Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Geochemical Studies of BIF in Wugang, North China Craton: Implication for the Genesis

북중국 우강 지역에 분포하는 호상철광상의 성인에 대한 지구화학적 연구

  • Moon, Inkyeong (School of Earth and Environmental Sciences, Seoul National University) ;
  • Lee, Insung (School of Earth and Environmental Sciences, Seoul National University) ;
  • Yang, Xiaoyong (School of Earth and Space Sciences, University of Science and Technology of China)
  • 문인경 (서울대학교 지구환경과학부) ;
  • 이인성 (서울대학교 지구환경과학부) ;
  • Received : 2019.01.14
  • Accepted : 2019.05.15
  • Published : 2019.06.28
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Abstract

The Wugang banded iron formation (BIF) is located within the Taihua complex at the southern margin of the North China Craton (NCC). In this study, we analyzed major elements and rare-earth elements in iron ores from the Wugang BIF, to study the type of BIFs and their formation mechanism in combination with previously-published data from the literature. We found that the iron ores from the Wugang BIF display two types of banding textures, which can be described as weak banding or no banding. The samples are composed of coarse-grained magnetite, quartz, pyroxene, and amphibole. Based on our geochemical results, mixing of a hydrothermal fluid with sea water led to the precipitation of the Wugang BIF, and there is evidence of crustal contamination. These results, combined with previous literature data, almost all of the iron ores lack Ce anomalies, though some samples show negative Ce anomalies. Our results indicate that the Wugang BIF was formed in a dominantly reducing environment, although the surfaces were relatively oxidized. Geochemical evidence suggests that the Wugang BIF iron ores were formed in a near-shore continental-shelf environment or in a back-arc basin. The BIF is known as interbedded with migmatite, amphibole gneiss, minor quartz and marble, which indicating lack of volcanic materials input. This study, combined with previous results on geochemical interpretation of related wall rock of Wugang BIF, demonstrated that Wugang BIF belongs to Superior-type BIF.

우강 호상철광상은 북중국 남쪽 끝 부분의 타이후아 복합체에 위치 하고 있다. 본 연구에서는 우강 호상철광상에서 산출되는 철광석 시료의 전암 분석 결과의 해석을 통하여 우강 호상철광상의 유형과 성인을 이해하고자 하였다. 이 광상의 철광석의 조직은 밴딩 구조가 약하게 나타나는 것과, 밴딩 구조가 나타나지 않는 것 두 가지로 분류할 수 있다. 주요 구성 광물들은 조립질의 자철석, 석영, 휘석, 각섬석 등이다. 지구화학적 연구 결과 우강 호상철광상은 해수와 0.1~1 %를 차지하는 열수로부터 철을 공급받아 형성 되었다. 또한 이 과정에서 육지성 물질로부터의 철 공급이 있었음을 확인하였다. 이전 연구 결과와 종합해 보았을 때, 대부분의 철광석에서 Ce 이상치는 뚜렷하게 나타나지 않지만 일부 철광석에서는 음의 Ce 이상치를 보였다. 이러한 결과는 우강 호상철광상은 환원 환경이 우세한 해양 환경에서 형성되었지만, 상대적으로 산화된 해양의 표층 환경의 가능성을 제시해 준다. 이러한 지구 화학적 특징을 바탕으로 우강 호상철광상이 형성된 지구조적인 환경은 대륙붕 연안이나 후열도 분지환경이라 생각된다. 또한 우강 호상철광상은 혼성암, 각섬석 편마암, 규암, 대리암이 함께 산출되는데, 이는 연구 광상이 화산 활동과 밀접한 연관성이 없음을 지시한다. 본 연구에서는 지금까지 보고된 지구화학적 분석 결과와 이번 연구 결과를 종합해 우강 호상철광상이 슈피리어 유형 호상철광상의 특징을 보임을 확인하였다.

Keywords

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Fig. 2. Stratigraphic section of the Wugang BIF (Liu et al., 2018).

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Fig. 3. Photos of iron ores from the Wugang BIF.

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Fig. 4. Photomicrographs of iron ores from the Wugang BIF.

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Fig. 5. PAAS (Post Archean Australian Shale)–normalized REY patterns of iron ores from the Wugang BIF (red solid line). Comparable data are (Liu et al., 2018).The values of the high–temperature hydrothermal fluid (Bau and Dulski, 1999) and seawater (Alibo and Nozaki, 1999) are shown for comparison.

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Fig. 6. The (Ce/Ce*)SN vs (Pr/Pr*)SN diagram (Bau and Dulski, 1996).

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Fig. 7. Elemental ratio plots with three component (Alexander et al., 2008). Comparable data (Liu et al., 2018) are plotted together. The values of the high–temperature hydrothermal fluid (Bau and Dulski, 1999), seawater (Alibo and Nozaki, 1999) and upper continental crust (Rudnick and Gao, 2003) used three end members.

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Fig. 1. (a) Geological map of the North China Craton and location of study area, modified after Zhao et al. (2005). (b) Simplified geological map of the Wugang area (Li et al., 2014).

Table 1. Major elements (wt.%) of the Wugang BIF and average BIFs in NCC

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Table 2. Rare earth elements (ppm) compositions and their ratios of the Wugang BIF

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