Geologicheskii Vestnik

The chemical composition and temperature conditions of chlorite formation in metasomatic rocks of the Karagaykul ore occurrence, located in the Main Ural Fault zone in the Southern Urals, were studied. The chlorite composition was determined using a TESCAN VEGA Compact scanning electron microscope with an Xplore 15 energy-dispersive spectrometer (Oxford Instruments) at the Institute of Geology, Ufa Federal Research Center, Russian Academy of Sciences, Ufa. A geothermometer was used to estimate the temperatures of chlorite formation [Cathelineau, 1988]. It is shown that in barren propylites, chlorite is represented by ripidolite, brunsvigite, clinochlore, and pennine. The formation temperature of ripidolite is estimated at 330–364 °C, brunsvigite at 292–294 °C, clinochlore at 234–254 °C, and pennine at 208 °C. Chlorite of ore-bearing propylites corresponds to ripidolite, pycnochlorite, and diabantite, which crystallized at a temperature of 204–350 °C. Ripidolite of barren propylites is more ferruginous (X(Fe) = 0.60–0.93) compared to ripidolite of ore-bearing propylites (X(Fe) = 0.37–0.45). The main mechanism of isomorphic substitution in the chlorite structure, which controlled the changes composition chlorite from ripidolite to pennine/diabantite, is represented by the substitution of Mg²⁺«Fe²⁺ in octahedral layers. In addition to the isomorphic substitution of Mg²⁺«Fe²⁺ in chlorite, chermakite substitution has been established with a decrease in its share in the chlorite of ore-free (pennin) and ore-bearing (diabantite) propylites. In propylites, the change in chlorite composition was controlled by the temperature and composition of the mineral-forming fluid. In ore-free propylites, temperature played an important role in the substitution of Mg²⁺«Fe²⁺ in chlorite. In ore-bearing propylites, the change in the composition of chlorite, in addition to temperature, was influenced by the activity of sulfide sulfur. Propylite chlorite crystallized in the temperature range of 204–364 °C corresponds to the temperature range of formation of propylite biotite-actinolite, epidote-chlorite and albite-chlorite-calcite facies. Their formation took place under mesothermal conditions.

Chlorite, propilites, crystallization temperature, ore occurrence

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