Geochemical study of Cretaceous magmatic rocks in Chuzhou region, low Yangtze River metallogenic belt: implications for petrogenesis and Cu–Au mineralization

et al. 2020

Minerals

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The Hucunnan porphyry- and skarn-type Cu–Mo deposit is located in the south of the central Shizishan ore field of the Tongling ore-cluster region. The intrusive Hucunnan granodiorite, outcropping in this deposit, has adakitic geochemical features, and its magma is proposed to have originated from partial melting of the oceanic crust mixed with mantle-derived materials. The porphyry-type orebody is hosted in the granodiorite, whereas the skarn-type orebody occurs in the contact zones of intrusions and country rocks. The δ34S values of pyrite from the skarn orebodies ranged from +3.9 to +4.7‰ (avg. +4.3‰, n = 6), while those of the porphyry orebodies ranged from +5.1 to +6.2‰ (avg. +5.6‰, n = 4). 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of the pyrites from the skarn orebodies were 38.04–38.45 (avg. 38.26), 15.55–15.66 (avg. 15.59), and 18.16–18.54 (avg. 18.44), respectively (n = 6). The pyrites in the porphyry orebodies had 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of 38.24–38.36, 15.51–15.662, and 18.10–18.41, respectively (avg. 38.32, 15.58, 18.22; n = 4), respectively. The metallogenic model ages from Re–Os isotopic dating were 138.7 ± 1.9 and 140.0 ± 2.8 Ma, respectively. Geochemical data indicate that the ore-forming fluids in the skarn stage are characterized by high temperature, low acidity, and high oxygen fugacity, and the ore-forming materials were mainly from magma and partly from stratum, proving that the skarn orebody has more stratum materials than the porphyry orebody.

Section: Metallogenic Modelsupporting

confidence: 89%

Geochemical Study of Cretaceous Magmatic Rocks and Related Ores of the Hucunnan Cu–Mo Deposit: Implications for Petrogenesis and Poly-Metal Mineralization in the Tongling Ore-Cluster Region

et al. 2020

Minerals

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“…During the Late Mesozoic, the Lower Yangtze area was an active continental margin setting [91] and was closely associated with the subduction of the Paleo-Pacific oceanic plate [92], resulting in the widespread emplacement of Late Mesozoic intrusive rocks [93][94][95]. Subduction of the Paleo-Pacific slab resulted in intense dehydration, and the overlying mantle wedge was metasomatized by the melts/fluids, forming an enriched lithospheric mantle.…”

Section: Ore-forming Processmentioning

confidence: 99%

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

Lu²,

et al. 2020

Minerals

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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.

“…In contrast, some other authors argue that these Mesozoic magmatic rocks in eastern China were mainly formed by the paleo-Pacific plate subduction (Ling et al, 2009;Sun et al, 2013;Sun et al, 2007). Through comparative study on the region and the adjacent adakites with Cu-Au mineralization on the aspects of geochemistry, oxygen fugacity and water contents of the magmas, some authors suggest that these Cu-Au-bearing adakites were formed during oceanic subduction beneath the Eurasian plate (Liu et al, 2010a;Wang et al, 2014;Wang et al, 2013;Xie et al, 2012;Zhang et al, 2017;Hu et al, 2017). According to existing statistics, 65% of Cu and Au reserves in the world are from porphyry Cu-Au deposits (Sun et al, 2010), and most of them are formed in the subduction zone.…”

Section: Tectonic Settingmentioning

confidence: 99%

“…Along the LYRB, gold usually occurs as a by-product in most gold-rich porphyry-/skarn-related Cu-Fe deposits and porphyry Cu deposits (Yang et al, 2011b), and rarely as 'Au-only' deposits. These deposits are usually associated with High-K calc-alkaline diorite to granodiorite porphyries with adakitic affinities (Deng et al, 2016;Fan et al, 2017;Hu et al, 2017;Li et al, 2014;Song et al, 2014;Wang et al, 2013;Wu et al, 2017;Xie et al, 2012;Zhang et al, 2014). The newly discovered Paodaoling Au deposit, which is located in the Anqing-Guichi ore cluster, LYRB, has been revealed by current exploration to have total Au reserves of more than 35 tons, with an average Au grade up to 1.73 g/t in the primary ore bodies, significantly higher grade than typical porphyry Au deposits (0.3 g/t to 1.5 g/t) (Cooke et al, 2005;Kerrich et al, 2000).…”

mentioning

confidence: 99%

Mineralization, Geochemistry and Zircon U‐Pb Ages of the Paodaoling Porphyry Gold Deposit in the Guichi Region, Lower Yangtze Metallogenic Belt, Eastern China

Duan

Acta Geologica Sinica (Eng)

Deng

et al. 2018

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The newly discovered Paodaoling porphyry Au deposit from the Guichi region, Lower Yangtze River Metallogenic Belt (LYRB), contains >35 tons of Au at an average grade of ∼1.7 g/t. It is a porphyry ‘Au‐only’ deposit, as revealed by current exploration in the depths, mostly above –400 m, which is quite uncommon among coeval porphyry mineralization along the LYRB. Additionally, there are also Cu‐Au bearing porphyries and barren alkaline granitoids in the Paodaoling district. Zircon LA‐ICP‐MS U‐Pb dating of the Cu‐Au‐bearing porphyries yield an age of 141–140 Ma, falling within the main magmatic stage of the LYRB, whereas the barren granites give an age of 125–120 Ma, coeval with the regional A‐type granites. The Cu‐Au‐bearing porphyries are LILE‐, LREE‐enriched and HFSE‐depleted, typical of arc magmatic affinities. The barren granites are HFSE‐enriched, with lower LREE/HREE ratios and pronounced negative Eu anomalies. The Cu‐Au‐bearing porphyries in the Paodaoling district have high oxygen fugacities and high water content. Pyrite sulfur isotopes of the Paodaoling gold deposit indicate a magmatic‐sedimentary mixed source for the ore‐forming fluids. Based on the alteration and poly‐metal zonation of the deepest exploration drill hole from the Paodaoling Au deposit, we propose that Cu ore bodies could lie at depth beneath the current Au ore bodies. The magmatism and associated Cu‐Au mineralization of the Paodaoling district are likely to have formed in a subduction setting, during slab rollback of the paleo‐Pacific plate.