Search

The Tethyan domain from China to Iran hosts many important sediment-hosted Pb–Zn deposits but most have been poorly documented. This study summarizes the salient features of these deposits and discusses the type of ore, tectonic setting, and important ore controls, on the basis of new geological observations and previous publications. The Tethyan domain is characterized by the young and extensive Himalayan–Tibetan and Zagros orogens that formed through collisions between the India/Arabia and Eurasia continents since the Late Cretaceous or early Cenozoic. Abundant Mississippi Valley-type (MVT) and subordinate clastic-dominated (CD, also known as SEDEX) Pb–Zn deposits occur in this domain, including in central and eastern Himalayan–Tibetan orogen in China, the Indian passive margin in southern Pakistan, and various tectonic units of Iran. Economically important deposits contain 0.1–21 Mt Pb + Zn and have total metal resources of ∼75 Mt with ∼48% being oxidized ores. All major deposits known in this domain are MVTs (i.e., the Jinding, Huoshaoyun, Mehdiabad, and Angouran deposits). Mississippi Valley-type Pb–Zn deposits occur in continental-collision-related fold-and-thrust belts and forelands, where deposits are mostly located on the margin of the Eurasian continent, with some in the Indian and Arabian continental margins. Clastic-dominated Pb–Zn deposits occur in central Iran and southern Pakistan, hosted by deep-water siliciclastic sequences of the early Cambrian rifted continental margin of Gondwana and the Jurassic passive continental margin of India, respectively. The youngest mineralized rocks and ages constrain that some important MVT deposits (e.g., the Jinding, Chaqupacha, and Angouran deposits) were formed after a main phase of regional compression, during a regional, large-scale strike-slip or crustal-extension stage in a continental collision setting. In sense of lithologic structure, important ore controls for MVT deposits include evaporite diapir structure, carbonate/evaporite dissolution–collapse structure, pre-existing barite, and porous dolostone. Much of the primary sulfide ore in this domain has been oxidized by supergene processes. This is particularly pronounced in the newly discovered Huoshaoyun deposit, where almost all sulfides have been oxidized to smithsonite and cerussite. An understanding of tectonic setting, ore controls, and supergene processes is essential in exploring for MVT deposits in this domain. Unlabelled Image • Abundant Mississippi Valley-type (MVT) deposits and minor clastic-dominated (CD) deposits • MVT deposits in continental collisional forelands and fold and thrust belts • MVT ore formations in a regional strike-slip or crustal-extension stage in a continental collision setting • MVT ore controls: evaporite diapir, carbonate/evaporite dissolution–collapse, pre-existing barite, and porous dolostone • Supergene process occurring in many sediment-hosted Zn–Pb deposits [ABSTRACT FROM AUTHOR]

The 1600 km-long Gangdese magmatic belt features extensive Paleocene–Eocene I-type intrusive rocks and coeval volcanic successions, which can be divided into Group I (~69–53 Ma), Group II (~53–49 Ma), and Group III (~49–43 Ma), corresponding to Neo-Tethyan slab rollback, Neo-Tethyan slab breakoff, and ongoing Indian-Asian collision, respectively. The magmas from these three groups show significant variations in geochemical and isotopic compositions, which provide the information of the growth of continental crust in southern Tibet. The most voluminous magmatism in the Gangdese belt occurred during ~53–49 Ma. High zircon saturation temperature (up to 800 °C) and Ti in zircon temperature (up to 980 °C) estimations suggest there is a period of thermal anomaly during ~53–49 Ma. Starting from ~53 Ma, magmas have increased K 2 O contents, and their zircons have decreased Th/U ratios, and Y and Yb contents. Zircons from Group II have the most heterogeneous Hf isotopic compositions (εHf (t)  = −5.3 to 15.1). These are evident of ingress of asthenosphere mantle in the arc, extensive crustal melting, and magma mixing. Magma underplating during this time is the main mechanism for the growth of continental crust. With the Indian-Asian collision going on, the magmas in Group III show high Th/Y and La/Yb ratios and K 2 O contents, but significantly low Tzr and T(ti-zr) values (mostly below 750 °C). These features suggest the water-fluxed melting of early arc residues occurred in the late stage of growth of continental crust. The crust has been thickened and nearly mature at this stage. This study has great implication on understanding of growth of continental crust in orogenic belts. [ABSTRACT FROM AUTHOR]

New major and trace elemental, Sr–Nd–Pb isotope, and zircon U–Pb geochronological and Hf–O isotope data of post-collisional potassic and ultrapotassic volcanic rocks (PVRs and UPVs, respectively) along with geochemical data of PVRs, UPVs, and Mg-rich potassic rocks (MPRs) in the literature are used to constrain their mantle source and genesis. The PVRs, UPVs, and MPRs share similar geochemical features but with some discrepancies, suggesting that they were derived from subcontinental lithospheric mantle (SCLM) with isotopic heterogeneity resulting from the varying contributions of subducted Indian lower crust into the mantle source (ca. 6–20%, ca. 8–30%, and ca. 9–30%, respectively). The zircon Hf–O isotopic compositions of these rocks can be classified into two groups, including Group I rocks with high δ 18 O (6.7–11.3‰), low ε Hf (t) (− 17.0 to − 12.0), and old Hf crustal model ages (1.87–2.19 Ga) that indicate an ancient SCLM source, and Group II rocks with δ 18 O values of 6.8–10.7‰, ε Hf (t) values of − 11.8 to − 6.3, and younger Hf crustal model ages (1.50–1.86 Ga). The negative correlation defined by δ 18 O and ε Hf (t) of Group II samples suggests a two-component mixing between mantle- and crust-derived melts, in which the latter would be the subducted Indian lower crust as indicated by the similar negative ε Hf (t) values between Group II samples (− 11.8 to − 6.3) and the High Himalayan gneiss (− 14.2 to + 0.3). Thus we propose two enrichment events to account for the Hf–O isotopic compositions of the PVRs and UPVs/MPRs: the first involves the enrichment of the overlying SCLM that was metasomatized by fluids derived from dehydration of the subducted Indian lower crust, and the second invokes the enrichment of the overlying SCLM metasomatized by melts of the already dehydrated different proportions of the Indian lower crust. We argue that break-off of the northwards subducted Indian Plate in the early Miocene caused the asthenospheric upwelling under the Indian plate through slab window, resulting in varying degrees of partial melting of the overlying metasomatized heterogeneous SCLM to produce the primitive magmas of the PVRs, UPVs, and MPRs in an extensional setting. These observations and interpretations imply that the Indian lower crust was subducted beneath the Lhasa terrane in the Early–Middle Miocene. [ABSTRACT FROM AUTHOR]

Baiyangping Pb–Zn–Cu–Ag deposit is located in Lanping basin, northwestern Yunnan province. The deposit is composed of a few ore veins and can be divided into several ore blocks. The ore bodies are primarily hosted in Mesozoic carbonate, sandstone and siltstone along the north–south-striking, NWW-striking and NE–SW-striking fault zones. There are breccia, massive, vein like and disseminated ores. The main ore minerals are sphalerite, galena, gratonite, jordanite, tetrahedrite series minerals, chalcocite, chalcopyrite, realgar, orpiment, bournonite, cobalt-bearing arsenopyrite, argentite, kongsbergite, cobaltine, siegenite. The sizes of fluid inclusions in Baiyangping deposit are generally less than 10 μm and have the shape of round, oval, irregular, etc. The ore-forming fluid system is Ca 2+ –Na + –K + –Mg 2+ –Cl − –F − –NO 3 − brine system. The freezing temperature of fluid inclusions in mineral deposits ranges from −26.4 to −0.2 °C, average −14.6 °C; the homogenization temperature is concentrated in 120–180 °C, and the salinity is between 0.35 and 24.73 wt% (NaCl eq ), average 16.9 wt% (NaCl eq ). δ 13 C PDB and δ 18 O SMOW values of hydrothermal calcite range from −4.16‰ to 3‰ and −2.5‰ to 20.4‰, respectively. δ 34 S values of sulfide minerals range from −10.2‰ to 11.2‰, average 5.6‰. The sulfide samples yield 206 Pb/ 204 Pb values of 18.609–18.818, 207 Pb/ 204 Pb of 15.548–15.842 and 208 Pb/ 204 Pb = 38.514–39.556. C–O–S–Pb isotope compositions of the Baiyangping deposit indicate a homogeneous carbon source, and the carbon in hydrothermal calcite is derived from the dissolution of carbonate rock strata, the ore-forming fluid belongs to basin brine fluid system, which is mixed with the precipitate water, sulfur in sulfides and sulfosalts is derived from thermal chemical sulfate reduction, and the thermal decomposition of sulfur-bearing organic matter. The metal mineralization material is from sedimentary strata and basement. The late Pb–Zn polymetallic mineralization event superposed within early Cu–Co polymetallic mineralization event resulted in the differences of ore-forming elements for Baiyangping deposit. [ABSTRACT FROM AUTHOR]

Abstract: Different hypotheses have been proposed for the origin and pre-Cenozoic evolution of the Tibetan Plateau as a result of several collision events between a series of Gondwana-derived terranes (e.g., Qiangtang, Lhasa and India) and Asian continent since the early Paleozoic. This paper reviews and reevaluates these hypotheses in light of new data from Tibet including (1) the distribution of major tectonic boundaries and suture zones, (2) basement rocks and their sedimentary covers, (3) magmatic suites, and (4) detrital zircon constraints from Paleozoic metasedimentary rocks. The Western Qiangtang, Amdo, and Tethyan Himalaya terranes have the Indian Gondwana origin, whereas the Lhasa Terrane shows an Australian Gondwana affinity. The Cambrian magmatic record in the Lhasa Terrane resulted from the subduction of the proto-Tethyan Ocean lithosphere beneath the Australian Gondwana. The newly identified late Devonian granitoids in the southern margin of the Lhasa Terrane may represent an extensional magmatic event associated with its rifting, which ultimately resulted in the opening of the Songdo Tethyan Ocean. The Lhasa−northern Australia collision at ~263Ma was likely responsible for the initiation of a southward-dipping subduction of the Bangong-Nujiang Tethyan Oceanic lithosphere. The Yarlung-Zangbo Tethyan Ocean opened as a back-arc basin in the late Triassic, leading to the separation of the Lhasa Terrane from northern Australia. The subsequent northward subduction of the Yarlung-Zangbo Tethyan Ocean lithosphere beneath the Lhasa Terrane may have been triggered by the Qiangtang–Lhasa collision in the earliest Cretaceous. The mafic dike swarms (ca. 284Ma) in the Western Qiangtang originated from the Panjal plume activity that resulted in continental rifting and its separation from the northern Indian continent. The subsequent collision of the Western Qiangtang with the Eastern Qiangtang in the middle Triassic was followed by slab breakoff that led to the exhumation of the Qiangtang metamorphic rocks. This collision may have caused the northward subduction initiation of the Bangong-Nujiang Ocean lithosphere beneath the Western Qiangtang. Collision-related coeval igneous rocks occurring on both sides of the suture zone and the within-plate basalt affinity of associated mafic lithologies suggest slab breakoff-induced magmatism in a continent−continent collision zone. This zone may be the site of net continental crust growth, as exemplified by the Tibetan Plateau. [Copyright &y& Elsevier]

Abstract: The relationship between potassic felsic intrusions, cospatial and cotemporal with potassic mafic magmatism, and strike–slip displacement along the Ailao Shan-Red River shear zone in western Yunnan, SW China has been highly controversial. We report 22 new SHRIMP zircon U–Pb ages from 19 potassic felsic intrusions located as far as 150km east and 50km west of the shear zone to constrain temporal relationships. The results show that the felsic intrusions in western Yunnan were emplaced between 36.9±0.3Ma and 32.5±0.3Ma. This age range is significantly shorter than previous dating of 38Ma to 23Ma using K–Ar and Ar–Ar methods from 15 intrusions, indicating that the latter are reset or cooling ages. Potassic felsic intrusions are coeval with potassic mafic volcanic rocks (36.6Ma to 33.4Ma) in the same area, supporting a possible genetic link between the two end members. The dated intrusions occur over a 200km wide zone across the Ailao Shan-Red River shear zone; therefore they are unlikely genetically related to shearing. Rather, potassic mafic magmatism in western Yunnan may be related to delamination and melting of previously subduction-modified mantle lithosphere along the Mesozoic Jinsha suture reactivated in the Eocene–Early Oligocene, following the India-Asia continental collision; potassic felsic magmas were crustal melts hybridized with mafic liquids. Delamination in turn facilitated and localized initiation of the Ailao Shan-Red River shear zone at ca. 32Ma during continental extrusion. [Copyright &y& Elsevier]

To investigate the behavior of Li isotopes during magmatic differentiation and the petrogenesis of Cu-bearing ore deposits, a suite of post-collisional adakitic rocks from Qulong region, southern Tibet, was studied. Their lithologies range from diorite through granodiorite to granite porphyry with the latter containing giant Cu deposits. Detailed evidence of field observation and geochemical signature suggest that these three sets of rocks were most likely formed by various degrees of partial melting and fractional crystallization from the same source. The dioritic enclave, granodiorite and granite porphyry have δ7Li values ranging from 0.2 to 8.2‰, 3.1 to 6.8‰, and 3.9 to 7.4‰, respectively. Most of these samples are overlapping in Li isotope composition, comparable to other granitoids worldwide, indicating insignificant Li isotope fractionation during partial melting and magma differentiation in adakite-like rocks. By contrast, their Li concentrations are mainly controlled by fractional crystallization as suggested from different modal mineralogy. This process does not lead to further enrichment of Cu although they have initial high concentrations (an average of ∼ 104 ppm). In comparison, granite porphyry has extremely high Cu contents (up to 2000 ppm) and their δ7Li values are positively correlated with Cu content, suggesting the involvement of magmatic fluids that most likely exsolved from deep magma chamber. Such fluids not only modified the Li isotopic compositions of granite porphyries, but also extracted metal elements from the highly evolved magma, eventually resulting in the Cu mineralization. Our work here provides new insight into the formation and evolution of the porphyry Cu-bearing deposit. [ABSTRACT FROM AUTHOR]

• Fluids in the three skarn stages are characterized by complex volatile system, respectively. • Isotopic data showed a primary magmatic source, mingled with meteoric water at the late stages. • Boiling, temperature falling and f O 2 rising are the key to metal deposition at the retrograde stage. • f O 2 and temperature decreasing play role in metal precipitation at the late hydrothermal stage. Scheelite mineralization accompanied by traces of chalcopyrite occurs in skarn systems in the giant Zhuxi deposit in the Taqian area, Northeastern Jiangxi province, South China. Three paragenetic stages of skarn with ore deposition have been recognized: the prograde skarn, retrograde skarn and hydrothermal quartz-sulfide stages. Microthermometer data showed that the prograde skarn were formed at relatively high temperatures (450–>500 °C) and pressures (0.97–1.38 kbars) and low oxidation to weak reduction conditions. The Raman microprobe data demonstrated that the fluid of the stage was H 2 O–NaCl/KCl/CaCl 2 ± CH 4 /C 2 H 4 system. The retrograde skarn alteration formed at 1.24 kbars and relatively medium temperatures (280–320 °C), and the ore-forming fluid was H 2 O–NaCl/KCl/CaCl 2 system. During the hydrothermal quartz-sulfide stage, the fluids were methane-bearing aqueous, low-salinity (0.9–8.0 wt% NaCl eqv) and low homogeneous temperature (160–240 °C). Correspondingly, the minimum fluid pressures were evaluated between 75 and 252 bars. The H- and O-isotopic values from the prograde and retrograde stages implied that the mineralizing fluids were derived principally from magmatic water. The mineralizing fluids in the quartz-sulfide hydrothermal stages were mingled with magmatic water with some meteoric water as well as minor contributions of wall rocks. The sulfur and lead isotopes indicated that ore-forming materials including sulfur, lead, copper, zinc and iron in the Zhuxi deposit were derived from local magmatic and sedimentary sources. Geological, fluid inclusion and isotopic data supported that the Zhuxi deposit is a typical skarn-type W(Cu) deposit related to ilmenite-series granitic rocks and formed in a compressional tectonic environment. [ABSTRACT FROM AUTHOR]

• Coqen zircon xenocrysts were originated from ancient recycled continental crustal. • Zircons record the temporal evolution of magmatism and crustal thickness in Coqen. • Lhasa terrane evolutionary process is restored by these zircon xenocrysts. The Cenozoic volcanic rocks of Coqen are located in the western central Lhasa subterrane, where knowledge of the regional lithospheric architecture and related magmatic processes is still lacking. To address this issue, we used in situ U–Pb dating, Lu–Hf isotopic and mineral inclusion analysis in zircon xenocrysts among trachyandesite. These zircons from volcanic samples yielded wide U–Pb ages from 18 Ma to 2424 Ma, showing three significant age peaks at ∼ 246 Ma, 193 Ma, and the most intense one at 128 Ma, which represent three major magmatic processes that developed in the area. The earliest zircon dates suggest the age of volcanic eruption in the Coqen area was not earlier than 18 Ma. Zircon xenocrysts trace elements data point to the continental crust origin of central Lhasa subterrane. We provide the evidence for evolutive magmatism of the Lhasa terrane by calculating ΔFMQ, and show that the oxygen fugacity goes from reduced to oxidized (Cambrian to Miocene). The very low ε Hf (t) indicate a long-term magmatic event sequence, with the Zenong Group having the most vigorous magmatic activity. The old U–Pb ages and T DM C confirmed that an ancient basement of the Precambrian exist in the middle Lhasa terrane. Our work also restores the tectonic and crustal thickness evolutionary process of Coqen area even entire Lhasa terrane. In the back of a series of thickening and thinning processes, the Tibetan crust drastically thickened at ∼ 54 Ma, and gradually created what is now believed to be the thickest crust in the world. [ABSTRACT FROM AUTHOR]

The Nancha gold deposit, located in the central part of southern Jilin Province in the northeastern portion of the North China Craton, contains orebodies hosted in a Proterozoic metamorphosed volcanic–sedimentary sequence. The distribution of the orebodies is controlled by NNE-trending brittle–ductile shear zones and faults. The gold orebodies consist of auriferous quartz veins and auriferous altered rocks. Mineralization can be divided into three stages: (1) quartz–pyrite, (2) quartz–gold–polymetallic sulfide, and (3) quartz–carbonate, with gold being introduced mainly in the second stage. Three types of fluid inclusions were identified in the vein mineral assemblages based on petrography and laser Raman spectroscopy: NaCl–H 2 O (W-type), CO 2 –H 2 O (C-type), and pure CO 2 (PC-type). Crystals in the early quartz–pyrite stage veins mainly contain C-type primary fluid inclusions and rare PC-type inclusions. The fluid inclusions in these veins completely homogenize at temperatures of 273–432 °C and show low salinities of 0.63–7.78 wt.% NaCl equiv. In the middle quartz–gold–polymetallic sulfide stage, all three types of fluid inclusions were observed. These fluid inclusions homogenize at temperatures of 132 to 255 °C and show salinities of 0.83–11.72 wt.% NaCl equiv. In contrast, crystals in the late quartz–carbonate stage contain only W-type fluid inclusions that show homogenization temperatures of 132–255 °C and salinities of 0.35–7.86 wt.% NaCl equiv. These data indicate that the metallogenic system evolved from a CO 2 -rich metamorphogenic fluid to a CO 2 -poor fluid due to inputs of meteoric waters. Fluid boiling and mixing caused the rapid precipitation of sulfides and gold. Trapping pressures estimated from boiling C-type fluid inclusions were 152–367 MPa in the ore-forming stage. This suggests an alternating lithostatic–hydrostatic fluid system controlled by a fault-valve activity at a depth of 13.8–15.2 km. One hydrothermal sericite sample from an auriferous quartz vein yielded an 40 Ar/ 39 Ar isotopic plateau age of 170.1 ± 1.9 Ma, indicating that mineralization occurred in the Middle Jurassic and was unrelated to the volcanics and intrusions in the mineralized area. The characteristics of H–O–S–Pb isotopes and fluid inclusions suggest that the ore-forming fluids were of metamorphic origin, with the S originating from Proterozoic crustal components and the Pb originating from a mixture of ore-forming metamorphogenic fluids and host rocks. The results, combined with existing data on the regional geology, ore geology, fluid inclusions, H–O–S–Pb isotope geochemistry, age of mineralization, and tectonic setting, indicate that the Nancha gold deposit was an orogenic-type system that formed in a Middle Jurassic accretionary orogenic regime, following subduction of the Paleo-Pacific Plate beneath the Eurasian continent. [ABSTRACT FROM AUTHOR]

(a) Main crustal processes within magmatic plumbing system underneath the ultrapotassic Zhuopan pluton. (b) Petrogenetic model for the 37–30 Ma mafic potassic–ultrapotassic volcanic and plutonic rocks in western Yunnan, highlighting their distinct magmatic ascent paths and processes in the crust. [Display omitted] • Clinopyroxene zoning and textures record a complex magma history. • Clinopyroxenes crystallized at two crustal levels with distinct depths. • Crustal contamination and magma recharge took place in the magma system. • The Zhuopan pluton originated from a metasomatized lithospheric mantle. • Potassic–ultrapotassic volcanic and plutonic rocks differ in element systematics. Ultrapotassic rocks that are rare and volumetrically minor have attracted much attention due to their genetic link with the terrestrial mantle evolution and specific tectonic settings. However, crustal processes that may be involved in the generation of these rocks are poorly known despite extensive studies on their mantle sources. The ultrapotassic Zhuopan pluton in western Yunnan, southeastern Tibetan Plateau, consists chiefly of clinopyroxene-rich mafic–intermediate rocks and well preserves clinopyroxene textures and zoning, implying its potential record of valuable information on crustal processes. This pluton was emplaced at ∼ 36 Ma, suggesting its formation in the post-collisional setting associated with the India–Asia collision. Clinopyroxenes have three distinct types and form complex zoning patterns, with colorless clinopyroxene at the core, pale green at the mantle, and dark green at the rim. The clinopyroxene–liquid thermobarometer indicated that the clinopyroxenes crystallized in two magma reservoirs at depths of ∼ 18 and ∼ 10 km. The in situ clinopyroxene Sr isotopes revealed that wall-rock contamination had taken place and then was punctuated by recharge with a relatively evolved magma, leading to the resorption of pre-existing clinopyroxenes. The Zhuopan plutonic rocks were formed through evolution within multi-stage crustal reservoirs from the primary mafic magma derived from a subduction-metasomatized lithospheric mantle. Together with the coeval (37–30 Ma) potassic–ultrapotassic volcanic counterparts, we determined that the two differ in elemental systematics. This may have resulted from distinct magmatic ascent paths and processes in the crust. We also concluded that the generation of these coeval potassic–ultrapotassic rocks was triggered by massive lithospheric delamination. [ABSTRACT FROM AUTHOR]