电子探针在蚀变矿物晕研究中的应用

本文选择3种成因的微晶岩石,用电子探针直接在光薄片上进行常规全岩成分分析的实验,并将实验结果与化学分析结果作对比,说明用电子探针粗束斑缓慢移动样品和用细束斑面积扫描两种方法,对某些岩石进行化学成分分析的可行性。作者还采用上述方法,对湘西沃溪Au-Sb-W矿床蚀变矿物晕进行矿物—地球化学微剖面研究,揭示了有关热液矿床围岩蚀变作用过程中元素迁移的规律、岩石退色的机理,提供了矿床成因的信息。

THE APPLICATION OF THE ELECTRON PROBE IN THE STUDY OF THE ALTERATION MINERAL HALO

The alteration mineral halo is the product of "diffusion" and "metasomatism" of ele- ments in the process of hydrothermal alteration. The size of the halo, the features of the mineral association and the distinctness of the alteration mineral soning are all controlled by such factors as the nature of hydrothermal fluids and the composition of wall rocks. An intensive study of the minerals in the halo and their geocbemical features may give us some important information for mineral prospecting. On the basis of studies of the alteration of the Lejiawan antimony deposit of Guang- dong, the Woxi gold-antimony-tungsten deposit of Hunan and the Jingyang pyropbyllite deposit of Fujian, the author selected three kinds of microcrystalline rocks of different ori- gins for whole-rock analysis using an electron probe analyser. The author did not use the conventional rock-melting method for sample preparation, but directly measured the chem- ical composition of a rock on an oriented polished thin sections of the rock by using a thick electron beam spot while moving the sample very slowly along a path across the thin sec- tion. By averasing the measurements along 3-5 parallel paths, obtained the results of the whole rock composition of the rock sample. The comparison of the results with the data from the wet chemical analyses indicates that the measuring accuracy may reacb 5% for those elements with a content of more than 10% and reach 10% for those elements with a content of 1-9%, which implies that the use of these methods for the analysis of the com- position of some rocks is workable and of practical significance. The author has also applied these methods in the study of the alteration mineral halo and undertaken a study of the mineralogical-geochemical microsection of the "bleached rocks" of the Woxi gold-antimony-tungsten deposit of Hunan. The results of the study in- dicate that "bleached rocks" are the product of hydrothermal alteration of chlorite-sericite phyllite and that they are not formed in a single stage of alteration but are the final product of superimposed multiple stages of hydrothermal alteration. It has been revealed that in the process of altertion, Fe, Mn, Ti and Mg diffuse towards hydrothermal veins, while K, Na, Si and Ca diffuse towards wall rocks. This revelation provides grounds for the hy- pothesis that the ore substances of some hydrothermal metallic mineral deposits are de- rived from wall rocks.