The Role of Magma Mixing in Generating Granodioritic Intrusions Related to Cu–W Mineralization: A Case Study from Qiaomaishan Deposit, Eastern China

Abstract

The newly exploited Qiaomaishan Cu−W deposit, located in the Xuancheng ore district in the MLYRB, is a middle-sized Cu-W skarn-type polymetallic deposit. As Cu-W mineralization is a rare and uncommon type in the Middle-Lower Yangtze River Belt (MLYRB), few studies have been carried out, and the geochemical characteristics and petrogenesis of Qiaomaishan intrusive rocks related to Cu-W mineralization are not well documented. We studied two types of ore-bearing intrusive rocks in the Qiaomaishan region, i.e., pure granodiorite porphyry and granodiorite porphyry with mafic microgranular enclaves (MMEs). Age characterization using zircon LA-ICP-MS showed that they were formed almost simultaneously, around 134.9 to 135.1 Ma. Granodiorite porphyries are high Mg# adakites, characterized by high-K calc-alkaline and metaluminous features that are enriched in LILEs (e.g., Sr and Ba) and LREEs, but depleted in HFSEs (e.g., Nb, Ta, and Ti) and HREEs. Moreover, they have enriched Sr-Nd-Hf isotopic compositions (with whole-rock ( 87 Sr/ 86 Sr) i ratios (0.706666−0.706714), negative ε Nd (t) values of −9.1 to −8.6, negative zircon ε Hf (t) values of −12.2 to −6.7, and two-stage Hf model ages (T DM 2) between 1.5 and 2.0 Ga). However, compared to host rocks, the granodiorite porphyry with MMEs shows variable geochemical compositions, e.g., high Mg#, Cr, Ni, and V contents and enriched with LILEs. In addition, they have more depleted I Sr , ε Nd (t), and ε Hf (t) values (0.706025 to 0.706269, −6.4 to −7.4, and −10.6 to −5.7, respectively), overlapping with regions of Early Cretaceous mafic rocks derived from enriched lithospheric mantle in the MLYRB. Coupled with significant disequilibrium textures and geochemical features of host rocks and MMEs, we propose that those rocks have resulted from mixing the felsic lower crust-derived magma and the mafic magma generated from the enriched mantle. The mixed magmas subsequently rose to shallow crust to form the ore-bearing rocks and facilitate Cu-W mineralization.

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

“…Based on LA-ICP-MS zircon U-Pb dating, the rockforming ages of the quartz-diorite porphyry from the Chating porphyry Cu-Au deposit and the Kunshan biotite pyroxene diorite are 145.5±2.1 Ma and 131.8±2.1 Ma, respectively. Combined with previous and our own results regarding magmatic zircon U-Pb geochronology in the Xuancheng region (Table 5; Jiang et al, 2015Jiang et al, , 2017Lu et al, 2018b;Qi et al, 2019Qi et al, , 2020Xu et al, 2020), the Mesozoic magmatism in the Xuancheng area can be divided into the following two stages (Fig. 6):…”

“…Weidun-Shuangjing deposit) were preliminarily summarized (Wang et al, 2014;Liu and Duan, 2015;Liu X M, 2016;Hong et al, 2017;Feng et al, 2018). For example, Qi et al (2019Qi et al ( , 2020 carried out research on the sources and deep dynamic processes of magma, as related to the Magushan and Qiaomaishan skarn-type deposits.…”

“…Based on systematic geological surveys and scientific investigation in recent years, this paper systematically summarizes the genetic types and geological characteristics of the major metal deposits in this region. In addition, according to insitu zircon LA-ICP -MS U-Pb dating, molybdenite Re-Os dating and H-O-C Mao et al, 2011;Zhou et al, 2017); (b) geological and mineral map of the Xuancheng region (modified from Qi et al, 2019Qi et al, , 2020. Abbreviations: JLSF, Jiulianshan thrust fault; JDF, Jiangnan deep fault.…”

“…The northern part of the MLYB tectonicmagmatic belt produces intrusive bodies such as the Chating, Tongshan, Qiaomaishan, Shizishan and Liujishan intrusive rocks, which are primarily controlled by the NEtrending fault and the folded interlayer collapse structure, which clearly predate the magmatic activity in these areas. The lithology of the intrusive rocks is mainly that of diorite porphyry, quartz-diorite porphyry and granodiorite (porphyry) rocks, belonging to a high potassium calcalkaline series (Qi et al, 2019(Qi et al, , 2020Xu et al, 2020). The intrusive rocks, which were related to the porphyry skarntype Cu-Au-Mo deposits at this stage, are similar to the first stage intrusive rocks of the MLYB in terms of rockforming age, petrogenesis and mineralization types Xie et al, 2011Xie et al, , 2012Yang and Lee, 2011;Wu et al, 2012;Zhou et al, 2017).…”

“…In particular, the discovery of the Chating large porphyry Cu-Au deposit (Qian et al, 2017;Xie et al, 2018), which was a prelude to the key prospecting work in this area and the subsequent discovery of several skarntype Cu-Mo, Cu-W deposits and hydrothermal vein type Pb-Zn polymetallic deposits. Some scholars have therefore suggested that the Xuancheng area has the potential to be a new important ore cluster district in the MLYB (Lu et al, 2018a;Qi et al, 2019Qi et al, , 2020Xu et al 2020). Considerable attention has thus been paid to the area, with some research work being conducted in the region.…”