CHEMICAL CHARACTERISTICS OF MINERAL-FORMING MEDIA OF CASSITERITE-QUARTZ DEPOSITS FROM FLUID INCLUSIONS DATA

The study of chemical environment of cassiterite-quartz ore mineralisation was carried out using the samples of lul'tin (Chukotka), Cinovec and Krupka ore deposits (Krusne Hory Mountains ore region, Czech Republic). Bulk analytical methods of fluid inclusion studies in minerals of pre-ore and post-ore mineral assemblages were used. The results were compared with previous data obtained by use of microthermometry of the individual fluid inclusions. The deposits on study belong to the vein-greisen type and are located within the metamorphised sandstone-shale series associated with the leucocratic granite stock bodies. Our fluid inclusion data were interpreted as an evidence of the formation of ores after the temperature was decreased up to 400 degrees C. The deposition of tin-tungsten ores was a result of heterogenisation of low mineralised aqueous-carbon dioxide solutions. The composition of oreforming solutions is characterised by the following properties: predominance of NaCl up to 1 M concentration; increased role of fluorine and lithium, the latter in the case of Krusne Holy Mountains; high sulfur, S(II) content up to 10-(1,2) M and Sigma As up to 10(-1,7) M. Increased alcalinity and oxidation of mineralforming solutions are considered as tbe favouring factors of Sn-W ore deposition. Both chemical processes are interpreted as a result of the local fluid boiling as well as by mixing of magmatic fluids of long living hydrothermal systems with infiltration waters of the meteoric origin.