Revaluation of alluvial deposits residual reserves of boulder chrome ores of the Saranovsky ore field

Abstract

Relevance of the work. After the collapse of the USSR, local ferroalloy industry experienced a deficit in certain types of mineral raw materials, in particular in chromium ores. In Perm Krai, in the vicinity of the village Sarany, medium and small-scale deposits of primary magmatic and fragmental slop wash ore of high iron content and alumina are known, previously used only as refractory raw materials. In the 1990–2000s, technologies for producing commercial and conversion ferrochrome with low chromium content (“charge-chromium”) using chromium ores of the Ural region, including ores from deposits of the Saranovsky group, were developed and introduced on an industrial scale. All this entailed the need for geological and economic revaluation of the reserves of known deposits, including placers of wash ores partially affected by mining operations of previous years. The revaluation included not only the residual natural reserves of deposits, but the technogenic formations in their areas containing underextracted ore round stones as well. Currently, the project for the development of boulder placers is being successfully implemented. The experience gained may be of interest in reassessing the residual reserves of objects of scarce types of mineral raw materials characterized by a complex "natural-technogenic" structure. Purpose of the work: to summarize the experience of joint revaluation of residual natural reserves and technogenic formations on the areas of placer deposits of boulder chrome ores aimed at ensuring the maximum completeness of excavation of scarce raw materials. Method and methodology of the work carried out. The main idea of the work is to jointly reassess the industrial importance of the residual reserves of boulder chrome ores contained in natural and man-made formations in placer areas. Given the relatively simple mining and geological conditions and small volumes of annual production, the criterion of “minimum industrial output of ore boulders”, which achieves equality of the recoverable value of mineral raw materials to the operating costs of obtaining marketable products, is proposed to be applied to the residual reserves of the placer, and not to individual geological blocks. This approach obliges the subsoil user to conduct continuous mining of the remaining reserves, to involve in the industrial development reserves of low-productive geological blocks, including those represented by technogenic formations, the average yield of ore boulders from which, as a rule, is lower than the estimated industrial minimum. The rational choice of placers that are simultaneously mined is justified by economic indicators used in the evaluation of mining projects (net present value, profitability index, budget efficiency, etc.), taking into account the “individual” characteristics of individual deposits. The proposed approach to involving in the development of reserves of low-productive areas (including technogenic formations) can be implemented not only at the level of individual deposits, but at the level of a group of “converging” differently productive placers as well, when both highly productive and “poor” placers are being developed, the reserves of which in the traditional assessment are classified only as off-balance sheet (potentially economic). Results of the works. The description is given of methodological approaches to the revaluation and rational use of residual reserves of boulder chrome ores disrupted by mining operations of previous years. The experience gained can be used to evaluate other mining facilities that contain natural and technogenic formations of different productivity on their area.