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Skarn Evolution and Fe-(Cu) Mineralization at the Pocheon Deposit, Korea

한국 포천 광상의 스카른 진화과정 및 철(-동)광화작용

  • Go, Ji-Su (Dept. of Earth & Environmental Sciences, Korea University) ;
  • Choi, Seon-Gyu (Dept. of Earth & Environmental Sciences, Korea University) ;
  • Kim, Chang Seong (Dept. of Earth & Environmental Sciences, Korea University) ;
  • Kim, Jong Wook (Dept. of Earth & Environmental Sciences, Korea University) ;
  • Seo, Jieun (Dept. of Earth & Environmental Sciences, Korea University)
  • 고지수 (고려대학교 지구환경과학과) ;
  • 최선규 (고려대학교 지구환경과학과) ;
  • 김창성 (고려대학교 지구환경과학과) ;
  • 김종욱 (고려대학교 지구환경과학과) ;
  • 서지은 (고려대학교 지구환경과학과)
  • Received : 2014.06.29
  • Accepted : 2014.08.28
  • Published : 2014.08.28

Abstract

The Pocheon skarn deposit, located at the northwestern part of the Precambrian Gyeonggi massif in South Korea, occurs at the contact between the Cretaceous Myeongseongsan granite and the Precambrian carbonate rocks, and is also controlled by N-S-trending shear zone. The skarn distribution and mineralogy reflects both structural and lithological controls. Three types of skarn formations based on mineral assemblages in the Pocheon skarn exist; a sodiccalcic skarn and a magnesian skarn mainly developed in the dolostone, and a calcic skarn developed in the limestone. Iron mineralization occurs in the sodic-calcic and magnesian skarn zone, locally superimposed by copper mineralization during retrograde skarn stage. The sodic-calcic skarn is composed of acmite, diopside, albite, garnet, magnetite, maghemite, anhydrite, apatite, and sphene. Retrograde alteration consists of tremolite, phlogopite, epidote, sericite, gypum, chlorite, quartz, calcite, and sulfides. Magnesian skarn mainly consists of diopside and forsterite. Pyroxene and olivine are mainly altered to tremolite, with minor phlogopite, talc, and serpentine. The calcic skarn during prograde stage mainly consists of garnet, pyroxene and wollastonite. Retrograde alteration consists of epidote, vesuvianite, amphibole, biotite, magnetite, chlorite, quartz, calcite, and sulfides. Microprobe analyses indicate that the majority of the Pocheon skarn minerals are enriched by Na-Mg composition and have high $Fe^{3+}/Fe^{2+}$, $Mg^{2+}/Fe^{2+}$, and $Al^{3+}/Fe^{2+}$ ratios. Clinopyroxene is acmitic and diopsidic composition, whereas garnet is relatively grossular-rich. Amphiboles are largely of tremolite, pargasite, and magnesian hastingsite composition. The prograde anhydrous skarn assemblages formed at about $400^{\circ}{\sim}500^{\circ}C$ in a highly oxidized environment ($fO_2=10^{-23}{\sim}10^{-26}$) under a condition of about 0.5 kbar pressure and $X(CO_2)=0.10$. With increasing fluid/rock interaction during retrograde skarn, epidote, amphibole, sulfides and calcite formed as temperature decreased to approximately $250^{\circ}{\sim}400^{\circ}C$ at $X(CO_2)=0.10$.

Keywords

Pocheon;skarnification;sodic-calcic;magnesian(Mg);calcic;ore-forming environment;Na-Ca;Ca

Acknowledgement

Supported by : 연구재단

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