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Discovery and significance of the Sc-Nb-REE-enriched zone in the paleocrust of weathering atop the Permian Emeishan basalt in the western Guizhou, China (Vol. 41, No.4/5, 2021) TEXT SIZE: A A A

GUN Min-shan1, CAI Guo-sheng1, ZENG Dao-guo1*, JIN Zhong-guo2, DU Lin1, XIANG Ming-kun1, XUE Hong-fu1, SHEN Qi-jun3, HUANG Zhi-long4

(1. Institute of Geological and Mineral Exploration, Non-Ferrous Metals and Nuclear Industry Geological Exploration Bureau of Guizhou, Guiyang 550005, China;
2. Non-Ferrous Metals and Nuclear Industry Geological Exploration Bureau of Guizhou, Guiyang 550005, China;
3. Land Mineral Resources Reserve Bureau of Guizhou Province, Guiyang 550005, China;
4. Stake Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China) 

Abstract: The palaeocrust of weathering, widely developed within the unconformity between the Permian Emeishan basalt and the Longtan Formation in the Sichuan-Yunnan-Guizhou area, is characterized by stable layer, large thickness, and multi-elemental enrichments. However, very few studies have been carried out on its mineralization and resource potential. In this paper, it has been found that there are obvious Sc, Nb and REE enrichments in the palaeocrust of the Shuicheng-Nayong area based on the systematic petrogeochemical investigation. Samples of the enrichment layer have Sc2O3 contents ranging from 40×10-6 to 133×10-6, with an average of 73×10-6, Nb2O5 contents ranging from 30×10-6 to 392×10-6, with an average of 229×10-6, ΣRE2O3 contents ranging from 0.052% to 0.214%, with an average of 0.093%. The Sc, Nb and REE enrichments show obvious characteristics of differentiation and stratification. The Sc enrichment mainly occurred in iron-bearing claystones in the middle and lower parts of the palaeocrustunder a weakly reduced environment. The Nb and REE enrichments occurred mainly in aluminous and carbonaceous claystones in upper part of the palaeocrust under a transition environment from oxidation to reduction. The LREE-enriched patterns and the highest REE enrichment in carbonaceous claystone and carbonaceous shale indicate that organic matter may have played an important role in processes of the migration and enrichment of REE elements. REE distribution patterns, La/Yb-ΣREE diagram and δEu characteristics indicate that REE could be mainly sourced from Emeishan basalts with possibly minor contribution from intermediate-acidic igneous rocks. This study shows that these paleocrusts of weathering in the Sichuan-Yunnan-Guizhou area may have relatively large resource potential of Sc, Nd and REE and could become important layers of the palaeocrust-type (palaeoweathering-sedimentary type) Sc, Nb, and REE deposit in future with great values of exploration, evaluation, and research.
 
Keywords: Sc-Nb-REE; Permian Emeishan basalt; Paleocrust of weathering; Western Guizhou

ACTA MINERALOGICA SINICA Vol. 41, No.4/5, 2021, page 531-547

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