한국광물학회지 (Journal of the Mineralogical Society of Korea)

  • 제17권4호
  • /
  • Pages.309-325
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  • 2004
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  • 1225-309X(pISSN)
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  • 2288-7172(eISSN)
한국광물학회 (The Mineralogical Society of Korea)
권호 표지

호주 퀸즈랜드 주 캔닝턴 광상 모암의 아연-첨정석-규선석-석류석에 관한 연구 :변성작용과 아연-광화작용에 대해서

Gahnite-Sillimanite-Garnet Mineral Assemblage from the Host Rocks of the Cannington Deposit, North Queensland, Australia: Relationship between Metamorphism and Zn-Mineralization

  • 김형수 (강원도 춘천시 강원대학교 지질학과)
  • 발행 : 2004.12.01
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초록

연구는 호주 퀸즈랜드 주 북서부에 위치하는 은-납-아연 캔닝턴 광상은 호상편마암, 미그마타이트, 규선석-석류석 편암 그리고 각섬암으로 구성된 모암 주변부에서 발달해 있다. 모암에서 산출되는 규선석의 세 가지 다른 결정형태, 규선석을 포획광물로 함유한 아연-첨정석과 석류석 반상변정은 모암의 변성작용과 아연과 관련된 광화작용에 대한 지질학적 지시자로 사용되었다. 변성작용과 아연 광화작용과의 관계는 프로그램 THERMOCALC를 이용하여 KFMASH (K$_2$O-FeO-MgO-A1$_2$O$_3$-SiO$_2$- $H_2O$), KFMASHTO (K$_2$O-FeO-MgO-A1$_2$O$_3$-SiO$_2$-$H_2O$-TiO$_2$-Fe$_2$O$_3$), NCKFMASH ($Na_2$O-CaO-K$_2$O-FeO-MgO-Al$_2$O$_3$-SiO$_2$-$H_2O$) 그리고 MnNCKFMASH (MnO-$Na_2$O-CaO-K$_2$O-FeO-MgO-Al$_2$O$_3$-SiO$_2$-$H_2O$) 화학계에서 이들 세 가지 광물의 공생관계와 규선석-석류석-부분용융의 상평형 관계를 이용하여 결정하였다. MnNCKFMASH와 NCKFMASH계에서 부분 용융은 KFMASH와 KFMASHTO계에서 보다 낮은 온도에서 일어나며, MnNCKFMASH 계에서 용융 온도는 암석 화학 성분의 Na+Ca+K)의 비가 증가함에 따라 감소하는 경향을 보인다. 캔닝턴 광상의 모암은 MnNCKFMASH계의 경우 최고 온도와 압력 환경에서(634$\pm$62$^{\circ}C$, 4.8$\pm$1.3 kbar) 약 15% 용융되지만, KFMASHTO계하에서는 부분 용융이 일어나지 않는다. 규선석의 등변성도선과 모드 비의 변화를 근거로, 주상과 능면형의 규선석과 주상의 규선석을 포획하는 아연-첨정석 반상변정은 부분 용융을 포함하는 온도와 압력의 증가(약 550～$600^{\circ}C$, 2.0～3.0 kbar에서 700～75$0^{\circ}C$, 5.0～7.0 kbar)로 인한 것으로 생각된다. 또한 이와 같은 변성작용 동안의 최대 수축 변형 방향은 남-북 그 다음 동서 방향으로 주로 D$_1$과 D$_2$ 변형작용 동안에 형성되어졌다. 결론적으로 아연-첨정석의 성장과 관련된 아연 광화 작용은 D$_2$ 동안에 일어났고 그 후 부분 용융과 후기 변형/변성작용에 의해 재배치 또는 재농집 되어진 것으로 생각된다.

The Cannington Ag-Pb-Zn deposit, northwest Queensland, Australia developed around the host rocks composing banded and migmatitic gneisses, sillimanite-garnet schist and amphibolite. Three crystal habits of sillimanite, gahnite (Zn-spinel) and garnet porphyroblasts occurred on the host rocks of the Cannington deposit could be used to delineate metamorphism that closely associated with Zn-mineralization in the deposit. Linkages the metamorphism to Zinc-mineralization is determined in four chemical systems, KFMASH (K$_2$O-FeO-MgO-Al$_2$O$_3$-SiO$_2$-$H_2O$), KFMASHTO (K$_2$O-FeO-MgO-Al$_2$O$_3$-SiO$_2$-$H_2O$-TiO$_2$-Fe$_2$O$_3$), NCKFMASH (Na$_2$O-CaO-K$_2$O-FeO-MgO-AlO$_3$-SiO$_2$-$H_2O$) and MnNCK-FMASH (MnO-Na$_2$O-CaO-K$_2$O-FeO-MgO-AlO$_3$-SiO$_2$-$H_2O$), using THERMOCALC program (version 3.1; Powell and Holland 1988). Partial melting in MnNCKFMASH and NCKFMASH systems occurs at lower temperature than in the KFMASH and KFMASHTO systems. The partial melting temperature decreases with increasing of Na/(Na+Ca+K) of the bulk rock compositions in the MnNCKFMASH system. The host rocks have melted ca 15 vol.% in the MnNCKFMASH system at peak metamorphic conditions (634$\pm$62$^{\circ}C$ and 4.8$\pm$1.3 kbar), but partial melting have not occurred in KFMASHTO system. Based on calculations of sillimanite isograd in different systems and sillimanite modal pro-portion, prismatic and rhombic sillimanite and gahnite porphyroblasts including prismatic sillimanite inclusion probably have resulted from pressure and temperature increasing through partial melting (from 550～$600^{\circ}C$, 2.0～3.0 kbar to 700～75$0^{\circ}C$, 5.0～7.0 kbar), furthermore have experienced N-S then W-E crustal shortening during D$_1$ and D$_2$ deformation. Consequently, Zinc mineralization related to gahnite growth occurred during D$_2$ and was redistributed and upgraded by partial melting and retrograde metamorphism into structural and rheological sites during shearing in D$_3$.

키워드

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