Abstract
The newly discovered Magushan Cu-Mo polymetallic deposit, located in southeastern Anhui, eastern China, is a middle-scale skarn-type polymetallic deposit with different ore types of veinlets-disseminated skarn (the primary type), quartz veins, and porphyry. LA-ICP-MS zircon U–Pb analyses yielded a crystallization age of 135.7 ± 1.5 Ma for the ore-related granodiorite in Magushan. The granodiorites are I-type granites in nature, characterized by metaluminous and high-K calc-alkaline characteristics. They are enriched in large ion lithophile elements (LILEs, e.g., Ba, Th, and U) and light rare earth elements (LREEs), and depleted in high field strength elements (NFSEs, e.g., Nb, Ta, and Ti) and heavy rare earth element (HREEs), with slightly negative Eu anomalies (Eu/Eu* = 0.81–0.86). These granodiorites show high Mg# (mainly > 40) values, high MgO (1.73–1.96 wt. %) and low Na2O (<4.21 wt. %) contents, with whole-rock (87Sr/86Sr)i ratios (0.708877 to 0.710398), negative εNd(t) values of −5.4 to −5.2, and negative zircon εHf(t) values of −4.60 to −1.37, with old two-stage Hf model ages (TDM2) between 1.2‒1.5 Ga. Besides, they are characterized by high radiogenic Pb isotopic compositions with (206Pb/204Pb)i = 18.44–18.56, (207Pb/204Pb)i = 15.66–15.67, and (208Pb/204Pb)i = 38.77–38.87. These granodiorites are characterized by high zircon Ce4+/Ce3+ ratios (average 893) and Eu/Eu* ratios (average 0.51), indicating high magmatic oxygen fugacities. The distinct geochemical and isotopic features suggest that the Magushan granodiorites could be formed by metasomatized mantle-derived magmas, mixing with materials from Neoproterozoic crust that is widely distributed in the Southern Anhui. This study concludes that the formation of the Magushan Cu-Mo polymetallic deposits may largely depend on an oxidizing environment and multi-sources mixed of mantle- and crust-derived materials.
Highlights
The Lower Yangtze region (LYR), located on the eastern segment of Yangtze block, can be separated into two important metallogenic belts: Jiangnan Tungsten belt (JNB) in the south and the Middle-Lower Yangtze River Metallogenic belts (MLYRB) in the north, which are bounded by the Yangxing-Changzhou Fault (YCF) (Figure 1)
We selected granodiorites associated with other Cu–Mo deposit for comparison in the Jiangnan Fault region (JNF)
Three stages of magmatism were identified in the MLYRB: (1) first stage (148–135 Ma), adakitic rocks related to Cu–Au polymetallic deposits, (2) second stage (134–129 Ma), sub-alkaline to alkaline mafic to intermediate volcanic/sub-volcanic rocks associated with magnetite-apatite deposits, and (3) third stage
Summary
The Lower Yangtze region (LYR), located on the eastern segment of Yangtze block, can be separated into two important metallogenic belts: Jiangnan Tungsten belt (JNB) in the south and the Middle-Lower Yangtze River Metallogenic belts (MLYRB) in the north, which are bounded by the Yangxing-Changzhou Fault (YCF) (Figure 1). MLYRB is distinguished by the widespread porphyryand skarn-type Cu–Au–Fe–Mo deposits, related to the Mesozoic I-type or adakitic granitoids [1,2,3,4,5], whereas the JNB is famous for the tungsten polymetallic mineralization, with occurrence of many giant to large-scale tungsten polymetallic ore deposits, e.g., Zhuxi [6], Dahutang [7], Yangchuling [8], Dongyuan [9], and Xiaoyao [10]. A variety of large- and medium-sized Cu–Mo polymetallic deposits have been discovered and explored within the Jiangnan Fault region (JNF) between the MLRYB and the JNB, such as Matou Cu–Mo deposit [11], Jitoushan Cu–Mo–W deposit [12], Anzishan.
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