Genetic Types, Spatiotemporal Distribution of Ore Deposits and Sources of Ore‐forming Materials in the Xuancheng Area, Anhui Province

Abstract

AbstractIn recent years, several large and medium‐sized ore deposits have been discovered in the shallow cover of Xuancheng, Anhui Province, indicating that this area has a productive metallogenic geological background and may be a potential prospecting region. Based on systematic investigation, the geological and mineralization characteristics of porphyry Cu‐Au deposits and skarn Cu‐Mo‐W deposits in this region have been summarized. Zircon U‐Pb dating (LA‐ICP‐MS) of the Chating quartz‐diorite porphyry and the Kunshan biotite pyroxene diorite yield concordia ages of 145.5 ± 2.1 Ma and 131.8 ± 2.1 Ma, respectively. Meanwhile, the Re‐Os dating analyses for molybdenite from the Shizishan and Magushan skarn Cu‐Mo deposits yielded 133.81 ± 0.86 Ma and 143.8 ± 1.4 Ma ages, respectively. When viewed in conjunction with previous studies, it is suggested that twostage (the early stage of 145–135 Ma and the late stage of 134–125 Ma) magmatism may have occurred during the Mesozoic in Xuancheng region. Early stage intrusive rocks are distributed along both sides of the Jiangnan deep fault (JDF). The intrusive rocks to the north of the JDF are mainly quartz‐diorite porphyry and granodiorite (porphyry) rocks, related to porphyry Cu‐Au deposits and skarn‐type Cu‐Mo‐W deposits. These deposits belong to the first stage of the porphyry‐skarn copper gold metallogenic belt of the Middle‐Lower Yangtze Metallogenic Belt (MLYB), associated with the high potassium calc‐alkaline intermediate‐acid intrusions. The magmatic and ore‐forming materials are mainly derived from the enriched lithospheric mantle. South of the JDF, the Magushan granodiorite is a representative intrusive rock of the first stage I‐type granite, which hosts the Magushan Cu‐Mo skarn deposit, similar to the W‐Mo‐Cu skarn deposits in the Eastern Segment of the Jiangnan Uplift Metallogenic Belt (ESJUB). The magmatic and metallogenic materials mainly came from the Neoproterozoic basement, with the possible participation of a small amount of mantle components. The late stage magmatism was dominated by volcanic rocks with a small amount of intrusive rocks, which were consistent with the limited volcanic‐intrusive activities in the second stage of the MLYB. The H‐O stable isotopes of ore deposits in the region indicate that the ore‐forming hydrothermal fluids of the porphyry and skarn deposits were mostly of magmatic water for the ore‐forming stage, the percentage of meteoric water obviously increasing during the late ore‐forming stage. The ore‐forming materials of the deposits are mainly from the deep magma with a few sedimentary wall rocks, according to the stable carbon isotopes of the carbonates in the ore deposits. Additionally, according to previous research, the molybdenite from the MLYB has a higher Re content than that of the ESJUB. The higher content of Re in the molybdenite from the Shizishan deposit is identical to that of MLYB rather than ESJUB, whereas Re characteristics in molybdenite of Magushan deposit are similar to that of ESJUB. The differences in Re characteristics indicate the different deep processes and ore‐forming material sources (mainly mantle composition for the former and crustal materials for the latter) of these ore deposits on opposite sides of the JDF.