determine the value of the deposit. On the other hand in the case of uncertain and irregular deposits, the value of which varies between very wide limits, as, for example—in most metal mines and especially mines of gold and silver—a very large number of samples must be taken—sometimes not more than two or three feet apart—in order that the average value of the ore may be known within reasonable limits of error. The sampling of a large mine of this character may cost many hundreds of pounds. This applies with even greater force to estimates of undeveloped portions of the property. If the deposit is regular and uniform, the value of undeveloped areas may sometimes be predicted with confidence. In the majority of instances, however, the estimates of undeveloped ore contain a large element of uncertainty. In order to determine the probable profit and life of the mine a definite scale of operations must be assumed, the money required for development and plant and for working capital must be estimated, the methods of mining and treating the ore determined, and their probable cost estimated. Where the deposit is uncertain and the element of risk is large, we must adopt a high rate of interest on investments of capital in our computations of value—in some cases as high as 10, 15 or even 20%. Where the deposit is regular and the future can be predicted with some degree of certainty, we may be justified in adopting in some cases possibly as low as 5%. The interest on the annual contribution to the sinking-fund or its equivalent should be reckoned at a low rate of interest, for such funds are assumed to be invested in perfectly safe securities. Allowance must be made for the period of development during which there are no contributions to the sinking-fund and within which no interest is earned on invested capital.
Mining Education.—It is necessary to have the work directed by men thoroughly familiar with the characteristics of mineral deposits, and with wide experience in mining. For the purpose of training such men special schools of mining engineering (écoles des mines, Bergakademie) have been established in most mining countries. A student of mining must receive thorough instruction in geology; he must study mining as practised in different countries, and the metallurgical and mechanical treatment of minerals; and he should have an engineering education, especially on mechanical and electrical lines. As he is called upon to construct lines of transport, both underground and on the surface, works for water-supply and drainage, and buildings for the handling, storage and treatment of ore, he must be trained to some extent as a civil engineer. As a foundation his education must be thorough in the natural and physical sciences and mathematics. In addition there have been established in many countries schools for the education of workmen, in order to fit them for minor positions and to enable them to work intelligently with the engineers. These miners’ schools (Bergschule, écoles des mineurs) give elementary instruction in chemistry, physics, mechanics, mineralogy, geology and mathematics and drawing, as well as in such details of the art of mining as will best supplement the practical information already acquired in underground work. The training of a mining engineer merely begins in the schools, and mining graduates should serve an apprenticeship before they accept responsibility for important mining operations. It is especially necessary that they should gain experience in management of men, and in the conduct of the business details, which cannot well be taught in schools.
Accidents.—Mining is an extra-hazardous occupation, and the catastrophes, which from time to time have occurred, have caused the enactment of laws to protect the lives of the men engaged in underground work. These laws are enforced by mine inspectors who are empowered to call upon the courts and other government agencies to enforce their authority. While in some cases these laws are unnecessarily stringent and tend to restrict the business of mining yet on the whole they have had the effect of reducing greatly the loss of life and injuries of miners where they have been well enforced. This is evident from fig. 20, which shows the number of men killed in the coal and metal mines of Great Britain for a series of years. As will be seen from this diagram the most serious source of death and injury is not found in mine explosions, but in the fall of rocks and mineral in the working places. This danger can be reached only in small degree by laws and inspection; but the safety of the men must depend upon the skill and care of the miners themselves and the officers in charge of the underground work. Great loss of life and injury occur through the ignorance, carelessness and recklessness of the men themselves. who fail to take the necessary precautions for their own safety, even when warned to do so. Mining laws have proved chiefly serviceable in securing the introduction of efficient ventilation, the use of safety-lamps, and of proper explosives, to lessen the danger from tire-damp and coal-dust in the coal-mines, the inspection of machinery for hoisting and haulage, and prevention of accidents due to imperfection in design or in working the machinery.
Fire-damp and dust explosions are caused by the presence of marsh-gas in sufficient quantity to form an explosive mixture, or by a mixture of small percentages of marsh-gas and coal-dust, and in some cases by the presence of coal-dust alone in the air of the mine. Explosive mixtures of marsh-gas and air may be fired by an unprotected light. But when coal-dust is present, and little or no marsh-gas, an initial explosion—such as is produced by a blown-out shot—is required. To guard against explosions from this cause it is necessary to use explosives in moderate quantities and to see that the blast-holes are properly placed, so that the danger of blown-out shots may be lessened. In dry and dusty mines the danger may be greatly lessened by sprinkling the working places and passages, and the removal of the accumulated dust and fine coal. Where large quantities of fire-damp are present, safety-lamps of approved pattern must be used and carefully inspected daily. The use of matches and naked lights of any kind must be prohibited. To lessen the danger from blasting operations the use of special safety explosives is required in Great Britain and some European countries. The use of such explosives decreases to some extent the danger from dust explosions; but experiment shows that no efficient explosive is absolutely safe, if used in excessive quantity, or in an improper manner. Absolute security is impossible. as is proved by the many and serious disasters under the most stringent laws and careful regulations that can be devised.
| Fig. 20.—Death-rate from various classes of accidents in and about all mines in the United Kingdom from 1873 to 1900. |
Mine fires may originate from ordinary causes, but in addition they may result from the explosion of fire-damp or from the accidental lighting of jets of fire-damp issuing from the coal. In some mining districts the coal is liable to spontaneous combustion. A fire underground speedily becomes formidable, not only in coal but, also in metal mines, on account of the large Mine Fires. quantity of timber used to support the excavations. Underground fires may sometimes be, extinguished by direct attack with water. The difficulty of extinguishing an underground fire in this way is, however, very great, as on account of the poisonous products of combustion it is impossible to attack it except in the rear, and even there the men are always in great danger from the reversal of the air current, or back-draught from the fire. Further, the burning of the timber produces falls of ground, making necessary the excavation and removal at times of hundreds of tons of heated rock and
