Econ. Environ. Geol. 2002; 35(3): 211-220

Published online June 30, 2002

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Alteration and Mineralization in the Xiaoxinancha Porphyry Copper Deposit, Yianbin, China: Fluid Inclusion and Sulfur Isotope Study

Chil-Sup So1, Bai-Lu Jin2, Seong-Taek Yun1*, Chul-Ho Heo1, Seung-Jun Youm1

1Department of Earth and Environmental Sciences, Korea Universituy, Seoul 136-701, Korea
2Geological Survey #6, Bureau of Geology and Mineral Resources of Jilin Province, China

Correspondence to :

Seong-Taek Yun

styun@mail.korea.ac.kr

Received: April 6, 2002; Accepted: June 14, 2002

Abstract

The Xiaoxinancha Cu-Au deposit in the Jilin province, located in NNE 800 km of Beijing, is hosted by diorite. The ore mineralization of Xiaoxinancha Cu-Au deposit show a stockwork occurrence that is concentrated on the potassic and phyllic alteration zones. The Xiaoxinancha Cu-Au deposit in the south is being mined with its reserves grading 0.8% Cu, 3.64 g/t Au and 16.8 g/t Ag and in the north, grading 0.63% Cu, 3.80 g/t Au and 6.8 g/t Ag. The alteration assemblage occurs as a supergene blanket over deposit. Hydrothermal alteration at the Xiaoxinancha Cu-Au deposit is centered about the stock and was extensively related to the emplacement of the stock. Early hydrothermal alteration was dominantly potassic and followed by propylitic alteration. Chalcocite, often associated with hematite, account for the ore-grade copper, while chalcopyrite, bornite, quartz, epidote, chlorite and calcite constitute the typical gangue assemblage. Other minor opaque phases include pyrite, marcasite, native gold, electrum, hessite, hedleyite, volynskite, galenobismutite, covellite and goethite. Fluid inclusion data indicate that the formation of this porphyry copper deposit is thought to be a result of
cooling followed by mixing with dilute and cooler meteoric water with time. In stage II vein, early boiling occurred at 497oC was succeeded by the occurrence of halite-bearing type III fluid inclusion with homogenization temperature as much as 100oC lower. The salinities of type III fluid inclusion in stage II vein are 54.3 to 66.9 wt.% NaCl + KCl equiv. at 383o to 495oC, indicating the formation depth less than 1 km. Type I cupriferous fluids in stage III vein have the homogenization temperatures and salinity of 168o to 365oC and 1.1 to 9.0 wt.% NaCl equiv. These fluid inclusions in stage III veins were trapped in quartz veins containing highly fractured breccia, indicating the predominance of boiling evidence. This corresponds to hydrostatic pressure of 50 to 80 bars. The d34S value of sulfide minerals increase slightly with paragenetic time and yield calculated d34SH2S values of 0.8 to 3.7‰. There is no mineralogical evidence that fugacity of oxygen decreased, and it is thought that the oxygen fugacity of the mineralizing fluids have been buffered through reaction with magnetite. We interpreted the range of the calculated d34SH2S values for sulfides to represent the incorporation of sulfur
from two sources into the Xiaoxinancha Cu-Au hydrothermal fluids: (1) an isotopically light source with a d34S value of 1 to 2‰, probably a Mesozoic granitoid related to the ore mineralization. We can infer from the fact that diorite as the host rock in the Xiaoxinancha Cu-Au deposit area intruded plagiogranite; (2) an isotopically heavier source with a d34S value of > 4.0‰, probably the local porphyry.

Keywords alteration, ore mineralization, porphyry copper, fluid inclusion, sulfur isotope

Article

Econ. Environ. Geol. 2002; 35(3): 211-220

Published online June 30, 2002

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Alteration and Mineralization in the Xiaoxinancha Porphyry Copper Deposit, Yianbin, China: Fluid Inclusion and Sulfur Isotope Study

Chil-Sup So1, Bai-Lu Jin2, Seong-Taek Yun1*, Chul-Ho Heo1, Seung-Jun Youm1

1Department of Earth and Environmental Sciences, Korea Universituy, Seoul 136-701, Korea
2Geological Survey #6, Bureau of Geology and Mineral Resources of Jilin Province, China

Correspondence to:

Seong-Taek Yun

styun@mail.korea.ac.kr

Received: April 6, 2002; Accepted: June 14, 2002

Abstract

The Xiaoxinancha Cu-Au deposit in the Jilin province, located in NNE 800 km of Beijing, is hosted by diorite. The ore mineralization of Xiaoxinancha Cu-Au deposit show a stockwork occurrence that is concentrated on the potassic and phyllic alteration zones. The Xiaoxinancha Cu-Au deposit in the south is being mined with its reserves grading 0.8% Cu, 3.64 g/t Au and 16.8 g/t Ag and in the north, grading 0.63% Cu, 3.80 g/t Au and 6.8 g/t Ag. The alteration assemblage occurs as a supergene blanket over deposit. Hydrothermal alteration at the Xiaoxinancha Cu-Au deposit is centered about the stock and was extensively related to the emplacement of the stock. Early hydrothermal alteration was dominantly potassic and followed by propylitic alteration. Chalcocite, often associated with hematite, account for the ore-grade copper, while chalcopyrite, bornite, quartz, epidote, chlorite and calcite constitute the typical gangue assemblage. Other minor opaque phases include pyrite, marcasite, native gold, electrum, hessite, hedleyite, volynskite, galenobismutite, covellite and goethite. Fluid inclusion data indicate that the formation of this porphyry copper deposit is thought to be a result of
cooling followed by mixing with dilute and cooler meteoric water with time. In stage II vein, early boiling occurred at 497oC was succeeded by the occurrence of halite-bearing type III fluid inclusion with homogenization temperature as much as 100oC lower. The salinities of type III fluid inclusion in stage II vein are 54.3 to 66.9 wt.% NaCl + KCl equiv. at 383o to 495oC, indicating the formation depth less than 1 km. Type I cupriferous fluids in stage III vein have the homogenization temperatures and salinity of 168o to 365oC and 1.1 to 9.0 wt.% NaCl equiv. These fluid inclusions in stage III veins were trapped in quartz veins containing highly fractured breccia, indicating the predominance of boiling evidence. This corresponds to hydrostatic pressure of 50 to 80 bars. The d34S value of sulfide minerals increase slightly with paragenetic time and yield calculated d34SH2S values of 0.8 to 3.7‰. There is no mineralogical evidence that fugacity of oxygen decreased, and it is thought that the oxygen fugacity of the mineralizing fluids have been buffered through reaction with magnetite. We interpreted the range of the calculated d34SH2S values for sulfides to represent the incorporation of sulfur
from two sources into the Xiaoxinancha Cu-Au hydrothermal fluids: (1) an isotopically light source with a d34S value of 1 to 2‰, probably a Mesozoic granitoid related to the ore mineralization. We can infer from the fact that diorite as the host rock in the Xiaoxinancha Cu-Au deposit area intruded plagiogranite; (2) an isotopically heavier source with a d34S value of > 4.0‰, probably the local porphyry.

Keywords alteration, ore mineralization, porphyry copper, fluid inclusion, sulfur isotope

    KSEEG
    Apr 30, 2024 Vol.57 No.2, pp. 107~280

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