Wall rock alteration and aeochemistry of andesitic rocks in the Mulgum iron mine area

Mineralogical and lithogeochemical studies were carried out in the Mulgum iron mine in Kyongsang province in order to investigate wall rock alteration as a guide to ore and to find out the geochemical variation around the veins. Strontium isotope analysis by the whole-rock Rb-Sr isochron method was applied to the determination of the age and petrogenesis of the wall rock, Dodaedong andesite porphyry. Wall rocks taken from the underground of the mine reveal remarkable changes in mineralogy, physical properties, and chemical composition with distance from the veins. Geochemical correlation coefficient for nickel-cobalt couple in wall rocks is 0.73. Nickel and cobalt display similar variation around the veins, but the mean content of nickel and cobalt is almost close to background. Copper shows the abnormal distribution in wall rocks towards the veins. An age calculated from a isochron for Dodaedong andesite porphyry is 104.7+-35.1 m.y. (middle Cretaceous) with the intial 87Sr/86Sr ratio of 0.7065+-0.0006. The 87Sr/86Sr ratio is higher than the expected value for volcanic rocks of intermediate to basic composition, which were generated in the subduction zone. This phenomenon implies that magma originated from the subduction zone might be contaminated by radiogenic 87Sr, which were probably derived from old sialic rocks or their derivatives. (Author)