41
elements Sn and F, but W, Mo, Cu, Fe, Pb, Zn ores are coupled to
hydrothermal manifestations. The large deposit Ivigtut of cryolite (Аl, F)
has been found in Southwest of Greenland, where the field Ilimaussak (U,
Th, TR), is bound with syenites.
The carbonatite bodies of middle age Riphean and younger are
connected to the intercontinental riftic belt of East Africa. The compound
complex Palabara is located to the east from Buchveld lopolite. It is
composed of concentric intrusions of pyroxenites and syenites, with
carbonatites, containing industrial ledges of copper, uranium, zinc and
apatite, which are accompanied by magnetite, apatite, infrequent elements,
fluorite, phlogopite and vermiculite. In the massives of alkaline basic rocks
Pylanesberg carbonatites, the same complex of mineral resources with
industrial concentrations of uranium, yttrium and fluorite is contained.
Proterozoic carbonatites, found in
Canada and India,
are also regarded to the
riftic structures.
In Proterozoic, a great number of large and unique ores of моnomineral
and complex uranium deposits have formed on ancient shields and
platforms. Among them are selected the following types of deposits:
nonconcordance; the complex uranium ores in hematite’s breccias of
Оlimpic Dam (Australia); stratiformal uranium and vanadium-uranium
deposits in the province Francevill (Africa); polymetal stratiformals and
veins uranium deposits of the province Катаnga (Africa), Canadian and
Ukrainian shields. Along with them, the uranium deposits appeared, as a
rule, in epochs immediately following the above noted periods of tectono-
magmatic activizations.
The climatic factors influenced the intensity of processes of formation
stratiformal deposits of uranium. At first, the stability of oxides of uranium
in nonoxygen environment of late Archean and early Proterozoic has
stipulated the possibility of origin uranium and gold placers, the formation
of which in the later oxygen’s epochs has practically impossible. Secondly,
with appearance of oxygen-rich atmosphere in the middle of the Proterozoic
the dissolubility of joints of uranium and their migratory capacity in near-
surface waters has increased. This factor promoted
their delivery to carbonic
chemical barriers, where in the renovated conditions the deposition of
uranium and formation of numerous deposits of high-quality ores in post
Karelian epoch took place. In further, owing to arising zones of leaching of
uranium its contents in near-surface waters has declined, and the losses of
metal on paths of migration of uranium waters have increased, because of
development the biosphere, therefore possibilities of formation sedimentary
deposits of rich uranium ores were confined in more younger epoch
(Kudryavtsev, 1996).
IV. P l a t f o r m i c – g e o s y n c l i n a l and o c e a n i c c y c l e
(900 -200 Ma) of geological development of the Earth is subdivided into
three stages: 1. late Riphean – Vend (900-600 Ma), 2. Cambrian-Silurian
(600-400 Ma) and 3. Devonian – early Triassic (400-200 Ma).