Литосфера (Jun 2017)
Geological structure and perspectives for mineralization of the Kichany structure, Tiksheozersky greenstone belt (Northern Karelia)
Abstract
Mineral deposits in the Neoarchean greenstone belts in the Fennoscandian Shield, especially in its eastern (Russian) part, are not as numerous as in Archean belts of Canada, Australia, or Southern Africa. The goal of the present paper is to show with an example of Tiksheozersky belt, that Neoarchean greenstone belts in Northern Karelia and Kola Peninsula do contain ore occurrences, typical to greenstone belts in the world, therefore prospects of these geological structures for mineral deposits are not uncovered fully. Ore occurrences of jaspilite, massive sulfide pirrhotite ore, molybdenite with uranium and graphite, arsenopyrite, and gold were found in the Kichany structure of the Tiksheozersky belt. Jaspilites and massive sulfide ores were considered as syngenetic to volcanic-sedimentary host rocks. Occurrences of molybdenite, arsenopyrite, and gold are epigenetic, controlled by zones of alteration. Zonality in ore-bearing altered rocks, peculiar properties of their chemical and mineral composition, as well as composition of rock-forming and ore minerals, were studied in detail. Age of processes of alteration was estimated with different geochronological methods. Dating of zircon grains from the molybdenite occurrence with LA-ICP-MS method showed two events 2600-2700 Ma (formation of host rocks) and 2100-1900 Ma (regional metamorphism) in their formation. Estimation of age of quartz-garnet-tourmaline metasomatite from arsenopyrite occurrence with composition of monazite gave 1789 ± 47 Ma, it corresponds to post-metamorphic event, probably connected with intrusions of tourmaline granites. Gold mineralization in quartz metasomatite and skarnoid has near the same age: titanite, which contains inclusions of gold, formed 1739 ± 15 Ma ago. Hence, occurrences of gold, arsenopyrite, and molybdenite formed in Neoarchean rocks during Palaeproterozoic (Svecofennian) metamorphic-metasomatic events. Gold mineralization is the most promising in the belt. Position of gold occurrences is controlled by thrust zones, gold concentrates in altered amphibolite with arsenopyrite-pirrhotite mineralization.
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