黔西南泥堡金矿围岩与矿石的对比及其成矿机制研究

Comparative study of the wallrock and ore and ore forming mechanisms at the Nibao gold deposit,Guizhou,China

泥堡金矿的矿体主要赋存在构造蚀变体及逆冲断层破碎带中,受地层和断裂的双重控制。本文在岩相学研究的基础上应用X射线粉晶衍射分析(XRD)结合电子探针分析(EMPA)确定和量化了围岩和矿石的蚀变矿物及载金砷黄铁矿,对比了围岩和矿石的特点,并利用主微量元素分析矿化过程中围岩与矿石之间的元素带入带出通量,探讨了泥堡金矿蚀变矿物与成矿的关系及成矿机制问题。分析结果表明,黄铁矿(主要的载金矿物)与石英呈负相关,与伊利石呈正相关;矿石发生了去碳酸盐化作用,矿石中的黄铁矿大多具有环带结构,部分围岩也发生了去碳酸盐化作用,而围岩中的黄铁矿一般不具有环带结构;Au明显加入到构造蚀变体的矿石中,而CaO、MgO、S、Ba、Be等从其围岩中带出;Au、Sc、As和Fe_2O_3明显加入到逆冲断层破碎的矿石中,SiO_2、CaO、Sr、W、Be等则显示从其围岩中带出。综合分析认为,去碳酸盐化和硫化作用是泥堡金矿的主要成矿机制。在矿化前,去碳酸盐化作用为成矿提供了有利的环境;在成矿过程中,矿化通过硫化作用形成了黄铁矿的载金含砷边缘。

The majority of the orebodies at the Nibao gold deposit are controlled by a reverse fault and an unconformity between the Middle Permian and Upper Permian stratigraphie units. In this paper, based on petrographic study, X-ray diffraction （XRD） analysis and microprobe analysis （EMPA） were integrated to identify and quantify the altered minerals and gold bearing arsenian pyrite, make a comparative study of the characteristics between the wallrock and the ore. Major and trace element analyses were used to determine the element fluxes during mineralization. The main objective of this paper is to understand the relationship between altered minerals and the ore forming, and the ore-forming mechanisms at the Nibao gold deposit. The results indicate that pyrite shows a negative correlation with quartz and a positive correlation with illite. Ore samples have undergone decarbonation, and pyrite in the ore samples generaUy shows core-rim texture. A part of wallrock samples also have undergone decarbonation, but pyrite in the wallrock samples does not show core-rim texture. Au was added to the ore, while CaO, MgO, S, Ba and Be were removed from the wallrock in the uncomformity. In the reverse fault, Au, Sc, As and Fe2O3 were added to the ore while SiO2, CaO, Sr, W and Be show the characteristics of being removed from the wallrock. The integrated results suggest that decarbonation and sulfidation are the main ore forming mechanisms at the Nibao gold deposit. Before mineralization, decarbonation provides favor environment for ore forming. During the ore forming process, minerlization through sulfidation to form gold bearing arsenian rims on pyrite.