ORES OF PLATINUM 67 
rocks include pre-Devonian granite and porphyry; granites 
and porphyries intrusive into the Devonian; syenite- 
Porphyrites, quartz-keratophyres, and aplites that are 
Carboniferous and perhaps partly Permian. The character- 
istic igneous rocks of the Urals are serpentines and dunites, 
which are intrusive into the Lower Devonian limestones, 
and basic diabases, which range in age from the pre-Devonian 
to Upper Carboniferous or Permian. 
The Urals were compressed by mountain movements after 
the Artinskian (Upper Carboniferous), and some of the folds 
have been overturned westward. The dunite was at first 
regarded as the only parent rock of platinum, but it is also 
found in olivine-pyroxenite, gabbro, and serpentine. The 
Plagi F16, 24.—PLATINUM IN PYROXENITE. 
atinum in pyroxenite replacing and corroding the pyroxenite, P; from 
the Urals. (After Duparc and Tikonowitch, 1g20.) 
placers from which the main supply is obtained (Fig. 23) rise 
on the dunite masses. In pyroxenite, according to Dupare 
and Tikonowitch (1920, La Platine et les Gites Platiniferes de 
POural, P. 80), the platinum * generally forms a local cement 
between the crystals of pyroxene; ” it is often found in 
Nodular segregations of chromite; in the dunite it is seen 
excessively rarely ” (ibid., p. 193). The platinum is doubt- 
less of deep-seated origin; but as it in part replaced the 
chromite and ferro-magnesian minerals, and has been moulded 
on the olivine and pyroxene, Beck truly described the plati- 
Um as the last formed mineral in the rock (Fig. 24). 
South Arrica—The Transvaal is expected to become the 
chief Producer of platinum, as it includes large deposits, 
estimated to contain 5 dwt. to the ton, at Lydenburg in the