铂族元素在地壳中的富集:以布什维尔德杂岩为例(英文)  

The concentration of PGE in the Earth's crust with special reference to the Bushveld Complex.

作　　者：Tony Naldrett Judith Kinnaird Allan Wilson Gordon Chunnett 

机构地区：[1]School of Geosciences,University of the Witwatersrand,Johannesburg,South Africa [2]Anglo Platinum,Johannesburg,South Africa

出　　处：《地学前缘》2008年第5期264-297,共34页Earth Science Frontiers

摘　　要：地幔是地壳铂族元素富集的主要源库。铂族元素迁移主要有两个途径：（1）地慢部分熔融物质侵入地壳；（2）地幔板片就位于俯冲/碰撞带。前一途径比后一途径重要得多。地幔物质进入地壳造成铂族元素富集并成为可供开采的主矿产而非副产品，这一过程可包含许多成矿作用机制：（i）基性侵入体中Ni-Cu硫化物矿浆的发育，岩浆冷却与分离结晶作用导致富含Cu，Pt，Pd的硫化物矿浆的形成；（ii）层状侵入体一定层位形成高品位的铂族元素硫化物层，伴生或不伴生铬铁岩；（iii）富铂族元素及硫化物的岩浆沿着层状侵入体的边缘就位；（iv）直至层状侵入体结晶分异作用晚期的硫化物不混溶滞后分离；（v）不发育硫化物不混溶作用的铬铁矿结晶作用；（vi）低程度硫化物浸染带中的热液作用与铂族元素富集；（vii）乌拉尔一阿拉斯加型侵入体重结晶过程中的铂族元素与铬铁矿的次生富集作用，岩体在风化过程中形成砂矿床；（viii）黑色页岩形成过程中Pt的富集。南非布什维尔德火成杂岩蕴藏世界Pt资源的75％，Pd资源的54％，Rh资源的82％，并具有（ii）、（iii）、（iv）、（v）、（vi）成矿作用的实例。在这些作用中，作用（ii）形成的现有经济储量和资源量占90％，作用（iii）占9％。Merensky矿层（占总资源量30％）是一个铂族元素富集层位，它含1～3铬铁矿薄层，在可采宽度内硫化物平均含量为1％～3％（质量分数）。硫化物一般被认为是铂族元素的主要聚集体。该矿层由两个或两个以上含硫化物的基性热岩浆上升；12聚而成。这些岩浆的汇聚造成超镁铁质堆晶岩的厚度（主要是斜方辉石岩，某些地区包括橄榄岩）变化于50cm至数米之间。开采通常集中在厚度不到1m的地带。矿层的成因至今仍存在争议，一些观点认为铂族元素来自下The Earth＇s mantle is the principal reservoir from which platinum-group element （PGE） concentrations in the crust are derived. The transfer of the PGE is accomplished by two main methods, first the development of mantle partial melts and their intrusion into the crust, and second the emplacement of mantle slabs in the subduction/collision zones. The first mechanism is far more important than the second. Once in the crust, a number of mechanisms serve to concentrate the PGE sufficiently and they can be exploited economical- ly as the principal product, rather than as a by-product. These include （i） the development of an Ni-Cu sulfide liquid in a marie intrusion, the concentration of this liquid, followed by cooling and fractional crystallization that results in a residual sulfide liquid highly enriched in Cu, Pt, and Pd; （ii） the formation of layers of very high-PGE tenor sulfides at specific horizons within a layered intrusion, either with or without associated ehromitite; （iii） the emplacement of magma carrying PGE rich sulfide along the margins of layered intrusions; （iv） the delayed separation of immiscible sulfides until the late stages of the differentiation of a layered intrusion; （v） chromite crystallization without the development of sulfide immiscibility; （vi） hydrothermal redistribution and concentration of PGE from zones of low grade disseminated sulfide; （vii） secondary concentration of PGE along with chromite during recrystallization of Ural-Alaskan intrusions and the subsequent development of placer deposits during the weathering of these bodies; and （viii） the concentration of Pt during the formation of black shale deposits. The Bushveld Igneous Complex of South Africa hosts 75% of the world＇s resources of Pt, 54% of Pd resources, and 82% of Rh resources, and contains examples of mineralization formed by processes （ii）, （iii）, （iv）, （v）, and （vi） listed a little earlier in the article. Of these, process （ii） accounts for 90% of the cur

关 键 词：铂族元素矿床 布什维尔德杂岩 铬铁矿 

分 类 号：P618.53[天文地球—矿床学]