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By M. P. Hardy, C. J. H. Brest van Kempen, H. N. Maleki

To evaluate the influence of uniformly tensioned roof bolts on roof stability, mechanically anchored roof bolts were installed using the conventional bolter and a specially developed thrust and torque controlled retrofitable box mounted on a bolting machine. Thirteen thousand bolts were installed over 19 crosscuts in a 4 heading development in an operating coal mine. Geological , bolt and mine parameters were recorded at bolt installation, and bolt tension histories, roof sag and other changes evident in the rooms, crosscuts and intersections were recorded over a 2 month period. In all, 24 variables and 11 responses were quantified at 67 bolt clusters. These data were analyzed statistically to determine the significant variables influencing roof stability. As the mine development was safe and stable during the monitoring period, roof sag after two months was used as an index to quantify "stability." The variables of significance were shown to be coefficient of variation of bolt tension, bolt anchorage capacity, roof lithology, roof shape, standard deviation of bolt tension, and dip of roof lithologies. It was concluded that of the variables with which the mine operator has control, bolt tension uniformity was the most significant parameter at this mine. Other variables, such as intersection type and time between mining and bolting , were not significant, whereas, some other potentially significant variables such as horizontal stress or roof joint frequency did not vary sufficiently for their influence on stability to be evaluated.

Jan 1, 1986

By R. Woods

INTRODUCTION Gaudin (1), considered that "the mechanism of mineral collection is the central problem of flotation theory". From their work on adsorption phenomena in flotation for more than fifty years (2), Gaudin and his co-workers have made major contributions to the elucidation of this mechanism, a fact acknowledged by their contemporaries in the field (e.g. (3)). Their investigations in a number of areas, e.g. demonstrating that submonolayer quantities of adsorbed collector species can induce flotation, or identifying the influence of substances which can activate or depress (1), have helped to provide the basis for and the development of a theory to account for the interaction between mineral and collector. It was established in the late fifties (4) that the presence of oxygen is a prerequisite for the flotation of metal sulfides with thiol collectors. This fact rendered inadequate the concept of simple ion adsorption being responsible for rendering these minerals hydrophobic. The requirement for oxygen has been explained (1) in terms of this species being a component in chemical reactions between the sulfide surface and the collector. Gaudin has been instrumental in identifying the products of chemical reactions at sulfide minerals (1.5), a line of work which has been continued particularly by Finkelstein and co-workers in South Africa (6). In presenting a detailed mechanism of the mineral-collector- oxygen interaction, it has often been considered that the mineral surface - must first be oxidized to a metal oxy-sulfur species which

Jan 1, 1976

By D. A. Karvonen

Although the economy in the Province of Saskatchewan has historically been agriculturally oriented, a major new source of wealth has been realized through natural resources such as petroleum and natural gas, coal and uranium and since the 1960's - potash. Potash or potassium chloride, in the form in which it is presently produced in Saskatchewan is used primarily as fertilizer, a source of potassium, one of three essential elements required for healthy plant growth with about 5 percent of production sold to the chemical industry for use in such products as soap and liquid detergent, glass and ceramics, textiles and some pharmaceuticals. Saskatchewan is estimated to have approximately 40 percent of known world potash reserves and its ten active mines account for some 25% of annual world production. The development of this resource was recognized to be important to the development of Saskathcewan. In an effort to guarantee a fair and lasting economic benefit to the Province of Saskatchewan the Potash Corporation of Saskatchewan (PCS) was created on February 4, 1975 through an Order-in-Council under the Crown Corporation's Act and later on April 1, 1976, the Potash Corporation Act provided for its continuation. PCS was given the mandate to acquire ownership of a significant portion of the potash mining capacity in Saskatchewan and to establish an organization capable of operating the facilities, marketing the product and conducting all of the other activities necessary for a successful corporation competing in the world potash industry.

Jan 1, 1983

By Scott G. Britton

The first section of this text delves into construction engineering techniques for successfully completing necessary underground production support projects. I will discuss alternative design concepts, installation practices, materials and material costs, completion time, and necessary labor for individual projects. The emphasis of this section is on describing each project thoroughly and providing a practical guide for the supervisor or engineer. There are four main construction categories for typical underground mining projects. These are: 1) Transportation of men and supply materials. This refers to track and wire installation and roadbed grading and ballasting. 2) Ventilation, composed of overcasts, man doors, regulators, and stoppings. 3) Drainage, including sumps, pumping stations, drainage networks, pumps, and face drainage. 4) Haulage of coal and rock from the face to the outside. The focus here is in the installation of belt lines, belt drives, transfer points, and vibrating bins/feeders. The first section shall fully discuss these four categories in regard to the construction engineer or supervisor designing, building, or improving a system. In addition, special projects such as surge bins, rotary dumps, and underground offices not classified under these categories will be discussed. For manageable purposes, I have limited the installation discussions to one or two approaches I feel have merit. The variation of installations in coal mining is endless, each with its own advantages and disadvantages. Therefore, the reader should not dismiss or restrict his thinking to only the approaches in the text. It serves as a guide only.

Jan 1, 1983

By J. D. Pitts

Long distance slurry pipeline systems for steam coal, iron concentrates, copper concentrates, and limestone, first used nearly 60 years ago, are now transporting nearly three billion ton-miles annually. At this time a phosphate concentrate pipeline is nearing start-up and systems for transporting coking coal, lead/zinc concentrates, and fly ash are planned. The solids pipeline concept was first patented in the early 1900's and put into practice in the 1950's. Table 1 summarizes the major elements of several presently operating commercial systems. Increased control system sophistication has been accompanied by significant drops in control equipment size and cost, as illustrated by recent cases of pipeline operation with progressively more advanced level of control: 1) The Consolidation Coal (Ohio) and Savage River (Tasmania) iron concentrate pipelines started in 1957 and 1967, respectively, used simple hard-wired control logic. 2) The Black Mesa (Arizona) coal slurry pipeline commissioned in 1971 added a hard- wired programmable logic controller for some of the start-up and shutdown routines. 3) Two years after its start-up in 1974 the Pinto Valley (Arizona) copper concentrate pipeline was tied into the concentrator digital computer system for data logging. 4) The Samarco (Minas Gerais, Brazil) iron concentrate pipeline which came on-line in mid-1977 was the first slurry system to use a dedicated supervisory computer for its control. Communication to remote areas was via micro- wave and buried cable.

Jan 1, 1979

By T. J. Close

The Silver Peak Range North Wilderness Study Area was deleted from the list of US Bureau of Land Management lands in Nevada to be considered for wilderness designation. This decision was based in part on the US Bureau of Mines mineral investigation of the wilderness study area which found indications of precious- and base-metal-resources. The study area lies between the Silver Peak and Dyer mining districts of west-central Nevada. The Bureau examined 13 mineralized sites, most of which were previously unknown and unclaimed. These sites are along two zones that cross the study area from the Silver Peak mining district to the Dyer mining district. The two zones transect a volcanic center of fractured and altered rocks that contain epithermal veins of quartz and calcite with gold, silver, and base-metals. At the surface, these veins are poorly defined. Exposures of the more than forty veins examined were as thick as 17 ft and as long as 1000 ft. Samples from these veins contained significant amounts of precious- and base-metals-as much as 0.02 oz per ton gold, 2.1 oz per ton silver, 1.0% copper, 2.6% lead and 0.4 % zinc. No vein large enough or of high enough grade to be classified a mineral resource was disclosed by the sample data. However, most do have indications of precious- and base-metal-resources at depth. Subsurface exploration of some of the veins is recommended.

Jan 1, 1995

By Russell L. Wood

The title of this session seems to have been picked especially for this paper. It is 1984, it is the morning after, and there is one monumental hangover among many if not most of the oil companies that have invested in mining in the past decade or so. How an oil company looks at mining depends on what time period you are talking about. A few years back around the time of investment this is what they were probably looking at: 1. A balance sheet of their own that was beginning to go wild, with many of their commodity prices having already seen increases of two, three, or four fold, and with no end in sight. 2. A need to invest their earnings someplace fast before the stockholders or the government got too interested. And that someplace should be in an industry where their own management skills could be applied. (Only a true cynic would suggest that this is a form of job security) 3. In mining there was an industry amazingly similiar to their own, one working with non-renewable natural resources, dealing with the same types of government agencies, and having the same type of critics and pressures from the general population. 4. An industry that was somewhat backward as compared with their own, and one where a generous ration of the capital and management skills so handsomely bestowed upon the oil industry could be used to great advantage.

Jan 1, 1984

By D. K. Jorgensen

The Bullfrog and Montgomery-Shoshone deposits, near Beatty, NV, have a combined drill-indicated reserve of 15.8 Mt (17.4 million st) of ore. Average grade is 3.5 g/t (0.103 oz per st) gold and 8.2 g/t (0.24 oz per st) silver. The deposits occur in Miocene volcanic rocks that underwent large-scale movement within a detachment-faulted terrane. The principal host to gold mineralization is a strongly welded rhyolitic tuff that experienced brittle deformation during plate movement. Open space fractures and breccia were filled with quartz, calcite, and adularia accompanied by lesser pyrite, gold, and acanthite. Gold occurs as micrometer-sized particles within and adjacent to the low-angle fault and along associated listric-normal and tear faults. The Bullfrog and Montgomery-Shoshone are volcanic-hosted, detachment fault-related, epithermal quartz calcite stockwork gold deposits. Bullfrog's minable reserve is 13 Mt (14.3 million st) of ore grading 3.8 g/t (0.11 oz per st) of gold. At Montgomery-Shoshone, 2.7 Mt (3 million st) minable tons at 2.5 g/t (0.072 oz per st) are present. Preproduction stripping has begun at the Bullfrog ore body. A 7.7-kt/d (8500-stpd) carbon-in-pulp (CIP) mill is under construction. In 1990, Bond Gold expects to be producing about 6.2 t/a (200,000 oz per year) of gold.

Jan 1, 1990

By F. Gonzalez, A. Zambrano, J. Schwoebel, S. Kravits

Significant lost time delays were experienced by Carbonifera de Nueva Rosita, S.A. de C.V. ("CNR") during mining development of the Pasta de Conchos Mine ("the Mine") near Nueva Rosita, Coahuila, Mexico. Furthermore, methane gas concentration in the return air course had exceeded 1.0 percent. Resource Enterprises, Inc. ("REI") was contracted by CNR to recommend an approach to reduce methane emissions at the Mine. In order to recommend a degasification approach, REI and CNR obtained geologic and reservoir characteristics of the Double coal seam, Olmos Formation. A vertical core hole was drilled to obtain core samples to determine gas content (average 8.4 cm3/gm) and to conduct a slug test to estimate permeability (34 md). This information was used to simulate gas productivity and drainage effectiveness. The simulation indicated that underground horizontal boreholes would remove significant quantities of gas in advance of mining in a reasonable period of time. Based on the results of the simulation study, an underground degasification drilling program was initiated at the Mine. In a six month period, five long in-mine degasification boreholes were drilled in advance of CNR's three to five years mining projections. Peak gas production from the five boreholes (approximately 2,750 cumulative meters) had exceeded 45,000 m3/D. Results to date have indicated a general reduction in methane concentration in the return air course below 0.8 percent.

Jan 1, 1993

By Changwoo Lee

Under drastically deteriorated situations, diesel equipment was introduced to some of local coal mines, aiming at higher productivity and better safety. To accommodate various diesel equipment in conventionally developed mines, mining system itself had to be modified; much larger trackless haulage ways were excavated. Possible health hazards of diesel not taken into account at the beginning become a serious concern and effective control measures are being searched for. The purpose of this paper is to study the diffusion characteristics of diesel exhaust in local coal mines. One of the parameters affecting dispersion of diesel contaminants is the coefficient of turbulent diffusion. Since CO2 is known to be closely correlated with other contaminants such as CO, NO, NQ, SO2 and RCD, it was chosen as a tracer gas in a series of dispersion experiments. A large diesel passage as well as a conventional track haulage way were the sites for the experiments. Rectangular dispersion pulses were generated for 30 ~60 seconds and CO2 concentrations were recorded at several locations 50~190 m downwind. The diffusion coefficients calculated graphically vary between 0.10~0.48 m2/s at both haulage ways. The results are analyzed to find any correlation with the air velocity and the distance from the disperser. Skobunov's empirical formula is applied to the experimental data for comparison and the relationship between Reynolds number and Ex/Dp/sci0.4 Sc1…

Jan 1, 1995

By D. E. Ranta, John G. Stone

One of the steps in an ore reserve estimate is customarily a rigorous calculation of the in situ grade of the orebody itself. The result of this calculation is usually reduced by some purely arbitrary factor to force the calculation to agree with the observed grade of ore actually mined. The failure of the calculation to realistically depict the grade of ore actually extracted is in many instances not the result of either an incorrect calculation procedure or of sloppy mining practice, but is a direct consequence of unsuspected irregularities in the contact between the orebody and the surrounding wall rock. A pattern of holes spaced at 1.5-3.Om foot intervals, drilled as part of a pre-development program, will often reveal that a presumed "regular' ore/waste contact is, in fact, so highly irregular that it will be next to impossible to separate ore from waste during mining. In such an instance, 'fingers' of waste projecting into the mining block will substitute for equal volumes of ore left outside the mining limits. As a result, the grade of material actually mined will be less than the grade envisioned for the orebody. The volume of waste substituting for ore in the mining block is about 0.4X, where X = the average error in projecting the ore/waste contact between alternate holes in the test pattern, and is expressed in units of volume per unit of area of the contact surface.

Jan 1, 1992

By Lynne Chastain

The Eastern Shoshone and Northern Arapaho tribes of the Wind River Indian Reservation, Wyoming are interested in developing their industrial mineral resources. The U.S. Bureau of Indian Affairs (BIA), Division of Energy and Mineral Resources (DEMR) is assisting the tribes in evaluating the potential of their industrial mineral prospects for development. Gypsum occurs on both sides of the Owl Creek Mountains in the basal portion of the Jurassic Gypsum Springs Formation. The gypsum resources that are being evaluated crop out along the northern flank of the Owl Creek Mountains in the Sweetwater basin, a small topographic sub-basin of the Big Horn Basin. From October 1998, to April 1999, DEMR personnel mapped, sampled, and drilled the southcentral butte within the Sweetwater basin. Samples were analyzed for free and combined water, and major mineral oxides to determine gypsum purity. Gypsum purity averaged 93.6 percent for surface samples and 95.1 percent for drill core samples. The basal portion of the Gypsum Springs Formation is comprised of several beds of gypsum up to 9 feet (2.7 m) thick separated by 0.5 to 2.0 foot (0.15 to 0.61 m) thick lenses of siltstone and limestone. Overall gypsum in the formation ranges from 35 to 90 feet (11 to 27 m) in thickness. A resource of approximately 7 million short tons (st) (6.4 million metric tons [mt]) has been identified.

Jan 1, 2001

By Andrzej Wala

Constantly increasing demand for energy materials and metal ores brought about tremendous progress in mining techniques which are characterised by a high degree of mechanization and concentration of works. One of the recent trends in underground mining mechanization is connected with an application of heavy machines with diesel engines [l],[2]. The introduction of diesel engines in mining all over world caused not only improvement in economic conditions but also the necessity to prevent contamination of air in the mine by toxic agents in diesel exhaust emissions. A generally used way of eliminating exhaust gases is proper ventilation of the cross cut by means of providing permanent exchange of air that would guarantee in every point of the cross cut and in every moment the decay in concentration of exhaust gases beyond threshold limit [3][4][5][6][7][8][9][10]. The present paper is an attempt to define a mathematical model describing the changes of concentration in cross cut face to which fresh air is distributed by ventilators and tubes in a forcing way. Obtained model should offer its practical adaptability to engineering calculation of the amount of fresh air needed for diluting and eliminating exhaust gases beyond threshold limit. Justness of these models has been confirmed by investigation of the growth of nitrogen dioxide concentration in air environment in some cross cut faces of Kiirunavaara iron ore mine in Kiruna (Sweden).

Jan 1, 1980

By Alan G. Mayton, Jon C. Volkwein

The U.S. Department of the Interior, Bureau of Mines, in cooperation with an American firm, has been contributing toward the creation of a new highwall mining system for extracting coal in active, unreclaimed contour strip mines in the United States. The prototype system features the computer-based, remote control, video operation of a thin-seam continuous miner. Haulage is accomplished remotely also with a 76-m (250-ft) long multiple-unit continuous haulage (MUCH) conveyor system on rubber-tire vehicles. One aspect of this multi-faceted effort has been to design a ventilation system for removing dust generated at the face during the extraction process. The remote mining system eliminates the need for personnel in the mined workings. Ventilation is required to remove visible dust from the area inby two video cameras. These cameras are located approximately 6 m (20 ft) from the face, one on either side of a modified Jeffrey 102HP continuous miner. Removing the dust from this area provides the remote operator with constant visual monitoring of coal extraction at the face and thus, insures the effective operation of the mining system. A ventilation system was designed for use in a mine opening with a maximum cross-sectional area of roughly 4 sq m (44 sq ft) excluding the mining machinery. This paper describes the ventilation system and discusses how it was developed in view of the constraints imposed by the mining equipment, mining conditions, and the extraction process.

Jan 1, 1989

By Phillip O. Tyree, R. A. Metz, Joseph W. Mussey

Bio-epigenetic sulphur deposits occur in Pecos, Reeves and Culberson counties of far West Texas. Sulfate reducing bacteria, utilizing hydrocarbons as energy, transformed gypsum into replacement limestone and hydrogen sulfide. Hydrogen sulfide, retained in the pores of the replacement limestone, was subsequently oxidized by highly oxygenated groundwaters, and native sulphur precipitated. West Texas sulphur was first recognized at surface exposures by William P. Blake, a geologist attached to the Captain Pope Military/ Scientific Expedition of 1854. Attempts were made in the early 1900's to mine these sulphur vent exposures by a retort method, but the ventures met with little success. In 1967, Duval discovered a large sulphur deposit near some of the old sulphur works in Culberson County. Duval also expanded reserves in a small sulphur deposit in Pecos County. The Frasch process, developed for producing sulphur from Gulf Coast salt domes, proved successful in West Texas type sulphur deposits also. However, modifications of the process were necessary to provide economical and efficient sulphur recovery from the varied ore occurrences. West Texas conditions and logistics require the ultimate in productivity to be competitive in the domestic and foreign sulphur markets. Several companies, in addition to Duval, are producing or have produced sulphur in West Texas. As of June 1, 1984, a total of 29.87 million mt (29.4 million long tons) of sulphur had been produced west of the Pecos River. Duval corporation has produced more than 88 percent of that total.

Jan 1, 1992

By Cherie M. Tilley

The Stillwater Mining Co. of Nye, MT, is operating a platinum-palladium mine that requires an extensive system of footwall laterals to facilitate mine production. The 10-year mine plan calls for more than 48,300 lineal m (160,000 lineal ft) of footwall lateral. A rapid tunneling and raising system is necessary to sustain mine production schedules and achieve production goals. This article describes the results of using a Robbins 4.1-m-diam (l3.5ft-diam) tunnel boring machine (TBM) to develop the footwall laterals and a Robbins RBM-6SP raise boring machine to develop raises at the mine. The Stillwater Mining Co is a partnership between Chevron Resources Co. and Manville Corp. Chevron Resources is the managing partner. When the mine began production in September 1986, the owners were primarily concerned with the actual production of platinum and palladium, the grade minable and the amount that could be mined. As mine development and mine production proved feasible, the owners considered higher production levels. The Stillwater Mine is developed by a system of adits (known as footwall laterals) that are driven parallel to the ore bearing zone. This led mine officials to consider using a mechanical boring machine in the primary mine development. Previously, tunnel boring machines have not been used successfully in mining applications. Therefore, the owners decided to purchase a used machine to reduce the potential risk.

Jan 1, 1991

By Harold Wagner, Prakash Donde, Larry H. Heflin

INTRODUCTION The Washington Metropolitan Area Transit Authority is responsible for the planned 166 kilometer (103 mile) Metro rapid rail transit system in Washington, D.C. Some 117 kilometers (72.8 miles) of this system is in operation and contains 30.6 route-kilometers (19 miles) of rock tunneling. To complete the planned system an additional 1.6 kilometers (1.0 miles) of single track tunnels in rock are planned and additional contracts will consist of 4 kilometers (2.5 miles) of twin tunnel, resulting in 8 additional linear kilometers (5 miles) of single track tunnel contracts yet to be offered in soft ground. Three recent contracts in soft ground included the New Austrian Tunneling Method (NATM), along with conventional tunneling, as a bid option. Section E5a, Fort Totten Station and Tunnels, was the only one of the three to be constructed using the NATM option. This is the first application of the New Austrian Tunneling Method in soft ground in the United States. This paper will concentrate on the Fort Totten Station chamber NATM design, construction, and the instrumentation readings and evaluations which lead to an engineering back analysis which allowed a refinement of the bid design, resulting in a faster, more efficient construction. Design of the Fort Totten Station and Lines was done by Sheladia Associates. The design team included Greiner Engineering and Jenny Engineering with Mayreder-Consult of Austria, who was responsible for NATM design and NATM construction consultation.

Jan 1, 1991

By Reid Trent, Jon C. Volkwein

The U.S. Bureau of Mines is investigating a novel technique to control methane in underground mines by using methane oxidizing microorganisms termed methanotrophs. Coalbed methane has been responsible for many mine disasters and will continue to be a safety obstacle to mining deeper coal seams. Deeper seams of coal contain more methane gas, and better strategies for removing the methane will need to be developed. Methanotrophic microorganisms offer a novel alternative since they physically remove the methane, are commonly found in soils, and already have been found to exist in many foreign coal mines. Proposed applications of this concept include the inertization of buffer zones separating active mining areas from sealed gobs, reducing ventilation from ventilated gobs and reducing methane content from longwall gobs. Current work includes an assessment of the abundance of naturally occurring methanotrophs in U.S. mines, testing the amount of methane that various types of microorganisms can consume, studying the effects or use of the byproduct gases, and finally developing practical appl ications of this biotechnology to coal mining. This paper reports on the initial laboratory testing that measured the quantity of methane consumed by two types of methanotrophic microorganisms. Average rates of methane consumption were between 1 and 4 ml/hour in column flow tests. A possible gob application may require that 750 cfm of methane be consumed during periods of maximum outgassing. It is premature at this time to accurately scale from laboratory to mine application.

Jan 1, 1991

By Kirsten Corin, Belinda McFadzean, Cyril O’Connor, Jenny Wiese

As orebodies being mined globally are of ever-decreasing grades, the focus on the concentration process has moved increasingly to the challenges faced in management of the gangue minerals. This is especially so in the flotation of platinum group minerals (PGMs), where head grades are typically in the region of 4–7 g/t. Hence, in PGM operations, a typical recovery of about 80 percent requires depressing about 85 percent of the gangue minerals. In a flotation cell the main control parameters are reagent type and dosage, froth depth and air addition rate. This paper reviews research projects carried out over an extended period aimed at optimizing the depression of gangue minerals: both those that are naturally floatable and those, such as chromite, that are entrained.  This has involved comparing the two major depressants used in the industry — guar and carboxymethylcellulose (CMC) — in the depression of the relevant gangue minerals, as well as investigating their consequent effect on the behavior of the froth phase. Because most PGM flotation plants treat the ore as if all the PGMs are associated with sulfides, copper sulfate is widely used as an activator, but this can also lead to inadvertent activation of gangue minerals. Finally, chromite levels must be kept below 3–5 percent to avoid any negative effects on smelter performance, and thus it is important to reduce chromite recovery which mainly occurs due to entrainment through, for example, froth depth control.   

By John K. Adams

Phosphorus may be incorporated into sedimentary rocks in at least four different ways: (1) by the accumulation of detrital mineral fragments, (2) by the accumulation of phosphatic organic debris, (3) by diagenesis and (4) perhaps by the primary precipitation of calcium phosphate. Based-on the petrographic examination of Cretaceous and Tertiary sediments from the northern and central parts of the Atlantic Coastal Plain, Diagenesis is the most important of these mechanisms. Both syndiagenesis and epidiagenesis are required to explain the origin of all the diagenetic phosphate mineral species which occur in the northern and central parts of the coastal plain. Syndiagenesis produced much of the coastal plain's apatite. It was operative below the sediment-water interface while the substrate was being compacted. Compaction forced pore waters, which were enriched in phosphate by the decomposition of organic matter, upward through calcareous sediments. The PO43- radicle replaced the CO23- and calcareous nodules, pellets and shell fragments were converted to apatite. Epidiagenetic reactions occurred in the subaerial environment where downward percolating meteoric waters carried phosphate in solution to cites where cation activity was sufficiently high to form new minerals. Vivianite may form where ferrous iron is available and wavellite and variscite may form in the presence of aluminum rich minerals. Textural evidence suggests that many of the reactions were repeated. The present day appearance of apatite, vivianite, wavellite and variscite in the coastal plain may represent several generations of diagenesis.

Jan 1, 1972