Search Documents

By R. W. Geehan

The Yellow Pine zinc-lead mine, situated about 3-1/2 miles northwest of Goodsprings, Clark County, Nev., was explored by core drilling during the fall of 1942 and the summer and fall of 1944 by the Bureau of Mines in cooperation with the Federal Geological Survey. The Yellow Pine district was located in 1855. The original claims covering the Yellow Pine mine were located in the following years: Rover, 1892; Hilo, 1897; Bybee, 1900; Radio and Como, 1906. The mine was operated by the Yellow Pine Mining Co. from 1906 to 1929. This company was dissolved in 1935. At a later date, S. E. Yount and the Security First National Bank of Los Angeles, Calif., acquired ownership of the mine. Since 1939, the mine has been operated in a small way by leasers. Production has been at least 175,000 tons averaging about 10 percent lead and 25 percent zinc, with a gross yield of $5,785,174. Virtually all ore produced by this mine consisted chiefly of oxidized zinc and lead minerals and came from long, pipelike shoots in the 100-foot thick Yellow Pine limestone. Ore shoots are sharply defined; elsewhere, the limestone is nearly barren. Numerous faults cut the mine into blocks. Ore is now mined in an open stope, but in the past, large tonnages wore mined in stopes by square-set methods. Ore produced recently was shipped direct to smelters unprocessed; in the past, it was milled by gravity and produced separate lead and zinc concentrates.

Jan 1, 1949

By Staff

One hundred thousand miles of flying over the North country without a single air casualty; much of it over virgin territory probably never before visited by white men; some of it over regions that abound with possibilities for minerals; all of it effective, for exploration and the establishment of bases and supply-stations, and for the carrying of men and their tools and provisions- this, briefly, is the record of Northern Aerial Minerals Exploration, Limited, a Canadian company organized Jess than nine months ago, which has been functioning, without interruption, during spring, summer, and now into winter. Our planes have ranged from the Alaskan boundary on the west to the Labrador coast on the east, and from the Transcontinental railway north to the Arctic circle. Our prospectors, carried on trips of hundreds, and occasionally thousands, of miles, have gone over large sections of country which were never before explored, and at the end of the prospecting season the Company finds itself in possession of several groups of important gold claims, which look most promising. In addition to this, we have been in contact with deposits of almost every known mineral.

Jan 1, 1929

By D. J. A. Chambers, J. M. Wempen, K. D. Koper, M. K. McCarter, K. L. Pankow

"The EarthScope Transportable Array (TA) of broadband seismometers (www.usarray.org) was deployed across southwest Wyoming from November 2007 through May 2009. During this time period the Array Network Facility (ANF, anf.ucsd.edu) detected and located a total of six seismic events near the trona-mining district. This lack of seismicity is atypical compared to coal mines employing similar mining methods. In this study, eighteen months of continuous seismic data from several nearby TA stations are reexamined using conventional and correlation-based methods to detect seismic events. Waveform cluster analysis and epicentral locations are used to discriminate between mining induced seismicity (MIS) and seismic energy generated from surface blasts at nearby coal mines. The locations and magnitudes of the 143 newly detected MIS events are compared to regional subsidence as measured by Differential Interferometric Synthetic Aperture Radar (DInSAR). INTRODUCTION An abundance of natural resources and a favorable political climate have made southwest Wyoming home to multiple large mining operations. Among these operations are five underground trona mines located approximately 50 km west of Rock Springs, Wyoming. The trona mines employ room and pillar, longwall, and solution mining methods over an area roughly 900 km2, and produce a sizable portion of the world’s soda ash (Brown 1995). Historically, in the Rock Springs mining district, several relatively large magnitude seismic events have occurred. These events are thought to have been related to mining activity and have caused notable subsidence (Case 1997). The largest event in the region recorded by seismometers, ML 5.1, has been confirmed as the 1995 Solvay Trona Mine collapse (Pechmann et al. 1995). In addition, blasting at surface coal mines near Rock Springs produces significant amounts of seismicity; approximately 50% of all daytime seismic events in the Mountain time zone from 2007 to 2009 locate near an active surface mine in this region (Astiz et al. 2014). Much of the current research related to surface subsidence and induced seismicity focuses on wastewater impoundment (Ellsworth 2013) and hydraulic fracturing. The observable seismicity in geological injection environments is widely variable and McGarr (2014) has argued that, in such environments, the maximum amount of seismic energy that can be released is proportional to the injected volumes. Like injection environments, in extraction (mining) environments seismicity is highly variable depending on many geological and operational variables (Boltz et al. 2012; Carnec and Delacourt 2000; Fritschen 2010; Iannacchione et al. 2005; Sen 2013) and does not always correlate well spatially with subsidence, a surface expression of extraction at depth."

Jan 1, 2015

By S. R. Stine

The Cyprus Thompson Creek Mine is located at 2,286m (7500 feet) elevation in the Central Idaho mountains, 61.16 kilometers (38 miles) southwest of Challis, Idaho off State Highway 75. The Thompson Creek molybdenum deposit lies near the eastern border of the late Cretaceous Idaho Batholith within a complexly deformed sequence of Paleozoic sedimentary rocks. Molybdenum mineralization is contained in a composite biotite granodiorite-quartz monzonite stock considered to be genetically related to the Idaho Batholith intrusive event. The ore is being mined by open pit methods and delivered to the concentrator stockpile with an overland conveyor belt system. The concentrator is designed as a 22,680 metric tons (25,000 ton) per day plant at an average head grade of 0.1% Molybdenum.

Jan 1, 1986

By Eric Eisold

The Wachovia Headquarters and Arts and Cultural Campus project in Charlotte, NC includes a 1.5 million square foot, 48-story office tower, two museums, an Afro-American cultural center and a 1,200 seat theater for the performing arts. Public access to the Cultural Campus is through two pedestrian tunnels constructed under city streets connecting to parking garages. The 5.7 m wide by 4.7 m high mined tunnels were procured through a design-build contract. The tunnels were designed as initial/final shotcrete linings with a sprayed water barrier sandwiched between layers of shotcrete. In addition, the mix design was supplemented with a cementitious admixture to develop internal water resistant properties in the shotcrete.

By A. J. Phillips, A. A. Smith, J. S. Smart

THE preparation of a sufficient quantity of high-purity copper for extensive laboratory use in the study of impurity effects has been an integral part of a research program in progress at the Central Research Laboratory of the American Smelting and Refining Co. for the past several years. Initially the degree of purity desired was that necessary to meet two essential requirements for experimental accuracy: (I) no impurity was to be present in the copper in an amount capable of producing a detectable effect on the properties to be studied, (2) even the minor changes in properties caused by the addition of extremely small amounts of individual elements were to be measured without significant interference from contaminants. In the course of the investigation, evidence has accumulated to justify the conclusion that this copper is of exceptional purity; in fact, no impurity can be detected by any chemical method or spectrographic technique known to the authors. The present paper describes the method of production of the copper and presents some of its properties. PREPARATION OF HIGH-PURITY COPPER The elimination of impurities from commercial electrolytic copper is accomplished by a three-step purification process. The first operation consists of an electrolysis through a purified CuS04-H2SO4 electrolyte using bagged anodes, low current .density (5 amp. per sq. ft.) and low temperature (25°C. max.). The electrolyte is prepared from commercial Cu2SO4 and is purified by heating the solution and adding I gram Fe as Fe 2(S04)3 to each 100 grams dissolved copper; sufficient hydrated oxide of copper, prepared from Cu2SO4 and NaOH, is supplied to precipitate Fe(OH)3, which carries down arsenic, antimony, tin, selenium, tellurium and other minor constituents. Silver and remaining traces of lead are removed by addition of Na2S to the acidified filtrate, which is then refiltered after standing hot overnight. The cold solution is made up to 30 grams per liter Cu and 150 grams per liter H2S04 and introduced without addition agents into the electrolytic system, which consists of a double row of hard-rubber battery boxes with the inside webbing and partitions removed, arranged in seven steps of ascending height. Electrolyte is uniformly supplied to the two highest cells by glass siphons operating from a constant-level reservoir, and flows by gravity through the bank of seven cells, entering each at the bottom and leaving at the top. Glass air lifts continuously supply the returning liquid to the constant-level reservoir for recirculation. Each cell contains three 434 by 43a by I-in anodes cast from high-quality electrolytic wire bar copper, various lots of which have been used with equal success. The anodes are pinned to sheet copper hangars shaped to prevent crawl of the electrolyte to the multiple-wired bus bars-which would result in fouling of the contacts and hang inside wool flannel bags stretched over open wood frames. The deposit

Jan 1, 1941

Many states rely upon the Pennsylvania 1957 “Gas Well Pillar Study” to evaluate the coal barrier surrounding gas wells (Commonwealth of Pennsylvania, 1957). The study included 77 gas well failure cases that occurred in the Pittsburgh and Freeport coal seams over a 25-year span. At the time, coal was mined using the room-and-pillar mining method with full or partial pillar recovery, and square or rectangle pillars surrounding the gas wells were left to protect the wells. The study provided guidelines for pillar sizes under different overburden depths up to 700 ft. The 1957 study has also been used to determine gas well pillar sizes in longwall mines since longwall mining began in the 1970s. The original study was developed for room-and-pillar mining and could be applied to gas wells in longwall chain pillars under shallow cover. However, under deep cover, severe deformations in gas wells have occurred in longwall chain pillars. Presently, with a better understanding of coal pillar mechanics, new insight into subsidence movements induced by retreat mining, and advances in numerical modeling, it has become both critically important and feasible to evaluate the adequacy of the 1957 study for longwall gas well pillars. In this paper, the data from the 1957 study is analyzed from a new perspective by considering various factors, including overburden depth, failure location, failure time, pillar safety factor (SF), and floor pressure. The pillar SF and floor pressure are calculated by considering abutment pressure induced by full pillar recovery. A statistical analysis is performed to find correlations between various factors and helps identify the most significant factors for the stability of gas wells influenced by retreat mining. Through analyzing the data from the 1957 study, the guidelines for gas well pillars in the 1957 study are evaluated for their adequacy for room-and-pillar mining and their applicability to longwall mining. Numerical modeling is used to model the stability of gas wells by quantifying the mining-induced stresses in gas well casings. Results of this study indicate that the guidelines in the 1957 study may be appropriate for pillars protecting conventional gas wells in both room-and-pillar mining and longwall mining under overburden depths up to 700 ft but may not be sufficient for protective pillars under deep cover. The current evaluation of the 1957 study provides not only insights about potential gas well failures caused by retreat mining but also implications for what critical considerations should be considered to protect gas wells in longwall mining.

Jul 28, 2020

By A. Basçetin

Equipment selection in mining engineering is one of the most important decisions that affects the mine design, production planning and economic parameters in open pit and underground mining. Mine planning engineers generally use their intuition and experiences in decision making. Mostly, linguistic variables (the weather is raining, soil is wet, etc.) come into question and decision-makers may not know how these variables are computed. Since the advent of the fuzzy set theory, these uncertainties are easily interpreted in the decision-making process. The development of computer technology and programming of colloquial language with expert systems have considerably reduced decision-makers? burden. This paper reviews the development of a computer programme software called EQS (EQuipment Selection) that automates equipment selection in mining engineering using fuzzy set theory. The EQS with an introduction of the concepts and theories of multiple attribute decision-making, the fuzzy set theory, and EQS applications to mining industry problems with case studies are presented

Jan 1, 2006

By Seyyed Mehdi Radeghi Mehrjou

The current work investigates the behavior of inclined micropiles under seismic loads. The dynamic finite element method (FEM) was employed. Rayleigh damping was applied to the soil, and elastic beam elements were employed to model the micropiles. The micropile structure was assumed to have one degree of freedom as a column with concentrated mass. The numerical modeling of micropiles was performed to explore the effects of their inclination on their seismic performance within homogeneous soils with uniform stiffness. In addition, the effect of soil stiffness was studied by considering various stiffness in soil depth. The results from the studies have shown significant effects on the dynamic amplification and internal seismic-induced loads of inclined micropiles.

Sep 1, 2022

By Bin Xu, Qian Li, Qiang Zou, Yongbin Yang, Long Hu, Tao Jiang, Xuefei Rao

The recovery of palladium from the chloridizing leaching solution of spent Pd/Al2O3 catalyst was studied mainly by sulfide precipitation tests and chemical composition analysis. The effects of key parameters including sodium sulfide concentration, pH, addition rate, temperature, and stirring speed on palladium precipitation efficiency are systematically investigated and optimized.

Mar 1, 2017

By G. I. Mathieu

Research and development studies were carried out at the Canada Centre for Mineral and Energy Technology to produce a synthetic forsterite sand from asbestos tailings for Les Sables Olimag Inc. The National Research Council of Canada also supported and collaborated to the project. Theoretically, the technological approach consists of a heat at over 1300°C; however, the process without additive would result in the production of an enstatite-rich product (MgSiO3) having a fusion temperature less than 1600°C. The purpose was to foster the formation of forsterite (Mg2SiO4), a more refractory compound. The fabrication of the forsterite product requires pre-agglomeration of serpentine-MgO with a binder, which is stable at high temperature, to prevent the loss of the powdered magnesium oxide as dust in the kiln off gases and to maintain the mixture homogeneous during the process. Characterization of the end products with respect to mineral composition and thermal resistance are described. The synthetic forsterite in sand form was tested with success under a bath of liquid steel maintained at 1700°C for up to two hours. The advantages of the new sand and its potential applications will be reviewed.

Jan 1, 1992

By C. Green, J. Uhrie, C. Filippone, A. Guzman

A central aspect of heap leach management and recovery optimization is solution control. Insofar as each heap is unique in physical and metallurgical properties, it is essential to understand the hydraulic parameters that control the migration of solution on a case-by-case basis. Water Management Consultants, as part of an ongoing research effort for Phelps Dodge Process Technology Center, have adapted techniques of parameter estimation for application to data typically resulting from metallurgical column testing. The parameterization is completed within the context of a variably saturated flow model that allows interpretation of available hydraulic information collected during hydrometallurgical column tests. A novel interpretation approach is introduced to extract the necessary hydrodynamic parameters from typical hydrometallurgical data sets. Results from the application of the approach to standard metallurgical test data will be presented together with a discussion of the application of information gained to the design and operation of a heap.

Jan 1, 2002

By E. D. Slone, F. L. Dillard

When a new mine is in the planning stages, one of the most important decisions to be made is the selection of' face haulage equipment and the interrelated transportation system to the surface. Equally important is the method of transporting personnel supplies and repair parts from the surface to the working places. When Bell & Zoller management elected to open the new Zeigler mine in the No. 9 seam near Madisonville, Ky., last year, various transportation systems were considered. It was agreed early that a slope mine would be preferred to a shaft mine, and that belt conveyors would be more economical than a rail system.

Jan 1, 1970

By Britt H. Hatfield, Jiu-Chiuan Chen, Wen-Ruey Chang, David C. Christiani

Occupational exposures to whole-body vibration (WBV) at different frequency domains may differentially affect human comfort and the musculoskeletal system. Under this presumption, a frequency-based weighting scheme has been adapted in many widely accepted standards for WBV measurement. However, there is very little human data showing a direct link between WBV frequency and musculoskeletal disorders. We conducted an epidemiologic study to examine the association between WBV frequency and prevalence of low back pain (LBP) and to identify determinants of specific frequencies associated with LBP in urban taxi drivers. Methods The WBV frequency data were collected from 247 professional drivers (aged 44.6±8.3) who participated in an exposure validation study 1 of the Taxi Drivers’ Health Study (TDHS) in 2000. 2 In accordance with the ISO 2631-1 (1997) methods, we measured the frequency-weighted acceleration over drivers’ seat surface, under conditions representing randomly assigned destinations. We developed a WBV record-replay system at the Liberty Mutual Research Institute (LMRI) in Hopkinton, MA, USA. This system includes two tri-axial accelerometers (PCB Piezotronics, NY, USA), one RD-130T PCM data recorder (TEAC, Tokyo, Japan), and one LMWBV meter 2.0 (LMRI, MA, USA). Only the vertical axis of seat-surface WBV frequency was used in this study. To characterize the WBV frequency curve, we manually identified the presence of any peak within each of the following frequency range: <4, 4-10, 10-20, and >20 Hz. Information about the operating vehicles and driving environment was either collected from the vehicle registration record (manufacturer, year of make, transmission, engine size, etc.) or directly measured (wheel-base length, seat inclination, etc.). Structured interviews were conducted by an occupational physician to gather information on LBP that had led to medical attention or absence from driving in past year. We used multiple logistic regression to estimate the prevalence odds ratio (OR) associated with the presence of each index peak frequency, adjusting for age, body mass index, professional seniority, daily driving hours, seat inclination, and the intensity of predicted root-mean-square WBV exposure in m/sec2. For any revealed WBV frequency that was associated with LBP, we constructed a multiple logistic regression model to identify the personal and vehicle characteristics associated with the presence of WBV peak within the indicated frequency range.

Jan 6, 2006

Capture airborne respirable dust generated by an auger-type continuous mining machine to reduce workers&apos; dust exposure. Approach Install a water-powered scrubber system, operating at 1,400 psi, on the sides of the conveyor. The scrubber draws the dusty air from the face area and discharges cleaned air into the face return. How It Works Auger-type continuous miners pose unique ventilation and dust control problems. To protect face workers from the dust, the end of the brattice is usually maintained close to the face to increase ventilation effectiveness. However, it is taken down as the machine cuts toward the exhaust side to allow the machine to complete its cut. Often, the brattice is not reinstalled in a position to most effectively control

Jan 1, 1989

By Aly Mohammad, Dongyi Yue

"The design of rock sockets for drilled shafts and piles proves to be a challenge for the Design Engineer. The magnitude of loads on the shaft and the behavior of the rock are critical in determining the required socket length. Several acceptable methods are available in the literature to analyze a rock socket under a combination of axial loads, lateral loads and moments. This paper will present a state-of-the-art methodology to analyze rock sockets utilizing deformation characteristics of the rock. This design methodology was implemented in the design of a major project in New York City.The project discussed herein is a marine transfer station planned for construction at East 91st Street along the East River in Manhattan. In order to support the piers and platform structures at a site with relatively shallow depth of the bedrock, rock sockets were required for the drilled shaft foundations. Rock sockets were utilized to provide the required fixity to the foundations and the structures. Acting at the top of the rock sockets are large shear forces and moments created by the lateral loads transferred from the structure.Upon review of the available techniques, a simplified method was proposed and used to analyze the rock sockets with a significant magnitude of lateral loading. The method recognizes two mechanisms through which the lateral shear and moment are transferred to the rock; a) load transfer through horizontal resistance of rock and b) the vertical shear resistance of the bond between socket and rock.The first load transfer mechanism was analyzed using the p-y curve method based on a rock model developed by Reese. The second was analyzed using a bond stiffness derived from the formula and curves utilized in the AASHTO Specifications for calculation of rock socket displacement. By comparing the two mechanisms, the main contribution to the large horizontal shear force that developed in the rock socket is identified.The paper will present a summary of the design methodology utilized in determining the length of the rock socket. It is believed that the presented method will provide substantial cost saving in selecting the most economical and efficient design length."

Jan 1, 2005

By John D. VandeKraats

Yielding rock bolt support systems have been developed to accommodate ground movement in shifting ground such as in coal operations; in creeping ground such as salt, trona, and potash; and in swelling ground associated with some clays. These systems, designed to remain intact despite ground movement, should enhance mine safety and help contain costs in areas where rebolting of rigid non-yielding systems is typically required. Four such systems were tested in straight tensile pulls in the laboratory. They include the Slip Nut System from Dywidag Systems International USA, Inc., Ischebeck&apos;s bolt mounted Titan Load Indicator, Rocky Mountain Bolt Company&apos;s Yielding Cable Bolt, and a rock bolt installed variation of the yielding steel post developed by RE/SPEC Inc. The first two systems are currently marketed products and the latter two are prototype systems. Each system responds to load and displacement by yielding in a unique manner. All are designed to yield at predetermined loads. A description of each system and its yield function is provided. Each system was tested over its prescribed yield range in a test machine. At least five tests were performed on each system. Each system yielded and continued to provide support according to its design. Each shows promise for ground control use in shifting or creeping rock. This work helps to illustrate the comparative differences in performance between these specialized systems and the applications where they may be most useful.

Jan 1, 1996

By Jean-Marie Fecteau

The gold mine sector is presently facing low gold prices as well as technological challenges. Its competitiveness and survival will depend on new mining methods and equipment to improve ore extraction. In 1999, Natural Resources Canada has invested new funds over a period of three years at CANMET?s Experimental Mine to establish the Narrow-Vein Mining Project. A team of engineers and researchers specialised in mining, mechanics and electronics engineering are working to meet the critical need of ore-extraction technology. CANMET?s program in mechanisation and automation for narrow vein mining had, prior to 1999, realised several important achievements, many in co-operation with a consortium of mining companies (Soredem). The investment of new funds in this area will contribute to develop technologies to improve the productivity, as well as health and safety conditions of the narrow vein mining industry. Several important impacts of this project will be monitored. Specifically, a database of methods and equipment used in narrow vein mining is being developed. A key thrust is to identify operators? needs with respect to the development and automation of mining methods and equipment. Based on those needs, research and development projects will be created. The main problems identified following meetings with mine operators are described with a few elements of solution and the Web site created for the broadcast of the results is presented.

Oct 1, 2001

By Alexander Field

THE rate of elimination of carbon largely controls the time required to make a heat of steel by the basic open-hearth process and to an important degree determines the cost of refining. Practical experience has led to the generally accepted belief that the use of slags relatively high in iron oxide, such as are required to bring about rapid refining, leads to a certain sacrifice of quality in the product. As a consequence, a compromise must be made between the exceedingly slow rate of carbon drop which would correspond to the ideal case and the rapid rate which would best satisfy the condition of minimum cost. An increase in rate of refining necessarily implies an increase in the concentration of iron oxide dissolved in the metal. However, even for the infinitely slow rate that corresponds to slag-metal equilibrium, the metal would contain a certain definite concentration of dissolved iron oxide. It is a matter of great practical importance, therefore, to determine the quantitative relation between the minimum or equilibrium concentration of iron oxide in the metal and the higher concentrations which must actually obtain in practice. The present paper is devoted to the development of certain equations, derived from the established laws of physical chemistry, which will enable this relation between rate of refining and the degree of oxidation of the metal bath to be computed from operating data. No attempt is made to exhaust the possibilities of this general method of treatment. In considering rate of refining, attention is mainly confined to rate of carbon elimination. However, the equations are of a more general nature and their application may readily be extended. The results of the preliminary calculations given herein indicate that increased rate of refining may have a decided effect in increasing the concentration of iron oxide dissolved in the metal. The uncertainty. which attaches to the calculated value for this relationship arises in part from probable errors in experimental data on which the calculations are based, and in part from the lack of complete or favorably disposed information on basic open-hearth practice.

Jan 1, 1928

By Francis S. Kendorski

INTRODUCTION Caving offers the lowest cost per ton of any large-scale mining method, but its successful application demands an ore body that conforms to several rigid requirements. The deposit must be of wide areal extent, massive and not spotty in ore values, and insensitive to ore dilution. It must also be a rock mass that breaks up readily. There are only three active caving operations in the US-Climax, Henderson, and San Manuel-but caving methods have recently taken on new importance as deeper lower grade mineral occurrences and ore bodies are found. These deposits are too deep for surface min¬ing methods, and too low grade to support any type of underground mining except a bulk method such as caving. Announced discoveries or indications that may be amenable to caving include: Climax&apos;s Mt. Emmons molybdenum discovery in Colorado; Molycorp&apos;s Goat Hill molybdenum prospect in New Mexico; the Phelps Dodge molybdenum deposit in Beaver County, UT; Arizona copper occurrences such as Asarco&apos;s Sacaton, Hanna&apos;s Casa Grande, Noranda&apos;s Lakeshore, and Ken¬necott&apos;s Safford; Anaconda&apos;s suspected deep copper de¬posit in Butte, MT; Anaconda&apos;s Carr Fork, UT, deposit; and perhaps others. CAVABILITY&apos;S ROLE IN FEASIBILITY STUDIES Caving is a system of underground mining which removes support from underneath an ore body. As a result, the rock mass fractures, fails, and flows vertically downward by gravity to be collected in previously ex¬cavated funnels. Types of ore that have been mined by caving include molybdenum, copper, iron, nickel, as¬bestos, and diamonds (Julin and Tobie, 1973). It is primarily a large-scale method, with production rates of more than 45 300 t/d (50,000 stpd) having been achieved. However, the initial capital investment before return is very high, often in the hundreds of millions of dollars. The cavability of an ore body or mineral occurrence is a critical item in the feasibility study of a proposed mine, not only from the point of overall minability, but from the point of impact on other costs such as blasting, loading, hauling, crushing, and grade recovered. Aside from the often-asked question of, "Will it or will it not cave?" the real questions are, "Can we afford to make it cave, carry the rock away, and extract the mineral?" The last is not a topic of this chapter, but the first two are. The cavability of an ore deposit or mineral occur¬rence is based on many things, but clearly, if a large enough area is undermined, any rock mass will cave. The result could be a violent collapse as occurred at Urad, CO (Kendrick, 1970), or perhaps the rock mass will cave beyond the ore boundary. Another unfavor¬able result could be ore blocks that are too large for the equipment and orepasses to handle without considerable secondary blasting. Weak rock with numerous fractures may produce a very fine ore when it caves, resulting in dilution and ground control problems. DETERMINING STRUCTURAL DOMAINS It has long been recognized that the geologic nature of an ore body is important to cavability (King, 1946). Such items as weak rock material, intensity of fractur¬ing, and severity of faulting all contribute to the success of a caving operation, and information regarding these is required as a minimum for the cavability determination. In practice, the rock mass-defined as the blocks of intact rock together with the intervening fractures, joints, faults, bedding planes, and other discontinuities-that contains the ore body, as well as the surrounding and overlying rock, must be examined in a systematic and detailed fashion. Surficial geology maps must be pre¬pared, exploration holes drilled, and core logged for en¬gineering information. The fracturing of the rock mass must be studied to ascertain the three-dimensional dis¬tribution of fractures and their characteristics, and faults must be located and described. The strength and other mechanical properties of the rock material, the fracture surfaces, and the fault filling materials must be tested and reported for later use by designers and planners. With this basic information and an understanding of the geologic setting, the rock mass can be divided into one or more structural domains which tend to behave similarly in response to engineering activities (Robertson and Piteau, 1970). One must keep in mind that the determination of the structural domains goes beyond the geologic units present. Several lithologic units may be lumped together, while a single lithologic unit can be divided into multiple domains. Major faults often form their own domain, and the direction of engineering ac¬tivity-for example, cave advance to the north rather than the south-may alter rock mass behavior, resulting in different domains. As an example of the detailed rock fracture map¬ping required for such studies, the structural domain determinations at the Climax mine (Kendorski, 1973) are shown in Fig. 1. The circles are Schmidt equal area projections of the three-dimensional attitudes of frac¬tures (Ramsay, 1967) mapped in detail at various rock exposures. The attitude of fractures is important to the cavability determination since it dictates the directional behavior of the rock mass as it fails, and determines the effectiveness of arching, keying, and rock block inter¬locking. Low-angle fractures must be present to allow movement of the rock in the vertical direction during undermining (Mahtab and Dixon, 1976); if low-angle planes of weakness are absent, the rock mass may arch with a keystone effect, rather than moving vertically downward.

Jan 1, 1982