中国南方红土型金成矿系列研究综述

红土型金矿床是原生金矿化遭受红土化作用改造所形成的一种表生金矿床,包括"红色粘土型"和"铁帽型"金矿床.中国红土型金矿以风化再造型为主,受气候影响而主要分布在南方,并与岩金成矿系列分布基本一致.风化壳常量元素、稀土元素、粘土矿物系统研究表明,成矿作用环境时空变化整体受风化强度控制,其风化作用早期呈中碱性、晚期呈酸性,风化壳下部偏碱性、还原,项部偏酸性、氧化的特点.典型矿床因子分析揭示,红土型金成矿作用可分为氧化和水解两个阶段.氧化阶段风化较弱,基岩释放大量碱性离子,使成矿流体保持中性,金溶解并主要以Au(S2O3)23-形式迁移;水解阶段风化较强,硅酸盐矿物发生脱碱去硅作用,随着大气降水不断参与,成矿流体性质由中碱性缓慢过渡到中-酸性条件,金以胶体或氯化物络合物形式迁移.金一般在风化壳下部富集,表生矿物吸附、氧化还原界面处被Fe2 、Mn2 还原以及不同性质流体混合都能促使金的沉淀.

METALLOGENIC SERIES OF LATERITIC GOLD DEPOSITS IN THE SOUTH CHINA: AN OVERVIEW

Lateritic gold deposit,which includes both the red clay-typed and gossan-typed deposits,is a hypergene deposit formed by lateritic weathering and reforming process based on the primary gold-riched rocks.Since being controlled by climate,lateritic gold deposits are mainly distributed in the south China,and dominated by weathering reformed typed.The distributions of the deposits are inconsistent with the primary gold deposits.Detailed studies on major elements,REE and clay minerals of lateritic crust revealed that the variation of ore-forming environment was controlled by weathering strength.Moreover,from early to late,the environment changed from alkali to acid,and from lower to upper part of the profile,the environment varied from alkali and reduction to acid and oxidation.Factor analysis of main elements in typical lateritic gold deposits suggested that the ore-forming process can be divided into two stages,early oxidation stage and late hydrolization stage.The oxidation stage was characterized by weak weathering effect,and the parent rock released a grate deal of alkali ions,therefore,fluid kept neutrality and gold transported as Au(S_2O_3)~(3-)_2.Whereas,the hydrolization stage was characterized by strong weathering process,and silicate minerals underwent de-alkalization and de-silication caused by the continual participation of meteor waters.As a result,ore-forming fluids changed from alkali to acid,under which gold transported as colloid or chloride complex.Commonly,gold leached down and enriched at the lower part of the weathering crust,especially,absorbed by supergene minerals and deoxidized by Fe~(2+) and Mn~(2+) at the oxide-reduction surface and the mixing of different types of fluids accelerated the precipitation of gold elements.