Comparison on Metallogenic Differences of Porphyry Deposits between Luanchuan Mo-W and Zhashui-Shanyang Cu-Mo Ore-clusters in Qinling Orogenic Belt: Constraints of Magmatic Source and Metallogenic Conditions

The Luanchuan Mo-W ore district and the Zhashui-Shanyang Cu-Mo ore district are two typical porphyry ore districts formed in the post-collision setting during 152-140Ma in the Qinling Orogenic Belt. Despite significant differences in their mineralization, the controlling factors remain unclear. This study collected whole-rock geochemical data, Sr-Nd-Hf isotopes, and the compositions of zircon and apatite from both ore districts. A comparative analysis was conducted on aspects such as magmatic source, water content, oxygen fugacity, volatiles(F, Cl)and sulfur content to reveal the key controlling factors of their metallogenic differences. The Zhashui-Shanyang Cu-Mo ore district shows εHf(t) and εNd(t) variations ranging from −5 to 2 and −6.6 to −1.5, with (⁸⁷Sr/⁸⁶Sr)_i value close to the upper mantle (averaging 0.7051), indicating a mixture of melting of thickened juvenile lower crustal components with mantle-derived magmas in the magma source. The Luanchuan Mo-W ore district exhibits relatively low εHf(t) and εNd(t) values (averaging −18.38 and −14.63) and older Hf two-stage model ages, suggesting that the Mo-W-rich porphyries originated from the ancient Taihua Group basement and partial melting of the Yangtze Plate subducted continental crust sediment. Both ore districts' mineralized porphyries have high Sr and low Y, whole-rock Eu/Eu*＞0.6, low zircon saturation temperatures (<750 ℃), zircon Eu/Eu*＞0.3, zircon Ce_N/Ce_N*＞100, Ce/Nd＞10, whole-rock V/Sc＞5, and oxidation state＞FMQ+3, indicating characteristics of high water content and high oxygen fugacity in their mineralizing magmas. Furthermore, the Cu-Mo system in the Zhashui-Shanyang ore district is enriched in Cl, while the Mo-W system in the Luanchuan ore district is enriched in F, with similar S contents. These differences in the magma source are the fundamental reasons for the mineralization disparities between the two districts. Cl and F, as the main ligands for the migration of Cu and Mo in magmatic hydrothermal fluids, are another key factor causing the mineralization differences between the two ore districts. Enriched water, high S, and high oxygen fugacity magmas are important conditions for the formation of porphyry ore deposits in both districts, but they are not the direct causes of the mineralization differences.