Petrogenesis, Redox State, and Mineralization Potential of Triassic Granitoids in the Mengshan District, South China

Abstract

The Mengshan district is located in the eastern segment of the Jiangnan Orogen in South China. Multi-phase intrusions were emplaced in this district, with the medium-grained porphyritic biotite granite and its marginal phase (fine-grained porphyritic biotite granite) genetically related to metal and non-metal mineralization. In this study, zircon U–Pb ages and trace elements, whole-rock geochemistry, and Nd isotopes were systematically analyzed for medium- and fine-grained porphyritic biotite granite in the Mengshan district, with the aim of elucidating the origin, evolutionary process, redox state, and mineralization competency of the studied granites. The Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA–ICP–MS) zircon U–Pb dating provided a weighted mean age of 226.6 ± 0.5 to 225.9 ± 0.5 Ma for the studied Mengshan granites, synchronous with the late-episode Triassic magmatism-mineralization in South China. The studied Mengshan granites are high-Si and -K, low-P, and weakly peraluminous, exhibiting features of highly evolved I-type granites. The detailed whole-rock geochemistry and Nd isotopes, and zircon trace elements and Hf isotopes demonstrated that the studied Mengshan granites were likely derived from disequilibrium melting of Proterozoic metamorphic basements that were composed of meta-igneous and metasediments and underwent fractional crystallization of plagioclase, K-feldspar, biotite, Fe-Ti oxide, zircon, and apatite. Low whole-rock K/Rb (<150), Nb/Ta (<6), and Zr/Hf (<26) ratios and the metasomatized rim of zircon also suggest that the melt–fluid interaction occurred during the formation of more evolved fine-grained porphyritic biotite granite. The Mengshan granites have a relatively reduced redox state, revealed by their relatively low whole-rock Fe2O3/FeO ratios (mostly < 0.5), zircon Ce4+/Ce3+ ratios (mostly lower than 90), and oxygen fugacity (below ΔFMQ + 1.4). The data in this study indicate that the Mengshan granites, especially the more evolved fine-grained porphyritic biotite granite, are favorable for W, Sn, Mo (<0.3 Mt), and Cu (<1 Mt) mineralization. Moreover, the contact zone between the fine-grained porphyritic biotite granite (or other Triassic granites) and the Permian Maokou Formation (flint-nodule limestone) is a potential target region for wollastonite exploration.

A New Nephrite Occurrence in Jiangxi Province, China: Its Characterization and Gemological Significance

“…Among them, the Carboniferous Huanglong Formation, Permian Qixia Formation, Permian Leping Formation, and Permian Maokou Formation form a set of carbonate rock associations. These formations primarily consist of limestone, dolomitic limestone, dolomite, and carbonaceous rock (Figure 2) [26]. The Mengshan area has favorable conditions for mineralization.…”

“…The Mengshan composite pluton consists of Triassic granites (~217 to ~236 Ma) [28] and Jurassic-Cretaceous dikes (~135 Ma and ~142 Ma) [26,28]. Previous studies [26] divided the Mengshan Triassic granites into three stages.…”

“…The Mengshan composite pluton consists of Triassic granites (~217 to ~236 Ma) [28] and Jurassic-Cretaceous dikes (~135 Ma and ~142 Ma) [26,28]. Previous studies [26] divided the Mengshan Triassic granites into three stages. The first-stage granites constitute the main body (71%) and can be further subdivided into two phases: the transitional and marginal phases.…”

Geochemistry and geochronology of Upper Triassic sedimentary rocks from the south of the Dabie Orogen: Implications for the paleoenvironment, provenance and tectonic setting

“…Various geological features can be found in the Jiangnan Orogen, such as the Ophiolitic mélange, I‐type and S‐type granites, with ages ranging from 815 to 910 Ma (Charvet et al, 1996; Shu & Charvet, 1996; Sun et al, 2018; Yao, Cawood, et al, 2019). Tectono‐magmatic events occurred in the Jiangnan Orogen during the Mid‐Triassic porphyritic biotite granite (Yang et al, 2021).…”

Study on high-temperature friction and wear properties of Arc Ion plating Cr coating

“…Chromium is a slightly blue-silver-white metal that often exists in the form of chromite in nature [2] . Chromium metal has a high melting point, high hardness, and high corrosion resistance, among which the main reason for its high hardness is the manifestation of its crystal structure.…”