uniform
thickness of 3 to 4 inches and probably were formerly surfaces existing
between floods, each being covered by a later flow of gravel from
rainfall eroding veins farther up the mountain. Shafts sunk on the
hillsides from 27 to 50 feet in depth show values from 10 to 42 cents
per cubic yard. "The average is difficult to determine, as the gold is
not equally distributed. All the gold found is in well-rounded nuggets
ranging from 50 cents to $5 in value. There is a tradition of a lump
weighing 16 pounds, with probably 40 per cent of quartz, whose
discoverers were found murdered in their camp 16 miles north of Tucson.
The nugget had disappeared. In fineness the gold averages about 0.905.
Generally the placer material is dug, screened, and hauled to the creek
and there worked by rockers or sluiced when there is enough water. Many
dry washers have been tried, but most of the gold lies in the red,
clayey seams which apparently acted as "bed rock" for each period of
deposition. Pulverizing this adherent material gives good results with
the common bellows type of "dry wash." A boiler and pump were once used
to throw water against the creek bank, but the water at that time
proved insufficient for extensive operations.
Quijotoa district.—The
Quijotoa district, in Pima County, lies west of Tucson , extending north
and south some distance on both sides of the Mexican line. This area
has been worked in places for free gold by Indians and Mexicans for
hundreds of years. The gold is found from the surface down into a
strata of cement gravel or caliche. The caliche carries more gold than
the dirt above it. The Indians work the dirt above it, and then the
softer places in it by beating it in a rawhide bag, finally separating
the gold with hand machines, which are very crude affairs. The Quenner
machine was tried in this field, but conditions were not similar to
those where the machine has been the most successful. Therefore, the
production of gold is very much the same as formerly, only a few
hundred dollars a year, which is traded for supplies by the Indians and
Mexicans working the placers.
Greaterville district.—At
Greaterville, in Pima County, aoout 9 square miles of dry-placer gravel
have been operated intermittently for many years. A description of the
region is given in a paper ' published by the Survey.
The
pay streaks of gravel and clay averaging about 3 feet in thickness are
overlain to some extent with 12 feet of valueless surface material.
Bedrock is found from 40 feet in depth to within 6 inches of the
surface. Tests have proved the ground to yield an average of 35 cents
per yard in flake, fine, and coarse gold. The fineness of the gold
ranges from 0.800 to 0.850. Production is greatest when the gold can be
recovered by wet washing, although dry washing on a very small scale by
gambucinos is more prevalent.
DRY PLACERS IN NEVADA. By V. C.Heikel
Nevada
has dry placers near Battle Mountain in Lander County, in Lynn district
in Eureka County, at Round Mountain and Manhattan in Nye County, and
in Paradise district in Humboldt County.
Battle Mountain district.—In the Battle Mountain district of
1 H*l, J. M., Notes on placer deposits of Greaterville, Ariz.: Bull. U. S. Geol. Survey No. 430,1910, pp. 11-22,
