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Econ. Environ. Geol. 2022; 55(2): 171-181

Published online April 30, 2022

https://doi.org/10.9719/EEG.2022.55.2.171

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Au-Ag-bearing Ore Mineralization at the Geochang Hydrothermal Vein Deposit

Seok Jin Hong1, Sunjin Lee2, Sang-Hoon Choi2,*

1Intellegio, Seoul 08390, Korea
2Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju 28644, Korea

Correspondence to : *Corresponding author : cshoon@cbnu.ac.kr

Received: April 20, 2022; Revised: April 26, 2022; Accepted: April 26, 2022

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 original work is properly cited.

Abstract

The Geochang Au-Ag deposit is located within the Yeongnam Massif. Within the area a number of hydrothermal quartz and calcite veins were formed by narrow open-space filling of parallel and subparallel fractures in the granitic gneiss and/or gneissic granite. Mineral paragenesis can be divided into two stages (stage I, ore-bearing quartz vein; stage II, barren calcite vein) by major tectonic fracturing. 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, marked by deposition of pyrite with minor pyrrhotite and arsenopyrite; middle, characterized by introduction of electrum and base-metal sulfides with minor sulfosalts; late, marked by hematite with base-metal sulfides. Fluid inclusion data show that stage I ore mineralization was deposited between initial high temperatures (≥380°C) and later lower temperatures (≤210°C) from H2O-CO2-NaCl fluids with salinities between 7.0 to 0.7 equiv. wt. % NaCl of Geochang hydrothermal system. The relationship between salinity and homogenization temperature indicates a complex history of boiling, fluid unmixing (CO2 effervescence), cooling and dilution via influx of cooler, more dilute meteoric waters over the temperature range ≥380°C to ≤210°C. Changes in stage I vein mineralogy reflect decreasing temperature and fugacity of sulfur by evolution of the Geochang hydrothermal system with increasing paragenetic time. The Geochang deposit may represents a mesothermal gold-silver deposit.

Keywords Geochang deposit, Au-Ag, vein deposit, H2O-CO2-NaCl, mesothermal

거창 열수 맥상광상의 함 금-은 광화작용

홍석진1 · 이선진2 · 최상훈2,*

1(주) 인텔리지오
2충북대학교 지구환경과학과

요 약

거창광상은 영남육괴 화강암질 편마암 또는 편마암질 화강암 내에 발달한 열극을 충전하여 생성된 함 금-은 열수 맥상광상으로, 괴상 및 호상 조직과 함께 부분적인 각력상 조직 및 정동의 발달 등 복합적인 조직적 특성을 보여준다. 거창광상의 맥상 광화작용은 구조운동(tectonic break)에 의하여 광화 1시기와 광화 2시기로 구분된다. 광화 1시기는 석영맥의 생성과 함께 주된 함금·은 광물인 에렉트럼과 함께 황화광물 및 산화광물 등이 미량의 황염광물을 수반 산출한 시기로서, 공생관계와 광물조합 특성 등에 의하여 세 단계의 광화시기(초기, 중기, 후기)로 구분된다. 광화 1시기의 초기에는 주로 황철석, 자류철석, 유비철석 등이 산출되었다. 중기에는 주된 금-은 광화작용이 진행되어 에렉트럼과 함께 황동석, 섬아연석 등의 황화광물과 미량의 함 은 황염광물 등이 산출되었다. 후기에는 황철석, 섬아연석, 방연석 등과 함께 적철석 등이 산출되었다. 광화 2시기는 주 광화작용 이후의 금속 광화작용이 이루어지지 않은 방해석맥의 생성 시기이다.
거창광상의 주된 광화작용은 고온(≥380℃)의 H2O-CO2-NaCl계 열수유체 유입으로 시작되어 초기의 냉각과 비등작용, 중기의 불혼화용융 및 후기의 상대적으로 천부를 순환한 열수유체 또는 천수의 혼입 등에 의하여 ≥380℃~≤210℃의 온도조건에서 7.0 to 0.7 wt. percent NaCl 상당 염농도를 갖는 유체에서 진행되었다. 거창광상의 광물 공생관계 변화는 이러한 열수계의 진화에 의한 온도와 황 분압 조건의 감소 등의 환경변화가 반영된 결과이다. 거창광상은 중열수형 금·은 광상에 대비된다.

주요어 거창광상, 금-은, 맥상광상, H2O-CO2-NaCl 열수계, 중열수

Article

Research Paper

Econ. Environ. Geol. 2022; 55(2): 171-181

Published online April 30, 2022 https://doi.org/10.9719/EEG.2022.55.2.171

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Au-Ag-bearing Ore Mineralization at the Geochang Hydrothermal Vein Deposit

Seok Jin Hong1, Sunjin Lee2, Sang-Hoon Choi2,*

1Intellegio, Seoul 08390, Korea
2Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju 28644, Korea

Correspondence to:*Corresponding author : cshoon@cbnu.ac.kr

Received: April 20, 2022; Revised: April 26, 2022; Accepted: April 26, 2022

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 original work is properly cited.

Abstract

The Geochang Au-Ag deposit is located within the Yeongnam Massif. Within the area a number of hydrothermal quartz and calcite veins were formed by narrow open-space filling of parallel and subparallel fractures in the granitic gneiss and/or gneissic granite. Mineral paragenesis can be divided into two stages (stage I, ore-bearing quartz vein; stage II, barren calcite vein) by major tectonic fracturing. 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, marked by deposition of pyrite with minor pyrrhotite and arsenopyrite; middle, characterized by introduction of electrum and base-metal sulfides with minor sulfosalts; late, marked by hematite with base-metal sulfides. Fluid inclusion data show that stage I ore mineralization was deposited between initial high temperatures (≥380°C) and later lower temperatures (≤210°C) from H2O-CO2-NaCl fluids with salinities between 7.0 to 0.7 equiv. wt. % NaCl of Geochang hydrothermal system. The relationship between salinity and homogenization temperature indicates a complex history of boiling, fluid unmixing (CO2 effervescence), cooling and dilution via influx of cooler, more dilute meteoric waters over the temperature range ≥380°C to ≤210°C. Changes in stage I vein mineralogy reflect decreasing temperature and fugacity of sulfur by evolution of the Geochang hydrothermal system with increasing paragenetic time. The Geochang deposit may represents a mesothermal gold-silver deposit.

Keywords Geochang deposit, Au-Ag, vein deposit, H2O-CO2-NaCl, mesothermal

거창 열수 맥상광상의 함 금-은 광화작용

홍석진1 · 이선진2 · 최상훈2,*

1(주) 인텔리지오
2충북대학교 지구환경과학과

Received: April 20, 2022; Revised: April 26, 2022; Accepted: April 26, 2022

요 약

거창광상은 영남육괴 화강암질 편마암 또는 편마암질 화강암 내에 발달한 열극을 충전하여 생성된 함 금-은 열수 맥상광상으로, 괴상 및 호상 조직과 함께 부분적인 각력상 조직 및 정동의 발달 등 복합적인 조직적 특성을 보여준다. 거창광상의 맥상 광화작용은 구조운동(tectonic break)에 의하여 광화 1시기와 광화 2시기로 구분된다. 광화 1시기는 석영맥의 생성과 함께 주된 함금·은 광물인 에렉트럼과 함께 황화광물 및 산화광물 등이 미량의 황염광물을 수반 산출한 시기로서, 공생관계와 광물조합 특성 등에 의하여 세 단계의 광화시기(초기, 중기, 후기)로 구분된다. 광화 1시기의 초기에는 주로 황철석, 자류철석, 유비철석 등이 산출되었다. 중기에는 주된 금-은 광화작용이 진행되어 에렉트럼과 함께 황동석, 섬아연석 등의 황화광물과 미량의 함 은 황염광물 등이 산출되었다. 후기에는 황철석, 섬아연석, 방연석 등과 함께 적철석 등이 산출되었다. 광화 2시기는 주 광화작용 이후의 금속 광화작용이 이루어지지 않은 방해석맥의 생성 시기이다.
거창광상의 주된 광화작용은 고온(≥380℃)의 H2O-CO2-NaCl계 열수유체 유입으로 시작되어 초기의 냉각과 비등작용, 중기의 불혼화용융 및 후기의 상대적으로 천부를 순환한 열수유체 또는 천수의 혼입 등에 의하여 ≥380℃~≤210℃의 온도조건에서 7.0 to 0.7 wt. percent NaCl 상당 염농도를 갖는 유체에서 진행되었다. 거창광상의 광물 공생관계 변화는 이러한 열수계의 진화에 의한 온도와 황 분압 조건의 감소 등의 환경변화가 반영된 결과이다. 거창광상은 중열수형 금·은 광상에 대비된다.

주요어 거창광상, 금-은, 맥상광상, H<sub>2</sub>O-CO<sub>2</sub>-NaCl 열수계, 중열수

    Fig 1.

    Figure 1.Geological map of the Geochang deposit area (left side; modified from Cheong et al., 2018) with simplified geologic map of Korea showing the location of the Geochang Au-Ag deposit (right side).
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 2.

    Figure 2.Photographs of the Au-Ag-bearing hydrothermal vein outcrops (A and B) and the products of hydrothermal mineralization (C) at Geochang Au-Ag deposit. Abbreviations: asp=arsenopyrite, c-r=country rock, gn=galena, py=pyrite, qtz-v=quartz vein, sl=sphalerite.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 3.

    Figure 3.Mineral paragenesis of the Geochang Au-Ag deposit.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 4.

    Figure 4.Photomicrographs of mineral occurrence and assemblages at the Geochang Au-Ag deposit. Abbreviations: apob=arsenopolybasite, asp=arsenopyrite, cp=chalcopyrite, el=electrum, gn=galena, pob=polybasite, py=pyrite, pyr=pyrrhotite, qtz=quartz, sl=sphalerite, ht=hematiite.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 5.

    Figure 5.Histogram of homogenization temperatures (Th) of fluid inclusions in vein quartz of the Geochang Au-Ag deposit. Abbreviations: Type I=type I fluid inclusion, Type II=type II fluid inclusion, Type IV=type IV fluid inclusion.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 6.

    Figure 6.Histogram of salinities of fluid inclusions in vein quartz of the Geochang Au-Ag deposit. Abbreviations: Type I=type I fluid inclusion, Type IV=type IV fluid inclusion.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 7.

    Figure 7.Homogenization temperature (Th) versus salinity diagram for type I and IV fluid inclusions in vein quartz of the Geochang Au-Ag deposit. Abbreviations: Type I=type I fluid inclusion, Type IV=type IV fluid inclusion.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Fig 8.

    Figure 8.Fugacity of Sulfur versus temperature diagram for stage I of the Geochang Au-Ag deposit showing the possible sulfur fugacity and temperature ranges with sulfidation reactions. Abbreviations: Arg=argentite, Asp=arsenopyrite, Hm=hematite, Mt=magnetite, NAg=atomic fraction Ag in electrum, Po=pyrrhotite, Py=pyrite.
    Economic and Environmental Geology 2022; 55: 171-181https://doi.org/10.9719/EEG.2022.55.2.171

    Table 1 . Chemical composition of arsenopyrite from the Geochang Au-Ag deposit.

    Sample no.Weight %Atomic %
    FeAsSTotalFeAsSTotal
    GC 34-4-135.241.022.798.933.329.137.6100.0
    GC 34-4-235.141.222.899.033.329.137.6100.0
    GC 34-4-336.040.223.199.333.728.437.9100.0
    GC 34-4-434.942.721.499.033.730.535.8100.0
    GC 34-4-535.940.522.999.333.728.437.9100.0
    GC 34-4-635.142.721.299.033.930.735.5100.0
    GC 35-5-135.439.523.898.733.227.939.0100.0
    GC 35-5-235.140.722.898.733.528.737.8100.0
    GC 35-5-335.541.522.299.234.029.336.7100.0
    GC 35-5-435.739.923.398.933.727.938.4100.0
    GC 35-5-535.540.823.099.333.728.437.9100.0

    Table 2 . Representative chemical composition of electrum from the Geochang Au-Ag deposit.

    Sample no.Weight %Atomic %Remark*
    AgAuTotalAgAuAg/Au
    GC 34-1-147.152.799.862.038.01.6Early
    GC 28-1-645.252.897.961.039.01.6Middle
    GC 28-1-1241.055.996.957.242.81.3
    GC 28-2-159.338.597.873.826.22.8
    GC 34-3-147.052.399.362.237.81.6
    GC 34-3-250.349.699.965.035.01.9
    GC 34-3-354.144.798.868.831.22.2
    GC 34-4-153.646.399.967.932.12.1Late
    GC 34-4-254.145.199.268.731.32.2
    GC 34-4-355.045.4100.468.931.12.2
    GC 34-5-448.951.7100.663.336.71.7
    GC 34-5-543.156.9100.058.141.91.4

    *Substages of stage I..


    Table 3 . Representative chemical composition of sphalerite from the Geochang Au-Ag deposit.

    Sample no.Weight %Mole %Remark*
    ZnFeCdCuSTotalZnSFeSCdS
    GC 34-5-152.510.40.43.633.2100.180.819.20.0Early
    GC 34-5-257.08.60.433.499.485.314.70.0
    GC 16-1-257.77.10.51.031.397.787.112.90.0Middle
    GC 29-2-354.15.90.55.531.697.589.310.80.0
    GC 34-3-361.05.90.531.498.889.410.60.0
    GC 34-3-461.25.90.631.599.288.710.40.9
    GC 34-3-561.15.70.631.098.489.49.61.0
    GC 12-165.31.70.631.198.796.22.91.0Late
    GC 12-263.63.00.630.497.794.24.91.0
    GC 12-364.02.50.730.998.095.23.91.0
    GC 28-167.20.70.431.299.599.01.00.0
    GC 28-265.31.10.531.298.298.02.00.0
    GC 28-361.03.10.63.431.899.894.95.10.0
    GC 28-468.70.50.431.8101.499.10.90.0
    GC 29-2-461.13.30.62.331.498.693.96.10.0
    GC 34-1-165.61.40.533.7101.297.12.90.0
    GC 34-1-265.70.80.533.0100.099.01.00.0
    GC 34-463.72.80.533.2100.195.14.90.0

    *Substages of stage I..


    KSEEG
    Dec 31, 2024 Vol.57 No.6, pp. 665~835

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