Abstract
The metamorphosed weathering profile on the Saksagan plagiogranite at the base of the Krivoy Rog structure is of significant scientific and practical interest. It is exposed in numer ous drillholes and workings at the Ingulets, Rakhmanovo, Il'icha, Dzerzhinskogo, Kirova, and Libknekhta mines [2, 3, etc.]. However, sufficiently complete profiles of the metamor phosed saprolite (eluvium) are known only from isolated descriptions. The authors have examined the metamorphosed weathering pro file on the Saksagan plagiogranite in the Likhmanovsk (southern) part of the Krivoy Rog structure in DH 20630 near Rakhmanovo. The metasaprolite profile discovered here is highly representative of the Krivbass region. The Saksagan plagiogranite s have been dated at 2850±150 Ma [10]. There is still no direct evidence on the time of formation of the volcanics of the Novokrivorozhsk [New Krivoy Rog] group, which rest on basal monomict quartzose metasediments genetically associated with erosion of the chemically weathered sur face zone of the plagiogranites. From the com position, the lithological features of the rocks, the structural-stratigraphic position at the base of the Krivoy Rog synclinorial zone, and the presence of a break and a stratigraphic uncon formity with the overlying meta-terrigenous sediments of the Skelevat group of early Proterozoic age, the Novokrivorozhsk group may be correlated with the late Archean sedimentary-volcanogenic formations of the KonkskVerkhovtsevo supergroup. The lower age bound ary of the meta-terrigenous formations of the Skelevat group has been determined from authigenic concentrations of uranium to be 2500± 100 Ma [12]. Accordingly, the most likely age for the formation of the weathering profile on the plagiogranites in this region is late Proterozoic (2800-2600 Ma). Five zones may be observed in upward suc cession through the profile, the mineral and chemical compositions of which are given in Tables 1 and 2.
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