High-Cr and High-Al Chromitite Found in Western Yarlung-Zangbo Suture Zone in Tibet
详细信息
- 责任者：Xiong Fahui (State Key Laboratory for Continental Tectonics and Dynamics ; Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Yang Jingsui
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(6)
- 关键词：铬铁矿矿床 ; chromite deposit ; 雅鲁藏布江 ; Yarlung Zangbo River
- 页码：p.1878-1908
- 图表：illus., 7 tables, 134 refs.
- 分类号：1001
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Based on their mineral chemistry podiform chromitites are divided into high-alumina (Cr # =20～60)(Cr#=100×Cr/(Cr+Al))and high-chromium (Cr#=60～80) varieties ( Thayer,1970) .0nly one typeoccurs in a given peridotite massif,although some ophiolites contain several massifs which can have different chromitite compositions. We report here the first known occurrence of both high chrome and high alumina chromitite in a single massif,the Purang mafic-ultramafic body in the western Yarlung-Zangbo suture zone of Tibet. This massif consists chiefly of mantle peridotite,with lesser amounts of pyroxenite and gabbro. The mantle peridotites are mostly harzburgite and minor lherzolite; a few dike-like bodies of dunite are also present. Seven small,lenticular bodies of chromitite ore have been found in the harzburgite,with ore textures ranging from massive to disseminated to sparsely disseminated; no nodular ore has been observed. Individual ore bodies are2～6m long,0. 5 ～2m wide and strick NW,parallel to the main structure of the peridotite.0re bodies 1 and 6 consist of high-Al chromitite ( Cr # = 52～55) ,whereas orebodies 2,3,4 and 5 are high-Cr varieties ( Cr # = 63～89) . In addition to magnesiochromite,all of the orebodies contain minor olivine,amphibole and serpentine. Mineral structures show that the peridotites experienced plastic deformation and partial melting. The mineralogy and geochemistry of the Purang peridotites suggest that they formed originally at a mid-ocean ridge( MOR) and were later modified by suprasubduction zone ( SSZ) melts. Base on the chemical composition of spinel-olivine/clinopyroxene can identify Purang peridotite have three stage different partial melting,including the early partial melting (degree about 10% ) ,later partial melting (degree about20% ～30% ) ,and partialdecompression partial melting (degree about 15% ) . Compare to other typical high Al and high Cr podiform chromitite and peridotite in mineral assemblages,mineral chemistry andgeochemistry show that there are many similar character,even existence a good prospecting space.
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