贵州老万场红土型金矿地球化学特征及其成因

Geochemical Features and Genesis of the Laowanchang Lateritic Gold Deposit in Guizhou

对贵州西南部晴隆老万场红土型金矿与相关岩石(矿石)和喀斯特红土等进行了常量元素、微量元素和稀土元素地球化学比较研究,阐明了矿床的各类元素的地球化学特征,追溯了矿床的物质来源。研究表明,本类红土型金矿的物质来源是高硅质(石英)、富铁质(黄铁矿等)的富金矿(岩)石;具有Au-As-Sb-Hg-Tl-W-Ag-Ba的微量元素组合特征,与卡林型金矿十分相似,是原始卡林型金矿风化演化的产物。常量元素和稀土元素的研究表明,红土型金矿矿石一般具有原始卡林型金矿风化产物和喀斯特红土的混合特征。其成矿成土过程是:上覆于下二叠统茅口组石灰岩之上的卡林型金矿在喀斯特作用下,崩塌、垮塌堆积于喀斯特负地形的容矿系统中,除原始矿体的风化成土外,同时伴随掺合混合着喀斯特红土化作用。此种作用使矿石具有红土的特征,还对原始金矿的金品位具有稀释或贫化作用。

Comparative studies have been conducted on the macroelement, microelement and REE geo-chemical characteristics of the Laowanchang lateritic gold deposit and its related rocks and/or ores and karst laterite in Qinglong county, southwestern Guizhou. The studies indicate that the material source of this type of lateritic gold deposit is Au-rich rocks and /or ores with high siliceous material (quartz SiO2) and rich ferruginous material (pyrite etc. ). The deposit is very similar to the Carlin type gold deposit with respect to the Au-As-Sb-Hg-Tl-W-Ag-Ba microelement association. So it is considered to be the product of wealthering evolution of a primary Carlin type gold deposits. Macroelement and REE geochemical studies indicate that ores of this lateritic gold deposit the possess mixed features of the weathering product of a primary Carlin type gold deposit and karst laterite. The ore-forming process is as follows: the Carlin type gold deposit overlying the limestone of the Early Permian Maokou Formation collapsed and piled up in an ore-holding system with a negative karst landform during karst processes; then the primary orebodies were weathered and soil was formed, accompanied by karst lateritization. Karst lateritization imparted the features of laterite to the ores and also lowered the gold ore grade of the primary gold deposit.