storms,
when the overburden of ordinary beach sand has washed away, leaving the
black and heavier sand behind. The sands are dug up and washed in
"toms" or sluices, or are handled by concentrators.
Additional
interest has been taken lately in such of these beaches as yield
platinum as a by-product of the gold. Three miles south of Crescent
City, Humboldt County, the present beach is very wide and has long been
known to carry values in gold and platinum. Repeated efforts to extract
these values have previously met with failure. Within the last year,
however, a large plant with an improved system of concentration has
produced a considerable amount of gold, platinum, and iridosmine, while
working in the flat back of the sand dunes of the beach where
well protected from storms. Here a tract of more than 100 acres is said
to yield over $1 per cubic yard on the average from the surface to a
depth of 15 feet, which is the greatest depth to which mining has been
carried.
While
many beaches containing gold and platinum are known at several widely
separated points on the California coast line, notably at Little River,
Humboldt County; Aptos, Monterey County; Surf and Lompoc, Santa Barbara
County, no mining is in progress except some prospecting at Little
River. For many years experiments have continued to be made to work
these beach deposits on a large scale by various methods, but the
business still remains one of small proportions as far as total amount
of product annually is concerned.
Oregon.—The
high price of platinum in 1912 called more attention to such
gold-bearing sands near the mouths of the estuaries as contain
significant amounts of platinum as a by-product of the ocean beach
gold mining. Thus the beach inside of Coos Bay Head, on Coos Bay,
Oreg., is being worked for testing a centrifugal machine which is to
throw both gold and platinum on the surface of carpeting with which the
machine is lined. Ultimate success depends on the method of gathering
the sand which is said to be quite rich on, and for a foot above, the
shale bedrock, which is exposed and involves no stripping. The old
beach at Whisky Run, Coos County, has been worked by various devices
and usually with success. Lately it has been acquired with much
adjacent high beach land for work on a large scale with a traveling
beach dredge capable of working the richer spots below high-water mark
during calm weather and changing to the gulch during storms. This gulch
has been worked for years for gold, and considerable platinum has been
wasted which it is now hoped to recover. The stretch of 6 miles or more
of beach from Port Orford (Curry County) to Cape Blanco has been worked
spasmodically for gold for many years. The sand contains the greatest
proportion of platinum to gold known anywhere on the coast line.
Frequently the value of the platinum yield exceeds that of the gold.
This is due to the fact that Sixes River, which empties in the stretch,
drains several old beaches some miles in the interior, which are also
being redeveloped at this time. In addition to modern concentrators,
cheaper methods of collecting the sand are being added, especially
scrapers. At Gold Beach, south of the mouth of Rogue River, a new
machine is being tested for saving both gold and platinum, which has
been used with reported success on the fine gold in the sands of Snake
River, Idaho. It keeps the heavy sand from caking during the
concentration by means of a jig motion given to the water from a
separate compartment. The method of cleaning up the concentrates is
still to be determined. The ocean beach at this point is said to yield
40 cents a yard at the surface, and as high as $2 per yard in
the black sand at a depth of 15 feet. Some 39 ounces of platinum,
valued at $1,003, came from the black sands of Oregon during the year
1912 incident to mining for gold.
DRY PLACERS.
In
the arid regions of the Southwest, notably Arizona, southern
California, and adjoining areas in northern Mexico, gold has long been
known to occur in variable quantities, to some extent in veins but to
much greater extent in weatherworn, concentrated form in dry, loose
gravels near the surface and in lime-cemented gravel (caliche, argo masa) below.
Natural concentration of the gold liberated by breaking down of vein
croppings has been effected by the small annual rainfall of the country
gathering temporarily in depressed areas and channels and leaving the
heavier material in these depressions after it disappears. This
rainfall, however, is of insufficient quantity to be depended upon to
assist in present economical extraction by hydraulic methods used
elsewhere in recovery of placer gold.
The amount of gold taken from dry placers in the Southwest is very small.
