SHEN Chong-hui

(School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China)

Abstract: In this study, detailed observation by using microscopic and backscattered images (BSE) of the pseudomorphic turquoise and apatite in the Dahuangshan area, Anhui province, were conducted. Based on the study above, the in-situ electron probe microanalysis (EPMA) and chemical analysis of major and trace elements of the pseudomorphic turquoise and apatite were carried out. The results show that the Dahuangshan pseudomorphic turquoise has cone-like crystal form of apatite, with compact microcrystalline scaly, irregular spheroidal compact packing, and spheroidal gelatinous structures. The BSE images shows that the Dahuangshan turquoise and apatite both contain very fine rare earth mineral inclusions of monazite. The chemical analysis of major and trace elements and the in-situ EPMA analysis show that the Dahuangshan pseudomorphic turquoise is a solid solution mineral of the phosphorus-copper-iron-rich (chalcosiderite) end-member and aluminum-rich end-member. The Dahuangshan pseudomorphic turquoise and apatite are similarly composed of major P2O5 and minor F, Cl, and S elements, with similar primitive mantle-normalized distribution patterns of the trace elements and similar chondrite-normalized distribution patterns of rare earth elements. Thus, it is believed that chemical composition of the pseudomorphic turquoise was mainly originated from the apatite. Based on characteristics of rare earth elements of the apatite (δEu=0.25－0.28, δCe=1.20－1.27) and pseudomorphic turquoise (δEu=0.33－0.47, δCe=0.80－1.88), it is comprehensively discriminated that the Dahuangshan pseudomorphic turquoise was formed by the hydrothermal metasomatism of the apatite.

Keywords: Pseudomorphic turquoise; apatite; mineralogy; the Dahuangshan area, Anhui Province

ACTA MINERALOGICA SINICA Vol. 40, No.3, 2020, page 313-322