Abstract The Xiaobaishitou gabbro‐diorite pluton comprises a medium‐grained gabbro‐diorite suite and a fine‐grained diorite suite, which intrude the Kawabulag Group in the East Tianshan Orogen of the Central Asian Orogenic Belt (CAOB). A combination of mineral chemistry, zircon U‐Pb age, whole‐rock geochemistry, Sr‐Nd isotopes, and in situ zircon Hf isotopes for newly found gabbro‐diorite from the Xiaobaishitou district in the Central Tianshan Terrane (CTT) is presented to investigate the petrogenesis and tectonic or even crustal evolution of the East Tianshan Orogen. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb analyses indicate that the gabbro‐diorite was formed at 324.7 ± 2.4 Ma. The isolated clinopyroxene formed under higher P ‐ T ‐ ƒ O 2 melt conditions (10.7–14.6 kbar; 1199–1269°C; high ƒ O 2 ) than those for the hornblende, plagioclase, and zircon (557–687°C; moderate ƒ O 2 ) in the gabbro‐diorite, which reveals a multilevel, magmatic storage system. The gabbro‐diorite is characterized by fractioned REE patterns, enriched LILEs (e.g., Ba and Pb), negative anomalies of HFSEs (e.g., Nb and Ta), and low La/Yb and Sr/Y ratios, which are typically indicative of crustal contamination and accounted for by subduction‐related fluids. The rock also characterized by typical features of high compatible elements (MgO = 3.14–11.65 wt%, Cr = 1–157 ppm, Ni = 6–830 ppm), high Mg # (47 –74), positive ɛ Hf ( t ) values (+5.1 to +10.3) and ɛ Nd ( t ) values (+2.3 to +4.4). These features suggest that the Xiaobaishitou gabbro‐diorite was most likely derived from metasomatic mantle and contaminated minor crustal components. Taking into account the spatial and temporal distribution of the Carboniferous magmatic rocks in the CTT, we suggest the formation of the Xiaobaishitou gabbro‐diorite was attributed to southward subduction of the Kangguer Ocean.
The Keketale is the largest Pb–Zn deposit in the volcano‐sedimentary Maizi Basin of the South Altay Orogenic Belt (AOB), Northwest China. The stratabound orebodies are hosted in a suite of meta‐sedimentary rocks intercalated with volcanic rocks of the Lower Devonian Kangbutiebao Formation. The massive and banded ores representing the main mineralization stage are relatively well‐preserved in the ore district. This paper reports systematic geochronological results including the zircon laser ablation–multiple collector–inductively coupled plasma–mass spectrometry (LA‐MC‐ICP‐MS) U–Pb analyses on two meta‐felsic volcanic rocks from the Kangbutiebao Formation and Rb–Sr isotope dating on seven sphalerite samples from the main mineralization stage, together with some sulphur isotopic data to constrain the mineralization age and the genesis of the deposit. Rb–Sr isotope dating yield an isochron age of 398.2 ± 3.3 Ma generally synchronous with the zircon (LA‐MC‐ICP‐MS) U–Pb analyses of a meta‐rhyolite and a meta‐dacite from the strata (410.5 ± 1.3 Ma and 394.8 ± 1.9 Ma, respectively). The δ 34 S values of seven pyrite samples in the main massive and banded ores vary from −12.4‰ to −6.2‰, indicating that the main ore‐forming sulphur of the deposit was derived from bacterial reduction of seawater sulphate. By integrating the field, chronological, and isotopic evidences, we conclude that the Keketale Pb–Zn deposit is a VMS‐type deposit. Combining our results with the isotopic geochronology in the South AOB, we argue that the South AOB has undergone three mineralization episodes: the syndepositional mineralization (412–387 Ma), the subvolcanic hydrothermal‐related mineralization (382–379 Ma), and the epigenetic mineralization that is genetically linked to regional metamorphism and deformation (260–204 Ma). The Keketale Pb–Zn deposit is a product of the Devonian seafloor hydrothermal exhalation system in the South AOB.
East Junggar is an important part of the Central Asia Orogenic Belt and has developed a multi‐epoch and multi‐type metallogenic system. Yundukala is a recently discovered large intrusion‐related Au–Cu–Co deposit. The No. 1 main mineralization zone mainly occurs in the contact area between fine‐grained diorite and basalt. Massive and vein mineralization have developed there, but the ore‐bearing stratum, ore‐bearing intrusive rocks, and metallogenic ages are not clear. Zircon SHRIMP U–Pb dating of the porphyritic diorite and fine‐grained diorite yields ages of 416.1 ± 3.9 Ma and 411.1 ± 7.5 Ma, respectively. The dioritoid intruded into the ore‐bearing stratum, indicating that this formation is part of the Early Palaeozoic strata rather than the Middle Devonian Beishan Formation. The Re–Os isochron age of the chalcopyrite in the massive mineralization is 402.6 ± 5.2 Ma; thus, the massive mineralization is related to fine‐grained diorite and formed in the Early Devonian. Six sulphides and four sulphides from the vein mineralization yield Re–Os isochron ages of 352.8 ± 1.8 Ma and 354 ± 23 Ma, respectively, and the limited vein mineralization was formed during 353–354 Ma. The massive and vein mineralizations in the Yundukala deposit were formed in the Early Devonian and Early Carboniferous.
Xinxia Genga, Fuquan Yanga*, Chengdong Yanga , Jihua Qinb & Chaoquan Wenb a Key Laboratory of Metallogeny and Mineral Assessment, Ministry of Natural Resources, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, PR Chinab No. 4 Geological Team of the Xinjiang Bureau of Geology and Mineral Exploration and Development, Altay, Xinjiang, PR China
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