuan, ChinaCorresponding author. E-mail: songhhao@yeah.netSearch for more papers by this authorChengjiang ZHANG, Chengjiang ZHANG Chengdu University of Technology, Chengdu 610059 Sichuan, China Key Laboratory of Nuclear Techniques in Geosciences of Sichuan Province, Chengdu 610059 ChinaSearch for more papers by this authorZhengqi XU, Zhengqi XU Chengdu University of Technology, Chengdu 610059 Sichuan, China Key Laboratory of Nuclear Techniques in Geosciences of Sichuan Province, Chengdu 610059 ChinaSearch for more papers by this authorHuang Xiaodong, Huang Xiaodong Chengdu University of Technology, Chengdu 610059 Sichuan, ChinaSearch for more papers by this authorShiwei SONG, Shiwei SONG Chengdu University of Technology, Chengdu 610059 Sichuan, ChinaSearch for more papers by this author Hao SONG, Corresponding Author Hao SONG Chengdu University of Technology, Chengdu 610059 Sichuan, ChinaCorresponding author. E-mail: songhhao@yeah.netSearch for more papers by this authorChengjiang ZHANG, Chengjiang ZHANG Chengdu University of Technology, Chengdu 610059 Sichuan, China Key Laboratory of Nuclear Techniques in Geosciences of Sichuan Province, Chengdu 610059 ChinaSearch for more papers by this authorZhengqi XU, Zhengqi XU Chengdu University of Technology, Chengdu 610059 Sichuan, China Key Laboratory of Nuclear Techniques in Geosciences of Sichuan Province, Chengdu 610059 ChinaSearch for more papers by this authorHuang Xiaodong, Huang Xiaodong Chengdu University of Technology, Chengdu 610059 Sichuan, ChinaSearch for more papers by this authorShiwei SONG, Shiwei SONG Chengdu University of Technology, Chengdu 610059 Sichuan, ChinaSearch for more papers by this author First published: 29 December 2014 https://doi.org/10.1111/1755-6724.12380_30Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume88, Issues2Special Issue: Meeting Abstracts: The 14th Quadrennial International Association on the Genesis of Ore Deposits Symposium. August 19–22, 2014, Kunming, ChinaDecember 2014Pages 1283-1284 RelatedInformation

Adakitic rocks from slab melt-modified mantle sources in the continental collision zone of southern Tibet

Major-trace element and Sr–Nd–Pb isotopic data are presented for newly discovered adakitic rocks in the western Gangdese belt, southern Tibet. The Miocene (26–10 Ma) adakitic rocks from the southern Tibetan continental collision zones exhibit distinct differentiation trends typical of arc magmas. These rocks display geochemical affinities similar to those of Cretaceous (136–80 Ma) adakitic rocks derived from the partial melting of subducted Neotethyan slab in southern Tibet. The whole rock geochemical and isotope characteristics of the post-collision adakitic rocks reveal that their magmas likely originated from an upper mantle region previously metasomatized by slab melts during the Cretaceous subduction event. An interesting observation is that the E–W trending belt of adakitic rocks along the Yarlung Tsangpo suture zone occupies a fore-arc position, reflecting a geotectonic setting compatible with the genesis of adakitic magmas. The widespread occurrences of Cretaceous adakitic rocks in this region are interpreted to testify to the former location of the adakite-metasomatized mantle. Our favoured interpretation is that the spatial isotopic variation in the post-collision adakitic rocks is mostly linked to a westward increase in sediment input in the Tibetan mantle region. Under the framework of our paleo-subduction model, a slab break-off event that initiated at around 25 Ma would have allowed an asthenospheric upwelling beneath southern Tibet, which was instrumental in generating the post-collision adakitic magmatism in southern Tibet.

Geochronologic constraints on magmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gangdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe (SHRIMP). The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.