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By Irving M. Symonds

Compania Minera de Penoles, S. A., at its Avalos unit operates a lead-zinc concentrator having a capacity of about 600 short tons per day. Lead and zinc concentrates are made by flotation methods. The concentrator is at Terminal de Provi-dencia, in the state of Zacatecas, some 70 miles south of Saltillo, Coahuila. The Penoles-Avalos railroad operating between the plant and Estacion Avalos, a distance of 6 miles, makes connections with the Coahuila and Zacatecas railroad, which in turn connects with the Nacionales de Mexico at Saltillo. The three railroads are each of different gauge, requiring the transfer of all supplies and concentrates at each junction. The mill operates on company ores, on ores from leased mines, and as a custom mill. The custom business is very small. The lead concentrates are shipped to company smelters at Monterrey, Nuevo Leon and Torreon, Coahuila. Since the European war, all zinc concentrates have been shipped to the United States. Ore Treated The major source of ore supply is a group of four mines owned or leased by the company, some three miles south of the mill in the mountains, from which the ore is delivered to the mill by a gravity aerial tramway. Custom ore comes in by rail. The ores occur in chimneys. The upper levels contained oxidized siliceous ores of lead, copper, silver and gold, with varying amounts of zinc. These ores were direct-smelted. In the first two years of operation a good deal of the tailing loss was caused by the oxidized content of the ores milled. Much of the ore in the transition zones between the oxides and sulphides was not mined. The ores now being milled are clean, hard sulphides in a limestone gangue, with only occasional contamination of oxides. The lead and zinc sulphides are of coarse structure and are freed even above flotation sizes. The galena is usually "steel" colored, easily and quickly floated. When there is any oxidation, it is usually on the coarsest crystals. The zinc minerals vary a good deal in color; a resin sphalerite predominates but there are varying shades of brown marmatites. On an average, the zinc sulphides contain 64 per cent zinc. The only common copper mineral is chalcopy-rite. Little is known of the occurrence of gold and silver. Waste minerals are mainly limestone and pyrite, both of which are barren. The ores vary from 20 to 35 per cent pyrite. Mill heads for the year 1940 and the first eight months of 1941 are given in Table I.

Jan 1, 1943

By H. R. Stahl

The disseminated lead district of Southeast Missouri lies 70 miles south of St. Louis. The only metal of economic importance in the ore is lead, but minor amounts occur of iron, zinc, copper, cobalt, nickel, silver and cadmium. These minor metals, as might be expected, tend to concentrate in both the flotation and table middlings. In the past, some zinc has been recovered by differential flotation. The silver and cadmium tend to associate with the zinc, and some recovery is made of these two metals at the smelter. The lead occurs as galena, or lead sulphide. The minor metals are also present as sulphides. The presence of oxidized lead is suspected, but has not been definitely proved. The gangue is chiefly dolomitic limestone, with small amounts of sandstone and shaly glauconitic and chloritic minerals. The ore contains about 3.25 per cent lead, occurring as galena disseminated through the gangue. Some of the galena is very finely disseminated, and the mineral in the gravity tailings, or chat; is seldom or never in the free state. The method of treatment of the ore has been evolved over a period of 75 years; hence probably is not far from correct. The milling processes have tended toward simplification during the past 15 years, but recoveries have never been sacrificed for the sake of simplicity. In many cases, simplification of flowsheets has led to better recoveries and operating economies. A simplified flowsheet is shown in Fig. I. The St. Joseph Lead Co. operates four mills in the Flat River district, with a normal total capacity of about 21,000 tons per day, divided as follows: Federal mill, 11,000 tons; Leadwood mill, 4500 tons; Desloge mill, 3400 tons and Bonne Terre mill 2400 tons. The methods of concentration used at these plants are similar in principle; they differ mainly in details and in the type and size of the equipment used. The process of concentration may be divided into five main steps; i.e., dry crushing, wet grinding, classification with its attendant desliming, tabling and flotation. A brief description of these processes will be given, noting important differences in the various plants, and also noting the more important changes or developments of the past few years. Dry Crushing The run-of-mine ore is hoisted in skips, the capacity of these skips ranging from 23/4 tons to 81/4 tons. At the Desloge plant, the ore is hoisted in 2-ton mine cars on self-dumping cages. All ore is hoisted at shafts adjacent to the various crushing plants, no ore being transported on the surface. Primary breaking at all the mills is accomplished with 9E Telsmith breakers. Preliminary screening is provided ahead of most of these crushers, either by station-

Jan 1, 1943

By H. R. Stahl

The disseminated lead district of Southeast Missouri lies 70 miles south of St. Louis. The only metal of economic importance in the ore is lead, but minor amounts occur of iron, zinc, copper, cobalt, nickel, silver and cadmium. These minor metals, as might be expected, tend to concentrate in both the flotation and table middlings. In the past, some zinc has been recovered by differential flotation. The silver and cadmium tend to associate with the zinc, and some recovery is made of these two metals at the smelter. The lead occurs as galena, or lead sulphide. The minor metals are also present as sulphides. The presence of oxidized lead is suspected, but has not been definitely proved. The gangue is chiefly dolomitic limestone, with small amounts of sandstone and shaly glauconitic and chloritic minerals. The ore contains about 3.25 per cent lead, occurring as galena disseminated through the gangue. Some of the galena is very finely disseminated, and the mineral in the gravity tailings, or chat; is seldom or never in the free state. The method of treatment of the ore has been evolved over a period of 75 years; hence probably is not far from correct. The milling processes have tended toward simplification during the past 15 years, but recoveries have never been sacrificed for the sake of simplicity. In many cases, simplification of flowsheets has led to better recoveries and operating economies. A simplified flowsheet is shown in Fig. I. The St. Joseph Lead Co. operates four mills in the Flat River district, with a normal total capacity of about 21,000 tons per day, divided as follows: Federal mill, 11,000 tons; Leadwood mill, 4500 tons; Desloge mill, 3400 tons and Bonne Terre mill 2400 tons. The methods of concentration used at these plants are similar in principle; they differ mainly in details and in the type and size of the equipment used. The process of concentration may be divided into five main steps; i.e., dry crushing, wet grinding, classification with its attendant desliming, tabling and flotation. A brief description of these processes will be given, noting important differences in the various plants, and also noting the more important changes or developments of the past few years. Dry Crushing The run-of-mine ore is hoisted in skips, the capacity of these skips ranging from 23/4 tons to 81/4 tons. At the Desloge plant, the ore is hoisted in 2-ton mine cars on self-dumping cages. All ore is hoisted at shafts adjacent to the various crushing plants, no ore being transported on the surface. Primary breaking at all the mills is accomplished with 9E Telsmith breakers. Preliminary screening is provided ahead of most of these crushers, either by station-

Jan 1, 1943

By Frank R. Milliken, Robert Goodwin

In September 1937, the Ohio Copper Co. inaugurated the treatment of its copper-bearing mill tailings at Lark, Utah. These tailings had been accumulated during the regular operation of the Ohio Copper mine and mill over the period 1907 to 1919. Gravity concentration had been employed except for a comparatively short period in 1919, when flotation was used. The ore milled during that period assayed about I per cent Cu. The chief copper mineral, chalcocite, was disseminated in a shattered quartzite, mainly along fracture or cleavage planes. The quartzite gangue was extremely hard and grinding to liberation resulted in excessive sliming of the "sooty" chalcocite, with consequent high tailings losses. Recovery on the seven million tons treated was probably less than 60 per cent of the total copper content. As early as 1918, attempts had been made to sample the dump. In 1928, a complete sampling program was undertaken. The sampling consisted of seventy-four 5-in. post auger holes drilled to the full depth of the dump at regular intervals of 250 ft. Each 10-ft. portion thereof comprised a sample for analysis. Each sample was screened, rolled, divided into three parts, dried and assayed. The reject was retained for testing purposes. From the depth of the auger holes a contour map of the dump was plotted, Fig. I, which gives percentages of tonnage and copper content. The tonnage within the limit of the drill holes was estimated at about five million tons with an average content of 0.42 per cent Cu, 31 per cent of which (0.13 per cent) was acid-soluble. A screen analysis of the composite dump sample is shown in Table I. Flotation tests by several companies and individuals were then made, the results of which ranged from 62 to 74 per cent recovery. On the basis of these, a 200-ton pilot plant employing straight flotation was built and operated for a few months. Operation of this plant was unsuccessful, as no provision had been made to handle the copper-bearing solutions resulting from the water-soluble copper, a point that was overlooked in the laboratory test work. Attempts to decant the copper-bearing solution for precipitation in the usual manner ahead of flotation were not satisfactory because of low water recovery (owing to poor settling characteristics of the pulp) and contamination of the copper precipitate with unsettled slime. Low copper prices in 1931 necessitated the termination of testing. With the stimulus of higher copper prices in 1937, a review was made of metallurgical

Jan 1, 1943

By Robert Goodwin, Frank R. Milliken

In September 1937, the Ohio Copper Co. inaugurated the treatment of its copper-bearing mill tailings at Lark, Utah. These tailings had been accumulated during the regular operation of the Ohio Copper mine and mill over the period 1907 to 1919. Gravity concentration had been employed except for a comparatively short period in 1919, when flotation was used. The ore milled during that period assayed about I per cent Cu. The chief copper mineral, chalcocite, was disseminated in a shattered quartzite, mainly along fracture or cleavage planes. The quartzite gangue was extremely hard and grinding to liberation resulted in excessive sliming of the "sooty" chalcocite, with consequent high tailings losses. Recovery on the seven million tons treated was probably less than 60 per cent of the total copper content. As early as 1918, attempts had been made to sample the dump. In 1928, a complete sampling program was undertaken. The sampling consisted of seventy-four 5-in. post auger holes drilled to the full depth of the dump at regular intervals of 250 ft. Each 10-ft. portion thereof comprised a sample for analysis. Each sample was screened, rolled, divided into three parts, dried and assayed. The reject was retained for testing purposes. From the depth of the auger holes a contour map of the dump was plotted, Fig. I, which gives percentages of tonnage and copper content. The tonnage within the limit of the drill holes was estimated at about five million tons with an average content of 0.42 per cent Cu, 31 per cent of which (0.13 per cent) was acid-soluble. A screen analysis of the composite dump sample is shown in Table I. Flotation tests by several companies and individuals were then made, the results of which ranged from 62 to 74 per cent recovery. On the basis of these, a 200-ton pilot plant employing straight flotation was built and operated for a few months. Operation of this plant was unsuccessful, as no provision had been made to handle the copper-bearing solutions resulting from the water-soluble copper, a point that was overlooked in the laboratory test work. Attempts to decant the copper-bearing solution for precipitation in the usual manner ahead of flotation were not satisfactory because of low water recovery (owing to poor settling characteristics of the pulp) and contamination of the copper precipitate with unsettled slime. Low copper prices in 1931 necessitated the termination of testing. With the stimulus of higher copper prices in 1937, a review was made of metallurgical

Jan 1, 1943

By Joseph C. Kieffer

The Duquesne property of the Callahan Zinc-Lead Co. is about 20 miles east of Nogales, in southern Arizona. One mine is near the mill, but most of the mill feed is hauled in by truck from a number of small mines. The same sulphides are found in all the ores, in general, but the amounts vary considerably. All ores contain silver, copper, lead and zinc minerals but one mine ships ore high in silver and lead and low in copper and zinc; while another mine ships ore high in copper and zinc, and low in silver and lead. The common sulphides are galena, carrying most of the silver; chalcopyrite; sphalerite, carrying iron in solid solution; and pyrite, in a gangue consisting of limestone, quartz and garnet. Mineralization is fairly coarse. At the present grind of about 66 per cent minus 200 mesh most of the sulphides are liberated A small amount of chalcopyrite is locked up with the sphalerite and cannot be liberated at an economic grind, and the copper carried into the zinc concentrate with the sphalerite accounts for the comparatively poor recovery of copper in the copper-lead concentrate. Production oF Two Concentrates The milling problem, which was complicated by the extreme variation in the grade of the feed, was first attacked with the idea of producing a silver-copper-lead con- centrate and a zinc concentrate, both with satisfactory grades and recoveries. By February 1941, it was felt that these objectives had been attained, when the grades of the various products and the recoveries were as shown in Table I. A rough outline of the flowsheet and reagents used is as follows: Minus ¾-in. feed to a 7-ft. by 36-in. Hardinge ball mill working in closed circuit with a 36-in. Wemco classifier. The classifier overflow passes to the second cell of an 8-cell bank of No. 18 Special Denver Sub-A flotation machines (volume, 22.5 cu. ft. per cell). A rougher concentrate is removed from the second to the fifth cells inclusive, and returned to the first cell, which is the cleaner. A scavenger concentrate is removed from the sixth, seventh, and eighth cells, and returned to the third cell. Consump-

Jan 1, 1943

By Joseph C. Kieffer

The Duquesne property of the Callahan Zinc-Lead Co. is about 20 miles east of Nogales, in southern Arizona. One mine is near the mill, but most of the mill feed is hauled in by truck from a number of small mines. The same sulphides are found in all the ores, in general, but the amounts vary considerably. All ores contain silver, copper, lead and zinc minerals but one mine ships ore high in silver and lead and low in copper and zinc; while another mine ships ore high in copper and zinc, and low in silver and lead. The common sulphides are galena, carrying most of the silver; chalcopyrite; sphalerite, carrying iron in solid solution; and pyrite, in a gangue consisting of limestone, quartz and garnet. Mineralization is fairly coarse. At the present grind of about 66 per cent minus 200 mesh most of the sulphides are liberated A small amount of chalcopyrite is locked up with the sphalerite and cannot be liberated at an economic grind, and the copper carried into the zinc concentrate with the sphalerite accounts for the comparatively poor recovery of copper in the copper-lead concentrate. Production oF Two Concentrates The milling problem, which was complicated by the extreme variation in the grade of the feed, was first attacked with the idea of producing a silver-copper-lead con- centrate and a zinc concentrate, both with satisfactory grades and recoveries. By February 1941, it was felt that these objectives had been attained, when the grades of the various products and the recoveries were as shown in Table I. A rough outline of the flowsheet and reagents used is as follows: Minus ¾-in. feed to a 7-ft. by 36-in. Hardinge ball mill working in closed circuit with a 36-in. Wemco classifier. The classifier overflow passes to the second cell of an 8-cell bank of No. 18 Special Denver Sub-A flotation machines (volume, 22.5 cu. ft. per cell). A rougher concentrate is removed from the second to the fifth cells inclusive, and returned to the first cell, which is the cleaner. A scavenger concentrate is removed from the sixth, seventh, and eighth cells, and returned to the third cell. Consump-

Jan 1, 1943

By Arthur T. Allen

THE Kingsport formation, a part of the Knox dolomite of Ordovician age, is composed of 538 ft of dolomitc and limestone. Numerous bands, layers and nodules of chert, arenaceous and shale zones are present. The characteristics displayed by these features have been useful in mapping, prospecting and mining. Perhaps a better understanding of the origin of these zones will increase their usefulness. Introduction The presence of numerous bands, nodules, and irregular bodies of chert within the Kingsport formation in the Mascot locality has long been recognized. Oder and Miller1 mention the general characteristics, but do not deal with the chert occurrences in detail. When the occurrence of chert is studied in fresh exposures underground, a variety of characteristics is noted which has been useful in correlation and in detailing the sub-surface stratigraphy. Although the writer has no desire to enter into a controversy over the origin of chert, many observations have been made of its local characterigtics. A detailed stratigraphic section is included which shows the position of the individual horizons discussed in the following paragraphs. The term "chertification" has been adopted from Fowler and Lyden2 for use here. It refers to the replacement of lime- stone by introduced silicic acid. The writer uses it to refer to the occurrencc of introduced or original chert in limestone and dolomite. In this writing "syngenetic chert" refers to chert which has been deposited contemporaneously with the enclosing limestone or dolomite. Also, it is considered to include interstitial silica shown by chemical analysis and insoluble residues. The term "epigenetic" is applied to all chert which has been introduced after consolidation of the rocks in which it occurs, regardless of the nature of the depositing solutions. Syngenetic Chert It is the belief of the author that a large percentage of the chert found in the Kingsport formation is syngenetic. The widespread occurrence of similar nodules and bands of chert in the same horizon far from one another and far from areas of deformation or alteration of the enclosing rocks is difficult to explain by infiltration of the silica after compaction of the enclosing rocks. When chert of this type does occur near zones of movement it is likely to be involved in faulting and brecciation which indicates that it was deposited prior to deformation. Older Epigenetic Chert There are several occurrences of nodules in the Kingsport which seem to be epigenetic as pointed out in the following examples: A cherty zone occurs 26 ft above the o bed (Fig =). This is not always present but is found in the greater part of mine work-

Jan 1, 1949

By Arthur T. Allen

THE Kingsport formation, a part of the Knox dolomite of Ordovician age, is composed of 538 ft of dolomitc and limestone. Numerous bands, layers and nodules of chert, arenaceous and shale zones are present. The characteristics displayed by these features have been useful in mapping, prospecting and mining. Perhaps a better understanding of the origin of these zones will increase their usefulness. Introduction The presence of numerous bands, nodules, and irregular bodies of chert within the Kingsport formation in the Mascot locality has long been recognized. Oder and Miller1 mention the general characteristics, but do not deal with the chert occurrences in detail. When the occurrence of chert is studied in fresh exposures underground, a variety of characteristics is noted which has been useful in correlation and in detailing the sub-surface stratigraphy. Although the writer has no desire to enter into a controversy over the origin of chert, many observations have been made of its local characterigtics. A detailed stratigraphic section is included which shows the position of the individual horizons discussed in the following paragraphs. The term "chertification" has been adopted from Fowler and Lyden2 for use here. It refers to the replacement of lime- stone by introduced silicic acid. The writer uses it to refer to the occurrencc of introduced or original chert in limestone and dolomite. In this writing "syngenetic chert" refers to chert which has been deposited contemporaneously with the enclosing limestone or dolomite. Also, it is considered to include interstitial silica shown by chemical analysis and insoluble residues. The term "epigenetic" is applied to all chert which has been introduced after consolidation of the rocks in which it occurs, regardless of the nature of the depositing solutions. Syngenetic Chert It is the belief of the author that a large percentage of the chert found in the Kingsport formation is syngenetic. The widespread occurrence of similar nodules and bands of chert in the same horizon far from one another and far from areas of deformation or alteration of the enclosing rocks is difficult to explain by infiltration of the silica after compaction of the enclosing rocks. When chert of this type does occur near zones of movement it is likely to be involved in faulting and brecciation which indicates that it was deposited prior to deformation. Older Epigenetic Chert There are several occurrences of nodules in the Kingsport which seem to be epigenetic as pointed out in the following examples: A cherty zone occurs 26 ft above the o bed (Fig =). This is not always present but is found in the greater part of mine work-

Jan 1, 1949

By James Pollock

The possibility of colloidal deposition of cinnabar has been neglected. In opalite deposits cinnabar exists in particles within or near the colloidal size range. Colloidal processes have been admitted to be operative in hot springs and low-temperature deposits similar to most cinnabar deposits. Mercuric sulphide sols are stable to elevated temperature and pressure, and in nature probably are chiefly affected by the electrolytes in solution, dilution of colloid, and presence of protective colloids as silica. The stability of mercuric sulphide sols to electrolyte is measured, and shown to be greatly increased by dilution and by the protective action of silica. Mercuric sulphide sols follow the Schulze-Hardy valency rule, therefore the precipitating power of complex mixtures of electrolytes can be computed roughly. The stability of mercuric sulphide sols is shown to be greater than the equivalent precipitating power of the electrolytes in a hot spring depositing mercuric sulphide. It is concluded that finely divided or earthy types of cinnabar are colloidally deposited. Possibility of Collodial Deposition While colloidal solution has been suggested as a means of transport for a number of minerals, such as the sulphides of antimony, arsenic, and iron, it has been neglected in connection with mercury. This is surprising because there exists positive evidence that cinnabar is present in certain deposits in particles of colloidal or near colloidal size. Colloidal transport could result from either the rapid dilution or neutralization of alkaline sulphide solution bearing mercury coming in contact with deep ground waters, or from colloidal solution near the original source and subsequent flow to the point of deposition unchanged. That the dilution of a mercuric alkaline sulphide solution will precipitate mercury sulphide in colloidal form has been demonstrated a number of times and is easily confirmed. The dilution hydrolyzes the alkaline sulphide Na2S to the corresponding hydroxide and hydrosulphide NaOH and NaHS, and the diminution of the concentration of alkaline sulphide reduces the solubility. It is not the contention of this writer that colloidal deposition is the mode of transport of mercuric sulphide in all mercury deposits, but that the stability of a mercuric sulphide sol, as demonstrated below, in waters that are similar to those that have deposited mercuric sulphide necessitates consideration of this possibility in many deposits, especially those of the hot-spring and so-called opalite type. Evidence of Colloidal Deposition Ross1 has shown that most deposits of quicksilver are formed at low temperatures and pressures, and probably by solutions that have relatively simple chemical compositions. In most cases the solutions are probably similar to those observed in hot springs, and in two instances—at Steamboat Springs, Nevada, and Sulphur Bank, California—hot springs have been reported by Becker as actually depositing cinnabar.2 Opalite deposits were believed by early investigators to be surface phenomena

Jan 1, 1949

By James Pollock

The possibility of colloidal deposition of cinnabar has been neglected. In opalite deposits cinnabar exists in particles within or near the colloidal size range. Colloidal processes have been admitted to be operative in hot springs and low-temperature deposits similar to most cinnabar deposits. Mercuric sulphide sols are stable to elevated temperature and pressure, and in nature probably are chiefly affected by the electrolytes in solution, dilution of colloid, and presence of protective colloids as silica. The stability of mercuric sulphide sols to electrolyte is measured, and shown to be greatly increased by dilution and by the protective action of silica. Mercuric sulphide sols follow the Schulze-Hardy valency rule, therefore the precipitating power of complex mixtures of electrolytes can be computed roughly. The stability of mercuric sulphide sols is shown to be greater than the equivalent precipitating power of the electrolytes in a hot spring depositing mercuric sulphide. It is concluded that finely divided or earthy types of cinnabar are colloidally deposited. Possibility of Collodial Deposition While colloidal solution has been suggested as a means of transport for a number of minerals, such as the sulphides of antimony, arsenic, and iron, it has been neglected in connection with mercury. This is surprising because there exists positive evidence that cinnabar is present in certain deposits in particles of colloidal or near colloidal size. Colloidal transport could result from either the rapid dilution or neutralization of alkaline sulphide solution bearing mercury coming in contact with deep ground waters, or from colloidal solution near the original source and subsequent flow to the point of deposition unchanged. That the dilution of a mercuric alkaline sulphide solution will precipitate mercury sulphide in colloidal form has been demonstrated a number of times and is easily confirmed. The dilution hydrolyzes the alkaline sulphide Na2S to the corresponding hydroxide and hydrosulphide NaOH and NaHS, and the diminution of the concentration of alkaline sulphide reduces the solubility. It is not the contention of this writer that colloidal deposition is the mode of transport of mercuric sulphide in all mercury deposits, but that the stability of a mercuric sulphide sol, as demonstrated below, in waters that are similar to those that have deposited mercuric sulphide necessitates consideration of this possibility in many deposits, especially those of the hot-spring and so-called opalite type. Evidence of Colloidal Deposition Ross1 has shown that most deposits of quicksilver are formed at low temperatures and pressures, and probably by solutions that have relatively simple chemical compositions. In most cases the solutions are probably similar to those observed in hot springs, and in two instances—at Steamboat Springs, Nevada, and Sulphur Bank, California—hot springs have been reported by Becker as actually depositing cinnabar.2 Opalite deposits were believed by early investigators to be surface phenomena

Jan 1, 1949

By Paul T. Allsman, E. W. Newman

Trenching, sampling, and core drilling in Stillwater and Sweetgrass Counties, Mont., by the Bureau of Mines have delimited over 5,000,000 tons of chromite ore containing more than 20 per cent chromic oxide. The Benbow and Mouat-Sampson mines have been developed and are fully equipped for mining and milling 500 tons and 2000 tons a day, respectively. Introduction The Montana chromite deposits were the first to be explored under the Strategic Minerals Act of 1939. In June of that year, the Bureau of Mines started exploration by trenching, test pitting, sampling and diamond drilling, and completed the project in March 1943. The U. S. Geological Survey cooperated by mapping the geology and logging the cores. The project was to determine the extent and grade of the chromite ore and to indicate sufficient reserves to justify development and exploitation of the deposits for the national emergency. Exploration has indicated that the district contains the largest and most important reserve of chromite ore in the United States. The Benbow and Mouat-Sampson mines have been developed and a 500-ton concentrating mill has been constructed on the Benhow property and a 2000-ton mill on the Mouat-Sampson property. Concentrates were produced from the Benbow mill three months after the attack on Pearl Harbor, when the nation's major chromite supplies from foreign sources were cut off. History It has been known for 50 to 60 years that some chromite deposits existed in an east-west belt along the north escarpment of the Beartooth Mountains about 25 miles north of Yellowstone Park, but nothing was known of their size and extent until the war demand of 1917 and 1918 stimulated the search. In those years two properties in the Stillwater region were actively developed, but no shipments were made. The Benbow property was located in 1918 by a local group. The property comprised seven claims along the strike at the east end of the belt. An adit was driven several hundred feet on the Eclipse claim. The seven claims were sold to the Chromium Products Corporation of Livingston, Mont., and were subsequently patented. In 1929, an eastern group obtained an option, installed some equipment, and erected several log cabins. The "crash" in the market in 1929 caused the operators to drop their lease, and the property remained inactive until 1939, when the Bureau of Mines began its exploration. Fourteen claims were located on the Boulder River in 1918 and subsequently patented by the U. S. Chrome Corporation.

Jan 1, 1949

By Paul T. Allsman, E. W. Newman

Trenching, sampling, and core drilling in Stillwater and Sweetgrass Counties, Mont., by the Bureau of Mines have delimited over 5,000,000 tons of chromite ore containing more than 20 per cent chromic oxide. The Benbow and Mouat-Sampson mines have been developed and are fully equipped for mining and milling 500 tons and 2000 tons a day, respectively. Introduction The Montana chromite deposits were the first to be explored under the Strategic Minerals Act of 1939. In June of that year, the Bureau of Mines started exploration by trenching, test pitting, sampling and diamond drilling, and completed the project in March 1943. The U. S. Geological Survey cooperated by mapping the geology and logging the cores. The project was to determine the extent and grade of the chromite ore and to indicate sufficient reserves to justify development and exploitation of the deposits for the national emergency. Exploration has indicated that the district contains the largest and most important reserve of chromite ore in the United States. The Benbow and Mouat-Sampson mines have been developed and a 500-ton concentrating mill has been constructed on the Benhow property and a 2000-ton mill on the Mouat-Sampson property. Concentrates were produced from the Benbow mill three months after the attack on Pearl Harbor, when the nation's major chromite supplies from foreign sources were cut off. History It has been known for 50 to 60 years that some chromite deposits existed in an east-west belt along the north escarpment of the Beartooth Mountains about 25 miles north of Yellowstone Park, but nothing was known of their size and extent until the war demand of 1917 and 1918 stimulated the search. In those years two properties in the Stillwater region were actively developed, but no shipments were made. The Benbow property was located in 1918 by a local group. The property comprised seven claims along the strike at the east end of the belt. An adit was driven several hundred feet on the Eclipse claim. The seven claims were sold to the Chromium Products Corporation of Livingston, Mont., and were subsequently patented. In 1929, an eastern group obtained an option, installed some equipment, and erected several log cabins. The "crash" in the market in 1929 caused the operators to drop their lease, and the property remained inactive until 1939, when the Bureau of Mines began its exploration. Fourteen claims were located on the Boulder River in 1918 and subsequently patented by the U. S. Chrome Corporation.

Jan 1, 1949

By R. H. B. Jones

This paper reviews pertinent geology of the Biwabik iron formation, Mesabi Range, Minnesota. This iron formation is divisible into four members. Each member is distinctive and contains marker horizons, which are recog nizable throughout all phases of alteration from lean, fresh rock to high-grade iron ore. Some beds have a larger magnetite content than others. During the process of ore genesis, which is essentially an oxidation process, the magnetite content is lowered. Alteration from iron formation to ore includes both oxidation of iron minerals and silica removal by leaching and these distinct processes progress at variable rates for different locations and structures. Magnetic intensities, of each horizon of the iron formation are dependent chiefly upon its preoxidation magnetite content, upon the subsequent degree of oxidation, upon the character of the enclosing rocks, and on the extent of fracturing, folding, or faulting. The results of a number of magnetic surveys are described and are correlated with results of drill-hole and mine exploration and developmerit. The magnetic anomalies obtained are discussed in relation to phases of formation of ore within the iron formation. General Information One hundred years ago a party of surveyors, applying the principles of geophysical prospecting, discovered iron ore in the state of Michigan in the Lake Superior district. This event was officially reported as follows:' On Sept. 19 (1844) while running the east line of Town 47 North, Range 27 West, they observed by means of the solar compass remarkable variations in the direction of the needle, amounting to 87" from the normal. Ascribing this phenomenon to iron ore, they sought and found it in ledges or outcrops at several points. The solar compass referred to was invented by William A. Burt, deputy surveyor in charge of this party.2 It is used for determining the true meridian by an observation on the sun. Eight years later, on July 7, 1852, the first iron 're, consisting of 6 bbl. of Ore, was shipped from Marquette, Michigan. It was another 40 years before the first or> shipment left the Mesabi Range in Minnesota, in October 1892. It totaled 4245 tons. Fifty years later, 90 years after the original shipment, during 1942 the Lake Superior district shipped 93,495,392 gross tons of iron ore. Production came from Minnesota, Michigan, Wisconsin, and Ontario, Canada. Throughout the 90-Year period it was known that magnetic properties of most of the ore bodies, and of the iron formations in which they occur, affected the compass. This phenomenon, later to be made use of to outline areas of ground favorable for exploration, was at first a

Jan 1, 1949

By R. H. B. Jones

This paper reviews pertinent geology of the Biwabik iron formation, Mesabi Range, Minnesota. This iron formation is divisible into four members. Each member is distinctive and contains marker horizons, which are recog nizable throughout all phases of alteration from lean, fresh rock to high-grade iron ore. Some beds have a larger magnetite content than others. During the process of ore genesis, which is essentially an oxidation process, the magnetite content is lowered. Alteration from iron formation to ore includes both oxidation of iron minerals and silica removal by leaching and these distinct processes progress at variable rates for different locations and structures. Magnetic intensities, of each horizon of the iron formation are dependent chiefly upon its preoxidation magnetite content, upon the subsequent degree of oxidation, upon the character of the enclosing rocks, and on the extent of fracturing, folding, or faulting. The results of a number of magnetic surveys are described and are correlated with results of drill-hole and mine exploration and developmerit. The magnetic anomalies obtained are discussed in relation to phases of formation of ore within the iron formation. General Information One hundred years ago a party of surveyors, applying the principles of geophysical prospecting, discovered iron ore in the state of Michigan in the Lake Superior district. This event was officially reported as follows:' On Sept. 19 (1844) while running the east line of Town 47 North, Range 27 West, they observed by means of the solar compass remarkable variations in the direction of the needle, amounting to 87" from the normal. Ascribing this phenomenon to iron ore, they sought and found it in ledges or outcrops at several points. The solar compass referred to was invented by William A. Burt, deputy surveyor in charge of this party.2 It is used for determining the true meridian by an observation on the sun. Eight years later, on July 7, 1852, the first iron 're, consisting of 6 bbl. of Ore, was shipped from Marquette, Michigan. It was another 40 years before the first or> shipment left the Mesabi Range in Minnesota, in October 1892. It totaled 4245 tons. Fifty years later, 90 years after the original shipment, during 1942 the Lake Superior district shipped 93,495,392 gross tons of iron ore. Production came from Minnesota, Michigan, Wisconsin, and Ontario, Canada. Throughout the 90-Year period it was known that magnetic properties of most of the ore bodies, and of the iron formations in which they occur, affected the compass. This phenomenon, later to be made use of to outline areas of ground favorable for exploration, was at first a

Jan 1, 1949

By Lawrence B. Wright

The Republic district, Washington, is of new interest because of the discovery of new gold-silver ore within a unique structural pattern. The camp was revived in 1937 fol1owing installation of a plant to treat low-grade disseminated ore at Knob Hill and further stimulation followed discovery of "cross vein" breccia ores in 1939. Previous writers 1-2 ascribed the quartz veins to a latite porphyry stock, but are in disagreement as to its precise location and extent. This study leads to the conclusion that the ores have a more profound parentage linked to a broad system of thrust faults and folds, the mechanical origin of which is related to a southward trending (Sanpoil) syncline connecting with the Lewis and Clark zone of shift described by Billingsley and Locke3 in 1939. The Republic anticliue and a cross anticline recumbent against Cretaceous granodiorite. and involving some 4000 ft of Eocene andesite flows and early Miocene lake beds, localize the ores, mainly along the east flank, in a series of openings simulating drag folds and steeper than the folded flows. These broad structural features no doubt reach deeply into the basement rocks, where at appropriate crossings and junctions it is suggested that heat effects gave rise to ore-making materials, including, in this instance, intrusive breccias that later were mineralized, and comprising the broader bodies of new ores. The breccia ore is seen crosscutting the earlier narrow quartz veins with a welding of the two at junction areas by a second surge of ore minerals. The ore mined and developed since 1937 equals district production from 1896 to 1937 The ores are typified by cherty quartz, adularia and some barite, with fine pyrite and marcasite, polybasite, pyrargyrite, tetrahedrite and gold. Selenium is present, possibly with gold, as a normal selenide. The disseminated ores, as well as the vein and breccia ores, are localized principally in one 500-ft flow (Knob Hill andesite), which has been traced around the crest of the low northward-plunging Republic anticline. The gold-silver ratio in the earlier narrow veins is about I to 4 and in the disseminated and breccia ores, I to 7. The latter higher silver ratio is deemed to reflect the character of the second surge of mineralization. Sills and dikes of the Columbia River (Miocene) basalt cut the folded structure and ore, thus placing the mineralization in the middle Miocene. Introduction The Republic district of north central Washington is of new interest because of the discovery, development and extraction of new gold-silver ore; also, because of a unique local structural pattern believed to be integral with the broader tectonic mechanism of the continental framework. This district had 40 years of modest rating following its discovery in 1896. Its narrow ore bodies, complex mineralogy. and early inadequate metallurgy, together with the apparent bottoming of ore near 1000 ft, limited production to 300,000 oz of gold and 1,000,000 oz silver between 1897 and 1914. The camp was then reduced to lease Life until 1937, when the gold price increase of 1933 to $35 per ounce

Jan 1, 1949

By Lawrence B. Wright

The Republic district, Washington, is of new interest because of the discovery of new gold-silver ore within a unique structural pattern. The camp was revived in 1937 fol1owing installation of a plant to treat low-grade disseminated ore at Knob Hill and further stimulation followed discovery of "cross vein" breccia ores in 1939. Previous writers 1-2 ascribed the quartz veins to a latite porphyry stock, but are in disagreement as to its precise location and extent. This study leads to the conclusion that the ores have a more profound parentage linked to a broad system of thrust faults and folds, the mechanical origin of which is related to a southward trending (Sanpoil) syncline connecting with the Lewis and Clark zone of shift described by Billingsley and Locke3 in 1939. The Republic anticliue and a cross anticline recumbent against Cretaceous granodiorite. and involving some 4000 ft of Eocene andesite flows and early Miocene lake beds, localize the ores, mainly along the east flank, in a series of openings simulating drag folds and steeper than the folded flows. These broad structural features no doubt reach deeply into the basement rocks, where at appropriate crossings and junctions it is suggested that heat effects gave rise to ore-making materials, including, in this instance, intrusive breccias that later were mineralized, and comprising the broader bodies of new ores. The breccia ore is seen crosscutting the earlier narrow quartz veins with a welding of the two at junction areas by a second surge of ore minerals. The ore mined and developed since 1937 equals district production from 1896 to 1937 The ores are typified by cherty quartz, adularia and some barite, with fine pyrite and marcasite, polybasite, pyrargyrite, tetrahedrite and gold. Selenium is present, possibly with gold, as a normal selenide. The disseminated ores, as well as the vein and breccia ores, are localized principally in one 500-ft flow (Knob Hill andesite), which has been traced around the crest of the low northward-plunging Republic anticline. The gold-silver ratio in the earlier narrow veins is about I to 4 and in the disseminated and breccia ores, I to 7. The latter higher silver ratio is deemed to reflect the character of the second surge of mineralization. Sills and dikes of the Columbia River (Miocene) basalt cut the folded structure and ore, thus placing the mineralization in the middle Miocene. Introduction The Republic district of north central Washington is of new interest because of the discovery, development and extraction of new gold-silver ore; also, because of a unique local structural pattern believed to be integral with the broader tectonic mechanism of the continental framework. This district had 40 years of modest rating following its discovery in 1896. Its narrow ore bodies, complex mineralogy. and early inadequate metallurgy, together with the apparent bottoming of ore near 1000 ft, limited production to 300,000 oz of gold and 1,000,000 oz silver between 1897 and 1914. The camp was then reduced to lease Life until 1937, when the gold price increase of 1933 to $35 per ounce

Jan 1, 1949

By N. P. Peterson

The Castle Dome copper deposit is of the porphyry type and occurs in a body of quartz monzonite intruded into the pre-Cambrian formations and possibly into the lower part of Paleozoic limestones. The hypogene sulphide minerals include pyrite, chalcopyrite, and a little molybdenite, sphalerite, and galena. Pyrite and chalcopyrite are disseminated or occur in small closely spaced veins. The hypogene mineralization shows distinct zoning in the distribution of pyrite and chalcopyrite, so that the mineralized area can be subdivided into pyritc and chalcopyrite zones. Supergene enrichment, though not extensive, played an important part in the formation of the ore body, the chalcopyritc zone being the pro-tore. Several thin, gently dipping, diabase sills occur in the mineralized area, and the copper content of the rock in and near these sills is substantially higher than average. The formation of the ore body was caused by the combined effects of three forces: I. Zoning of the hypogene mineralization, 2. Richer copper metallization associated with the diabase sills, and 3. Supergene enrichment. Introduction The Castle Dome copper deposit is about 5 miles west of Miami, Arizona, and about 3 miles west of the Miami-Inspiration ore body. The Castle Dome open-pit mine is on the south flank of Porphyry Mountain, a prominent landmark of the region. In 1941 the deposit was being explored by the Miami Copper Co., but the exploration program was cut short when the decision was made to develop the property as a war project. The Castle Dome Copper Co., Inc., was organized as a wholly owned subsidiary of the Miami Copper Co., and arrangements were made with Defense Plant Corp. for developing and equipping the mine and for construction of a concentrating plant. Construction and development work was begun in January 1942, and milling operations started June so, 1943. Since that date, the mine has been in continuous operation by the Castle Dome Copper Co, under a lease agreement with Defense Plant Corp. producing copper at an average rate of 4,000,000 lb per month. To January I, 1946 the total production amounted to 121,088,000 lb of copper,4,271 oz of gold, and 211,755 oz of silver. A detailed study of the copper deposit and the surrounding area was undertaken by the U. S. Geological Survey in June 1943. Other members of the Survey participating in the work were C. M. Gilbert, G. L. Quick, and J. P. Albers. The results of this work will be published as a comprehensive report by the Geological Survey. General Geology The Globe quadrangle, which includes the Castle Dome area, was studied by F. L. Ransome1 of the Geological Survey in 1901 and 1902. His maps and descriptions were

Jan 1, 1949

By N. P. Peterson

The Castle Dome copper deposit is of the porphyry type and occurs in a body of quartz monzonite intruded into the pre-Cambrian formations and possibly into the lower part of Paleozoic limestones. The hypogene sulphide minerals include pyrite, chalcopyrite, and a little molybdenite, sphalerite, and galena. Pyrite and chalcopyrite are disseminated or occur in small closely spaced veins. The hypogene mineralization shows distinct zoning in the distribution of pyrite and chalcopyrite, so that the mineralized area can be subdivided into pyritc and chalcopyrite zones. Supergene enrichment, though not extensive, played an important part in the formation of the ore body, the chalcopyritc zone being the pro-tore. Several thin, gently dipping, diabase sills occur in the mineralized area, and the copper content of the rock in and near these sills is substantially higher than average. The formation of the ore body was caused by the combined effects of three forces: I. Zoning of the hypogene mineralization, 2. Richer copper metallization associated with the diabase sills, and 3. Supergene enrichment. Introduction The Castle Dome copper deposit is about 5 miles west of Miami, Arizona, and about 3 miles west of the Miami-Inspiration ore body. The Castle Dome open-pit mine is on the south flank of Porphyry Mountain, a prominent landmark of the region. In 1941 the deposit was being explored by the Miami Copper Co., but the exploration program was cut short when the decision was made to develop the property as a war project. The Castle Dome Copper Co., Inc., was organized as a wholly owned subsidiary of the Miami Copper Co., and arrangements were made with Defense Plant Corp. for developing and equipping the mine and for construction of a concentrating plant. Construction and development work was begun in January 1942, and milling operations started June so, 1943. Since that date, the mine has been in continuous operation by the Castle Dome Copper Co, under a lease agreement with Defense Plant Corp. producing copper at an average rate of 4,000,000 lb per month. To January I, 1946 the total production amounted to 121,088,000 lb of copper,4,271 oz of gold, and 211,755 oz of silver. A detailed study of the copper deposit and the surrounding area was undertaken by the U. S. Geological Survey in June 1943. Other members of the Survey participating in the work were C. M. Gilbert, G. L. Quick, and J. P. Albers. The results of this work will be published as a comprehensive report by the Geological Survey. General Geology The Globe quadrangle, which includes the Castle Dome area, was studied by F. L. Ransome1 of the Geological Survey in 1901 and 1902. His maps and descriptions were

Jan 1, 1949

By Lawson P. Entwistle

One of the important reserves of mangani-ferous iron ore is at Boston Hill, near Silver City, New Mexico. The area consists of a faulted block of gently dipping Lower Paleozoic shale, dolomite, limestone and sandstone, which has been intruded by a roughly circular mass of quartz-bearing monzonite porphyry and subordinate dikes. Prom a noselike protuherance of the intrusion radiate many premineral faults, which have localized much of the hypogene mineralization. Three important stages of hypogene mineralization can be recognized: (I) mesitite, a manganiferous iron magnesite, (2) quartz sulphides, and (3) barite-galena The carbonate stage is widespread but stronger near the intrusion. The quartz may have been derived from hydrothermal alteration of the igneous rocks. Barite-galena is most important in the Chloride Flat mining district, about one mile north, where argentiferous galena provided silver for the supergene ore. The hypogene carbonate, lean in iron and manganese, has been oxidized and consequently enriched by meteoric waters containing an excess of oxygen and carbon dioxide to form ore bodies of intimately mixed hematite and pyrolusite. The ore bodies, at one place attaining a length of 1600 ft., a width of 300 ft., and a thickness of 25 ft., are largely confined to areas of brecciation and to spreads from faults in Silurian dolomite beneath soft Devonian shale. Boston Hill comprises three rolling hills southwest of and adjoining the town of Silver City (pop. 5044), Grant County, N. Mex. The mining district covers less than 2 sq. miles. Silver City, on a branch line of the Atchison, Topeka, and Santa Fe Railway, is a supply point for the important mining communities at Santa Rita, Hurley, Hanover, Tyrone, and Mogollon. The Chloride Flat mining district adjoins Boston Hill on the north. History and Production Bonanza-type silver ores were discovered in the Chloride Flat mining district during the silver boom of the seventies and eighties, at which period it has been credited with as much as $5,000,000 production. In 1916 manganiferous iron ore was first shipped from the Boston Hill mining district to Pueblo, Colo., where it was mixed with manganese ore from Lead-ville and smelted into spiegeleisen. During 1926 and 1927 the Colorado Fuel and Iron Co. mined and churn-drilled part of the district. Mining operations ceased during the depression of the thirties, but production was resumed in 1937. Since 1916 the Boston Hill mining district has produced about 600,000 long tons of ore averaging about 12 per cent manganese and 35 to 40 per cent iron.

Jan 1, 1949