缅甸达贡山含镍风化壳地质地球化学特征及成矿作用

Geololgical-Geochemistry Characteristics and Minerogenesis of Nickel-Bearing Weathering Crust in Taguang Taung,Myanmar

缅甸达贡山含镍超基性岩的代表性风化剖面显示,该风化壳发育层带结构,自上至下依次为红土盖层—褐铁矿层—腐岩层—基岩。元素在该风化剖面上的分布特征显示,在风化作用中SiO2、MgO、CaO、Na2O等大量淋失,而TiO2、Al2O3、Fe2O3、MnO、Ni、Co、Cr2O3等则残留于岩体风化壳之中。Ni主要富集在腐岩层的中上部,平均含量1.56%(基岩Ni含量0.49%),系由上部含镍溶胶下渗在(腐岩层)弱碱性环境中发生次生沉淀的结果。腐岩层是该区红土型镍矿的重要找矿标志层位,Ni次生富集带深度6～30 m。除有利于成矿的岩浆岩、气候以及大地构造条件外,适度的风化强度有利于Ni次生富集成矿。

Typical weathering profile of nickel-bearing ultramafic rock in Taguang Taung,Myanmar,demonstrates that a band structure is developed in the weathering crust,including top laterite cover,upper limonite layer,under saprolite layer,and bottom ultramafic rock base.The characteristics of elements distributing in the profile reveal that SiO2,MgO,CaO,Na2O leached out,while TiO2,Al2O3,Fe2O3,MnO,Ni,Co,Cr2O3,etc.remained in the crust.Ni is concentrated in the middle-upper saprolite layer with Ni average content of 1.56%（compared to 0.49% Ni in ultramafic rock base）,because the saprolite may form a weak alkaline condition and benefit second precipite of Ni,infiltrating as a sol form in the crust.The saprolite layer is an important mark for exploration of laterite-type Ni deposits in Taguang Taung district,and Ni second precipitate belt is located at the depth of 6-30 m.In addition,a modest weathering of nickel-bearing ultramafic rock is good for Ni enrichment in the crust,apart from other beneficial conditons such as magma,climate and geotectonics.