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Genetic Environments of Au-Ag-bearing Geumhwa Hydrothermal Vein Deposit
함 금-은 금화 열수 맥상광상의 생성환경
Econ. Environ. Geol. 2021 Feb;54(1):49-60
Published online February 28, 2021;  https://doi.org/10.9719/EEG.2021.54.1.49
Copyright © 2021 the Korean society of economic and environmental gelology.

Sunjin Lee, Sang-Hoon Choi*
이선진 · 최상훈*

Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju 28644, Korea
충북대학교 지구환경과학과
Received January 18, 2021; Revised January 21, 2021; Accepted January 21, 2021.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
 Abstract
The Geumhwa Au-Ag deposit is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into two stages (stage I and II) by major tectonic fracturing. Stage II is economically barren. Stage I, at which the precipitation of major ore minerals occurred, is further divided into three substages(early, middle and late) with paragenetic time based on minor fractures and discernible mineral assemblages: early substage, marked by deposition of pyrite with minor wolframite; middle substage, characterized by introduction of electrum and base-metal sulfides with Cu-As and/or Cu-Sb sulfosalts; late substage, marked by hematite and Bisulfosalts with secondary minerals. Changes in vein mineralogy reflect decreases in temperature and sulfur fugacity with a concomitant increase in oxygen fugacity. Fluid inclusion data indicate progressive decreases in temperature and salinity within each substage with increasing paragenetic time. During the early portion of stage I, high-temperature (≥410°C), high-salinity fluids (up to ≈44 equiv. wt. % NaCl) formed by condensation during decompression of a magmatic vapor phase. During waning of early substage, high-temperature, high-salinity fluids gave way to progressively cooler, more dilute fluids associated with main Au-Ag mineralization (middle) and finally to ≈180°C and ≥0.7 equiv. wt. % NaCl fluids associated with hematite and sulfosalts (± secondary) mineralization (late substage). These trends are interpreted to indicate progressive mixing of high- and medium to low-salinity hydrothermal fluids with cooler, more dilute, oxidizing meteoric waters. The Geumhwa Au-Ag deposit may represent a vein-type system transitional between porphyry-type and epithermal-type.
Keywords : Geumhwa Au-Ag deposit, hydrothermal, fluid inclusion, vein deposits, halite

 

February 2021, 54 (1)