黔西南老万场红色粘土型金矿矿物特征及其意义

MINERALOGY AND ITS SIGNIFICANCE IN THE RED-CLAY PROFILE OF THE LAOWANCHANG GOLD DEPOSIT, SOUTHWESTERN GUIZHOU

对黔西南老万场金矿粘土层的矿物成分分析表明 ,粘粒级部分主要为高岭石、针铁矿和绿泥石 ,次为三水铝石、伊利石、石英、蒙脱石和锐钛矿 ,另有少量钾长石和斜长石 ;砂砾级部分主要为石英和风化的玄武岩、凝灰岩、粉砂质页岩和硅质岩岩屑 ,次为褐铁矿、铝土矿、锰质和钙泥质团块。矿物特征表明 ,粘土层是由峨眉山玄武岩、大厂层硅质岩、茅口灰岩和原生低温热液蚀变 (矿化 )岩风化的产物。矿床是在岩溶坍塌使成矿物质发生初步堆积 ,再经一定程度的红土化作用形成的红色粘土型金矿。

The analysis of mineral composition of the red\|clay profile in the Laowanchang gold deposit, southwestern Guizhou indicates that the clay fraction is composed mainly of kaolinite, goethite and chlorite with minor gibbsite, illite, quartz, montmorillonite and anatase, and trace K\|feldspar and plagioclase. The coarse\|grained fraction consists mainly of quartz and weathered clasts such as basalt, tuff, silty shale and siliceous rock, with minor conglomeration of limonite, bauxite, manganese nodule and calcrete. The characteristics of chlorite and weathered clasts of basalt and siliceous rock show that the red\|clay profile was developed partially from the weathering of basalt of the Emeishan Formation and siliceous rock of the Dachang Bed, respectively. The calcrete and euhedral quartz crystals with two\|end growth imply the profile was formed partially from the weathering of limestone of the Maokou Formation and low temperature altered rock. The lateritization was developed, but not thoroughly because different types of clay minerals, such as 2∶1 type (chlorite, illite) and 1∶1 type (kaolinite), co\|exist in the profile. During lateritizaton, the climate changed between cool\|arid and warm\|humid as indicated by the co\|existence of chlorite and kaolinite.\; The deposit, therefore, is a red\|clay type gold deposit formed firstly through the accumulation of ore\|forming material by karst collapse, and secondly through the halfway lateritization.