Cr-Fe deposit, occurring in the mid-cretaceous Luobusa ophiolite along the Luobusa fault zone, also known as Yarlung Zangbo (or, Brahmaputra) suture zone. The ophiolite consisting mainly of mantle peridotite and dunite overlying a mélange zone composed of pillow lavas, gabbros, pyroxenites and cherts in a serpentinite matrix. To the south, the ophiolite is separated from Triassic flysch by a steep reverse fault; to the north, it is thrust over the Tertiary Luobusa Formation and Gangdese granitic batholith. The ophiolite extends 42 km in an east–west direction and has an outcrop area of approximately 70 km2. Podiform chromitite ores, included in a dunite-harzburgite assemblage, occur discontinuously in a band in the upper mantle peridot- ites. They display massive, disseminated, brecciated and nodular textures and consist of magnesiochromite. On the basis of their composition and texture, the chromitites are believed to have formed by precipitation from boninitic melts interacting with the host peridotites. These chromitites have an unusual mineral as- semblage, including ultra-high pressure (UHP) minerals such as diamond and moissanite (SiC), as well as a number of highly reduced phases such as graphite, native chromium, iron, nickel, gold, copper and silicon identified by microprobe and X-ray diffraction studies. Some phases seem to have formed at the core/ mantle boundary. Among the unusual phases found are alloys (Fe/Si-phases, Ni/Fe-phases, Fe/Cr-phases, Ir/Fe-phases, W/Co-phases, Cr/C-phases, Ti/N-phases, Si/Ca-phases, Si/C-phases, etc.), as well as numerous new oxides, sulphides and arsenides.
Ref.:
- Bai, W.J., Zhou, M.F., Robinson, P.T., et al. (1993): Possible diamond-bearing mantle peridotites and chromites in the Luobusa and Dongqiao ophiolites, Tibet. Canadian Journal of Earth Sciences 30, 1650-1659.
- Meifu Zhou, Robinson, P.T., Malpas, J., and Li Zijin (1996): Podiform Chromitites in the Luobusa Ophiolite (Southern Tibet): Implications for Melt-Rock Interaction and Chromite Segregation in the Upper Mantle. Journal of Petrology 37(1), 3-21.
- Wenji Bai, Robinson, P.T., Qingsong Fang, Jingsui Yang, Binggang Yan, Zhongming Zhang, Xufeng Hu, Meifu Zhou, and Malpas, J. (2000): The PGE and base-metal alloys in the podiform chromitites of the Luobusa ophiolite, southern Tibet. Canadian Mineralogist 38(3), 585-598. [http://pubs.nrc-cnrc.gc.ca/mineral/mineral38/58538-3.pdf]
- Bai, W.J., Zhou, M.F., and Fang, Q.S. (2000): Origin of podiform chromitites, diamonds and associated mineral assemblage in the Luobusha ophiolite, Tibet. Seismological Press (Beijing), 98 pp. (in Chinese).
- Bai, W.J., Fang, Q.S., Zhang, Z.M., et al. (2001): Crystal structure of forstertite from podiform chromitite in Luobusha ophiolite of Tibet and its implications. Acta Petrologica et Mineralogica 20(1), 1-9 (in Chinese with English abstract).
- Bai, W.J., Yang, J.S., Fang, Q.S., et al. (2001): Study on a storehouse of ultrahigh pressure mantle minerals - podiform chromite deposits. Earth Science Frontiers 8(3), 111-121 (in Chinese with English abstract).
- Aitchison, J.C., Abrajevitch, A., Badengzhu, J.R.A., Davis, A.M., Luo, H., Liu, J.B., McDermid, I.R.C., and Ziabrev, S. (2002): New insights into the evolution of the Yarlung Tsangpo suture zone, Xizang (Tibet), China. Episodes 25(2), 90-94. [http://www.episodes.org/backissues/252/090-94%20Hongkong.pdf]
- Wenji Bai, Jingsui Yang, Qingsong Fang, and Binggang Yan (2003): An unusual mantle mineral group in ophiolite, Tibet. Presented at the Alice Wain Memorial West Norway Eclogite Field Symposium, Selje, Norway, June 21-28 2003. [http://www.ngu.no/FileArchive/165/2003_055.pdf]
- Jingsui Yang, Wenji Bai, Qingsong Fang, Binggang Yan, He Rong, and Robinson, P. (2003): Newly discovered coesite-kyanite aggregates in the Luobusa ophiolite, southern Tibet, China, originated from exhumed mantle ? Presented at the Alice Wain Memorial West Norway Eclogite Field Symposium, Selje, Norway, June 21-28 2003. [http://www.ngu.no/FileArchive/165/2003_055.pdf]
- Wenji Bai, Nicheng Shi, Qingsong Fang, Guowu Li, Ming Xiong, Jingsui Yang, and He Rong (2006): Luobusaite: A New Mineral. Acta Geologica Sinica 80(5), 656-659 (in Chinese with English abstract).
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Map Reference: 29°11'N , 92°0'E
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