The study of the ore bodies zonality by composition of olivine in the chromite deposit no. 219 of the Verkh-Neyvinsky massif (Middle Urals)

Abstract

The author considers chromite-bearing ore zone at deposit No. 217 of the southern part of the Verkh-Neyvinsky massif composed of dunites with disseminated chromite ores. The ore zone has a sustained thickness of about 50 meters, a meridional strike and a dip of 35°. Chromite ores are characterized by the clearly defined banding, the elements of occurrence of which exactly repeat the elements of occurrence of the ore zone as a whole. Under the ore zone, there is a block of dunites with vein-disseminated chromite ores. In general, we consider the ore zone as a typical late-magmatic deposit. Increased concentrations of chromospinelide form the ore bodies that are suitable for industrial processing.The study covers a change in the chemical composition of chromospinelide and olivine along the strike of the ore zone. Chromospinelide has a high chromium composition, slightly metamorphosed, and its composition is consistent throughout the entire ore zone. The iron content of olivine shows a clearly defined zonality from the maximum values at the edges of the zone (7-8 % Fa) to the minimum values at the center (3-4 % Fa). This is the first occurrence of corresponding zonality in the Ural deposits of chromite ores. In our opinion, the reason for the appearance of such zonality is in the primary redistribution of matter during the crystallization of chromites from the residual melt. In addition, in the studied samples, one can observe the repeatedly described phenomenon of post-crystallization redistribution of iron between the coexisting grains of olivine and chromospinelide. As in other cases described in the literature, redistribution happens in the narrow contact zone of both minerals.