Browsing by Subject "Economic geology"

The Kiimala Trend in Central Ostrobothnia, western Finland hosts orogenic gold de-posits. According to earlier studies conducted in the area by the GTK and Ou-tokumpu Exploration, the orogenic gold deposits contain varying amounts of gold ranging from 1.19 to 2.5 ppm and minor amounts of sulfides. In the Kiimala Trend area, the gold deposits of interest are Kiimala, Ängesneva, Vesiperä, and Pöhlölä. Fel-sic porphyries located in these areas are host rocks for orogenic gold, but little petro-logical and mineralogical information on the porphyries exists, and the available in-formation lacks both details and up-to-date data. During this study, the rocks in the Kiimala trend were mainly categorized as plagio-clase porphyries, plagioclase-porphyritic amphibolites, amphibolites, schists, sulfide veins, and diorites. Geochemically the rocks represent various types of gabbros and diorites. The rocks have been metamorphosed in amphibolite facies conditions during the Svecofennian orogeny. During the metamorphic events, low-salinity hydrothermal fluids altered the rocks resulting in saussuritization, sericitization, alkalization, calcifi-cation, epidotization, and chloritization. Hydrothermal fluids also caused the minerali-zation of gold-, iron-, arsenic-, and copper-bearing sulfides as well as the mineraliza-tion of various metals, most common being bismuth, lead, electrum, silver, and anti-mony. Common oxides are rutile that appears often as rims surrounding ilmenite, and hematite that is associated with hydrothermal veins. Most sulfides and oxides can be found as inclusions or in association with quartz and feldspars, exception being ilmen-ite, that can be found in biotite or chlorite.