Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Rock-magnetic Properties of Chimneys from TA25 Seamount in the Tofua Arc, Southwest Pacific

통가 EEZ내 TA25 해저산에서 채취한 열수광체의 암석자기학적 특성 연구

  • Kim, Wonnyon (Deep-sea & Seabed Resources Research Division, Korea Institute of Ocean Science & Technology) ;
  • Pak, Sang Joon (Deep-sea & Seabed Resources Research Division, Korea Institute of Ocean Science & Technology) ;
  • Lee, Kyeong Yong (Deep-sea & Seabed Resources Research Division, Korea Institute of Ocean Science & Technology) ;
  • Moon, Jai-Woon (Deep-sea & Seabed Resources Research Division, Korea Institute of Ocean Science & Technology) ;
  • Kim, Hyun Sub (Deep-sea & Seabed Resources Research Division, Korea Institute of Ocean Science & Technology) ;
  • Choi, Sun Ki (Deep-sea & Seabed Resources Research Division, Korea Institute of Ocean Science & Technology)
  • 김원년 (한국해양과학기술원 심해저자원연구부) ;
  • 박상준 (한국해양과학기술원 심해저자원연구부) ;
  • 이경용 (한국해양과학기술원 심해저자원연구부) ;
  • 문재운 (한국해양과학기술원 심해저자원연구부) ;
  • 김현섭 (한국해양과학기술원 심해저자원연구부) ;
  • 최선기 (한국해양과학기술원 심해저자원연구부)
  • Received : 2013.03.11
  • Accepted : 2013.05.29
  • Published : 2013.06.28
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Abstract

To identify rock-magnetic properties of volcanogenic hydrothermal sulfide deposits, chimneys were obtained from the Tofua Arc in Southwest Pacific, using a remotely operated vehicle (ROV) and Grab with AV cameras (GTVs). Three different types of chimneys used in this study are a high-temperature chimney with venting fluid-temperature of about $200^{\circ}C$ (ROV01), a low-temperature chimney of about $80^{\circ}C$ (GTV01), and an inactive chimney (ROV02). Magnetic properties of ROV01 are dominated by pyrrhotite, except for the outermost that experienced severe oxidation. Concentration and grain-size of ROV01 pyrrhotite are relatively low and fine. For GTV01, both magnetic concentration and grain-size increase from interior to margin. Pyrrhotite, dominant in the core, becomes mixed with hematite in the rim of the chimney due to secondary oxidation. High concentration and large grain-size of magnetic minerals characterize the ROV02. Dominant magnetic phases are pyrrhotite, hematite and goethite. In particular, the outermost rim shows a presence of magnetite produced by magnetotactic bacterial activity. Such distinctive contrast in magnetic concentration, grain-size and mineralogy among three different types of chimney enables the rock-magnetic study to characterize an evolution of hydrothermal deposits.

2012년 통가해저열수광상 개발 사업의 일환으로 통가아크 해저산 TA25에서 ROV와 GTV를 이용하여 열수황화물광체를 채취하였다. 채취된 광체 중 본 연구에서는 약 $200^{\circ}C$의 열수분출을 보인 고온성 활성침니(ROV01), $80^{\circ}C$의 열수분출을 보인 저온성 활성침니(GTV01), 그리고 비활성침니(ROV02)를 이용하여, 암석자기학적 특성을 규명하고 이를 바탕으로 광체의 진화과정을 알아보고자 하였다. ROV01의 자기적 특성은 주로 자류철석에 의해 나타나며, GTV01의 경우 광체내부는 자류철석이 주로 나타나지만 외곽으로 갈수록 자류철석과 적철석이 혼재하게 된다. 비활성침니인 ROV02는 오랜 산화작용으로 인해 외곽에서 적철석뿐만 아니라 침철석이 자류철석과 함께 나타나고, 최외곽에서는 magnetotactic bacteria의 작용에 의해 자철석이 존재한다. 포화잔류자화(saturation magnetic remanent magnetization, SIRM), 비자기이력잔류자화(anhysteretic remanent magnetization, ARM)/SIRM으로 나타낸 자성광물의 함량과 입자크기 변화는 침니의 특성에 따라 뚜렷한 차이가 난다. 고온의 ROV01에서 가장 적은 함량과 작은 입자크기를 보이며, 저온의 GTV01에서 점차 증가하다가 비활성침니인 ROV02에서 가장 높은 함량과 큰 입자크기를 나타내게 된다. 이러한 결과는 자성광물의 종류, 함량, 입자크기 변화 등의 암석자기학적 특성을 이용하여 기존 광물학적 접근방법으로 추적에 한계가 있었던 열수황화물광체의 진화과정에 대한 정보를 획득할 수 있을 것으로 판단된다.

Keywords

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