摘要
河台含金剪切带中稀土元素(REE)分布特征表明,在剪切过程中REE的活动性与流体/岩石的比例以及流体运移聚集的方式有关。在水/岩比低的深层韧性剪切环境形成的糜棱岩中REE的组成具有继承原岩的特点;在浅层脆性环境以充填方式形成的含金石英脉中REE的含量主要来源于流体;在中浅层过渡环境形成的含金硅质体中REE的分布则受到原岩和流体的共同影响。微量元素的研究证明了河台金矿的形成经历了三个阶段:①韧性阶段。由变质热液沿剪切带的渗滤扩散形成含An小于1×10^(-6)的糜棱岩;②韧-脆性阶段。因剪切带的张开和流体的充填交代在剪切带内产生含An 10×10^(-6)～100×10^(-6)的硅质岩或石英脉;③脆性阶段。受各种张性构造控制在剪切带以内或以外形成含Au 1×10^(-6)～5×10^(-6)的晚期石英脉。
The Hetai gold deposit is present within a shear zone hosted by metavolcano-sedimentary units in the upper part of the Late Proterozoic Sinian System. The shear zone, striking northeast and dipping northwest, is about 2km long and has an average thickness of 100m. Ores in the shear zone occur as a series of lenticular and vein-type bodies.
A three-stage model for the formation of the auriferous shear zone has been suggested. The early stage was characterized by ductile deformation during which auriferous mylonite containing less than 1×10^(-6) Au was formed. The second stage took place in an environment of ductile-brittle deformation where lenticular ores with about 10×10^(-6)～100×10^(-6) Au occurred. The third stage developed during brittle deformation accompanied by emplacement of auriferous quartz veins with 1×10^(-6)～5×10^(-6) Au.
A REE pattern analysis demonstrates that. in spite of important mineralogical and chemical changes of the original metamorphic rocks, no significant modification of lanthanide distribution occurred during ductile deformation of the shear zone that resulted in the formation of protornylonite, mylonite and ultramylonite. In contrast, extensive variations in REE patterns are observed in hydrothermal infiltration rocks which are products of the ductile-brittle and brittle deformation stage of the shear zone.Therefore, it seems that the REE behavior during dynamometamorphism was similar to that during metamorphism and hydrotermal alteration, as evidenced both by fluid/rock ratios and by REE patterns and REE abundances of the reacting fluids and rocks.
出处
《矿床地质》
CAS
CSCD
北大核心
1993年第3期202-211,共10页
Mineral Deposits
基金
国家自然科学基金
