Isotope (S–Sr–Nd–Pb) constraints on the genesis of the ca. 850 Ma Tumen Mo–F deposit in the Qinling Orogen, China

• The China's ∼850-Ma Tumen Mo–F deposit is a magmatic hydrothermal vein system.
• S–Sr–Nd–Pb isotopes indicate the ore-fluids originated from syenitic magmatism.
• Post-collisional extension causes the formation of Mo–F veins and syenites.
• The Eastern Qinling Mo belt experienced intensive pre-Mesozoic Mo-enrichment.
• The 850-Ma Mo–F mineralization preluded the breakup of Rodinia supercontinent.

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 δ34S values for sulfides from the Tumen deposit range between −7.1 and 5.0‰, with a bimodal distribution. The Stage 2 sulfides have δ34S 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 δ34S values indicate a possible magmatic source for the Stage 2 fluids. However, the δ34S 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 34S-depleted fluid for the Stage 3 sulfides was inherited from the host rocks in the Luanchuan Group with low δ34S 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 ɛNd(t) and lower ISr(t) values than the host rocks. The results suggests that the ore-forming fluids had ɛNd(t) > −4.8, ISr(t) < 0.7068, (206Pb/204Pb)i > 17.998, (207Pb/204Pb)i < 15.576 and (208Pb/204Pb)i < 38.201, which overlap the values of (ɛNd(t) = −3.8 to −1.3, ISr(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.

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