Arizona republican., 1902-01-22
Mines and Minerals
 ef Arizona
PLOMOsA PLACER FIELDS
Progress of the Enterprise For Their
 Successful Working.

! Dome range or the west, is strip of country remarkable for the extent
 and richness of it's pIacers. The val ley runs northward for thirty or forty miles, and is from ten to fifteen miles wide.
 Preliminary arrangements are now
 being made by company of eastern capitalists for the proposed dam and reservoir site on Bill Williams Fork of the Colorado river, and water is to
 be conducted by means or a canal to these placers. On the eastern side of
 the valley is the Plomosa placers and on the western side an extended de- posit of gold bearing gravel. which in
 various parts bear the names of Ochoa, Orc Fino and Middle Camp. and they lie at q distance of about forty-five
 miles from the projected dam. The reservoir will have a wonderful Stor- age capacity. The valley slopes to the
 north and affords very extensive field
 for irrigation, and as the soil is fer tile, and the climatic conditions favor able for agricultural and horticultural products, the objects of this company
 are two fold. and their operations will be very extensive. What is now an unproductive and barren waste of
 country is destined to become a rich
 mining and farming section. through
 the element that has made southern
 California what it is-water.
 The extent of these plaoers is as yet undetermined. The examinations made by experts on the Piomosa placer
 were confined 10 a strip of territory half
 g mile long and 1.5OO feet wide. This
 tract lies about two miles from the mountains and opposite a canyon, where large number of pits have been
 sunk to a bed of cemented gravel. which is richer than the remainder of
 the gravel Two of these shafts are
 said to be fifty feet deep, and others
 were found to be fifteen or twenty feet deep.
 This rich gravel has been worked by
 dry washes in preference to the gravel that was sampled by the companys experts. Nearer the mountain the gold is coarser. but the amount of gravel is much less.
 Men with dry washes have operated along the side of the mountain for
 distance of two miles, but the length
 of gravel deposit along the line where samples were taken is judged to be three or four miles. Its width. going
 from the mountain westward. was found to be four to four and one-half miles. The thickness of the great de-
 posit could not be ascertained. but there are deep ravines cut into the gravel by floods from the mountains and they afford miles of banks from ten to twenty-five feet high in which the upper layers of gravel are very well exposed. In was in these banks that the samples were taken. which was, done by scraping off the surface and cutting into the undisturbed gravel with careful avoidance of any ma terial that lay in the bottom of the ravines or that had been worked over by the rains There is no doubt at
 the distance from the mountain at which the samples were taken. the depth of this gravel deposit exceeds
 twenty yards or sixty feet, and there is every possibility that it is twice that. but reporting merely upon what was sampled. q depth of only, eight lizards was taken as the basis of eSti- mates. The average value of this gravel was found to be 64 cents per cubic yard. the gold being estimated
 at SIS per ounce. The metal itself is ! finer than this. however. being worth S19.17 to $19.3O per ounce. but there is always a certain amount of fine sand | cemented to even very small grains of gold. In the sampling there were no I failures, and the results lay between the extremes of 42 cents and S1.04 per
 cubic yard; wherever the gravel was tested it yielded gold.
 The sampling indicated that the inn mediate SuflaCe or the SIOuIu was lHe poorest part. and the deeper the gravel
 was penetrated the better were the re-
 suits A dry washer was used in lsampling. a machine which winnows the sand by means of a rotary fan. which blows under a fine screen, over which the sand passes in thin stream. The gravel is first thrown upon a coarse screen to separate the | layer pebbles. Tests by washing the |
 dinary gold pan with water. indicated that the loss did not exceed , cents per cubic yard. and contrary to the results of hydraulicking. the principal loss was not in fine gold. but in coarse particles which adhered to the larger pebbles. The dry washer saved the finest gold and apparently saved all of l it that was not adhering to large grain of sand.
 Confining deductions to the limits act ually explored, 2400x15OO feet. and eight yards deep. this block of gravel, con
 taining 3,2OO. 900 cubic yards, at GA cents l to the yard. would yield $2, ,04S, 900. The whole mass of gravel in the Plomosa placer seem to contain an hundred times this bulk.
 This placer is different from the gold gravels usually known, in having some what angular fragments of rock, in stead of thoroughly rolled pebbles. The distance from the mountain, from
 which the gold was derived, is so small, and the rushes of water which brought the gravel down were probably of such short duration, that complete round- ing of the water-worn pebbles was not produced. Much of the gold is also angular in shape.
 Plomosa means "lead-bearing," and l is given to this placer because 1t con tains pebbles of galena, a lead ore. These pebbles are derived, like the gold from veins in the mountains on the Hanks of which the placer lies Across the valley and about twelve