ORE AND SILICATE MAGNETIC PELLETS AS INDICATORS OF STRUCTURE AND FLUID REGIME, AS WELL AS MINERAL AND ORE FORMATION IN THE PRESENT-DAY BARANSKII HYDROTHERMAL SYSTEM, ITURUP-ISLAND

Ore and silicate spheric globules found in the present-day high-temper ature Baranskii (Iturup island) and Mutnovskii (Southern Kamchatka) hy drothermal systems are discussed. Using mineralogical, microprobe, and x-ray powder data, we identified the pellets of native iron, magnetit e, Fe-Ti-Mn silicates (shorlomite-type garnet), and zonal aggregates w ith iron cores rimmed by magnetite and iozite. The pellets contain tra ces (up to 5%) of Ni, Mn, Ti, and Cu; they are regularly shaped, often hollow, and highly porous, ranging in size from less than 0.1 to 1.7 mm. All the pellets are magnetic to a variable degree. It is assumed t hat the pellets are transported from a depth of greater than or equal to 1.5-2.0 km to metasomatites by a ''dry'' reduced fluid with a tempe rature not lower than 500-600 degrees C. The pellets are probably deri ved from a subintrusive diorite body or peripheral magma chamber feedi ng the hydrothermal system. The spheric globule occurrences mark the p osition of the heat-conducting fault zones (as deep as 1.5 km) in hors ts. Having high gas content, the hydrothermal fluid influences the geo logical structure of the system: the hydrothermal breccias form in zon es of hydrothermal solution boiling along the contacts with the subint rusive bodies. The fluid introduces Fe, Mg, Mn, Ti, Cr, Cu, Ph, Au, Ag , As, Al, Si, K, Na, Ca, etc. into the wall rocks. Concentrations of t hese and some other elements steadily increase from early to late stag es of hydrothermal deposit formation. Apparently, the present-day hi,o h-temperature volcanogenic hydrothermal systems correspond to the firs t stage of epithermal ore deposit formation.