Abstract

Several minor porphyry-type deposits occur at the margin of the granitoid complex of central Finland. They are associated with Proterozoic felsic to intermediary porphyries that intruded a previously deformed and metamorphosed metaturbidite-volcanic rock environment. Three examples from Pohjanmaa, central Finland, are given.The Cu-Au mineralization of Kopsa is located in an elongate, hypabyssal stock of tonalite porphyry, which measures 600 X 2,000 m, and is controlled by the intersection of northeast- and northwest-striking faults. The deposit shows a concentric zonal arrangement of base metal contents. The host rock has been affected by potassium metasomatism and by propylitic alteration, and pyrite-pyrrhotite zone occurs in the surrounding metaturbidites.The Mo mineralization of Rautio was emplaced at the center of a multiphase batholith, 15 X 25 km in size. The batholith exhibits a concentric arrangement of plutonic rocks; these are, successively from the margin to the center, diorite, monzodiorite, quartz monzodiorite, and granodiorite, the last being the host rock of the mineralization.The Mo occurrence of Vinnolinneva is located at the edge of a large continuous plutonic area. The host rock is a tonalite porphyry cutting a large quartz diorite to diorite body, 3x6 km in extent. The mineralization is of stockwork type with a dense network of quartz veins.

First Page Preview

First page PDF preview
You do not currently have access to this article.