First Data on Formation Conditions and Composition of Ore-Forming Fluids in Gold Occurrences of the Kostomuksha Iron Deposit, Karelia

摘要

The Precambrian Kostomuksha greenstone structure is the main iron ore and potential gold-bearing region in Karelia. However, the role of metamorphic fluid in the formation of gold mineralization had until recently remained controversial. The structure evolved in the Late Archean in riftogenic and orogenic stages. The Kostomuksha deposit is composed of the Gimoly series (basal conglomerates; biotite-magnetite, biotite-amphibole-magnetite, and magnetite quartz-ites; carbon-bearing, more rarely, tremolite schists and quartz-biotite schists; and interbeds of pyrite ores). The Gimoly series is cut by fine-grained felsite bodies (haelleflinta) along overthrusts in the deposit area and by potassic granites of the Shurlovaara Massif in the northern part. The most intense collision-related metaso-matic alterations and late quartz veins are restricted to the overthrust zones.