Handbook of strata-bound and strataiform ore deposits. Part 6. Cu, Zn, Pb and Ag deposits / Практическое руководство по стратиформным месторождениям твердых полезных ископаемых. Часть 6. Медные, цинковые, свинцовые и серебряные месторождения

Among the strata-bound ore deposits, the group of sandstone-type, sometimes called red-bed type, forms a complex case of genetic problems related to the detrital1 nature of the ore-bearing facies. The group of the so-called red-bed deposits appears to be homogeneous, even if some transitions are frequent, both towards volcano—sedimentary deposits and towards Kupferschiefer2. By origin, the term "red beds" is a term from sedimentary geology which is used for continental to subcontinental variegated detrital to ultradetrital series: according to the strict relationship of copper occurrences of Oklahoma with such an environment (Tarr, 1910), the term red beds has been used for the deposits themselves (Rogers, 1916; Finch, 1928). According to the frequent association with other elements (U, V , Ag), the meaning of the term was enlarged and finally it has become more or less synonymous with "sandstone type" because of the preferential localization of ores within the rocks of this group, even if the ore-bearing rock may belong to a different granulomere class (rudites). Of course, placer deposits are not included in this group although implications are evoked by some geologists. Typical economic minerals occurring in placer deposits are chemically stable and mechanically resistant under the physiographic conditions prevailing during weathering and erosion of the parent rocks, as well as during transport and sedimentation of the detrital grains among which the economic ores have become concentrated, chiefly by the effects of gravity. On the contrary, red-bed ore deposits are characterized by the low chemical and/or mechanical resistance of the economic minerals (sulphides, oxides, carbonates) under conditions prevailing during the period of ore concentration; the economic minerals in this case result from processes of deposition and concentration which involve chemical reactions of precipitation. <...>