Bisbee daily review., 1919-05-11
MIDDLEIMARCH MINE
 IS AMONG THE OLDEST
CContInned from Page onel

OulCIOp WdS Suldll dItds DuI II6 chimney increased in size materially as depth was eraehed On the fifth level it is oval-shaped, and about 50 feet by 70 feet in area, most of which is comemrcial ore. The chimney Or pipe ,has a dip of about 45 degrees, and lies within silicious limestone about midway between two large DOT phyry dykes The bottom of the in- clined shaft which is being sunk to develop both ore and water, is in in- trusive granite, which is probably the source of naturalization.
 Recent developments have indicated an improved grade of ore at depth. On the seventh level drift has shown 35 feet of high grade copper zinc ore carrying silver values from 3 to over 50 ounces per ton. The eighth level crosscut has just reached the ore-body on the contact of the granite and silicious limestone, at a little over SO feet from the shaft. The ore is exactly like that on the fifth and sixth levels, clean chalcopyrite with some silver values, but much higher grade than any ore encoun- tered above the secenth level. Assays show values from to 1696 copper across the ten feet of ore so far ex- posed, with high grade ore in the face, These developments are of great inn porta nee to the future fthe mine and are considered to indicate large body of ore of better grade than has been expected.
 The ore is typical contact meta mOrphic, made up of garnet, epidote. and calcite, with chalcopyrite, pyrite, and zinc blende. The latter is too low in percentage to be of value, and most of it is dropped in the flota tion treatment and goes into the tailing.
 Method of Mining
 The mining is now done by the shrinkage system until recently the ore was broken down in large open stopes. by the milling system. The ore is trammed from the chutes to a pocket over the shaft. From the pocket it is drawn to a measuring pocket which delivers into a one-ton skip. The latter dumps into a pocket from there to the mill bins.
 Milling Methods and Extraction
 The mill is a straight flotation mill, no gravity concentration being used. It was designed and erected by the writer in the latter part of 1917 and has since been operated as steadily as the limited water supply would permit. The excessively dry weather of the past two years decreased the flow of water to about one-third nor nal.
 The ore is crushed in 2 Telsmith No. gyratory crusher to IF" maxi mum, and is then fed by a plunger feeder to a fit. by 6 it. ball mill. The ball mill is in closed circuit with a 45" Atkins classifier, the finished pulp being elevated to Notation cells on the upper floor by 3" centrifugal sand pump.
 The rougher Notation cells used are the launder pneumatic type, as orig finally designed by George Crerar, "a ano improved by the writer by introduc tion of removable air pans in place O fthe fixed ones attached to the bot tom of the cells. The forth from these machines goes to a K. & K Notation machine for cleaning, and the finished concentrate flows to ponds, which when full are drained and the concentrate dried in the sun for two weeks. By this means the moisture is reduced to about 1296, except dur ing the short rainy season, when this method of drying is unsatisfactory.
 The tailing from the rougher ma chimes flows to PA by s, Dorr thick ener, for recovery of water The un- derflow is a thick mud, carrying off 60Re to- 659e. solids. Consumption of water per. ton ore treated is only about 200 gallons. The clear over flow from the Dorr thickener flows to a stump from which a centrifugal pump elevates it to the head of the mill.
 Flotation reagents used are main, ly coal tar with small percentages of No. 5 GINS. pine oil and creosote. Less than a pound of this mixture per ton of ore is used.
 The average grade of ore mined to date is 18@6 copper. The average ex- traction for the six months ending December 1, 1918, was 9026Gt of the copper content, as calculated from as- says. Screen analysis indicate that by closer classification and finer grading this could be brought up to 594o.
 
 a 200 h.p. Fairbanks-M Morse Type Y oil engine The oil used in this engine is the Richfield Oil Company's 27 plus fuel distillate. The same engine drives a Westinghouse 25 k.v:a., 250 volt,( alternating current generator, which supplies current for lighting and miscellaneous power purposes.
 The concentrates average 169c cop per and ounces silver The silica content is about 159o, and iron 21ac. They are marketed at the Copper Queen Shelter at Douglas, 60 miles distant. A Mack truck and a KisseI truck are used for hauling the con centrates to the railroad. oil being hauled on the return trip.
 Most of the equipment was pur- chased through Los Angeles firms and both the old Middlemarch Copper com pany and the new operating concern, the Arizona Middlemarch Copper com pany, are controlled by Los Angeles people. The directors of the latter company are: w. A. Potter, president;