Geochemical composition and paleoceanic environment of the Lower Cambrian black shale-hosted Qianjiaping vanadium deposit in the southern Qinling Region

doi:10.13745/j.esf.sf.2021.8.13

Abstract

Abstract:

The Qianjiaping vanadium (V) deposit is a typical Lower Cambrian black shale-hosted V deposit in the Southern Qinling Region. Vanadium mineralization in the Qianjiaping deposit mainly occurs in multilayered cherts with carbonaceous shale in the 1st member of the Shuigoukou Formation. To better understand the origin of vanadium and redox environment in Early Cambrian seawater in South Qinling, we report in this study the bulk geochemical compositions of the V-rich carbonaceous shale from the 1st member and the overlying muddy limestone from the 2nd member of the Shuigoukou Formation. The Y/Ho ratio is higher in the multilayered chert-mudstone samples than in the muddy limestone samples, indicating a dominant authigenic origin for V in the 1st member, whereas in the 2nd member V may be mostly derived from detrital components. Discrimination plots, Eu/Eu^*-V, Y/P₂O₅-Zr/Cr and Fe/Ti-Al/(Al+Fe+Mn), suggest V mineralization is mainly by precipitation from ambient seawater, while hydrothermal fluids plays a minor role. All samples showed negative Ce anomaly, ranging from 0.26-0.96. Together considering the comparatively high Mo/Sc, V/Sc, V/Cr and low Th/U ratios in the 1st member, we infer a redox stratified ocean during the early Early Cambrian in the Southern Qinling Region, which became entirely oxygenated during the late Early Cambrian.

Key words: Qianjiaping vanadium deposit, trace element, REE, ore genesis, redox environment, Southern Qinling Region

CLC Number:

XU Lingang, FU Xuerui, YE Huishou, ZHENG Wei, CHEN Bo, FANG Zhenglong. Geochemical composition and paleoceanic environment of the Lower Cambrian black shale-hosted Qianjiaping vanadium deposit in the southern Qinling Region[J]. Earth Science Frontiers, 2022, 29(1): 160-175.

Figures/Tables 13

Fig.1 Geological sketch map of the southern Qinling Region on the margin of the Yangtze Platform. Modified after [7, 21].

Fig.2 Geological map of the Qianjiaping vanadium deposit. Adapted from [13].

Fig.3 Cross-section of the Qianjiaping vanadium deposit in the southern Qinling Region

Fig.4 Field photos showing geological features of the Qianjiaping vanadium deposit

Fig.5 Photos and photomicrographs of typical hand specimen of vanadium ore and host rock from the Qianjiaping vanadium deposit

Fig.6 Stratigraphic column of the Qianjiaping vanadium deposit and sampling locations

Table 1 Major and (selected) trace element compositions of samples from the Qianjiaping vanadium deposit

Table 2 Rare earth element compositions of samples from the Qianjiaping vanadium deposit

Fig.7 Correlations between Th and Y/Ho (a) and Y and Y/Ho (b) for samples from the Qianjiaping vanadium deposit

Fig.8 PAAS-normalized REE+Y distribution patterns in samples from the 2nd (a) and 1st (b) member of the Shuigoukou Formation

Fig.9 Al2O3-∑REE binary plots for samples from the 2nd (a) and 1st (b) member of the Shuigoukou Formation in the Qianjiaping vanadium deposit

Fig.10 Discriminant plots for sediments with hydrothermal and hydrogenous origins. Basemaps in b, c and d adapted from [42].

Fig.11 Discriminant plots for redox conditions during the deposition of the Shuigoukou Formation in the Qianjiaping vanadium deposit

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