Geochronology and geochemistry of Middle Devonian mafic dykes in the East Kunlun orogenic belt, Northern Tibet Plateau: Implications for the transition from Prototethys to Paleotethys orogeny

The East Kunlun Orogen (EKO), as the west segment of the Central China Orogen, is the most important Triassic polymetallic metallogenic belt in China. In this paper, we summarize the geological characteristics (stratigraphy, structure, ore‐related plutons, wall rock alteration, and orebodies), ore‐forming fluids and materials, geochronology, and petro‐geochemistry of the representative porphyry–skarn Cu–polymetallic deposits, including the Saishitang, Hutouya, and Kaerqueka deposits in the EKO. The porphyry–skarn Cu deposits in the EKO are mainly distributed in tectonic units of the Qimantagh Belt and the Elashan Belt. Among them, the skarn Cu deposits provide the majority of Cu resources, which mainly occur in the contact zone between the Triassic granitoids and the volcanic–sedimentary rocks (e.g., the Ordovician–Silurian Tanjianshan Group and the Early to Middle Triassic Hongshuichuan Group), and the skarn and orebodies are mainly controlled by interlayer–gliding structures. Ore‐forming fluids of the porphyry Cu deposits are magmatic mixed with meteoric water, whereas the fluids of skarn Cu deposits are mainly of magmatic origin. The higher δ18O (>10‰) of garnet and pyroxene in prograde skarn and wide range of sulphur isotopic compositions (δ34S values from −8.9‰ to 11.0‰) suggest that ore‐forming materials of skarn Cu deposits were partially derived from the country rocks. Based on detailed field investigations, we identified four Cu mineralization types, including veinlet–disseminated Cu (Mo, Au) mineralization occurring within the intrusions, proximal skarn Cu (Fe, Pb, Zn, Au) mineralization, distal skarn Cu mineralization, and distal skarn Pb–Zn (Cu) mineralization. The porphyry–skarn Cu deposits are associated with magmatism that occurred mainly during 235–218 Ma. The ore‐related granitoids are mostly calc‐alkaline I‐type granites, derived from partial melting of the Precambrian basement rocks with various degrees of involvement of mantle components. Combined with the regional tectonic evolution, we conclude that the Cu mineralization in the EKO began with the closure of A'nyemaqen Ocean (~238 Ma) and subsequently culminated in a postcollisional setting (~225 Ma).

Section: Petrogenesis Of Ore‐related Granitoidsmentioning

confidence: 72%

“…I Sr versus ε Nd ( t ) diagram of the porphyry–skarn Cu deposits associated granitoids in the East Kunlun Orogen (EKO). Isotopic fields compiled by Xiong et al () are plotted for comparison. Symbols are as in Figure .…”

Section: Petrogenesis Of Ore‐related Granitoidsmentioning

confidence: 99%

Geological characteristics, metallogenesis, and tectonic setting of porphyry–skarn Cu deposits in East Kunlun Orogen

Wang

Chen

et al. 2018

“…The NKT is characterized by the Precambrian Jinshuikou Group metamorphic basement and widespread of the Early Palaeozoic and Mesozoic plutons with two age peaks of 420–400 and 260–220 Ma (Figure c; Z. Q. Liu, ). The Jinshuikou Group consists of marble, gneiss and amphibolite, and experienced amphibolite‐granulite‐facies metamorphism, which is covered by the Binggou Group with an unconformity contact (R. B. Li, Pei, et al, ; J. L. Li, Zhou, et al, ; Meng et al, ; R. Xia et al, ;Xiong, ; Xiong, Ma, Jiang, et al, ; Xiong, Ma, Zhang, et al, ). The Binggou Group comprises volcano‐sedimentary and low‐grade metamorphic rocks (Xiong, ).…”

Section: Geological Settingmentioning

confidence: 99%

Geochronology and geochemistry of the Late Devonian–Early Carboniferous volcanic rocks in Aksu River area, western end of the East Kunlun Orogen

Liu

et al. 2019

We present LA‐ICP‐MS zircon U–Pb dating, geochemical data for the Late Devonian–Early Carboniferous volcanic rocks in the Aksu River area, western end of the East Kunlun Orogen, with an aim to constrain the ages, petrogenesis, and tectonic setting of volcanic rocks and to comprehend the Late Devonian–Early Carboniferous tectonic evolution of the north branch of the Paleo‐Tethys Ocean. The Late Devonian–Early Carboniferous volcanic rocks are mostly composed of andesite and rhyolite. The new U–Pb ages show that the volcanic rocks formed in the Late Devonian–Early Carboniferous with ages of ca. 364–343 Ma. The volcanic rocks are classified as calc‐alkaline series. All of the volcanic rocks are characterized by enrichment in large‐ion lithophile elements (e.g., Rb, Ba, U, Sr, and K) and light rare earth elements and depletion in some high‐field‐strength elements (e.g., Nb, Ta, P, and Ti). The andesite samples have relatively high La/Nb (1.66–3.63) but low La/Ba (0.05–0.23) ratios, indicating the mantle source could be depleted mantle, and it had been metasomatized before partial melting. The rhyolite samples have low Nb/Ta and Zr/Hf ratios and Cr, Ni, and Co contents, which indicate that the material source was mainly crust derived and has experienced fractional crystallization process. Combined with our zircon U–Pb dating, geochemical data and geological field investigation, the tectonic setting of the Late Devonian–Early Carboniferous volcanic rocks is possibly related to the subduction process. Furthermore, the Paleo‐Tethys oceanic crust between the Bayan Har and East Kunlun‐Qaidam terrane northward subducted beneath the East Kunlun‐Qaidam terrane in the Late Devonian–Early Carboniferous, and the north branch of the Paleo‐Tethys Ocean between the Bayan Har and East Kunlun‐Qaidam terrane opening event should be earlier than this time (~364 Ma).

“…The EKO is 50–200 km long (Figure a) and can be divided into the North, Central, and South EKO, which are separated by the North East Kunlun, Central East Kunlun, and South East Kunlun faults, respectively (Xiong, Ma, Jiang, Liu, & Huang, ). The Nagengkangqieergou Ag‐polymetallic deposit is located in the Central EKO (Figure b).…”

Section: Regional Geologymentioning

confidence: 99%

Ore geology, fluid inclusions, and C–H–O–S–Pb isotopes of Nagengkangqieergou Ag‐polymetallic deposit, East Kunlun Orogen, NW China

Chen

et al. 2019

Several large Ag‐polymetallic deposits have been newly discovered in the eastern segment of the East Kunlun Orogen, with the largest one being the high‐grade Nagengkangqieergou deposit (3,017 tons Ag at 310.04 g/t). The Ag ore veins are hosted in the Palaeoproterozoic Jinshuikou Group and Upper Triassic Elashan Formation, principally along NW‐trending faults and volcanogenic ring fractures. Alteration and mineralization processes occurred in two periods (J and E), which are hosted in two different ore‐bearing sequences (Jinshuikou Group and Elashan Formation respectively). These two periods can be subdivided into Stages J‐I, J‐II, J‐III, and J‐IV and Stages E‐I, E‐II, and E‐III. Fluid inclusions in the ore‐bearing quartz and calcite comprise predominantly of vapour‐rich two‐phase (vapour + liquid) type and minor pure‐liquid type. Fluid inclusions in Stage J quartz and calcite homogenized mainly at 270–330°C, 250–310°C, 250–290°C, and 170–250°C, with salinities of 5–6 wt.%, 4–6 wt.%, 4–5 wt.%, and 3–5 wt.% NaCl equiv., respectively. Fluid inclusions in Stage E quartz homogenized mainly at 210–250°C, 170–230°C, and 150–170°C, with salinities of 6–7 wt.%, 4–5 wt.%, and 1–2 wt.% NaCl equiv., respectively. δ13C and δ18OSMOW values of the calcite samples are of −6.0‰ to −2.8‰ and 5.2‰ to 20.5‰, respectively. The results indicate a mantle‐derived magmatic source and low temperature alteration. and δDV–SMOW values of the quartz and calcite from the Jinshuikou Group vary from −1.9‰ to 9.0‰ and −116.5‰ to −69.3‰, respectively, whilst those of δ18OH2normalO quartz from the Elashan Formation vary from −11.6‰ to 7.8‰ and −99.7‰ to −86.7‰. The results indicate that the ore‐forming fluids are of medium‐low temperatures and low salinities and were originated from magmatic water to meteoric water. Sulfide δ34SV–CDT values of the Jinshuikou Group and the Elashan Formation are of −6.1‰ to 0.8‰ and −3.4‰ to 0.9‰, respectively, suggesting a mantle‐derived magmatic source. Sulfide 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the J‐period ores (18.190–18.622, 15.598–15.725, and 38.383–39.103, respectively) and E‐period ores (18.408–18.420, 15.746–15.758, and 38.879–38.895, respectively) are similar to those of granodiorite porphyry and Elashan Formation (sub)‐volcanic rocks, respectively, indicative of genetic connections between them. Integrating new evidence from fluid inclusions and C–H–O–S–Pb isotopes, we suggest that (a) mantle‐derived materials and their mixture with crust‐derived ones were critical to the ore formation, (b) the Nagengkangqieergou deposit was formed in a magmatic system and a (sub)‐volcanic system under the syn‐ and post‐collisional tectonics of the East Kunlun Orogen, respectively.