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By Gabriel Voicu, Harnois Luc, Marc Bardoux, Robert Crépeau

"Detailed petrographical and geochemical studies have been carried out on the igneous and sedimentary rocks in the Omai area, part of the Paleoproterozoic Barama-Mazaruni greenstonebelt, Guyana. The stratigraphic succession at Omai begins with basalts, associated with ma?c-ultrama?c intrusives and poorly-sorted conglomerates; these are overlain by andesites and quartz-feldspar porphyries, with pelites and tuffaceous sediments at the top. The volcanic-sedimentary succession was intruded by a quartz-monzodioritic stock (Omai stock) and granophyric rhyolitedikes. Several generations of ma?c dikes were intruded discontinuously from the Mesoproterozoicto the Permo-Triassic. Volcanic rocks range in composition from subalkaline basalt to high-silicarhyolites, with a gap between 60% to 70% SiO2, which suggests the suite is bimodal. Major, trace, and rare earth element criteria were used to subdivide the rocks into tholeiitic and calc-alkaline types. The tholeiitic rocks are characterized by ?at to moderately sloping chondrite-normalized REE patterns. On the basis of immobile trace-element ratios, the tholeiitic ma?c rocks from Omai have characteristics of immature intra-oceanic island arcs, or of E-MORB basalts affected by a strong arcsignature, as is commonly reported for back-arc basin basalts. The andesites, quartz-feldspar porphyries, rhyolites and quartz monzodioritic stock are calc-alkaline, with strongly sloping REE pat-terns, enrichments in the large-ion lithophile elements, and depletions in the heavy REE and high-?eld-strength elements, features which are typical of more mature island-arc settings.At Omai, two types of gold-bearing veins can be distinguished: vein sets (± stockworks) and tension veins, both post-dating the regional metamorphic peak at the level they were emplaced. The relationship between the gold mineralization and its host lithologies does not seem to be genetic. Rather, the emplacement of mineralization was strongly in?uenced by the rheological contrasts between the intrusive/subvolcanic bodies and the volcanic/sedimentary country rocks. These con-trasts helped to focus the regional stress upon the more competent intrusive subvolcanic bodies,resulting in brittle fracturing, and therefore in greatly enhanced permeability to hydrothermal ?uids.The Omai gold mineralization can be classi?ed as late tectonic, with its emplacement controlled by the last brittle to brittle-ductile stages of the Trans-Amazonian orogeny."

Jan 1, 1997

By Daryl R. Tweeton

The Bureau of Mines has developed PC-based tomographic computer programs for geophysical applications, and is making them available to potential users as part of a Bureau plan to facilitate the transfer of technology to industry. These programs were initially developed for predicting and monitoring the flow pattern of leach solution during in situ mining. Seismic crosshole tomography has located fractured zones of low seismic velocity and saturated zones of high seismic velocit above the natural water table. The Bureau has applied tomography also to assessing high-wall blast damage, and examining the integrity of mine-related geological structures. The tomographic programs include the straight ray pro ram BOMTOM (Bureau of Mines Tomography? and the program BOMCRATR (Bureau of Mines Curved Ray Tomographic Reconstruction) that can be run with either curved or straight rays. Both programs provide optional mathematical constraints to help counteract the nonuniqueness of reconstructions that occurs with crosshole data. They are available from the Bureau free of charge. With typical data sets, they can be run on a 386 microcomputer with 640 Kb RAM. BOMTOM was described in the Bureau Report of Investigations 9159, so this report emphasizes BOMCRATR. Curved and straight ray reconstructions using seismic field data collected while simulating injection of leach solution were compared. The curved and straight ray tomograms were quite similar even with velocity variations of more than 50 percent.

Jan 1, 1992

By R. A. Ford

The paper outlines: methods used for the determination of wear metals in motor and transmission oils; contaminents in motor, transmission and crusher lubricating oils; and viscosity determinations. Case histories and costs are presented to illustrate the value of an oil analysis program. Introduction NORANDA MINES LIMITED (BELL COPPER DIVISION) is located on the shores of Babine Lake, approximately 450 miles north of Vancouver, British Columbia. Access to the mine is by road from Topley, B.C., about 40 miles away. When a preventive maintenance analysis program was first considered, it was obvious that if samples were to be sent out for analysis, results would not be available for at least a week, due to the distance from any commercial laboratory. The assay laboratory was asked to investigate the possibility of determining wear metals on site. A limited program was started soon after production commenced, and this has now grown to include all large mobile equipment as well as crushers and grinding mills. The laboratory also now determines viscosity, fuel dilution, dirt and abrasives, glycol and water. All these results are ready within two days. This paper will outline the methods used, data interpretation, several case histories and the benefits from such a program.

Jan 1, 1977

By J. R. Dyni

Colorado nahcolite deposits, estimated at 29 billion metric tons, formed in an asp metric permanent-lake basin whose waters were rich in algae and sulfate-reducing bacteria. Nahcolite (NaHCOg) occurs in oil shale of the Green River Formation (Eocene) as aggregates (62 percent), disseminated crystals (24 percent), and impure beds (14 percent). Because much of the nahcolite is nonbedded, it will be mined with oil shale and can be concentrated to marketable grade by crushing and screening Impurities in nahcolite are kerogen, quartz, pyrite, and carbonate minerals. A promising new market for nahcolite is in the process of removal of sulfur dioxide from industrial stack gases. When heated, nahcolite reacts with sulfur dioxide to form sodium sulfate. Differences in thermally induced microporosity may explain why nahcolite is more reactive than trona, a possible competitor with nahcolite for SO2 removal. Limited production of nahcolite at one or possibly two localities is expected in the next several years, but large-scale production is probably at least 10 years away.

Jan 1, 1980

By C. L. Severy

The Reeder No. 1 well was drilled by the Bureau of Mines in cooperation with the Geological Survey as agents for the Defense Plant Corporation. The well is south of Crescent Junction near Thompson, Grand County, Utah. It was started May 5, 1942, and completed August 3, 1942, for the purpose of con-firming the presence of magnesium salts in a deeply buried bed. Drilling was done under contract by the Mack Drilling Co. This report contains an outline of the physical features of the well, a brief history of drilling, and a description of the deposits and occurrences of oil and gas encountered in the drill hole. The work performed by the Bureau of Mines is described in considerable detail, with particular emphasis on drilling procedure and sampling. The report is concluded with a brief description of core-sample preparation for analyses. Appendix A comprises a log of the drill hole, and appendix B is a tabulation of analyses of cores.

Jan 1, 1949

By Hugo Vásquez Rosas

El presente texto señala el valor relativo de las propiedades físicas de los minerales, así como presenta las ventajas e inconvenientes de los mismos. Para el reconocimiento de minerales tenemos las siguientes propiedades: color, clivaje, brillo o lustre, dureza y raya. Desde el punto de vista científico, estas propiedades se dividen en dos categorías: Las que son propiedades escalares y dependen por consiguiente de la simetría cristalina del mineral y aquellas que son independientes de esa relación. En ese sentido, las que pertenecen al segundo grupo son, teóricamente, más ventajosas, que las otras, por cuanto su valor no varía con la orientación del mineral. A ellas conesponde el color y la raya.

May 1, 1955

By Yun-tao Xin, Yu Yi, Kang Yan, Gang Li, Xiao-dong Lv

This study investigated the selective removal of arsenic from high-arsenic dust in alkaline systems and the effects of different leaching conditions. The results indicated that the liquid–solid ratio, NaOH concentration, and sulfur dosage had a significant influence on the process. The leaching efficiency of arsenic reached 99.57%, while that of lead was as low as 0.03% under appropriate conditions. In particular, the addition of sulfur can effectively promote the leaching of arsenic and reduce the dissolution of lead in the solutions. An artificial neural network was used to model the leaching process. It consisted of a back-propagation artificial neural network model with a “6–10–2” structure that could effectively simulate and predict the value with more than 99% accuracy. Based on the difference in weights of the different parameters in the neural network model, the relative importance of the parameters related to arsenic and lead leaching efficiency was obtained, which followed the order of NaOH concentration, liquid–solid ratio, sulfur dosage, temperature, time, and stirring speed.

Jul 29, 2021

By Leland E. Paulson

The Grand Forks Energy Research Center and Commonwealth Edison of Chicago jointly conducted tests in which 400 tons each of subbituminous coal and lignite were dried in a commercial scale dryer, oil sprayed and cooled, then shipped in open-top rail cars from Pekin, IL to Grand Forks, ND and stockpiled. Cars containing raw coal and dried coal that had not been oil sprayed were also transported for comparative purposes. The tests were conducted in August and November of 1974. The subbituminous coal was dried from 26 to 16 pct moisture and the heating value was upgraded from 8,420 to 9,650 Btu/lb. The lignite was dried from 39 to 22 pct moisture and its heating value was increased from 6,420 to 8,300 Btu/lb. Before loading subbituminous coal was cooled to 115° F and sprayed with oil at a rate of from 2 to 6 gal/ton. Similarly, lignite was cooled to 85° F and oil sprayed at rates of from 1 to 2 gal/ton. Both shipments arrived in Grand Forks with a minimum of difficulty. The subbituminous coal was subjected to 2 inches of rain during transit with no change in average moisture content. The cars containing dried and oil treated coal had less material lost to wind than either cars containing raw or untreated dried coal. With both dried lignite and subbitnminous shipments, a moderate increase in temperature was measured during transit. With the subbituminous shipments, ignition occurred near poorly fitted bottom dump doors, but was limited to a very small area. The dried lignite was shipped when ambient temperatures were below freezing, and frozen coal was noted around the edge of the car. At Grand Forks, the coal was stockpiled using proven techniques and has remained stable to this date.

Jan 1, 1975

By W. Hu

Traditionally, coarse wolframite ore processing has been done almost exclusively by gravity concentration methods. However, there has been a depletion of rich and coarse ore reserves and a proportional increase in the mining of low-grade, fine-grained complex ore feeds. This change has resulted in the need for better slime-processing technology. Research and development activities in this area have gained momentum, and recent innovations appear promising. This paper covers the recent innovations that have been made in dealing with tungsten ore slime processing. The new techniques include the application of a centrifugal cone separator, high-intensity wet magnetic separator, the use of phosphonic and arsonic acids as collectors in ultrafine wolframite flotation, and combined processes.

Jan 1, 1989

By Kanhaiya Mishra, Phanil. K. Mandal, S. K. Behera, P. S. Paul, Prashant Singh, C. N. Ghosh

The techno-economic and social benefits of cemented paste backfill (CPB) resulted in its wide acceptance by the mining industry. The Ordinary Portland Cement (OPC) remains the key binder but to diminish its economical constraints, suitability of alternate binders has been examined worldwide. The present study aimed to investigate the effect of partial replacement of OPC with fly ash on the CPB’s strength and to determine the most optimal mix to achieve the required strength (1 MPa at 28 days of curing) at the most cost-effective way using the Bayesian network (BN). The CPB mixes were prepared at 72 wt.% solid concentration with mill tailings (87–91%), OPC (6–13%), and fly ash (0–4%), and instantly after mixing, fresh (slump, bleeding, density) CPB properties were measured. The strength was tested at 7, 14, 28, and 56 days of curing and initially analysed through traditional model. The traditional models follow the aleatory principle and are considered not appropriate for geotechnical engineering. Hence, the BN model was developed and tested. The reliability of two classifiers in learning model structure was compared which gives Naïve Bayes as the highest reliable tool. The CPB’s strength is most sensitive to the OPC content. The most consistent mix(s) is mill tailings: 87–88%, OPC: 9–11%, fly ash: 1–4%. Adding fly ash at 89–91wt% mill tailings possesses high failure probability of the CPB. The collinearity test indicates that the fines percentage and chemical composition of CPB’s ingredients are highly correlated with its slump, bleeding, and strength development.

Jul 14, 2022

By Alfred H. Bell, George V. Cohee

In 1941 Illinois produced 134,139,000 bbl. of oil, or 9.5 per cent of the total for the United States, and ranked fourth among the states. The production for 1941 declined 9.2 per cent from the previous year's total of 147,647,000 bbl. Daily average production for 1941 was 366,000 bbl. At the beginning of the year daily production was slightly more than 326,000 bbl. and it remained at appoximately that amount until June, when there was a slight increase. The increase continued until the peak of 431,260 bbl. daily was reached for the week ending Oct. 4. Daily average production at the end of the year was approximately 387,500 barrels. The increased production during the last half of 1941 was largely due to the rapid development of the Johnsonville field, Wayne County, the Rural Hill field, Hamilton County, and the Benton field, Franklin County—new fields discovered in the current year (Fig' 1)—and the Woodlawn pool, discovered in 1940. Discoveries In 19 counties in southern Illinois, 44 new fields were discovered in 1941 (Fig. 2 and Table 2), and extensions to 40 fields were successfully completed (Table 3). At the end of the year there were 10,496 wells in the fields discovered since Jan. I, '937, as compared with 71965 wells at the end Of '940. The area proved for production in the new fields increased from 78,040 acres at the beginning of 1941 to 97,483 acres at the end of the year (Table I)—an increase of 19,433 acres, of which 9,955 acres are in the fields discovered during the current year, and the remainder of 9,478 acres in extensions to pools discovered earlier. Drilling During the past year, 3838 wells were completed in Illinois (Table 4), of which 2912 were oil producers, 13 were gas producers and 913 were dry holes; 76 per cent of the wells drilled were producers. Of the total number drilled, 591 wells are classified as "wildcat" and of these 84 (1 in 7) were successful in obtaining production. The results of an investigation to ascer-tain the reason for the locations of the wildcat wells are set forth in Table 5. Of the 591 wildcat wells, the 292 known to have been located by scientific methods were 21.6 per cent successful. The total footage of wildcat wells drilled in 1941 was 1,341,743 ft., of which a total of 216,995 ft. was drilled in successful wells. Exploration MEthods Subsurface geology and geophysics, largely the reflection seismograph, are still the principal methods used in exploration and development in the state. The number of seismograph parties operating throughout the year was as follows: seven parties on Jan. I, 1941; five on Apr. I; four On July I; eight on Oct. I; fifteen on Jan. 1: 1942.

Jan 1, 1942

By Alfred H. Bell, George V. Cohee

In 1941 Illinois produced 134,139,000 bbl. of oil, or 9.5 per cent of the total for the United States, and ranked fourth among the states. The production for 1941 declined 9.2 per cent from the previous year's total of 147,647,000 bbl. Daily average production for 1941 was 366,000 bbl. At the beginning of the year daily production was slightly more than 326,000 bbl. and it remained at appoximately that amount until June, when there was a slight increase. The increase continued until the peak of 431,260 bbl. daily was reached for the week ending Oct. 4. Daily average production at the end of the year was approximately 387,500 barrels. The increased production during the last half of 1941 was largely due to the rapid development of the Johnsonville field, Wayne County, the Rural Hill field, Hamilton County, and the Benton field, Franklin County—new fields discovered in the current year (Fig' 1)—and the Woodlawn pool, discovered in 1940. Discoveries In 19 counties in southern Illinois, 44 new fields were discovered in 1941 (Fig. 2 and Table 2), and extensions to 40 fields were successfully completed (Table 3). At the end of the year there were 10,496 wells in the fields discovered since Jan. I, '937, as compared with 71965 wells at the end Of '940. The area proved for production in the new fields increased from 78,040 acres at the beginning of 1941 to 97,483 acres at the end of the year (Table I)—an increase of 19,433 acres, of which 9,955 acres are in the fields discovered during the current year, and the remainder of 9,478 acres in extensions to pools discovered earlier. Drilling During the past year, 3838 wells were completed in Illinois (Table 4), of which 2912 were oil producers, 13 were gas producers and 913 were dry holes; 76 per cent of the wells drilled were producers. Of the total number drilled, 591 wells are classified as "wildcat" and of these 84 (1 in 7) were successful in obtaining production. The results of an investigation to ascer-tain the reason for the locations of the wildcat wells are set forth in Table 5. Of the 591 wildcat wells, the 292 known to have been located by scientific methods were 21.6 per cent successful. The total footage of wildcat wells drilled in 1941 was 1,341,743 ft., of which a total of 216,995 ft. was drilled in successful wells. Exploration MEthods Subsurface geology and geophysics, largely the reflection seismograph, are still the principal methods used in exploration and development in the state. The number of seismograph parties operating throughout the year was as follows: seven parties on Jan. I, 1941; five on Apr. I; four On July I; eight on Oct. I; fifteen on Jan. 1: 1942.

Jan 1, 1942

The western Cordillera of North America, including more than 99% of Alaska, is made up of an agglomeration of litho-tectonic terranes, some of which have undergone large rotations and (or) translations. The larger terranes can be broadly grouped into a small number of composite terranes based on affinities in their lithology, structure, and tectonic evolution. The terranes reflect repeated episodes of marginal rifting as well as formation of marginal arcs, island arc chains, back-arc basins, and oceanic plateaus since late Proterozoic time. Accretion to the continental margin occurred mainly from Middle Triassic through Early Cretaceous time. Major northward dispersal of terranes was largely during the existence of the Kula plate from about 85-55 Ma. Major rotations are the mid-Cretaceous opening of the Arctic Ocean basin with counterclockwise rotation of Arctic Alaska and Laramide oroclinal bending of western Alaska. The present complex Cordilleran geology along the northeast Pacific rim is a sum of these earlier accretionary processes together with continued Cenozoic faulting and deformation that has been superimposed upon the agglomerated displaced terranes over a broad segment of the continental margin.

Jan 1, 1990

By James F. Lemons

The potential production of cobalt from nickel sulfide deposits in Canada, from nickel laterite deposits in the Pacific Islands, and from the copper deposits of Zaire and Zambia will be a function of the cost of recovery of the primary nickel and copper products. This cost of production varies significantly for these deposits and is related to the differences in the cost of labor, energy, and supplies, to production technology, and to the grade and recovery of nickel, copper, and cobalt. This Bureau of Mines paper investigates these cost and technology differences as they relate to the cost competitiveness of the deposits in Canada, Zambia, Zaire, and the Pacific Islands.

Jan 1, 1984

By R. T. Richins

Coeur d'Alene Mines Corporation (CDE) is a precious metals mining company. The company's three mining operations are located In Nevada and Idaho. Collectively, these mines (Rochester in Nevada, and the Galena and Coeur In Idaho) produced about 61,000 ounces of gold and more than 7.5 million ounces of silver in 1991. The company is currently planning the development of two major properties; the Fachinal gold-silver project in Chile and the Kensington gold project near Juneau, Alaska. Fachinal and Kensington hold encouraging potential to significantly expand CDE's gold production during this decade. The permitting process for these two distinctly contrasting environmental settings, project design requirements and regulatory/political circumstances provide the basis for a comparative analysis of licensing and permitting requirements, timeliness of the permitting process and costs in the U.S. and Chile.

Jan 1, 1993

By E. A. Nesbitt

The important permanent-magnet alloys 15 years ago contained carbon and depended upon it for their permanent-magnet properties. In recent years great advances have been made in a number of new alloys substantially free of carbon. These include Remalloy,' an alloy of iron, cobalt, and molybdenum, the various iron-nickel-aluminum alloys of the Mishima2 type, and the more recent Alnico V3 in which the best properties are developed by heat-treating in a magnetic field. The Mishima and the Alnico types of alloys are very brittle and after casting must be ground to size. This article describes a permanent-magnet material4 that can be machined as cast, and when handled with some care can be rolled to thin sheet and drawn to fine wire. Optimum magnetic properties are developed by a simple heat-treatment, and at this time the ductility of the alloy disappears. If the cast alloy is heat-treated without cold-working the mag netic energy product is about 1.0 X 106. This material is called Vicalloy I (pronounced vicalloy, V for vanadium, I for iron, and C for cobalt). When the alloy is first hot-worked and then considerably reduced in area by cold-swaging, drawing or grooved rolling, it is found that after heat-treatment the magnetic energy product measured in the direction of previous extension can be increased to 2.0 to 3.5 X 106. These higher values have been obtained only after reductions in area of 75 to 95 per cent, and since the material hardens considerably during working, the reduction ordinarily can be accomplished only in fine wires, although larger sizes can be reduced by the use of powerful machinery. When the material has been cold-worked in such a manner as to improve its energy product substantially, it is called Vicalloy 11. Commercial use of Vicalloy has been made in the recording of speech. Tape 0.002 by 0.050 in. has been found superior in quality to all others tried, and is now used in the Western Electric Mirrorphone 5 In a variety of forms Vicalloy I or I1 is useful in many laboratory instruments, and in experiments in which the sizes and shapes required cannot be obtained with the other more brittle permanent-magnet materials. In 1936, during a study of other age-hardening magnetic systems, it occurred to the author that some of the iron-cobalt-vanadium alloys might be suitable for permanent magnets. The proportions of iron, cobalt, and vanadium were varied and a range of alloys of particular interest was found, as shown by the indicated area in Fig. I. The limits of this range of composition are 30 to 52 per cent iron, 36 to 62 per cent cobalt, and 4 to 16 per cent vanadium. The compositions indicated by points outside this area were also tested. Preparation and Properties OF Vicalloy I The alloys were usually cast in graphite molds into bars 3/4 in. in diameter and

Jan 1, 1946

By E. A. Nesbitt

The important permanent-magnet alloys 15 years ago contained carbon and depended upon it for their permanent-magnet properties. In recent years great advances have been made in a number of new alloys substantially free of carbon. These include Remalloy,' an alloy of iron, cobalt, and molybdenum, the various iron-nickel-aluminum alloys of the Mishima2 type, and the more recent Alnico V3 in which the best properties are developed by heat-treating in a magnetic field. The Mishima and the Alnico types of alloys are very brittle and after casting must be ground to size. This article describes a permanent-magnet material4 that can be machined as cast, and when handled with some care can be rolled to thin sheet and drawn to fine wire. Optimum magnetic properties are developed by a simple heat-treatment, and at this time the ductility of the alloy disappears. If the cast alloy is heat-treated without cold-working the mag netic energy product is about 1.0 X 106. This material is called Vicalloy I (pronounced vicalloy, V for vanadium, I for iron, and C for cobalt). When the alloy is first hot-worked and then considerably reduced in area by cold-swaging, drawing or grooved rolling, it is found that after heat-treatment the magnetic energy product measured in the direction of previous extension can be increased to 2.0 to 3.5 X 106. These higher values have been obtained only after reductions in area of 75 to 95 per cent, and since the material hardens considerably during working, the reduction ordinarily can be accomplished only in fine wires, although larger sizes can be reduced by the use of powerful machinery. When the material has been cold-worked in such a manner as to improve its energy product substantially, it is called Vicalloy 11. Commercial use of Vicalloy has been made in the recording of speech. Tape 0.002 by 0.050 in. has been found superior in quality to all others tried, and is now used in the Western Electric Mirrorphone 5 In a variety of forms Vicalloy I or I1 is useful in many laboratory instruments, and in experiments in which the sizes and shapes required cannot be obtained with the other more brittle permanent-magnet materials. In 1936, during a study of other age-hardening magnetic systems, it occurred to the author that some of the iron-cobalt-vanadium alloys might be suitable for permanent magnets. The proportions of iron, cobalt, and vanadium were varied and a range of alloys of particular interest was found, as shown by the indicated area in Fig. I. The limits of this range of composition are 30 to 52 per cent iron, 36 to 62 per cent cobalt, and 4 to 16 per cent vanadium. The compositions indicated by points outside this area were also tested. Preparation and Properties OF Vicalloy I The alloys were usually cast in graphite molds into bars 3/4 in. in diameter and

Jan 1, 1946

By G. E. Rencken, J. H. Potgieter, A. Narain, J. Smith

To conserve fresh water resources and comply with environmental regulations, DRDGOLD, a South African gold producer re-treating surface tailings, has transitioned to a fully closed water circulation system. Consequently, the accumulation of contaminants, as well as addition of reagents, has led to changes in water composition that have compromised leach performance and overall gold recovery. A two-sample t-test confirmed a significant difference in gold recoveries between the use of Rand Water, which was used as a benchmark, and untreated process water. Atomic absorption analysis of ERGO’s process water, confirmed the presence of iron, nickel, zinc, and manganese. A study of the effect of the identified contaminants on gold recovery showed that iron, nickel, and zinc have the largest negative effect on gold recovery, with iron and nickel being more detrimental than zinc. Sulphates were shown to have a possible passivation effect, which also influenced gold recoveries, although to a lesser extent than the heavy metals. Calcium, when present in excess, had a positive influence on gold recovery indicating the possible formation of a calcium aurocyanide complex. Lime softening successfully reduced the heavy metal and sulphate concentrations, and the gold recoveries obtained with the treated process water were similar to those as achieved with Rand Water.

Jul 1, 2021

In open cut gold mining at Mt Magnet and Reedy, grade control sampling is done with inclined RC drilling using one metre samples. In the small open cuts at Rothsay blasthole sampling was successfully used. Underground sampling for gold and copper grades at Rothsay is done using chip sampling. At the Youanmi open pits both Ditchwitch Earthsawing and RC drilling are used.All assay data are interpreted on sections and plans using a customised SURPAC system. Reconciliations of the grade control predictions of tonnes and grade against initial ore reserves, mining production and milling results are carried out monthly.

Jan 1, 1990

By F. H. Wilson, E. W. Palmer

G. L. Bailey (British Non-Ferrous Metals Research Association, London, England)—I was glad to see this further work on the structure and properties of the Cu-Ni-Fe alloys of low nickel content in which we have been so interested in the United Kingdom since before the war." The authors' data on the variation in solubility of iron in both 5 and 10 pct Ni alloys with temperature is based on more detailed observations than we have made but is generally in line with our own work. The difficulty in these matters is in the identification of the structures obtained. The precipitation of the second phase which we presume to be the a' solid solution, richer in nickel and iron, from the a solution with which it is in equilibrium occurs in such a fine state of division that its resolution by ordinary micro-graphic methods is impossible in the early stages. We have published some electron micrographs which illustrate the effects observed more clearly but we agree with the authors when they say that dark staining characteristics when the alloys are subjected to sea-water corrosion are more sensitive in detecting the presence of the a' phase than is the microscope. After taking this point into consideration, however, I confess to some difficulty in understanding Fig. 4. I can only assume that the precipitates visible at such a low magnification as 150 diam in these relatively coarse forms are produced from iron-rich areas of the initial solid solution due to inadequate homogenization. If this is so I find it difficult to accept the authors' contention that such local variations in iron concentration as are capable of giving the heavy precipitates shown in Fig. 4 do not in fact materially affect the solvus surfaces of their equilibrium diagrams. I share the authors' enthusiasm about the resistance to corrosion of these alloys by seawater but I am not fully in agreement with them on the vexing question of the best iron content for these alloys. In Fig. 3 of ref. 8, we give many results showing that the resistance of these alloys to impingement attack in the Jet Test increases as the iron content rises to 2 pct. With higher iron contents pitting at shielded areas is likely to occur. Admittedly the addition of 0.75 pct Fe produces a large improvement in corrosion resistance compared with a pure 90/10 Cu-Ni alloy, but the further improvement on raising the iron to 2 pct is substantial. We recommend from 1.5 to 2 pct Fe as the desirable range from the point of view of corrosion resistance. While it is true that British practice generally uses a hard tube, the corrosion resistance of the 10 pct Ni alloys has in our work been little affected by the structural condition. Although the annealed alloys blacken in seawater, this effect seems to be superficial and not to be accompanied by any real decrease in

Jan 1, 1953