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By K. Donahue

Clay minerals play an important role in the gravitational stability of man-made rock piles by affecting geotechnical and hydrological characteristics of the material. The Goathill North rock pile at the Questa Mine in northern New Mexico has been the focus of a multi-disciplinary study to determine the effect of weathering on rock pile stability and in particular to determine if clay minerals are forming in the rock pile due to surface weathering. The results of x-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicate the clay minerals found within the fine-grained soil matrix of the rock pile are of hydrothermal origins and did not detect any neoformation of clay minerals. The foremost mechanism for an increase in clay minerals within the rock pile is the physical break down of hydrothermally altered rock fragments to release hydrothermal clay minerals. The hydrothermal clay minerals within the rock pile show evidence of weathering by the dehydration of smectite from 2-water to 1-water interlayers within the clay mineral structure. This dehydration is most likely due to higher temperatures and low relative humidities in the Goathill north rock pile during surface exposure.

Jan 1, 2009

By Vladimir Admek, Paul W. Jeran, Michael A. Trevits

It has' been found that lithological conditions over the Pittsburgh Coal bed cause the subsidence coefficient to vary within the area of the subsidence trough. This precludes the use of European developed predictive models, which are based upon a constant subsidence coefficient. Regression analysis of the distribution of subsidence coefficients from 11 Bureau of Mines, U.S. Department of the Interior, longwall panel studies on the location relative to the edge of the panel has yielded a third degree polynomial equation. This equation has been incorporated into a BASIC computer program for use on a personal computer that allows users with no previous knowledge of the theory of subsidence to predict vertical movements over typical longwall panels in the Northern Appa1achian Coal Basin.

Jan 1, 1986

By Maurice Grieves

GC. Waterman Mr. Grieves' paper on "Shaft Sinking Today--A Boring Business Tomorrow" in the Dec. 1981 issue of MINING ENGINEERING is an excellent description of recent improvements in speed and costs of shaft sinking. However, shaft boring techniques are not a recent development. In 1935-36, the Idaho Maryland Co. (gold), Grass Valley, CA, bored the vertical 1.5-m-diam Idaho No. 2 ventilation and supply shaft to a depth of 346 m. The equipment was designed and perfected by Branner Newsome and was, I believe, described in "Transactions." Pickands Mather later bored a 1.8-m-diam shaft to a depth of about 305 m using Newsome's design. The Idaho No. 2 shaft cut through hard gabbro, diabase dikes, soft serpentine, very incompetent ankeritized serpentine and a strong fault zone. The completed shaft did not require timber support; the fault zone was cemented. Equipment consisted of a rotating 1.5-m or 3-m core barrel with a slotted bottom which cut a 76-mm kerf. The cutting agent was chilled steel shot introduced into the slot as needed. The driving mechanism and core barrel were lowered into the shaft, the former secured to the wall and the inshaft "engineer" operated the motors which controlled core barrel rpm and advance. After an advance of 1.5-3 m the equipment was lifted out of the shaft, a half(?) stick of powder cut off the drilled core, and it was hoisted to the surface with a cable attached to an eye bolt at the tope of the core. A "shift" consisted of three men: hoistman, equipment operator (down the shaft), and a surface laborer. Advance was variable as equipment and techniques were perfected. Near the end of the job advance was, as I remember, 1.5-3 m per shift. Costs were, as I recall, about $115/m. Up to 4 m cores were lifted out in one piece and swung to the dump by a stiff leg derrick. The Newsome equipment was relatively inexpensive to build and operate and his method should be (more than?) competetive with the methods described by Grieves. W.E. Hawes The author, in mentioning the South African developments of the cactus grab, ignores the parallel development of the Cryderman mucker in this hemisphere. Perhaps a slightly longer history of blind hold drilling would have been in order. Blind shaft boring got a major boost at the Nevada Test Site, as part of the nuclear weapons development, when it was essential to be able to quickly assess depth for weapons testing. One of the early civilian attempts to utilize this technology occurred when Kerr McGee drilled the shaft at the Section 19 Mine at Ambrosia Lake, NM. This twin masted drill rig belonged to a subsidiary of Kerr McGee, not Shaft Drillers. This was a difficult hole, due to bentonitic shales that decomposed. Later advances in drilling fluids eliminated this problem. The Conoco project referred to is not entirely correct, and needs minor amplification: The depth of the development (not pilot) shaft drilled was 684 m, at a diameter of 3.05 m, with a 2.16 m ID hydratatic casing being installed to a depth of 669 m. Conoco Inc., not Challenger, executed the drilling, however Conoco did use Challenger Drilling Company's Rig 14-S. Rig 14-S is unique in that it is specifically designed for shaft drilling, rather than being an oil field rig used for this service. All work was planned and directed by Conoco personnel. Deviation of the aforementioned shaft from vertical was 31 cm. Two smaller shafts (pilot shafts) were drilled with the same rig. These smaller ones were drilled 1.8 m in diameter, to depth of 665 m and cased with .91-m-diam casing, to depth of 650 m to be used as pilot holes for 5.5 m diameter shafts. The total elapsed time for all drilling, casing, cementing, and rig moves was 50 weeks. The constraints mentioned of vertical accuracy, torque, wall collapse, rig set up time, lining time etc., pumping out, etc., may not be as serious as the author implies. First, vertical accuracy: The record achieved by Conoco indicates that with reasonable care, good accuracy can be obtained, primarily by having a fair amount of weight in tension, rather than on the drill bit. Second, the amount of torque that can be applied to the drill stem has been greatly increased by the introduction of larger diameter drill stems, such as the new Hughes rig uses. Third, risk of collapse of shaft walls is minimal with the proper mud program. Basically, the walls are supported by the weight of the mud and it is not removed until some type of casing is installed and grouted in. Here in the real challenge of blind drilling shafts to devise a more economical method of lining bored shafts than using steel casing. The remaining issues were minor at Conoco, provided adequate planning and scheduling takes place. An excellent paper, "Shaft Drilling--Crownpoint Project" by Hassell H. Hunter, presented at the Fifth Uranium Symposium in Albuquerque in Sept. 1981 contains details of this project. A combination of blind boring, with enlargement by either mechanical means (boring machine, or tunneling type shield) or slabbing down, with muck removal through a larger bored shaft would seem to be the future trend in shaft development. The economics, especially for wet conditions, favor this concept over conventional sinking, as has been demonstrated at Kerr McGee --Churchrock, UNC--Churchrock and Conoco at Crownpoint.

Jan 3, 1983

By David Baughman, Steven Axen, Ray V. Huff, Donald H. Davidson

Introduction In situ leaching (ISL) is an alternative method of mining uranium from deposits that are low-grade, deeplying, and water-saturated. ISL recovers uranium by transporting fluids through rock rather than by moving rock, a concept the Chinese developed over 2000 years ago for water production. This technique eventually evolved into production systems for oil, gas, sulfur, and salt. More recently, in situ methods have been developed to produce shale oil, gasified coal, geothermal energy, uranium, and copper. ISL uranium operations began in the early 1960s with Sabine Production Co. in south Texas. About the same time, Utah Construction and Mining Co. (Anderson and Richie, 1968) started similar operations in Wyoming's Shirley Basin. During the 1970s, six commercial operations were started in south Texas, (USBM, 1978) and a number of pilot operations were in various stages of development in Colorado, Wyoming, and New Mexico. This paper reviews some of the technical and economic aspects of the ISL process and briefly discusses key subsurface engineering functions as¬sociated with well pattern design and operation. While flow characteristics of a deposit are of prime importance, the following information is also needed: Depth, ore grade, total contained metal, ore thickness, flow conductivity (permeability), void space in rock (porosity), mineral type and distribution, natural groundwater flow, and structural features. Solvent selection, which is important to the economic success of the operation, takes these factors into account: Composition, rate of metal solubilization, interaction with gangue minerals, impact on rock permeability, impact on materials of construction, trace metal solubilization, cost, availability, and handling problems. Overview of ISL An ISL operation consists of these functions (Fig. 1): 1. Chemicals to dissolve and maintain uranium in solution are prepared at the surface extraction facility. 2. A set of injection wells forces the solvent into rock pores of fractures using pressure in excess of the deposit's hydrostatic pressure. 3. Solvent travels through the rock and reacts with uranium minerals to dissolve them. The solvent usually consists of an oxidant and a complexing agent in an acidic or alkaline medium. 4. A set of production wells creates a low-pressure sump where metal-enriched solution is collected for transport to the surface. 5. The enriched solution is processed to recover uranium and to separate the leaching solution for recycling through the system. The economic performance of an in situ operation may be estimated by integrating these related factors: (1) the flow rate of solution processed through the system, (2) rates of fluid injection and production from wells, (3) the rate of mineral solubilization in the liquid phase, and (4) the volume of rock swept by the fluid. As these factors reveal, ISL involves the technical disciplines of petroleum engineering, ore deposit geology, and hydrometallurgical processing. Wellfield Design Just as mineral engineers use drillhole information to plan a conventional mine, in situ engineers use similar information to design a well field. A thorough knowledge of deposit geology and reservoir properties is required. Early application of pressure transient testing, such as

Jan 2, 1980

By A. Mahmoudkhani

Primary cementing is the process of placing cement in the annulus between the casing and the formations exposed to the wellbore. Portland cement was first used in 1903 in the Lopoc Field in California for well cementing. Since then, the major objective of primary cementing has always been to provide zonal isolation in oil, gas and water wells, i.e. to exclude fluid(s) in one zone from another zone in the well. To achieve this objective a hydraulic seal must be created between the casing and cement and between the cement and the formations, while at the same time preventing fluid channels in the cement sheath. This requirement makes primary cementing the most important operation performed on a well. Without complete isolation in the wellbore, the well may never reach its full producing potential. The industry knowledge on cements relies heavily on empirical data, but the chemistry, physics and structure of cement are not fully understood yet. The strength of concrete can be increased essentially by reducing its porosity through optimizing the size distribution of its components and filling the residual porosity of the hydrated cement phase with inorganic fillers. This approach has successfully utilized in different ways and several technologies for placing high performance oil and gas well cements have been developed over the last few decades. There are reasons to believe that the next source of improvement will lie in the fine-tuning of the hydrates themselves and of the different parameters that drive short (ionic?covalent bonding) and long (ionic correlation) interactions.

Jan 1, 2012

Remote methane detection State and federal regulations require frequent measurements to verify that safe methane levels are maintained in underground coal mines. Ventilation control is the primary means of maintaining safe methane levels. In the immediate face area, where the highest methane levels occur, methane measurements are required every 20 minutes during active mining. To perform these measurements, temporary roof supports must be erected. This allows a miner to reach the face. There a hand-held methanometer is used to make the measurements. This procedure is time consuming and potentially hazardous. To facilitate the measuring process and reduce the miner's exposure to roof falls, the US Bureau of Mines has developed a prototype optical device. It can measure methane remotely from distances up to 12 m (40 ft). The device uses two infrared signals, reflected from the coal face, rib, or roof. One signal is absorbed by the methane, the other is not. The ratio of the two signals determines the average methane concentration in the face area. The prototype detector has also been successfully tested at the Lake Lynn, PA Laboratory. Instantaneous responses were obtained for methane in the ventilation airflow and for methane layered near the roof. Conventional methanometers required from five to 25 seconds to respond to the methane in the ventilation airflow. They did not respond to methane in the roof layer. For more information about the Bureau of Mines' remote detection research, contact Richard W. Watson, US Bureau of Mines, Pittsburgh Research Center, Box 18070, Cochrans Mill Road, Pittsburgh, PA 15236 or call (412) 892-6630. Ignition suppression system The incidence has increased of fractional spark ignition at the mine face. One reason is the advent of mechanical mining. Another is the more difficult ventilation conditions associated with deeper and more extensive underground workings. To cope with the problem of frictional ignition, the Bureau of Mines initiated research to develop a system that would provide rapid detection of incipient methane-air ignition. Then, rapid dispersion of a quenching agent would ensure that the methane flame was extinguished while it was still relatively small. This concept was successfully demonstrated by suppressing explosions in the Bureau's Bruceton, PA experimental mine. But the bulkiness of the early storage-dispersal system proved impractical to retrofit onto face equipment. In a cooperative effort by the Bureau and the Mine Safety and Health Administration, a more compact system has been developed and is being tested. A continuous mining machine has been equipped with four 1.8-m-long (6-ft-long) and two

Jan 9, 1987

By G. L. Dollinger, J. P. Kindsvater, J. A. Gibson

DESIGN AND DEVELOPMENT OF A MOBILE MINING MACHINE INTRODUCTION Until recently, developing tunnels in hard rock has been accomplished either by the drill and blast method or by using large tunnel boring machines. Combining the flexibility of drill and blast with the safety, efficiency and productivity of a TBM has been the objective of mining machinery producers for many years. In 1979 The Robbins Company began developing a new type of tunnel boring machine called the Mobile Miner to meet these objectives. The development and testing of the Mobile Miner is the subject of this paper. CURRENT MINE DEVELOPMENT METHODS Both the drill and blast method and the use of a TBM have notable advantages and disadvantages. The drill and blast method, for example, allows much more flexibility, requires less setup time and has a lower initial cost than a TBM; however it requires the use of high explosives and blasting has a disrupting effect on the rock surrounding the development. A TBM, on the other hand, is safer to operate, more efficient, more productive and produces smooth tunnel walls without disturbing the surrounding rock. In longer straight drifts it will easily out distance the drill and blast method. The TBM, however, is limited to boring a circular cross section tunnel which must then be modified if a flat floor is required. It also has a higher initial cost and an extended setup period.

Jan 1, 1985

By V. G. Grechanyuk

The paper presents the mechanical properties of Cu-Mo composite materials depending on the molybdenum content. The influence of structural defects on the mechanical-physical properties of the condensates at stretching testing as well as of the lamellar grain dimensions upon the mechanical properties of Cu-Mo composite materials is also presented.

Jan 1, 2008

By Paul H. Johnson

Resource Engineering and Development, Inc. is desigining and building a portable 150 to 225 tpd, flotation-cyanide leach plant with unitized, skid-mounted components. This plant design, with its portability, low capital investment, and high recovery of silver and gold from many partially oxidized ores, is well suited to treat many small, highgrade deposits, old waste dumps, and old mill tailing piles. A description is given of flotation and/or cyanide leach tests run on 18 partially oxidized, newly mined ores; waste dump materials; placer slimes; and old mill tailings.

Jan 1, 1981

By P. Burmeister, R. A. Errath, A. Sapin

Sag Mills are becoming bigger in size almost every year. Concentrator plants are also becoming larger with more SAG and Ball Mills units with Gearless Mill drives installed in one plant. In contradiction to this development, concentrator plants are being built in increasingly remote areas, where the power supply and network conditions are not necessarily covering the needs for the operation of such plants. This paper describes sources of harmonic distortions and possible approaches to solve this problem. It also illustrates the permissible tolerances in terms of commutation of power electronics, based on already realized installations. Furthermore it explains how, and with which measures, harmonic currents created by non-linear loads with SAG and Ball Mill drives can be handled, and how harmonic standards can be fulfilled accordingly. Finally, this paper gives an overview about the technical impact of a strong versus weak network, and the economic relationship between them.

Jan 1, 2001

By I. A. Costa, Y. Fouquet, F. Barriga

"Lucky Strike and Menez Gwen are two hydrothermally active sites located along the border of the Azorean plateau, southwest of the Azores islands where the alteration processes affecting basaltic rocks are prominent (Costa et al., 2003). Here we report on a slabby brecciated rock, abundant at both Lucky Strike and Menez Gwen, composed mainly of basaltic fragments cemented by hydrothermal precipitates from warm fluid circulation system. Research reveals that hydrothermal alteration takes place mainly by replacement processes, in which silicification is dominant (Costa et al., 1997 and Costa, 2014).Petrographic observations, including scanning electron microscopy (SEM), microprobe analysis, and mass balance studies made on basaltic fragments within the breccia show that silicification is one of the main processes resulting from hydrothermal fluid circulation. This alteration process leads to complete replacement by silica, in extreme cases, forming an impermeable cap that may contribute to the formation of sub-seafloor sulphide deposits, including examples in the geological past."

Sep 1, 2014

By Ralph Spickermann

UK Seabed Resources (UKSR) signed a manganese nodule exploration contract with the International Seabed Authority on 8 February 2013 for a 58,000 km2 tract on the eastern edge of the Clarion Clipperton Zone (CCZ). UKSR is a private company based in the United Kingdom and established primarily to develop the commercial potential of the CCZ deposits. This is the first of many anticipated regulatory, market and technical milestones that are requisite for (1) environmentally responsible commercial scale production of nodule derived metals and (2) generation of revenue through their sale in the global commodities market. This presentation will describe the progress made to date in this effort and an industry-based perspective on the tasks and challenges that may lie ahead.

Sep 1, 2014

By L. Yuan

To reduce fire hazards from spontaneous combustion of coal in longwall gob areas, a series of computational fluid dynamics (CFD) simulations were conducted by National Institute for Occupational Safety and Health (NIOSH) to model the spontaneous heating of coal in longwall gob areas. The previous modeling results demonstrate that spontaneous heating of coal usually occurred behind the longwall shields and along the face with a bleeder ventilation system. Assuming a stationary longwall face, the spontaneous heating could turn to a spontaneous fire in several days for the most reactive coal under favorable conditions. When the longwall face advances, the spontaneous heating process will be significantly affected. In this study, the effect of longwall face advance on the spontaneous heating in the gob area is investigated using the CFD model developed in previous studies. One longwall panel with a bleeder ventilation system is simulated. The width of the panel is 300 m, while the length of the panel is changed between 1,000 to 2,000 m. The same permeability and porosity profiles are used for gobs with different lengths. The spontaneous heating first develops in the gob when the longwall face is stationary. Then, the face advances at a certain rate. The face advance is simulated as a series of discrete movements, and the effect of the face advance on the maximum temperature developed during the face stoppage is examined. Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

Jan 1, 2009

By Lloyd M. English

During the past 30 years, the research arena has changed significantly in all fields, mining included. The relative representation of the topics of research, how the research is performed and who has performed the research have all changed. Although there are a lot of subjective ideas and anecdotal "analyses" concerning these changes, there has been no actual study of these trends to verify the facts. This study was divided into six five-¬year periods for the purposes of comparison. Some of the trends analyzed are co-authorship, research areas, research sponsors and cooperative efforts. In today's research arena, 30 years is a long time. Technology has advanced more rapidly than in any time previously and that pace continues to increase. There are more researchers, more tools for research and an increasing number of companies, agencies and institutions engaged in research. The pace of change and its impact is often discussed and debated at professional meetings and in institutions that engage in research. These conversations will often influence the research decisions of the participants in directions to take or subjects to pursue.

Jan 1, 1995

By M. J. Gula, S. S. Xue, E. P. Horwitz

A study has been conducted to remove iron from sulfate solutions using Eichrom's Dipexo® extractant, P,P'-di(2ethylhexyl) methanediphosponic acid (H2DEH[MDP]). It is found that this extractant can effectively and selectively extract ferric ion from highly acidic solutions. Ninety-nine percent of the iron was extracted from a simulated feed solution in a single stage. The separation factor, Fe/Zn, was 106. Over 90% of the iron in a loaded organic can be recovered in an aqueous solution by reductive stripping. This paper presents the experimental results. A new process for iron removal using Dipex extractant is described and discussed.

Jan 1, 1999

By Douglas A. Anderson

Mine the Internet? You bet. Precious information resources are there to be found by those willing to explore. Of course, the stratigraphy and the exploration tools must be learned. This article is is designed to help learn those tools and how to find the information that can help the reader. However, beware the Internet. It can be addicting. On the other hand, information can be found that you never suspected. And users can make contact with people who might otherwise never have crossed their paths.

Jan 1, 1996

By J. S. Gardner, J. J. Zaluski

I. INTRODUCTION West Virginia has a long history of coal production.1 The state at one time led the nation in total coal production, while at the same time coal from West Virginia constituted one quarter of total U.S. coal production.2 In more recent years, however, West Virginia’s level of coal production has been reduced in comparison to that of other states due to the high relative cost of producing coal in the state.3 Another blow to the producers of coal in West Virginia is the action known as Bragg v. Robertson.4 In 1998 various individual plaintiffs, as well as a conservation group known as the West Virginia Highlands Conservancy, filed a civil action under a provision of the Surface Mining Control and Reclamation Act of 1977, Pub. L. No. 95-87, §522, 91 Stat. 445 (codified at 30 U.S.C. §§1201-1328) ("SMCRA" or the "Act") that allows declaratory and injunctive relief against state and federal officials for non-compliance with the Act.5 The plaintiffs generally claimed that the Director of the West Virginia Department of Environmental Protection ("WVDEP") had exhibited a pattern of violating mandatory non-discretionary duties under SMCRA and the West Virginia state regulatory program.6 These non-discretionary duties involved many areas of regulation, including water quality standards, disturbance of wetlands, hydrologic reclamation plans, Approximate Original Contour ("AOC") requirements and AOC variances, post-mining land uses, contemporaneous reclamation, and as explained later, the "buffer zone rule."7 In addition to these claims against WVDEP, the plaintiffs also alleged that certain individual members of the Army Corps of Engineers (the "Corps") had failed to carry out statutory duties under the Clean Water Act (the "CWA") and the National Environmental Policy Act ("NEPA").8 Generally, the complaint stated that the Corps did not have statutory authority under the CWA to regulate valley fills created for the purpose of the disposal of waste material, i.e., the overburden associated with mountain top mining.9 Alternatively, the plaintiffs claimed that even if the Corps could regulate valley fills, the Corps violated NEPA by issuing nationwide permits without required analysis. Finally, the plaintiffs asserted that the issuance of a nationwide permit for surface mining valley fills is unlawful.10

Jan 1, 2001

By Rodney K. Morrison

MARTA, The Metropolitan Atlanta Rapid Transit Authority, is building a 53 mile heavy rail transit system to serve the City of Atlanta. Phase A of the Rail System, consisting of approximately 14 miles of at-grade, aerial and subway construction is underway. Metropolitan Atlanta lies in the Piedmont Geologic province of Georgia and is underlain by rocks of essentially granitic and gneissic nature. The soils encountered are primarily silty sands which are in-place weathering products of the parent rock and exhibit their relic structure. In general, these materials have presented no unique construction problems other than those created-by proximity of manmade structures, local availability of ground water, and top of rock elevation. The subway sections of primary interest in this paper consist of hardrock and soft ground tunnels and extensive cut-and-cover sections. The cut-and-cover construction includes excavations as deep as 80 feet. Temporary support systems in these deep excavations consist of soldier pile-timber-lagging or soldier pile-tremie concrete (SPTC) walls with internal bracing or tiebacks. In shallow cut-and-cover sections, where right-of-way economics permitted, slopes were laid back partially or fully to reduce or eliminate the need for bracing systems. Dewatering systems were required in most open cut excavations. Due to the close proximity of utilities and existing structures to the MARTA

Jan 1, 1979

Narrow vein mining, with enough challenge and also where the cutting edge technology can be applied, is still a very important and exciting portion of the mining industry. Based on the deposit characteristics, the most flexible mining method, cut and fill, has been being tested mining this high grade Northern Nevada property, Hollister, since the year of 2008. In the last three years, 254,000 tons of ore were hauled out of the portal and 23,000 feet of development were excavated underground with the winning of several safety and environmental awards. Together with mine geology, the essential segments include mining cycle, ground control, ventilation, grade control and backfill method in cut and fill stopes were covered in this paper.

Jan 1, 2012

By Kerry Spickelmier

Editor's note: information for this feature was taken from the published APCOM proceedings. Computer trends, with special focus on the reasons for computer use, grabbed the lion's share of attention at the 23rd worldwide meeting on the Application of Computers and Operations Research in the Mineral Industry (APCOM 23). However, technical topics did not provide the meeting's sole focus. The last-minute inability of certain former communist countries to fund the travels of a few scheduled speakers was a reminder that science does not operate in a void. As with all technical progress, the APCOM presentations raised interesting questions regarding interrelated organizational dynamics and political and socioeconomic issues. Consider US Bureau of Mines (USBM) research to design an expert control systems to "duplicate" an experienced, "good" operator during automated underground roof bolting. In his presentation of the project, Takach, Jr. stressed the importance of preserving the ability to switch from automatic to manual drilling control. From a technical standpoint, this allows the expert system to "learn" from a good operator. As important, he said, is that this flexibility decreases the human operator's sense of being replaced by the machine. The question arises: Which will loom larger in union minds, increased operator safety through remote opera¬tion or the potential for total operator replacement? Like any new product, computer technology relies on marketing to aid its acceptance and use. Consider, too, a decision support system, by Schena and Gochin, for mineral resource management in a developing country. The authors said "the analysis permits the assessment of the overall socioeconomic consequences of mineral prospects and allows incorpo-

Jan 1, 1992