Stable Isotope and Fluid Inclusion Studies of the Daebong Gold-silver Deposit, Republic of Korea

대봉 금-은광상에 대한 유체포유물 및 안정동위원소 연구

  • 유봉철 (충남대학교 자연과학대학 지질환경과학과) ;
  • 이현구 (충남대학교 자연과학대학 지질환경과학과) ;
  • 김상중 (충남대학교 자연과학대학 지질환경과학과)
  • Published : 2003.12.01

Abstract

The Daebong gold-silver deposit consists of mesothermal massive quartz veins thar are filling the fractures along fault shear (NE, NW) Bones within banded or granitic gneiss of Precambrian Gyeonggi massif. Based on vein mineralogy, ore textures and paragenesis, ore mineralization of this deposits is composed of massive white quartz vein(stage I) which was formed in the same stage by multiple episodes of fracturing and healing, and transparent quartz vein(stage II) which is separated by a major faulting event. Stage I is divided into the 3 substages. Ore minerals of each substages are as follows: 1) early stage I=magnetite, pyrrhotite, arsenopyrite, pyrite, sphalerite, chalcopyrite, 2) middle stage I=pyrrhotite, arsenopyrite, pyrite, marcasite, sphalerite, chalcopyrite, galena, electrum and 3) late stage I=pyrite, sphalerite, chalcopyrite, galena, electrum, argentite, respectively. Ore minerals of the stage II are composed of pyrite, sphalerite, chalcopyrite, galena and electrum. Systematic studies (petrography and microthermometry) of fluid inclusions in stage I and II quartz veins show fluids from contrasting physical-chemical conditions: 1) $H_2O-CO_2-CH_4-NaCl{\pm}N-2$ fluid(early stage I=homogenization temperature: 203∼3$88^{\circ}C$, pressure: 1082∼2092 bar, salinity: 0.6∼13.4 wt.%, middle stage I=homogenization temperature: 215∼28$0^{\circ}C$, salinity: 0.2∼2.8 wt.%) related to the stage I sulfide deposition, 2) $H_2O-NaCl{\pm}CO_2$ fluid (late stage I=homogenization temperature: 205∼2$88^{\circ}C$, pressure: 670 bar, salinity: 4.5∼6.7 wt.%, stage II=homogenization temperature: 201-3$58^{\circ}C$, salinity: 0.4-4.2 wt.%) related to the late stage I and II sulfide deposition. $H_2O-CO_2-CH_4-NaCl{\pm}N_2$ fluid of early stage I is evolved to $H_2O-NaCl{\pm}CO_2$ fluid represented by the $CO_2$ unmixing due to decrease in fluid pressure and is diluted and cooled by the mixing of deep circulated meteoric waters ($H_2O$-NaCl fluid) possibly related to uplift and unloading of the mineralizing suites. $H_2O-NaCl{\pm}CO_2$ fluid of stage II was hotter than that of late stage I and occurred partly unmixing, mainly dilution and cooling for sulfide deposition. Calculated sulfur isotope compositions ({\gamma}^{34}S_{H2S}$) of hydrothermal fluids (3.5∼7.9%o) indicate that ore sulfur was derived from mainly an igneous source and partly sulfur of host rock. Measured and calculated oxygen and hydrogen isotope compositions ({\gamma}^{18}O_{H_2O}$, {\gamma}$D) of ore fluids (stage I: 1.1∼9.0$\textperthousand$, -92∼-86{\textperthansand}$, stage II: 0.3{\textperthansand}$, -93{\textperthansand}$) and ribbon-banded structure (graphitic lamination) indicate that mesothermal auriferous fluids of Daebong deposit were two different origin and their evolution. 1) Fluids of this deposit were likely mixtures of $H_2O$-rich, isotopically less evolved meteoric water and magmatic fluids and 2) were likely mixtures of $H_2O$-rich. isotopically heavier $\delta$D meteoric water and magmaticmetamorphic fluids.

Keywords

Daebong gold-silver deposit;Ore mineralization;Fluid inclusion;Isotope

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