福建马坑、阳山铁矿床的矽卡岩分带特征及其与矿化分带的关系

CHARACTERISTICS OF THE SKARN ZONING OF THE MAKENG AND YENGSHAN IRON ORE DEPOSITS IN FUJIAN AND THIER RELATIONSHIP WITH THE MINERALIZATION ZONING

福建马坑和阳山是两个伴有多金属(钼)矿化的重要钙矽卡岩型铁矿床,位于永一梅上古生代拗陷东南部的北东向龙漳次一级基底断裂凹陷带中。有关本区钙矽卡岩型铁矿床的一般地质情况、交代矿化特征和生成条件,作者等已于1980年作过介绍。本文着重对上述两个矿区的矽卡岩类型、分带特征、交代作用中组分迁移规律及其与矿化分带的关系进行论述。

There are two main types of skarn in the Makeng and Yangshan skarn iron ore deposits: 1. Calcic-skarn of early stage. It consists manly of granets (grossularite-andradite series), pyroxenes (diopside-salite-hedenbergite series), vesuvianites, epidotes-clinozoisites, plagioclases and orthoclases, in the exoskarn it is usually accompanied by magnetitization, while in the endoskarn, molybde-nitization;2. Manganese calcic-skarn of later stage. It is composed chiefly of Mn-hedenbergites, bustamites, pyroxmangites, Mn-ilvaites, Mn-wollastonites, which are associated with mineralizations of sphalerites, galenas and pyrites. These two types of skarn are closely related to each other but show distinct zoning either in small metasomatic column or in the whole deposit. They are both the products of the metasomatic action of a unified process of the skarn mineralization and may make up a new minerogenetic series of skarn mineral deposits. In this paper eight examples of various kinds of skarn metasomatic columns with corresponding mineralization zoning are given in detail. The data of belance compute of petrological chemical analysis of skarn zones for the main metasomatic columns suggests the migration law of major chemical elements in the skarn metasomatic process, the skarn components like alumium, silicon and calcium as well as part of iron and magnesium are mainly from the primary country rocks. But the most part of iron and manganese are carried up by hydrothermal solutions. The infiltration metasomatism of the chemical components between aluminosilicats (diabasic diorites, granites and other clastic rocks) and carbonate rocks play the major role in the formation of the -;karns, while the diffusion metasomatism also makes important contribution. Detailed investigation of the paragensis of the skarn minerals, especially that of the couples of pyroxene-garnet minerals indicates that calcic skarn andits associated magnetitizations are formed in the condition of lower acidity of the solution with higher oxygen fugacity. Along with the evolution of the sk-arns, the acidity of solution increaces and the manganese skarn, which is acco-mpaied by polymetallic sulfide mineralizations, gradually takes the place of the calcic skarn.