Geology and Mining Methods

Latouche, or the Beatson plant of the Kennecott Copper Corpn., is located in the Prince William Sound district of Alaska about 80 miles west of Cordova and 60 miles from Seward.

Ore was discovered and claims located on Latouche Island in July, 1897. The mines were worked in a desultory manner until 1910, when the property was acquired by the Kennecott Copper interests. The first shipment of ore was made in 1904; only the higher grade ore was mined and no attempt was made to treat the ore until it was taken over by the Kennecott company. Since that time the mine has been developed to produce 1500 tons a day and a mill has been erected for treating this tonnage, using flotation entirely. The orebody is more or less lenticular in shape with a maximum width of about 280 ft. and a length of about 800 ft. The southern end of the lens is split by a horse of waste for about 400 ft. The hanging-wall limit is a well-defined fault associated with a band of pyrrhotite, having an average dip of 60°. There is no defined foot wall, the value of the ore governing the limits of the mining; in one part of the mine, however, it is defined by a minorfault. The orebody is in a shear zone of the country rock of graywacke and slate. The principal mineral is chalcopyrite associated with pyrite and quartz.

The mine is situated a few hundred feet from tidewater; the mill is on the beach and the ore is hoisted direct from the mine through a vertical shaft into the mill bins. Until the past year practically all the mining had been conducted in open pits. During the past two years, the ore above the 200-ft. level has been developed and a system of stoping devised to recover this ore; however, this system has not been in use long enough to give any definite results as to costs or efficiency. It consists, principally, of dividing the orebody into stopes, across the full width of the orebody, 70 ft. wide with a pillar 30 ft. wide between the stopes. Raises are driven through the stopes at intervals of about 60 ft. and all the ore is broken by drilling from these raises; in other words, similar to a shrinkage stope, doing the drilling from the raises instead of setting up on the broken ore as is customary. The ground is very much broken up by clay slips and seams running in every direction. Shrinkage stoping had been

unsuccessful because of the time necessary to bar down and the impossibility of making the back safe, because of these slips. On the upper level, in the higher grade ore, some square setting was done, but the average grade of the ore precludes the use of this system throughout the mine.

Some exploration work has been done with the diamond drill, but for the greater part drifts and crosscuts have been driven to explore the ground. In sampling, all crosscuts and drifts, as well as raises, are sampled in 5-ft. intervals and a double groove 1½ in. deep by 6 in. wide is cut in each working place. It has been found that results, even with such large samples and double sampling, are approximately 20 per cent, too high. It is estimated that 12 cu. ft. in place and 20 cu. ft. broken produce a ton of ore.

Underground Mines

Mine Openings, Shafts, or Tunnels

The mine has two entrances, a vertical shaft and a main-level tunnel. The main-level tunnel is 970 ft. long from the portal to the central point of the orebody. It is about 7 by 7 ft. in size. Where timber is used, the measurements are 6 by 6½ ft. inside the timber. The shaft is 360 ft. deep with three compartments, each compartment being 5 by 5 ft. inside the timbers. Loading pockets are located below the main level and below the 200-ft. level.

Underground Development Plans

The 200-ft., 150-ft., and main levels are shown in Figs. 1-3. The curves on the 200-ft. level have a radius of 35 ft.; on the 150-ft. level a radius of 30 ft. is used. All the main haulage tracks have 35-lb. rails; on the 150-ft. level, 16-lb. rails are laid, this track being used only for hauling supplies. Track grade is carried uniformly at 0.5 per cent.

The main compressed-air line is 6 in. No. 20 gage galvanized ventilating pipe, 10 in. in diameter, is used.

Mining

Drilling and Blasting.—The following is a list of drills used, together with the size of the steel:

The single-taper cross bit is used on all steel. Holes are tamped with mud enclosed in parafine paper cartridges, and firing is done with fuse and caps or with electric blasting caps and magneto.

The explosives used are 40 per cent, gelatine and 40 per cent. Red Cross manufactured by the du Pont company.

Tramming and Haulage.—Granby 3 and 4-ton side-dump cars are used, dumping direct into the shaft ore pockets.

Baldwin-Westinghouse storage-battery 4½-ton locomotives furnish the motive power. The rails are 35 lb., the gage 24½ and the grade 0.5 per cent.

Underground Storage and Dumping.—The underground storage consists of the two shaft ore pockets, each with a capacity of about 250 tons. The cars dump directly into these pockets, the ore then being drawn to the measuring pocket in the shaft and then loaded into the skips.

Hoisting.—The man hoist is a Coeur d’Alene Hardware & Foundry Co., electric hoist having a 36 by 36-in. drum driven by a 100-hp., 440-volt

motor. A single-deck cage with spring safety dogs and ¾-in. plow-steel rope is used.

The ore hoist is a Wellman-Seaver-Morgan double-drum geared electric hoist having 60 by 42-in. drums driven by a 150-hp., 440-volt Westing- house motor.

The cable used is 1 1/8-in- plow steel; the skips hold 4 tons and are operated in balance; the hoisting speed is 600 ft. per min.

Pumping.—The pumping is not a serious problem; the following electrically driven pumps take care of the entire mine: One Gould triplex pump, 70 gal. capacity; one Gould triplex pump, 275 gal. capacity; one Gould triplex pump, 80 gal. capacity.

Air Compression.—One Chicago Pneumatic Tool Co. compound compressor of 1730 cu. ft. capacity driven by a direct-connected, 2200- volt, 295-hp., synchronous motor supplies the mine with compressed air.

Ventilation.—Natural ventilation has been relied on but with increase in the amount of bulldozing on the 150-ft. level, attendant with increased mining underground, an electrically driven fan of 30,000 cu. ft. capacity is being installed. The ventilation system is shown by the dotted lines and arrows on the accompanying figures.

Lighting.—The mine is lighted by electricity, the circuit being 110 volts. Several types of globes have been used—carbon, mazda type B, and mazda mill type. The mazda mill-type 50-watt globe has been found the most satisfactory. Small carbide cap lamps are used by the miners.

Telephone.—The telephone is used for general underground communication. Electric signals are used in the shaft.

Records of Unit Production

For the year 1922, the total production was 274,863 dry tons (2000 lb.) ore milled. Tonnage broken amounted to 349,071 tons. The following data are based on the tons broken and not on the tons milled.

Work in the mine is done either on day’s pay or on the bonus system. Bonus is paid on footage driven, in development work, or on footage drilled, in stoping.

Bluff mining, 92,365 tons broken.
Tons per man per hour……………………………………………9.68
Man-hours per ton…………………………………………………..0.103

Stopes, 226,199 tons broken.
Tons per man per hour…………………………………………….9.30
Man-hours per ton…………………………………………………….0.107

Stope preparation and development in ore, 30,507 tons broken.
Tons per man per hour…………………………………………….0.661
Man-hours per ton…………………………………………………….1.51

No work done in rock or waste.

All underground labor:

Tons per man per hour………………………………………….1.76
Man-hours per ton…………………………………………………0.57

Surface force:

Negligible.

All mine labor;

Tons per man per hour……………………………………………1.67
Man-hours per ton…………………………………………………..0.60

Total labor turnover for the year 1922 for the entire plant was 248 per cent.; for the mine alone, 235 per cent.

Total labor cost, expressed in percentage of total cost of mining, was 59.1 per cent.

Records of Units of Supplies Used

Explosives used on ore-breaking on bluff ore was 0,3 lb. per ton; on stoping, it amounted to 0.3 lb. per ton broken.

All timber, lagging, and poles used amounted to 0.020 ft. B.M. per ton ore broken.

Power required was: