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Mineral Geochemistry of the Albite-Spodumene Pegmatite in the Boam Deposit, Uljin

울진 보암광산의 조장석-스포듀민 페그마타이트의 광물 지화학 조성 연구

  • Park, Gyuseung (School of Earth and Environmental Sciences, Seoul National University) ;
  • Park, Jung-Woo (School of Earth and Environmental Sciences, Seoul National University) ;
  • Heo, Chul-Ho (Critical Minerals Research Center, Korea Institute of Geoscience and Mineral Resources)
  • 박규승 (서울대학교 지구환경과학부) ;
  • 박정우 (서울대학교 지구환경과학부) ;
  • 허철호 (한국지질자원연구원 희소금속광상연구센터)
  • Received : 2022.09.01
  • Accepted : 2022.09.29
  • Published : 2022.09.30

Abstract

In this study, we investigated the mineral geochemistry of the albite-spodumene pegmatite, associated exogreisen, and wall rock from the Boam Li deposit, Wangpiri, Uljin, Gyeongsangbuk-do, South Korea. The paragenesis of the Boam Li deposit consists of two stages; the magmatic and endogreisen stages. In the magmatic stage, pegmatite dikes mainly composed of spodumene, albite, quartz, and K-feldspar intruded into the Janggun limestone formation. In the following endogreisen stage, the secondary fine-grained albite along with muscovite, apatite, beryl, CGM(columbite group mineral), microlite, and cassiterite were precipitated and partly replaced the magmatic stage minerals. Exogreisen composed of tourmaline, quartz, and muscovite develops along the contact between the pegmatite dike and wall rock. The Cs contents of beryl and muscovite and Ta/(Nb+Ta) ratio of CGM are higher in the endogreisen stage than the magmatic stage, suggesting the involvement of the more evolved melts in the greisenization than in the magmatic stage. Florine-rich and Cl-poor apatite infer that the parental magma is likely derived from metasedimentary rock (S-type granite). P2O5 contents of albite in the endogreisen stage are below the detection limit of EDS while those of albite in the magmatic stage are 0.28 wt.% on average. The lower P2O5 contents of the former albite can be attributed to apatite and microlite precipitation during the endogreisen stage. Calcium introduced from the adjacent Janggun formation may have induced apatite crystallization. The interaction between the pegmatite and Janggun limestone is consistent with the gradual increase in Ca and other divalent cations and decrease in Al from the core to the rim of tourmaline in the exogreisen.

본 연구에서는 경상북도 울진 왕피리에 소재한 보암 Li 광산의 조장석-스포듀민 페그마타이트와 그 주변에 형성된 외영운암(exogreisen)의 광물 지화학 조성을 EDS로 분석하고 그 의미를 고찰하였다. 보암 광산은 화성활동 단계와 영운암화 단계의 두 단계를 거쳐 형성되었다. 전자에서는 조립질 내지 중립질의 스포듀민, 조장석, 석영, K-장석으로 구성된 조장석-스포듀민 페그마타이트가 관입하였으며, 후자에서는 페그마타이트의 조장석화 및 영운암화 과정에서 세립의 조장석 및 이와 공생하는 백운모, 녹주석, 인회석, 컬럼바이트족 광물(CGM, columbite group mineral), 마이크롤라이트, 석석 등이 형성되며 화성활동 단계의 광물을 부분적으로 교대하였다. 이 과정에서 주변암인 장군석회암과 맥의 경계면에는 전기석, 석영, 백운모로 구성된 외영운암이 형성되었다. 광물 지구화학 분석 결과에 따르면 화성활동 단계 대비 영운암화 단계에서 녹주석과 백운모에 Cs 함량이 더 높고 CGM의 Ta/(Nb+Ta) 또한 더 높게 나타난다. 이 같은 사실은 영운암화에 관여한 용융체가 페그마타이트를 형성한 용융체에 비하여 더 많은 분화 과정을 거쳤음을 지시한다. 영운암화 단계에서 형성된 인회석의 조성은 Cl이 결핍되고 F가 부화되어 있어 보암 광산이 S형 화강암 기원의 Li-Cs-Ta(LCT) 페그마타이트에 해당하는 특성을 지닌다. 화성활동 단계에 형성된 중립질의 조장석은 평균 0.28 wt.%의 P2O5를 갖는데 비해 영운암화 단계에 형성된 세립질의 조장석은 EDS 검출한계 미만의 P2O5를 지닌다. 영운암화 단계에 형성되는 인회석과 마이크롤라이트는 화성활동 단계 대비 Ca가 부화되었음을 지시한다. 따라서, 조장석 내 P의 결핍은 용융체에 있던 P가 주변암으로부터 Ca가 공급됨에 따라 인회석의 형태로 소진되어 결핍된 결과로 해석할 수 있다. 외영운암의 전기석은 중심에서 외곽으로 갈수록 Ca를 비롯한 2가 양이온의 함량이 증가하고 그에 따라 Al의 함량이 감소하는 화학적 누대구조를 보인다. 이는 영운암화 단계에서 장군석회암으로부터 용융체에 Ca가 점차 공급되었다는 가설에 부합한다.

Keywords

Acknowledgement

본 연구는 한국지질자원연구원에서 수행하는 주요 사업 '국내 바나듐(V) 등 에너지 저장광물 정밀탐사기술 개발 및 부존량 예측(GP2022-008)'의 지원을 받아 수행하였으며 이에 감사드립니다. 지질 조사 및 시료 채취를 도와주시고 연구에 관해 조언해 주신 오일환 박사님께 감사드립니다. 연구 진행 전반에 걸쳐 많은 도움을 준 서울대학교 지구환경과학부 해양암석지구화학 연구실 학생 여러분께 감사드립니다. 마지막으로 논문의 심사를 맡아주시고 유익한 조언을 주신 익명의 심사위원분들께 감사드립니다.

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