JI Yan-bing 1,2, DU Li-juan 1,2,3*, HUANG Zhi-long 3, CHEN Jun 1,2, LI Bo 4, LI Xin-zheng 1,2, LIU Lin-lin 1,2, YANG Zai-feng 1,2

(1. College of Resources and Environmental Engineering, Guizhou University, Guiyang 550025, China;
2. Key Laboratory of Karst Georesources and Environment, Guizhou University, Ministry of Education, Guiyang 550025, China;
3. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Science, Guiyang 550081, China;
4. Faculty of Land and Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China)

Abstract: The Yangla copper deposit located in the Sanjiang Tethys metallogenic domain is a typical skarn deposit. A series of alterations, with obvious alteration zonation characteristics, are developed from the intrusion to the wallrocks in this deposit. However, previous studies on altered minerals of the Yangla copper deposit mainly focused on the anhydrous skarn stage minerals such as garnet. The lack of systematic mineralogical and compositional studies on the widely developed retrograde alteration stage minerals such as chlorite had restricted the comprehensive understanding of the mineralization process of the Yangla copper deposit. Therefore, in this paper, taking the chlorite in the skarn type mineralization of the Yangla copper deposit as the research object, we have carried out the chemical composition analysis of chlorite by using electron probe microanalysis (EPMA) and LA-ICP-MS in-situ technology and given results below. Two types of chlorite in the Yangla copper deposit have been classified. The early chlorite (Chl-Ⅰ) was intergrown with the andradite, chalcopyrite and other sulfides, and the late chlorite (Chl-II) was often intergrown with a large amount of calcite. Both types of chlorite belong to Mg-rich chlorite with trioctahedral structure, indicating that they were formed in a relatively reduced environment. The Tschermark substitution mechanism of Fe2+ and Mg2+ is the main substitution mechanism for major elements of two types of chlorites; 2) The calculation results of the chlorite geothermometer range from 140 ℃ to 281 ℃, with an average of 224 ℃. The temperatures of chlorites are gradually decreased from the Chl-Ⅰ to Chl-Ⅱ chlorites, indicating that they were formed in the range of medium and low temperature hydrothermal alteration; 3) From the early mineralization stage (Chl-Ⅰ) to the late mineralization stage (Chl-Ⅱ), the concentrations of trace elements (Sc, Ti, Ga, V) in chlorites are decreased, which may be related to the gradual decrease of the hydrothermal fluid temperature, indicating that the Ti, Sc, Ga, V-rich chlorite is closely related to mineralization and it can be used as an effective indicator for the relevant mineralization. Therefore, the study of compositions of trace elements in chlorite is of certain significance for the mineral exploration.

Keywords: chlorite; skarn deposit; trace elements; ore-forming fluids; Yangla copper deposit

ACTA MINERALOGICA SINICA Vol. 43, No. 3, 2023, Page 343