Mohave County miner., 1911-09-16
Mining at Great Depth.

ally subsidiary or the Calum ct & Hecla Mining company, belongs the credit of having the deepest shaft in the world and the deepest underground workings from which mineral is being extracted. No shaft crosses the Cal umet conglomerate at depth of 4,500 feet measured from the collar of the shaft, and is now down to a depth of B., 273.5 feet, it having at that depth cut the Osceola amygdaloid and passed through it. It is interesting to note that at the upper portion of this lode considerable native copper was found. In a short time this shaft will be ex- tended at least 10 feet farther in the cutting out of stump, thus making it over a mile in depth.
 No. 3 shaft of the Tamarack has been sunk to depth of 5,222 feet. The col larof this shaft, however, is 3l feet higher than that of No. 5. This No 3 shaft crosses the Calumet conglomerate at about 4,65o feet. At the so-called eighteenth level a crosscut driven 800 feet to the west reached the lode at a vertical depth of 5, lSl feet, from which point a slope has been sunk 300 feet to the twenty-irst level, below which there is a sump of seven feet. The bot tom of this incline is 5,36S feet below the collar of No. 3 Tamarack shaft, measured vertically. The Calumet conglomerate dips at an angle of ap- proximately 3S degrees to the west, so that measured on the incline this point is very nearly 5000 feet from the out crop. At this point the lode looks fair ly good and is sufficiently rich to war rant its extraction and treatment.
 The longest incline shaft in the Lake Superior copper country is No.4 Cal umet shaft of the Calumet & Hecla Mining company, which is down to the eighty-first level, this being approxi- mately distance of 8, 100 feet along. the slope at an incline of about 3S degrees.
 The rate of increase of temperature
 
 not excessive, the rock temperature at a depth of 5000 feet vertical being ap- proximately 90 degrees F., and if pro- per means of ventilation are used there IS no difficulty in operating at this depth. If, however, proper connect ions are not made, the air becomes ex- cesSively humid, thus materially re- ducing the efficiency of the miners. The mechanical difficulties in mining at these depths consist in the necessity of keeping the timber close to the working faces because of the great pres sure due to the superincumbent mass of rock, ana the method of mining HOW used is similar to the lOng-wall retreat ing method of the coal mines.
 When it comes to hoisting ropes it is impossible to keep the same high fact or of safety as in shallower mines, this factor being oftener reduced to 3.5. This, however, has led to no serious consequences other than that of some increased expence because of the nee essity of more frequent changing of the | ropes, so as not to keep them too long in service.
 It is fortunate that ID the Lake Su- | periOr copper mines, after getting down below the fractured surface zone, | practically no water is found. On the . lowest levels of the Tamarack mine the | only water visible is a slight seepage, | which is extremely bitter to the taste. | Analyses of the water have shown the | presence of chlorides and bromides of | sodium and magnesium. There has | been considerable discussion as to the | origin of this water, some thinking it is | the remnant of prehistoric ocean wa ters and others believing that it Is the | water which deposited the minerals. | However, from a practical point of view | the fact is that these mines, at the | deepest levels, make only a little more | water than is necessary for the use of | air drills. No pumps are installed in | the mine and the little excess of water is bailed out once a week, or oftener. |
 There is a gradual decrease in cop per contents of the rock as depth is at tained, which has been made up for by i increased efficiency and improved | methods-Mining Record.
 naan Minin0 fo Saonra HoII !