22 ECONOMIC GEOLOGY 



nent. Experience has shown that the deep ores even at a greatly 

 increased expense of mining may be mined at a profit. Butte 

 shows a zone of oxidation, a zone of sulphide enrichment, and a 

 zone of permanent value in which the workings may be carried 

 far below the surface and still obtain a definite value of metal. 

 The Michigan copper mines and the gold mines on the west coast 

 of British Columbia are examples of mines far below the surface 

 carried on at a profit in the zone of permanent value, as the owners 

 know exactly what to depend upon. 



(8) The gross value of ore deposits is to be determined only 

 by actual measurement of ores blocked out and the determination 

 of the values by careful and conscientious sampling with sufficient 

 precaution to assure the owner that the results are absolutely 

 correct. It is a very easy matter to guess on the quantity of ore, 

 but it would be an easy matter to make an overestimate or under- 

 estimate, for the only estimate that can receive credence is that 

 based upon the ores actually blocked out. It is an easy matter 

 in the sampling of ore chutes to arrive at an erroneous conclusion 

 by a failure to sample the material of an entire vein and find where 

 the value lies. If the purpose is to find out the value of an entire 

 vein, samples are collected in different places; one from near the 

 center, one near the hanging wall, one near the foot wall, one from 

 across the top of the adit, one from the center, and one from near 

 the bottom of the vein exposed. This method will not only tell 

 where the pay streak lies, but also give the average of the entire 

 face. 



Ore bodies like other bodies have three dimensions and there- 

 fore can be blocked out only by actual development. These ore 

 bodies must be cut and drifted upon at sufficient intervals to 

 determine length, thickness, and form of the valuable chutes. 

 The ore bodies may be divided into three classes: 



(1) Ore actually in sight; (2) ore technically in sight; and (3) 

 ore that under the conditions existing should be expected with 

 proper development of the property. 



(10) The next step is the determination of the method of min- 

 ing and treatment of the ores for all time and whatever grade and 

 kind, and to calculate the cost of converting ore into money. 

 Here are 11 factors: Cost of mining, labor and supplies; cost of 

 development, labor and supplies; cost of reduction; teaming; 

 milling; loss in mill; loss in smelting; commission paid to smelter; 

 cost of equipment of mine; cost of equipment of mill; cost of 



