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The Zhifang Mo deposit is located in the northeastern Qinling Orogen along the southern margin of the North China Craton. The deposit represents a quartz-vein system hosted in the Mesoproterozoic Xiong'er Group volcanic rocks. We identify three hydrothermal stages (early, middle and late), characterized by veinlets of quartz–pyrite, quartz–molybdenite–pyrite–chalcopyrite–galena–sphalerite, and quartz–carbonate assemblages, respectively. Five molybdenite samples from the Zhifang deposit yield Re–Os ages ranging from 241.2 ± 1.6 Ma to 247.4 ± 2.5 Ma, with an isochron age of 246.0 ± 5.2 Ma (2σ, MSWD = 7.4), and a weighted mean age of 243.8 ± 2.8 Ma (2σ, MSWD = 5.5). The Re–Os age shows that the Mo mineralization occurred during the Indosinian Orogeny, and suggests that the mineralization is unrelated to the Yanshanian magmatism or the Paleo-Mesoproterozoic volcanic–hydrothermal event. This study also reports a new Sr–Nd–Pb isotope dataset from ore sulfides in an attempt to constrain the source of the ore-forming fluids. Ten sulfide samples from middle stage of the Zhifang Mo deposit yield I Sr (t) ratios of 0.710286–0.711943, with an average of 0.711004; ε Nd (t) values between − 19.5 and − 14.8, with an average of − 16.7; and ( 206 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i and ( 208 Pb/ 204 Pb) i ratios of 17.126–17.535, 15.374–15.466 and 37.485–37.848, with averages of 17.380, 15.410 and 37.631, respectively. One pyrite from the early stage yield I Sr (t) of 0.722711–0.722855, with an average of 0.722783, which is higher than those of the middle stage sulfides and suggests equilibration with wallrocks. The ε Nd (t) values are in the range of − 17.3 to − 16.6 with a mean at − 17.0; and ( 206 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i and ( 208 Pb/ 204 Pb) i ratios are 17.386, 15.405 and 37.622, respectively. The ore sulfides show higher Pb-isotope ratios, higher ε Nd (t) and lower I Sr (t) values than the host rocks. The results suggest that the ore-forming fluids had lower I Sr (t), and higher ε Nd (t) values than the ore sulfides, and were possibly sourced from the Dengfeng Complex. The southward subduction of the North China Craton beneath the Huaxiong Block during the Triassic was possibly responsible for the formation of the Waifangshan orogenic Mo system. [ABSTRACT FROM AUTHOR]

The Dashui porphyry granitoids in the western Qinling Orogen are spatially associated with the Dashui gold deposit, but their ages and tectonic setting have not been well defined yet in previous studies. This paper reports the results and understandings obtained from our original study in geochronology and isotope and element geochemistry. SHRIMP zircon U-Pb dating yielded ages of 213.7 ± 2.7 Ma for granitic stock and 215.1 ± 2.5 and 210.2 ± 1.6 Ma for granitic dikes. The granitoids are characterized by high LREE but low HREE and HFSE. They have (87Sr/86Sr) i ratios of 0.706 to 0.709 and εNd(t) values of −5.3 to −7.6. The majority of zircons in the Dashui granitoids have εHf(t) values ranging from −6.2 to 6.7 and TDM2(Hf) ages from 743 to 1464 Ma. The isotope signatures, together with La/Y and Mg# values, show that the magmas are mainly sourced from partial melting of a subducted slab, and possibly assimilated immature sediments during upward migration. Thus, the Dashui granitoids most likely formed in a volcanic arc where supra-subduction zone melts assimilated lower crustal material no later than 215 Ma. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zircon U-Pb ages record two phases of granitic magmatism of 159 and 145 Ma. • Molybdenum and W are enriched in porphyry by prolonged fractionation and high f O2. • Scheelite petrography and compositions reflect mechanisms of Mo-W mineralization. • Porphyry-skarn Mo-W systems may be controlled by magmatic sources and wall rocks. Eastern Qinling Orogen is the largest Mo province in the world, hosting nine giant Mo deposits. Four giant Mo deposits contain economic W mineralization, while the mechanism of W mineralization remains unclear. The Yechangping deposit is a representative porphyry-skarn Mo-W deposit, with four paragenetic stages of prograde skarn, retrograde skarn, polymetallic sulfides and carbonate stage. Magmatism at Yechangping includes early barren monzogranite porphyry at 159.0 ± 1.5 Ma and late ore-related granite porphyry at ca. 145 Ma, and the latter porphyry shows a higher magmatic fractionation than the early barren monzogranite porphyry. Both barren and ore-related porphyries have similar high magma oxidation states, which may efficiently extract Mo during partial melting and hinder subsequent molybdenite crystallization until the porphyry-skarn Mo mineralization. Three types of scheelites are distinguished by their texture, paragenetic relationship and geochemistry, including Sch-1a in the retrograde skarn stage, and Sch-1b and Sch-2 in the polymetallic sulfides stage. Scheelite displays decreasing MoO 3 contents from 7.01–51.59 % in Sch-1a, through 3.15–17.51 % in Sch-1b, to 0–1.51 % in Sch-2. The decreasing MoO 3 contents in scheelite are attributed to the transformation of dominant Mo-bearing phases, i.e., from retrograde skarn stage powellite to polymetallic sulfides stage molybdenite. We suggest that the Mo-W mineralization is triggered by the decreasing oxygen fugacity, p H, and temperature, supported by thermodynamic modeling. In addition, the precipitation of fluorite and destabilization of fluorine complexes may have also promoted the Mo-W mineralization. Zircon Hf isotopes yielded ε Hf (t) values of −14.9 to −7.5 and T DM2 ages of 1671–2147 Ma, indicating that Yechangping porphyries were primarily sourced from the ancient basement of the Huaxiong Block, with additional contribution from the North Qinling Accretionary Belt. Skarn W mineralization in the southern part of Huaxiong Block may be controlled by both magmatic fertility and carbonate wall-rocks. [ABSTRACT FROM AUTHOR]

The Waifangshan Mo-quartz vein cluster occurs at the northernmost margin of the Qinling Orogen. The orebodies occur as quartz veins and are controlled by low-angle faults. We identify three hydrothermal stages, characterized by veinlets of quartz–pyrite, quartz–molybdenite–pyrite–chalcopyrite–galena–sphalerite, and quartz–carbonate assemblages, respectively. The early-stage quartz veins were structurally-deformed, brecciated, and filled by non-deformed middle- or late-stage veinlets, suggesting that the mineralization is associated with a tectonic transition from compression to extension. Five molybdenite separates from the Zhifang Mo deposit yield individual Re–Os ages from 241.2 ± 1.6 to 247.4 ± 2.5 Ma, with a weighted mean age of 243.8 ± 2.8 Ma. Individual Re–Os isotope ages of four molybdenite samples from the Badaogou Mo deposit range from 238.9 ± 2.1 to 255.8 ± 2.2 Ma, with a weighted mean age of 246 ± 10 Ma. Four analyses of molybdenite separates from the Xiangchungou Mo deposit yield individual Re–Os isotope ages of 243.8 ± 8.8 to 247.7 ± 4.4 Ma, with a weighted mean age of 246.0 ± 1.1 Ma. All of these data yield a weighted mean age of 241.9 ± 1.9 Ma, coeval with the accretionary orogeny. We thus conclude that the Waifangshan Mo-quartz veins formed during a transition from continental arc to back-arc setting. The Waifangshan Mo-quartz veins share similar geological, geochemical and geochronological features with the orogenic-type systems. We propose that the Waifangshan Mo-quartz veins are an orogenic-type Mo mineralization, and possibly represent the deepest member in the crustal continuum model of the orogenic-type mineral systems. The molybdenite samples from the Mo-quartz veins in the Waifangshan area have low Re contents (1.457 to 39.16 ppm), suggesting a continental crust-dominated source. [ABSTRACT FROM AUTHOR]

The Tumen Mo–F deposit is located on the southern margin of the North China Craton in central China. The deposit represents a fluorite-vein system hosted by carbonate rocks in the Neoproterozoic Luanchuan Group. Previous studies identify four hydrothermal stages at the deposit characterized by: Stage 1 veins of white fluorite, Stage 2 purple fluorite–molybdenite–pyrite (–galena), Stage 3 calcite–galena–pyrite–sphalerite (–chalcopyrite), and Stage 4 carbonate assemblages. The δ 34 S values for sulfides from the Tumen deposit range between −7.1 and 5.0‰, with a bimodal distribution. The Stage 2 sulfides have δ 34 S values of −2.7 to 5.0‰ that are similar to that of granitic rocks, but different from andesite in the Xiong’er Group, amphibolitic gneiss in the Taihua Supergroup and the carbonaceous shale and chert in the Luanchuan Group. The near-zero δ 34 S values indicate a possible magmatic source for the Stage 2 fluids. However, the δ 34 S values for the Stage 3 sulfides have negative mean and a restricted range from −7.1 to −4.6‰, which is different from that of the Xiong’er Group and Taihua Supergroup. The 34 S-depleted fluid for the Stage 3 sulfides was inherited from the host rocks in the Luanchuan Group with low δ 34 S values of −12.4 to 7.2‰. New Sr–Nd–Pb isotope data obtained from fluorite at Tumen indicate that the fluorite has higher Pb-isotope ratios, higher ɛ Nd(t) and lower I Sr (t) values than the host rocks. The results suggests that the ore-forming fluids had ɛ Nd(t) > −4.8, I Sr (t) < 0.7068, ( 206 Pb/ 204 Pb) i > 17.998, ( 207 Pb/ 204 Pb) i < 15.576 and ( 208 Pb/ 204 Pb) i < 38.201, which overlap the values of ( ɛ Nd(t) = −3.8 to −1.3, I Sr (t) = 0.7006–0.7061 for Neoproterozoic syenite in Qinling Orogen. This suggests that the deposit is related to a magmatic hydrothermal vein system associated with Neoproterozoic syenitic magmatism. [ABSTRACT FROM AUTHOR]