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The Kaladawan Fe–Mo ore field in Altyn (Xinjiang Province, NW China) contains six Fe (–Mo) deposits, with total proven reserves of 60 Mt Fe and 10,000 t Mo. Tabular, lensoidal and stratiform orebodies occur in the Cambrian foliated marble, phyllite, carbonaceous slate, chlorite–sericite schist and quartz–sericite schist along the exocontact zone of the Kaladawan granite. Skarns are extensively developed and dominated by garnet, pyroxene, epidote, tremolite and actinolite, with minor chlorite, zoisite, quartz and calcite. Ore minerals are mainly magnetite and molybdenite. Five alteration and mineralization stages (I–V) were identified: the prograde (I) and retrograde (II) skarns are characterized by assemblages of garnet–pyroxene and epidote–tremolite–actinolite, respectively, intruded and replaced by mineral assemblages of magnetite–epidote–zoisite (III), quartz–sulfides (IV) and calcite–chlorite (V) in younging order. The Kaladawan garnet contains more andradite (61.2–94.4 mol%) than grossularite (37.5–5.0 mol%). Pyroxene is Mg-rich and Fe-poor, with an endmember range of 55.4–94.7 mol% diopside and 42.5–4.7 mol% hedenbergite. Amphibole comprises mainly tremolite and actinolite. The Kaladawan skarn mineral contents resemble typical skarn Fe and Mo deposits. In-situ LA-ICP-MS magnetite trace element analysis had identified unusually high Mg, Mo and Cr concentrations. The high Mo and the absence of molybdenite inclusions in magnetite suggest that the hydrothermal fluids may have been Mo-rich. The magnetite also contains similar (Ti + V) and (Al + Mn) values with typical skarn Fe deposits. Therefore, the Kaladawan Fe–Mo mineralization is best attributed to be skarn-type, and related to the Kaladawan granite intrusion. [ABSTRACT FROM AUTHOR]

The Great Hingan Range is located in the eastern sector of the Central Asia Orogenic Belt, and is the second important Mo province in China, next to the Qinling–Dabie orogenic belt. Previous studies concluded that all the Mo deposits (Mo-only or Mo-dominated polymetallic) in the area were formed in the Mesozoic, and related either to the syn- to post-collisional setting following the closure of the Paleo-Asia Ocean, or to the westward subduction of the Pacific plate. However, the fluids forming the giant Diyanqin'amu porphyry Mo deposit in the area disagree with the features of collision-type Mo deposits, but accord with those of the subduction- or continental arc-type. The Mo mineralization is hosted in the Late Jurassic volcanic rocks and genetically related to the buried porphyritic granite and aplitic granite. Two porphyritic granite samples yield LA-ICP-MS zircon weighted mean 206 Pb/ 238 U ages of 158.7 ± 0.8 Ma (MSWD = 0.64, 2σ) and 158.0 ± 0.9 Ma (MSWD = 0.38, 2σ), respectively. The aplitic granite yields a zircon U–Pb weighted mean 206 Pb/ 238 U age of 156.9 ± 1.1 Ma (MSWD = 0.48, 2σ), slightly younger than the porphyritic granite. Seven molybdenite samples from the ores yield Re–Os isotope ages of 156.1 ± 2.2 to 158.1 ± 4.3 Ma. These ages constrain that the Diyanqin'amu Mo system was formed in the period of 159–156 Ma. The granites at the deposit have high contents of SiO 2 , K 2 O and Al 2 O 3 , and low contents of TiO 2 , MgO and CaO, showing a peraluminous high-K calc-alkaline affinity. These granites and the host volcanic rocks are characterized by enrichment of K, Rb, U, Pb, Th and LREE, and depletion of Nb, Ta, Ti and HREE, with negative Eu anomaly, which are similar to magmatic rocks in the Andean arc. Zircon grains from the granites show positive ε Hf ( t ) values of 4.2–9.0, with T DM2 (Hf) ages of 0.63–0.94 Ga. These geochemical data imply that the granites at Diyanqin'amu are highly fractionated I-type, formed in a continental arc generated by the southeastward subduction of the Mongol–Okhotsk oceanic plate. [ABSTRACT FROM AUTHOR]

The Central Tianshan Terrane (CTT) in the Eastern Tianshan (Xinjiang, NW China) is an important Pb–Zn metallogenic belt and played a pivotal role in crustal evolution and collisional tectonics of the southern Central Asian Orogenic Belt. The Shaquanzi gabbro and Hongyuan granodiorite are located in the northern margin of the CTT and associated with Pb–Zn mineralization. Zircon U–Pb dating yielded weighted mean ages of 307.2 ± 1.5 Ma and 301.2 ± 1.5 Ma for the Shaquanzi gabbro and the Hongyuan granodiorite, respectively. These rocks are medium-K calc-alkaline series and enriched in large ion lithophile elements (LILEs; e.g., K, Rb, Ba) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), displaying typical arc affinities. The Shaquanzi gabbro shows low Nb/Ta (11.0–14.2), a high Mg # range (56–59), positive zircon ε Hf (t) (+ 3.30 − + 7.26) and whole rock ε Nd (t) (+ 0.70 − + 1.38) values, and low I Sr ratios (0.704858–0.705137), which indicate that the protolith was probably derived from the sub-continental lithospheric mantle that had been metasomatized by subduction-related fluids. The Hongyuan granodiorite contains hornblende but lack of Al-rich minerals and has low I Sr ratios (0.704769–0.706211 < 0.707), suggesting an I-type origin. Moreover, the Hongyuan granodiorite has positive ε Hf (t) (+ 1.12 − + 5.57) and ε Nd (t) (+ 0.38 − + 1.86) values, with high Mg # (52), variable Nb/Ta ratios (12.6–12.9), low contents of Ni, Cr and Co and Pb isotopes ( 206 Pb/ 204 Pb = 17.461–18.299, 207 Pb/ 204 Pb = 15.541–15.581, 208 Pb/ 204 Pb = 37.456–38.129), suggesting the Hongyuan granodiorite was generated by partial melting of juvenile crust sources mixed with some mantle-derived materials. Combined published works with our new geochronological, geological, geochemical and isotopic data, we propose that the CTT may have evolved from a continental arc to a syn-collisional setting during the period of ca. 307–301 Ma. The continuing southward subduction of the Junggar oceanic slab beneath the CTT in the Late Carboniferous resulted in extensive arc-related volcanic rocks emplacement that had indirect links to the Pb–Zn mineralization (e.g., reworked/upgraded). [ABSTRACT FROM AUTHOR]

Zircon U–Pb ages of high Mg dioritic dikes in the Mesoproterozoic Kawabulake Group in the Eastern Tianshan area, NW China indicate that they were emplaced in the Early Carboniferous at 353–348 Ma. The dikes consist of medium-grained plagioclase and hornblende with minor clinopyroxene and trace quartz. They are characterized by intermediate SiO 2 (60–62 wt.%), low TiO 2 (0.63–0.71 wt.%), relatively high Al 2 O 3 (15.1–15.8 wt.%) and MgO contents (3.45–4.15 wt.%) with Mg# generally higher than 56 (56–59). The geochemistry of the high Mg diorites suggest they were formed by similar magmatic processes to sanukitoid high Mg Andesites such as those of the Setouchi volcanic belt, Japan. Zircons from the high Mg dioritic dikes have ε Hf( t ) values of −6.8 to +14.5. The dominantly positive values suggest a juvenile source, whereas the small number of negative values suggests mature components were also incorporated into the source. Similarly, the positive ε Nd( t ) values (0 to +2.2) are interpreted to reflect a juvenile source whereas the negative values of (−5.2 to 0) suggest participation of old crustal rocks in the petrogenesis of the diorites. The variable ε Hf( t ) and ε Nd( t ) values suggest that the mature material was assimilated during magma ascent rather than in the mantle wedge which would result in more uniform values. Mass balance calculations suggest that the dioritic dikes were derived from sources composed of approximately 97% juvenile mantle-derived material and 3% sediment. Petrographic, elemental, and isotopic evidence suggest that the dioritic dikes were generated by partial melting of depleted mantle that migrated into the shallow crust where it assimilated older sedimentary rocks of the Mesoproterozoic Kawabulake Group. [ABSTRACT FROM AUTHOR]