This paper presents a complex mineralogical and geochemical characteristic (based on SEM-EDS, ICP-MS analysis) of the fahlband rocks of the Kiv-Guba-Kartesh occurrence within the White Sea mobile belt (WSMB ). The term “fahlband” first appeared in the silver mines of Kongsberg in the 17th century. Now fahlbands are interlayers or lenses with sulfide impregnation, located in the host, usually metamorphic rock. The level of sulfide content in the rock exceed the typical accessory values, but at the same time be insufficient for massive ores . Fahlbands are weathered in a different way than the host rocks, so they are easily distinguished in outcrops due to their rusty-brown color. The studied rocks are amphibolites, differing from each other in garnet content and silicification degree. Ore mineralization is represented mainly by pyrrhotite and pyrite, and pyrrhotite grains are often replaced along the periphery by iron oxides and hydroxides, followed by pyrite overgrowth. At the same time, the rock contains practically unaltered pyrrhotite grains of irregular shape with fine exsolution structures composed of pentlandite, and individual pyrite grains with an increased Ni content (up to 5.4 wt.%). A relatively common mineral is chalcopyrite, which forms small grains, often trapped by pyrrhotite. We have also found single submicron sobolevskite and hedleyite grains. The REE composition of the fahlband rocks suggests that they are related to Archean metabasalts of the Seryakskaya and Loukhsko-Pisemskaya structures of the WSMB, rather than with metagabbroids and metaultrabasites common in the study area.
The article presents the results of studying the rocks of the pyroclastic facies of the Mriya lamproite pipe, located on the Priazovsky block of the Ukrainian shield. In them the rock's mineral composition includes a complex of exotic mineral particles formed under extreme reduction mantle conditions: silicate spherules, particles of native metals and intermetallic alloys, oxygen-free minerals such as diamond, qusongite (WC), and osbornite (TiN). The aim of the research is to establish the genesis of volcaniclastic rocks and to develop ideas of the highly deoxidized mantle mineral association (HRMMA), as well as to conduct an isotopic and geochemical study of zircon. As a result, groups of minerals from different sources are identified in the heavy fraction: HRMMA can be attributed to the juvenile magmatic component of volcaniclastic rocks; a group of minerals and xenoliths that can be interpreted as xenogenic random material associated with mantle nodules destruction (hornblendite, olivinite and dunite xenoliths), intrusive lamproites (tremolite-hornblende) and crystalline basement rocks (zircon, hornblende, epidote, and granitic xenoliths). The studied volcaniclastic rocks can be defined as intrusive pyroclastic facies (tuffisites) formed after the lamproites intrusion. Obviously, the HRMMA components formed under extreme reducing conditions at high temperatures, which are characteristic of the transition core-mantle zone. Thus, we believe that the formation of primary metal-silicate HRMMA melts is associated with the transition zone D".