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By Thomas C. Patton, Eric S. Cheney

L-D gold mine is 3 miles south of Wenatchee, central Washington. Recognition of locally mappable conglomerates, sandstones, and shales within the Paleocene (?) Swauk formation led to the discovery that the known epithermal gold mineraliza¬tion is limited to a previously unknown imbricate thrust zone of unknown displace¬ment cutting the open folds o f the area. Hypabyssal intrusions also are most nu¬merous along the trace of the thrust faults. Yakima basalt of Miocene age uncon¬formably overlies the Swauk formation, thrust faults, and the intrusions. The L-D mine is in a northwesterly trending imbricate fault block of nearly vertical strata. Microscopic native gold, electrum, and naumannite occur in quartz veins and as low¬grade disseminations in the well-silicified portions of arkosic sandstones. Fault gouge on the "footwall fissure" limits ore to the hanging-wall block of the fault. Epithermal mineralization and alteration are spatially related to the nearby intrusions. Right lateral north-south faults offset the ore a maximum of 300-400 ft along any one fault. From 1949 until January 1967, when the L-D mine closed, 1,036,572 dry tons of ore valued at $14,962,305 and averaging 0.396 oz Au per ton and 0.607 oz Ag per ton were mined. Recognition of the structural control of the mineralization and altera¬tion within the Swauk formation suggests several areas within and outside of the mine that warrant further exploration. For example, the high-angle faults, imbricate thrusts, and the intrusions of this area are on strike with similar features along the major Entiat fault zone 10 miles to the northwest. The L-D gold mine (previously called Squilchuck, Wenatchee, Golden King, Gold King, and Lovitt) is located in Squilchuck Canyon about three miles south of Wenatchee, Chelan County, Wash. (Fig. 1) on the eastern edge of the Cascade Mountains. The major stratigraphic unit in the area is the nonmarine early Tertiary Swauk formation, which is predominantly com¬posed of arkosic sandstone. The lack of laterally per¬sistent units and the paucity of outcrops heretofore have precluded all but the grossest subdivision of the Swauk.' As a result, the true significance of the open folds in the Wenatchee area was not recognized, and although the geology within the mine was known, the structural setting of the mine was virtually unknown. During the present investigation, several locally map¬pable units were discovered within the Swauk which, in conjunction with mine maps, indicate an imbricate thrust zone. The epithermal gold mineralization, most of the hypabyssal intrusions, and the zones of hydrother¬mal alteration are located within or near this thrust zone. The purpose of this paper is to: (1) to describe this structural setting, rather than the detailed mine geology already presented by Lovitt and Skerl,2 and (2) to sug¬gest that from an exploration standpoint, this struc¬tural setting may be repeated in areas inside and outside of the mine area. Stratigraphy and Structure of the Swauk Formation General: The Swauk formation contains three distinct lithologies. Typical Swauk sandstone is gray on fresh surfaces, poorly sorted, weathers tan, and is cross¬bedded; it consists of 40-60% quartz, 20-40% feldspar, and up to 10% muscovite and biotite 9 The typical shale is gray to dark brown, very soft, and interbedded with silty sandstones; sharp contacts exist between the

Jan 1, 1972

By Randolph C. Specht

A two year study was made of the waste disposal of the pebble rock phosphate industry. Solid slimes are impounded in large settling areas and the process water is re-used. Clear effluent was not found to be toxic to fish or animal life in field tests or in controlled experiments. Survey: The pebble rock phosphate mining and washing operations in Florida (fig. 1) are along the river basins of the Alafia to the west and the Peace to the east. The elevation of the area varies between 40 and 170 ft above sea level. Effluents from the operations find their way into one of the two river systems (fig. 2), the Peace River which flows into Charlotte Harbor and the Alafia into Tampa Bay, both along the Gulf of Mexico. There are no major industries along these rivers below the phosphate operations. On the Peace River, the town of Arcadia, approximately 50 miles below the phosphate operations, obtains its water from the river. No other communities along the rivers use them as a source of water supply. Small communities, farms, and ranches are located along the rivers and both rivers drain vast swamp areas. Complaints had been received at the office of the Chief Sanitary Engineer, of the Florida State Board of Health,' that both rivers were turbid at various times and that fishing in the Alafia River was "not as good as it used to be." Tests made by another agency on the dissolved oxygen content of the Alafia River revealed that the oxygen content, at times, was comparatively low.= However, it was not shown that the phosphate wastes had any effect upon the oxygen content of the stream. The river waters are normally brown in color due to drainage from vast swamp areas and are very shallow, from 2 to 6 ft in depth. Turbid waters have been noted in streams coming from the present phosphate operations and also from streams along which there are no operations at the present time. It was learned from "old timers" that, when many more companies than at present were operating along both the Alafia and Peace Rivers forty or fifty years ago, no attention was paid to prohibiting the disposal of slimes along the river basins. During dry periods now in some of the river swamps where drainage ditches have been dug, it is indicated clearly that phosphate slimes were disposed of directly into the river swamps for many years past. Places have been observed where there were alternating strata of phosphate mud, leaf mold, and quartz sand. The former practice of indiscriminate disposal of wastes accounts for some turbidity, particularly after heavy rains and washouts and during clearing of land and digging of drainage ditches. During a six months' period in which a large tract of land was being cleared and drainage ditches dug, a small stream (Six Mile Creek), which previously had been clear, showed a turbidity of 600 ppm and remained turbid until the clearing was completed; after which the stream again flowed clear. An interview with the operator of the municipal water plant, which is about 50 miles below the phosphate operations on the Peace River and which used this river as a source of supply, revealed that there had been no taste in the water for the past ten years, other than that occasionally encountered from increased growth of algae. The operations of each of the cooperating com-

Jan 1, 1951

By O. M. Schaus

REDUCED activity of mining, because of the business recession, had the effect of lowering working time, hence of reducing exposure to accidents, so it is probable that 1938 will be found to have had a lesser number (both fatal and nonfatal) though the accident rate may remain about the same as in 1936 and 1937. During periods of re-employment, such as occurred during 1936, 1937, and 1938, the new men entering the industry are less experienced and not as well trained in accident prevention as are the older, more experienced men and are frequently subject to more accidents. This situation should tend to correct itself as the new employees be- come better trained.

Jan 1, 1939

By Alan Kissock

MOLYBDENUM is thought of as one of the rarer elements, for though it occurs in almost every country of the world it is seldom found in commercial quantities. In this country, however, there is one deposit which makes the term "rare" a misnomer. There are two commercially mined molybdenum minerals: molybdenite, the sulfide, and wulfenite, a lead molybdate. Of these two only the former is of any con- sequence but wulfenite is of mineralogical interest. It is frequently associated with oxidized lead ores and particularly in arid sections. Deposits, however, are usually quite superficial. It is highly oxidized and yet it does not appear to be an alteration product for it apparently disappears below water level and I know of no case where primary molybdenite, or in fact any molybdenum whatever has been identified below these surface wulfenite occurrences. The genesis of wulfenite would make an !- interesting study.

Jan 1, 1933

By Donald M. Liddell, G. C. RIDDELL

THE cosmic ray continues to engage the attention of the physicists, and according to Millikan and Compton, experiments of the past summer indicate that these rays must come from interstellar space, but not from the stars themselves. According to press reports of the International Congress of Physicists at Rome, the view was given there that these rays have an initiating potential of over 750,000.000 volts. In the field of spectrographic investigation great strides have been made. The U. S. Naval Research Laboratories (R. F. Mehl and G. E. Doan of Lehigh) have just finished a year's work with a "radium torch" or "shadowgraphic apparatus" in the field of the X-ray, that bids fair to displace the latter to a great extent. The torch is more powerful., easier to operate and cheaper. Penetration of 10 in. of steel has been accomplished, which. is much -beyond the- -scope-, of the X-ray..

Jan 1, 1932

By A. B. Parsons

AN often repeated criticism of the profession of engineering is that it is as a whole it lacks solidarity. organization, co-ordination, and leadership. Significantly, the critic, are all engineers. Other members of the body politic either do not know about the absence of organization or they do not care. If engineers have no organization they have a plethora of organizations. There exist in the United State, today some 350 societies. institutes. clubs, associations, and councils of engineers and engineering technologists and this number excludes several hundred local chapters of national societies. trade associations, and local engineers' clubs of purely social character- Successful engineers must be proficient in analyzing, planning, and co-ordinating. but it is generally admitted that for their profession as a whole their success in this respect has been indifferent.

Jan 1, 1943

By H. M. Howe

A Discussion of the paper of Professor Howe, presented at the London Meeting, July, 1906, and printed in Bi-Monthly Bulletin, No. 14, March, 1907, pp. 169 to 274. SECRETARY'S NOTE.-M. Beutter's introductory remarks, being simply a resume of Prof. Howe's paper, with a disclaimer of the intention to criticise it, have been omitted, and the remainder of this contribution has been somewhat condensed, without omitting any essential statements. M. BEUTTER, St. Etienne* (communication to the Secretary-+):-Professor Howe observes in paragraph 47 of his paper that the fluid-compression of steel. diminishes piping by forcing the liquid and viscous metal, while the pipe is forming, or after it has formed, into the space so produced, and proceeds to study the different systems of compression, alluding to the four principal ones: Whitworth, Illingworth, Williams, and Harmet. Having now for many years had in use the last-named process, that of M. Henri Harmet, I shall attempt to explain the difference between it and the three other processes named. The Harmet process does not diminish or close the pipe after it has formed, but prevents it from forming; and I may add that it is the only one of the four which produces this result. It is true that the Whitworth process diminishes the interior hollow by localizing it around the central axis of the ingot, which is afterwards removed by trepanning the hollow forgings for which this process has been, I believe, always exclusively used. The Illingworth and Williams processes, which, in my opinion, are applicable only to small ingots, of necessity allow the pipe to form, or (to use the expression of Professor Howe) they allow the surface of the lake of liquid steel to sink into the interior of the ingot, since they involve waiting a certain time before compression, so that (in the case of the Williams process) the ingot-mold can be opened without dan¬ger, or (in the case of the Illingworth process) so as to avoid the risk that the steel may enter the grooves produced by the removal of the distance-bars. During the time required for

Jul 1, 1907

By E. M. Chance

HERBERT M. WILSON, Pittsburgh, Pa. (written discussion).-Permit me to endorse the author's conclusions and their form of presentation as ,being, in my judgment, the last word 'on the subject of lights for the illumination of coal mines. I also feel that the open-flame oil lamp has outlived its usefulness, and that it should go, in the interests not only of safety but of efficiency. Where an open-flame lamp can be used with safety in non-gaseous mines, the acetylene light adds materially to efficiency by its better illumination, and to safety for the numerous reasons given by Mr. Chance. The latter, however, lays chief stress on the value of the acetylene because of its non-fouling and non-obscuring effect on the atmosphere. Another important advantage over any other form of illumination is the clear, bright light projected at the point where the workman may look for danger. The better illumination materially safeguards the worker against obstacles over which he may stumble when traveling, and against dangers from falls of roof or of coal, weakness in timbering, and similar conditions. The acetylene lamp, where it may be used with safety, has advantages even over the present electric cap lamp, in that it gives a higher luminosity; and when the miner comes to learn its signals, as he will in time, just as he learns those given by the open-flame or the safety lamp, he will find that the acetylene lamp is a fair detector not only of methane but of carbon dioxide, as clearly shown by Mr. Chance. The only, serious objection, raised against the use of carbide lamps. has been recently in Pennsylvania, due to the belief of the State Mine Inspection Department that it endangered miners working on pillar work, or other places where carbon dioxide might accumulate, or where there is lack of sufficient ventilation, and because it was believed that the indications of the carbide lamp would not give the miner sufficient warning. On this point Mr. Chance has clearly shown the fallacies of the objections. I may add that for those unable to detect carbon dioxide with the acetylene lamp, the maximum of protection would be afforded by using an open oil lamp or a flame safety lamp in such places; or, because the miner might not watch his oil light, a better, protection still would be offered by a sufficient number of daily inspections of such working places by a fire boss or other official, with flame safety lamp.

Jan 4, 1917

By Elmer A. Jones

Development work in mines of St. Joseph Lead Co., Southeast Missouri, using trackless loading equipment shows definite advantages: Speed of cleaning, ability to work on steep grades and sharp crosscuts, good later tracking conditions, and possibility of wasting rock in old abandoned stopes.

Jan 1, 1950

By E. R. Smith

ANALYSIS of the requirements for gun perforation equipment suitable for penetrating casing and cement showed that these points would be involved: (1) Powder charges electrically detonated under high fluid lieads and at remote distances. (2) Selective firing of sliots in sequence. (3) Sufficient velocity for the bullet to penetrate at least two strings of seamless casing and all cement beyond the strings. (4) Heat-treatment of steels to withstand great pressures and penetration. (5) Esclusiorl of fluid under extremely high hydrostatic pressure. (6) Stranded steel wire line acting as weight - suspending and current - carrying medium. (7) Firing controls operated above the surface. (8) Determining gun depth and suspended weight by means of the wire line. (9) Portability for field use.

Jan 1, 1936

By W. M. Myers

Certain minerals possess inherent color and other properties that make them suitable for the pigmentation of paints, mortar, plaster, concrete, face brick, and other materials. Their production is one of the most ancient of mineral industries and their use by primitive man is well known. These natural pigments have some economic factors in their favor, particularly wide geographic distribution, low cost of production, ease of preparation, chemical stability, and permanence in use so that they continue to form the basis of a small but useful industry. When used in paints such pigments act as a filler and supply body and opacity in addition to color. Natural mineral pigments are prepared for the market by the comparatively simple operations of washing, grinding, blending, and calcining. Any one, or all of these processes may be applied to a single pigment. The development of synthetic pigments and the use of by- product materials have introduced competition with the products of nature and are having a growing influence on the economic position of the mined minerals.

Jan 1, 1949

By H. J. Wogner

STORAGE of natural gas in underground reservoirs is one of the most important developments in the natural gas industry in recent years. However, it is only when we consider this development together with proved fuel reserves, the know-how of the fuel technologist, and the possibility of making manufactured gas available over large areas, that we begin to appreciate fully the impact that underground storage of gas may have on the future growth and development of large areas in the United States. During the past winter, shortages of natural gas in the industrial East were given wide publicity and domestic consumers were requested to reduce their requirements to a minimum, so that war plants might have sufficient gas to continue operations. Curtailments would have been more drastic except for the fact that large volumes of natural gas had previously been stored in underground reservoirs. Storage of natural gas in depleted or partly depleted gas or oil sands is not new, having originally been tried, as far as I know, about 1915. About five or ten years later an attempt was made to store manufactured gas in a depleted gas sand. This proved unsuccessful at first because the gas was not properly cleaned and the impurities plugged the pores in the sand.

Jan 1, 1945

By N. A. Ziegler

IN every research it is desirable to eliminate as many variables as possible and to leave only a few to be investigated one at a time. Metallurgical problems are no exception. Some of the variables that are difficult to control are the size, the distribution, and the orientation of the grains in a metallic test piece. It is therefore very desirable to obtain isolated metallic grains (single crystals, as they are commonly called) large enough to enable one to study their mechanical and physical properties. The present investigation is a part of magnetic research work on iron and iron alloys, undertaken to obtain, if possible, the magnetic properties of pure iron (Fe). This paper will deal primarily with the preparation of single crystals of iron and their mechanical properties, while another paper, by T. D. Yensen, now in preparation, will deal specifically with their magnetic properties. The work with "single crystals" is attracting more attention every year among the investigators in metallurgy. Van Liempt1 gives an interesting summary of the work done and the different methods used in the preparation of metallic single crystals. Briefly stated, the four principal methods used are the following: 1. The cooling of a liquid metal in such a way that the crystallization would start at one point only, causing the entire liquid to solidify as one crystalline unit. This method can be successfully applied to the majority of the metals that do not have any allotropic transformations in the solid state. It has been used and described by a number of investigators,2 but it has never been successfully applied to iron on account of allotropic transformations.

Jan 1, 1930

By A. B. Young

THERE were produced in this country in 1923 probably in the neighborhood of 12,000 or 13,000 tons of refined and crude arsenic, by far the greater portion coming as a by product of smelting operations. Early this year copper smelters were producing arsenic at the rate of about 425 tons per month and lead smelters at the rate of 7;0 tons per month. During the entire eighteen years prior to 1919, there were produced in the United States only 47,000 tons of arsenic, which amounts to only 25 per cent. of the present output. The great increased demand has come about through the augmented use of arsenates as insecticides and arsenates as weed killers. In an extract from "Mineral Resources of the United States" on "Arsenic in 1922," Messrs. Heikes and Loughlin say, "The minimum possible demand for arsenic in 1923 was estimated at the end of 1922 to be about 13,000 tons, including 2000 tons for plate glass manufacturers, 3000 tons for lead arsenate, 3500 tons for calcium arsenate, 1500 tons for weed killers, 1200 tons for Paris green, 1000 tons for sheep dips and 750 tons for proprietary mixtures. More recent information, however, indicates twice as great a demand for calcium arsenate." The latter has found great use in the last three or four years as a weapon to combat the boll weevil pest of the southern cotton belt. ~t the present writing refined white arsenic is being quoted on the New York market at from 13)d c. to 1455 c. per Ib., while the average price during the eighteen-year period just mentioned was 4.8 c.

Jan 1, 1924

By Robert Schorr

A Discussion of the Paper by Robert Schorr, read at the Atlantic City meeting, February, 1904. (Washington Meeting, May, 1905.) E. T. DUMBLE, Houston, Texas (communication to the Secretary*) :-In addition to the list of publications mentioned by Mr. Schorr and those by Prof. Hofman, I call attention to the following references : Studi sulle Lignite, by Capacci. Turin (1890). (An excellent work.) Report of Brown Coal Industry in Germany. J. Cosmo Newberry. Department of Mines, Victoria (1892). Second Report of the Royal Commission. on Coal Supply. Vol. II. London (1904). Peat Fuel: Its Manufacture and Use. Report of the Bureau of Mines of Ontario, 1903. Mr. Schorr says : " Brown coal and peat are briquetted as a rule without binder," but this statement is entirely true only so far as raw peat is concerned, and it is but partly true of brown coal. With regard to raw peat, briquetting without bond is carried on successfully both in Europe and America, and the development of the industry in Canada is fully described in the Bureau of Mines report for 1903, mentioned above. While there is still room for improvement in the efficiency of some of the arrangements for drying the peat previous to briquetting, a very satisfactory fuel is made at a price which enables it to compete with coal. During the late strike in the anthracite regions of Pennsylvania, the manufacture of peat: briquettes received a considerable impetus, and possibly the attention directed to it on this account may result in a. considerable increase in the output. In Canada. the peat when it is first excavated from the ground

Mar 1, 1905

By Bror Nordberg

SAND and gravel are unconsolidated granular materials resulting from the natural disintegration of rocks. The two materials nearly al- ways occur together, variably proportioned in widely available de- posits. A commercial sand comprises the fine granular material, usually less than f in. in diameter (ASTM Designation C58-28), and gravel consists of the coarse, granular material larger than sand (ASTM Designation C125-46T). Gravel falls within the range of 1/4 in. and a top size usually of 3 ½ in. Chemical definition is impossible. Sand and gravel are always of secondary origin. They were formed from various massive rocks through the action of chemical and mechanical forces; then transported, abraded, washed, sorted, and classified by streams, glaciers, waves, or winds, to be redeposited in beds as they are found. Chief disintegrating forces in the reduction of rocks into granular particles were frost, rain, the dissolving action of acid and alkaline ground waters, the mechanical action of streams and waves, and the action of glaciers. Method of formation and deposition have imparted physical properties to sands and gravels that largely determine the commercial value of the materials for particular use and influence the manner of exploitation. In the early days of the commercial industry, purchasing specifications were relatively lenient but in. the past decade much more rigid quality requirements have had to be met for acceptance by all classes of purchasers. The trend to further severity in requirements is a challenge to the industry that commands full knowledge of the nature of raw materials at hand and skillful application of processing into commercial products. Mechanical strength, the ability to resist disintegration, chemica

Jan 1, 1949

By D. L. Gardner, H. L. Barr

The following report covers the history of the development of the mine, present equipment, methods and costs of mining and milling. In addition, a description of the ore deposit is given with emphasis on the origin of the fractures, mode and types of ore occurrence, and mechanics of granite emplacement. An endeavor has been made to present a complete and accurate statement of the San Mauricio mine, the highest grade gold mine in the Philippine Islands. Credit is gratefully acknowledged to the mine staff for descriptions and details regarding their particular field of work. All analyses were made by Mr. T. A. DeVore, head chemist, San Mauricio Mining Co. Messrs. Edward Wisser, J. E. Fyfe, A. F. Skerl and W. B. Meek, geologists, have contributed geologic information and ideas, for which thanks are extended. The Executive Committee of Marsman and Co., Inc., Managers of the Company, has kindly given permission for publication. Mr. J. B. Stapler, Division Manager, Marsman and Co., has had the courtesy to read the manuscript and to give critical and helpful suggestions. Location of Area and Scope of Work San Mauricio Mining Co. controls a group of 113 claims that lie immediately north of the town of José Pafiganiban (formerly Mambulao), Camarines Norte, Luzon, P. I. (Fig. 1). Exploration work commenced in the spring of 1934; active development began in the fall of that year and has continued to the present date. Mill construction was begun Ocl,. 15, 1935, and production started March 10, 1936. Total production to June 1, 1939, is P10,499,105.15 ($5,249,552.57).

Jan 1, 1941

By D. L. Gardner, H. L. Barr

The following report covers the history of the development of the mine, present equipment, methods and costs of mining and milling. In addition, a description of the ore deposit is given with emphasis on the origin of the fractures, mode and types of ore occurrence, and mechanics of granite emplacement. An endeavor has been made to present a complete and accurate statement of the San Mauricio mine, the highest grade gold mine in the Philippine Islands. Credit is gratefully acknowledged to the mine staff for descriptions and details regarding their particular field of work. All analyses were made by Mr. T. A. DeVore, head chemist, San Mauricio Mining Co. Messrs. Edward Wisser, J. E. Fyfe, A. F. Skerl and W. B. Meek, geologists, have contributed geologic information and ideas, for which thanks are extended. The Executive Committee of Marsman and Co., Inc., Managers of the Company, has kindly given permission for publication. Mr. J. B. Stapler, Division Manager, Marsman and Co., has had the courtesy to read the manuscript and to give critical and helpful suggestions. Location of Area and Scope of Work San Mauricio Mining Co. controls a group of 113 claims that lie immediately north of the town of José Pafiganiban (formerly Mambulao), Camarines Norte, Luzon, P. I. (Fig. 1). Exploration work commenced in the spring of 1934; active development began in the fall of that year and has continued to the present date. Mill construction was begun Ocl,. 15, 1935, and production started March 10, 1936. Total production to June 1, 1939, is P10,499,105.15 ($5,249,552.57).

Jan 1, 1941

By L. M. Barker

The New Cornelia Branch of the Phelps Dodge Corporation is at Ajo, Pima County, Ariz. It is at the southern terminus of the Tucson, Cornelia and Gila Bend Railroad, which connects with the Southern Pacific Railroad at Gila Bend, Ariz., approximately 43 miles to the north. History Early history of the Ajo district has been related by A. W. Allen1 and by T. A. Rickard.2 Briefly, steps looking to the large-scale development of the ore body were instituted as early as 1912. This work culminated in the equipment of the property for open-pit mining by steam shovels. Ores initially mined carried economic amounts of copper carbonates as the principal copper-bearing mineral. Treatment methods developed for the extraction of the copper content involved leaching and a 5000-ton leaching plant was constructed and placed in operation in early 1917. Description of methods and equipment employed in this plant has been given by A. A. Tobelmann and James A. Potter.3 As exhaustion of the carbonate ore body neared, and mining operations exposed an adequate tonnage of sulphide ores, a 5000-ton concentrator was constructed for their treatment. That plant has been described by H. Kenyon Burch.4 Construction was completed and the plant was placed in operation in early 1924. Changes made in the original plant to improve practices and increase production will be the subject of subsequent paragraphs of this paper. Geology Description of the geology of the Ajo district has been published by Ira B. Joralemon5 and by James Gilluly.6 The ore occurs chiefly in the porphyritic facies of Cornelia quartz monzonite, though appreciable

Jan 1, 1939

By L. M. Barker

The New Cornelia Branch of the Phelps Dodge Corporation is at Ajo, Pima County, Ariz. It is at the southern terminus of the Tucson, Cornelia and Gila Bend Railroad, which connects with the Southern Pacific Railroad at Gila Bend, Ariz., approximately 43 miles to the north. History Early history of the Ajo district has been related by A. W. Allen1 and by T. A. Rickard.2 Briefly, steps looking to the large-scale development of the ore body were instituted as early as 1912. This work culminated in the equipment of the property for open-pit mining by steam shovels. Ores initially mined carried economic amounts of copper carbonates as the principal copper-bearing mineral. Treatment methods developed for the extraction of the copper content involved leaching and a 5000-ton leaching plant was constructed and placed in operation in early 1917. Description of methods and equipment employed in this plant has been given by A. A. Tobelmann and James A. Potter.3 As exhaustion of the carbonate ore body neared, and mining operations exposed an adequate tonnage of sulphide ores, a 5000-ton concentrator was constructed for their treatment. That plant has been described by H. Kenyon Burch.4 Construction was completed and the plant was placed in operation in early 1924. Changes made in the original plant to improve practices and increase production will be the subject of subsequent paragraphs of this paper. Geology Description of the geology of the Ajo district has been published by Ira B. Joralemon5 and by James Gilluly.6 The ore occurs chiefly in the porphyritic facies of Cornelia quartz monzonite, though appreciable

Jan 1, 1939