O mineralizacji uranowej w permo-karbonie depresji śródsudeckiej

Jerzy B. Miecznik



The paper presents results of regional studies on geological setting of uranium mineralization in the Permo-Carboniferous of the Intra-Sudetic Depression. The studies showed that uranium was supplied to that basin in result of volcanic activity in the Westphalian and Stephanian times. This conclusion is supported by the record of hydrothermal uranium mineralization in Carboniferous volcanic rocks and stratigraphic position of uranium concentrations of the sedimentary type (Westphalian B-Autunian).
The volcanic activity from the Late Carboniferous resulted in origin of trachybasalt and rhyodacite lava flows and explosive eruptions of the rhyolite type. At that time (i.e. in the Westphalian), the Rusinowa-Grzmiąca volcanic belt began to form along the Struga dislocation which • separates the Wałbrzych Basin and Sowie Góry Block.
The belt is formed of craters of the maar type and shallow rhyolite intrusions, arranged in a linear way. From the Early Stephanian till the earliest Autunian, that is for quite a long time it acted as an alimentary area of local importance. Sedimentary series deposited in the Stephanian (and early Autunian) times, presumably in the form of alluvial fans, are characterized by very high share of volcanogenic material.
Rhyolites of the Rusinowa-Grzmiąca volcanic belt display quartz-dolomite veins with uranium mineralization (nasturan, black blende and secondary uranium minerals) and Pb, Zn, Cu and Fe sulfides. Moreover, numerous small uranium concentrations of the sedimentary type are known from sandstones, conglomerates, mudstones and claystones of the Upper Silesian, and fairly large concentrations - from Stephanian coals (Okrzeszyn deposit).
The richest uranium concentrations are known from the Silesian-Rotliegend passage beds in the proximity of the Rusinowa-Grzmiąca volcanic belt. They are connected with a sharp unconformity related to movements of the Intrastephanian phase (Grzmiąca deposit). Uranium concentrations from contact of unoxidated rocks and those oxidated due to secondary processes are clearly epigenetic in character.
Shows of uranium mineralization known from Permian sequences are mainly related to black shale horizons (Anthracosia Shale and Walchia Shale). Uranium concentrated in these rocks mainly came from the Carboniferous. However, a supply from areas surrounding the Intra-Sudetic Depression (for example, the Karkonosze-Izera Massif) is also inferred.

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