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Chlorite is present extensively in many types of deposits. The mechanism underlying the chemical variations in chlorite remains unclear. The Naruo porphyry deposit is a giant copper porphyry deposit in the Duolong ore district of Tibet. Chlorite, which is abundant in this deposit, has yet to be studied systematically; hence, we used principal component analysis (PCA) to assess the correlation between chlorite elements and various types of mineral deposits. We then conducted a preliminary investigation into its mineralogy and geochemistry to better understand its formation process and identify potential prospecting indicators. The PCA method proved effective in discerning two distinctive element signatures within the chlorite and categorising them into four deposit types: orogenic Au deposits, granite-type U deposits, and skarn-type Sn deposits that exhibit high FeOand low MgO distinguishing them from porphyry copper deposits. The chlorite in the Naruo deposit is classified as either early metasomatic (M-type), consisting mainly of clinochlore, or late hydrothermal (H-type), primarily consisting of clinochlore and chamosite. This classification suggests that H-type chlorite formed in a reductive environment conducive to Cu precipitation at medium temperatures (255°C-342°C). Al-Si and Fe-Mg substitutions were found to be the primary processes involved in its generation. Additionally, from the mineralisation centre outwards, there was an observed decrease in Si content as well as the Fe/(Fe+Mg) ratio in H-type chlorite, along with decreases in temperature, sulphur, and oxygen fugacity of allchlorites; conversely, increases were observed for Al content along with Mg and Mn elements in H-type chlorite. Chlorite is useful for exploring porphyry copper systems as an indicator mineral. [ABSTRACT FROM AUTHOR]

The Jiama deposit, a significant porphyry‐skarn‐type copper polymetallic deposit located within the Gangdese metallogenic belt in Tibet, China, exemplifies a typical porphyry metallogenic system. However, the mineral chemistry of its accessory minerals remains under‐examined, posing challenges for resource assessment and ore prospecting. Utilizing electron microprobe analysis and LA‐ICP‐MS analysis, this study investigated the geochemical characteristics of apatite in ore‐bearing granite and monzogranite porphyries, as well as granodiorite, quartz diorite, and dark diorite porphyries in the deposit. It also delved into the diagenetic and metallogenic information from these geochemical signatures. Key findings include: (1) The SiO2 content, rare earth element (REE) contents, and REE partition coefficients of apatite indicate that the dark diorite porphyry possibly does not share a cogenetic magma source with the other four types of porphyries; (2) the volatile F and Cl contents in apatite, along with their ratio, indicate the Jiama deposit, formed in a collisional setting, demonstrates lower Cl/F ratios in apatite than the same type of deposits formed in a subduction environment; (3) compared to non‐ore‐bearing rock bodies in other deposits formed in a collisional setting, apatite in the Jiama deposit exhibits lower Ce and Ga contents. This might indicate that rock bodies in the Jiama deposit have higher oxygen fugacity. Nevertheless, the marginal variation in oxygen fugacity between ore‐bearing and non‐ore‐bearing rock bodies within the deposit suggests oxygen fugacity may not serve as the decisive factor in the ore‐hosting potential of rock bodies in the Jiama deposit. [ABSTRACT FROM AUTHOR]

The Bangongco–Nujiang metallogenic belt of Tibet is a main suture zone in the Qinghai–Tibet Plateau, which is known as an important porphyry–epithermal–skarn Cu-polymetallic mineralization zone in China. The western part of the Bangongco–Nujiang metallogenic belt exposes several medium high-silica terrestrial alkaline volcanic rocks with strong alteration influenced by collision orogeny. Some research has shown that clues to mineralization such as malachite and gossan are found on the surface. However, volcanic rock areas with varied topography place a huge burden on geological investigation, and the existing research on predicting mineralization is relatively scarce. This paper describes the extraction of alteration mineral information based on medium spatial resolution and hyperspectral resolution images, establishing a spectral library of alteration minerals in this area. By analyzing radar data, digital elevation, and synthesis results of different spectral bands, we combine remote sensing with geographic information technology to establish crater markers. The extraction results from multisource and chemical exploration data are superimposed onto the analysis of mineralization characteristics and geological conditions so as to establish the mineralization signatures for terrestrial volcanic rock areas. Eighteen mineralization prospect areas were identified, which can provide technical support for future mineralization research in this belt. [ABSTRACT FROM AUTHOR]

The Xiongcun Cu–Au ore district is in the southern middle Gangdese Metallogenic Belt, Tibet, and formed during Neo-Tethyan oceanic subduction. The Xiongcun ore district mainly comprises two deposits, the No. I and No. II deposits, which were formed by two individual mineralization events according to deposit geology and Re–Os isotopic dating of molybdenite. The No. I deposit is similar to a reduced porphyry copper–gold deposit, given the widespread occurrence of primary and/or hydrothermal pyrrhotite and common CH4-rich and rare N2-rich fluid inclusions. The No. II deposit, similar to classic oxidized porphyry copper–gold deposits, contains highly oxidized minerals, including magnetite, anhydrite, and hematite. The halogen chemistry of the ore-forming fluid from the No. I and No. II deposits is still unclear. Biotite geochemistry with halogen contents was used to investigate the differences in ore-forming fluid between the No. I and No. II deposits. Hydrothermal biotite from the No. I deposit, usually intergrown with sphalerite, is Mg-rich and classified as phlogopite and Mg-biotite, and hydrothermal biotite from the No. II deposit is classified as Mg-biotite. Hydrothermal biotite from the No. I deposit has significantly higher SiO2, MnO, MgO, F, Li, Sc, Zn, Rb, Tl, and Pb contents and lower Al2O3, FeOtot, Cl, Ba, Cr, V, Co, Ni, Y, Sr, Zr, Th, and Cu contents than the biotite from the No. II deposit. Hydrothermal biotites from the No. I and No. II deposits yield temperatures ranging from 230 °C to 593 °C and 212 °C to 306 °C, respectively. The calculated oxygen fugacity and fugacity ratios indicate that the hydrothermal fluid of the No. I deposit has a higher F content, oxygen fugacity, and log(fHF/fHCl) value and a lower log(fH2O/fHF) value than the hydrothermal fluid from the No. II deposit. The biotite geochemistry shows that the No. I and No. II deposits formed from different hydrothermal fluids. The hydrothermal fluid of the No. I deposit was mixed with meteoric waters containing organic matter, resulting in a decrease in oxygen fugacity and more efficient precipitation of gold. The No. I and No. II deposits were formed by a Cl-rich hydrothermal system conducive to transporting Cu and Au. The decreasing Cl, oxygen fugacity, and temperature may be the key factors in Cu and Au precipitation. Biotite geochemistry allows a more detailed evaluation of the halogen chemistry of hydrothermal fluids and their evolution within porphyry Cu systems. [ABSTRACT FROM AUTHOR]

The Bangbule skarn lead‐zinc (Pb‐Zn) deposit (>1 Mt Zn + Pb) is located in the western Nyainqentanglha polymetallic metallogenetic belt, central Tibet. Lenticular orebodies are all hosted in skarn and developed in the contact zone between the quartz porphyry and carbonate strata of the mid Paleozoic Middle to Upper Chaguoluoma Formation as well as in carbonate and sandstone beds of the Upper Paleozoic Laga Formation. As a newly discovered skarn deposit, the geological background and metallogenesis of this deposit remain poorly understood. Detailed petrological, geochemical and geochronological data of the ore‐related quartz porphyry, helps constrain the mineralization age and contributes to discussion on the ore genesis of the Bangbule deposit. Both endoskarn and exoskarn are identified in the Bangbule deposit. From quartz porphyry to carbonate formation, the exoskarn is zoned from proximal garnet skarn to distal pyroxene skarn. Zircon U‐Pb dating results show that the quartz porphyry formed at 73.9 ± 0.8 Ma. Geochemical analysis results show that the quartz porphyry has high contents of SiO2 (71.40–74.94 wt%) and K2O + Na2O (3.76–8.46 wt%) with A/CNK values of 0.69 to 1.06. Besides, the quartz porphyry is enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and have low εNd(t) (from –8.25 to –8.19) and high initial (87Sr/86Sr)i values (0.713611–0.714478). Major, trace elements and whole‐rock F concentration analysis results from the endoskarn samples show higher TFe2O3, MgO, CaO, Pb + Zn, W, Sn, Mo and F etc., and lower alkalis (K2O, Na2O, Sr and Ba) than those of fresh quartz porphyry, indicating that the early ore‐forming fluids were an Ca‐Fe‐F‐enriched fluid. Massive ore in the proximal skarn might be related to the high F content in the magma, which lowered the solidus temperature of the quartz porphyry magma and caused a lower temperature of the ore‐forming fluids, as well as facilitating the precipitation of sphalerite and galena. Based on the geochemical characteristics presented in this study, we propose that the ore‐related quartz porphyry was formed by partial melting of crust materials with some juvenile crustal component input. The partial melting of the middle‐upper crust after the initial enrichment of lead and zinc elements are important for the formation of Pb‐Zn deposits. The case study of the Bangbule deposit has proven that there is still a crust‐derived magmatic source region in the western segment of the central Lhasa terrane. Therefore, there is still great potential for Pb‐Zn mineralization and Pb‐Zn exploration. [ABSTRACT FROM AUTHOR]

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The Naruo porphyry copper deposit containing more than 2 Mt of copper is located in the Duolong ore district in the west of the Bangongco–Nujiang belt in central Tibet. New zircon U‐Pb, biotite 40Ar/39Ar, zircon (U‐Th)/He ages, published age data together with thermal modeling were presented in this paper to investigate the thermal history of Naruo deposit. Thermal modeling reveals a prolonged magmatic‐hydrothermal evolution firstly cooling from ∼700°C to ∼350°C at 120 Ma, then cooling to 230°C at 106 Ma and maintaining at 200°C from 106 to 90 Ma which is attributed to multiple magmatic events and thermal effect of strike‐slip fault. Affected by thrust nappe structure, the sample was consistent with 120°C from 70 to 63 Ma. The Naruo deposit started to experience exhumation at a rate of ∼0.07 km/Myr since 60 Ma which is related to India‐Asia collision. The prolonged magmatic‐hydrothermal evolution process might have important influence on the Naruo deposit. The ore‐related intrusions preserved in the foot walls of strike‐slip fault and thrust nappe structure are the objects of future exploration in the Duolong ore district. [ABSTRACT FROM AUTHOR]

Demingding is a promising porphyry Mo-dominated deposit recently discovered in the eastern Gangdese metallogenic belt in Tibet, China. We present zircon U-Pb-Lu-Hf isotopic studies, as well as geochemical data of the late monzogranites and the prior rhyolites from the Demingding porphyry deposit to uncover their origin and geodynamic mechanism. Zircon U–Pb dating yielded precise crystallization ages of 17.3 ± 0.6 Ma (MSWD = 2.5) and 186.5 ± 3.0 Ma (MSWD = 2.0) for monzogranite and rhyolite, respectively. The monzogranite is characterized by high-K calc-alkaline, adakitic affinities, and positive zircon εHf(t) values (+0.9∼+5.6, avg.+3.1) with TDM2 (0.73–1.04 Ga), while the rhyolite has εHf(t) values of (+2.1∼+7.3, avg.+5.2) and TDM2 of (0.76–1.09 Ga) similar to the monzogranite. Our results suggest that the Demingding porphyry Mo (Cu) deposit is related to magma generated from the Neo-Tethyan oceanic subduction. The subsequent monzogranite porphyry was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by continental collision crustal thickening in Miocene. The lower positive εHf(t) values of monzogranites suggest minor inputs from the Mo-rich ancient crust, suggesting that Mo favors the silicate melt. Such magmatic events and special metallogenesis typify intracontinental processes and porphyry copper deposits, which are normally confined to oceanic subduction and Cu-dominated style, thereby making the continental setting and Mo-dominated style of Demingding exceptional and possibly unique. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Dongga Au deposit can be classified as subepithermal deposit. • Fluid mixing between magmatic water and meteoric water triggers gold precipitation. • The Dongga and No.2 deposits constitute a porphyry system, reflecting a continuous fluid evolution. The Dongga Au deposit (9.55 t Au; average grade = 6.9 g/t [up to 61.6 g/t]) is located in the Xiongcun giant porphyry Cu–Au district of the Gangdese porphyry Cu belt, Tibet. Its mineralization age, ore-forming processes, and relationship to adjacent porphyry mineralization remain unclear. To address this, we conducted a geological, pyrite Re–Os dating, He–Ar–H–O–S–Pb isotopic, and fluid inclusion study of the Dongga deposit. Pyrite samples from ore-bearing chlorite–sulfide veins yielded a weighted-mean Re–Os age of 178.4 ± 2.6 Ma (MSWD=0.01), implying the deposit formed during the Early Jurassic. Fluid inclusion analyses yielded homogenization temperatures of 237–360 °C for quartz–sulfide veins and 125–201 °C for late quartz veins, with corresponding salinities of 2.7–43.8 and 0.9–9.9 wt% NaCl eq , respectively. Fluid inclusion analyses of pyrite samples yielded 3He/4He and 40Ar/36Ar values of 0.50–1.08 Ra and 325.1–559.4, respectively, and δD and δ18O fluid values of –86.2 ‰ to –72.1 ‰ and –5.6 ‰ to 3.9 ‰, respectively. The He–Ar–H–O isotopic data suggest the mineralizing fluids were derived mainly from a crustal source with a small mantle contribution, and also contained a mixture of magmatic and meteoric waters. The S (δ34S = –1.57 ‰ to –0.55 ‰) and Pb (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.17–18.41 ‰, 15.55–15.63 ‰ and 38.15–38.37 ‰, respectively) isotopic compositions of pyrite suggest the ore-forming metals were derived from a magma source in the mantle containing minor amounts of subducted sediment. Based on the geology, and isotopic and fluid inclusion data, we infer that mixing between magmatic and meteoric waters was the main trigger of Au precipitation. In addition, based on the geochronological, spatial, and genetic relationships with the adjacent No.2 deposit in the Xiongcun ore district, we propose that the Dongga Au deposit is a sub-epithermal deposit, which represents the transition between porphyry and epithermal deposits. The two deposits constitute a porphyry system and record the continuous evolution of hydrothermal fluids transported outwards in a porphyry system. [ABSTRACT FROM AUTHOR]

[Display omitted] • The monzogranite porphyry at Wubaduolai was derived from juvenile Tibetan lower crust, with contributions from Indian plateand metasomatized mantle. • The magma that formed monzogranite porphyry at Wubaduolai is oxidized and hydrous. • The monzogranite porphyry at Wubaduolai has lower potential for copper mineralization than rocks from Zhunuo and Beimulang deposits. The Wubaduolai deposit is a newly discovered porphyry copper deposit in the Zhunuo-Beimulang ore-concentrated area of the Gangdese belt. The monzogranite porphyry is the causative intrusion in the deposit with a zircon U-Pb age of ∼16 Ma. Monzogranites have high Sr (332–673 ppm) and Sr/Y ratios (35–69), typical of adakite affinity. They have initial 87Sr/86Sr ratios of 0.7083–0.7093 and ε Nd (t) values between −9.2 and −7.1. The zircon ε Hf (t) values range from −6.45 to −2.09 and zircon δ 18O values have a narrow range of 7.4 to 8.1 ‰ for the porphyry. These geochemical characteristics indicate that the parental magma was derived from juvenile Tibetan lower crust, with contributions from Indian plate-released fluids and metasomatized mantle-derived mafic magmas. The porphyry shows high values of log w(Fe 2 O 3 /FeO) (>0) and V/Sc (mostly > 12) in whole rock and high values of △FMQ (4.13–5.79), 10000 × (δ Eu)/Y(>4), and low Dy/Yb (<0.3) in zircons, suggesting that the magma was oxidized and hydrous. The oxidized and hydrous parental magma is consistent with those evaluated for the Zhunuo and Beimulang deposits. The three-component mixing model result shows that compared with the ore-related porphyries in the Zhunuo and Beimulang deposits, the Wubaduolai intrusion has higher proportion of Indian plate-released fluids and mafic magmas and lower proportion of juvenile Tibetan lower crust. Therefore, we suggest that although the causative intrusions have similar oxygen fugacity and water content, the source has more Indian continental crust and mantle-derived materials and fewer juvenile Tibetan lower crust materials at Wubaduolai, implying that the Wubaduolai monzogranite porphyry has lower potential for mineralization. [ABSTRACT FROM AUTHOR]

The Mamupu skarn‐type Cu‐Au polymetallic deposit represents the first discovery of a medium deposit in the southern Yulong porphyry copper belt (YPCB), eastern Tibet. The Cu‐Au mineralization mainly occurs as chalcopyrite in breccia, within the plate‐like carbonate interlayer, being closely related to chloritization (e.g., chlorite, magnetite and epidote) and skarnization (e.g., diopside, tremolite and garnet). The ore‐related quartz syenite porphyry (QSP) and granodiorite porphyry (GP) were emplaced at 40.1 ± 0.2 Ma and 39.9 ± 0.3 Ma, respectively. The QSP of Mamupu is an alkaline‐rich intrusion, relatively enriched in LREE, LILE, depleted in HFSE, with no significant negative Eu and Ce anomalies, slightly high (87Sr/86Sr)i, low ∊Nd(t), uniform (206Pb/204Pb)i and ∊Hf(t) values, which indicates that the porphyry magma may be caused by both the mixing of metasomatized EM II enriched mantle and thickened juvenile lower crust. The QSP in the Mamupu deposit shares a similar genesis of petrology to other ore‐related porphyries within the YPCB. High oxygen fugacity and water content of the magmas are essential for the formation of porphyry and skarn Cu deposits. The QSP has similar high magmatic oxidation states and water content to the Yulong deposit, which indicates that the Mamupu has a high prospecting potential. Differences in the geological characteristics and scale of mineralization between the Mamupu and other YPCB deposits may be due to the different emplacement depths of ore‐related intrusions, as well as differences in the surrounding rocks. [ABSTRACT FROM AUTHOR]

Porphyry deposits supply most of the world's Cu and Mo resources. Most porphyry deposits are developed in magmatic arcs above subduction zones. However, abundant Miocene porphyry Cu-Mo deposits have been found in the post-collision stage in Tibet, more than ∼30 Myr after the Indian-Eurasian continental collision. The magma source and the enrichment process of ore-forming elements for these post-collision porphyry deposits remain controversial. Here, we present Sr-Nd-Mo isotope compositions of a suite of mineralized and barren igneous rocks from the Rongmucuola pluton in the Miocene post-collisional Qulong porphyry Cu-Mo deposit in Tibet to reveal their magma sources and ore-forming processes. Our results indicate that the mineralized and barren igneous rocks in the Qulong deposit were derived from a cogenetic source with similar Sr-Nd isotope compositions (87Sr/86Sr (i) = 0.7049–0.7050 and ε Nd (t) = −0.24 to 0.20). However, the mineralized igneous rocks have large variations in δ98/95Mo values (−0.30‰ to 0.74‰; relative to NIST SRM 3134) and Mo/Ce ratios (0.01 to 4.84) compared to those of the barren igenous rocks (δ98/95Mo = −0.74‰ to −0.02‰; Mo/Ce = 0.01 to 0.04). In combination with the higher LOI values, Mo/Ce and Cs/Ta ratios and Cu concentrations and lower Ce/Pb ratios of the mineralized igneous rocks relative to the barren igneous rocks, we propose the mineralized igneous rocks were affected by ore-forming hydrothermal fluids originated from the exsolution of later co-genetic magmas, which significantly changed the isotopic and elemental compositions of intrusions and resulted in Mo mineralization. The fluid-rock interaction modeling supports this interpretation and successfully reproduce the observed δ98/95Mo and Mo/Ce compositions of mineralized igneous rocks. Our study indicates that the exsolved magmatic-hydrothermal fluids have heavy Mo isotopes, and the fluids with a slightly heavier Mo isotope composition have the greatest potential for mineralization. As the water-rock reaction progresses, leading to the precipitation of Mo-rich minerals, ore-forming fluids with a heavier Mo isotope composition may not have significant mineralization potential. This highlights that Mo isotope system is an effective tool to study the ore-forming processes of porphyry deposits. [ABSTRACT FROM AUTHOR]

Explanation: From Lakange Mo (Cu) deposit to Jiama Cu polymetallic deposit to Bangpu Mo mineralization to Qulong Cu-Mo deposit to Bangpu Cu mineralization, the Cl contents in apatite gradually increase, but the F contents in apatite gradually decrease, and the S content is similar but variation. It indicates that the Mo-dominated porphyry deposit formed from F-S-rich magma, whereas the Cu-dominated porphyry deposit formed from Cl-S-rich magma. [Display omitted] • There are two different magmatic-hydrothermal systems that formed the Bangpu Mo-Cu deposit. • Cu and Mo mineralization contain zircon and apatite with different geochemical features. • Cu mineralization was related to Cl-rich porphyry system, whereas Mo-mineralization was related to F-rich porphyry system. The Bangpu deposit, located in the eastern part of the Gangdese Porphyry Copper Belt, Tibet, is a porphyry Mo-Cu deposit in a continental collisional orogenic belt. Cu and Mo mineralization occurred separately in the Bangpu deposit. Mo (Cu) mineralization occurred mainly in the monzogranite porphyry (MP), while Cu (Mo) mineralization occurred mainly in the diorite porphyry (DP). The cause of such spatial differences in Cu and Mo mineralization in the Bangpu deposit remains unclear. In this study, the mineral chemistry of apatite and zircon was investigated to reveal the differences in the nature of ore-forming magma between Cu (Mo) and Mo (Cu) mineralization in the Bangpu deposit. The chondrite-normalized REE patterns of the apatite grains from the MP were enriched in LREEs with negative Eu anomalies, whereas those from the DP and biotite monzonitic granite (BM) had strong negative Eu anomalies with no obvious differentiation between LREEs and HREEs. The DP, MP, and BM have a low T TiZ range from 657 °C to 917 °C and a high AST range from 687 °C to 1079 °C. The zircon grains from the DP and MP had different Th/U ratios and T TiZ values, indicating that these porphyry samples probably experienced different magma crystallization or crystal fractionation histories. The zircon Ce4+/Ce3+ and Eu/Eu* ratios indicate that the ore-bearing DP and MP have higher oxygen fugacity than the BM. The F, Cl, and S contents in the apatite showed that the DP magmas were Cl- and S- rich, whereas the MP magmas magmas were F- and S- rich. The Bangpu porphyry Mo-Cu deposit results from two superimposed magmatic-hydrothermal systems. Mo was mainly partitioned into the F-rich magmatic-hydrothermal system released from the MP, and Cu was mainly partitioned into the Cl-rich magmatic-hydrothermal system released from the DP. Our results show that zircon and apatite geochemistry can be used to explain the spatial distribution of Cu and Mo mineralization in porphyry Cu-Mo systems. [ABSTRACT FROM AUTHOR]

This paper describes the discovery of porphyry Cu–Au ore bodies (No. 2 and No. 3) in Xiongcun, Tibet, China, through the investigation of stream sediments, soils and rocks. The study area (Xiongcun), located in the city of Xigaze, has a complex topography due to its complicated geological background. The Xiongcun No. 1 ore body will soon be mined, 15 years after its discovery. However, recent research on stream sediments, soils and rocks around the No. 1 ore body has revealed notable Cu anomalies on the periphery. With the successful application of exploratory geochemistry data in the anomaly locations, the No. 2 and No. 3 ore bodies have been revealed. The ore reserves of the No. 2 and No. 3 ore bodies are estimated to reach 1.64 million tons of Cu, more than 80 tons of Au and 200 tons of Ag. We expect that our findings will not only enhance the understanding of the reanalysis of anomalies surrounding the discovered deposits but also contribute to the evaluation of the ore-prospecting potential of this plateau region. [ABSTRACT FROM AUTHOR]

An intensive study of the geochemical characteristics (including the volatile elements Cl and S) of apatite associated with porphyry deposits was undertaken to address the debate about the crust- or mantle-derivation of their copper and gold and to better understand the controls on the transport of metals in magmatic fluids in post-subduction settings. New geochemical data on apatite reveal parameters to discriminate mineralized porphyry systems across Iran and western China (Tibet and Yunnan), from coeval barren localities across this post-subduction metallogenic belt. Apatites in fertile porphyries have higher Cl and S concentrations (reflecting water-rich crystallization conditions) than those from coeval barren ones. Our new isotopic data also indicate these volatiles are likely derived from pre-enriched sub-continental lithospheric mantle, metasomatized by previous oceanic subduction. This study demonstrates that refertilization of suprasubduction lithospheric mantle during previous collision events is a prerequisite for forming post-subduction fertile porphyries, providing an evidence-based alternative to current ore-enrichment models. [ABSTRACT FROM AUTHOR]

The Qulong porphyry Cu–Mo deposit, generated in the Miocene post-collisional extension environment of the Gangdese Copper (Molybdenum) Metallogenic Belt, is one of the largest porphyry Cu deposits in China. This study reports the noble gas isotopic compositions of volatiles released from fluid inclusion reserved in pyrite from the Qulong deposit. 3He/4He and 40Ar/36Ar ratios range from 0.54 to 1.015 Ra and 300–359, respectively. Concentrations of 4He and 40Ar range from 1.77 to 2.62 × 10−8 cm3 STP and 1.7–34 × 10−8 cm3 STP, respectively. The isotopic composition of noble gases indicates that the ore-forming fluids of the Qulong Cu–Mo deposit were a mixture of fluid containing mantle component, which is exsolved from the porphyry magma, and crustal fluid characterized by atmospheric Ar and crustal radiogenic He. The δ34S values of pyrite and molybdenite range from − 0.52‰ to 0.31‰, with an average of − 0.12‰, indicating a magmatic origin. More mantle components were involved in the Cu–Mo deposit than in the Mo–Cu deposit in the Qulong-Jiama ore-district. [ABSTRACT FROM AUTHOR]

Zhuno is the only large porphyry copper deposit that preserves the complete magmatic system in the western part of Gangdese porphyry copper belt. Intrusions in the Zhunuo deposit include pre‐ore porphyritic monzogranite, syn‐ore monzogranite porphyry, and post‐ore quartz syenite‐normal granite porphyry, high‐Cr granite porphyry, normal diorite porphyry, high‐Mg diorite porphyry (diorite enclave), potassic lamprophyre, and ultrapotassic lamprophyre. Enriched Sr–Nd isotopic composition and high MgO, LILE, HFSE, LREE, and compatible element (Cr, Ni) contents of the ultrapotassic lamprophyre indicate that the magma derived from the enriched Lhasa lithospheric mantle, which had been metasomatized by fluids and sediment‐derived melts associated with Neo‐Tethyan oceanic subduction and subsequent Indian continental lithosphere subduction. The depletion of the Sr–Nd isotopic composition and MgO (or Mg#), Cr, and Ni content of the normal diorite porphyry manifest that the magma source is juvenile Lhasa lower crust instead of Indian mantle. Geochemical characteristics indicate that the magma sources of the quartz syenite‐normal granite porphyry, high‐Mg diorite porphyry‐diorite enclave, and potassic lamprophyre was derived from ancient Lhasa middle‐upper crust, crust‐mantle transition zone, and enriched Lhasa mantle without Indian lithosphere contribution, respectively. Their similar Sr–Nd isotopic compositions demonstrate a uniform Sr–Nd isotopic reservoir from crust to mantle in Zhunuo area. The major and trace element compositions suggest that the high‐Cr granite porphyry was formed by mixing of quartz syenite‐normal granite porphyry and ultrapotassic lamprophyre magmas. High Sr/Y values and low Y contents of the monzogranite and monzogranite porphyry display adakitic properties. The major and trace element contents and Sr–Nd isotopic composition indicate the monzogranite‐monzogranite porphyry are likely from mixing of the normal diorite porphyry magma with the quartz syenite‐normal granite porphyry magma, rather than with the high‐Mg dioritic (high‐Mg diorite porphyry‐diorite enclave) and/or potassic‐ultrapotassic magmas. According to the spatial and temporal consistency of the adakitic and potassic‐ultrapotassic rocks with the N–S‐trending rifts, Indo‐Asian convergence rate reduction, and uplifting model of Tibetan Plateau, we infer that the magma genesis of the Zhuno intrusions is attributed to decompressional partial melting of Lhasa crust‐mantle triggered by the tearing of the subducting Indian Plate. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is characterized by the largest crustal thickness on Earth, although the timing of formation of the plateau remains debated. In this study, we present in situ laser ablation‐inductively coupled plasma‐mass spectrometry zircon U–Pb ages and Hf isotopes, and whole‐rock geochemical data on porphyritic granitoids of Sebuta in the central Lhasa block. Our zircon U–Pb data indicate that these rocks emplaced at ca. 89 Ma, in the early Late Cretaceous. Geochemically, the Sebuta biotite granite porphyry can be broadly divided into two subtypes, namely metaluminous porphyry and peraluminous porphyry. The metaluminous porphyry has high SiO2, Al2O3, Sr, low Y and Yb contents, and high Sr/Y and LaN/YbN ratios, showing adakitic features. These rocks have high K2O and Th contents, low Ti/Eu and Nd/Sm ratios, indicative of a continental crust affinity. Positive zircon εHf(t) values, along with high Mg#, Cr and Ni, imply that the Sebuta adakitic porphyry was most likely derived from partial melting of a delaminated thickened juvenile lower crust, and that the initial melts interacted with mantle peridotite during ascent. The field features, petrographic characteristics, formation age, ore‐bearing potential, and Hf isotope of the peraluminous porphyry are similar to those of the Sebuta adakitic porphyry, indicating that the peraluminous porphyry was likely formed by contamination with ancient crustal material and fractional crystallization from the same primary adakitic magmas which generated the Sebuta adakitic porphyry. Residual phases of amphibole + plagioclase + garnet + rutile in the source region, together with previous studies, suggest that the crust beneath the central‐northern Lhasa block experienced thickening during the early Late Cretaceous, and had already been thickened to more than 50 km by the Late Cretaceous (ca. 89 Ma). [ABSTRACT FROM AUTHOR]

Miocene postcollisional potassic and adakitic rocks are widely distributed in the southern Lhasa terrane and western central Lhasa terrane. However, coeval potassic and adakitic rocks in eastern central Lhasa terrane were rarely recognized, and their origins and formation mechanism remain controversial. In this paper, we provide new geochronological and geochemical data for the Miocene postcollisional potassic and adakitic intrusions exposed in the Qingdu area, eastern central Lhasa terrane, southern Tibet. The Qingdu Miocene intrusions consist of quartz monzonite porphyry and biotite granite with coeval zircon U–Pb ages of 14.1 Ma and 14.0 Ma, respectively. They have high SiO2 (67.98–75.32 wt.%), Al2O3 (14.13–14.78 wt.%), and K2O (4.06–6.18 wt.%) and low MgO (0.25–1.46 wt.%) contents. They are both enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with high (La/Yb)N (25.37–42.32) ratios. The biotite granite samples have low Y (7.10–9.96 ppm) and Yb (0.61–0.85 ppm) contents, and high Sr (229–384 ppm) contents and high Sr/Y (30–41) ratios, which show adakitic geochemical characteristics, whereas the quartz monzonite porphyry samples show potassic geochemical characteristics. They display initial (87Sr/86Sr)i ratios of 0.7083–0.7103, εHf(t) values of −6.7 to −0.1, εNd(t) values of −8.96 to −7.44, (208Pb/204Pb)i ratios of 39.028–39.110, (207Pb/204Pb)i ratios of 15.662–15.684, and (206Pb/204Pb)i ratios of 18.541–18.577. These signatures indicate that both the potassic and adakitic intrusions are more likely to originate from partial melting of a thickened lower crust, which were mainly the products of the binary mixing between the juvenile and ancient crust components. Based on the spatial distributions and isotopic features of the postcollisional potassic and adakitic rocks in the Lhasa terrane, we suggest that the differences of the lower crustal composition played a crucial role in causing the geochemical variations of the Miocene postcollisional adakitic and potassic rocks in Lhasa terrane. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • With the granite porphyry intrusions as the center outward form alteration zonation. • From stage I to stage V, ore-forming fluids gradually evolved from magmatic to meteoric water in origin. • Ore-forming materials were derived mainly from the granite porphyry. • The Longgen Pb–Zn deposit is a typical skarn deposit. • Fluid cooling caused by fluid mixing was the most crucial mechanism for Pb-Zn deposition. Abstract The medium-sized Longgen Pb-Zn deposit deposit (proven Pb + Zn resources of 0.13 Mt, 3.21% Pb and 2.43% Zn) is located in the western Nyainqentanglha belt in southern Tibet. The orebodies occurring as stratiform, lenticular and vein types are hosted in the skarn or marble along the contacts between the limestones and the granite porphyries. Alteration zonations are observed from granite porphyry to limestone, the proximal garnet is reddish-brown and becomes more pale brown and green with distance. The values of grossular gradually increase, while the andradite end members gradually decrease with distance (And (92.5−99.5) Gro (0.5−7.5) Pra (0.0−0.1) to And (9.0−36.5) Gro (63.4−90.9) Pra (0.1−0.5)). Similarly, the values of diopside (Di 9.2–30.4 Hd 65.9–89.9 Jo 0.6−3.7 to Di 65.2–77.6 Hd 21–33.2 Jo 1.3−1.7) gradually increased close to the limestone. Retrograde metasomatic minerals overprint the prograde skarn and are dominantly composed of epidote, actinolite, ilvaite, and chlorite. The ore minerals consist mainly of galena and sphalerite, followed by magnetite, pyrite, pyrrhotite, chalcopyrite, molybdenite and bornite. At least five stages have been recognized, and from stage I to stage V, the δ18O fluids values are 7.7% to 8.3%, −6.0% to −4.4%, −8.8% to −6.4%, −8.7% to −3.3%, and −13.2%, respectively. The δD values from stages I to V are −141.1% to −129.4%, −136.5% to −124.2%, −129.5% to −106.4%, −126.6% to −101.4%, and −106.8%, respectively. The δD and δ18O fluids indicate that the ore-forming fluids gradually evolved from magmatic to meteoric in origin. The main types of fluid inclusions for the Longgen deposit are liquid-rich inclusions. Laser Raman analysis indicates that the fluid inclusions within the studied minerals are dominated by H 2 O, although some contain CO 2 gas. Given the fluid inclusion data, the ore-forming fluids of stages I and II were most likely high-temperature (460–480 and 340–360 °C) and low-moderate salinity (7.9–15.0 and 2.4–12.6 wt% NaCl eq.) fluids, which were formed in a magmatic–hydrothermal system in stage I and as a mixture of magmatic and meteoric waters in stage II. In the subsequent stages (III and IV), the fluids changed to moderate temperature (230–270 and 160–200 °C) and low-moderate salinity (0.2–14.8 and 0.9–10.6 wt% NaCl eq.) mixed fluids of magmatic and meteoric waters. In the last stage V, the fluids changed to low-temperature (130–160 °C) and low-salinity (0.2–5.6 wt% NaCl eq.) meteoric water. The δ13C values in calcite lie within a narrow range of −6.1% to −4.4%, similar to that for the magmatic source, which indicates that the carbon was sourced from the granite porphyry. Sulfur (δ34S = 0.4–5%, estimated δ34S fluids = 2.77%) and lead isotopic compositions of sulfides (206Pb/204Pb = 18.549–18.776, 207Pb/204Pb = 15.685–15.839 and 208Pb/204Pb = 38.94–39.592, similar to the whole-rock values for the granite porphyry) indicate that the ore-forming materials were derived mainly from the granite porphyry, which originated from the Nyainqentanglha Group. Consequently, taking the data together suggests that the Longgen Pb–Zn deposit is a typical skarn deposit related to Palaeocene magmatic-hydrothermal systems, and that fluid cooling caused by fluid mixing is the most crucial mechanism for Pb-Zn deposition. [ABSTRACT FROM AUTHOR]

The Baomai porphyry Cu-Mo deposit is a newly discovered deposit located in the northern section of the Yulong porphyry Cu belt, eastern Tibet. It is associated with Eocene biotite monzogranite intrusions that were emplaced into Paleoproterozoic Ningduo Group and Middle-Upper Triassic sedimentary rocks. A biotite monzogranite porphyry with a zircon U-Pb age of 42.7 Ma was intruded by several post-ore diorite porphyry dikes (ca. 37.8 Ma). Alteration mineral assemblages consistent with argillic, phyllic, and hornfels were identified in ore-bearing porphyries and host rocks at Baomai. Argillic and phyllic alteration assemblages are spatially related to high-grade Cu and Mo mineralization, whereas hornfels alteration is accompanied by weak Cu mineralization. Molybdenite from the mineralized porphyry returned a Re-Os isochron age of 42.6 Ma, and is considered to represent the age of porphyry-style mineralization at the deposit. Ore-bearing porphyries in Baomai are high-K (K 2 O/Na 2 O >1), alkaline-rich intrusions rich in LREE, LILE (e.g., Rb, U, K), depleted in HFSE (e.g., Nb, Ta, P and Ti) and contain absent or slightly negative Eu anomalies and no significant Ce anomalies. Slightly high 87 Sr/ 86 Sr ratios (0.7064–0.7076), low ε Nd(t) values (−2.5 to −4.6), uniform ( 206 Pb/ 204 Pb) i ratios (18.70–18.75) and positive ε Hf(t) values (0–5.3) of ore-bearing porphyries at Baomai indicate that they share the same or similar petrogenesis to other mineralized porphyries within the Yulong porphyry Cu belt. The porphyries were likely generated from partial melting of phlogopite-bearing amphibolite or amphibolite eclogite with a low degree of crystal fractionation, and related to enrichment mantle (EMII) transformed or mixed by older subducted slab-derived fluid. Actually, there are no significant three stages of ore-bearing magmatic activities in Yulong porphyry Copper belt (Hou et al., 2003b), Eocene intrusions (37–43 Ma) and regional strike slip faulting were all important factors in controlling the formation of these Cu-polymetallic deposits during the Eocene India-Tibetan collision. [ABSTRACT FROM AUTHOR]

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 ± 0.2 Ma and monzogranite with zircon U–Pb age of 17.1 ± 0.1 Ma. 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 18.4 wt.% NaCl equiv. Quartz has δ 18 O SMOW values of 6.2–9.3‰, while sulfides have δ 34 S V-CDT values of −5.1‰ to 0.1‰, 206 Pb/ 204 Pb of 18.722–18.849, 207 Pb/ 204 Pb of 15.640–15.785, and 208 Pb/ 204 Pb 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 ∼2 km east of the Luobuzhen, is characterized by high concentrations of Cu (up to 1450 ppm) and Mo (up to 130 ppm) 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 ∼20 km 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. [ABSTRACT FROM AUTHOR]

The Tiegelongnan deposit is a newly discovered super-large porphyry-epithermal Cu-(Au) deposit in the western part of the Bangong Co-Nujiang metallogenic belt, Tibet (China). Field geology and geochronology indicate that the porphyry mineralization was closely related to the Early Cretaceous intermediate-felsic intrusions (ca. 123-120 Ma). Various epithermal ore and gangue mineral types were discovered in the middle-shallow part of the orebody, indicating the presence of epithermal mineralization at Tiegelongnan. Potassic, propylitic, phyllic and advanced argillic alteration zones were identified. 40Ar/39Ar dating of hydrothermal biotite (potassic zone), sericite (phyllic zone), and alunite (advanced argillic zone) in/around the ore-bearing granodiorite porphyry yielded 121.1±0.6 Ma (1σ), 120.8±0.7 Ma (1σ) and 117.9±1.6 Ma (1σ), respectively. Five hydrothermal mineralization stages were identified, of which the Stage IV pyrite was Rb-Sr dated to be 117.5±1.8 Ma (2σ), representing the end of epithermal mineralization. Field geology and geochronology suggest that both the epithermal and porphyry mineralization belong to the same magmatic-hydrothermal system. The Tiegelongnan super-large Cu-(Au) deposit may have undergone a prolonged magmatic-hydrothermal evolution, with the major mineralization event occurring at ca.120-117Ma. [ABSTRACT FROM AUTHOR]

The Gangdese is a newly explored porphyry copper ore belt in China. Except for the Cu (± Mo ± Au) porphyry deposits there are some Mo (± Cu ± W) porphyry and skarn deposits in this belt. Two pulses of molybdenite mineralization are recognized in the central Lhasa subterrane with ancient continent crust, including the Paleocene–Eocene (65–52 Ma) porphyry Mo and skarn Mo–W deposits formed during the rollback of Neo-Tethyan oceanic slab in collisional setting, and Miocene (21–15 Ma) porphyry Mo–Cu deposits generated in the postcollisional setting. The Gangdese copper deposits also occur during these two periods but are distributed in the southern Lhasa subterrane dominated by juvenile crust through mantle-derived magmatism resulting from Neo-Tethyan ocean lithosphere subduction. The intrusions related to molybdenite mineralization have relatively lower bulk-rock ε Nd (t) and higher ( 87 Sr/ 86 Sr) i values, lower zircon ε Hf (t) values and older Hf model ages, lower molybdenite Re contents, and more radiogenic Pb isotopes than the coeval copper related porphyries in the Gangdese belt. In addition, the Miocene Mo–Cu related intrusions generally have lower zircon Ce 4 + /Ce 3 + ratios than the Miocene Cu (± Mo) related intrusions. These data indicate that more contributions from mature continental crustal materials play crucial role in the generation of Mo than Cu porphyry mineralization in the Gangdese belt. The Eocene Mo related intrusions are characterized by high SiO 2 (68–76%) and K 2 O (5.1–5.9%) concentrations, enrichment of large-ion lithophile elements (LILE), depletion of high field strength elements (HFSE), and low Sr/Y (7.5–23.8) ratios. Their Sr–Nd isotope compositions (ε Nd (t) = − 3.4 to − 4.6; 87 Sr/ 86 Sr (i) = 0.70622–0.70679) indicate that they are associated with partial melting of mantle wedge mixing with significant amounts (55%–65%) of middle-upper crustal materials. The Miocene Mo–Cu related intrusions have relatively high SiO 2 (64%–73%) and K 2 O (1.9–4.8%) contents and are characterized by enrichment of LILE, depletion of HFSE, and high Sr/Y ratios (55–189). Their Sr–Nd isotope compositions (ε Nd (t) = − 4.6 to − 3.4; 87 Sr/ 86 Sr (i) = 0.70622–0.70679) are indicative of derivation from remelting of previously subduction modified Tibetan lithosphere with significant amounts (50%–70%) of middle-upper crustal materials. For the Gangdese Mo (± Cu) porphyry mineralization, Mo metal was suggested to be derived from the middle–upper crustal materials, particularly the Carbonaceous–Permian marine sedimentary, whereas Cu metal to be sourced from the Gangdese Miocene Cu fertile magmas. The exploration targeting of the Gangdese molybdenite deposits should be focused on southern part of the central Lhasa subterrane where the Carbonaceous–Permian strata occur. The occurrence of Mo–Cu porphyry deposits could provide clue for targeting Cu–Mo porphyry deposits in the Gangdese belt. The Gangdese molybdenite deposits share many similarities with the East Qinling molybdenite deposits, such as type of ore deposits, geodynamic setting of their formation, variable Mo grades and high F contents. [ABSTRACT FROM AUTHOR]

The Tiegelongnan Cu (Au) deposit is the largest copper deposit newly discovered in the Bangong-Nujiang metallogenic belt. The deposit has a clear alteration zoning consisting of, from core to margin, potassic to propylitic, superimposed by phyllic and advanced argillic alteration. The shallow part of the deposit consists of a high sulphidation-state overprint, mainly comprising disseminated pyrite and Cu-S minerals such as bornite, covellite, digenite, and enargite. At depth porphyry-type mineralization mainly comprises disseminated chalcopyrite, bornite, pyrite, and a minor vein molybdenite. Mineralization is disseminated and associated with veins contained within the porphyry intrusions and their surrounding rocks. The zircon U-Pb ages of the mineralized diorite porphyry and granodiorite porphyry are 123.1 ± 1.7 Ma (2σ) and 121.5 ± 1.5 Ma (2σ), respectively. The molybdenite Re-Os age is 121.2 ± 1.2 Ma, suggesting that mineralization was closely associated with magmatism. Andesite lava (zircon U-Pb age of 111.7 ± 1.6 Ma, 2σ) overlies the ore-bodies and is the product of post-mineralization volcanic activity that played a critical role in preserving the ore-bodies. Values of −4.6 ‰ to + 0.8 ‰ δ34S for the metal sulfides (mean − 1.55 ‰) suggest that S mainly has a deep magmatic source. The H and O isotopic composition is (δD = −87 ‰ to −64 ‰; δ18OH2O = 5.5 ‰ to 9.0 ‰), indicating that the ore-forming fluids are mostly magmatic-hydrothermal, possibly mixed with a small amount of meteoric water. The zircon εHf(t) of the diorite porphyry is 3.7 to 8.3, and the granodiorite porphyry is 1.8 to 7.5. Molybdenite has a high Re from 382.2 × 10−6 to 1600 × 10−6. Re and Hf isotope composition show that Tiegelongnan has some mantle source, maybe the juvenile lower crust from crust-mantle mixed source. Metallogenesis of the Tiegelongnan giant porphyry system was associated with intermediate to acidic magma in the Early Cretaceous (~120 Ma). The magma provenance of the Tiegelongnan deposit has some mantle-derived composition, possibly mixed with the crust-derived materials. [ABSTRACT FROM AUTHOR]

The Paleocene-Eocene ore deposits in the Gangdese Metallogenic Belt, Tibet, are thought to have been formed during the main period of India-Asia continental collision. This paper reports the whole-rock major element, trace element, and Sr-Nd-Hf isotopic compositions and zircon trace element contents of volcanic and intrusive rocks from the Paleocene Yaguila skarn Pb-Zn-Ag deposit and adjacent Eocene Sharang porphyry Mo deposit in the central Lhasa terrane, Tibet. Geochemical signatures and Nd-Hf isotopic compositions indicate that the Yaguila Cretaceous rhyolitic rocks were formed by the melting of ancient continental crust, whereas the Paleocene causative granite porphyry may have resulted from the interaction between mantle-derived and crustal-derived materials when continental collision was initiated. The dramatic increase of ε Nd (t) values between emplacement of the granite porphyry and later porphyritic biotite granite suggests a greater involvement of mantle materials during the crystallization of the barren biotite granite stock. The post-ore Miocene granodiorite porphyry has a similar geochemical signature to the Sharang Miocene dykes, suggesting they were both generated from melting of enriched lithospheric mantle. Nd-Hf mixing calculations indicate an increasing contribution of mantle materials in Paleocene to Eocene intrusions, consistent with the regional tectonic model of Neo-Tethyan oceanic slab roll-back and break-off. Zircons from both the Yaguila and Sharang ore-related porphyries have higher Ce anomalies than those from the barren granitoids, suggesting that Mo mineralization was closely related to highly oxidized and differentiated magma. The fertile intrusions in the Yaguila-Sharang district contain Eu N /Eu N ∗ values from 0.3 to 0.6, higher than the non-mineralized intrusions. The processes of early crystallization of plagioclase and/or SO 2 -degassing from underlying magma can explain the observed negative Eu anomalies in zircon. [ABSTRACT FROM AUTHOR]

[Display omitted] • The variation of Pos2200 in the Cimabanshuo-Luobuzhen area is mainly controlled by Tschermak substitution in white mica crystals. • The indications of SWIR (Pos2200 < 2203 nm, Dep2200 > 0.2, IC > 2.0) have been established at the Zhu'nuo ore-cluster district for rapidly identifying potential porphyry copper mineralization. • Three H/M centers and a new porphyry metallogenic system in the Cimabanshuo-Luobuzhen area have been identified based on the indications of SWIR. The Zhu'nuo ore-cluster district in the western Gangdese belt, southern Tibet, is characterized by a significant Cu geochemical anomaly, where the Zhu'nuo super-large porphyry Cu deposit (PCD) was discovered by stream sediment geochemical method. However, due to the extended coverage of volcanic rocks of the Linzizong group and the large area of ore-forming element anomalies, it is quite difficult to locate the concealed PCDs only by geochemical method. Therefore, the application of new technical methods is urgently needed to guide the exploration breakthroughs in the Zhu'nuo district. Recently, our studies have shown that the wavelength variation of diagnostic absorption peaks of alteration minerals measured by shortwave infrared (SWIR) spectrometry is closely related to the mineralization temperature in the Zhu'nuo PCD, which can be footprints to trace the hydrothermal and/or mineralization (H/M) centers of porphyry ore systems. Hence, we carried out SWIR studies in the Luobuzhen-Cimabanshuo areas with high Cu geochemical anomaly. In this study, sixteen alteration minerals were identified by SWIR, consisting mainly of white mica, chlorite, epidote, and kaolinite. Among them, the white mica and chlorite were widely distributed in the study area, and the Al-OH wavelength position of white mica (∼2200 nm; Pos2200) and Fe-OH wavelength position of chlorite (∼2250 nm; Pos2250) varied between 2191–2219 nm and 2239–2260 nm, respectively. Moreover, there is an increasing trend of Pos2200 from porphyry center to periphery, whereas Pos2250 shows the opposite tendency. When combined with geochemical anomalies of stream sediments and geological characteristics and SWIR features in the Zhu'nuo PCD in study area, three potential H/M centers, namely Cimabanshuo, South Luobuzhen and Ya'nuri, were determined, which are dominated by short wave anomalies (Pos2200, 2191–2206 nm; Pos2350, 2243–2250 nm). Significantly, we showed that the Dongshibu-Hongshan-Luobuzhen may belong to the same porphyry system by SWIR. And SWIR implies that the true center is located in South Luobuzhen (H/M II), which has great prospecting potential in its depth, rather than the previously recognized Dongshibu Cu prospect delineated by stream sediment data. We found that the Dongshibu Cu prospect does not show any alteration information associated with porphyry mineralization as reflected by SWIR, consistent with the barren Cu results from the late drilling validation. This decoupling may be caused by the long-term migration and weathering of stream sediment samples, during which the obtained geochemical anomaly do not represent their in-situ information. Therefore, caution must be taken when using stream sediment data to delineate prospecting targets. Instead, SWIR is a potentially powerful vectoring tool to aid exploration for porphyry systems, especially in the western regions where the level of prospecting work is extremely low. [ABSTRACT FROM AUTHOR]

We report the copper isotopic composition of Cu sulfides in the Tiegelongnan high-sulfidation (HS) copper deposit, Tibet, and investigate the possible application of Cu isotopes to mineral exploration. The copper isotopic values of samples from four drill holes display consistent progressive increase with depth to 400 m below surface, with an overall variation of δCu of up to 7.60‰ (−4.76 to 2.84‰). Such a large range is very different from that observed in Cu porphyry deposits which commonly exhibit a small δCu range (<1‰), with decreasing values with depth. The large δCu variation is likely of supergene origin and reflects strong leaching under oxidized conditions. The systematic increase of δCu with depth can be explained by the release of isotopically heavy Cu at the top and its transport downward, which is supported by the coupling of positive δCu values with high Cu grade and the occurrence of both negative and positive δCu values in two drill holes. Mass-balance consideration on the basis of Cu isotopes can indicate mineralized zones which have been eroded or have not been found yet. Such mineralized targets, if buried at depth, could be located using Cu isotopes. [ABSTRACT FROM AUTHOR]

The Zhibula Cu skarn deposit (19.5 Mt ore @ 1.64%), near the Qulong porphyry Cu–Mo deposit, is located in the Gangdese porphyry copper belt in southern Tibet. The deposit is a typical metasomatic skarn that is related to the interaction of magmatic-hydrothermal fluids and calcareous host rocks. Stratiform skarn orebodies are mainly distributed in the contact between tuff and marble in the lower part of the Jurassic Yeba Formation. Endoskarn zonations for an outward trend are observed in the granodiorite, which grade from a fresh granodiorite to a weakly chlorite-altered granodiorite, a green diopside-bearing granodiorite, and a dark red-brown garnet-bearing granodiorite. The Zhibula granodiorite and monzogranite have similar secondary ion mass spectrometry (SIMS) zircon U–Pb ages of 16.9 ± 0.3 Ma and 17.0 ± 0.2 Ma, respectively. They exhibit different fractional crystallization from granodiorite (SiO 2 = 64.8–69.3 wt.%) to monzogranite (SiO 2 = 72.3–76.8 wt.%). Both the granodiorite and monzogranite are characterized by high Al 2 O 3 (12.6–16.7 wt.%) and K 2 O (1.5–5.5 wt.%) contents, high Sr/Y (35–151) and La/Yb (19–48) ratios, and variable MgO (0.16–3.91) and Mg# (31–61) values. They display features of enrichment in large ion lithophile elements (LILEs, e.g., Rb, Ba, Sr, and K), depletion in high field strength elements (HFSEs, e.g., Nb, Ta, Ti, and P), and moderate negative Eu anomalies (δEu = 0.58–0.98). They show restricted in situ zircon Hf isotopic compositions (+6.7 to +8.8; only one sample is +4.5) and consistent δ 18 O values (+6.0‰ to +6.6‰). The geochemical data indicated that the Miocene Zhibula granitic intrusions formed by the magma that were characterized by high Sr/Y ratios and were derived from the partial melting of the thickened juvenile lower crust, which may have been metasomatized by the slab melts during subduction of the Neo-Tethyan oceanic crust and were induced by the convective removal of the thickened lithosphere. In addition, the Zhibula Cu skarn deposit and the Qulong Cu–Mo deposit form a significant porphyry–skarn ore system. [ABSTRACT FROM AUTHOR]

The Lakange porphyry Cu-Mo deposit within the Gangdese metallogenic belt of Tibet is located in the southern-central part of the eastern Lhasa block, in the Tibetan Tethyan tectonic domain. This deposit is one of the largest identified by a joint Qinghai-Tibetan Plateau geological survey project undertaken in recent years. Here, we present the results of the systematic logging of drillholes and provide new petrological, zircon U-Pb age, and molybdenite Re-Os age data for the deposit. The ore-bearing porphyritic granodiorite contains elevated concentrations of silica and alkali elements but low concentrations of MgO and CaO. It is metaluminous to weakly peraluminous and has A/CNK values of 0.90-1.01. The samples contain low total REE concentrations and show light REE/heavy REE (LREE/HREE) ratios of 17.51-19.77 and (La/Yb)N values of 29.65-41.05. The intrusion is enriched in the large-ion lithophile elements (LILE) and depleted in the HREE and high field-strength elements (HFSE). The ore-bearing porphyritic granodiorite yielded a Miocene zircon U-Pb crystallization age of 13.58 ± 0.42 Ma, whereas the mineralization within the Lakange deposit yielded Miocene molybdenite Re-Os ages of 13.20 ± 0.20 and 13.64 ± 0.21, with a weighted mean of 13.38 ± 0.15 Ma and an isochron age of 13.12 ± 0.44 Ma. This indicates that the crystallization and mineralization of the Lakange porphyry were contemporaneous. The ore-bearing porphyritic granodiorite yielded zircon εHf( t) values between −3.99 and 4.49 (mean, −0.14) and two-stage model ages between 1349 and 808 Myr (mean, 1103 Myr). The molybdenite within the deposit contains 343.6-835.7 ppm Re (mean, 557.8 ppm). These data indicate that the mineralized porphyritic granodiorite within the Lakange deposit is adakitic and formed from parental magmas derived mainly from juvenile crustal material that partly mixed with older continental crust during the evolution of the magmas. The Lakange porphyry Cu-Mo deposit and numerous associated porphyry-skarn deposits in the eastern Gangdese porphyry copper belt (17-13 Ma) formed in an extensional tectonic setting during the India-Asia continental collision. [ABSTRACT FROM AUTHOR]

Processes generating fertile magma and associated porphyry Cu deposits in post-collision tectonic settings remain uncertain. Dabu, located in the Gangdese porphyry Cu belt of southern Tibet, is a typical porphyry Cu–Mo deposit that formed in a post-collision setting. The deposit records two stages of magmatism: an Eocene (46 ± 1 Ma) barren monzogranite (EG); and a fertile Miocene (15 ± 1 Ma) monzogranite porphyry (MMP). These intrusions have similar Sr–Nd ( 87 Sr/ 86 Sr (i) = 0.70514 to 0.70573, εNd(t) = − 2.78 to + 0.77) and zircon Hf (εHf(t) = + 3.46 to + 8.85) isotopic compositions that fall within the range of the Palaeocene–Eocene Gangdese Batholith and the coeval Linzizong volcanics and plot on a mixing line between Tethyan basalts and Indian Ocean pelagic sediments. These features, coupled with the variable Sr/Nd, Sr/Th, Ba/Th, and Rb/Y ratios of the intrusions, are indicative of a common source involving basaltic lower crustal melts underplated during the Palaeocene and Eocene. The basaltic material was sourced from a mantle wedge that was metasomatized by Neo-Tethyan slab-derived fluids and oceanic sediments. The MMP, however, formed under a higher magmatic oxygen fugacity than did the EG, as indicated by their higher zircon Ce 4 + /Ce 3 + ratios (87-1112) and higher f O 2 values (ΔFMQ = 5), determined using ilmenite–magnetite mineral pairs. The decompression and discharge of SO 2 during the Linzizong volcanic event and the fractionation of magnetite could account for the low oxygen fugacity (Ce 4 + /Ce 3 + = 58–164; ΔFMQ = − 0.3) of the EG as well the limited development of porphyry deposits associated with the Gangdese Batholith. The MMP and Miocene mineralization-related intrusions within other Gangdese porphyry Cu deposits have high Sr/Y and V/Sc ratios and a negative correlation between Dy/Yb and SiO 2 , all of which are indicative of the crystallization of hornblende from a hydrous mafic melt. The EG and Gangdese Batholith, however, have low Sr/Y and V/Sc ratios and decreasing Sr concentrations over a wide range of SiO 2 contents, indicating that these intrusions formed from dry melts that had undergone significant plagioclase fractionation. Late-crystallized hornblende is generally present as small crystals within early formed feldspar phenocrysts in the EG, which is in good agreement with a rapid increase followed by a decrease in Y and Dy concentrations at ~ 60 wt.% SiO 2 . In addition, apatite in MMP has F (2.66–3.72%) and Cl (0.06–0.53%) volatile contents that are higher than those of apatite from EG (0.85–1.50% F and 0.02–0.03% Cl). These geochemical and mineralogical characteristics suggest that EG formed from a relatively dry magma with < 4.0% H 2 O, whereas MMP formed from a more hydrous magma with > 5.5% H 2 O. It is here proposed that long-lived subduction caused the high oxygen fugacity conditions of the arc magma by adding oxidized components to the sub-arc mantle in addition to F, Cl, S, and Cu. Long-term metamorphic dehydration resulted from the India–Asia collision, and subsequent crust thickening and shortening was responsible for the high water contents by continuously replenishing the basaltic melts at the base of the lower crust. Both subduction-related metasomatism and late-collision-related metamorphic dehydration controlled the genesis of fertile magma that formed the post-collision porphyry Cu–Mo deposits of southern Tibet. [ABSTRACT FROM AUTHOR]

Jiru is a poorly studied Cu deposit located in the west segment of the Gangdese porphyry Cu belt (GPCB), 200 km west of Lhasa. The deposit consists of both collisional- and postcollisional-stage porphyry-type Cu systems, which are genetically associated with the early Eocene granitoid batholith and the Miocene Jiru porphyry stock, respectively. In this study, we present zircon U–Pb LA-ICP-MS dates and Hf isotopes, whole rock geochemical and Pb isotope geochemical data for the main intrusions in the Jiru deposit. The early Eocene granitoid samples (~ 49 Ma) are characterized by magmatic arc geochemical features, slightly concave REE patterns and well-developed negative Eu anomalies. These geochemical characteristics suggest that the granitoid melts were generated by partial melting of a metasomatized mantle, and that the melt had undergone fractional crystallization of amphibole and plagioclase. In contrast, the Miocene porphyry intrusions (16.4–15.5 Ma) at Jiru are characterized by high K contents, adakitic affinities (e.g., high Sr/Y and La/Yb ratios), subduction signatures (e.g., enriched Cs, Rb, Ba and depleted Nb, Ta, Ti), positive zircon ε Hf (t) values (1–6) and variable 208 Pb/ 204 Pb ratios (38.5–39.0), similar to other post-collisional porphyry intrusions in the Gangdese belt. Based on the above features, we propose that the Miocene porphyry intrusions at Jiru were generated by partial melting of subduction-modified lower crust. Well-developed negative Eu anomalies and low Sr/Y ratios (generally < 20) of the least fractionated samples of the Early Eocene granitoids indicate that water content of the primitive collision-related magma was < 4 wt.%, but increased to over 4 wt.% with fractional crystallization, as evidenced by very weak negative Eu anomalies and relatively high Sr/Y ratios (~ 40) for some samples with SiO 2 contents of ~ 67 wt.%. Upper crustal differentiation, which would increase water content of residual magma, is thought to be a key step in the formation of the collision-stage Cu mineralization at Jiru. The presence of Eocene porphyry Cu–Mo mineralization indicates that sulfide precipitation at the base of the orogenic lower crust during the first-stage arc magmatism is not needed in the formation of the postcollisional porphyry Cu deposit at Jiru. This implies that the source of metal and S for postcollisional porphyry Cu deposits is more complex than originally considered. [ABSTRACT FROM AUTHOR]

The coexistence of aqueous fluid inclusions and silicate melt inclusions in quartz phenocrysts from porphyrites at the Bangpu porphyry Mo–Cu deposit, Tibet, China were examined to characterize the immiscibility processes during the magmatic to hydrothermal transition. The physical and chemical environment during crystallization of the magmas has been reconstructed on the basis of microthermometric experiments and trace element microanalysis. Compositions of melt and brine fluid phases are determined using Synchrotron radiation X-ray fluorescence analysis, SEM–EDS and Laser Raman spectroscopy analyses. Brine fluids were directly exsolved by a crystallizing melt, and the simultaneous entrapment of volatile-rich (brine fluid) and volatile-poor immiscible phases (silicate melt) occurred at 670–700 °C and 1.6–1.95 kbar when the magma had H 2 O contents between 5 and 6 wt% and crystal contents of 60–80%. A later low-density fluid with a higher Mo concentration exsolved after about 80–90% crystallization had occurred. This fluid contained significant concentrations of Cl, Na, K, Ca, Fe, Cu, Zn, Rb, and small amounts of Mn, Br and Pb. Immiscibility of magmatic fluids can lead to different metal partitioning behaviors between residual melt and volatile phases, which generate variable metal ratios. Copper was partitioned preferentially into the brine phase, in contrast to the behavior observed in other porphyry Cu deposits. Ore deposition by a dense brine could explain the partially deep Cu mineralization. Condensation of brine from a later low-density parental fluid could be an efficient mechanism to concentrate shallow Cu mineralization and broadly distributed Mo mineralization. The source of the Mo mineralizing fluids probably was a particularly large magma chamber that crystallized and fractionated at depth greater than upper continental crust level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Here we characterize the geology and mineralization of the Sangri porphyry-skarn Cu-Mo deposit. • Zircon and garnet U-Pb, molybdenite Re-Os and K-feldspar Ar-Ar geochronology link magmatism, mineralization and alteration. • The Multi-isotopic dating could help to construct the defined time-framework of porphyry system. Obtaining a precise time framework has been a key but difficult problem for the study of metallogenic porphyry systems. This is more complicated when there are several stages of intrusion emplacement, different alterations, and mineralization events. To solve this problem, the Sangri porphyry-skarn Cu-Mo deposit in the Bangongco-Nujiang metallogenic belt, Tibet, was used as a study site for multiple isotopic dating studies. Zircon U-Pb dating of different intrusions shows that the magmatism of intermediate-felsic intrusions dates from 83.2 ± 0.8 Ma to 81.7 ± 0.7 Ma. Garnet U-Pb dating places the skarn as being formed in 83.2 ± 2.3 Ma. Re-Os dating of molybdenite in quartz-molybdenite vein and Ar-Ar dating of K-feldspar indicate ore-forming and alteration periods of 82.6 ± 0.6 Ma and 80.3 ± 1.8 Ma, respectively. The Sangri deposit is a product of magmatic-hydrothermal mineralization between 84 and 80 Ma in the Late Cretaceous. The mineralization of the Sangri deposit and precise geochronology data indicate that there was a Late Cretaceous metallogenic event in the Central Bangongco-Nujiang metallogenic belt, which provides a new clue for regional exploration and metallogeny. Finally, multi-element isotopic dating is shown to be an important method for constructing the time framework of porphyry systems. [ABSTRACT FROM AUTHOR]

The Miocene porphyry Cu-(Mo) deposits in the Gangdese orogenic belt in southern Tibet were formed in a post-subduction collisional setting. They are closely related to the Miocene adakite-like porphyries which were probably derived from a thickened basaltic lower crust. Furthermore, mantle components have been considered to have played a crucial role in formation of these porphyry deposits (Hou et al. Ore Geol Rev 36: 25-51, ; Miner Deposita doi:, ). In this study, we present zircon Hf isotopes and molybdenite Re-Os ages on the newly discovered Gangjiang porphyry Cu-Mo deposit in southern Tibet to constrain the magma source of the intrusions and the timing of mineralization. The Gangjiang porphyry Cu-Mo deposit is located in the Nimu ore field in the central Gangdese porphyry deposits belt, southern Tibet. The copper and molybdenum mineralization occur mainly as disseminations and veins in the overlapped part of the potassic and phyllic alteration zones, and are predominantly hosted in the quartz monzonite stock and in contact with the rhyodacite porphyry stock. SIMS zircon U-Pb dating of the pre-mineral quartz monzonite stock and late intra-mineral rhyodacite porphyry yielded ages of 14.73 ± 0.13 Ma (2 σ) and 12.01 ± 0.29 Ma (2 σ), respectively. These results indicate that the magmatism could have lasted as long as about 2.7 Ma for the Gangjiang deposit. The newly obtained Re-Os model ages vary from 12.51 ± 0.19 Ma (2 σ) to 12.85 ± 0.18 Ma (2 σ) for four molybdenite samples. These Re-Os ages are roughly coincident with the rhyodacite porphyry U-Pb zircon age, and indicate a relatively short-lived episode of ore deposition (ca. 0.3 Ma). In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS indicate that the ε( t) values of zircons from a quartz monzonite sample vary from +2.25 to +4.57 with an average of +3.33, while zircons from a rhyodacite porphyry sample vary from +5.53 to +7.81 with an average of +6.64. The Hf data indicate that mantle components could be partly involved in the deposit formation, and that mantle contributions might have increased over time from ca. 14.7 to 12.0 Ma. Combined with previous works, it is proposed that the Gangjiang deposit could have resulted from the convective thinning of the lithospheric root, and the input of upper mantle components into the magma could have played a key role in the formation of the porphyry deposits in the Miocene Gangdese porphyry copper belt in the Tibetan Orogen. [ABSTRACT FROM AUTHOR]

Abstract: The Duolong porphyry Cu–Au deposit (5.4Mt at 0.72% Cu, 41t at 0.23g/t Au), which is related to the granodiorite porphyry and the quartz–diorite porphyry from the Bangongco copper belt in central Tibet, formed in a continental arc setting. Here, we present the zircon U–Pb ages, geochemical whole-rock, Sr–Nd whole-rock and zircon in-situ Hf–O isotopic data for the Duolong porphyries. Secondary ion mass spectrometry (SIMS) zircon U–Pb analyses for six samples yielded consistent ages of ~118Ma, indicating a Cretaceous formation age. The Duolong porphyries (SiO2 of 58.81–68.81wt.%, K2O of 2.90–5.17wt.%) belong to the high-K calc-alkaline series. They show light rare earth element (LREE)-enriched distribution patterns with (La/Yb)N =6.1–11.7, enrichment in large ion lithophile elements (e.g., Cs, Rb, and Ba) and depletion of high field strength elements (e.g., Nb), with negative Ti anomalies. All zircons from the Duolong porphyries share relatively similar Hf–O isotopic compositions (δ18O=5.88–7.27‰; εHf(t)=3.6–7.3), indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization. This, along with the general absence of older inherited zircons, rules out significant crustal contamination during zircon growth. The zircons are mostly enriched in δ18O relative to mantle values, indicating the involvement of an 18O-enriched crustal source in the generation of the Duolong porphyries. Together with the presence of syn-mineralization basaltic andesite, the mixing between silicic melts derived from the lower crust and evolved H2O-rich mafic melts derived from the metasomatized mantle wedge, followed by subsequent fractional crystallization (FC) and minor crustal contamination in the shallow crust, could well explain the petrogenesis of the Duolong porphyries. Significantly, the hybrid melts possibly inherited the arc magma characteristics of abundant F, Cl, Cu, and Au elements and high oxidation state, which contributed to the formation of the Duolong porphyry Cu–Au deposit. [Copyright &y& Elsevier]

Abstract: Porphyry deposits are usually thought to form from subduction-related calc-alkaline magmas in magmatic arc settings, although some porphyry deposits also occur in post-collisional extensional settings. The post-collisional deposits remain poorly understood. Here we describe the igneous geology, alteration mineralogy and mineralization history of Qulong, a newly-discovered porphyry Cu–Mo deposit in southern Tibet that belongs to the post-collisional class. The deposit is associated with Miocene monzogranite–granodiorite intrusions and is hosted partly by Jurassic andesitic–dacitic volcanic rocks. The deposit contains 7.1 Mt Cu and 0.5 Mt Mo metal. The ~19.5 Ma granodioritic–monzogranitic Rongmucuola pluton with diorite enclaves is the earliest Miocene intrusive unit. It was intruded by a regularly-shaped stock (P porphyry) and then thin dikes (X porphyry) of monzogranite at about 17.7 Ma. The main Cu–Mo mineralization is associated with the P porphyry. A barren diorite porphyry intruded the P and X porphyries around 15.7 Ma. Petrologic trends of the intrusions suggest that the Miocene intrusions have similar origins and probably formed by fractionation of a deeper magma chamber. Emplacement of Miocene porphyries, controlled by the Qulong anticline, is in direct response to the rapid uplift/erosion of the Gangdese arc batholiths in southern Tibet. Miarolitic cavities and unidirectional solidification textures, key evidence for volatile separation, have been recognized in the P and X porphyries, respectively. Early potassic alteration, characterized by quartz–K feldspar (±anhydrite), pervades the P porphyry and Rongmucuola pluton. Laterally, this alteration grades into quartz–biotite–anhydrite (±K feldspar), which affects all Miocene intrusions except the latest dioritic porphyry. Wall rocks of Rongmucuola pluton and Jurassic andesitic–dacitic volcanics within 1–1.5 km of the porphyries are dominated by pervasive potassic alteration. An outer halo of propylitic alteration (epidote–chlorite±calcite) extends up to 2 km away from the deposit. Feldspar-destructive alteration (sericite–chlorite±clay minerals) has overprinted most of the potassic and part of the propylitic alteration. The alteration is strongly pervasive in the interior of the porphyry bodies and occurs as vein halos away from the porphyry bodies. The earliest quartz–K feldspar alteration and veins are barren, whereas approximately 60% of the Cu reserves is associated with slightly later quartz–biotite–anhydrite alteration. Barren assemblages are related to irregular quartz (–K feldspar±anhydrite) veins, which are truncated by the X porphyry. Cu sulfide-bearing assemblages are associated with discontinuous chalcopyrite (±biotite) and continuous quartz–anhydrite–chalcopyrite (±molybdenite) veins. Deposition of Cu–Mo with abundant anhydrite occurred during or between emplacement of closely related porphyries from high temperature magmatically-derived fluids, and was probably caused by the disproportionation of SO2. [Copyright &y& Elsevier]

Remote sensing (RS) of alteration zones and anomalies can provide information that is useful for geological prospecting and exploration. RS is an effective method for porphyry copper mineral exploration and prospecting prediction. More specifically, the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) data, which include 14 spectral channels from visible light to thermal infrared, are useful in such cases. This study uses visible-shortwave infrared and thermal infrared ASTER data together with surface material spectra from the Duolong porphyry copper ore district to construct an RS-based alteration zonation model of the deposit. In this study, an RS alteration zoning model is established based on ground-spectral alteration zoning results. The methods include PCA (Principal Component Analysis), Ratio, and Slope methods. The information obtained by each method is different. RS-based alteration zonation is developed based on the intersection of maps, resultant from the different methods for extracting information related to different minerals. The alteration zonation information extracted from ASTER RS data is consistent with geological observations. Using information from the RS-based model, we mapped the alteration minerals and zones of the Duolong ore district, thereby identifying prospecting target areas of the deposit. [ABSTRACT FROM AUTHOR]

Jiama is a super-large porphyry copper–polymetallic deposit located in the Gangdese metallogenic belt of southern Tibet. The deposit consists of a combination of a polymetallic skarn, Cu–Mo mineralization at the contact between the Jiama Porphyry and hornfels, and distal Au mineralization in fault. The current metal reserves are 7.4 Mt Cu, 0.6 Mt Mo, 1.8 Mt Pb–Zn, 6.65 Moz Au, and 360.32 Moz Ag, with a skarn to porphyry–hornfels host-rock ratio of ~3:1. Based on detailed field and laboratory investigations, this paper indicates that: (i) the skarn and porphyry–hornfels orebodies are almost entirely preserved; (ii) the emplacement age of the Cu-bearing plutonic rocks is earlier than the plutons containing elevated Mo assays; (iii) the permeability of the wall rocks gradually decreases in an upward direction; (iv) the fluid temperature during the precipitation of Cu was higher than that of the Mo mineralization; (v) the lithospheric pressure during the precipitation of Cu and Mo was the same; (vi) the laser Raman spectroscopy shows that the fluid carrying the Cu was rich in magnetite, hematite, and anhydrite, and the fluid carrying Mo was rich in pyrite, CO2, and CH4; and (vii) the SR–XRF mapping shows that the concentration of Cu in the mineralizing fluid was high and that of Mo was low when Cu was deposited. Conversely, the concentration of Cu was relatively low and the concentration of Mo was relatively high during deposition of the Mo. This study also shows that the temporal and spatial separation of Cu and Mo in the porphyry copper–polymetallic deposit at Jiama was associated with the emplacement of the Jiama Porphyry. Transportation of mineralized fluid was controlled by the permeability of the wall rocks, and deposition of the metals related to changes along a redox front and pressure releases during hydrothermal brecciation at the roof of the Jiama Porphyry. [ABSTRACT FROM AUTHOR]

• Magmatic-hydrothermal water was dominant at the Rongna deposit. • The epithermal mineralization was partially related with the dissolution and re-precipitation of porphyry-style sulfides. • Leaching downward of contracted vapor formed telescoped epithermal alteration and mineralization. • Zinc (Zn) was enriched in the distal fluid of the Rongna deposit. The giant Rongna Cu-(Au) deposit is a recently discovered low-grade composite porphyry-high sulfidation epithermal system in the Duolong ore district of central Tibet. We present fluid inclusion petrography, microthermometry, stable isotope (H, O), and fluid-compositional data (LA-ICP-MS) to constrain the fluid evolution of the Rongna deposit. Hydrothermal quartz and muscovite formed in the porphyry stage yielded fluid values of 8.2 ± 1.0‰ δ18O H2O , and −75 ± 19‰ δD H2O (n = 13). Pyrophyllite, kaolinite, and dickite define the isotopic composition of the epithermal fluid (δ18O H2O = 2.2–8.3‰, δD H2O = −87 ~ −45‰). This epithermal fluid of lighter oxygen isotope and heavier hydrogen isotope composition still has a magmatic-hydrothermal signature and rules out any significant involvement of meteoric water. The very high concentration of Cu in fluid inclusions from epithermal veins and the common sulfide replacement features suggest that the epithermal mineralization may be partially related with the dissolution and re-precipitation of the porphyry-stage sulfides. Combined with fluid inclusion petrography and microthermometric data, it is indicated that a single-phase fluid exsolved from magma at depth and underwent boiling and cooling, forming the porphyry alteration and mineralization. With decrease of temperature and pressure, the ascending vapor contracted into acid aqueous fluid, leaching downward to develop the telescoped high-sulfidation epithermal alteration and mineralization. [ABSTRACT FROM AUTHOR]

The giant Bolong porphyry Cu deposit (with proven Cu resources of 2.08 Mt. and 0.9 t Au) is located in the Bangongco–Nujiang metallogenic belt, northwestern Tibet. Copper mineralization has a genetic relationship with the granodiorite porphyry. Zircon laser ablation inductively coupled plasma mass spectrometry U Pb dating gives crystallization ages of 124.5 ± 1.1 and 121.4 ± 0.6 Ma (Early Cretaceous) for the first and second stages, respectively, of the Bolong ore-bearing granodiorite porphyry. Geochemical analysis indicates that the Bolong ore-bearing granodiorite porphyry samples exhibit obvious light rare earth element enrichment, high initial ratios of 87Sr/86Sr (0.7076–0.7098) and low values of εNd(t) (−7.7 to −3.5), with T DM2 (Nd) ages of 1.21 to 1.55 Ga. Ratios of (206Pb/204Pb) t , (207Pb/204Pb) t , and (208Pb/204Pb) t are 16.96–17.79, 15.48–15.52, and 36.72–37.74, respectively. Zircons yield εHf(t) values of −1.3 to 9.1 and 2.7 to 10.5 and T DM2 (Hf) ages of 0.59–1.26 Ga. These isotopic signatures suggest that the primary magma of the Bolong ore-bearing granodiorite porphyry originated mainly from mixing of crust-derived felsic and metasomatized mantle-wedge-derived mafic melts. The Bolong ore-bearing granodiorite porphyry rocks have high log f O 2 values ranging from −14.56 to −11.3 and −14.19 to −11.4 respectively, corresponding to △FMQ +1.7 to △FMQ +2.6 and △FMQ +2.2 to △FMQ +2.8, respectively. The Bolong porphyry Cu Au deposit formed in a continental arc tectonic setting, during the northward subduction of the Bangongco–Nujiang Ocean in the Early Cretaceous. Unlabelled Image • The Bolong ore-bearing granodiorite porphyry crystallized at ca. 121 to 124 Ma. • Ore-bearing granodiorite porphyry magma formed by mixing of mafic and felsic melts. • The Bolong ore-bearing granodiorite porphyry rocks have high log f O 2 values (above FMQ +2). • The Bolong porphyry Cu Au deposit was formed in a continental arc setting. [ABSTRACT FROM AUTHOR]