The Cordova daily times., 1919-02-08
KENNECOTT COPPER MINING

Bonanza mine is borrowed from MT. Moffit:
 The Bonanza mine is Tn the noun tains between the Kennecott glacier and Mccarthy creek, ut an elevation of 5000 feet. The first large ore- bodies found were in the magnetism limestone, so that at one time 1t was supposed this rock had controlled the ore deposition and work was conduct ed accordingly. This supposition had to be given up, however, as tEe work proceeded, for ore was found in both the magnetism and the non-magnes- ian limestone. In the early days a great deal of talk was heard of the favorable" lime, by which was meant the magnetism lime. Also, a great deal of talk is heard locally about bedding-planes. The bedding planes, or flat faults, indicate the movement of one limestone bedon an- ether, or movement along plane par allel or approximately parallel to the planes or bedding. Bedding-plane faults occur in the lower part of the Chitistone limestone at many places and at least four are recognized in the Bonanza mine. The ore is dom- inantly chalcocite The great ore- bodies belong primarily to the yer tical fault system and have been found at the intersection of the yer tical with the fiat faults. They lie above the flat fault and terminate sharply against the underlying lime- stone. The exposures at the surface of the Bonanza mine show no more oxidized ore than those in some of the lower levels. Oxidized ore con- tinues to the 700-ft level. All small veins in stringers must be closely fol- lowed for many of them develop into valuable bodies of ore within short distances.
 The copper deposits of the Jumbo mine resemble in most respects those of the Bonanza. The mine is in the Chitistone limestone, just above the contact with the underlying green stone. The width of the ore-bearing ground worked is not less than it., yet the limits of the ore have not yet been reached. In form the ore bodies are like those of the Bonanza, large tabular masses of chalcocite re- placing limestone along the north easterly faults. Ore was deposited in great quantities at the insection of the vertical and bedding-plane faults, between the 400 and 6O0-ft. levels.
 The great orebody lay for the most part above the bedding-plane fault between it and the magnetism lime stone. It extended from point a short distance above the 6O0-ft. level to point 30 it. above the 4O0-ft level. In projection on horizontal plane 1t had length of 400 fit. A horizontal section of the orebody at the 500-ft. level is shown. This great mass ot ore was practically solid chalcocite, with which was mixed an almost in- significant quantity of included limestone. It has yielded 5O,0OO tons of copper ore, much of which ran 76 per cent. This is the largest single body of this grade of copper ore ever mined.
 The Erie mine is little more than 31a miles north of Kennecott and less than 14 mile from the galcier. The ore so far uncovered is much more oxidized than that of the Bonanza and Jumbo mines. At least one well-de- fined bedding-fault was encountered. This mine is equipped with an aerial tram 2700 it. long, running between the lateral moraine of the Kennecott glacier and the upper adit. Most of the ore shipped from Kennecott Is of high grade and requires no concen- tration. Part of it, however, is con centrated in the mill, the tailing from which is treated in the teaching plant with ammonia, which dissolves the copper carbonate. By this process 65 to 72 per cent of the copper content is recovered from the tailing. The loss is probably due to the fact that fine particles of chalcocite are not attack ed by the amm0nia. Much experi- mental work is being done to perfect the leaching-plant. The difficulties encountered have been mechanical rather than chemical.
 The Mother Lode mine is situated northeast of the Bonanza mine. Since 1913 it has made shipments of ore each winter. This property has just been purchased by the Kennecott Copper corporation. The ore is chiefly
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