GEOLOGICAL BASIS OF THE DEPOSIT
The Jáchymov deposit is located in the central part of the Ore Mountains crystalline complex and represents a classic example of a hydrothermal vein-type polymetallic deposit. The mineralization is primarily associated with north-south trending veins cutting through the gneiss and granite basement rocks. Historically, the deposit was exploited mainly for silver, while the uranium mineralization was long regarded as an undesirable by-product.
The principal uranium mineral is pitchblende (uraninite), composed predominantly of uranium dioxide (UO₂) with a variable proportion of U₃O₈. Uranium occurs here in association with nickel, cobalt, bismuth, arsenides, and silver-bearing minerals. This mineralogical composition led miners as early as the 16th century to encounter unusual “black veins,” which, however, had no economic value within the metallurgical technologies of the period.
A distinctive feature of the Jáchymov deposit is the relatively high concentration of uranium mineralization within a limited area. This characteristic later proved crucial both for the development of radiochemistry and for the post-war industrial extraction of uranium.
In terms of isotopic composition, natural uranium contains approximately 99.3% of the isotope U-238, about 0.7% of the fissile isotope U-235, and trace amounts of U-234. It is the presence of U-235 that makes uranium a strategically important raw material for nuclear technologies.
