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Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie–Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon238U–206Pb age of 123.2 ± 1.1 Ma and a molybdenite Re–Os isochron age of 122.5 ± 2.7 Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial87Sr/86Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [(206Pb/204Pb)i, 16.423–16.699; (207Pb/204Pb)i, 15.285–15.345; (208Pb/204Pb)i, 37.335–37.633], and is characterized by low ϵNd(t) and ϵHf(t) values (−14.92 to −14.22 and −21.67 to −19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionatedI-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35 km). The ores also have low radiogenic Pb isotopes (206Pb/204Pb, 16.592–17.674;207Pb/204Pb, 15.300–15.476;208Pb/204Pb, 37.419–37.911) and low Re content in molybdenite (5.693–10.970 ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit. [ABSTRACT FROM AUTHOR]

The Early Cretaceous geology of the western Dabie Mountains is characterized by widespread granitoid pluton emplacement and associated Mo mineralization. We report LA–ICP–MS zircon U–Pb and molybdenite Re–Os dating, whole-rock chemical and Sr–Nd–Pb isotopic compositions, as well as in situ zircon Hf isotopic geochemistry, for the Dayinjian granite in the region to better constrain its petrogenesis. U–Pb zircon dating yielded a weighted average age of 124.9 ± 1.3 Ma (mean square weighted deviation (MSWD) = 0.51, 2σ). Re–Os isotopic dating of molybdenite from the Dayinjian ore deposit yielded an isochron age of 125.07 ± 0.87 Ma (MSWD = 0.015), and a weighted average age of 124.54 ± 0.67 Ma (MSWD = 0.34). The petrogenesis and metallogenesis of the Dayinjian complex are related to the onset of widespread post-orogenic magmatism and local mineralization in the western Dabie orogen. Whole-rock geochemistry indicates that the Dayinjian granite is a highly fractionated calc-alkaline granite possessing relatively high (87Sr/86Sr) i ratios (0.706379–0.707173), low ϵNd(T) values (–15.62 to –15.17), high Nd model ages (  = 2.15–2.18 Ga), and low radiogenic Pb isotopes ((206Pb/204Pb) i  = 16.793–16.979, (207Pb/204Pb) i  = 15.379–15.487, and (208Pb/204Pb) i  = 37.559–37.976). Its magmatic zircons also exhibit very low ϵHf(T) values (–24.80 to –17.80) and old Hf model ages (  = 2.31–2.75 Ga). These isotopic compositions suggest that the Dayinjian granite is probably of anatectic origin and was derived from the lower crust at a depth <35 km, similar to the western Dabie gneiss. Ore-bearing fluids were produced during late-stage magmatic hydrothermal activity and were thereafter influenced by the circulation of meteoric water that concentrated molybdenite in open-space areas. [ABSTRACT FROM PUBLISHER]

The Wangjiazhuang porphyry–breccia Cu(–Mo) deposit is located in the Zouping volcanic basin, western Shandong Province. Seven molybdenite samples yield a Re–Os weighted mean age of 127.8 ± 0.7 Ma (2σ), which is identical within error to the zircon weighted mean 206 Pb/ 238 U age of 128.3 ± 1.3 Ma (2σ) determined for quartz monzonite samples. The host rock is characterized by high concentrations of K 2 O (4.26–4.53 wt.%), Na 2 O (4.97–5.76 wt.%), LILEs and LREEs, and high Mg# (> 40), and low concentrations of HFSEs and HREEs, with K 2 O/Na 2 O ratios of 0.76–0.88. The quartz monzonite also has high Sr/Y (69.9–112.5) and (La/Yb) N (22.0–30.0) ratios, similar to adakitic rocks worldwide. Relatively low initial 87 Sr/ 86 Sr ratios (0.70549–0.70556), high ε Nd ( t ) values (2.58–3.06), high radiogenic Pb [( 206 Pb/ 204 Pb)i = 18.3424–18.4606, ( 207 Pb/ 204 Pb) i = 15.5692–15.5985, ( 208 Pb/ 204 Pb) i = 38.1714–38.2734] and high zircon ε Hf ( t ) values (− 2.1 to + 4.3) indicate that the magma was likely derived from the partial melting of subducted oceanic crust which then reacted with the peridotitic mantle wedge. Both the breccia and porphyry ores have a narrow range of δ 34 S (− 4.8 to + 2.1‰) and Pb isotopic compositions ( 206 Pb/ 204 Pb = 18.295–18.402, 207 Pb/ 204 Pb = 15.551–15.573, and 208 Pb/ 204 Pb = 38.215–38.331), suggesting that the ore metals were extracted primarily from the quartz monzonite or similar source. Subduction of the Paleo-Pacific slab during the Early Cretaceous resulted in the formation of the Wangjiazhuang quartz monzonite and associated Cu(–Mo) deposit in western Shandong Province. [ABSTRACT FROM AUTHOR]

Abstract: The Jinshajiang–Red River porphyry Cu–Mo metallogenic belt is an important Cenozoic porphyry Cu–Mo mineralization concentrating zone in the eastern Indo‐Asian collision zone. New zircon U–Pb and molybdenite Re–Os ages and compilation of previously published ages indicate that porphyry Cu–Mo deposits in the belt did not form at the same time, i.e., the porphyry emplacement and relevant Cu–Mo mineralization ages of the Ailaoshan–Red River ore belt in south range from 36.3Ma to 34.6Ma, and from 36.0Ma to 33.9Ma, respectively, which are obviously younger than the porphyry emplacement ages of 43.8–36.9Ma and the relevant Cu–Mo mineralization ages of 41.6–35.8Ma of the Yulong ore belt in north. Tectonic studies indicated that the Jinshajiang fault system in north and Ailaoshan–Red River fault system in south of the Jinsjiang–Red river belt had different strike-slip patterns and ages. The right-lateral strike-slip motion of the Jinshajiang fault system initiated at ca. 43Ma with corresponding formation of the Yulong porphyry Cu–Mo system, whereas the left-lateral strike-slip motion of the Ailaoshan–Red River fault system initiated at ca. 36Ma with corresponding formation of the Ailaoshan–Red River porphyry Cu–Mo system. Therefore, the different ages of porphyry Cu–Mo systems, between in north and south of the Jinshajiang–Red River belt, indicate that the porphyry Cu–Mo mineralization is closely related to the divergent strike-slip movements between the Jinshajiang and Ailaoshan–Red River strike-slip faulting resulted from the Indo‐Asian collision. The tanslithospheric Jinshajiang–Red River faulting caused partial melting of the enriched mantle sources of alkali-rich porphyries by depressurization or/and asthenospheric heating, and facilitated the migration of alkali-rich magmas and the corresponding formation of alkali-rich porphyries and relevant Cu–Mo deposits in the belt. [Copyright &y& Elsevier]

Abstract: The Tianyu mafic–ultramafic intrusion is one of many important sulfide-bearing mafic–ultramafic intrusions in the eastern Tianshan terrane located in the southern margin of the Central Asian Orogenic Belt in north Xinjiang, NW China. The origin of sulfide mineralization in these intrusions, their relationship with Permian basalts and A-type granites, and the geodynamic setting of the bimodal magmatism in the region are controversial. In this paper we use zircon U–Pb age, Hf–Sr–Nd–Os isotope and lithophile–chalcophile trace element constraints from the Tianyu mafic–ultramafic intrusion to address these important issues. The U–Pb age of zircon from the Tianyu intrusion determined by SIMS is 280±2Ma. This confirms that the Tianyu intrusion is coeval with most sulfide-bearing mafic–ultramafic intrusions and some basalts and A-type granites in the Tianshan region. Similar to coeval basalts in the nearby Tuha basin, the Tianyu intrusive rocks are characterized by negative Nb anomaly and elevated εNd values varying between −1 and +4.6. The negative Nb anomaly in the Tianyu intrusion is not as pronounced as in the coeval A-type granites but the εNd values for these bimodal rocks are similar. The εHf values of zircon from the Tianyu intrusion are positive, varying between 3 and 8. These values suggest that the parental magma of the Tianyu intrusion was dominated by melt derived from a depleted source mantle. The γOs values of pyrrhotite from the Tianyu intrusion are high, ranging from 725 to 995, which can be modeled by selective assimilation of sulfide from the lower and upper crusts. Negative Pt anomaly is present in relatively sulfide-rich samples such as semi-massive and massive sulfide ores but not in sulfide-poor samples, which is more consistent with the effect of post-magmatic hydrothermal alteration than the original signature of the parental magma. The results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the Tianyu intrusion was depleted in all PGE, which is consistent with previous sulfide segregation at depth. Our data and modeling results support the model of decompression melting of upwelling asthenosphere due to slab break-off during a transition from oceanic subduction to arc–arc or arc–continent collision in the Permian. Decompression melting of the upwelling asthenosphere in the region produced mafic magma. Partial melting in the lower parts of a juvenile arc crust due to mafic magma underplating produced granitic melts. Mixing of the mafic magma with a small amount of granitic melts at depth followed by contamination with the upper crust at a higher level formed the parental magma of the Tianyu intrusion. PGE depletion in the parental magma of the Tianyu intrusion can be attributed to sulfide segregation associated to the first stage of crustal contamination at depth. We suggest that the formation of sulfide ores in the intrusion was related to the second stage of crustal contamination in the upper crust. [Copyright &y& Elsevier]

Abstract: The timing and genesis of the major Ni–Cu–Co sulfide deposit in the Xiangshan intrusion have been studied based on newly obtained in-situ U–Pb, Hf and Re–Os isotopic analyses. The SIMS U–Pb zircon ages of the gabbro hosting the Ni–Cu–Co sulfide deposit indicate that the Xiangshan intrusion was emplaced at 279.6±1.1Ma (95% confidence level, MSWD=1.30, n =15). On the basis of combined geological and geochronological evidence, we suggest that the Xiangshan and other adjacent Ni–Cu deposits were formed in the same period. Sulphides have low common Os concentrations and high Re/Os ratios, similar to sulphide ores from the Duluth, Sally Malay and Voisey Bay complexes. The Re–Os isotopic data from the disseminated and massive ores from the Xiangshan intrusion do not form a single isochron, as they have different initial Os ratios. The Hf and Os isotopic data suggest that the Xiangshan intrusion and associated Ni–Cu–Co mineralization were derived from crustally contaminated mantle melts. The geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative Nb, Sr, and Ti anomalies similar to N-MORB and E-MORB. We suggest that the mafic–ultramafic rocks and associated Ni–Cu mineralization of the Eastern Tianshan orogen formed in an Alaska-type subduction zone-arc setting. Some diagnostic features of ridge–trench interaction are present in the Chinese East Tianshan orogen (e.g. granites, adakites, high-Mg andesites, near-trench magmatism, Alaskan-type mafic–ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, and orogenic gold deposits). The above distinctive rock groups are probably related to the same thermal event, ridge subduction, as in the Cenozoic orogen of Alaska. We suggest that ridge subduction is the most plausible mechanism to provide the necessary heat. Ridge subduction provides an important promising model for understanding many aspects of the evolution of the Chinese Eastern Tianshan orogen, and by inference, throughout much of Central Asia. [Copyright &y& Elsevier]