| Summary: | Summary: The purpose of this paper is to give a petrographic and mineralogic description of a dyke complex, consisting of a metadiabase and a quartz keratophyre. The type locality is the northern part of the Kiirunavaara apatite-rich iron ore, situated in northern Sweden. In this part of the mine, the dyke complex has caused problems with rock stabil ity and water inflow. The dyke is well mapped from drill holes and mining. It cuts the ore body from the footwall to the hanging wall, striking N 75-80 W and dipping 50-60 S. Within the 2-8 m thick metadiabase, the quartz keratophyre appears as a thin, unconform "dyke in dyke", i.e. it does not penetrate the main dyke at all levels. Sections in both the footwall and hanging wall show large balls of the metadiabase, enclosed in the quartz keratophyre. Consequently, the latter formed late in the Kiirunavaara ore region. The metadiabase has a 'blast ophitic' texture, mainly consisting of albite and biotite with accessory amphibole (act-trem). The quartz keratophyre consists of albite and quartz phenocrysts in a matrix with partly granophyric intergrowth of albite and quartz. The albite phenocrysts show chessboard twinning. The same type of amphibole (act-trem), appears as an accessory mineral. Whole rock, trace element and mineral analyses are presentated in tables and in the following text. There is no evidence of a magmatic differentiation trend, neither for the metadiabase, nor for the quartz keratophyre (variation diagrams, Figs. 11 and l2). The contents of Na (mean value 4.19 wt%) and especially K (mean value 2.82 wt%) are high for a basalt (Tab. 2a). However, the mineralogy of the metadiabase is of secondary origin. The albites and biotites look altered, are full of inclusions and grow into each other. To summarize, the mineralogy coincides with that of a spilitic rock, as follows: l. The major minerals consists of highly sodic plagioclase and - as augite is absent - actinolite, chlorite and epidote or chlorite and hematite. Olivine is typically missing (Turner ...
|
|---|