cured concessions for working a large area of platinum gravels in this district. Later it was reported1 that
the Anglo-Colombian Development Co. had nearly completed a dredge on
Condoto River and expected to begin working within a short time. The
report states that sanitary precautions have been taken in the
construction of the town and shops of this company, located at the
junction of San Juan and Condoto rivers. The prevalence of fever in the
Choco district is well known, and if foreign labor is to be
successfully used every sanitary precaution must be taken.
The
same correspondent states that prospecting by drill on the Opogodo
property of the Colombian Gold & Platinum Syndicate (Ltd.), had
already proved 1,000,000 cubic yards of gravels, carrying platinum,
iridium, osmiridium, and gold to the value of $0.50 a cubic yard.
GERMANY.
The
discovery of platinum in Westphalia in December, 1913, caused
considerable excitement and no little discussion. In view of the fact
that the matter received widespread notice the following extracts from
an article by Prof. P. Krusch2 may be of interest to those who are engaged in the industry.
During
the last year the Royal Geologic Society of Berlin has begun a special
geological survey of the district. This specialized map brings out the
fact that the oldest platinum-bearing formation known to date belongs
to the " Gedinnien," and may therefore have to be reckoned as Silurian.
Following this we note a series of most varied horizons irregularly
distributed up to the uppermost middle Devonian, where the shales are
still subject to mineralization. The distribution of platinum is
closely dependent on the stratigraphy and structure of the district.
In
such districts as I have examined the slates and graywaeke formations
play the main part. Platinum has been found in diabase and basalt, but
as I have not determined this, I will restrict myself to the former
formations. In isolated instances the slates have carried more platinum
than the graywaeke. The Siegerland miner lays great stress on the
cropping of graywaeke. * * *
1
have made a microscopic study of the platinum-bearing graywaeke
formations. The normal graywaeke is an elastic rock which consists
mainly of quartz and slate, which is bound with a clay cement. It is
therefore made up of the fragments of other rocks. The fragments were
laid in water with imperfect separation by specific gravity. Frequently
the graywaeke contains feldspars which are partly kaolinized. Denckmann
found such conglomerate with distinct granite pebbles. * * *
The
microscopic study reveals that the cement of the rocks is not merely
clayey or siliceous, but is also carbonaceous. The younger formations,
bearing platinum, gold, or zinc, are distinguished by the cement
regardless of geologic age. While the majority of the younger sediments
are of loose texture, the graywaeke are really cemented.
The
platinum-bearing beds belong to the marine sediments. * * * As a result
of microscopic investigation, it is safe to say that the ore minerals
are partly concentrated in the cement and are more rarely found in the
fragments which have been recemented to form the graywaeke. * * *
Of
great interest are the occasional gold particles found in the slides.
They are extremely small and are found in the cement. This appearance
of gold was not surprising to me. With high magnification, 240 to 1,
small black scales can be seen in the cement, very seldom in the
quartz. It is impossible to tell anything about them under the
strongest power. They are easily distinguished from the coarser
graphite scales which are seen occasionally. They frequently show
crystalline structure. By very fine grinding it is often possible to
float these specks on water. L'p to now I have not gathered enough of
them to make
iMin. Jour. (London), vol. 108, p. 157, Mar. 6, 1915.
2 Krusch,
P., The platinum deposit of Germany's Paleozoic (Trans, by F. Sommer
Schmidt) ; Min. and Sci. Press, vol. 109, pp. 879-881,-Dec, 5, 1914.
