The Krivoi Rog region of Ukraine is world-famous for its gigantic iron ore deposits. A 10-11 km diameter (or > 8 km, according to Krochuk and Sharpton 2002), perhaps originally 15-18 km large, now deeply eroded impact structure, known as Ternovka or Terny (Nikolskiy 1991; Nikolskiy et al. 1981, 1982; Val'ter 1988), is located in the Proterozoic fold belt of the Krivoi Rog basin, at 49o01'N/33o05'E. Ternovka was formed about 375 ± 25 Ma ago. Both iron and uranium ores have been mined here from several open pits and have also been known for decades from numerous underground workings and boreholes (Masaitis 1989). Mining of uranium ores ceased in 1967 (Grieve and Masaitis 1994). The ores occur in crater floor rocks as well as in impact breccias of this deeply eroded impact crater.
Ore formation was the result of Lower Proterozoic hydrothermal and metasomatic overprint on ferruginous quartzites, among other lithologies, which led to the formation of several mineralized zones that also involved uranium mineralization and that are now exposed in the crater floor. Postimpact hydrothermal activity caused uranium remobilization and the generation of secondary pitchblende veining. In 1994, Grieve and Masaitis estimated the remaining ore reserves for the Pervomaysk open pit mine at 74 million metric tons, but also mentioned additional lower-grade reserves of some 675 million tons. Due to macro-deformation as the result of the impact event, large blocks of iron ore have been displaced and rotated, and mixed in with barren blocks. This geological situation, a direct consequence of the impact event, causes some difficulties during mining operations. A positive result of the impact event is, however, the advantage of working deformed (highly fractured) ore, which proves beneficial
during the extraction and processing stages (as it requires less mechanical work during the ore comminution stage).
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