西藏雅鲁藏布江缝合带中段日喀则地幔橄榄岩中发现金刚石等异常矿物

本文报道了雅鲁藏布江缝合带中段日喀则蛇绿岩地幔橄榄岩中发现与该带东西段蛇绿岩岩体中相似的金刚石和特殊地幔矿物群。日喀则地幔橄榄岩体以方辉橄榄岩为主,含少量二辉橄榄岩和纯橄岩,辉石岩和辉长岩呈脉状产在方辉橄榄岩中。通过重砂分选实验,在465kg的方辉橄榄岩大样中发现了30余种特殊矿物群,包括金刚石、自然金、自然铬、自然铜等自然元素矿物类;碳硅石等碳化物类;方铁矿、赤铁矿、磁铁矿、刚玉、铬尖晶石、金红石、锡石、黑钨矿等氧化物类;镍黄铁矿、方铅矿、辉钼矿、辉锑矿、闪锌矿、毒砂等硫化物类;Ag-Au等合金矿物类;橄榄石、辉石、锆石等硅酸盐岩类;白钨矿等钨酸盐岩类;萤石等氟化物类。金刚石和自然金、自然铬、自然铜连同碳硅石的发现表明岩体存在强还原环境,这套特殊矿物组合指示日喀则地幔橄榄岩可能与雅鲁藏布缝合带其他蛇绿岩一样,经历了深地幔演化过程。

Diamond and Other Exotic Minerals Discovered from the Xigaze Mantle Peridotite in the Yarlung-Zangbo Suture Zone, Tibet

Here we report for the first time discovery of an unusual mineral group in the harzburgites of the Xigaze ophiolite, which lies in the middle section of the Yarlung-Zangbo suture. The mineral features are similar to those found in mantle peridotites in the eastern and western sectioins of the Yarlung-Zangbo suture. The Xigaze ophiolite consists mainly of harzburgite, and minor lherzolite and dunite, with pyroxenite and gabbro dikes cutting the harzburgite. More than thirty unusual minerals were obtained by standard mineral separation techniques from a 465 kg of harzburgite sample, including native elements such as diamond, gold, chrome, copper; carbide such as moissanite; oxides such as wustite, hematite, magnetite, corundum, spinel, cassiterite, wolframite; sulfides such as pentlandite, galena, stibnite, molybdenite, sphalerite and arsenopyrite; Ag-Au alloy minerals; silicates, tungstates and fluoride. The presence of diamond, native Au, Cr, and Cu, together with moissanite, indicates a strong reducing environment. The set of unusual mineral assemblages indicate that the Xigaze ophiolite as other ophiloites in this suture may have experienced deep mantle evolution.