四川省美姑县瓦西村一带南红玛瑙矿产出特征及形成过程分析

Characteristics of occurrence and Genesis of Nanhong agate deposit in Waxi area,Meigu county,Sichuan province

四川省美姑县瓦西村一带南红玛瑙主要产于上二叠统宣威组的紫红色泥质、砂质砾岩中,底板为灰绿色硅质砾岩,顶板为紫红色泥岩、粉砂岩等。该矿区玛瑙颜色主要有柿子红、玫瑰红、樱桃红、冰飘红、红白料、白料等,南红玛瑙的块度多介于0.5~5 cm之间,半透明不透明状,油脂光泽,断面呈贝壳状。玛瑙矿呈椭球状或扁球状分布于砾岩之中,其分布不甚均匀。玛瑙砾石质地坚硬而脆,敲击易碎裂。晚二叠世初期,强烈的岩浆活动导致大规模的玄武质岩浆喷溢地表,形成大面积分布的峨眉山玄武岩,岩浆期后富硅质热液在玄武岩的气孔中逐次沉淀成玉髓等矿物,最终形成玛瑙;晚二叠世晚期,随着峨眉山玄武岩的风化与剥蚀,岩石中的玛瑙被水流搬运、迁移,呈砾状在湖、沼地段沉积,堆积于宣威组底部,形成含玛瑙矿砾岩层。

Nanhong agate deposit occurs mainly in purple red argilaceous and sandy conglomerate of Xuanwei formation of Upper Permian Series.The foot wall rock is gray green siliceous conglomerate,the top wall rock purple red mudstone and siltstone etc.The agate is mainly in persimmon red,rose red,cherry red,ice floating red,red colors and is divided into raw materials,such as red-white agate,wrapped silk agate,white agate and agate like ice seeds.The agate is hard and fragible,semi-transparent or opaque in size 0.5-5 cm with greasy luster and she'll like cross section.The agate deposit is a elliptical or a flat spherical mass in the conglomerate.During Early Late Permian Epoch strong magmatism led to intensive and extensive magmatic upwelling and eruption onto the surface and basalt in large area was formed in Emeishan area.The Si-rich post-magma hydrothermal fluid precipitated gradually the agate consisting of minerals of chalcedony and so on in fumarole of the basalt.In late period of Late Permian Epoch the basalt in Emeishan area was exposed to weathering and erosion and the agate transported to lake or marsh where the agate deposited at the bottom to form agate deposit.