Tertiary
conglomerates appear to have been laid down in a basin whose upper
surface is now about 1,600 feet above sea level. Platinum is found in
the streams only where the conglomerate has been eroded; stream beds
above the areas underlain by that formation are barren. The stream
deposits are reconcentrations from the older gravels. The tertiary
conglomerate is composed of rounded bowlders of basic rocks, among
which diabase, melaphyre, perido-tite, and dunite have been recognized.
The bowlders were derived from the breaking down of a series of rocks
of Jurassic and Triassic age, which are of widespread occurrence on the
western side of the middle Andean Range. In the gravels of the San Juan
drainage there are about equal quantities of gold and platinum, but in
the Atrato basin platinum constitutes approximately 15 per cent of the
value, the remainder being gold.
The
most productive area is held by English and American capital. What
appears to be a conservative estimate gives a total of 336,000,000
cubic yards of gravel that can be considered as reserves, with
68,000,000 cubic yards as proved ground capable of producing at a
profit under present working conditions. It is well understood that
prospecting in the Choco is difficult and this estimate of reserves may
oe revised in the light of future work.
The
Anglo-Colombian Development Co. completed a dredge on Condoto River in
July, 1915, which operated for some time. That the enterprise was.
successful seems to be indicated by press notices1 to the
effect that more dredges are contemplated and that a preliminary
survey is already under way for the development of electric power.
Information
concerning the platinum deposits of Atrato River has recently been
received by the Survey, which indicates that there are considerable
areas from the headwaters to a point below Bete that might well repay
more thorough prospecting. In the samples of gravels from the vicinity
of Quibdo received by the Survey gold is much more abundant than
platinum, but there appear to be sufficient quantities of platinum to
be of interest.
NEW SOUTH WALES.
According
to reports received from the United States consul at New Castle,
Australia, 56 ounces of platinum, valued at $2,316, was produced in New
South Wales in 1915, as against 244 ounces in 1914. The platinum is
found in the gold placer deposits of the northern beaches, on Evans
River, in the Fineld gold fields, and in the Parks district.
RUSSIA. 'V
According
to information received from the United States consul-general at
Moscow, the output from several platinum districts in Russia in 1915
was 108,202.95 troy ounces, as officially reported, a decrease of
48,572 ounces from 1914. It is stated that the Nicholai-Pavdinsky Co.
has completed a platinum refinery at Ekaterinburg, which will be under
government control.
Platinum is produced in greatest abundance in the South Verkho-turshi district, followed by the Perm district, the North Verkho-
i Eng. and Miu. Jour., vol. 100, p. 976, Dec. 11,1915; idem, p. 119, Jan. 8, 1916.
