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By A. Arik

1his paper presents a modified ordinary kriging technique referred to as the "Nearest Neighbor Kriging" (NNK). The method is a simple and practical tool to use when the ordinary kriging (OK) results are unreasonably smooth, especially when estimating recoverable ore reserves for deposits with skewed grade distributions. NNK is robust and globally unbiased like OK. However, it is more advantageous over OK because it can control some of the smoothing and conditional bias which have been the major pitfalls of OK in many grade estimation cases. The paper details the methodology of NNK and its application to a gold deposit.

Jan 1, 1998

By Rodolfo V. de la Cruz

Abstract. The Hoskold mineral valuation method was critically examined. The original derivation was presented and found to contain a number cf erroneous assumptions as follows: the sinking fund must be available for reinvestment in another property; the series of reinvestment of the sinking fund results in a perpetual annuity to the investor, and; evaluation of the present value of the net cash flows at the speculative rate of interest. The proper procedure of deriving the Hoskhold mineral valuation formula was discussed and illustrated with a cumulative cash position diagram, a useful tool in economic evaluation and investment decision methods.

Jan 1, 1980

By P. D. Morrell

Jetbelt is the trade name for the air supported belt conveyor. It does not use troughing rollers. Jetbelt conveyors support the conveyor belt on a thin film of air. The belt rides in a steel trough which has small holes equally spaced along the bottom of the trough. Air comes through the holes under the belt, thereby supporting the belt. The air pressure is provided by a single centrifugal blower that creates very low pressure, between 249 Pa and747 Pa [10" and 30" water column], depending upon the tonnage being conveyed. The volume of air required ranges between .001415 m3/S and .00283 m3/S [3 and 6 CFM] per lineal foot of conveyor. Therefore, depending on tonnage being conveyed, a 304.8m[1000'] conveyor might require as little as 1.415m3/S [3000 CFM] or as much as 2.83m3/S [6000 CFM.]. (See Figure 1) Horsepower requirements can be less than troughing idler conveyors and considerably less than some other forms of bulk conveying. Savings are most significant in horizontal and down hill (regenerative) conveyor designs. Horsepower to lift material, of course, does not change.

Jan 1, 1984

By J. A. Herbst

Ball mill grinding circuits can be subject to upsets that arise from variable characteristics of the feed ore. These upsets are transients in critical circuit variables such as ball mill mass holdup, circulating load, sump level, cyclone efficiency and product particle size. They may occur frequently so that the operation is continuously fluctuating or they may be of such magnitude that some of the equipment is overloaded, resulting in shutdown, or an undesirable product particle size. The feed ore characteristics that influence ball mill circuit behavior in this manner include the grindability of the ore, the eventual transport characteristics of the ore in the mills and the feed ore size distribution. Control strategies for grinding circuits using conventional proportional-integral (PI) control have limitations to their effectiveness in controlling against feed ore disturbances. The first of these are the interactive nature of two or more control loops on a single circuit. Under some circumstances they begin to fight each other, increasing control error and settling time. PI control loop gain constants can be tuned to give best response for some set of conditions but once these change, as they would with a change in the feed ore, they are no longer the "best" ones (Shinsky, 1967). Due to these limitations, alternatives to conventional PI control strategies have been investigated for grinding as well as other mineral processing operations. These alternatives, all computer-based, include self tuning regulators, decoupling control and optimal control (Herbst and Bascur, 1983).

Jan 1, 1984

By Robert E. Barry

For new coal-fired power plants, federal regulations require that emissions of sulfur dioxide be limited to 1.2 pounds for every million BTU'S burned. This is equivalent to coal with a sulfur content of roughly 0.7 percent for Eastern bituminous coals and roughly 0.6 percent for Western sub-bituminous coals. The states and their political subdivisions are free to apply more stringent standards and to develop implementation plans covering existing and new units. Most Western-sub-bituminous coals contain less than 1% sulfur and hence their use, in many cases, will allow a utility to meet the regulations. However, there are problems in using such coals in furnaces designed for Eastern bituminous coals, and furthermore it will take many years to open mines and provide transportation facilities to utilities which are now burning coals with a higher sulfur content. Moreover, pending federal legislation would outlaw strip mining on land to which the federal government owns the mining rights. Those utilities who, for one reason or another, intend to continue burning Eastern bituminous coals with sulfur contents in excess of 1 percent are faced with removing SO2 from the stack gases. The alternative of utilizing coal gasification where the sulfur is removed prior to burning in a power plant is still in the early stages of development. Therefore, a large number of processes are under development for SO2 control.

Jan 1, 1974

By Ole Bernt Lile

The well-known method of C. Schlumberger, Mise a la masse, has become a popular method again in ore exploration in Norway after many years of dominance by EM methods. The principle of the method is to place a current electrode within a conducting ore body and remove the other electrode to a great distance. (Figure 1). Often it is convenient to place a return electrode on each side of the area explored. The method is best suited for ores that have a conductivity contrast, relative to the host rock, of several orders of magnitude. The potential drop within the ore itself may then be neglected and the ore contact against the rock may be regarded as an equipotential surface. One may say that the ore body is electrically charged. Therefore, in Norway the method is now most often called the Charged Potential Method (abbreviated CP). The most usual way to present data obtained by CP, is to draw equipotential lines based on potential values measured in profiles on the surface. Such a potential map gives an immediate picture of the outcrop of the ore and also indicates disturbing conductors in the neighborhood. It may also be useful to look at the potential profile and its horizontal gradient along the strike axis of the potential map. These profiles may give information about the strike length of the conductor. Figure 2 shows the theoretical profiles of potential and gradient along the axis of the potential picture on the surface over a charged line plunging 15 degrees. It may be seen that the maximum of the gradient curve clearly indicates the lower end of the conductor. Figure 3 shows the corresponding pro- files over a charged line plunging 45 degrees. In this case, it is not possible to see an indication on the curve of the lower end. Only curve fitting could help interpretation in this case.

Jan 1, 1975

By Sureshan K. Moothedath

This paper provides a mechanistic representation for floc formation, growth and degradation and presents results from an experimental study of batch flocculation in which step changes were made in the impeller speed, flocculant addition, and slurry concentration. A discussion of the experimental results is included in terms of the mechanisms of floc formation and size-change.

Jan 1, 1993

By Gerald L. Dollinger, Joseph A. Roby, David Krauter, Kenneth Deering

Three high performance TBM's equipped with large diameter (483mm) disc cutters are currently operating in Norway. This paper summarizes the design philosophy, field performance and ongoing technical development of these cutters. Included are discussions of the early problems encountered with their usage and the solutions to these problems that have been developed. Also included are discussions of the penetration rates and cutter usages observed. From this data it is concluded that high performance TBM's with large diameter cutters can produce significant improvements in both overall performance and in cutter costs under hard rock conditions.

Jan 1, 1991

By S. V. Krishnan

In the upgrading of finely-disseminated iron ores, selective desliming is the critical step which must be controlled in order to achieve efficient flotation. A prerequisite for selective desliming is a properly-dispersed pulp; sodium silicate is commonly used as a dispersant. The mechanism by which sodium silicate acts as a dispersant in the presence of calcium ions was examined by streaming potential measurements, settling tests, abstraction density determinations, selective flocculation tests and scanning electron microscope observations. The study established that calcium silicate precipitates on the mineral surfaces dispersed the pulp. Although sodium silicate was a nonselective dispersant, the addition of corn starch aided the flocculation of goethite over quartz at low silicate additions, but became ineffective at higher silicate levels. A model is presented to explain the dispersant mechanism of sodium silicate in the presence of calcium ion for selective flocculation of iron ores.

Jan 1, 1982

By Sun K. Kim

Hydrometallurgical processes are not free of environmental regulations. A clear understanding of the regulations under which the minerals industry operates delineates processing requirements at early stages. This paper deals' with federal environmental regulations with emphasis on the hazardous waste regulations promulgated in May, 1980. The procedure of EP toxicity test and an example of the test are described. Brief account is given of the current trend and future outlook of regulations.

Jan 1, 1982

By Richard E. Barrett

The relationship between coal characteristics and power plant performance has become a matter of increasing interest to utilities. This relationship can affect the value of coals, decisions as to coal washing, setting penalties for delivery of coal that fails to meet specifications, and justifying buying better coals (at higher costs) before public utility commissions. The study described in this paper was directed to identifying how coal characteristics impact on boilers and related coal and gas handling systems. TVA data for the period 1962-1980 was the basis for the study. Models were developed for boiler efficiency, boiler availability, and maintenance costs as a function of such coal characteristics as ash, sulfur, and moisture content and boiler age. Boiler load and maintenance efforts were considered as variables in some of the models, but were found not to be statistically significant. Although the results of this study are strictly applicable to only the TVA system, they can serve as guides or first approximations for other utilities.

Jan 1, 1983

By Edwin S. Smith

One of the many responsibilities of mining engineers and mill superintendents is to provide for the safe and economic disposal of wastes (or tailings) remaining after a mineral has been extracted from an ore. The cost of disposal of these tailings exerts a considerable influence on the minimum grade of ore extracted from the mine. It varies to a great extent with each project and is dependent on many diverse factors, such as the local topographical, meteorolgical, geological and seismological conditions together with the applicable water pollution laws of the area. The process used to extract a mineral from an ore determines the physical characteristics of the tailings and thus is one of the more important factors to be considered when planning disposal facilities. Today's trends .in ore-processing operations complicate the problems of waste disposal: recently developed extraction methods result in the production of finer tailings, the use of lower grade ores produces greater volumes of wastes, while the enhanced land values in the vicinity of industrial plants preclude the former practice of spreading wastes laterally and force the expansion of waste desposits upwards to greater heights. The frequent occurrence of stability problems in waste deposits indicates that many mining organizations may not be employing current soil mechanics concepts and practices. One of the most spectacular, and often most disastrous, types of tailings dike failure is that resulting from liquefaction of the fine particles combined with a breach of the main retaining dike.

Jan 1, 1967

By W. M. Ma, W. L. Zhong, Syd S. Peng

In a longwall section that consisted of 7 longwall panels, there were two high pressure gas transmission pipelines across the panels burying from 3 to 10 ft. below the surface. One pipeline was 20 in. in diameter while the other was 24 in. in diameter. In order to investigate the stress conditions sustained by the pipelines during underground longwall mining, strain gages were mounted on the pipelines above panel #3, #4, and #5. Survey monuments were also installed along but near the pipelines. This paper presents a subsidence prediction method and the preliminary results of the pipelines' stress conditions as affected by underground longwall mining.

Jan 1, 1986

By J. J. Scott

Friction Rock Stabilizers, trade name Split Set*, is a new support system invented by the author and under development by Ingersoll-Rand and Lee-Norse Company. Split Sets are a substitute for standard bolts or fully grouted resin bolts and have certain advantages which are: 1. Improved safety for the miner 2. A rational design is possible based on rock mechanics principles 3. Supports can be made either to be yieldable or rigid 4. Supports can be used to build a roof beam or to suspend roof material 5. It is cheaper than the resin system and costs about the same as standard bolts.

Jan 1, 1974

By D. E. Ranta, G. H. Giroux, A. W. Randall, D. A. Barr

Zinc-lead ores of the Pine Point District, Northwest Territories, Canada, are hosted in paleokarst cavities within a Middle Devonian carbonate barrier complex. Of the nearly 100 deposits found, most are irregularly distributed along two main regional stratigraphically controlled trends. The ores, which occur predominantly as open space filling, form deposits most of which average one million tonnes in size with an average grade of 10% combined zinc plus lead. Geological features related to karsting control not only distribution of deposits but also their shape, size and grade. The higher grade ore in these deposits generally occurs in a relatively small core area. Consequently, accuracy of reserve estimation is dependent on drill-hole density and understanding of karst geometry. Several case examples will be reviewed to demonstrate the relationship between shape, size and grade of deposit, geological reserves and drill-hole density, along with a discussion of geological ore reserve estimation methods.

Jan 1, 1992

By Joel Nonnweiler, David Young, John Hawley

The Sacramento Regional County Sanitation District has implemented a billion-dollar interceptor system master plan, including the 31 km (19 mile) long Lower Northwest Interceptor (LNWI). For the two LNWI Sacramento River crossings, pipe-jack/micro tunnel drives in excess of 300 meters (1,000 ft) from 30 meter (100 ft) deep shafts in mixed soil conditions below the water table were considered, as were600 meter (2,000 ft) tunnel drives utilizing pressurized-face tunnel boring machines. Operation and maintenance concerns, predicted flood scour, and levee concerns are discussed. A risk assessment process was used to select both profile and construction method. Construction will begin in mid 2004.

Jan 1, 2003

By K. L. Johnson

Networks of monitoring wells were established prior to mining at four longwall mine sites in the Appalachians to monitor the effect of mining on water levels, water quality and well yield. Two of the sites were located in stream valleys and the other two sites were located on hilltops. The depth to the mined seam ranged from 500-850 feet with the deeper cover being associated with the hilltop sites. Maximum declines in groundwater levels during and after mining were an order of magnitude less in the stream valley aquifers than in the hilltop aquifers. However, water levels in hilltop wells located outside the area immediately above the panel were unaffected. Water quality changes in wells as a result of longwall mining were negligible at all four sites. Increases in aquifer transmissivity and well yield were much more pronounced in the stream valley aquifers than in the hilltop aquifers. The significantly larger recharge area for the stream valley aquifers than that for the hilltop aquifers may partially account for the differing responses of these two classes of aquifers to longwall mining. These observations appear to be consistent with the stress-relief fracture model for Appalachian Plateau groundwater hydrology proposed by Wyrick and Borchers in 1981.

Jan 1, 1986

By Dan J. Van Roosendaal

A closely spaced grid of survey points was installed over the tensile zone of a longwall panel in southern Illinois and monitored daily during subsidence to document the complex ground-surface movements associated with dynamic subsidence. Vertical and horizontal displacements were used to calculate maximum tilts and principal strains within the grid. The dynamic nature of subsidence is made evident by changes in both the direction and magnitude of maximum tilts and principal strains. The maximum tilt (smax) of 0.036 and maximum tensile strain (Emax) of 0.027 were measured after subsidence and were oriented transverse to the longwall panel. Observations of surface fracturing were correlated with strain determinations to estimate a surface strain at incipient cracking (E;) of 0.006 to 0.009. Using shallow inclinometers, a linear variation of horizontal displacement with respect to depth was observed, suggesting a neutral¬axis bending mechanism for near-surface deformation. Horizontal displacements transverse to the longwall panel reduce to zero at a depth of 40 feet. A linear relationship between strain and curvature was used to estimate ground-surface curvatures associated with Emax (0.00068 ft-1) and E; (0.00015 to 0.00023 ft-1). The curvature estimates are consistent with published results.

Jan 1, 1986

By J. J. Crowhurst

The Carson Hill mine in Calaveras County, California, was explored and developed by Grandview Resources Inc., as an open-pit heap-leached operation, with production commencing in the fall of 1986. Grandview entered the district in 1983 after a 40-year period of quiescense, the initial contact being by Barden Stevenot, V.F. Hollister, and J.J. Crowhurst. The last dividend declared by the Carson Hill Gold Mining Corp. was 3 1/2$ per share paid in January 1943. The mine was originally discovered in August 1848 by Jim Carson. Preceding the entry by Grandview in 1983, Cyprus Mines explored Carson Hill in 1975, and drill exposed a mineral inventory of 7.3 Mt (7,982,000 tons) averaging 1.4 g/t (0.040 oz per ton) gold. From that time until the Grandview entry, R.W. Thomssen and B.E. Stevenot continued investigations into the potential of the deposit. Grandview successfully investigated many of the metallurgical problems involved with heap leaching the ore. Metallurgical investigations were con- cluded under the direction of R.S. Shoemaker. By November 1984, J.A.C. Ross had prepared a prefeasibility report that included the earliest Grandview investigations. This report concluded that the deposit contained at least 6.8 Mt (7,440,000 tons) of ore that average 1.5 g/t (0.045 oz per ton) gold and that this ore could be mined with a 2: 1 stripping ratio. A final feasibility report was prepared by D.W. Pringle in September 1985. It showed a final ore reserve of 14.7 Mt (16,160,000 tons) of 1.7 g/t (0.049 oz per ton) gold. Attached is a description of the geology of the deposit from an internal report covering Cyprus activity in 1975 and a brief portion of USBM IC 6940 (1937). General location and geologic maps attached are from the Pringle report.

Jan 1, 1990

By N. Harrigle, Tsutsumi

Very fine wet sizing of minerals such as kaolin, precipitated calcium carbonate, lime milk, and clay slip is a difficult process to achieve using standard vibrating screens. With particle sizes ranging in the sub-microns combined with the agglomerating tendencies of certain materials, screen blinding becomes a serious issue. Sizetec, Inc. has developed an innovative screening equipment to help solve this problem. The High Performer Screen uses powerful linear vibrations to help break apart agglomerated particles and prevent screen blinding. Optionally fitted with the Air Explosion Screen Cleaning System, compressed air can be periodically injected into the screen underflow chamber to clean the screen surface without the use of water sprays. This paper highlights some of the key features of the Sizetec High Performer Screen and describes typical performance that can be expected based on results from various trials conducted in the kaolin industries.

Jan 1, 2002