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Formation of secondary non-sulfide zinc ore in Cho Dien Pb - Zn deposits

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The upper part of ore bodies was weathered and completely oxidized. Difference in geochemical behavior of lead (Pb) and zinc (Zn) in the oxidation process of Pb-Zn ore led to the formation of non-sulfide zinc ore in the Cho Dien deposit. Oxidation of primary Pb-Zn ore minerals such as sphalerite, pyrite and galena creates a low pH environment and transforms zinc from immobile (sphalerite - ZnS) to mobile (Zn2+) and is retained in solution under low(acidic) pH conditions; whereas lead has the tendency to form soluble minerals (anglesite, cerussite). The acid neutralization of the surrounding rockcauseszinc to precipitate to form secondary non-sulfide zinc minerals. | Vietnam Journal of Earth Sciences, 40(3), 228-239, Doi:10.15625/0866-7187/40/3/12615 Vietnam Academy of Science and Technology Vietnam Journal of Earth Sciences (VAST) http://www.vjs.ac.vn/index.php/jse Formation of secondary non-sulfide zinc ore in Cho Dien Pb - Zn deposits Nguyen Thi Lien, Nguyen Van Pho Institute of Geological Sciences, (VAST), 84 Chua Lang, Dong Da, Hanoi, Vietnam Received 13 November 2017; Received in revised form 28 March 2018; Accepted 30 May2018 ABSTRACT Non-sulfide zinc ore in the Cho Dien deposit has been exploited for a long time and remains the major exploited ore in Cho Dien. There are numerous studies of Cho Dien Pb-Zn ore, however, many of the studies have dedicated to description of mineralogical and chemical compositions. Built on the mineralogical studies and the content of Pb and Zn in groundwater determined by reflective microscope, SEM, EPMA and ICP-MS methods, the study explained the formation of secondary non-sulfide zinc ore in the Cho Dien deposit. The upper part of ore bodies was weathered and completely oxidized. Difference in geochemical behavior of lead (Pb) and zinc (Zn) in the oxidation process of Pb-Zn ore led to the formation of non-sulfide zinc ore in the Cho Dien deposit. Oxidation of primary Pb-Zn ore minerals such as sphalerite, pyrite and galena creates a low pH environment and transforms zinc from immobile (sphalerite ZnS) to mobile (Zn2+) and is retained in solution under low(acidic) pH conditions; whereas lead has the tendency to form soluble minerals (anglesite, cerussite). The acid neutralization of the surrounding rockcauseszinc to precipitate to form secondary non-sulfide zinc minerals. Keywords: Non-sulfide zinc ore; Cho Dien Pb-Zn ore; secondary zinc ore. ©2018 Vietnam Academy of Science and Technology 1. Introduction 1 “Non-sulfide zinc” is a term used by previous researchers, referred to a group of ore deposits consisting of Zn-oxidized minerals, mainly represented by smithsonite, hydrozincite, .