Alteration of rocks, massive sulfide ores and perspectives for gold mineralization of the Panarechenskaya structure (the Kola peninsula)

The present paper has been written on the base of petrographical, geochemical, and mineralogical study of massive sulfide ores and their host rocks from the Panarechenskaya tectonic-volcanic structure in the central part of the Imandra-Varzuga belt. The massive sulfide deposit is situated in the northern part of the western caldera of the Panarechenskaya structure in medium-acid volcanics of the Samingskaya unit. Massive sulfide ore forms lens bodies 0.1-4 m thick, and have been traced with drillholes for 100 m. Lenses of massive sulfides are accompanied by zones of intense sulfide dissemination up the cross section. Host rocks are intensively altered, the main alteration processes are carbonatization and silicification. Silicification is accompanied by re-deposition of ore minerals in quartz and quartz-carbonate veinlets. The main ore mineral is pyrite, minor sulfides are chalcopyrite, pirrhotite, marcasite, arsenopyrite, galena, sphalerite, and some other sulfides, as well as rarely tellurides of Pb, Ag, Bi, Au, and native gold (electrum). Precious metal mineralization is noted mainly in zones of disseminated sulfides near massive sulfide lenses. Au content in the ores is 0.25-0.35 ppm, Ag content is 1.75-2.25 ppm, Au/Ag ratio varies within 1/6-1/7 interval. High geochemical background can serve as a source of precious metals for formation of gold deposits during later superimposed hydrothermal processes. Our investigations have shown that the Panarechenskaya structure, and, first of all, its western caldera, is the area promising for gold deposits, and exploration works should concentrate on searching for quartz-carbonate mineralized veins and zones of silicification.