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By Dan Armour

Bolting solutions traditionally offered only wet drilling or dry drilling options; each with advantages and disadvantages. Joy Mining Machinery has developed a Mist Drilling System that incorporates the best of both types of drilling. Compared to wet drilling, mist drilling offers as much as a 90% reduction in water use. As a result, floor and roof conditions are tremendously improved. This offers a safer and more comfortable work environment for operators. Mist drilling can offer a significant reduction in noise levels compared to dry drilling and in recent trials, bit life has been greatly improved. Holes are cleaner and operators experience less exposure to respirable dust.

Jan 1, 2005

By R. C. Freas

Composite materials are finding new applications daily, ranging from automotive parts to synthetic lumber. The variety of applications seems almost limitless. However, these emerging products bring both new opportunities and new challenges to the field of industrial minerals. One of the primary challenges is from alternative materials other than industrial minerals. Thus the question is asked whether industrial minerals will truly benefit from the growth in market applications for composite plastics. This article highlights some of the opportunities for industrial minerals while focusing on performance and competitive demands on mineral products intended for use in this developing market.

Jan 1, 2000

By Steinar L. Ellefmo, Fredrik Søreide

"The Norwegian University of Science and Technology (NTNU) and Nordic Ocean Resources AS, with support from Statoil ASA have carried out a project reviewing the knowledge about seabed mineral resources in Norway to identify and prioritize needs for further research and development.A special focus area in the project has been to increase the knowledge of possible massive sulfide mineralizations along the Mid-Atlantic Ridge. This Ridge is a subsea mountain range which separates the Eurasian and the North American continental plates. In this area, seafloor massive sulphides (SMS) are formed from the volcanic and hydrothermal activities along the Ridge. A large part of the North-Atlantic Mid-Atlantic Ridge between Jan Mayen and Spitsbergen is located on the Norwegian shelf.Analysis and interpretations of multibeam data have been carried out by NTNU in cooperation with the Russian Institute for Geology and Mineral Resources of the Oceans in order to disclose relevant areas for the formation of SMS deposits. This analysis has identified several promising areas."

Sep 1, 2014

By Kimberley MacHardy, Ann Maest, Greg Lawson, James Kuipers

Although water quality predictions are often made in Environmental Impact Statements (EIS's) as part of the National Environmental Policy Act (NEPA), comparisons between predicted and actual water quality conditions are rarely reviewed. A comprehensive review of predicted and actual water quality conditions was conducted for a number of large U.S. hardrock mines with EIS’s. For mines with large differences between predicted and actual conditions, factors responsible for the deviations, such as characterization and modeling errors or engineering failures, were identified. Recommendations are made for how the NEPA process could be modified to better predict water quality at hardrock mine sites.

Jan 1, 2005

By George L. Wilhelm

Timber support of mine openings continues to be an effective system for ground support, due to its avail¬ability, flexibility, and ease of installation. Timber support of mine openings as a primary method to support loose rock has been replaced to a large extent by rockbolting and by filling systems. How¬ever, the many designs of square-set timber and varia¬tions of crib and stull support that have been developed to suit many stope configurations have proven reliable over many years of application. Integrated in modern excavation and stoping methods, timber remains an im¬portant ground support material for today's mines. ADVANTAGES AND DISADVANTAGES OF TIMBER SYSTEMS Timber, when used as a part of the total support system, is recognized for its unique support properties. More than a cover to prevent minor falls of ground, timber systems have been carefully designed to provide adequate support with sufficient compressive qualities to achieve a safe working environment in extremely diffi¬cult ground conditions. In some cases, a timber support method is designed to yield while retaining its protec¬tive support qualities. Little or no initial investment in equipment or plant is required for incorporating timber into the mining support system. Low cost cutoff saws and portable chain saws are sufficient equipment for effective use of dimen¬sioned (sawed) or round (stull) timber support. Until recently, small sawmills of various complexity were com¬mon at mine surface plants. Sawmills at the mine sites have generally been replaced by timber vendors' mills. Suppliers have been able to use efficient cutting and lumber handling methods to reduce the cost of mine timbers. Most suppliers will package dimensioned mine timber into bundles that are suitable for handling down mine shafts and on level conveyances. The principal disadvantage of timber as a support method is higher material cost and labor cost associated with its labor-intensive installation. Furthermore, stand¬ing timber reserves of mine quality wood are in short supply in some areas, and heavy competition exists for alternative uses of the timber supplies. Vendors are reluctant to supply large cross section dimension tim¬bers relatively free of defects. Some mine operations require 4.8-m (16-ft) lengths of firm timber over 0.09 m2 (144 sq in.) in section and these are difficult to obtain in large quantities. APPLICATION OF TIMBER FOR MINE SUPPORTS Timber used in mine support has been cut from many species of trees. A firm hardwood with physical properties similar to western Douglas fir has been pre¬ferred in the US. Other harder and softer woods, how¬ever, have been used when readily available or where the specific strength or crushing quality of the wood is a desired specification of the support system design. Hard¬ wood, commonly oak, has been used where maximum crushing resistance is required. Mahogany and fir are widely used for shaft guide timber. Normally, timber is used with its core axis parallel to the long axis of the timber dimension. However, in some cases, it is placed normal to its core in a "butt" log position, so as to provide maximum resistance to abrasion of the ore passage adjacent to the cut end of the block. By selective placement of timber block¬ing, controlled resistance to ground closure can be achieved which will prevent early failure of primary sup¬port members of the timber structure. Timber is widely used in modern mining operations as a construction member for chute-lip support. These designs are tailored to each operation to conform to the dimensions of the haulage equipment being used. As a construction material, wood requires none of the spe¬cial equipment necessary for placement of concrete or steel support. Placement of these alternate support ma¬terials requires carefully dimensioned and engineered excavation for their installation. Wood can be easily sawed to fit on location. The successful use of timber in heavy ground de¬pends on the careful and accurate placement of block¬ing and bracing to achieve the controlled yielding re¬sistance needed to support the mine opening. Similarly, frequency, size, and placement of top and bottom block¬ing stulls in flat-bedded deposits are carefully determined to provide adequate support at the mining face. Con¬trolled caving through failure of the stulls may be required as the scope retreats from the earlier mined-out sections. The support program must achieve both of these dimensionless qualities by specification of stull frequency and size. The utility of the square set-system of ground sup¬port and timber support is described in Chap. 2, re¬printed from US Bureau of Mines Information Circular 6691. Four examples of effective use of timber for support of stoping and other mine openings are pre¬sented in other chapters in this section. The Gilman mine's use of Mitchell slice stoping described in Chap. 3 is an early modification of the square-set mining system. This application proved reli¬able for heavy ground and overcame some of the dis¬advantages of conventional square-set timber. Chap. 4 describes the Burgin mine's use of timber with other reinforcement material. This combination of materials achieved high strength and control with yielding com¬ponent members necessary for heavy, squeezing ground. Chap. 5 describes the Bunker Hill mine's use of square¬set timber in a new configuration that provides an effi¬cient and safe support for stoping using small load¬haul-dump (LHD) mobile equipment. Chap. 6 describes some considerations in placing the widely used stull in bedded ore deposits. Finally, in Chap. 7, cost calcula¬tions for

Jan 1, 1982

By P. Ulrich, V. Svalbonas

The early to mid 1980s was a period of mining consolidation, and many senior design engineers retired from the mill industry. Similar conditions have existed in the last few years. This creates a loss of a tremendous amount of experience. This paper is a look back by two senior mill designers who survived the dips in both time periods. From a continuous design practice of over 25 years, mill designs and fabrication practices are surveyed with a view of identifying what works, and is necessary, and what doesn’t, or is not necessary, in the creation of a safe, economic, long-lived grinding mill.

Jan 1, 2001

By P. Zhang

A multiyear, comprehensive study of flotation reagents used in phosphate beneficiation was conducted. The study involved the evaluation of pure fatty acid compounds, comparison of various anionic collectors and testing of iso-acids. Various C12 to C22 fatty acids were tested as Florida phosphate collectors. The saturated fatty acids were found to be very poor collectors when using the standard conditioning procedure, whereas the unsaturated C16 to C22 fatty acids showed fair to good phosphate collecting ability. The C18 fatty acids oleic, impure oleic and linoleic and the C20 eicosenoic acid were shown to be the best phosphate collectors. The best flotation results were obtained using Liqro GA tall oil and oleic acid. Four isostearic/iso oleic acid type fatty acid collectors were compared with a commercial grade oleic acid and with Liqro GA tall oil as phosphate collectors using standard laboratory conditioning and flotation procedures. The most selective collector evaluated was Century 1108, a high isostearic acid-type reagent. However, it was concluded that this excellent-performing reagent was too expensive for commercial use. Overall, the most promising reagent was probably Century MO-5. This collector is essentially an iso-oleic acid/stearic acid mixture (not isostearic acid), and it costs much less. This program laid a sound foundation for developing single collector, all anionic flotation processes.

Jan 1, 2009

By Mark N. Savit

It is indeed a rarity for a non-engineer, let alone a lawyer, to even be considered for a mining-related award, especially where that award is for significant contributions to technical progress in the mining and exploration sectors. So, when I was notified that I had received this award, I struggled for a topic that would meld the legal world that I operate in with the engineering driven world of exploration and extraction. The most exciting part of my job has always been the opportunity to absorb the technical details of the cases I work on and, in effect, translate them for a lay audience. Too often, I have found, lawyers, judges, legislators and yes, even regulators who lack a technical background simply give up trying to understand the details of the very conditions or processes that they are trying to describe and simply repeat phrases told to them by their client or by a retained expert.

Jan 1, 2008

By K. A. Lewandowski

Agglomeration techniques are widely used by industry to form fine particles into larger masses that are easier to handle and process. One area where agglomeration is potentially useful is in heap leaching operations. With-out agglomeration, fine particles travel through the heap, clogging the spaces between the larger particles and resulting in poor leach solution flow. Poor flow of leach solution will result in long leach rates and/or decreased metal recovery. Agglomeration immobilizes the fine particles and therefore improves heap permeability to fluid flow. Additional additives (binders) are needed to prevent agglomerates from breaking up as leaching solution percolates through the heap. Type II Portland cement and lime are two well-known binders used in gold and silver leaching, but these are limited to alkaline leaching environments. Various other products have been tested as binders, including polymers. This paper summarizes the benefits of agglomeration in heap leaching and the results obtained from the testing of several different agglomeration binders in heap leaching operations.

Jan 1, 2009

By Satoshi Honda, Mitsuru Shimizu, Tatsuji Nagao, Motoaki Kurisu, Hirokazu Izumi, Toshinori Takahashi, Hiroyuki Itoi

"1. INTRODUCTION Grade separation of roads and railway tracks is an effective method for solving traffic-related issues in cities. However, in urban areas where the existing traffic infrastructure is already overcrowded, construction of new roads often faces problems especially in the proximity of existing structures. This paper summarizes the construction plan and results of new road tunnel construction in the proximity of the piers of elevated tracks on the Tokaido Shinkansen railway.2. SUMMARY OF CONSTRUCTION AND ISSUES Auxiliary Route No. 26 as specified in the Tokyo urban plan is a project by the Tokyo Metropolitan Government, covering the construction of a new road with a total length of 22.3 km currently on the way to completion. In Shinagawa Ward, Tokyo, Auxiliary Route No. 26 is designed to cross the railway tracks of the Yokosuka Line and the Tokaido Shinkansen Line, so for this project, the East Japan Railway Company (JR East) was commissioned to design and build a road crossing under the railway tracks (Sumiyoshi Underpass). Figures 1 through 3 show a sketch of the Sumiyoshi Underpass. The Sumiyoshi Underpass was planned as a two-lane tunnel for vehicles, which was to cross under the railway tracks of the Yokosuka Line and the Tokaido Shinkansen Line at an angle of 70 degrees. The structure concerned is a single-story single-span box culvert structure with the following dimensions: 11.5 m wide, 7.7 m high and 31.6 m long. The Tokaido Shinkansen Line tracks were constructed on a girder-type elevated bridge built in the 1960s, and the foundation piles of the piers (P7 and P8) in the proximity of this crossing box culvert of RC structure were constructed using an earth drill method. The crossing structure for this project is located extremely close to the piers of the Tokaido Shinkansen railway tracks, with a minimal separation of 0.4 m, and the most significant issue of this project was construction in a manner that would not obstruct the normal operations of the Tokaido Shinkansen (Figure 4). Initially, we considered installing a temporary earth retaining structure in the proximity of the piers, cutting the ground and building an RC box, but concluded that it would be very difficult to apply this method because of probable excessive displacements in the Shinkansen railway piers. That is why we decided on the use of a non-open cut method in order to minimize the impact on the piers."

Jan 1, 2016

By J. Kretschmann, N. Nguyen

"The Vietnamese economic growth of more than 5% per year leads this country to an enormous demand for raw materials. In the duration of ongoing expansion, the big challenge in the coming decades will be to make this process as sustainable as possible when it comes to economic, environmental and social objectives. Risk management especially in occupational safety and health (OSH) in enterprises is one of the most important tools to achieve this aim. But until now, this has not been taken into priority by Vietnamese coal mining enterprises. Main reasons for this situation can be found in deficient legislative conditions and in non-synchronized risk management systems. In contrast, Germany has implemented an adequate legal system and the German mining industry has gained lots of experiences in risk management, especially in occupational safety and health. This paper seeks to point out specific challenges how to improve occupational safety and health in Vietnam by transferring and applying German methods and standards."

Jan 1, 2011

By Donald J. Olson

The North 27th St. ISS Extension tunnel will, under present plans, be the last constructed section of Milwaukee Metropolitan Sewerage District?s (MMSD?s) existing deep tunnel system. The 6.5 m (21 ft) finished diameter tunnel is approximately 3,260 m (10,590 ft) long and is located in NE Milwaukee County. When disputes over the pro-cesses to be used in owner-directed pre-excavation grouting in rock threatened the completion date stipulated between MMSD and the State of Wisconsin, the MMSD and J.F. Shea, the contractor, entered into a unique agreement. Shea accepted responsibility for all shaft and tunnel grouting and water control during the project in exchange for settlement of claims related to grout quantities and perceived delays. This significantly reduced risk for the MMSD and helped ensure the stipulated completion of the project.

By David Hopkins, Steve Klein, Bradford Townsend, Ed Sum, Derek Penrice

INTRODUCTION The Transbay-Caltrain Downtown Extension (DTX) Project involves the construction of an approximately 1.5-mile rail line that will extend Caltrain commuter service and the future California High Speed Rail system into downtown San Francisco. The underground rail extension will be constructed by mined tunnel and cut-and-cover methods. Tunneling challenges include difficult ground conditions, low rock cover, the presence of historic buildings along the alignment, and the large tunnel span, ranging from approximately 50 to 65 feet. Three mined tunnel construction methods were evaluated: the Stacked Drift Method, the New Austrian Tunneling Method/Sequential Excavation Method (NATM/SEM), and Tunnel Boring Machines (TBM). This paper describes the challenges presented within the mined tunnel section, and summarizes the evaluation of tunneling methods that led to the selection of NATM/SEM. PROJECT OVERVIEW The existing Transbay Terminal opened in downtown San Francisco in 1939. This facility is antiquated, and does not meet current building seismic safety standards or the transportation needs of the Bay Area. For these reasons, San Francisco voters approved Proposition H in 1999, which proposed to construct a new or rebuilt regional transit center at the site of the existing terminal and extend Caltrain commuter rail ser-vice to the new transit center. The new transit center is the hub of the Transbay Transit Center (TTC) Program, which will greatly enhance regional transit service by providing connectivity for six Bay Area transit providers at one facility. The program will be the largest inter-modal centerwest of New York City. The TTC Program is comprised of two major projects, the Transit

Jan 1, 2007

By Paul L. Russell

Interest in the western oil shales of the US began in about 1908, with the first retort in Colorado constructed in 1917. The most successful early developments were near Elko, NV, where the Catlin Shale Products Co. produced more than 1.9 dam3 (12 000 bbl) of shale oil during 1920-1924 and at Rulison, CO, where a US government operation produced about 570 in 3 (3 600 bbl) of shale oil during 1926-1929. Plentiful low-cost crude oil was developed about this time and shale oil was of little or no interest until after World War II. From 1944 to about 1972, several companies, and the US government, operated shale oil mines and recovery plants in Colorado. While technical successes were achieved and an estimated 40-56 clam' (250 000-350 000 bbl) of shale oil were produced, economics were not favorable and commercial production was not achieved. In recent years domestic production of crude oil supplies has not kept pace with US consumption. The growing shortfall has been met with imports. The cost of imported oil has continued to escalate and increased US dependence on petroleum imports are national concerns, because of the negative impact on US balance of payments and an increasing dependence on other nations for US energy needs. In 1978, petroleum imports equaled about 44% of demand, up from 23% in 1970, but down from 48% in 1977 because of availability of Alaskan North Slope crude oil. Reduced domestic consumption and other factors have reduced current imports to about 40-45% of de¬wand-but at ever increasing cost. The growing shortage of crude petroleum and its increasing cost have resulted in renewed worldwide interest in oil shales. In the past, the main obstacle to oil shale development (progress toward commercial production) has been economics-shale oil cost too much to develop and thus could not compete with conventional petroleum crudes. Even with today's inflated energy prices, some experts say the production of synthetic crude oil from oil shale is, at best, marginally economic. The 1973-74 Arab oil embargo and increased crude oil costs-along with the federal government's offer to lease oil shale lands-resulted in renewed

Jan 1, 1981

By C. L. Jiang, B. K. Parekh, X. Shao

Among the impurities present in phosphate ore, dolomite is the most difficult to remove. This is because dolomite and phosphate have similar chemical compositions and because the dissolved species of dolomite is adsorbed on the surface of the phosphate mineral. A new amphoteric surfactant was found to be a suitable collector for the separation of dolomite and phosphate. Flotation results showed that the new amphoteric collector had a high flotation selectivity for dolomite over a wide pH range. studies on the flotation of francolite and dolomite in each other's supernatant demonstrated that the dissolved ions had little effect on the selectivity of the new collector. It was found, however, that the dissolved ions were detrimental to the flotation separation using sodium oleate as collector. From a mixture offrancolite and dolomite containing 26.2% P2O5, a phosphate concentrate containing 35.2% P205 with a 90% recovery was obtained using 290 g/t of the amphoteric collector. The rejection of MgO was 81.41 %.

Jan 1, 1999

By A. W. Khair

This paper deals with the design characteristics of cutting tools and the operating parameters these tools are usually subjected to. Eight types of cutting tools/bits with different geometrical shapes and sizes were tested in a linear cutting apparatus, utilizing concrete blocks. The objectives of these experiments were to study the performance of each type of bit, make qualitative assessment of each bit geometry and size and establish cutting parameters for efficient utilization of the tools. During the experiment required forces Fx, Fy, and Fz, cutting, penetrating and lateral forces respectively and audible and sub-audible noises were measured. In these experiments, the depth of cut was kept constant to 1.5 inch while the bit spacing was varied 1.5,2.25 and 3.0 inch (3.75,5.6 and 7.5cm respectively). The results of these experiments indicated that by optimum ratio of depth of cut to bit spacing, the cutting face will be cleaned with the least ridge/land remains between the bit groves, resulting in least specific energy consumption, more large and less fine product particles and substantial reduction of audible noise. The results of these experiments also showed that proper bit design not only decreased cutting energy consumption but also reduced audible noise.

Jan 1, 2001

By J. W. Jamieson, J. Escartin, A. Steinführer

Evidence of hydrothermal activity on two Mid-Atlantic Ridge oceanic core complexes (OCCs), at 13º30’N (the Semyenov 1 through 5 fields) and 13º20’N (the Irinovskoe field) (Fig. 1) were studied using CTD casts, dredges, TV-grabs and SP surveys during previous research cruises to these sites (Cherkashev et al., 2013, McLeod et al., 2009). In late 2013, the Semyenov and Irinovskoe fields were revisited, this time with an autonomous underwater vehicle (AUV) and a remotely-operated vehicle (ROV) during the ODEMAR (Oceanic Detachments at the Mid-Atlantic Ridge) cruise on the French research vessel "Pourqoui Pas ?". Here we present the first visual surveys and direct sampling of these vent sites. High-resolution (~2 m) bathymetry of the 13º30’N and 13º20’N OCCs and their associated vent fields was collected during 4 and 5 AUV dives, respectively, using the GEOMAR AUV "ABYSS" (Fig. 1). These surveys were flown between 70 m and 100 m above the seafloor, typically at a constant height to reduce vehicle movement. The AUV was equipped with Eh, turbidity, and temperature sensors in order to detect active hydrothermal venting. Over twenty ROV dives with the ROV "VICTOR 6000" allowed for the visual exploration of the OCCs and collection of 59 hydrothermal rock samples from the vent fields. As a result of these exploration activities, the first robust estimates of the size of the deposits, and the geologic controls on sulfide accumulation at these sites can be determined.

Sep 1, 2014

By A. Adu-Acheampong

A geotechnical study was conducted to identify the cause(s) of stope instability at the Ashanti Mine (Obuasi, Ghana). As part of the investigation, laboratory testing of rock was performed and the rock mass was classified according to the Q-System (Barton et al., 1974).Numerical analyses were performed using the computer program FLAC (Itasca, 2001). The observed failure zone around the stopes was simulated using both Mohr-Coulomb and Hoek-Brown (Sheorey,1997) models. Yielding along peripheral graphite bands and tensile failure were clearly identified to be the major contributors to stope instability.

Jan 1, 2003

By J. O. Marsden

Part I in this series of papers considered the chemistry of medium-temperature pressure leaching of copper sulfide concentrates and reviewed the metallurgical testing and initial process development for this technology. This initial work resulted in the development of a process flowsheet utilizing superfine grinding (to a P98 of 12 to 15 µm and P80 of 6 to 7 µm), pressure leaching at 160° to 170ºC, followed by conventional solution extraction (SX) and electrowinning (EW) for the recovery of copper. However, this process required a significant amount of concentrated acid to be fed to the pressure leach vessel to meet the reaction requirements, representing a cost of between $0.03 and 0.05/lb copper (2006 basis) produced by the process. It was immediately recognized that the development of a process that did not require such a large acid addition would be advantageous. This paper, which is Part II in the series, describes the development of a process that incorporates medium-temperature pressure leaching and direct electrowinning (DEW) in a novel and innovative process flowsheet. Phelps Dodge (a subsidiary of Freeport-McMoRan Copper & Gold Inc.) refers to this as the ?MT-DEW-SX? process. Part III in this series covers the large-scale demonstration of the MT-DEW-SX process at Bagdad, Arizona; and Part IV addresses the development and design of a full-scale commercial application at Morenci, Arizona.

Jan 1, 2007

By Christopher J. Bise

INTRODUCTION Before a mine is planned in detail, a preliminary analysis is often conducted. This preplanning permits the mining engineer to make a rapid assessment as to whether or not a particular mining property warrants further consideration. In fact, a properly conducted preplanning phase can come within 10% to 20% of the actual results, thereby saving the mining engineer valuable time before committing himself to a fine-tuned analysis. The questions to be answered by mine preplanning are (1) What will be the operating conditions for the mine? and (2) How long will it take to complete the project? To answer these questions, calculations dealing with reserve estimation, production planning, man- power planning, and project scheduling are conducted. The following sections discuss these various phases of mine preplanning in greater detail. RESERVE ESTIMATION The estimation of the various characteristics of a reserve, such as quantity, grade, and thickness, is an ongoing process throughout the life of a mining venture. However, the reserve-estimation phase of mine planning is more closely associated with the preplanning phase. There are many different techniques employed in reserve estimation of solid mineral deposits; variations among them are introduced because of such considerations as ease of application or level of accuracy. In any event, each technique is developed in the following manner: (1) the mineral body is represented pictorially and then subdivided into blocks related to one or more samples of exploration data, (2) the area and volume of each block is determined, (3) the volumes are converted to representative tonnages (or, for example, grades), and (4) the results are tabulated. To illustrate this procedure, the polygonal (area-of- influence) technique will be presented due to its ease of application, flexibility in dealing with different deposits, and general acceptance. The polygonal method assumes that all characteristics of a mineral body extend halfway between a point of observation and any other point of observation. The explored portion of the mineral body is represented by polygonal prisms whose depths relate to the characteristic in question (grade, thickness, etc.) and whose plane bases relate to the area of influence of each point of observation (drill hole, etc.) as shown in Fig. 1. The polygons must be constructed in a definite order, usually clockwise and from the periphery to the center of the deposit. Table 1 can then be used to calculate the characteristics in question. Since, by definition, the polygonal method assumes that the characteristics of a mineral body extend half- way between points of observation, it becomes readily apparent that the evaluation of a vertical-drill hole exploration program requires that the sides of the polygons be formed by the intersection of perpendicular bisectors (Fig. 2). Figs. 3 and 4 show correct and incorrect construction of the polygons. The criterion for correct construction of the polygons is that all points within a particular polygon must be closer to its rallying point than those located in any other polygon. This is clearly not the case for certain points that are located in the polygon containing rallying point B in Fig. 4. Although this method can be used where the drill holes are irregularly spaced, calculations become less tedious when a square net (Fig. 5) or a chessboard (Fig. 6) grid is adopted. The numbers shown in Figs. 5 and 6 represent the relative weight for each of the shaded areas. In general, the greater the number of polygons, the more continuous the mineral body, and the more regular the grid, then the more accurate the computations will be. PRODUCTION PLANNING Before an acceptable evaluation of the production potential of a mine can be determined, a thorough exploration program should be conducted. It seems obvious that the nature and properties of the deposit and adjacent strata, the presence of impurities, and other mining conditions should be adequately determined prior to production planning and equipment selection. The lack of sufficiently detailed knowledge of the many mining parameters has led to the failure of numerous operations. For example, targeted production tonnages and equipment sizes for a coal mine are intimately related to the seam thickness. Needless to say the quality of information that is gathered from an exploration program can have a tremendous impact on the production plan. Production plans are developed initially by determining reasonable shift tonnages per operating section. Most of the time these values are developed from his-

Jan 1, 1986