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Econ. Environ. Geol. 2022; 55(1): 53-61

Published online February 28, 2022

https://doi.org/10.9719/EEG.2022.55.1.53

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Genetic Environments of Au-Ag-bearing Gasado Hydrothermal Vein Deposit

Youngjin Ko1, Chang Seong Kim2, Sang-Hoon Choi3,*

1Korea Mine Rehabilitation and Mineral Resources Corp., Wonju, 26464, Korea
2PrimoResource Ltd., Goyang, 10564, Korea
3Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju, 28644, Korea

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

Received: February 19, 2022; Revised: February 23, 2022; Accepted: February 23, 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 Gasado Au-Ag deposit is located within the south-western margin of the Hanam-Jindo basin. The geology of the Gasado is composed of the late Cretaceous volcaniclastic sedimentary rocks and acidic or intermediate igneous rocks. Within the deposit area, there are a number of hydrothermal quartz and calcite veins, formed by narrow open space filling along subparallel fractures in the late Cretaceous volcaniclastic sedimentary rock. Vein mineralization at the Gasado is characterized by several textural varieties such as chalcedony, drusy, comb, bladed, crustiform and colloform. The textures have been used as exploring indicators of the epithermal deposit. Mineral paragenesis can be divided into two stages (stage I, ore-bearing quartz veins; stage II, barren carbonate veins) considering major tectonic fracturing event. Stage I, at which the precipitation of Au-Ag bearing 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 and pyrrhotite with minor chalcopyrite, sphalerite and electrum; middle, characterized by introduction of electrum and base-metal sulfides with minor argentite; late, marked by argentite and native silver.
Au-Ag-bearing mineralization at the Gasado deposit occurred under the condition between initial high temperatures (≥290°C) and later lower temperatures (≤130°C). Changes in stage I vein mineralogy reflect decreasing temperature and fugacity of sulfur (≈10-10.1 to ≤10-18.5atm) by evolution of the Gasado hydrothermal system with increasing paragenetic time. The Gasado deposit may represents an epithermal gold-silver deposit which was formed near paleo-surface.

Keywords Gasado, Au-Ag, electrum, epithermal, vein deposit

함 금-은 가사도 열수 맥상광상의 성인

고영진1 · 김창성2 · 최상훈3,*

1한국광해광업공단
2프리모리소스
3충북대학교 지구환경과학과

요 약

가사도광상은 옥천대 남서부 해남-진도분지의 남서익부에 위치하며 백악기 후기 유천층군에 대비되는 화산쇄설성 퇴적암류 내에 발달한 열극을 충진하여 생성된 함 금-은 열수 맥상광상으로, 각력상 및 정동조직과 함께 부분적인 미정질조직, 빗살조직, 블레디드조직, 호상조직, 칼세도니조직 및 콜로폼조직 등 천열수광상의 조직 특성을 보여준다. 가사도광상의 맥상 광화작용은 구조운동에 의하여 광화 I기와 광화 II기로 구분된다. 광화 I기는 금-은 광화작용이 진행된 주 광화시기로, 석영맥 내에 주된 함금-은 광물인 에렉트럼과 함께 황화광물 및 함 은 광물 등이 산출한다. 광화 II기는 주 광화작용 이후 금속 광화작용이 이루어지지 않은 방해석맥의 생성 시기이다. 광화 I기는 광물의 공생관계와 산출하는 광물 조합 특성 등에 의하여 3개의 세부 광화시기(초기, 중기, 후기)로 구분된다. 광화 I기의 초기에는 황철석, 자류철석의 산출로 시작되어 소량의 황동석, 섬아연석 및 에렉트럼을 수반하여 산출한다. 광화 I기 중기는 주된 금·은 광화작용이 광화 I기의 초기 말부터 계속하여 진행된 시기이다. 주로 에렉트럼과 함께 황동석, 섬아연석, 방연석 등이 함 은 광물인 휘은석 등을 수반하여 산출한다. 광화 I기 후기는 휘은석과 자연은의 주된 생성 시기이다.
가사도광상 함 금-은 광화작용은 약 290∼≤130°C의 온도 조건에서 열수계의 냉각작용에 의해 진행되었으며, 이때의 황 분압조건은 ≈10-10.1∼≤10-18.5atm이었다. 함 금-은 가사도광상은 광상·광물학적 특성, 지화학적 환경변화 및 광화작용의 온도 조건 등으로 미루어 천부 환경에서 생성된 천열수 맥상광상이다.

주요어 가사도, 금-은, 에렉트럼, 천열수, 맥상광상

Article

Research Paper

Econ. Environ. Geol. 2022; 55(1): 53-61

Published online February 28, 2022 https://doi.org/10.9719/EEG.2022.55.1.53

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Genetic Environments of Au-Ag-bearing Gasado Hydrothermal Vein Deposit

Youngjin Ko1, Chang Seong Kim2, Sang-Hoon Choi3,*

1Korea Mine Rehabilitation and Mineral Resources Corp., Wonju, 26464, Korea
2PrimoResource Ltd., Goyang, 10564, Korea
3Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju, 28644, Korea

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

Received: February 19, 2022; Revised: February 23, 2022; Accepted: February 23, 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 Gasado Au-Ag deposit is located within the south-western margin of the Hanam-Jindo basin. The geology of the Gasado is composed of the late Cretaceous volcaniclastic sedimentary rocks and acidic or intermediate igneous rocks. Within the deposit area, there are a number of hydrothermal quartz and calcite veins, formed by narrow open space filling along subparallel fractures in the late Cretaceous volcaniclastic sedimentary rock. Vein mineralization at the Gasado is characterized by several textural varieties such as chalcedony, drusy, comb, bladed, crustiform and colloform. The textures have been used as exploring indicators of the epithermal deposit. Mineral paragenesis can be divided into two stages (stage I, ore-bearing quartz veins; stage II, barren carbonate veins) considering major tectonic fracturing event. Stage I, at which the precipitation of Au-Ag bearing 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 and pyrrhotite with minor chalcopyrite, sphalerite and electrum; middle, characterized by introduction of electrum and base-metal sulfides with minor argentite; late, marked by argentite and native silver.
Au-Ag-bearing mineralization at the Gasado deposit occurred under the condition between initial high temperatures (≥290°C) and later lower temperatures (≤130°C). Changes in stage I vein mineralogy reflect decreasing temperature and fugacity of sulfur (≈10-10.1 to ≤10-18.5atm) by evolution of the Gasado hydrothermal system with increasing paragenetic time. The Gasado deposit may represents an epithermal gold-silver deposit which was formed near paleo-surface.

Keywords Gasado, Au-Ag, electrum, epithermal, vein deposit

함 금-은 가사도 열수 맥상광상의 성인

고영진1 · 김창성2 · 최상훈3,*

1한국광해광업공단
2프리모리소스
3충북대학교 지구환경과학과

Received: February 19, 2022; Revised: February 23, 2022; Accepted: February 23, 2022

요 약

가사도광상은 옥천대 남서부 해남-진도분지의 남서익부에 위치하며 백악기 후기 유천층군에 대비되는 화산쇄설성 퇴적암류 내에 발달한 열극을 충진하여 생성된 함 금-은 열수 맥상광상으로, 각력상 및 정동조직과 함께 부분적인 미정질조직, 빗살조직, 블레디드조직, 호상조직, 칼세도니조직 및 콜로폼조직 등 천열수광상의 조직 특성을 보여준다. 가사도광상의 맥상 광화작용은 구조운동에 의하여 광화 I기와 광화 II기로 구분된다. 광화 I기는 금-은 광화작용이 진행된 주 광화시기로, 석영맥 내에 주된 함금-은 광물인 에렉트럼과 함께 황화광물 및 함 은 광물 등이 산출한다. 광화 II기는 주 광화작용 이후 금속 광화작용이 이루어지지 않은 방해석맥의 생성 시기이다. 광화 I기는 광물의 공생관계와 산출하는 광물 조합 특성 등에 의하여 3개의 세부 광화시기(초기, 중기, 후기)로 구분된다. 광화 I기의 초기에는 황철석, 자류철석의 산출로 시작되어 소량의 황동석, 섬아연석 및 에렉트럼을 수반하여 산출한다. 광화 I기 중기는 주된 금·은 광화작용이 광화 I기의 초기 말부터 계속하여 진행된 시기이다. 주로 에렉트럼과 함께 황동석, 섬아연석, 방연석 등이 함 은 광물인 휘은석 등을 수반하여 산출한다. 광화 I기 후기는 휘은석과 자연은의 주된 생성 시기이다.
가사도광상 함 금-은 광화작용은 약 290∼≤130°C의 온도 조건에서 열수계의 냉각작용에 의해 진행되었으며, 이때의 황 분압조건은 ≈10-10.1∼≤10-18.5atm이었다. 함 금-은 가사도광상은 광상·광물학적 특성, 지화학적 환경변화 및 광화작용의 온도 조건 등으로 미루어 천부 환경에서 생성된 천열수 맥상광상이다.

주요어 가사도, 금-은, 에렉트럼, 천열수, 맥상광상

    Fig 1.

    Figure 1.Geologic map of the Gasado deposit area (left side; modified from Kim, 2016) with simplified geologic map of Korea showing the location of the Gasado Au-Ag deposit (right side). Beach 1, 2 and 3 represent the location of Beach No. 1, Beach No. 2 and Beach No. 3 vein, respectively.
    Economic and Environmental Geology 2022; 55: 53-61https://doi.org/10.9719/EEG.2022.55.1.53

    Fig 2.

    Figure 2.Photographs of the Au-Ag bearing hydrothermal simple vein outcrops (A) and branching or anastomosing vein (B) at the Gasado deposit.
    Economic and Environmental Geology 2022; 55: 53-61https://doi.org/10.9719/EEG.2022.55.1.53

    Fig 3.

    Figure 3.Photographs of the products of hydrothermal mineralization at the Gasado Au-Ag deposit. Scale bar represents 1cm. A: colloform and chalcedony texture, B: chalcedony texture, C: drusy texture. Abbreviations: py=pyrite, py+sl+gn=pyrite+sphalerite+galena, qtz=quartz.
    Economic and Environmental Geology 2022; 55: 53-61https://doi.org/10.9719/EEG.2022.55.1.53

    Fig 4.

    Figure 4.Vein mineral paragenesis of the Gasado Au-Ag deposit.
    Economic and Environmental Geology 2022; 55: 53-61https://doi.org/10.9719/EEG.2022.55.1.53

    Fig 5.

    Figure 5.Photomicrographs of mineral occurrence and assemblages at the Gasado Au-Ag deposit. For descriptions of each photograph, refer to the text. Scale bar represents 20μm. Abbreviations: Arg=argentite, Cp=chalcopyrite, El=electrum, Native Ag=native silver, Po=pyrrhotite, Py=pyrite, Sl=sphalerite, Uy=Uytenbogaardtite.
    Economic and Environmental Geology 2022; 55: 53-61https://doi.org/10.9719/EEG.2022.55.1.53

    Fig 6.

    Figure 6.Sulfur fugacity versus temperature diagram for Au-Ag mineralization of stage I at the Gasado Au-Ag deposit with sulfidation reactions. Abbreviations: Ag=native silver, arg=argentite, py=pyrite, po=pyrrhotite.
    Economic and Environmental Geology 2022; 55: 53-61https://doi.org/10.9719/EEG.2022.55.1.53

    Table 1 . Representative chemical composition of electrum from the Gasado Au-Ag deposit.

    Sample no.Weight %Atomic %Remarks*
    AuAgSTotalAuAgAg/Au
    GSD-151-6-152.9045.830.0098.738.761.31.58Early
    GSD-151-7-148.5049.330.0097.835.065.01.86Early
    GSD-151-7-241.8854.900.0096.829.570.52.39Early
    GSD-151-8-158.7339.610.0098.344.855.21.23Early
    GSD-151-8-354.5243.790.0098.340.559.51.47Early
    GSD-152-4-255.6243.090.0098.741.458.61.41Early
    GSD-152-7-152.5845.910.0098.538.561.51.59Early
    GSD-152-7-250.5847.840.4598.936.763.31.73Early
    GSD-182-2-131.0267.970.5399.520.080.04.00Middle
    GSD-182-5-136.5661.700.9299.224.575.53.08Middle
    GSD-192-1-148.6351.370.00100.034.165.91.93Early
    GSD-193-1-248.0550.480.0098.534.365.71.92Early
    GSD-193-2-123.1575.590.7199.414.485.65.96Middle
    GSD-193-2-239.3158.451.1198.926.973.12.72Middle
    GSD-193-2-441.9357.570.0099.528.571.52.51Middle
    GSD-193-2-543.6154.650.0098.330.469.62.29Middle
    GSD-193-3-128.9070.140.0099.018.481.64.43Middle
    GSD-193-4-333.6366.370.00100.021.778.33.60Middle
    GSD-193-441.3156.021.4698.828.871.22.48Middle
    GSD-193-537.4862.280.0099.824.875.23.03Middle
    GSD-193-8-136.7762.310.0099.124.475.63.09Middle
    GSD-251-1-143.2955.290.0098.630.070.02.33Early
    GSD-251-2-161.8637.180.0099.047.752.31.10Early
    GSD-251-2-255.7542.910.0098.741.658.41.41Early
    GSD-251-4-164.4134.470.0098.950.649.40.98Early
    GSD-251-5-153.5844.660.0098.239.760.31.52Early
    GSD-251-5-263.8034.460.0098.350.349.70.99Early
    GSD-252-1-151.9146.970.0098.937.762.31.65Early
    GSD-252-2-162.3136.510.0098.848.351.71.07Early
    GSD-252-3-164.4334.800.0099.250.349.70.99Early
    GSD-252-4-143.0955.340.0098.429.970.12.35Early
    GSD-253-1-133.3764.930.0098.322.078.03.55Middle
    GSD-253-1-543.9354.350.0098.330.769.32.26Middle
    GSD-253-2-143.7255.650.0099.430.169.92.32Middle
    GSD-253-3-136.3462.010.0098.424.375.73.12Middle

    *Substages of stage I..


    Table 2 . Representative chemical composition of sphalerite from the Gasado Au-Ag deposit.

    Sample No.Weight %Mole %Remark*
    ZnFeMnSTotalZnSFeS
    GSD-151-1-165.90.90.033.2100.098.41.6Middle
    GSD-151-1-263.91.10.034.499.498.02.0Middle
    GSD-151-1-363.11.50.034.599.297.22.8Middle
    GSD-151-5-262.52.00.035.5100.096.53.5Early
    GSD-151-6-262.82.00.035.2100.096.33.7Early
    GSD-151-7-363.60.70.034.999.298.81.2Middle
    GSD-151-7-662.01.00.037.0100.098.11.9Middle
    GSD-151-7-764.10.80.035.1100.098.51.5Middle
    GSD-151-8-262.62.20.034.599.396.04.0Early
    GSD-151-8-462.62.00.034.298.896.53.5Early
    GSD-151-9-164.41.20.034.4100.097.82.2Middle
    GSD-152-4-164.30.60.035.1100.098.81.2Middle
    GSD-192-3-261.71.50.035.598.797.32.7Middle
    GSD-193-1-464.60.90.033.999.398.51.5Middle
    GSD-193-4-464.90.40.433.699.498.50.7Middle
    GSD-193-8-263.52.60.033.9100.095.54.5Early
    GSD-252-5-262.12.40.734.8100.094.64.2Early
    GSD-253-1-260.63.90.035.5100.093.07.0Early
    GSD-253-1-362.53.90.033.5100.093.16.9Early
    GSD-253-2-261.73.60.034.7100.093.66.4Early
    GSD-271-1-257.12.00.040.9100.096.13.9Early

    *Substages of stage I..


    KSEEG
    Jun 30, 2024 Vol.57 No.3, pp. 281~352

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