Porphyry-Related Metamorphosed Au-Ag and Cu-Mo Deposits in the Precambrian of the Fennoscandian Shield

Abstract

The Pellapahk Cu-Mo and Oleninskoe Au-Ag deposits in the western segment of the Russian Arctic in the Kolmozero–Voronya greenstone belt are considered two parts of an Archean (2.83–2.82 Ga) porphyry-epithermal system, probably the oldest one defined in the Fennoscandian Shield. Formation of the Oleninskoe Au-Ag deposit at the epithermal stage of the system is indicated by the spatial and genetic relationships with the sills of granite porphyry, the geochemical association of ore elements (Au, Ag, Cu, Pb, Sb, As), an Au/Ag ratio of <0.2, and the multiplicity of silver mineralization with different Ag, Cu, Pb, Sb sulfosalts. The geological–structural characteristics of the Oleninskoe and the Pellapahk, i.e., their location in a shear zone, the morphology and size of ore bodies, the scale of the deposits, and the intensity and zoning of rock alteration, do not oppose this model. Mineralized rocks of the Pellapahk Cu-Mo and Oleninskoe Au-Ag deposits were amphibolite metamorphosed in the Neoarchean and again in the Paleoproterozoic. Structures of sulfide melt crystallization formed in the ores during metamorphism, those are fine intergrowths of galena, argentotetrahedrite, pyrargyrite, pyrrhotite, ullmannite, stutzite, and other mineral phases of low-melting-point metals such as Ag, Cu, Pb, Sb, As, Bi.

Keywords

• Fennoscandian Shield
• Kolmozero–Voronya belt
• Oleninskoe Au-Ag deposit
• Pellapahk porphyry deposit
• alteration, gold
• silver