Black,
and Chaoosh creeks and the headwaters of the Tagil, in the
Nijni-Tagilsk region. Besides these two districts, which furnish
practically the output of the Russian mines, there are numerous
outlying areas in which small quantities of platinum are mined. These
are, in a sense, new deposits, as they have not been described until
recently. They are of great interest, as they not only extend the known
platinum-producing area in the Urals, but furnish, through a study of
their deposits, valuable data as to the geological occurrence of the
metal.
An
excellent description of these smaller deposits, together with a great
deal of interesting detail in regard to the platinum region of the
Urals in general, is given in an article by Mr. Chester TV. Purington
on the "Occurrence of Platinum in the Ural Mountains,"a from which the following notes are taken:
A brief summary of the newly reported localities is as follows:
1.
The gravels of the Petropavlovsk and other creeks which head in
the olivine-bearing rocks of Chistop and Choi-Ekba mountains, lying
about 100 miles north of the Iss Valley. The production of this region
is slight, only about 55 ounces per annum.
2.
The valleys of the Immyana and Chirok rivers. The latter is a
branch of the Solda, which flows into the Tura below Verkotur. The
annual yield is about 1,000 ounces.
3.
The Bolshoi and Mali Kamenushka creeks, which lie in the area
adjacent to the Nikolai Pavdinsk and Shuvalov grants, the annual
production amounting to about 3,160 ounces.
4.
The Sosnovka and Mali Kosva creeks, which probably derive their
platinum from the dunite which outcrops on Kosvinski Hill near the
boundary of the Rastessk and Nikolai Pavdinsk grants. The production of
these creeks is about 5,800 ounces per annum.
5.
The left bank of the Vergran River at Bogostlovsk, about 50 miles
north of the last-named localfty. The yearly platinum production is
from 250 to 500 ounces.
6.
The Lobva, Lyalya, and Nyasma rivers in the Vagransk, Znamensk,
and Nijni Turinsk districts, to the north of the Iss Valley.
7.
At Neviansk, Verk Isetsk, Alapavsk, Bilimba, Sisertsk, Kishtim,
and Miask, to the south of the Iss. The annual production is about 400
ounces.
There
are many other places in the neighborhood of those already named in
which platinum is known to exist, but in such insignificant quantities
that the occurrences are not worthy of individual mention.
Whatever
the locality of the platinum, it is invariably associated with the
olivine rocks, especially with the so-called dunite, which consists of
olivine with chromite. This dunite is without doubt the mother rock of
the platinum. Mr. Purington says of it:
Assays
of the dunite show the presence of platinum and gold up to the amount
of 0.037 ounces per ton. Exhaustive tests have not been made, hut they
lead to the inference that the platinum is present in the dunite, and
that it must contain an enormous amount; and they bring up the question
of the possibility of the exploitation of deep platinum mines. There is
no doubt that in the midst of the dunite masses there exist some richer
areas, favorable alike on account of primary or magmatic and secondary
processes, -which might he worked advantageously at the present time.
It is to be noted that all the localities favorable to the occurrence
of platinum are characterized by the presence of dunite. Occurrences of
this rock are found for a great length, north and south, along the
narrow Ural ridge. To the north of the Iss Valley a strip of dunite
occurs uninterruptedly. Platinum makes its appearance wherever dunite
is exposed.
As
to the possibilities of further discoveries of platinum-bearing gravel,
careful prospecting in the northern Urals should disclose new deposits,
for the plutonic rocks, including the dunite favorable to the
occurrence of platinum, run on the east slope of the mountains to the
Arctic Ocean, and this vast region for a distance of
a Eng. and Min. Jour., May 5 and 12, 1904.
