Page 172 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 169
today as far east as the east lines of Secs. 30 and 31, innumerable small piles of coarse boulders and hollow places on the surface nearby may be seen, where screening operations have been con- ducted in the years past. With the exception of Slapjack and Jones hills, probably all the high-grade placer ground has been removed, and future profitable operations must depend on large- scale production methods applied to ground that probably con- tains less than 30c per cubic yard.
POSSIBILITIES OF THE DISTRICT
The Hillsboro or Las Animas mining district is considered
to be one of the favorable areas in Sierra County in which to conduct campaigns in search of new ore deposits and the down- ward extension of known superficial deposits.
The lode mines unfortunately are largely caved, and hence it was impossible during the investigation to search for shoots of sulfide ore that might extend belbw water level. At the Op- portunity mine such sulfide veins have been found in the draw north-northeast of the old main shaft, where erosion has out- stripped weathering processes. The main portion of the vein, which averages 4 feet between walls, assays over a considerable distance between $5 and $7 per ton, while the quartz stringers, which have a combined maximum width of 6 inches, have assayed between $50 and $80 per ton. In a few places the wall- rock beyond the vein proper can be classed as low-grade milling ore. Assuming a 6-inch streak of $75 ore and a 31/2-foot width of $6 vein material, the entire vein would be valued at $14.62 per ton. The tonnage of such ore is not known, as no attempt has been made to block out reserves. Other veins of a similar nature are probably present in the district. (See footnote, page 59.)
Within the oxidized zone the veins have been extensively worked for their free-milling gold, and except for small ore shoots in virgin ground, pillars left behind in old stopes, and old stope fill, not a great deal of new ore is to be expected at this horizon. Virgin ground may yield some hand-sorted ore which, on the basis of recent shipment records, should assay about $25 per ton in value, and old stopes in the district may contain rela- tively large awounts of fill assaying from $4 to $6 per ton, which can probably bk. treated effectively by simple amalgamation, con- centration or flotation.
The most favorable places to look for sulfide ores are under known shoots of oxidized ores that have been mined to water level, or at other points along the veins that have been important producers in the past, as the Rattlesnake, Bonanza, Opportunity and others in the southern part of the district. The extensions of these veins into Copper Flat deserve investigation. In the south- ern part of the monzonite intrusion in Copper Flat, ores of gold and silver in quartz veins and disseminated copper sulfide ores have been mined, and oxidized surface ores of copper have been