On the classification of geological and industrial types of magnesite deposits

Subject study . Classification of industrial types of magnesite deposits. Aim . To detail the existing classification of magnesite deposits based on a set of defining features. Materials and methods . Materials – a set of lithological-facies, structuralmineralogical and isotope-geochemical features of magnesite deposits. Method – analysis of both our own and literary data for the classification of industrial types and clarification of their genesis. Results . The author’s genetic classification of industrial magnesite deposits is given in accordance with the principles of “specific classiology” and the allocation of taxonomic (crystalline structure, shape of ore bodies) and descriptive features of deposits. Two groups of magnesites are distinguished: A – clear-crystalline in pre-Mesozoic sequences and B – cryptocrystalline in Mesozoic-Cenozoic sequences. Within group A, there are sheet-like deposits of crystalline magnesites (A-2) in carbonate strata and lenses of talcbreunnerite stones among hyperbasites (A-3). Both types have signs of hydrothermal-metasomatic formation. This group includes layers of micritic magnesites associated with subaerial coastal-marine conditions and microbial-diagenetic stages of carbonate accumulation (A-1). The second group includes types associated with the weathering crust of hyperbasites: infiltration-residual stockwork (B-1), sheet clastochemogenic (B-2) and biochemogenic sedimentary-diagenetic (B-3). The distribution of stable isotopes forms non-overlapping areas with reduced δ 18 O values in the group of crystalline magnesites and a maximum in micritic and even higher values for the group of cryptocrystalline. Conclusions. The fundamental difference between the identified groups of magnesite deposits lies in the source of Mg: from seawater (types A-1 and A-2) or from hyperbasites (types A-3, Б-1, Б-2 и Б-3).