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By A. G. Ulsoy

In recent years there has been an Increasing Interest In the application of automatic control theory to mineral processing systems, and numerous applications of mineral process control have appeared in the literature. A general approach to the synthesis of mineral process control systems is presented. The first phase of the control system design consists of specifying the control objectives, process variables and their interactions; these topics will be discussed with specific reference to mineral processing. The second phase Is con¬cerned with selection of control strategies algorithms, instrumenta¬tion, and other components of the control system and is discussed at length. These concepts are then illustrated by a flotation control case study.

Jan 1, 1981

By William G. Kegel

Apart from a usable product and good mining conditions, the greatest asset for a profitable coal mining organization is an effective mine maintenance program. The first step in achieving this is to have good mechanics-or men who want to be mechanics and are interested in knowing, more about the design and control of the machines in their charge. A good mechanic's knowledge and ability result from ambition, curiosity, and determination. Starting with these qualities, the aspiring mechanic can launch his career by learning all he can about mechanics, electricity, and hydraulics. Though the path is rough, the end result is rewarding. Mining machinery probably receives as much, if not more, abuse as any other heavy equipment in use today. Considering the conditions under which much of the repair work must be done, it is essential that the mine operator has the best men and tools to perform the work. Mining machines, from their inception, have utilized the electric motor; and down through the years of mechanization, this power source has undergone many changes to better adapt it to the job. The first motors used were direct-current (d-c) motors since d-c power was the most economical power source for mining at the time of early mechanization. These motors were large open-type machines which are seldom used in modern mining. Because of the mine environment, the d-c motor has been reduced in size to better suit the application in mining machines and is now manufactured with dust-tight or explosion-proof enclosures. The d-c motor is constructed with either (or both) series and shunt fields located on the stationary part of the motor (stator) and an armature coil wound on the rotating part of the motor (rotor). Power is supplied to the armature by brushes which are held stationary and make sliding contact with the armature. The brushes requires regular and careful maintenance because worn or defective brushes will cause heat or arcing which can destroy the motor. D-c motors can be used as d-c generators when mechanical power is supplied to them by the rotating

Jan 1, 1981

By William Petruk, J. R. Schnarr

The behaviour of minerals during flotation of a fine-grained pyrite-rich base metal ore was investigated by studying the feeds. concentrate and tailings from every flotation cell in the mill of Brunswick Mining and Smelting Corp. Ltd. Bathurst. New Brunswick. The samples were analyzed for Zn, Pb, Cu. Fe, Ag. Sb, Sn, Bi, In. Hg, Mo and As. Mass balances were computed and recoveries of all metals from each cell. from each circuit and from the mill were calculated. The percentages of sphalerite. galena and chalcopyrite occurring as free grains in each product were determined with an image analyser, as were size analyses for free mineral grains and middling particles, and compared with screen analyses. The results show that the behaviour of minerals is defined much better by the recovery of free mineral grains than by the recovery of elements. The recovery of free sphalerite in the zinc circuit is 96 wt %, whereas Zn recovery from the same circuit is 88 wt %. the difference being due to unliberated sphalerite. The recovery of free sphalerite from the mill feed is 88 wt % and Zn 78 wt %. The recovery of free galenafrom the mill feed is 88 wt % and Pb 64 wt %. The recovery of free chalcopyrite is 75 wt % and Cu 45 wt %. Size analyses show that more sphalerite and chalcopyrite can be liberated by regrinding. but the galena is so fine grained that regrinding would not necessarily improve liberation. Silver occurs mainly in tetrahedrite and galena; the main loss in the tailings is due to large (+ 26 um) and small (-1 um} free and unliberated tetrahedrite grains.

Jan 1, 1981

By G. Swiatnicki, w. Chruscielewski, T. Domanski

INTRODUCTION The inherent errors of simple passive track detectors /SPTD/ used for estimation of exposure to the radon daughters /RnDP/ amount to about 30% /Do75/ while for active detectors only reach about 3 - 4% /Ph78, Du79/. The large error inherent in SPTD is the result of strong dependence of its calibration coefficient on the equilibrium Rn RnDP in the vicinity of detector /0r80/. Nevertheless the SPTD shows many advantages and seems to be very useful for to the estimation of individual exposure of miners to RnDP /Do81a/. For this reason the investigations are undertaken to improve SPTD so that it might provide information about the equilibrium Rn : RnDP during exposure. If the equilibrium would be known then one could use a suitable calibration coefficient yielding a better precision of the measurement. So far, some investigations of the improved type of SPTD have been conducted. One was based on the concept of using the so called diffusion barrier permitting to differentiate the tracks originating from Rn and RnDP /Fr77/. Such improved detector has been named a passive differentiating track detector /PDTD/. However, own investigations have shown /Do81b/ that this type of detector cannot provide precise informations about equilibrium Rn : RnDP. For this reason the investigations of the new idea of PDTD have been carried out. The new model presented below is based on the use of the absorbers of alpha particles. THEORETICAL CONSIDERATIONS The first variant of the concept is as follows: The differentiating detector consists of two portions of detective foil /track detector/ but only one is covered with an aluminium absorber. Thickness of the absorber is carefully selected so that only RaC' particles /7.7 MeV/ can pass the barrier. The second portion of the detective foil records all alpha particles originated from Rn and RnDP i.e. works like a SPTD. The scheme of such a detector, the so called two-fields passive differentiating track detector /PDTD-2/ is shown in the Fig. 1. It is possible to introduce a parameter that can characterize the equilibrium Rn RnDP, namely, the so called track density ratio /TDR/. The definition of this parameter for the considered type of detector is TDR2 = D1•D2-1. One can expect the simple proportion to hold: [ ]

Jan 1, 1981

By Everson P. T, Moyle F. J

Magnesite-rich and dolomite-rich ores from the Savage River region of Tasmania are being considered as potential feed material for a commercial process for production of magnesia.Two selected samples have been characterized by chemical analysis, X-ray diffraction, and differential thermal and thermogravimetric analysis. The materials differ in calcination behaviour, with magnesite decomposing at a significantly lower temperature than dolomite. Calcination conditions have a marked effect on the rate and percentage of magnesium dissolved as the bicarbonate when slurries of the calcine are leached with carbon dioxide. From a process point of view, the feed should have the highest possible magnesite/dolomite ratio, while the optimum calcination conditions are determined by the behaviour of the magnesite component of the feed.From batch calcination tests, it is apparent that the optimum calcination conditions for magnesite-rich ore are a temperature in the vicinity of 700°C and a calcination time of one hour.

Jan 1, 1981

By Lloyd W. Trevoy

Commercial production of heavy minerals from plant tailings streams is undergoing study by Syncrude Canada Lrd. When tar sand from an open pit mine is processed and up- graded to synthetic crude oil, heavy minerals can be recovered from the extraction circuit and can be upgraded to provide concentrates of zircon and titanium minerals. The titanium minerals concentrate consisting of a mixture of ilmenite, leucoxene and rutile, could be utilized as recovered or could be upgraded to synthetic rutile. With the construction of further synthetic crude oil plants in Western Canada a large reserve of heavy minerals will become available for utilization.

Jan 1, 1981

By Hoskings R

Conceptual studies of the run of mine stockpiling and reclaiming requirements at Thiess Bros Pty Ltd South Blackwater coal mine commenced in 1975.Final selection of equipment was made in 1978 and the equipment was commissioncd in June 1979. Equipment selection was made after extensive investigation and visits to existing facilities throughout the world.The equipment selected is described and compared with the alternatives. Foundations were designed to minimise clean up effort and to ensure stabilily of equipment under design wind loading without storm bays. Programmable logic control enables the stacking and reclaiming facility to provide a blended feed to the coal preparation plant.

Jan 1, 1981

By William H. Wiese

Anecdotal reports of high rates of congenital malformations and spontaneous abortions at the Shiprock Indian Health Service Hospital in San Juan County, New Mexico prompted an interview survey, obtaining data from families of 26 former uranium miners and 30 controls. Results supported the possibility of increased fetal wastage and congenital malformations. However, definitive conclusions were obviated by methodologic limitations in terms of selection of cases and controls and interviewing technique, as well as very low numbers and lack of statistical significance. The Council of Environmental Quality (1980) published a report which singled out San Juan County, nationally, as having an extra-ordinary high rate of congenital anomalies reported from birth certificates in the years 1973-75. San Juan County is in the northwest corner of New Mexico and includes the northeastern edge of the Navajo Indian Reservation. It has been the site of uranium mining and milling and also of coal mining (Clement Associates, 1980). While much attention has been focused on lung cancer and chronic lung disease as health hazards to uranium miners, virtually no attention has been focused upon possible reproductive effects that may result from exposure to radiation. Could these reports indicate such an additional arena of health effect either on miners or on others living in the vicinity of the mines and mills? The biologic and epidemiologic literature does not lend much support for adverse genetic outcome. The UNSCEAR report (UNSCEAR, 1977) summarizes much of the existing data. For example, on the basis of many animal studies and what has been observed in atom bomb survivers in Japan, it has been estimated that mutation rates resulting from low LET radiation to paternal germ cells would be 60 X 10-6 recessive and 20 X 10-6 dominant mutations per gamete per rad. There would be a five-fold increase in the number of recognizable abortions. The doubling dose for genetic disorders in mice is estimated at 100 rads. The assumption has been that low levels of exposure, such as might be received occupationally from uranium mines and mills or environmentally will produce reproductive effects that would defy distinction from background rates. However, the possibility can not be dismissed. In man, spermatogonia are thought to be three-fold more sensitive than in the mouse. Also, the high LET radiation from alpha particles is as much as 20-fold more effective in inducing changes in meiotic and post meiotic stages of cells, compared with low LET radiation. There is some degree of localization of alpha emitters in testicular tissue after inhalation of radon and radon daughters (Blanchard, R.L. and Moore, J.B., 1971; Pohl, E., 1964). The slopes of doseeffect curves are affected by type radiation and rate of administration. Data on such curves are poorly defined and debated as to whether there may be increased or decreased effect per unit dose at low levels of high LET radiation. Increased rates of aberrations of chromosomes in peripheral lymphocytes cultured from uranium miners have been reported (Brandom, W.F., et al., 1978). At cumulative exposures of 100 working level months (WLM) or less, a range of exposure lower than the limit of current occupational standards, the aberrations were increased more than two-fold. Our interest has led us to pursue the question of reproductive effects along three separate paths of inquiry: studies of the secondary sex ratio, cytogenetic study of human sperm, and studies of rates of congenital anomalies. I will present the thrust of our findings, most of which remain preliminary, comment on their interpretation and limitations, and indicate directions needed for future research. The secondary sex ratio is the ratio of males to females at birth. In the U.S., the ratio averages around 1.05. Ratios in blacks are somewhat lower (1.025) than in whites (1.053). For American Indians, the data are less definite. Values from Oklahoma and California are similar to whites (1.05). Southwestern tribes have, as we shall see, varying levels. The theoretical effects on sex ratio resulting from irradiation of the zygote are based on the principles of sex-linked genetics, including differential effects of lethal dominant and recessive mutations on the sex chromosomes, complicated by possible non-disjunctional events. Observations have done little to clarify, confirm or refute the theories. The sex ratio of progeny of survivers of the atomic bomb showed little change (Schull, W.J., Otake, M., and Neel, J.V., 1981). Observations in children of uranium miners having been inconsistent. Most frequently cited is a study of miners in Czechoslovakia (Müller, C., Razicka, L., and Bakstein, J., 1967). Compared with children born to miners prior to the start of mining, the sex ratios of children born after the start of mining were decreased -statistically significant after correcting for birth order. The ratios in first-born children were, before the start of mining, 1.118, and, after the start of mining, .713. In the interview survey at Shiprock, the sex ratio in families of non-miners was 1.03, and in families of miners it was 0.73 (p < .05). Dr. Alan Goodman at the University of New Mexico has studied trends in the sex ratio in the general population in New Mexico and Arizona with particular reference to counties in the Four Corners area and the Navajo Indian Reservation, areas where uranium mining has been active_ His findings (unpublished) are as follows: (1) Beginning in the early 1950&apos;s, there has been a modest, but persistant and statistically significant decline in the secondary sex ratio for the state of New Mexico compared with the U.S., a decline that roughly parallels the emergence of uranium mining in the Grants mineral belt in northwestern New Mexico. (2) Data available for the 11 years since 1969 show that among the five counties with ratios significantly lower than the state

Jan 1, 1981

By J. J. deBarbadillo

This Bureau of Mines report describes a process for recovering chromium and other metals from superalloy scrap. Laboratory-scale experiments were conducted to test a complex flowsheet utilizing a wide range of extractive metallurgical operations. The novel basis for the process is the fonnation of a sulfide matte in which chromium is concentrated in a discrete chromium sulfide phase. Mineral processing and hydrometallurgical procedures are used to separate chromium sulfide from the other matte constituents. The products of the process are a chromium-nickel alloy suitable for reuse in the superalloy industry, electrolytic nickel, electrolytic cobalt, and iron-molybdenum residue. Recovery of the principal elements contained in the scrap is chromium--93 percent, nickel--99 percent, cobalt--96 percent, and molybdenum--92 percent.

Jan 1, 1981

By Naomi H. Harley, Daryl E. Bohning, Isabel M. Fisenne

INTRODUCTION Underground mines in many parts of the world have elevated levels of short-lived 222Rn daughters. Lung cancer implicating exposure to short-lived daughters is documented in the U.S., Czechoslovakia, Canada, Sweden, the U.K., France and Newfoundland. An elevated lung cancer mortality (in excess of that expected) has been observed when cumulative exposure to alpha emitting short-lived 222Rn daughters (218Po, 214pb 214Bi 214Po) is greater than about 60 working level months (WLM) [1]/ (Hewett, D. 1979). This is equal to an absorbed alpha dose of about 30 rads to shallow basal cells in bronchial epithelium. Long-lived alpha emitters are also present in underground mines, and especially uranium mines because of airborne particulates containing uranium. The 238U parent of this primordial series supports other long-lived emitters 234U 230Th, 226Ra, Pb(210Po) which are in some degree of radioactive equilibrium with the parent 238U. Airborne particulates can be present due to drilling on the face of the ore body as well as in all parts of the mine through resuspension from the mine floor. Particles from 1 µm to about 5 µm penetrate the nose with reasonable efficiency and deposit primarily in the tracheobronchial tree. They are removed by ciliary motion (the bronchial escalator) but deliver an alpha dose to basal cells in bronchial epithelium during clearance in the same manner as short-lived 222Rn daughters. It is the purpose of this work to indicate the alpha dose to basal cells in bronchial epithelium delivered by the long-lived emitters 234, 238U. The dose calculations reported here based upon a few measured values of these isotopes in air in uranium mines in New Mexico and Colorado. MEASURED 234, 238U IN URANIUM MINE ATMOSPHERES In 1979, the U.S. Bureau of Mines undertook a study to evaluate personal monitors to be worn by miners to measure short-lived 222Rn daughters. One of these devices sampled air at 100 cm3/min through a 13 mm glass fiber filter, with a small pump worn on the belt. Alpha particles emitted by 222Rn daughters on the filter were measured continuously by a thermoluminescent dosimeter (TLD) chip. Each monitor was worn by a miner for a 170 hour working month and approximately one cubic meter of air was sampled during this period. Six different mines were selected for the test in New Mexico and Colorado. The mines used either wet or dry drilling methods. Miners in each location were equipped with the personal monitors. Subsequent to their use in evaluating the shortlived daughters, Dr. Robert Droullard of the Bureau generously gave us these filter samples along with a few blank glass fiber filters from the same box of filters used in the study so that long-lived emitters present in these mine atmospheres could be determined radiochemically. Four of the samples have been run for 234, 238U. The radiochemical procedure for uranium is adapted from USDOE, Environmental Measurements Laboratory Manual (Harley, J.H., 1976). Briefly, the samples were placed in platinum crucibles, spiked with 232U tracer and pretreated with nitric and hydrofluoric acid. The residue was fused with potassium fluoride to transpose to pyrosulfate. The fused cake was dissolved in 7 [N] hydrochloric acid and the solution passed through an anion exchange column to isolate uranium. Iron was removed using mercury cathode electrolysis. Uranium was electrodeposited onto platinum dies and counted using solid-state alpha spectrometry. The samples from each type of mine (wet and dry) were analyzed. The samples in the "wet" mine in New Mexico were selected on the basis of the original TLD measurement because they were near the maximum occupational standard for radon daughters. These samples should also represent upper limits to longlived activity encountered, since they were obtained at drilling operations on the face of the ore body. Samples collected in the "dry" mine in Colorado were pot associated with a particular location in the mine and should be representative of a month long overall exposure in many locations and operations. The values are shown in Table 1. The two uranium isotopes are in equilibrium and their alpha activity

Jan 1, 1981

By A. E. Raddatz

In an attempt to develop technology to use domestic resources in place of imported bauxita, the Bureau of Mines investigated sulfurous acid leaching to extract alumina from kaolin. The process consists of leaching the calcined kaolin with a 30 wt-pct S02 solution at 60° C and 160 psig for 17 hours, fil¬tering the leach slurry, precipitating monobasic aluminum sulfite from the filtrate at 110° C and 60 psig, a& decomposing the sulfite in the spent liq¬uor at 150° C and 55 psig to produce crude alumina. Purification of the crude alumina was accomplished using a modified Bayer process. Results from closed-circuit tests employing the sulfurous acid process showed that overall extraction of alumina from kaolin was 67 pct. Production of 1 ton of alumina would require 3.6 tons of calcined kaolin, 0.7 ton of sul¬fur dioxide, and 8.4 tons of water. After purification by a modified Bayer process, the alumina product contained the following; impurities, expressed in weight-percent: Fa203, 0.009; S, 3.6; Si02, 0.07; Ti02, 0.002; K20, 0.017; and P205, 0.03.

Jan 1, 1981

By Donna Wallace

Past EPA groundwater monitoring programs required that contamination not leave the boundaries of a disposal facility. New regulations under the Resource Conservation and Recovery Act (RCRA) require that once hazardous waste constituents are detected beyond the limits of the disposal area, a program to define the rate and extent of contaminant migration must be instituted. Future regulations are likely to include even more stringent groundwater protection criteria. The implications of both the existing and probable future groundwater protection and monitoring requirements in terms of using geologic containment as a means of disposing of hazardous waste are explored in this paper.

Jan 1, 1981

By D. G. Hartley

The major copper loss at Mount Lyell is in the coarsest particles presented to flotation. An analysis of data collected from the five primary and six secondary ball mill circuits showed that grinding was limited by low breakage rates in secondary mills, possibly due to oversize balls. For 5 months, the make-up ball size for one secondary mill was reduced from 50 to 30 mm. Frequent steady-state tests indicated that overall average breakage rates could be increased by about 70% using smaller balls. A mathematical simulation of the whole circuit with increased breakage rates showed that the resultant finer grind was likely to improve copper recoveries by about 22.

Jan 1, 1981

By Gary A. Nowlan

The Casa Grande West-Santa Cruz porphyry-¬copper deposit is in the Basin and Range physiographic province west of Casa Grande, Arizona (Fig. 1). The Casa Grande West portion of the deposit is controlled by Casa Grande Copper Company and the Santa Cruz portion by ASARCO. The deposit contains at least 350,000,000 metric tons of rock with greater than 1 percent Cu. The deposit is covered by at least 300 m of sediment, with no visible expression of the deposit at the land surface. The deposit is in an area of prime agricultural land that depends heavily upon well irrigation because of a hot and arid climate. Because of the deep sedimentary cover, the chance is extremely remote that the geochemistry of soil or stream sediment would reflect the deposit even if the land surface were not disturbed by many years of farming. Irrigation wells of the area generally bottom in the sedimentary cover. The purpose of the study is to see if the Casa Grande West-Santa Cruz deposit is geochemically reflected in ground waters over and near the deposit.

Jan 1, 1981

By Dell H. Adams

COAL EXPLORATION Coal exploration may be defined as the acquisition of data necessary to define and acquire a block of coal which can be mined at a profit. Unlike ore minerals, coal resources are widespread and relatively abundant with supply exceeding demand in almost every case. Thus simple discovery of coal is generally not enough. The chemical and physical variability of individual coal seams, the capital intensive nature of coal mine development, and the changing patterns of utilization require that a multiphase, three-dimensional evaluation be made of each potential reserve. Factors which must be investigated include not only the quantity and quality of the coal but also the geologic, hydrologic, and engineering characteristics of the seam and its surrounding strata. Acquisition of property to provide a secure base for exploration and mine development is equal in importance to the geologic and engineering programs. The successful development of a coal reserve requires that control of coal and, in the case of a strip mine, the surface be in the form of contiguous blocks of sufficient size to support mining. PHASES OF EXPLORATION The high capital risks of coal exploration and land acquisition dictate that a multiphase program be utilized to minimize initial risk. In such a program, phased development of the data insures that each increase in capital expenditures will be justified by a corresponding increase in the level of confidence in the ultimate success of the project. Each phase is designed to provide sufficient data and property control to facilitate the decision whether to proceed to the next phase of development or to discontinue the program (Table 1). The first phase of a typical exploration program consists of a pre-

Jan 1, 1981

By Noel G. Thomas

"This paper will identify where the industry is heading with iron· ore in the next ten years. From a customer&apos;s point of view, an indication of the changing, yet expanding, market will be made. This will progress further into the most likely changes in chemical and physical requirements of the ore products. No definite target can be set for 1990, but the logic from the direction of the changes will be established.IntroductionThe tonnage and quality of iron ore produced in the eighties will be heavily influenced by energy and investment considerations. That&apos;s not a great pronouncement, but this paper will explain how these two factors are :(I) influencing a disproportionate growth of electric furnace capacity and a greater use of scrap for iron units, in place of Iron ore;(2) influencing chemistry specifications; and(3) causing extensive examination of ore agglomerate form. Inflating investment costs are emphasizing the need for more productive blast furnaces, and the iron ore burden is under heavy examination as to how it affects productivity and coke rate."

Jan 1, 1981

By John Durkin

This report discusses the configuration and system deployment for the postdisaster surface seismic system for detecting and locating trapped miners. It analyzes the results of 15 field tests to define a signal model, background noise levels, and subarray performance. A waveform modeling procedure is described and compared with observed waveforms. The resulting similarity indicates that the major factors affecting the signal amplitude, waveform, and spectral character are understood. A model is presented which gives the sig-nal amplitude as a function of source type, source depth, and horizontal off-set between source and receiver. Using this model a curve is presented which gives the range at which a signal will be detected for different signal and noise levels. Finally, and most important relative to the mission of the system, the ability of the system to detect signals on one or more subarrays is put into a probabilistic framework. For a strong source it is almost certain that a subarray directly over the source will detect the signal. After signal processing, it is highly likely that signals will be detected on sufficient subarrays to locate the trapped miner. Location errors have been found to be less than 100 ft in the majority of cases. Techniques have been used that can reduce the location errors to this level even when soil layer variation between subarrays is severe.

Jan 1, 1981

By Jean-Paul Drolet

"The ultimate aim of the Law of the Sea Conference, held under the auspices of the United Nations, is to ensure that all aspects of the use of the sea are covered by international law. The question facing the nations of the world can be stated as: "" Who will control and benefit from the use and the wealth of the sea?""The United Nations Conference on Law of the Sea - known as UNCLOS - which reconvened in New York during the latter part of August 1978 was the third such Conference in the UN&apos;s history. The concepts of sovereignty over the territorial sea and freedom on the high seas have remained fundamental to the international law o f the sea until our time. The legal regime based on these two concepts developed initially from state practice meant that the unilateral actions taken by one or more countries were eventually accepted and followed by others.It was not until 1958, during the first Geneva Conference on the Law of the Sea (pursued in a second Conference in 1960) that the Law of the Sea was codified and modified to a certain extent by the then independent nations of the world in the four multilateral conventions on territorial sea and contiguous zone, continental shelf, high seas, and fishing and conservation of living resources.A third Conference got under way many years later when the members of the UN met in New York at the end of 1973 for preliminary discussions . This meeting stemmed largely from the need to fill gaps in existing international legislation which did not cover the new uses of the sea. The Conference was subsequently reconvened a number of times - in Caracas (1974), in Geneva (1975) and twice in New York (1976) for what was called "" substantive negotiating sessions."" A sixth session was held in New York in 1977; a seventh, held in Geneva at the beginning of 1978, recessed and reconvened in New York at the end of August 1978. This is what is referred to, in international jargon, as the seventh session of the Third United Nations Conference on the Law o f the Sea. The following dates are the principal markers of a saga which began some twenty years ago with the purpose of regulating the use of the oceans."

Jan 1, 1981

By Peter F. Weiss, H. Riedler, I. M. Moschitz, A. Olsacher, G. B. Fettweis

CONTENTS : 1. NATURAL FACTORS Geology Petrography and Rock Mechanics Mining System Orientation Rock Bolting System Movability of the Ore Grain Size Distribution Permeability Contamination Value of the Ore Hydrology 2. TECHNICAL FACTORS Height Length and Width Drawing Areas Time Factor Water Predrainage Surf ace Draining Underground Draining Advancing Slitting Sequence of Development Initiation of the Caving Process Drawing Rate 3. SPECIFIC MINING RULES Advancing Development Drawing Rate Interruption of Drawing (Water Distribution, Concentration of Mud, Dilution) Blasting 4. CONTROLS Safety Controls for Operation Computerised Drawing Control Structure of the Computer Program Hard Ware Print Outs 5. SUMMARY 6. ACKNOWLEDGEMENTS 7. REFERENCES Under the heading "Development System for Block Caving under Severe Conditions" a report was presented to this congress regarding a magnesite mine using block caving for several years. On account of the experience gathered in this mine and the results of far reaching exchange of experience, as well as under due consideration of the international literature it is tried to systematically list and briefly discuss the following factors that have to be considered for development and draw control of block caving. 1. NATURAL FACTORS It is self evident that this implies all those circumstances given by nature and which cannot be altered by man. Any mining activity is subjected to those and the success is depending on how far technology can be adjusted to those conditions. Geology Deposits of considerable thickness with rather steeply inclined flat-faced contacts are optimal for block caving. While vertically there is practically no limitation- for the deposit, theoretically, the smallest horizontal basis apt for operating block caving is the minimum area necessary to get the rock to completely cave in by undercutting and drawing. Practically, only consider- ably bigger main dimensions are found, mainly because of technical factors (machinery and equipment) and economic factors (cost ratio of exploration vs. development, danger of contamination).

Jan 1, 1981

By Robert B. Parsons

"Originally intended to be implemented in 1977, but actually introduced effective May 6, 1974, the earned depletion regulations have been substantially refined and modified since their appearance on the Canadian tax scene, so that this important legislation now consists of a highly complicated set of rules which even the most astute follower of tax law has considerable difficulty sorting out!This month, Tax Notes attempts to cut through this bewildering array oj regulations, in reviewing the main features of the earned depletion allowance applicable to mining operations. Despite the phase-out of earned depletion allowances for most oil and gas operations as part of the federal government&apos;s new National Energy Program, earned depletion provisions are still alive and well for the mining sector, although they might well be slowly strangling to death in their own entanglement of complexity!"

Jan 1, 1981