The Florence tribune., 1901-06-22
MAMMOTH GOLD MINE.
One of PlnaI County's Steady Pro-
 ducers.
Interesting Description of the Property
 from Professional Standpoint.
By Vim. p. Blake, F. c. s. Director Ariz-
 ona School of Mlnesl

By Vim. P. Blake, F. c. S., Director Ariz-
 ona School of Mines.l
 The recent csving in of large DOT tion of the Mammoth gold mine af- lords text for short discourse upon methods of working large ore deposits without costly timbering.
 The Mammoth is one of the leading gold mines of Arizona, noted for it's lsrge bodies of low grade ore. It is in the southern portion of Pinal county, about fifty miles north of Tucson. It has long been worked, but for the past four years has been under the ca pable and energetic management of the Hon. George r. Blair, who has greatly improved upon former condi- uons of working, especially in the in- troduction of the Bleichert system of wire rope transportation by which the ores are taken at trihing cost from the mines to the eighty-stamp mill on the San Pedro river, six miles distant and many feet lower. The whole plant is very interesting and instructive example of mining, hoisting, transport ing, milling, and the final treatment of the tsilings by cyaniding. The con- ditions may be said to have been ad- verse on all sides. There is no watet or timber at the mine, aud fuel for motive power at the mill costs $8 to $15 per cord. But with the descending buckets of ore on one side the ascend. ing buckets carried water on the other.
 lt has been proposed by Manager Blair to secure water-power on the Ar ayaipa creek, some twenty-five miles distant, for the development of electri- cal energy to be conveyed to the mill and to the mine. But as the water sup- ply is uncertain, this plan may now be superseded by the erection of power plant on the railway at Tucson and the conveyance of the energy to the mine and mill nearly fifty miles away. In this event it is probable that oil-fuel will be used.
 The country rock of the Mammoth and of the Mammoth Collins group ad- Joining is coarse-g grained porphyritic granite, like that at Oracle and the gold fields near Mesa and Florence. It is highly colored, over considerable areas, with red oxide of iron, and is traversed by several dykes of fine grained, light-colored porphyry in as- soeiation with which the gold bearing quartz veins occur. The ore is be- lieved to have averaged in value from g to 80 per ton, and it has been free- milling, though the tailings have al- ways been rich and have yielded har- vest to the two companies which have been working them by the cyanide process. Considerable punches of high grade lead ore have been encountered in mining, and the mineral cabinets of the country have been enriched by beautiful crystaliizations of wolfenite, vauadiuite and descloizite.
 The mine is opened to depth of 760 feet by a central vertical shaft, with drifts on the lode at intervals of 10C feet. The vein dips westwardly at az angle of from seventy to eighty de- grees. The chief ore shute or chimney of pay ore descends from the surface some distance north of the shaft, to the 760 level, aud has practically beer worked out to that depth. It Is this portion of the mine which has beel wrecked by the caving.
 The recent caving is not the first il the history of the mine. From the POI level down to the 800 level larg amount of ore was extracted iron stopes in some places about sixty fee wide. There was no thorough timber ing. It was chiefly by stulls and som square sets at intervals. Portions ( the walls fell iD and left large cavit between the bottom of the 200 and tn 500. This broken, dangerous groun was a constant menace to the lowe levels below the 500, which it was ii tended to make secure by thoroug timbering with square sets. The 6OI 700and 760 were so timbered, usin ten-inch square posts with silis an caps eight inches by ten inches. II 600-foot level was specially braced au Jagged with the expectation of resis ing any heavy fall of earth from abov
 The Mammoth has thus been gre
 consumer of timber. For the la
 three years an average of 50, 900 feet
 squared timber per month has been T
 quired. The quantity put into u mine has ranged from 40,000 feet
 80,0O0 feet, at an average cost of abo
 S47.50 per thousand feet. This timo
 is all hauled to the mine by teal
 from the railroad at Tucson, and h
 been heavy item in the cost of wor
 ing the mine.
 The caving occurred on the night
 April 18th, without warning, at t
 north end of the mine from the surfa