摘要
京希—伊尔曼德金矿床的热液蚀变在空间上有明显的分带性,中心蚀变带以强烈的硅化为主,典型的蚀变矿物组合为石英或玉髓和地开石,中间带为高级泥化带,以地开石-高岭石-石英或玉髓为特征;外带为以蒙脱石-高岭石-伊利石-其他粘土矿物等矿物组合为主的泥化带,蚀变强度和矿物组合的分带性是温度、压力和化学梯度的反映,是流体在不断的水或流体—岩石反应和成分交换的产物。该矿床成矿流体演化过程为:早期酸性(pH=2～3)含矿流体在沿断裂上升过程中,受围岩灰岩中的流体(pH为中性)缓冲,在其进入高渗透性的碎屑岩层时,流速和水—岩石或流体—岩石反应大大加快,并在与大气降水的混合作用下,pH值逐步升高(3～5),产生了流体的温度及成分梯度,在温度和压力迅速下降的条件下,金及蚀变矿物沉淀、结晶生长,形成了蚀变空间分带,中心带保存完好的多孔状石英和地开石等高级泥化矿物组合说明该矿床是高硫化热液体系作用下的产物。
Spatial zonal features are well shown in the hydrothermal alteration distribution of the Jingxi-Yelmend gold prospect. The central zone is characterized by intense silicification with a quartz/chalcedony-dickite assemblage. The intermediate zone shows advanced argillic alteration with a dickite-kaolinite-quartz/chalcedony-se-mectite assemblage. The outer zone is characterized by an argillic alteration assemblage of kaolinite-illite. Such zonation is a reflection of temperature, pressure and chemical gradients, suggesting there is continuous fluid/ rock reaction. The fluid inclusions indicate that the fluids related to the alteration and mineralization have temperatures generally between 180-270℃ and relatively low salinity (Max. 5. 3 wt% NaCl equiv. ). The evolution of the ore fluids has undergone three stages; (1) Early-stage acidic (pH = 2-4) ore fluids were buffered by fluid in neutral limestones while flowing upward along steep faults and the pH values were slightly increased. (2) The pH value was increased to 3-5 when the ore fluids reached highly permeable epiclastic rocks (conglomerate and conglomeratic sandstone) and rapidly reacted with the country rocks, particularly with the assistance of in-charging meteoric water. In this stage, the composition, temperature and pH values were changed and the physicochemical gradients were generated. Highly concentrated residual SiO2 and most acidic (pH<3) fluids were retained in the central part of the fluid-flowing zone, where vuggy quartz (acidic leaching) and dick-ite occurred while the marginal parts have relatively high pH values and inter mediate-argillic alteration was developed. With the decreasing of temperature and pressure (boiling) , and increasing of oxidation for the ore fluids, the alteration zonation was formed and gold was deposited.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2001年第4期518-526,共9页
Acta Geologica Sinica
基金
中澳合作项目"中国新疆吐拉苏地区金矿勘察"
中国科学院知识创新项目(编号KZCX2-101
关键词
热液蚀变
蚀变分带
成矿流体演化
金矿床
矿床地质
空间分布
hydrothermal alteration
advanced argillization
ore fluid evolution
fluid/rock reaction
high sulphidation
gold deposit
Jingxi-Yelmend
