COMPOSITIONAL CONTRAST BETWEEN ALTERNATING BEDS AS A CONDITION PROMOTING ORE DEPOSITION

Abstract

In the sedimentary sequence of the Ustarasay-Brichmulla ore district there are three members that consist of alternating thin beds and differ in composition of their constituent rocks. Thus, the lower member is dominated by hornfelsed and dolomitic mudstones; the middle, 'transitional' member, as mentioned above, consists of interbedded dolomitic mudstone, sandstone, siltstone and dolomite, but in the upper member, the Brichmulla, dolomitic and calcareous mudstones are combined with dolomitic and clayey limestones. Known deposits and ore occurrences in the Ustarasay-Brichmulla ore district are confined to these members, whereas compositionally homogeneous formations and members, even when consisting of 'favorable' rocks like limestone, lack ore. This trend shows that compositional contrast between alternating strata could be a favorable condition for the localization both of individual ore shoots and, on the larger scale, of ore deposits themselves.