四川凉山南红玛瑙结构特征及成因探究

Structural Characteristics and Formation of Nanhong Agate in Liangshan, Sichuan

结合矿区实地考察及偏光显微观察、X射线粉晶衍射、拉曼光谱等测试分析对四川凉山南红玛瑙的结构特征及其成因等进行了探究。研究结果表明,四川凉山南红玛瑙主要分为致密块状、条带状、“水晶芯”三种结构。凉山南红玛瑙成矿初期多形成致密块状结构,伴随岩浆喷发,岩浆中的挥发性流体、高温的大气水与母岩反应,球粒状玉髓开始生长形成隐晶质的致密块状结构玛瑙。隐晶质玉髓和晶质石英之间的过渡区域易形成平行、环状条带结构。条带的颜色会因热液中周期性致色元素的不同有所差异,条带的宽窄也会因二氧化硅热液喷入的量不同而呈现出厚薄不一。单个条带内,粗粒、低结构缺陷的石英与细粒、高结构缺陷的玉髓、斜硅石交互生长的情况会导致局部有两种或三种结构交互出现。“水晶芯”结构的形成与温度升高二氧化硅热液降温至结晶温度的时间增长及形成后期热液浓度降低以致晶核减少有关,Al元素的存在也促使了水晶芯的形成。

In combination with the mineral exploration,structural characteristics of Nanhong agate in Liangshan, Sichuan Province were studied by polarizing microscope, X-ray powder diffraction, Raman spectra. The results show that the structure of Nanhong agate is mainly divided into three types: dense block structure, strip structure and crystal core structure. In the early stage of mineralization of Nanhong agate, dense block structure was formed. With the eruption of magma, the reaction of volatile fluid and high temperature atmospheric water in the magma with the parent rock, the spheroid chalcedith began to grow and formed dense block structure of cryptic agate. The area between cryptocrystalline chalcedonite and crystalline quartz is easy to form parallel, annular band structure. The color of the strip will vary due to the different periodic chromic elements in the hydrothermal solution, and the width and thickness of the strip will vary due to the different amount of silica hydrothermal injection. In a single strip, coarse-grained, low-structurally deficient quartz interacts with fine-grained, high-structurally deficient chalcedony and clinicite, resulting in local interaction of two or three structures. The formation of the "crystal core" structure is related to the increase of the time cooling of the silica hydrothermal solution and the crystallization temperature as well as the decrease of the crystal nucleus due to the decrease of the hydrothermal concentration in the late stage of formation. The presence of Al element also promotes the formation of the crystal core.