Page 170 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 167
the surface and evaporated there, and since the bed of this mate- rial is 2 or more feet in thickness, it indicates a rather prolonged period of neither deposition nor erosion of fan material. At the present time the three streams that built up the fan are degrad- ing it, and where they have cut deep enough to destroy the cal- iche bed, they have redistributed the gold in irregular runs and lenses farther down the fan. In the course of this reworking, much gold has been carried away, and that remaining has been reduced in size, is in flatter scales, and its fineness has been increased.
Black sand accompanies the gold in varying amounts. It is composed principally of magnetite and of limonite pseudomor- phic after pyrite. The pseudomorphs that have been broken and worn down in their migration from the veins to their resting place in the placers are apt to contain but little gold, but the un- broken ones often contain specks or wires of gold. Much of the black-sand concentrate, after separating the free gold particles from it as far as is commercially feasible, would be sufficiently valuable to save and ship to the smelter.
The Luxemburg placers, optioned to the Consolidated Gold Fields of New Mexico, Inc., consist of approximately 500 acres at the apex of the alluvial fan and include the area drained by Grayback, Hunkidori and Greenhorn gulches. These placers in- clude Slapjack and Jones hills, both of which are capped by remnants of the original caliche bedrock. The placer gold is concentrated in runs and boulder chokes above this bedrock, the boulder chokes consisting of accumulations of coarse boulders which have acted as dams to slow up the flood waters over the fan and cause them to drop their load of gold. From Slapjack Hill 10,000 cubic yards of gravel mined by underground methods through a tunnel and treated in a dry concentrator yielded $3.65 per yard in gold over .900 fine. Jones Hill has a similar remnant of the original caliche bed, from above which high-grade gravel has been obtained in underground .workings ; this hill is capped with a thin patch of basalt. The lower ground within the Lux- emburg placers, which has been reworked from the original de- posits, is said to average better than 40c a yard from the surface to an average depth of 15 feet. (See plate VII.)
In Dutch Gulch north of the Luxemburg ground, placer gold has been recovered from the main gulch and its tributaries as far west as the El Oro property. Over 700 acres of this ground is controlled by the Animas Consolidated Mines Co. This com- pany set up a specially rigged combination screening and wash- ing plant, which is fed by a dragline excavator. It is understood that for one run of 4,000 cubic yards put through the machine the recovery of gold was 43c per yard and that the tailings from the machine ran over 10c, the gold in the tailings being of the same character as that recovered. The operation was conducted in the creek bed, where a false bedrock is 9 to 17 feet below the