Hydrothermal hematite veins and breccias with rare earth elements mineralization at the Cape Korabl’ amethyst deposit (Kola region)

Abstract

Introduction: The article presents the results of geological and mineralogical studies of the first discovered iron oxide occurrences (hematite veins and breccias in the sandstones of the Tersky formation) with associated rare earth mineralization on the Tersky coast (Kola region) in the eastern part of the Cape Korabl’ amethyst deposit. Methodology: A scanning electron microscope was used to study the morphology and internal structure of minerals. Chemical analysis of hematite was performed using an electron probe microanalyzer. Chemical analysis of rare earth minerals, barite, apatite, and rutile was performed using a scanning electron microscope. Results and discussion: Three varieties of iron oxide minerals have been identified (titanomagnetite, porous and lamellar hematite). Titanomagnetite was found exclusively in host sandstones and was comparable in size to rock-forming minerals (quartz, feldspar), which indicates the allotigenic nature of the mineral. Porous hematite formed during the diagenesis stage, had a porous structure and filled the interstices between quartz and feldspar and acts as cement in the host sandstones. Lamellar hematite formed during hydrothermal processes, made up the bulk of hematite veins and breccias, and also occurs as single grains in the host wall sandstones. REE oxides, phosphates and carbonates were found in veins, breccias and wall-bearing sandstones and are represented by loparite-(Ce), monazite-(Ce), parisite-(Ce), bastnaesite-(Ce). Other accessory minerals were barite and rutile. According to preliminary data, a hydrothermal-metasomatic method of formation of iron oxide manifestations that occurred during the post-Riphean tectonothermal activation of the Kandalaksha aulacogen could be suggested. Based on the data obtained, a model for the formation of hematite veins and breccias was proposed. According to textural characteristics and mineral composition, the iron oxide occurrences in the eastern part of the Cape Korabl’ deposit were similar to the classic iron oxide gold-copper deposit type (IOCG) - Olympic Dam (Australia), which suggests a similar mechanism of their formation. Conclusions: Iron-saturated solutions were formed during the dissolution of authigenic porous hematite in the host sandstones of the Tersk formation by hydrothermal fluids. Porous hematite, the formation of which occurred at the stage of diagenesis, was characterized by an increased content of Ti, which probably entered the mineral-forming system during the dissolution of allotigenic titanomagnetite. During tectonic unloading, (meso)epithermal veins and breccias of anchimonineral hematite composition were formed. Hydrothermal hematite has a characteristic lamellar morphology and was characterized by the absence of Ti and an increased content of W and V.