The Fergana Valley is at the western end of the Tien Shan mountain system. Paleozoic marine sedimentary rocks were folded and invaded by granites during the Permian Period. In the area of the Fergana Valley platform conditions prevailed from Jurassic to early Oligocene time, during which both continental and marine deposits collected. Then during the late Oligocene, orogenic activity (docking of the India plate onto Asia) led to relative subsidence of the Fergana graben and deposition of several thousand meters of continental sediments within the graben.
Carnotite deposits are present in the southern part of the Fergana Valley for more than 100 km in an east-west direction along the foothills of the Alay Mountains, which are on the south. The best-known of these are the Tyuya-Muyun copper-uranium deposits (40o 22' N, 72o 35' E). These deposits were known long ago to the Chinese, who worked them for copper. Operations for recovery of largely radium began in 1908 but ceased in 1914. Some mining was resumed in 1923. The mineral tyuyamunite (a calcium uranovanadate) is named for this locality. The district contains several uranium-vanadium-bearing barite veins, copper-bearing barite veins, and purely barite veins. These veins occur in Carboniferous limestone in a belt about 3 km long. The veins fill solution channels in the limestone and commonly have a pipe-like structure. The ore occurs largely as stalactitic forms on the walls of caves in the limestone.
Popov (1939, Sovetskaya Geologiya) states that within the "continental Cenozoic molasse in Northern Fergana there is a quite extensive, although discontinuous occurrence of ore-bearing sandstone.These deposits are said to duplicate almost completely the carnotite deposits of Colorado and Utah." These deposits occur within an area of 2,500 sq km around Kokand and Fergana. In the Uygur-Say deposit ((41o 02'N, 71o 12'E) the uranium ore is in greenish-gray Neogene arkose, which is 5.7 to 8.5 m thick and extends laterally for more than 7 km. The mineralization took place where south-flowing streams off the mountains on the north intersected the main west-flowing streams that drain Fergana Valley. The initial phase of uranium deposition is thought to have occurred simultaneously with deposition of the host alluvial sandstones and underlying lacustrine clay beds. Dispersed uranium minerals are present in both the clays and sandstones. Uranium and radium were carried in solution to be precipitated on carbonized plant remains. The modern ore bodies were formed during a second phase of ore deposition by circulating subsurface waters. The ore minerals are concentrated as lenses on the flanks of structures or in structural sags as well as at the base of the weathered zone. Other ore bodies are associated with concentrations of plant remains. The uranium minerals are cryptocrystalline bright yellow, greenish yellow, and brownish yellow vanadates.
The Curies worked with radium from the Tyuya-Muyun deposit.
Taken from James W. Clarke, 1984; U. S. G. S. Open-File Report
84-0513.
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