RHYTHMIC ZONING OF VEIN CARBONATES

Abstract

Oscillatory zoning in carbonates of gold ore deposits Darasoon, Shkolnoye and silver-polymetallic deposit Prognoz is studied. Alternation of dolomite and Mn-ankerite rhythms is observed at Darasoon deposit. Single rhythm of carbonates from Prognoz deposit varies by sideritic composition from Mg-Mn-sideritic (oligonite-sideroplesite). Limited Mg-Mn mineral content in siderite can be defined according to the solvus line on diagram FeCO3-MgCO3-MnCO3. Rhythmic alternation of rhodochrosite, calcite, dolomite and Fe-Mn-kutnahorite is observed at Shkolnoye deposit. Oscillatory zoning formation is characteristic for self-organizing system "crystal-solution" at diffusion crystal feed. Composition and thickness of rhythms depend on joined values-starting solution composition, crystal growth rates, concentration anomaly, thickness on the crystallization front, component diffusion rates, coefficient joined crystallization values, phase diagram of the growing crystals. The most important role for oscillatory zoning rise belongs to a limited isomorphic miscibility (or miscibility gap) in isomorphic mineral series rows of minerals crystallized. Rhythmic carbonate crystals grow from fluid viscous enough in the system CaO-Mg-FeO-MnO-CO2-H2O in the presence of alkaline and other components.