ORES OF GOLD 63

others by Becker (Ann. Rep. U.S.G.S., 1896-7, pp. 163-7),
and restated with explanation of the two chief difficulties by
the author in 1907 (Tr. I.M.M., xvii, pp. 2-41). It has been
fully confirmed by the detailed survey of the field by E. T.
Mellor (Tr. G. Soc. S. Afr., xiv, xvi, xviii, 1911-15) of the
Geological Survey of South Africa, and the work by R. B.
Young (The Banket, 1917). The Banket of the Gold Coast
Is also a placer, according to Sir A. E. Kitson (Gold Coast
GS. Bull, i, 1935, p. 8).
The future of the Rand depends on the depth to which
the Banket can be mined, and the field has the great advantage
 that the rise of underground temperature is abnormally
slow. Mining has already reached the depth of 7000 feet in
the Village Deep Mine, and plans have been prepared for its
extension to 10,000 feet, which will be more accessible on
the Rand than elsewhere, owing to the slow increase of
underground temperature. .
The gold was probably derived from gold-quartz veins
Dear the granite-schist contact that passes N. of Johannesburg;
 and, as a granitic mass is exposed on the southern
side of the Rand basin near Vredeport, the contact zone there
May have contributed gold to the beds in that district. As
the gold particles are exceptionally small they may be wide-SPread.
 Attention has been called by J. B. Tyrrell (Tr.
LM, 1016, and Econ. Geol., xii. pp. 717-21) to an analogous
€ase of the occurrence of placer gold in minute particles in
the Upper Cretaceous Edmonton Sandstone of Alberta ;
the gold was derived from a distant range in British Columbia
and only the smallest particles reached the sea. This gold
has only peen concentrated to a payable grade where recent
rivers have cut through the sandstone ; there was no wide-Spread
 tidal action as on the Rand. i
Morro VELHo—The Brazilian mine, Morro Velho in
Minas Geraes, is one of the most interesting in the world.
It is workeq by the St. John del Rey Mining Co. which was
foundeq in 1830. The mine has an extensive literature,
including Miller and Singewald (Eng. and Min. Journ., ci,
bg Pp. 207-12); Hussak (Centralbl. f. Min., 1902, pp. 69-92);
fo F. Calvert (Min. Res. Mines Geraes, 1915). It is now 7000
he deep and is one of the two deepest of existing mines.
ts ore differs from that of any gold-quartz lode by maintaining