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By H. M. Cooper, R. F. Abernethy

Determination of the fusibility of coal ash consists in melting a pyramid of the ash to fluid under prescribed conditions . The conditions of the test are specified by the American Society for Testing Materials4/ and must be adhered to strictly if comparable results are to be obtained . The Society formerly specified a particular type of furnace , but with improvements in design of both electric and gas furnaces , it was decided by the Society to specify only essential details of the test . The Chairman of Committee D - 5 , Coal and Coke , of the American Society for Testing Materials suggested that the Coal Analysis Section of the Bureau of Mines conduct a cooperative investigation on the effect of furnace type and atmosphere upon fusibility of coal ash . The Coal Analysis Section enlisted the aid of a number of laboratories using the more common furnaces to cooperate in the investigation . Four types of gas furnaces burning natural and manufactured gases and two types of electric furnaces with different methods of maintaining a reducing atmosphere were employed . The results from the survey are tabulated herein , and some comparisons are made . There were not enough data from any particular furnace and atmosphere to make a reliable statistical analysis . However , definite tendencies are evident , and attention is called to them by direct comparison. in tables .

Oct 1, 1943

By Joseph A. Hrabik

The Bureau of Mines compared the feasibility of mining deep phosphate deposits by a borehole mining system with mining by proven conventional techniques. An economic comparison of the borehole mining system with conventional dragline and bucket wheel excavator mining systems was completed at various mining depths and production rates. Hypothetical phosphate deposits, with various overburden thicknesses and reserve tonnages, were defined. Geologic conditions necessary for the application of the borehole system were identified. Discounted cash flow analyses based on derived capital and operating costs were used to generate rates of return and product prices. Borehole mining was found to be more economical where overburden thickness was 150 ft or greater; however, at 50- and 100-ft thicknesses, conventional surface mining was more economical. Overburden thickness has a great effect on the economic feasiblity of the conventional mining systems but less effect on the economics of borehole mining. Economies of scale are only realized in conventional mining, since larger equipment is employed to achieve greater production, whereas increased production from borehole mining is achieved using additional equipment units. A comparison of the environmental effects of borehole and conventional surface mining systems showed that borehole mining is environmentally more desirable.

Jan 1, 1983

By E Hernandez, I Agustian, W Kusumohastuti

PT Freeport Indonesia is completing the first underground gyratory crusher excavation at their Deep Mill Level Zone (DMLZ) mine located in the mountains of Jayawijaya, District of West Papua, Indonesia. DMLZ is an underground block cave mine with an expected output of 80 000?t/d and a scheduled production start in 2015.In order to deliver crushed ore to the mill through the existing conveyor belt, the DMLZ block cave mine will construct two 1000?kW 1.6?×?2.3?m gyratory crushers with their own respective ore flow conveying systems underground. Each crusher is composed of top, middle, and bottom chambers with an ore bin. This system includes a series of high capacity conveyors approximately 5 km in length including transfer stations and support facilities.The development methodology required a combination of lateral development by jumbo drilling machines and vertical development by mechanised raise climbers (MRC) due to the complexity of the chamber design.This paper will discuss the project scope, design and development methodology, ground conditions, innovative survey controls, and the challenges faced due to the remote location.CITATION:Hernandez, E, Kusumohastuti, W and Agustian, I, 2014. Excavating the first underground Gyratory Crusher at the Deep Mill Level Zone mine, PT Freeport Indonesia, in Proceedings 12th AusIMM Underground Operators’ Conference 2014 , pp 43–50 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Mar 24, 2014

By Jean-Yve Tremblay, Michel Prud'homme

"IntroductionIndustrial minerals include a group of more than fifty minerals which are marketed into almost all the sectors of industry; they are the backbone of many manufacturing industries. Table I shows major end-uses for industrial minerals in manufacturing sectors.At Energy, Mines and Resources, industrial minerals are divided in three major categories: (I) agro chemicals and chemicals, (2) construction mineral s, and (3) ceramics and specialty minerals. A listing of the major groups of minerals is shown in Table 2.Agro-chemicals and chemicals are sold on the basis of their chemical content and purity. Construction minerals or structural minerals are distinguished by their performance as low cost and bulky commodities. Ceramics and specialty minerals are performance-specific and are sold for their property on imparting functions on end-products. Industrial minerals have unique characteristics that are useful in many stages of processing; from crushed size to micronized fillers a single mineral ca n serve a broad range of industries because of its intrinsic properties.The Industrial Minerals Industry in CanadaCanada has a large industrial minerals base and is a world leader in the production of some of them. The total value of product ion of these minerals has grown by 115% over the last 10 years despite the misfortune of asbestos.Industrial minerals have shown remarkable growth in the past 20 years at an average annual rate of 9.2%, compared to 7.8% for metallic minerals. In 1986, the value of industrial minerals rose to $4.9 billion, or 14% share of the Canadian mineral production. Figure I shows the value of production of the mineral industry for the period 1966-1986.The leading segment in industrial minerals segment since 1976 is the chemicals and agro-chemicals sector which has an average annual growth rate of 5.75 % in terms of value of production. During the same period, the growth rate for the whole Canadian mining industry was 1.37% per annum. The chemicals and agro-chemical s sector increased its contribution to the total value of production of 2% to 6070 despite the growing share of fuel minerals with 59%."

Jan 1, 1988

By Sandeep Kumar Jeripotula, Govinda Raj Mandela, Aruna Manglapady

Dumper operators are frequently exposed to whole body vibration (WBV) in surface mines. Surface mining activities involve the amalgamation of comparatively high intensity of vibration and extended exposure durations. Efficient risk reduction mandates knowing of important phases of a task that poses a threat to health of dumper operators. So far in India very limited studies have been reported on WBV exposure with regard to surface mines. This paper evaluates WBV of dumper operators based on ISO 2631-1:1997 Standards and European Union (EU) Directive 2002 for different phases of job cycle. Six dumpers were considered for this study and the vibration measurements were made for all the four phases of the job cycle by placing the triaxial accelerometer on the operator’s seat-surface and at the seat-back, independently. The findings of the study revealed that the haulage task (loaded travel and empty travel) remains the chief contributor to vibration exposure according to seat-surface and seat-back measurements. Maximum frequency weighted root mean square (RMS) of 1.12 m/s2 and 1.09 m/s2 were reported for empty travel task for seat-surface and seat-back measurements, respectively. For seat-surface measurements based on RMS, Z axis remains as the dominant axis of vibration for all the dumpers during haulage task, whereas for seat-back measurements, the dominant axis varies between X and Y. Exposure action value (EAV) based on RMS has exceeded the threshold value of 0.5 m/s2 for all the dumpers during loaded travel and empty travel for seat-surface as well as for seat-back measurements.

By Wilbert J. Huff

The organization of the'Explosives Division is indicated by the accompanying chart (fig. 1). As this has been discussed in a previous report3/, it will not be considered further in this report. The activities of the various units are outlined below. I. INFLAMMABILITY OF GASES AND VAPORS4/ Determination of the Explosion Hazards of Combustible Gases and Vapors Found in Mines and Industries The Explosives Division maintains, at the Pittsburgh Experiment Station, a laboratory specially equipped for the determination of the explosion hazards of combustible gases and vapors. Of particular importance, is the determination of the chemical composition within which explosions may occur and beyond which there is no danger of explosion, combustion or inflammation. These limits, known as the limits of inflammability, as determined by this and other laboratories, have been compiled in Bulletin 279 of this Bureau. The last revised edition (1931) of this bulletin has been exhausted. Since it was published, the Pittsburgh laboratory has determined the limits of about 40 combustibles and has ascertained more precisely and accurately many previously published limits.

Jan 1, 1938

By Fernando Pajuelo Rincón

El presente trabajo señala el proceso de la explotación de los conjuntos de vetas en la Compañía Minera Huarón, su optimización y función en la producción de las estructuras estrechas y totales de la producción minera. Para tal proceso se utilizó los vehículos electromecánicos (LHD) de pequeñas dimensiones que se adecúen a los parámetros técnicos y explotación de las estructuras. Asimismo, para cada conjunto se aplicó el sistema de corte y relleno ascendente mecanizado a fin de obtener una mejor selectibilidad, seguridad, productividad y economía de la estructura mineralizada.

Nov 24, 1986

By K. C. Dean

The Bureau of Mines, following passage of the Solid Waste Disposal Act of 1965, was authorized to conduct research on methods for utilizing, stabilizing, or reclaiming mineral wastes. This report summarizes laboratory research conducted by the Bureau and cooperative field studies made with the mineral industry to reduce the environmental impacts of air and water pollution deriving from mineral wastes. Utilization research showed that both dry-press and steam-cured building bricks and ceramic tile could be made from copper mill tailings and other discarded mineral wastes. Sponge iron was produced from steel mill and amination industry wastes, and valuable mineral products were extracted from such diverse sources as flue dusts and uranium tailings. Mineral wastes were combined with agricultural and/or sewage wastes to make artificial soils that have the potential of resolving several disposal problems by production of a useful commodity. Physical, chemical, and vegetative stabilization methods were evaluated, singly and in combination, for reclamation potential on copper, uranium, lead-zinc, and asbestos tailings. Suitable methods were developed in the laboratory for overcoming major adverse conditions of these wastes such as salinity, heavy metal toxicity, acidity, basicity, lack of nutrients and organics, and unstable surfaces. Field testing of these methods was performed on a variety of mineral wastes. Costs for the various stabilization and utilization-procedures developed were also determined.

Jan 1, 1986

By W. L. Crentz

Before Korea was partitioned along the 38th parallel following World War II, the coal fields of South Korea, with the possible exception of the Samchok area, were not considered important to the industrial needs or Japan or Korea. Much of the demand for electric power in South Korea was met by hydroelectric installations north of the 38th parallel. Following cessation of hostilities between Japan and the' Allied nations in 1945, hydroelectric power continued to flow into South Korea from the north until 1949, when the North Koreans severed the power lines into South Korea, thereby forcing that section of the country to depend almost entirely upon coal to generate electric power.

Jan 1, 1953

By N. Sauret-Szczepanski, G. Patry, S. Gauthier, G. Potvin, C. Munger

Adsorption/thermal desorption with sorbent cartridges and analytical method using gas chromatography coupled to mass spectrometry (GC/MS) was developed for the determination of tetrafluoromethane (CF4) and hexafluoroethane (C2F6) emitted from primary aluminum smelters. A customized cartridge was built like a packed column with a stainless steel tube filled with a specific resin. The optimization of adsorption and desorption parameters was carried out to support the PFC sampling for all aluminum production technologies. The proposed method showed good linearity for concentrations ranging from 10 to 500 ppbv for CF4 and from 5 to 500 ppbv for C2F6 with correlation coefficients above 0.999. In certain conditions, the detection limits of the analytical method reached 0.3 ppbv for CF4 and 0.15 ppbv for C2F6- Using this methodology, a field campaign was carried out using a sequential sampler allowing the simultaneous sampling of PFC with cartridges and sampling bags. The results showed no significant difference (t-test) between the two sampling technologies and no breakthrough was observed from the cartridges .

Jan 1, 2006

By Phillip N. Yasnowsky

The thrust of this Bureau of Mines report is to relate the size of automobiles to the price of gasoline, and the use of minerals in automobile manufacture to the size of automobiles. Only one of the many plausible scenarios of public reaction to higher gasoline prices, a switch to economy size automobiles, is developed. No account is taken of other potential impacts such as improvements in public transportation or increased occupancy per vehicle. Furthermore, a gasoline price increase is the only incentive to the greater utilization of economy cars that is considered. A gasoline price increase to $0.60 per gallon would reduce the amount of minerals required to produce the automobiles sold in the United States by an estimated 15 percent. Gasoline prices of $0.80 and $1 per gallon would cause declines in mineral requirements for U.S. automobile sales estimated at 26 percent and 35 percent, respectively.

Jan 1, 1974

By Thomas E. Finch

Engineering mine design encompasses a range of situations, and each situation has its own range of detail and fineness. The most time consuming, and perhaps repetitive design situation involves evaluation of new or alternate mining methods. Many man years are consumed examing alternatives conjured up at all levels of the design team, from the number crunching engineer to the engineering manager. Many alternatives are intuitively disregarded, some are briefly evaluated and thrown out, and many others are started but not completed due to time constraints. All alternatives have similar input characteristics and evaluation procedures. In the design process, production requirements are known and equipment production capabilities are generated to determine the numbers and costs of an equipment type required to match a given situation. The end result is some comparative figure, typically cost per ton or yard upon which a decision is built. The similarity of input data and problem solving techniques lends design to computer solution. Computer aided equipment evaluation is not new to the mining industry. An existing and accepted technique is exemplified with the programs used by truck manufacturers. Given a haulage profile and production requirements, the number of anyone capacity, horsepower, tire size, gear ratio or similar characteristically identified truck can be determined. This information can be outputted in varying degrees of complexity and the results used with equally varying percentages of credibility by design or production engineers. Most engineers are willing to accept-the computer's effort with relief and a desire for belief. Although inherently more complex, the ultimate end of computer manipulation should be total mine design. This is an extremely large step in the evolution of mine design, and not many engineers, including the authors, believe the results would be directly applicable or necessarily correct. As with computer simulations of an operation, total computer design of mines requires such complex and lengthy input that each mine might be manually designed more quickly and cheaply. The existence of computer programs which initially evaluate a mining system or part of the system is upon us, however.

Jan 1, 1978

By E. R. Palowitch

Coal wasted with mine refuse represents losses in overall recovery of merchantable coal to the mine operator and a concomitant reduction in domestic reserves of available coal. Fraser, Kelley, and Graham3/ in studying the available coal in mine refuse in the Pittsburgh district of western Pennsylvania have estimated that at least 1 ton of mine refuse is produced for each 10 tons of merchantable coal and that 20 percent of this mine refuse might be recovered as salable coal by mechanical cleaning. SUMMARY This investigation dealt with the mechanical recovery of coal from wine refuse by a dense-medium washery employing pulverized mine rock as the dense medium and operating at a rate of 175 tons per hour. Two types of mint refuse were tested: Freshly mined and that .which had been mined 2 years before and piled on a waste dump.

Jan 1, 1955

By M. E. Rossi

This paper discusses the use of Conditional Simulation (CS) models to provide mill feed grade profiles for different time periods. The conventional approach of classifying block estimates as ore or waste generally does not adequately represent dilution, lost ore and the anticipated grade control data, including variability of mill feed from the pit and possible stockpiles. The detailed simulation of grade control practices can be done, but at the Pre- or Feasibility stage of the project may be impractical, since drawing dig limits on multiple benches is tedious and time consuming. Using the Feasibility Grade Control (FGC) method as developed by the Centre for Computational Geostatistics (CCG, University of Alberta-Edmonton), the CS models can be processed quickly to establish dilution and lost ore, and predict daily or short-term feed to the mill. The simulated nodes can be aggregated into selective mining units with adequate representation of likely geometries to be recovered from the pit, to mimic anticipated selectivity. An example from a large copper deposit is shown. The study provides an estimated stream of tonnages and grades fed to the plant by mining periods of interest and based on a specific mine design and schedule. The resulting cash flows support the economic and financial analyses of the Feasibility Study; also leads to improving mine schedules; and aids in developing blending schemes if necessary. INTRODUCTION The conventional approach of separating mineralized material into ore or waste categories does not always include a realistic amount of dilution and ore loss. Also, often it does not provide a good estimate of the grade that will be fed to the mill. If the grade control estimates are unbiased, they will over the long run represent the long-term average of grades fed to the mill; but the anticipated variability of mill feed from the pit and stockpile sources may be misrepresented. Some references on traditional grade control implementations can be found in Chunnett (1982); Davis et al. (1989); Srivastava et al. (1992); and Nowak (1992). Alternative methods based on economic variables improved significantly on the purely grade-based control methods, see Douglas et al. (1994). Further developments involved the use of geostatistical conditional simulations (CS) and profit models, which in several cases have been successfully implemented (Aguilar and Rossi, 1996; Rossi, 1997; Deutsch et al., 2000; Norrena and Deutsch, 2002; Neufeld, 2005; Jewbali and Dimitrakopoulos, 2009). But they can be impractical, mostly due to the lack of understanding of the methodology involved; even if semi-automatic dig limit drawing is implemented, there is always a need for is tedious and time consuming checking and corrections, even if using a single profit model derived from the simulated grades.

Jan 1, 2019

By J. Lovering, H. Wilhelm, P. Siewert

Introduction The Afton property is located 290 km (180 miles) by air east-northeast from Vancouver and 14 km (8.7 miles) west of Kamloops, a city of 60,000 people, in south central British Columbia, Canada. The mine is adjacent to the Trans-Canada Highway at an elevation of 670 m (2198 ft) above sea level. The ore body is a porphyry copper deposit that has undergone supergene alteration. The major economic minerals in the supergene zone are native copper and chalcocite with chalcopyrite and bornite in the hypergene areas. The grade is 1% with an overall copper distribution - 70% native, 25% chalcocite, and 5% chalcopyrite with bornite and covellite. The ore also contains important but variable amounts of gold and silver. The mill was designed to treat 6350 t/d (7000 stpd). Semiautogenous grinding was selected to minimize capital cost and because of the expected high clay content of the ore, which would have caused problems in a conventional crushing and screening plant. Test work indicated that a recovery of 87% was possible in a circuit incorporating both flotation and gravity separation. Flowsheet Run-of-mine ore is crushed in a 1.06 x 1.65-m (3.5 x 5.4-ft) Allis Chalmers gyratory crusher set at 228.6 mm (9 in.), closed side setting. The surge pocket, below the crusher, is emptied by a Hydrastroke feeder onto number one conveyor, which discharges onto a 180,000-t (198,416-st) coarse ore stockpile. Six Hydrastroke feeders on two conveyors withdraw the crushed material from the bottom of the pile. These two conveyors, in turn, discharge onto the belt feeding the semiautogenous mill. The live storage in the stockpile is approximately 22,000 t (24,250 st), sufficient for three days' mill feed. Primary grinding is accomplished in an 8.5-m (28-ft) diam by 3.7-m (12-ft) long Koppers (Hardinge Cascade) mill (Fig. 1) containing a 10% ball charge and driven by a 4000-kW dc variable speed motor. The mill dis¬charge is pumped by a 10 x 12 G.I.W. pump to a 1.22 x 4.88-m (4 x 16-ft) stationary screen sloped at 20°. Screen oversize returns to the semiautogenous mill (SAM), and the undersize flows by gravity to the ball mill discharge pump box. Secondary grinding is performed in a 5-m (16.4-ft) diam by 8.84-m (29-ft) Koppers overflow ball mill driven by a 3430-kW synchronous motor through an air clutch. The mill is in closed circuit with a Krebs Cyclopac containing 10 635-mm (25-in.) cyclones and the cyclone overflow, at 35% solids and 65% to 70% -200 mesh, is flotation feed. In order to limit the buildup of native copper, circulating in the secondary grinding circuit, a portion of the underflow from the cyclones is processed in a circuit containing screens, cyclones, and shaking tables to produce a finished metallic copper concentrate. Primary mill variable speed drive The overall waste to ore ratio at Afton was 4.5:1. The mining was to be done with only three shovels, which meant that it was highly unlikely that more than one of them would be in ore at any one time. The resulting inability to blend the mill feed made it impossible to prevent wide swings in the grade and grindability. The variable speed do drive motor installed on the semiautogenous mill was selected because of the extreme variability of the Afton ore body. This variability has persisted throughout the lifetime of the mine. There are times, however, when due to ore conditions, the mill is operated at full speed (78% of critical) for extended periods of several shifts duration. There are other times when the mill speed may be changed several times in a 12-hour shift due to changing ore conditions. When ore is processed that contains a fairly large proportion of fine native copper, the primary mill speed and, consequently, the tonnage may be reduced to improve the secondary grind and to maintain an acceptable grind and recovery. High clay ores require less mill speed and more dilute grinding densities. In the latter case, the slower primary mill speed also helps to minimize damage to the mill liners. Approximately 57% of the time the mill operates between 90% and 100% of full speed or between 71% and 78% of critical. The variable speed is also used for inching during mill relines.

Jan 1, 1987

By Robert H. Bedford

The Rogan-Mallery tin property is in the foothills on the south slope of the Tehachapi Mountains, Kern County, Calif. It was first visited by the senior author in August 1942, and exploration by means of trenching and diamond drilling began in May 1944 and was concluded in August of the same year. Cassiterite, associated with iron-rich gossan, occurs in a limestone roof pendant at places near or at its contact with the underlying granitic rocks. The cassiterite grain sizes range from 20 mesh to 150 mesh. Surface and diamond-drill samples showed tin ranging from traces up to 122.6 pounds per ton. Exploration by the Bureau of Mines included 2,100 cubic yards of trenching and the drilling of 11 diamond drill holes totaling 1,000 feet. Dana Hogan, president of the Rogan Petroleum Co. of Los Angeles, Calif.) brought these projects to the attention of the Bureau of Mines in July 1942, and the following month a Bureau engineer made a preliminary examination in company with Hillard Mallery, of 408 Ruby Street, Redondo Beach, Calif., the man who discovered them.

Jan 1, 1949

By B. I. Matshediso, J. Kaavera, E. Shemang, T. K. Dintwe, L. S. Teseletso, K. Fichani

The minerals sector continues to draw attention from policy makers who would want to see both old and new mineral projects add value to the minerals in the host country. The current technological development in the leaching of manganese oxide ores to produce a high-purity manganese sulphate monohydrate, a compound that is used in the manufacture of batteries for electric vehicles or long-life storage cells for the renewable energy market, has led to junior mining companies spearheading this technology in new projects across the globe. In this paper, we researched the high-purity manganese sulphate monohydrate project pipeline and used projected production volumes and C1 cash costs to construct the industry supply curve for six projects, including the K.Hill project owned by Giyani Metals Corporation near Kanye, in the southern part of Botswana. The aim was to determine the ideal conditions that would provide a comparative advantage for further local value addition to high-purity manganese sulphate monohydrate and to the end user product. The results showed that while the estimated C1 cash costs would place the K.Hill project as the second highest cost producer from among five projects, it would nonetheless have healthy profit margins due to the high projected price of high-purity manganese sulphate monohydrate. The study recommended policy options, which, if implemented, could further encourage the exploitation and value addition of battery metals in Botswana.

May 27, 2025

The panic bars (and associated linkages and electrical circuitry) that are defined in this document are a machine operator-actuated control for the emergency deenergization of the tram motors on self-propelled, electric and diesel face equipment: including haulage equipment such as shuttle cars. There are nine basic types of panic bars (and several variations) that arc recommended in this document, but all of the panic bars are characteristically of the "fire door" type that is frequently encountered on outside exit doors of many public and some commercial buildings. It is also the intent of the following panic bar designs that, when emergency brakes are added to the face equipment machinery for which they arc required, that they be designed and hooked up so that actuation of the panic bar will result in automatic application of the emergency brakes (immediately following the deenergization of the tram motors). The following panic bar design requirements are a restatement of the proposed requirements defined in the Federal Register, requirements cited in "Guidelines for the Design and Installation of Devices for Deenergization of Self-Propelled Electric Face Equipment/Automatic Emergency Brakes" by C. E. Lester and J. D. Greenhalgh of MESA, and Bendix recommendations that were formulated as a result of discussions with personnel al the various machine manufacturers and underground coal mines that we surveyed, discussions with G. L. Judy (our consultant), etc:

Jan 1, 1974

By Elias Rigopoulos

In the present study the reductive behavior of dust from the rotary kilns (RK), in ferronickel production from nickeliferous Greek laterites, is investigated. The study concerns dust of various origins (washing towers, electrostatic filters, polycyclones) and pellets made from the dust. Reducibility was studied in the temperature range of 700 °C to 850 °C in a laboratory tube furnace. Experimental results showed that reduction degree increases with temperature up to about 800 °C. The rate of reduction is great during the first minutes, giving a reduction degree R% equal to about 25%, in only a few minutes. After this, the rate is decreasing until it diminishes to zero after about 10-20 minutes of reaction. Maximum reduction degree achieved is 26 to 28%. Rates and reduction degrees at various temperatures are higher for the dust samples than those of the respective pellet samples. Keywords: Ferronickel, metallurgy, laterites, pellets, reduction

Jan 1, 2004

By H. S. Sichel

"The valuation of diamond ferous deposits depends on (i) the density distribution, (ii) the size distribution of stones and (iii) the selling price structure prevailing at a particular time.In the density distribution the stochastic variable is defined as the Dumber of individual stones found per sample unit irrespective of the stone size. The density distribution is discrete and allows for barren sample units.As diamonds often occur in clusters, a Poisson mixture distribution is derived which is entirely new, as existing discrete distributions cannot represent the stone number frequencies found in nature.For the sizes of diamonds, which are measured by weight, a new compound logarithmic normal distribution is developed.Combination of (i), (H) and (iii) leads to a meaningful appraisal of diamond ferous ground expressed in monetary value per production unit of mining.Finally, confidence limits are calculated which allow for inference from sampling to recovery."

Jan 1, 2014