Page 56 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

GENERAL FEATURES 55
Mexico and Their Economic Features." They are incorporated in Part V of that bulletin under the head of "Economic Features of Prospecting, Mining and Milling," pages 159-172, and only a brief summary is given in this report.
Mining costs range from $1.50 to as high as $10.00 per ton at average-scale operations. The low-cost limit may be obtained when the full width of the vein or deposit is mined as ore, and where all handling is by gravity through ore chutes and adit tunnels. Similar work, which requires hoisting from depths of 100 to 500 feet with small equipment, increases costs to between $2.50 and $3.50 per ton. Sorting ore in stopes or on the surface adds rapidly to the cost of mining, and where only quartz stringers are saved from the vein matter, it may amount to $10.00 per ton or more. In the development of the small mine it is always desirable to keep in ore whenever possible. The small ore body will not pay for much deadwork in the nature of shafts and long adit tunnels, and at the same time yield a profit. If in following the ore, large and valuable bodies are uncovered, there is then ample time in• which to consider a more elaborate plan of development and extraction. Too often the long tun- nel or deep shaft driven to intersect a vein not sufficiently devel- oped at shallower levels has resulted in the complete failure of the operation. The cost of reopening and equipping an old mine may range from $100 to $300 per ton of daily capacity. These figures include cleaning out, retimbering and sampling all old workings, laying track, providing drainage, pumping equipment, headframe, hoist, mine surface plant, compressor and all work- ing tools and equipment. They do not provide for new devel- opment work or general surface costs. Similar costs for a new mine may range from $250 to $500.
Mill operating costs vary from a low of 50c a ton in a simple amalgamating plant to around $1.00 for amalgamating and tab- ling combined. The costs of flotation and cyaniding are some- what higher in small plants, ranging from $1.50 to $3.50 per ton treated. Milling, which is advisable for some ores and essential for others, serves three purposes : (1) It separates waste mate- rial from the ore and reduces thereby the transportation and smelting charges, (2) it produces a concentrate that can be prof- itably marketed where the untreated ore possibly cannot, and (3) it produces from an uncommercial complex ore a number of profitable products. There is danger, however, that at a small property too large a mill will be built, or that a mill will be pro- vided before sufficient ore is blocked out to insure repayment of the money expended and a fair profit from operation. It is helpful to have milling facilities available during the development of a mine, as at least a part of the costs may be paid out of profits derived from treating the ore. The following factors should be considered, however, before deciding to construct a mill : At least 95 per cent of all prospects do not develop enough ore to be