Page 151 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

150 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
would require numerous crosscuts into both walls at both hori- zontal and vertical intervals.
It is reported that at 2,000 feet from the portal in the lower tunnel, the vein or lens that was being followed broke up into several branches that made out into the footwall, and that the main fracture in the breast of the tunnel was barren. At 1,800 feet from the portal, the main drift was also following along a barren streak in the breast, but at this point a stringer of ore making into the footwall was followed by a drift that encoun- tered a parallel lens measuring 12 feet between walls. In this lens was a high-grade seam 2 to 15 inches wide. The remainder of the vein contained considerable pyrite and was said to assay between $5 and $6 per ton, with the high-grade seam assaying up to $80. It is thought that the upper tunnels were driven on this lens of ore. The lens upon which the lower tunnel was driven for 1,800 feet is reported to assay in gold from a few dollars to $75, with silver occurring ounce for ounce with the gold, and to contain from 4 to 5 per cent in copper. The lens is from a fraction of an inch to 4 inches wide. In places the ande- site between walls carries up to $7 in gold. At about 1,700 feet from the portal of this tunnel, a small mineralized seam makes off into the hanging wall, and another lens has been opened up that contains a white quartz seam up to 4 inches wide carrying only subordinate sulfides, the value consisting of free gold. Only one vein is visible on the surface of tbis property. Several hun- dred feet from the portal of the lower tunnel, an 80-foot winze has recently been sunk, and drifting for 100 feet north and the same distance south has disclosed 18 inches of mixed oxide and sulfide ore in the north drift, and a 4-inch streak of sulfide ore in the south drift. At this level the vein appears to be 18 inches wide, but the true hanging-wall probably has not been reached. The seam of gouge that is so persistent on the footwall of the Bonanza vein and is from 1 to 18 inches wide with an average of 6 inches, is reported to assay $6 in gold in many places.
The history of this property is fragmentary, and only partial detailed production figures are available. A mill was constructed in 1904 and began operating in December of that year. From December, 1904, to September, 1905, according to Gordon, 48 the net returns on ores from the Bonanza mine were $7,099.29 from shipping ore, $4,821.02 from concentrates, and $23,801.51 from bullion, making a total for the period of $34,721.82. At first the mill had 10 stamps, but the number was soon increased to 20. The returns from three cars of hand-sorted ore shipped in 1905 gave assay returns as follows : Gold 8.65 ounces, silver 32.3 ounces, copper 14 per cent, iron 15.7 per cent, insoluble 47.47 per cent, and sulphur 16.83 per cent. In 1931 development work was done by the Colorado-New Mexico Gold Mining & Milling
48Gordon, C. H., op. cit. (U. S. G. S. Prof. Paper 68), p. 276.