Gold and Silver production in 1912 Page 35



	258	MINERAL RESOURCES, 1912.

	tain the gold is coarser, but the gravel is much less. Miles of the great deposit extending westward from the mountains, and from 3 to 4 miles in width, have been cut into by floods from the mountains, forming deep ravines, and they afford miles of banks 10 to 15 feet high in which the upper layer of gravel is well exposed. From these banks, as far as investigations could be made, samples gave an average return value of 64 cents per cubic yard with gold estimated at $18 per ounce. * * * There were no failures. The results lay between the extremes of 42 cents and $1.04 per cubic yard. To get the limit of the deposit it would be necessary to pursue the tests to points where gold failed. * * * A dry washer was used, winnowing the sand by means of a rotary fan, which blows under a fine screen over which the sand passes in a thin stream. * * * The limit of the gravel actually explored was 2.400 by 1,500 feet and 8 yards deep. * * * Within this area bedrock was not reached at any time * * * Across the valley and about 12 miles from the Plomosa placer is another bed of gravel of similar extent and of high quality. * * * This western mass of gravel is occupied at various places by three camps all rich in gold, and all differing materially in character of gravel. Middle Camp, the most northerly of the three, has granite gravel; Oro Fino, in the center, has much porphyritic slate; and La Cholla, at the south, is mostly composed of quartzite and schist pebbles. * * * At La Cholla * * * which is nearer the mountains, there is a siliceous cement, very rich, but also so very hard that it requires to be broken by powder before going to the dry washer. At Oro Fino the shale bedrock is very near the surface. In Middle Camp there is cement, but of a much softer kind. * * * (Here most of the sampling was performed.) * * * [The camp (?)] occupies the east and west valley crossing the mountain range, a mile wide and 4 or 5 miles long. * * * This is the chosen locality for the individual dry washer, who takes his machine to some point where the bedrock can be reached quickly. It is here that the rich seams of gravel on the bedrock yield from four to ten times the value of the thicker gravels, and in crevices there have been found nuggets worth $10 to $25. La Cholla, south of Middle Camp, lies along the foot of the mountains like Plomosa and is 3 or 4 miles in length. * * * The depth of the gravel is irregular in passing from Middle Camp through Oro Fino to La Cholla. Forty years ago Colorado River was the main gateway, and freight for many years entered that way. The value of these placers was known to the miners who, in that early day, passed over all the region adjoining the Colorado, but the almost total absence of water in the mountains compelled the miners to pack their rich dirt to the river or to distant national tanks to be washed. Oro Fino was the most celebrated camp of that day; there the soft shale bedrock rises to the surface, and when the art of dry washing was learned the rich bedrock was the scene of active work and much of it has been washed and rewashed many times. Surrounding the post office of Quartzsite, in the Plomosa mining district, and extending in every direction covering an area of about 7,500 acres, is found dry-placer ground with values to an average depth of 15 feet and varying from 5 to 50 feet. The gold content per cubic yard is reported to average in coarse gold from 10 cents to several dollars. Efforts are being made to get a combination of equipment which will successfully work the desert gravels and gold-carrying cement gravels at a minimum cost per yard. At a point south of Quartzsite and 17 miles north of Ehrenberg, on Colorado River, a reduction plant capable of handling 2,000 cubic yards of gravel every 24 hours is reported under construction. The machinery consists of a Barnett dredger, a Quenner disintegrating machine, and a Stebbins concentrator. La Paz district.—The placer deposits near the Dome Rock Mountains, in Yuma County, were among the earliest discoveries in central western Arizona. This region, embracing the La Paz district, is described in a Survey report¹ giving a brief history of the region, which is also mentioned in other early reports.³ In the La Paz district the dry placers lie in Ferra, Garcia, Ravenna, and Goodman gulches, about 9 miles northeast of Ehrenberg. The gravel is more or less enriched throughout, but the greater values ¹ Bancroft, Howland, Bull. U. S. Oeol. Survey No. 451, 1911, p. 85. 2 Raymond, R. W., Mining statistics west of the Rooky Mountains, vol. 1872, p. 330, and vol. 1874, p. 344.