Page 86 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 85
work on this level that would prove a tonnage of ore. On the 100-foot level the writer saw numerous stringers and bunches of vein matter in an oxidized zone of the vein that was said to assay well in silver and gold ; the gold is in the free state, and the silver occurs as the chloride and bromide. The material hand sorted from this vein during the early operations was said to as- say as high as 2,200 ounces silver and up to 100 ounces of gold a ton. Many small specimens may be seen on the dump, where sorting was done, which contain specks of free gold and crusts and fillings of silver chloride associated with small amounts of malachite and azurite in a matrix of quartz and massive limon- ite. According to Gordon, 38 who saw the lower levels of this mine, "The U .S. Treasury vein evidently carries a large amount of low-grade milling ore and under proper management might develop into a paying property."
To the southeast, the Treasury vein leaves the andesite and enters Magdalena limestone, crossing a north-south contact be- tween these two rocks. On the St. Cloud group, ore has been shipped that contains more copper, associated with the gold and silver, than does the ore from, the same vein where it traverses the andesite. The vein here is nearly 20 feet wide and is charac- terized by a surface outcrop of highly silicified and partly iron stained limestone. The last shipment of ore from the St. Cloud workings is.said to have been made in 1893.
COLOSSAL AND MIDNIGHT MINES
The Colossal and Midnight mines are on the Treasury vein south and east of the St. Cloud workings. The Colossal is re- ported by Mr. Ed James to have produced $75,000 in gold-silver ores that in some shipments carried as high as 10 per cent cop- per. At the Midnight mine the vein in the limestone is con- spicuous for the presence of contact-metamorphic minerals, in- cluding garnet, epidote and calcite, in the wallrock, and for the abundance of copper staining in the upper part of the vein. A mill was erected on this property, but it was in poor condition at the time of the writer's visit. The last shipment of concentrate was made in 1925. In that year it is said that between 4,000 and 5,000 tons of shipping and concentrating ore was taken from the mine. In the past few years the mine workings have caved badly and are mostly inaccessible.
Mills were erected and operated in this part of the district on the U. S. Treasury and Midnight properties, and several smaller plants operated from time to time. Only the Treasury and Midnight mills remained standing in 1932, with part of the milling machinery still in place. On the whole, the mines appear to have been systematically developed, and the plants are of ap- propriate size in view of the prospects for ore and show evidence of good workmanship and economical construction methods.
38 Gordon, C. H., op. cit. (U. S. G. S. Prof. Paper 68), p. 265.