Geology

THE more common and familiar metals, when in finished form and ready for the manufacturing industry, are readily salable in the open market at prices which are quoted daily or weekly in the press. Small or medium-sized producers usually sell them through metal brokers or selling agencies that receive a brokerage fee for their efforts. This applies to electrolytic copper, blister copper, electrolytic zinc, spelter (zinc metal prepared by other than electrolytic methods), pig lead, and mercury.

The tonnage of ore reserves is estimated from maps and sections that show the limits of ore and the average grade of the workings that have been sampled. (The methods of averaging a series of samples are described in Chapter 2.)

With Pinching or Swelling of Replaced Beds

Nature of Problems

The character of the subsidence, its extent, and the time when it will develop over an underground opening seems to depend upon many factors, the most important of which are the size and shape of the opening and its depth below the surface; the number and attitude of incompetent beds, bedding planes, faults, and joints; the method of mining and the rate at which mining operations advance; and the com-position, physical character, and shearing strength of the material.

The good prospector works methodically, knocking a córner off every outcropping rock and cracking open pieces of float, especially if they are dark or rusty-looking. If he suspects them of containing gold, he may need to roast them in a fire or in a forge to free the gold particles before grinding and testing in the pan. Gravel and soil are likewise panned to reveal heavy minerals.

The prospector's manipulation of the pan has been described as follows:

In an operating mine, a plant of some sort is already in existence and the immediate minimum rate of production is determined by the capacity of this plant, provided, of course, that there are no physical obstacles to prevent the delivery of ore at this rate. If this rate uses up the ore in a very short time, so much the better from the standpoint of profit per ton and present value of anticipated earnings. The present size of the plant need not, however, place an upper limit on the assumed rate of production.

Published Records. A certain amount of authoritative information in regard to the ore occurrence, past production and geology is usually to be found in published reports, particularly those of the government and state geological surveys.

In the United States and most parts of the British Empire, as well as in many Latin American countries, nearly every mining district has been described either in general or in detail, and many of these reports include not only the geology but the history and records of production for the more important mines of any district.

Localization of ore at vein intersections is very common. A classic example, the Neue Hoffnung Mine at Freiberg, is familiar to all students from the figures in the texts. A common type of oreshoot at an intersection is shown in Figure 98, and many other examples have been described. In some districts, though, intersections appear to have no ore-localizing effect whatever. This is the case at Oatman, Ari-zona.

Cadmium, Indium, Germanium, Gallium

All of these metals are by-products of treating zinc ore. No ore is mined primarily for its cadmium content but zinc ores rich in cadmium are treated preferentially and command a premium. Indium has important industrial uses and may become still more important. Little germanium and gallium are used at present but they are said to have future possibilities.

Cobalt