Late Triassic U-bearing and barren granites in the Miao'ershan batholith, South China: Petrogenetic discrimination and exploration significance

Abstract

The Miao'ershan uranium ore district is one of the most important granite-hosted uranium producers in South China. There are several Triassic granite plutons in the Miao'ershan batholith, but uranium ore deposits mainly occur within the Douzhashan granitic body. Precise zircon U-Pb dating indicated that these Triassic granite plutons were emplaced during 204 to 215 Ma. The Douzhashan U-bearing granite lies in the central part of the Miao'ershan batholith, and has higher U contents (8.0 to 26.1 ppm, average 17.0 ppm) than the nearby Xiangcaoping granite (5.0 to 9.3 ppm, average 7.0 ppm) and the Yangqiaoling granite (6.4 to 18.3 ppm, average 11.5 ppm) in the south part of the batholith. The Douzhashan granite is composed of medium-grained two-mica granite, whereas the Xiangcaoping and Yangqiaoling granites are composed of porphyritic biotite granite. Both the Xiangcaoping and Douzhashan granites have high A/CNK ratios (>1.10), high (87 Sr/ 86 Sr)i ratios (>0.720) and low εNd(t) values (-11.3 to-10.4), suggesting that they belong to strongly peraluminous S-type granites. The Douzhashan granite has low CaO/Na2O ratios, high Rb/Sr and Rb/Ba ratios, indicating a partial melting origin of clay-rich pelitic rocks. In contrast, the Xiangcaoping granite formed from clay-poor psammite-derived melt. The Yangqiaoling granite shows different geochemical characteristics with the Douzhashan and Xiangcaoping granites, indicating a different magma source. The Yangqiaoling granite has higher εNd(t) of-9.4 to-8.3 and variable A/CNK values from 0.98 to 1.19, suggesting a mixture source of meta-sedimentary rocks and meta-igneous rocks. Crystallization fractionation is not the main mechanism for U enrichment in the Douzhashan granite. We suggest that U-rich pelitic rock sources may be the key factor to generate peraluminous U-bearing granites in South China. Searching for those granites which are reduced, strongly peraluminous and were derived from U-rich pelitic rocks, is the most effective way for exploring granite-hosted U deposits.

Contrasting alteration textures and geochemistry of allanite from uranium-fertile and barren granites: Insights into granite-related U and ion-adsorption REE mineralization

“…They are mainly hosted by or occur adjacent to granites and formed at around 110−50 Ma (Hu et al 2008;Bonnetti et al 2018;Zhong et al 2019;Chi et al 2020). Most of the granites related to uranium mineralization are of Triassic (251−205 Ma) and Jurassic age (180−142 Ma; Zhao et al 2011Zhao et al , 2016Chen et al 2012;Zhang et al 2017bZhang et al , 2018aChi et al 2020). The formation of granite-related uranium deposits in this region has been linked to regional crustal extension events (Hu et al 2008;Luo et al 2015;Zhong et al 2019;Chi et al 2020).…”

“…Allanite has been shown to be susceptible to alteration (Wood and Ricketts 2000;Poitrasson 2002). The alteration mechanisms of allanite mainly involve the transformation of allanite to epidote and replacement by secondary allanite, REE-fluorocarbonates, calcite, fluorite, thorite, and clay minerals (Zhao et al 2011(Zhao et al , 2016Zhang et al 2018a). Generally, the formation of these uranium deposits has been linked to the regional Cretaceous to Tertiary crustal extension and related mafic magmatism, which could have provided thermal energy for fluid circulation that resulted in the mobilization of uranium from U-rich rocks (Min et al 1999;Hu et al 2008;Mao et al 2013;Chi et al 2020).…”

Ductile shear deformation and gold mineralization in the Hetai goldfield of the Yunkai Massif, South China Block

“…The Qinling‐Dabie‐Sulu Orogen is located to the north margin of the SCB, which is adjoined to the Indosinian Block by the Red River Fault to the southwest (Li, Santosh, Zhao, Zhang, & Jin, ; K. Qiu & Deng, ; K. Qiu, Marsh, Yu, Pfaff, Gulbransen, Gou, & Li, ; K. Qiu et al, ). The Yangtze and Cathaysia blocks were amalgamated together to form the united SCC during the late Neoproterozoic (D. Xu et al, ; Yao, Shu, & Santosh, ; Yao, Shu, Santosh, & Li, ; Yao, Shu, Cawood, & Li, ; Yin et al, ; L. Zhao, Guo, et al, ; K. Zhao, Jiang, et al, ). However, during the later Neoproterozoic and early‐middle Ordovician, the SCB split again, resulting in a complex intracontinental rift arrangement (K. Qiu et al, ).…”

“…Abundant syntectonic granite intrusions are distributed in the deeper basement at the center of the Yunkai Massif, including charnockite intrusions with zircon U–Pb ages ranging from 448 to 405 Ma (C. Chen et al, ; Lin, Wang, & Chen, ; D. Wang et al, ; Figure ). The Indosinian magma mainly produced a series of Al‐rich granites (including cordierite and garnet), which are generally NE–SW‐trending along the western side of the Luchuan‐Cenxi Fault and the eastern side of the Wuchuan‐Sihui Fault; their zircon U–Pb ages mainly range from 242 to 220 Ma (C. Chen et al, ; L. Zhao, Guo, et al, ; K. Zhao, Jiang, et al, ; Zhong et al, ; Figure ). The Yanshanian intrusions are mainly distributed along the Wuchuan‐Sihui Fault (Lin et al, ).…”

Mineralogy and geochemistry of pitchblende in the Changjiang U ore field, Guangdong Province, South China: Implications for its mineralization

“…These deposits mainly occur in the granites of the Nanling magmatic belt, in the volcanic rocks of the Ganhang volcanic belt and in the carbonaceous and siliceous pelitic sedimentary rocks along the Jiangnan Orogen (Hu et al, 2008;Luo et al, 2015;Zhang et al, 2020). The granite-related U deposits in the SCUP generally display close spatial and genetic relationships with several typical granitic complexes, such as Miao'ershan, Taoshan, Guidong and Zhushuangshan (Min et al, 2005;Hu et al, 2008;Zhao et al, 2011Zhao et al, , 2016Chi et al, 2020;Zhang et al, 2020Zhang et al, , 2021. These deposits formed in six episodes, namely, ~140 Ma, ~120 Ma, ~100 Ma, ~90 Ma, ~70 Ma and ~50 Ma, which kept pace with the activity of Cretaceous-Paleogene mafic magma and a red bed basin in this region (Hu et al, 2004(Hu et al, , 2008Luo et al, 2015Luo et al, , 2017.…”