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Identifying magma fertility is an important task in ore genesis research. In this paper, we use apatite chemistry and Sr-Nd isotopes for such a study. The apatite crystals are from four Cretaceous coeval granodiorite intrusions with different styles of hydrothermal mineralization in the Tongling ore district, South China. The selected intrusions are Hucun, Dongguashan, and Xinwuli, which host both porphyry and skarn Cu deposits, and the Chaoshan, which hosts a skarn Au deposit. The abundances of apatite major and trace elements, such as Mn, V, Ce, S, F, Cl, and Cu, together with the whole-rock compositions, are used to decipher the oxidation states, volatile compositions, and Cu fertility of the parental magmas. The apatite Sr-Nd isotope compositions are used as tracers for the magma sources. The results show that: (1) the parental magma of the Au-mineralized intrusion is less oxidized and has higher S-Cl contents than those of the Cu-mineralized intrusions, and (2) the proportion of mantle-derived melt is much higher in the former than in the latter. The results also reveal that the Cu-mineralized intrusions have highly variable apatite Cu-Cl-S compositions. Specifically, the Xinwuli intrusion has much higher Cu but lower Cl-S contents in apatite than the other two intrusions, indicating that a Cu-rich magma is not universally required for the formation of hydrothermal Cu deposits. This study demonstrates that apatite is a robust petrogenetic and metallogenic indicator for porphyry and skarn-type Cu-Au ore deposits. [ABSTRACT FROM AUTHOR]

The Duolong porphyry Cu-Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole-rock elemental and Sr-Nd-Pb isotope and zircon Hf isotopic data of syn- and post-ore volcanic rocks and barren and ore-bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu-Au mineralization. LA-ICP-MS zircon U-Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore-bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post-ore basaltic andesite. All the samples show high-K calc-alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc-type magmas. Syn- and post-ore volcanic rocks show initial Sr ratios of 0.7045-0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408-18.642, (207Pb/204Pb)t of 15.584-15.672 and positive zircon εHf(t) values of 1.3-10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore-bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054-0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5-9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong-Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]