Abstract
The Precambrian gold deposit Pedrolampi belongs to the structure controlled type and is located within the intersection between the submeridianal and northwestern schistosity and rock metasomatical alteration zones of the Elmus area in Central Karelia. Structural and mineralogical investigations performed allowed us to confirm that gold-sulfide ore formation occurred in the Late Archean within the submeridianal zone, and more late silver and copper mineralization overlapped along the zones of NW schistosity in the post-Yatulian period. Submeridianally striking quartz veins of the Pedrolampi deposit are boudinaged by NW deformations, and along these zones chlorite‐tourmaline-bearing metasomatites with Ag‐Au‐Cu mineralization developed. The formation temperature of metasomatites, veins, and ores descended from 400 up to 110 ° C and lower in the zone of oxidation. The ore-formation temperature is close for both types of ores and accounts for 270‐ 290 ° C (ore type-1) and 240 ° C (ore type-2). The simple mineral composition (gold‐pyrite), the presence of platinoids and Hg, and the low content of Ag in gold in ore type-1 prove their more high-temperature character and additional source of metals at the early ore-formation stage. Gold‐chalcopyrite mineralization in the ores of ore type-2 formed under lower temperatures and was accompanied by Cu and Ag afflux. Pedrolampi is a Precambrian mesothermal genetically polystage small gold deposit with resources accounting for about 10 t. The Precambrian gold deposit Pedrolampi is located in the intersection between submeridianal and northeasternly directed zones of schistosity and metasomatical alteration of Central Karelia rocks. New data on the geology and magmatism of the Elmus area belonging to the Segozersk-Vedlozersky greenstone belt, ore mineralogy, and ore-boundary alterations of the Pedrolampi area make it possible to consider it as a polygenetic mesothermal gold-sulfide deposit (with resources accounting for about 10 t) formed in the late AR and altered in the early PR. The geological structure of the Elmus area is composed of Neoarchean and Paleoproterozoic rocks (Fig. 1). Upper Archean (Lopian) strata strike in the submeridianal direction. Metabasalts and tuffs in the lower part of the section are overlapped by volcanogenic sedimentary rocks (banded and aglomerated tuffs and volcanites represented by quartz‐carbonate‐mica‐chlorite, chlorite‐cericite shales, sometimes with veinletimpregnated pyrite ores). In the upper part of the section occur metasandstones and polymictic conglomerates. These conglomerates belong to the molasse formations (accumulated in the basin of a strike-slip fault nature) similar to the strata occurring in the Koykarsky structure located to the south. Weakly rounded pebbles of 1‐ 10 cm in size within these conglomerates are presented by apo-tuff schists, porphires, and quartz. Archean strata are broken by bodies and dikes of pyroxenites, gabbro, rhyodazites, granite-porphyres, diorites, and
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