杭州市之江组网纹红土的矿物学特性

Mineralogy of Zhijiang plinthitic red clay in Hangzhou city

用 X射线衍射分析和 X射线荧光分析对杭州西郊之江组网纹红土红、白网纹的矿物进行了分析 .细土化学组成表明 :红网纹中铁、锰、磷的含量明显高于白网纹 ,而其他元素则一般是后者高于前者 ,红网纹中铁富集明显 ;两种网纹的 Ti/Zr比相近说明它们的物质来源一致 .X射线衍射分析表明 ,红、白网纹各粒级矿物组成的差异仅体现在前者含晶态氧化铁矿物 ,而后者则没有检测到 ,它们的层状铝硅酸盐矿物组成相似 .红网纹中出现的氧化铁主要为针铁矿和赤铁矿 ,其中针铁矿的铝同晶替代量高达17.7mole% .据分析 ,红白网纹是氧化铁在还原条件下迁移的基础上进行红化作用而形成的 .

The mineral compositions of red and white plinthites separated from Zhijiang plinthitic red clay near Hangzhou,Zhejiang province were analysed by means of XRD and XRF The total Fe ,Mn and P contents in red plinthite were much higher than those in white one, whereas other elements in red plinthite were generally lower than those in white one,and iron oxides were obviously enriched in red plinthite The similar value of Ti/Zr ratio in these two plinthites suggested that they were derived from same parent material XRD patterns showed the only difference of mineral compositions between red and white plinthites were iron oxides,i e ,crystalline iron oxides (goethite and hematite) in significant quantity were detected in red plinthite,but no in white plinthite The types and abundance of their aluminosilicate minerals were almost same Al substitution degree in goethite was 17 7 mole% 。Based on results obtained, it was suggested that red and white plinthites were formed by reduction translocation of iron oxides,followed by rubification