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By Jerry Wang, Greg Bold, Mahmood Khwaja, Rebecca Caldon, William Simcoe

Phase III and Phase IV of the Beaver Creek Clean River Project, Albany, NY, includes microtunnel construction of 2,320 feet of 48-inch/36-inch internal diameter (ID) conveyance pipe and a 525 foot long 9.5-ft horseshoe shape roadheader excavated tunnel. Notable challenges were encountered during the construction including mixed face tunnel conditions, undocumented existing fill ground conditions that resulted in settlement during shaft construction, and unstable tunnel face conditions. This paper discusses several of the key challenges encountered during construction and selected solutions to construction sequencing and methodology to successfully complete Phase III and Phase IV of the Beaver Creek Clean River Project.

Dec 1, 2022

By Peter Dunn

London Mining Plc. is developing an iron ore project in Sierra Leone. The Marampa mine is a brownfield development effort, having been operated by others since the 1930?s until low iron ore prices forced closure. Peak production of the prior operations was approximately 2.5 Mt/a in the 1960?s. Following civil war In Sierra Leone, London Mining obtained the mining license in 2006 and commenced activity to redevelop the Marampa mining and processing operations. There are two ore deposits of interest for development as well as a resource comprised of tailings from previous operations. Phase 1 will be the mining of the tailings resource with a 1.8 Mt/a plant producing 66 per cent Fe sinter feed, expandable to 3.6 Mtpa. The first phase is currently under construction with start-up expected in the third quarter of 2011. Phase 2 will include development of the two ore deposits. These deposits are weathered secondary ore and the main primary ore resource. Phase 2 is currently under prefeasibility study and targets a final 16 Mt/a concentrate production in 2016. Outotec partnered with London Mining on testing efforts to develop the magnetic separation flowsheet using SLon VPHGMS machines to process the Marampa material. This paper explains the flowsheet development process for the weathered and primary ores commencing with sample characterization and detailed parametric investigations to evaluate SLon performance. The final flowsheet configuration is explained, including expected circuit recoveries and concentrate quality, clearly demonstrating the performance of the SLon VPHGMS circuit in iron ore tailings treatment applications.

May 1, 2011

By H. I. Aaronson, W. L. Winterbottom, G. M. Pound

On the basis of a statistical thermodynamic treatment of the data of smithz2 on the activity of carbon in austenite, a Darken and smith23 deduced that the interaction energy, wy, between carbon atoms occupying nearest-neighboring interstitial sites is repulsive. Aaronson, Domian, and pound 24 (ADP) have applied two different statistical thermodynamic analyses to the same data. One analysis, a composite of the treatments of Darken and Smith,23 Speiser and Spret-nak," and Kaufman, Radcliffe, and Cohen,26 primarily takes account of the positional entropic effects of wy in dilute solutions. The other, due to Lacher 27 and Fowler and Guggenheim," is also applicable to more concentrated solid solutions. The equations which both analyses produce for a,, can be rearranged so that, when In a,, is plotted against the appropriate function of the carbon content of the austenite, the plot will have a slope of unity when the correct value of wy is employed. Since no other constant need be simultaneously evaluated in order to make this determination, ascertaining the most probable value of wy from Smith's data on the bases of these analyses was an elementary problem in least-squares statistics. ADP demonstrated that the wy's obtained from both analyses vary with temperature in a statistically significant manner. McLellan, Gerrard, Horowitz, and sprague 29 (MGHS), on the other hand, have recently made a new statistical thermodynamic study of a,, and have concluded from this study that wy is independent of temperature. The equation which they derived for a,, is: where 0 = ratio of the mole fraction of carbon atoms to that of iron atoms, z = number of sites from which occupancy is excluded by the presence of a carbon atom and the repulsive character of its interaction with nearest-neighboring carbon atoms (z = zb in Ref. 24), and x = a geometric parameter taking account of overlapping of the exclusion shells of nearby carbon atoms. z is 1 when wy = 0 and 13 when wy = Q. For a given value of z there is a definite value of X . In the absence of an equation connecting z and X, MGHS computed geometrically the value of x at several integral values of z; x increases from 0.47 to 8.67 as z is increased from 2 to 5. MGHS fitted Eq. [I] to the a,, data of Ellis, Davidson, and Bodsworth30 at 925° and 1050°C and to the data of smithz2 at 1000°C. Confining z to integral values in the range 4 to 6, and also somewhat restricting AG, the values of z, X, and AG were sought which would minimize the average root mean square percent deviation, D, of the calculated a,, values from those obtained experimentally. Finding that D was almost always smallest when z = 5, they concluded that z is independent of temperature. Since:23, 26 where R = gas constant and T = absolute temperature, and w,, was considered to be similarly invariant, this statement cannot be strictly true. The temperature range employed, however, was small and the interval between the values of z tested was sufficiently large so that the results could still be consistent with a constant The statistical treatment of the a,, data applied by MGHS is clearly quite approximate. Since more than three values of a,, are available at each temperature, z, and X, and AG have actually been over deter mined, rather than underdetermined as their treatment implies. In order to make more complete and exact use of the a,, data, we shall employ the Legendre Method of Least Squares, as described by Whittaker and Robinson. This technique permits conversion of the overdetermined system of equations produced by the substitution into Eq. [I] of the available pairs of a,, and 0 data at a given temperature into an even determined system. Solution of the latter system yields the most probable value of each of the three constants. This procedure will allow a statistically rigorous test to be made of the conclusion drawn by MGHS in respect of the temperature dependence of In order to obtain linear iiequations of conditions" from Eq. [I], the exact values of the three unknown constants are replaced by G/RT = =/RT + y, where z, i, and aG are estimated values of the constants. This allows the conditional equations to be written in the form:'l where fi -f6, i, =/RT) = the right-hand side of Eq. [I] for a given pair of ayi and values. When applied to Eq. [I], these relationships become: The i equations of condition are reduced to three "normal equations" in the manner discussed by Whittaker and Robinson. The normal equations are then solved for a, ß, and y. Both of these operations are most conveniently performed by means of the computer technique of Winterbottom and Gjostein.32 This technique was used iteratively until the value of 0 (the most sensitive of the three correction factors) became 10.01. (Until they became small, a, 8, and y

Jan 1, 1969

By W. W. Norton

THE gradually increasing proportion of sulphide ores which lead smelters of to-day are called upon to handle has caused the roasting problem to become one of ever greater importance. We may look back a score of years or so and recall the old hand roasters, some of which turned out a finely divided roasted product, and others fashioned with a "fuse-box" wherein the roasted ore was slagged. Then came mechanical furnaces of several types, the Brückner cylinder, the Brown-O'Harra, the Ropp, and others, all designed to cut out the cumbersome hand labor of the old reverberatories. Roasting costs were thereupon reduced and tonnages stimulated to a gratifying extent. However, it seems to have been early recognized that this very feature of a greater amount of roasted sulphide ore as compared with oxide ore brought with it a train of difficulties at the blast furnaces. The mechanically roasted ore was fine physically, the blast furnaces were choked and the troubles of the smelterman were not at an end. Then the Huntington-Heberlein pot system of roasting appeared upon the scene, and later on the Dwight-Lloyd machines were invented, and inasmuch as both of these processes were designed not only to roast the ore but to agglomerate it as well, it was apparent that distinct steps in advance has been achieved. At the Murray plant, modern up-to-date roasting practice is fully exemplified and there are now in successful operation roasting furnaces or devices of several sorts: namely, Godfrey revolving-hearth furnaces, Wedge multiple-hearth mechanical roasters, Dwight-Lloyd. sintering machines, and Huntington-Heberlein pots. Godfrey and Wedge furnaces will properly handle material high in sulphur, say ores with 25, 30, and 35 per cent. of that element; D. &.L. machines and H. & H. pots will positively not treat efficiently ores or mixtures containing anywhere near the sulphur content mentioned, but are confined to charges containing in the neighborhood of 15 or 18 per cent. In passing, it may also be explained that, so far as the knowledge of the writer goes, Godfrey and Wedge furnaces do not economically eliminate sulphur to an extent

Jan 8, 1914

By B. C. Wonsiewicz, G. Y. Chin

THE presence of deformation bands in cold-worked metals is known to influence the development of deformation textures1 but has not been considered in any theoretical treatments. At the present time the most rigorous theory of deformation textures appears to be based on Taylor's concept of homogeneous deformation of a crystal within a polycrystalline aggregate.' For each crystal the Taylor theory allows the operation of several equivalent combinations of five or more slip systems. Hence deformation bands can arise from the operation of a separate combination of slips in each of several portions within a crystal. On the other hand, a second type of band may occur as a consequence of slip on systems other than those selected on the basis on homogeneous deformation. This type appears to be associated with crystals of symmetrical orientations, such as the [loo] and [lll.] axial orientations in drawn wires of fcc single crystals studied by Ahlborn.3 In this note we propose a simple mechanism of deformation banding of the second type, and compare the theoretical results for wire drawing of [loo] and [Ill] with Ahlborn's observations. In outlini the model requires that the work to accomplish a given overall shape change by banding be less than or equal to the work to accomplish the same change by homogeneous deformation. While the work by homogeneous deformation, WH = ?T ;dri, can be calculated exactly by the equivalent methods of Taylor2 or of Bishop and Hill,4 the work by banding, WB, is less certain. The latter consists of 1) Wi, work by slip within a band, 2) Wb, work associated with formation of a boundary between bands, and 3) Wc, work to correct the difference in shape change arising from banding and homogeneous deformation. The Wi term can be evaluated explicitly for a band with an assumed set of slip systems, but a satisfactory analysis of Wb and Wc has not been obtained. Since WB = Wi + Wb + Wc WH, for banding to occur, however, a necessary condition is Wi = WH . Hence it seems reasonable to choose a band with the lowest value of Wi among competing bands consistent with Wi = WH, and then minimize Wb and Wc by arranging the physical configuration of the selected band. Wc is minimized by combining neighboring bands such that their net strain matches the macroscopic strain as closely as possible, and Wb is minimized by enforcing strain compatibility across the boundary between two neighboring bands, similar to the case of a grain boundary.5 It is realized that this procedure is not completely satisfactory, but it does seem to explain Ahlborn's observations reasonably well. The procedure is now outlined for the two corner orientations. a) [l00]. Fig. 1 shows a (100) stereographic projection. The results of the Taylor analysis for axi-symmetric flow by homogeneous deformation6 show that, while [loo] itself is unstable, the rotation of the tensile axis will nevertheless be confined to within about 15 deg from [loo]. Alternatively, less work may be expended by banding with slip on a pair of systems with primary-conjugate relationship, e.g., (ll1)[10l.I + (li1.)[110]. The latter represents minimum Wi for all possible bands.* Since there are four symmetrically

Jan 1, 1970

By G. T. C. Emere, E. C. Hunter

The use of cylindro-conical settlers for the clarification of underground water by E. C. HUNTER- (Associate) G. T. C. EMERE-, B.A. (Hons.) (Keele) (Visitor) This paper analyses the performance of conical settlers on Harmony Gold Mine from 1959 to the present time, and describes the investigation that was undertaken to substantiate and improve the use of conical settlers for a new pump chamber in another part of the mine.

Jan 5, 1977

Discussion of the paper of ALBERT D. BROKAW, to be presented at the Colorado meeting, September, 1915, and printed in Bulletin No. 1:16, April, 1918, pp. 947 to 950. LEE HAGER,* Houston, Tex. (written (discussion t).-In no other oil region of the world, perhaps, have the geological principles, of such high value in many fields, found so little practical application as in the

Jan 8, 1918

By Jared Ball, Benjamin Hogg

There are over 100 process parameters that can be monitored during a single Peirce-Smith (PS) converter batch operation. To support a consistent operation it is important to select the correct Key Performance Indicators (KPI’s) to monitor. They should be strategically chosen to drive the desired behaviour with enough flexibility to endure process variations. At the Xstrata Copper Smelter in Mount Isa most of the PS converter operators have very little experience and are often lacking in the appropriate education or training to properly understand the process. For this reason 10 simple KPI’s were chosen that could be easily comprehended and monitored by all smelter personnel. KPI compliance has been supported by relevant project work in the converter area. Charge sequence trials have been performed in an effort to reduce splash and optimise activity time. The online measurement of full and empty ladle weights has enabled an immediate indication of skull size, skim/slag carryover, and metal loss.

Jan 1, 2009

By Carl A. Allen

Page Introduction................... 367 FactoRs Affecting the Choice of Method......... 367 Review of Stoping Methods.............. 368 Underhand Stoping................ 368 Overhand Stoping................ 370 Longitudinal or Flat-Back Stoping........... 371 Rill-Cut Stoping................. 372 Saw-Tooth Back Stoping.............. 372 Shrinkage Stoping................ 372 Combination Stoping................373 Side Stoping.................. 374* Breast Stoping................. 374 Sublevel Stoping.........,....... 374 Square-Set Stoping................ 376 Filling Methods................. 376 Caving Methods of Mining......... 376 Top Slicing.................. 377 Sublevel Caving................. 379 Block Caving ................. 380 Back Caving into Chutes.............. 381. Costs of Mining Methods.............. 382 Costs of Willing and Blasting. Comparison of Stoping Methods ... 383 Lighting................... 386 Timbering and Handling Ore in Stopes.. A Comparison of Square-Set and Top-Slicing Methods..............386 Tramming.................... 380 Mining oF the Massive Porphyry CoppeR Deposits ....390 Utah Copper and Boston Consolidated Mines.....391 Ray Consolidated Mine.............. 392 Miami Mine.................. 392 Inspiration Mine................ 395 Ohio Copper Mine...........395 Development.................... 398 Appendix..................... 399 Costs of Mining................. 399 Costs of Development............... 406

Jan 1, 1915

By D. McBride

Representative samples are required from process streams in order to accurately measure chemical and physical characteristics. This information can then be used by process operators and metallurgists to evaluate the process and effect control actions for the operation. The capture and presentation of representative samples can be critical to measuring values, such as elemental analysis and particle size, with on-line or near-stream analyzers. A comprehensive multi-physics model has been developed and used to better understand the effects of slurry flow and particle segregation under certain operating parameters. An algebraic slip model coupled with a free surface algorithm is used to track motion and position of particles and phases within a specified geometry.

Jan 1, 2009

In August, 1975, North Broken Hill Limited announced that an intersection of 37.3 m of high grade lead-silver-zinc mineralisation, assaying 26.2 per cent Pb, 495 g/tonne Ag and 21.2 per cent Zn had been obtained at its Mine at Broken Hill, 520 m north-east of its No. 3 Shaft and slightly below the No. 36 level (1581 m). Subsequent drilling confirmed the presence of the extension of the Broken Hill Orebody on the north-western side of the Globe Vauxhall Retrograde Shear Zone and defined 1.8 million tonnes of high grade mineralisation. The area containing this mineralisation was subsequently named the Fitzpatrick Area in tribute to the late Mr. W.E. Fitzpatrick a former Member of the the Board and Manager of the Ccnpany's Broken Hill operations. This paper describes in brief the exploration programme leading up to the discovery, the general geology of the area and the proposed future exploration progranme for further extensions of the orebody within the mining leases of North Broken Hill Limited.

Jan 1, 1983

By Burgess J, Brownrigg A

The world steel industry underwent rapid growth from 1950 to 1970. Since that time, production growth has been relatively slow, with declining production in the developed countries and increasing production in some newly developing countries. Since 1970, Western World crude steel production has been static at around 450 million tonnes, with cycles around this level in a 100 million tonnes band.

Jan 1, 1992

By E. A. Schmidt

In 1962, while investigating the tungsten potential in the Thompson Creek area for Union Carbide Corp., Henry T. Eyrich obtained anomalous concentrations of molybdenum (up to 19 ppm Mo) from stream sediment samples collected along Pat Hughes Creek, a tributary to Thompson Creek. Follow-up investigations by Eyrich during the same year disclosed the presence of a hydrothermally altered and molybdenite-bearing granitic exposure in the headwaters of Pat Hughes Creek about 2.4 km (1.5 miles) upstream from the sample point. The altered outcrop measured about 549 by 305 m (1800 by 1000 ft), contained abundant northwest-trending quartz veins locally with molybdenite, and was overlain and surrounded by the Challis volcanic extrusive sequence of mid-Tertiary age. Eyrich's subsequent soil and rock chip geochemical sampling program over the altered outcrop area showed a general increase in the molybdenum content to the northwest toward the postmineral Challis volcanic cover. Over a distance of about 305 m (1000 ft), values in the altered intrusive rock increased from less than 5 ppm Mo to over 600 ppm Mo, with aconcomitant intensity of the hydrothermal alteration pattern. Based on these geochemical results and on preliminar; megascopic hydrothermal alteration studies, Eyrich correctly concluded that the altered outcrop is an erosional window and that molybdenum mineralization of sufficient grade could exist beneath the Challis volcanic cover some distance further to the northwest. His recommendation to test the area of potential molybdenum mineralization with several drill holes was, however, declined by Union Carbide in 1962. The property remained unclaimed until 1967, when Eyrich joined Cyprus Mines Corp. Acting on Eyrich's recommendation, Cyprus immediately staked 26 lode mining claims to cover not only the altered intrusive outcrop, but also the northwest trend of mineralization where it projected beneath Challis volcanic rocks. Eleven of these claims are now patented.

Jan 1, 1991

By Norman E. Lehman

Pyrometasomalic mineralization occurs within meta-morphosed Paleozoic carbonates intruded by Laramide granodiorites. Two types of alteration developed shams in the district. The dominant type is post-magmatic which developed an early hydrous endoskarn phase, and intermediate anhydrous exoskarn phase, and a late hydrous phase affecting both sham types. A rare, second type is magmatic in age, lacks the hydrous phases, and developed a mineralogically-zoned endoskarn. Garnet exoskarns lacking associated plutonic rocks are stratigraphically controlled and contain an early anhydrous phase, an intermediate hydroxyl-bearing phase, and a late hydrous phase associated with base metal deposition.

Jan 1, 1981

By J. C. Shyne, T. D. Gulden

The steady-state creep behavior, in compression, of indium containing a dispersion of atomized glass particles was studzed over a range of temperature, stress, and composition. The observed behavior was not consistent with a simple model of dislocation climb over dispersed particles. From room temperature to about 100°C the temperature dependence could be described by an activation energy about one and a half times that of self-dijfusion in indium while at higher temperatures a much higher ternperature dependence was observed. THE value of dispersion-hardened and precipitation-hardened alloys has long been recognized. The mechanism of hardening, however, is not completely understood, especially at elevated temperatures where dispersed particles increase creep resistance. Following the suggestion of Schoeck1 that the rate of creep in dispersion-hardened materials is controlled by dislocation climb over second-phase particles, Ansel and weertman2 derived steady-state creep equations for dispersion-hardened materials. Their derivation was based on dislocation climb over non-deformable spherical particles in a metallic matrix. For low stresses they predicted a linear relation between applied stress and steady-state creep rate. For stresses large enough to cause dislocations to pinch off around the precipitate particles, the theoretical creep rate was shown to be proportional to the fourth power of stress. For very high stresses an exponential stress dependence was predicted. In all cases the theoretical creep rate is linearly proportional to the diffusion coefficient. This provided the primary temperature-dependent factor. Subsequently, Ansel and Lenel3 reported some experimental data on SAP, a composite of aluminum and aluminum oxide, that was in good qualitative agreement with the above theories. Their experimental creep rates, however, were four orders of magnitude less than the theory predicts. This was attributed to a low density of active dislocation sources in the material; somehow the dispersed particles inactivated the dislocation sources instead of merely interferring with dislocation motion. Meyers and sherby4 have recently reported on the creep behavior of SAP. Their results were inconsistent with a simple dispersion-strengthening model and led them to conclude that a continuous network of oxide controls the high-temperature mechanical characteristics of SAP. Because of the rather complex mechanical behavior of SAP and the lack of agreement about the morphology of its oxide phase, it appeared desirable to study the creep of a dispersion-strengthened material of controlled morphology. For the present work a dispersion of spherical glass particles imbedded in a matrix of indium was chosen. The microstructure of this material was similar to the idealized uniform dispersion of hard spheres in a deforming matrix assumed by Ansel and Weertman in their theoretical treatment. SPECIMEN PREPARATION For experimental convenience, it was decided to use a low melting-point metal in this investigation. It was necessary that the metal not be oxidized readily up to its melting temperature and that it wet the second-phase particles. It was desired that the material chosen for the dispersed phase be available as a fine powder with closely controlled size and shape. The material chosen to satisfy these requirements consisted of a matrix of indium metal containing a dispersion of atomized particles of a soft soda-lime-silica glass ranging from 5 to 30 µ in diam. The glass particles had a highly regular spherical shape. The composite was made by stirring the glass powder into liquid indium maintained at a temperature just above the melting point of indium, 156°C. The creep specimens were prepared by a hot pressing operation. Five to ten g of the mixture were placed in a steel die and pressed at 125°C for 5 min under a pressure of 30,000 psi. The resulting specimens were cylinders about 3/8 in. in diam and ranged from 0.4 to 0.7 in. high. By following this procedure a uniform dispersion was obtained in the creep specimens. Typical microstructures of specimens containing twenty and forty volume percent glass powder are shown in Figs. 1 and 2. Unfortunately, grain size could not be determined by the metallo-graphic techniques used. CREEP TESTING PROCEDURE Creep tests were performed in compression under constant stress. The specimens were placed in

Jan 1, 1963

By E. M. Hill, D. E. Walsh, J. T. Hollow, H. K. Lin

Fairbanks Gold Mining, Inc. (FGMI) began blending and processing True North ore at their Fort Knox mill on April 12, 2001.Gold extraction subsequently dropped from 88% to 71% during the last week of April 2001. 25% of the gold values remaining in the leach tailings were gravity recoverable free gold. Significant quantities of stibnite and arsenopyrite were also identified in the tailings. In laboratory bottle roll tests, the gold extraction from a composite of leach circuit feed collected during the same period was 72.6%, when leached at an average NaCN concentration of 0.16 g/kg. The extraction increased to 82.4% and 91.7% with 0.5 g/kg NaCN, and 0.5g/kg NaCN plus 0.075 g/kg Pb(NO3)2, respectively. A passivating layer surrounding liberated gold particles and resulting from sulfide mineral dissolution, likely contributes to reduced gold recovery, which can be substantially increased by the addition of lead nitrate. Lead species remain in the solid residues after leaching and were not mobilized using Meteoric Water Mobility Procedure.

Jan 1, 2003

By M. Leroux, S. R. Rao, J. A. Finch

"Poor Pb-Zn selectivity during Pb flotation in laboratory tests on a Mississippi Valley-type Pb-Zn ore was traced to apH effect. In the pH range, 9.5 to 11.0 sphalerite floated readily without copper activation. Compared to sphalerite flotation with copper activation this procedure gave equivalent selectivity but reduced flotation rate.Possible mechanisms of this sphalerite flotation without copper activation are discussed. Activation by Fe(OH)2 is suggested, the Fe- + ions being derived from superficial oxidation of pyrite in the ore. IntroductionGalena and sphalerite commonly occur together. A typical procedure, using xanthate collectors, is to float the galena first, at pH - 8, followed by flotation of sphalerite after activation with copper (II) sulphate at pH - 10 (to depress pyrite).Flotation tests following this procedure in an undergraduate laboratory course with a Pb-Zn ore from Polaris failed to achieve consistent selective flotation of galena. Occasionally a considerable amount of sphalerite, even though unactivated with CUSO4, floated. This was traced to accidentally high pH. A systematic study was carried out which revealed that sphalerite floated readily in the pH range 9.5 to 11.0 without activation by CuSO4 This paper describes the results of the study and discusses a possible mechanism of this flotation of sphalerite."

Jan 1, 1987

By E. E. Barker

Although flotation was known to be a successful process prior to 1312, Utah Copper Co.'s ores were not entirely treated by this process until 1923. Experiments had been conducted, of course, prior to that time, and in February, 1917, the first unit of the Arthur plant was changed over from gravity concentration to flotation. On May 16, 1918, the entire Arthur plant was on flotation, excepting the coarse concentrate which was tabled prior to fine grinding. The reasons for the delay in adopting flotation at these plants were, first, that it was decided to await the outcome of the litigation with the Butte & Superior Mining Co., which began with an injunction served on Oct. 3, 1911. This litigation continued for years. Then the demands on the plants in the war years 1916, 1917 and 1918, really precluded any further drastic changes during that period, as all efforts were bent on maximum tonnage, and the cry of tonnage, rather than of recovery, was the major issue. The postwar depression followed these years of intensive production, so that it was not until 1922 that the Magna plant was equipped to use this process. Excepting, then, the amount of coarse concentrate that was tabled, 1923 was the first year when the Utah Copper Co.'s ores were on a full flotation basis. Effect of Flotation on Ore Reserves The object of this paper is to point out the effect that flotation has had on the operations of the Utah Copper Co. In 1905, when D. C. Jackling began making history in copper, the ore reserves were 34,000,000 tons, with a grade of 2 per cent. copper and a mill capacity of 700 tons daily. The point of cut-off between nonprofitable and profitable grades was 1.2 per cent. A few years later the capacity was increased to 6000 tons, when 1.1 per cent. became the point of cut-off. Ore reserves had climbed to 80,000,000 tons, having a grade of 1.9 per cent. In 1911 there was an ore reserve of 300,000,000 tons, with a grade of 1.5 per cent. and a cut-off of 1 per cent.; in 1918 the ore reserve was approximately 400,000,000 tons, and a grade of 1.38 per cent., and point of cut-off 0.95 per cent., based on normal costs and prices. Up to this

Jan 1, 1928

By James R. Boyle

The value of Alabama's nonfuel mineral production in 1987 was $446.6 million, an increase over that of 1986 and the first increase in 3 years. Alabama was second in the Nation in production of bauxite and ferroalloys; third in bentonite, crushed dolomite, crushed marble, and fire clay; and fourth in masonry cement. Trends and Developments.-Employment in the minerals industry remained relatively low for the second year even though the overall unemployment rate dropped to 7.9% by December. Employment in mining and primary metals dropped about 10% and 2%, respectively.

Jan 1, 1989

By Richard H. De Voto

The McDonald Gold Project and two satellite gold deposits near Lincoln, Montana, contain at least 9.9 million ounces of gold and 30 million ounces of silver. The McDonald gold deposit alone contains 7.2 million ounces of gold reserves that can be open-pit mined and processed by cyanide heap leaching at a projected cash operating cost of $190 per ounce. The deposit is predominantly oxidized with no chance of acid production, and can be mined, operated, and reclaimed with minimal permanent environmental disturbance other than the creation of an open pit filled with a fresh-water lake which would support trout. The Seven-Up Pete Joint Venture, the owner of the McDonald Gold Project, commenced permitting of an open-pit, heap-leach operation in November 1994. In 1998, Montana citizens passed an anti-cyanide, open-pit mining initiative, 1-137, which banned any new open-pit gold mine which uses cyanide processing, The Venture has conducted extensive studies, including metallurgical testing of the treatability of McDonald ores with alternative lixiviants, and has determined that all other mining and metallurgical treatment systems are vastly uneconomical in the recovery of gold and silver from the McDonald deposit. Therefore, the Venture's proposed open-pit mining and cyanide heap-leach processing is the only technology that can be applied economically to the McDonald deposit. Further, the analyses convincingly demonstrate that the proposed open-pit, cyanide heap leaching technology results in maximum resource conservation of this valuable and unique deposit and poses far less risk to human health and the environment than any of the alternative technologies.

Jan 1, 1998