| Abstract |
The precipitations of sulfides from the Kamchatka modern hydrothermal systems Kireunsky, Dvukhyurtochny, Apapel’sky, Vilyuchinsky, Mutnovsky were studied by EMPA, XRD, ICP and RFA methods. Among other ore minerals were revealed sulfides – pyrite, melnikovite-pyrite, marcasite, sphalerite, chalcopyrite, galena, cinnabar, coloradoite, metacinnabar. Pyrite is the most widespread (common) mineral. It varies in form, size, inner structure features, chemical composition and microstructure. The most common forms of pyrite are framboids, idiomorphic crystals and their aggregate. Their size varies from 5-10 micron to 3-5mm. According to the chemical composition and microstructure they are divided into two groups: homogeneous and heterogeneous. Among the homogeneous the zonal pyrite is widely spread due to the alteration of “anomalous” zones enriched with arsenic, antimony, copper, mercury, silver and “normal” zones with stoichiometric composition. Pyrites with compound heterogeneous composition were also revealed. It is caused by the unequal (cloud-like, mosaic, subblock) separation of definite micro-zones enriched usually with silver, arsenic and sometimes gold. Gold on the detection limit EMPA was revealed only in pyrites from Voinovsky hot spring deposits (the northern part of the Mutnovsky hydrothermal system and Mutnovsky gold-polymetallic deposit, Southern Kamchatka). Here were revealed pyrites with gold concentration 0.45-0.65% mass in definite cloud-like separated microheterogeneities. Arsenic is the most widespread admixture of pyrite. Its concentration may reach 3-5% mass in definite zonal crystals and framboids. Antimony is another admixture of pyrite. It is also involved in structure of zonal crystals and framboids. Its concentration may reach 2-3% mass. Mercury is one of the most common admixture of pyrite. Along with arsenic and antimony it concentrates in form of definite microzonal strips inside the zonal crystals and framboids. Silver and copper are common admixtures of pyrite in carbon pipes and other deposits on slopes of submarine volcano named after Piip (NW of the Pacific Ocean). The framboid pyrites from the Dvuhyurtochnaya hydrothermal system (Central Kamchatka) are the unique geological phenomena. The system is located 85 km westward far from Klyuchevskoy volcano. According to their chemical composition and physicochemical characteristics of water the Dvuhyurtochny systems are nitric sulphate-chloride-sodium, siliceous (H2SiO3 – 130-159 ppm), boric (H3BO3 – 80-95 ppm), arsenious (As – 0.25-3.8 to 8.5 ppm), high-temperature (maximal t=78), alkalescent (pH 8.0). These are common infiltration therms with atmosphere origin. Their cationic and anionic composition is a result of interaction between water and volcanic rocks in the zones of leaching. This water causes deposition of various minerals and aggregate with anomalous concentrations of mercury (150-1000 m), arsenic (200-670 ppm) and antimony (100-230 ppm). Sulfide globule-sferoloids with amazing zonal structure are of particular interest. Such a framboids are formed not only on the bottom of a thermal chamber around the pulsing streams of hot water. They deposit on the plant residues that are located on the hot ground within the “drying zone” around the thermal chamber. They are revealed in fine-dispersed black deposits along the brook running out of the spring. Their morphology resembles spherical sulfide formations from gold-bearing conglomerates Witwatersrand. In definite zones of such a framboids the concentration of mercury, arsrnic and antimony may reach 18.5, 6.7 and 2.3% correspondingly. Sulphur of such a framboids belongs to the anomalously heavy type according to its isotope composition. Cinnabar has the second place for its distribution in the modern hydrothermal systems in Kamchatka. In association with coloradoite, metacinnabar is in the deposits of the Apapelskaya hydrothermal system (Central Kamchatka). Chalcopyrite, galena, sphalerite are rare minerals. They were revealed in deposits from Mutnovskaya, Vilyuchinskaya hydrothermal systems. The modern hydrothermal systems in Kamchatka provide an opportunity to study sulfide topomorphism and diversity of conditions for their formation. We may consider some of them as elements long-life ore generating hydrothermal systems. |