西藏雅鲁藏布江缝合带东段泽当豆荚状铬铁矿特征

Feature of Zedong podiform chromitite,eastern Yarlung-Zangbo suture zone in Tibet

泽当蛇绿岩位于雅鲁藏布江缝合带东段，岩体由地幔橄榄岩、辉长辉绿岩、辉石岩、火山岩等组成。地幔橄榄岩主要为方辉橄榄岩、纯橄岩和二辉橄榄岩。在方辉橄榄岩中发现7处豆荚状铬铁矿，矿石类型主要有致密块状和浸染状。出露地表的长度0．5—3m，厚0．2～1m。矿体的延伸方向为北西向，与岩体展布的方向一致，铬铁矿的Cr#=67．9—88．5，属于高铬型铬铁矿。泽当地幔橄榄岩岩相学特征以及矿物组合、矿物化学成份及岩相学特征，显示岩体至少存在两次的部分熔融过程，即为早期的MOR构造背景，以及后期SSZ环境的改造。铬铁矿的铂族元素（PGE）以富集Os、Rh、Pd，亏损Ir、Ru、Pt的负斜率分布模式，表明其形成过程中经受后期熔体／流体的改造。对比罗布莎岩体的矿物组合，矿物化学和地球化学等特征，显示泽当豆荚状铬铁矿矿体与典型高铬型具相似性，存在较大的找矿空间。

The Zedong ophiolite is in the eastern Yarlung-Zangbo suture zone （YZSZ） of Tibet, which consists chiefly of mantle peridotite, with lesser amounts of pyroxenite and gabbro. Seven small, lenticular bodies of chromitite ore have been found in the harzburgite, with ore textures ranging from massive to disseminate to sparsely disseminate. Individual ore bodies are 0. 5 ~ 3m long, 0. 2 ~ lm wide and striek NW, parallel to the main structure of the peridotite, both of them are high-Cr chromitite （ Cr~ = 67. 9 ~ 88.5 ）. The mineralogy and geochemistry of the Zedong peridotites suggest that they formed originally at a mid-ocean ridge （MOR） and were later modified by suprasubduction zone （SSZ） melts. Platinum group elements （PGE） of Zedong ophiolite have negative slope patterns with enrich Os, Rh, Pd, loss of It, Ru and Pt, indicating the process of modified by melt/fluid. Compare to Luobusa podiform chromitite and peridotite in mineral assemblages, mineral chemistry and geochemistry show that there are many similar character, even existence a good prospecting space.