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By Louis P. Gignac

The Lac Shortt gold deposit is located in Northwestern Quebec, at some 115 km west of the Opemiska Division and 380 km northeast of the Lac Dufault Division, as shown on Figure 1. Falconbridge's exploration crews drilled the first six holes in the gold-bearing ore zone in 1979. After further diamond drilling from surface in 1980, the decision was taken to carry out an underground exploration program. A three-compartment shaft was sunk to a depth of 340 metres in 1981 and 1982; it was followed by an extensive exploration program, which included 1073 metres of cross-cutting and footwall drifting, 645 metres of ore drifting and 11 200 metres of diamond drilling. The underground work was completed by mid-winter 1983. It was followed by a complete feasibility study of the Lac Shortt Project. After some $Can 14.2 millions in exploration expenditures, the Board of Directors of Corp. Falconbridge Copper approved in July 1983 additional expenditures of $Can 45 millions to bring the Lac Shortt Mine in production at the capacity of 261 000 tonnes per year. Gold price was $US 425 per ounce at the time.

Jan 1, 1985

By A. Mukherjee

This paper presents an analytical technique for prediction of the damaged rock zone (DRZ) around a circular drift subjected to an anisotropic stress field (analytical solution exists only for the case of hydrostatic stress field). The method can readily be adapted to micro or personal computers. Stress concentrations around the drift are calculated at the centers of small rock elements, using the analytical solutions for a hole in an infinite plate. Potential failure of a rock element is assumed to be governed by the Coulomb failure criterion. When the failure condition is exceeded for an element, the excess shear stress is transferred to the neighboring elements. Progressive failure is allowed to occur until convergence is obtained. The final configuration of the damaged rock zone so obtained can be used to assess rock support requirements, as well as modified modulus and permeability of the DRZ.

Jan 1, 1988

By Fred W. Stuart

Microprocessor technology has revolutionized the business community by placing tremendous computing power in the hands of the end-user for a very inexpensive price tag. The range of applications covers process control, to office automation, to personal computing capabilities. With the influx of this new technology, which these systems have to offer, also comes some unique operational and control considerations. But before we address these items, let us lay a foundation of common terms to be used throughout this presentation. Due to the rapid advances in microprocessor technology, where a new generation of computers is announced every two or three years, it becomes difficult to define a microprocessor system and have it valid for an extended period of time! Therefore, for this presentation, we will be dealing with a subset of microprocessors called Personal Computers or PC's. At the heart of a PC is a Central Processing Unit or CPU. The CPU performs the actual program and command execution. The programs dealing with driving the various peripheral equipment is referred to as the Operating System (for example: DOS : Disk Operating System, CP/M - Control Program/Microcomputers, etc.). The CPU is normally housed in an enclosure which contains power regulators, peripheral equipment interfacing 'cards', and expansion 'slots' to enlarge the capabilities of the PC system.

Jan 1, 1989

By Jerzy F. Sobala

Large - scale tests at the Polish Safety in Mines Institute /established in 1925 as "Barbara" Experimental mine/ performed in underground and surface experimental galleries, simulating conditions in roadways in mines, are the basic source of knowledge about development and propagation of explosions. Investigations up to 1973 were performed under the Institute's former research director Professor W.B. Cybulski s supervision, whose handbook concerning combating of coal dust explosions in collieries has been also published in the U.S. (2), and are continued until now. For investigating explosions the "Barbara" Mine disposes of 170 m /7.5 sq m/, 200 m /5 sq m/ and 400 m /7.5 sq m/ underground gallieries as well as of 10 m, 25 m, 44 m and 100 m surface galleries. For example, in the 200 m gallery more than 5200, and in the 400 m gallery - more than 2200 test explosions have been performed. Basing on determination of explosion hazard in roadways in collieries and on data of scientific research performed at the Safety in Mines Institute, the strategy of combating the explosion hazard in mines was elaborated; it includes mainly diminishing of coal duet. deposition in roadways, and -because of the possible inefficiency of this safety means in some roadways in mechanized collieries -- the introduction of three additional defence lines against coal dust explosions. It should be mentioned that at the "Barbara" Mine the problem of coal dust explosion initiation was elaborated as contract work for the U.S. Bureau of Mines. The main aim of this paper is to discuss some aspects of methods and measures for combating coal dust explosion hazard in highly mechanized mines in the Polish mining industry where in some roadways explosible coal dust is present, but it is not the aim to evaluate the effectiveness of methods and measures for diminishing the make-up of coal dust and coal dust deposition rates in roadways.

Jan 1, 1980

By Ronald R. H. Cohen, Margaret W. Staub

Two pilot scale bioreactors designed to treat acid mine drainage primarily using sulfate reducing bacteria were constructed underground at the Eagle Mine Superfund site in Minturn Colorado. The project was designed to test th applicability of microbiological treatment on water with high metals concentration and to test the process in an underground environment. Objectives were, 1) to compare metal removal, pH increase, and sulfate reduction in a single stage reactor with a double stage reactor of equal volume at varying flow rates; 2) to determine where within the substrate treatment occurs· and 3) to examine volume versus surface ara as a design parameter for optimizing metal removal processes. Results from the reactors showed that the single stage reactor and double stage reactor performed equally well for the removal of Cd, Cu, Pb, Fe, Mn, and Zn. pH increased above 6.5 in both reactors. Greater than 97% of metals were removed within the first ten inches of substrate. Volume proved to be a more useful parameter for determining removal rates than area. Using volume as a design parameter rather than surface area enables PMDT systems to be constructed as packed columns rather than broad wetlands, Thus, space requirements are significantly reduced.

Jan 1, 1993

By MOHAMED WAEL, ANASTASIA GOEVA, ABDULAZIZ TAWFEEQI, IHTISHAM TARIQ, S. M. ZAKIR HOSSAIN, NIAZ ALI KHAN, MUHAMMAD FAISAL IRFAN

Carbon dioxide (CO2) mineral carbonation is a carbon capture and storage (CCS) technique that can sequester CO2 permanently in the form of durable carbonate minerals. Extendable permanent storage capacity — onshore and offshore storage reservoirs — and the exothermic nature of the mineralization process make this technique attractive [1]. In the present study, maximum carbonation efficiency for aqueous mineral carbonation was achieved through two steps: optimization of calcium leaching from cement kiln dust followed by the reaction of pure CO2 with the calcium hydroxide precipitates formed by hydroxylation using sodium hydroxide (NaOH). Optimization of calcium leaching is highly important, as it is a rate-limiting reaction step in mineral carbonation and also influences and enhances the carbonation efficiency. To maximize the calcium leaching as well as carbonation efficiency, response surface methodology — with either Box-Behnken design or central composite design — was applied. It is the most well-known statistical, fully randomized and bias-free method for determining optimized conditions using quadratic regression models.

By K. Sasaki, T. Murakami, S. Akibayashi, Q. Wei

A numerical analysis and an experiment were done on groundwater flow past a bore hole with a cylindrical obstacle at its center. Flow around the obstacle in the bore hole was studied in detail. Two dimensional governing equations to simulate this flow were written for the hydraulic head and seepage velocity in a porous medium and for the vorticity, stream function, and velocity in the bore hole. These equations were non-dimensionalized and solved by using the alternating direction implicit and successive-over-relaxation finite difference methods. Flow visualization experiments and velocity measurements in the bore hole were done with a two dimensional model composed of a porous medium. The numerical analysis procedures were validated by a comparison of numerical and experimental results. Effects of the Reynolds number and obstacle size on flow in the bore hole are clearly shown in the velocity and streamline profiles. The quantitative relation between the seepage velocity in the porous medium and the velocity of flow around the obstacle in the bore hole also were estimated.

Jan 1, 1996

By Connie Travers, Ann Maest, James Kuipers, David Atkins

The science of predicting future water quality at hardrock mine sites has been practiced for at least the past 30 years. As part of the National Environmental Policy Act (NEPA), mines and other industrial facilities in the United States on federal land are required to estimate impacts to the environment, including direct impacts to water quality and indirect impacts that are later in time but still reasonably foreseeable (Kempton and Atkins, 2000; Bolen, 2002). Facilities on private land in the United States may also be subjected to State or federal processes that may or may not require prediction of potential impacts to water resources. Other countries have followed a similar approach, largely based on the requirements of NEPA. A wide array of scientific approaches has been used to predict water quality that could result from construction, proposed expansion, or other action at an industrial facility. In this study, we review the methods and models used to predict water quality at hardrock mine sites, with an emphasis on uncertainties associated with these techniques. Because water quantity and quality are interrelated, methods and models used to predict water quantity will also be discussed, but the emphasis will be on how these methods relate to water quality. This study brings together technical information on water-quality predictions at mine sites in a single paper, and attempts to present a straight-forward approach to using and evaluating the results of the methods and models used to predict water quality at mine sites. Approaches developed primarily in the United States, Canada, and Australia and applied in these countries and in other parts of the world, especially in the last 10 years, are discussed, and the format of the study is geared toward use by regulators of hardrock mines. The approach and results of this study could also be used by environmental managers at mine sites and community groups, and allows for the creation of a checklist for prediction methodology used at mine sites.

Jan 1, 2005

By Yi Luo, FENGLIANG WU

Mine gob has long been a safety concern in the coal industry due to the air flowing through the gob area. Therefore, knowledge of the airflow distribution and locations of hazard zones in longwall gob is important to prevent and control these hazards. Due to the inaccessibility of mine gob, many numerical studies have been performed to simulate gob air leakage using computational fluid dynamics (CFD) programs, but most of the studies isolated the gob from the mine ventilation network (MVN) with only predefined pressure boundary conditions. The MVN is, in fact, not static in a dynamic longwall mining process, and it consequently changes the boundary conditions and the gob flow field (GFF). Therefore, the MVN should be incorporated in the CFD model to prescribe the transient boundaries. However, it is very challenging to couple the 1D MVN and the 2D/3D GFF to make the mine ventilation simulation realistic. This research uses a proposed novel finite tube method (FTM) to couple the MVN and GFF. In the FTM, the GFF is discretized into a finite number of flow tubes, each of which is formed by two adjacent streamlines. These tubes connect the MVN into a new coupling network. Based on the FTM, a model for gas migration in gob is established for delineating the hazard zones of explosive methane concentration and spontaneous combustion.

By BEN WANG, HAORAN LI, YALI FENG, JINRONG JU

Acidic wastewater is at present directly neutralized with lime or limestone, which wastes resources such as titanium, scandium and iron and generates a great deal of solid waste. This study proposes a novel approach for the separation and recovery of titanium, scandium and iron from acidic wastewater, and utilization of red gypsum. The proposed process not only recovers valuable metals from acidic wastewater but also treats the red gypsum that has previously been dumped.

Aug 1, 2022

By Alberto Tarsitani

The existing Rome-Florence railroad capacity is inadequate for the traffic volume. To increase this capacity and to reduce the traveling time the Italian National Railroad Administration has decided to provide an additional 400% of rail capacity. This new rail line will be known as the Direttissima Roma-Florence line. It is planned to operate the trains on this connection at speeds of 250 km per hr. Table 1 lists the main design characteristics. [TABLE 1. Design Characteristics Design speed250 km per hr Maximum inclination80 00 (0.8%) Minimum curve radius3000 m Minimum vertical curve radius30,000 m Maximum superelevation in curve 425 mm Type of rail60 kg per m welded] The new rail line will be connected to the existing one by means of high speed switches called "interconnections" so that parts of the new line can be used also by local trains. Construction works for this new line have been divided by the railroad administration into eight sections. Five of these have already been committed to joint ventures. Castiglione Tunnel is a part of the fifth section, 42 km in length, which has been awarded to Consorzio Ferrofir which is a joint venture composed of the construction firms of Astaldi - Di Penta - Lodigiani - Sogene.

Jan 1, 1974

By Frank E. Kottlowski

Widespread high-calcium (HC) limestones in New Mexico and adjoining areas, are low in magnesium, but some units include shale interbeds that would be deleterious for usage in sulfur removal. In southwest New Mexico, southeast Arizona, and adjoining parts of Mexico, limestones in the thick Mississippian Escabrosa, Pennsylvanian-Permian Horquilla, and Cretaceous U-Bar units are HC as are strata in the Mississippian Lake Valley, Pennsylvanian formations, Permian Hueco, and parts of the Permian Capitan Limestone of south-central and southeast New Mexico and west Texas. In north-central and central New Mexico, many limestones in the Pennsylvanian Madera Formation are HC as are some of the Cenozoic travertines. In northwest New Mexico, where the present-day mine-mouth coal- fired power plants occur, there are no HC limestones, but to the north in southwest Colorado some beds of the Mississippian Leadville Limestone and Pennsylvanian Hermosa Formations are HC. HC limestones considered contain at least 95 percent calcium carbonate and less than 3 to 5 percent magnesium carbonate. Limits for other impurities are alumina, 1 percent; silica, 2 percent; sulfur 0.05 percent; phosphorous, 0.02 percent; and iron oxide, about 1 percent. Chemical and physical requirements differ slightly depending upon the ultimate use.

Jan 1, 1995

Throughout the 1970s, the US Bureau of Mines rode an ebb tide in Washington political circles. In rapid fire succession, the agency lost its mine health and safety enforcement responsibility (1973), a large portion of its energy research responsibility (1975), and then its fuel statistics functions plus a sizable portion of its coal R&D (1977). By 1978, johnny-come-latelies in the Energy, Labor, and Interior Departments had siphoned away from the Bureau some $125 million in program responsibilities as well as 900 of its employees. The bruising decade came to a close with a Department of Natural Resources proposal that, in its original form, would have scattered the Bureau’s responsibilities to the winds. There is no doubt in my wind,” said Lindsay Norman, acting director of the Bureau of Mines (see box), “that were the Bureau to continue down the path it was on, the next step was closing the doors and going out of business.” The doors are still open, but erosion of responsibilities had a devastating effect on the resources available to fulfill the Bureau’s mission. Devastating,too, in terms of internal morale, considering the Bureau had six directors in a 10-year span. “When the troops are in the trenches and are being shot at,” Norman said, “they need a leader—hopefully, a permanent one— that can get them advancing. This is something the Bureau did not consistently have in the 1970s.” In September 1978, Roger Markle climbed aboard as director of the Bureau to rejuvenate the 70-year-old agency. He resigned only six months later* but the program Markle set in motion is being carried through by Lindsay Norman. Since Norman’s appointment as acting director, he has spent considerable time on the road explaining his agency’s redefined goals. At one such stop in Duluth, Norman and his two deputy directors, Charles Kenahan and Mike Kaas, answered the following questions.

Jan 6, 1980

By Jorge Lanza

SUMMARY La Granja copper deposit, in terms of volume, is among the five largest deposits in the world and represents reserves of three thousand million tones. The field consists of a 40 m. thick layer of copper lying over the secondary ore and further down the primary copper. The flotation process has indicated a recovery rate of 88 to 90 percent and concentrates of 27 to 32 percent of copper. The acid leaching process of low grade ore produces financially acceptable results. To carry out the project, it is necessary to build long distance pipelines and a port. Both the Feasibility Study and the Environmental Impact Study on the project have been approved by the Peruvian government. INTRODUCTION La Granja is located in the district of Querecoto, province of Chota, in the department of Cajamarca, in the Northwest of the country (Figure 1). Geographically it is situated on the eastern slopes of the Andean mountains at an altitude of 2,000 to 2,700 m.a.s.1. (Figure 1). The site is an 8 hour car ride from the city of Chiclayo, capital of the department. The first 60 km. are over a paved road and the remaining distance is over a narrow hard dirt road. The copper porphyry of La Granja was discovered between 1969 to 1971 during some geochemical prospecting activities carried out by the State mining institution, Ingeomin (currently Ingemmet). From 1978 to 1982, Ingemmet continued with its geochemical and geophysical studies supported by a German technical assistance program. A total of 19 bore- holes were drilled (5,814 m.) and a 90 m. long tunnel made. This study calculated reserves of 175 million MT. In 1993, Minero Peru drew up a technical-financial study based on the above studies and proposed a 12 year extraction operating program: 20,000 MT daily using the leaching process, followed by 13 years of operation using the flotation process with the same daily volumes. In 1994, Cambior Inc. won an international auction in order to carry on further exploration work and to have a purchasing option. Since that date the company

Jan 1, 1998

By I. E. Odom

An electron optical and microprobe study was made to determine the physical and chemical nature of the silica minerals that occur as natural impurities in bentonite and montmorillonitic fuller&apos;s earth clay products (both granular and powder) and that occur in <10-µm dusts from plants that process these products. The purpose of the study was to determine if discrete "free" silica minerals, such as quartz, could be observed using SEM and EDS methods. No “free" silica minerals could be observed in the SEM images of the granular and powdered products, either among or on the surfaces of the particles. Also, no “free" silica could be identified by either SEM or EDS analyses of the dusts, even though quantitative X-ray diffraction analysis indicated that trace amounts of quartz occurred in all samples. It was determined that these quartz and other silica minerals were encapsulated or coated by montmorillonite. Vigorous washing, however, removed some of the clay coatings, so that small amounts of silica minerals could be seen by SEM and EDS analysis. It was found that all primary crystalline quartz grains in the bentonites have diagenetic overgrowths consisting of a mixture of montmorillonite, opaline silica and possibly microcrystalline quartz. Detrital quartz grains in the fuller&apos;s earth have thin diagenetic overgrowths of opaline silica, also containing montmorillonite. The clay encapsulation of the silica minerals in the products studied, as well as in the potentially respirable (<10-µm) dust produced during manufacturing of bentonite and montmorillonitic fuller&apos;s earth clay products, is considered to be an important factor influencing the potential health effects (e.g.. silicosis) of the contained silica. Even if clay dust containing silica should be inhaled, the montmorillonite encapsulating the quartz and other silica minerals would prevent direct contact of the silica with lung tissue. The clay encapsulation of quartz, as well as the highly hydroscopic nature of montmorillonite, may explain why not a single confirmed case of silicosis has ever been reported among plant workers in more than 65 years of production.

Jan 1, 1998

By O. J. R. Baena

Mining activity in the Segovia region in NE Colombia is the main source of employment in the local economy. This has created major problems of illegality and informality mining associated with a high social and environmental impact, as inefficient technologies are used and high consumption of toxic substances required in the process of gold recovery by amalgamation and cyanidation. In this work is presented mineralogical characterization of six local mills and studied beneficiation processes developed in them. With the results presented a proposed plant design that eliminates the use of mercury by replacing gravity concentration processes taking advantage of the characteristics of the treated material. Significant results were obtained regarding the recovery of precious metals and present a methodology that can be replicated in other mineral beneficiation plants that use gold amalgamation processes. This implies a significant reduction in mercury use and decreased risk of human contamination associated with this.

Feb 23, 2014

By Sidney M. Cohen

[Portland cement is a product made from a combination of limestone and argillaceous material which would supply the necessary amounts f calcium, silica, alumina and iron to form cementious compounds when fired at high temperatures. The resulting mixture, usually around 80% limestone and 20% argillaceous, is ground nine (80% -200 mesh), blended and then fired1 (2600-2700°F) to produce a cement clinker from which the final cement product is produced by grinding. The argillaceous component can be shale, clay, slate or other sources of the individual components of silica, alumina and iron. This paper deals with a case where a clay component was under consideration. The planned Plant site was to be located at a well defined limestone deposit. When it came to the argillaceous component, the nearest uniform deposit of clay was over 50 miles away and would require purchase of land or clay from the owner plus the daily delivery costs to the plant site. This situation made the plant site economically questionable. It was decided that a local clay deposit, which was available at the plant site but was orginally not considered due to lack of chemical uniformity and its high free silica content, would be reconsidered.]

Jan 1, 1983

By Gus H. Goudarzi

The apatite deposits in east-central Bahia, Brazil, are about 50 km east of Serra do Jacobina, between lat. 11° and 12° S. and long. 39°40&apos; and 40° W. Apatite was found and examined at 15 localities in a mineralized belt that strikes about N.25° - 30 W. over a distance of about 100 km, but the size of the deposits has not yet been determined. Rocks of the region consist of a sequence of Precambrian migmatites and quartz feldspar paragneisses containing units of pyroxene-rich rocks, lenses of sillimanite-bearing quartzite, amphibolite zones, and calc-silicate marble lenses. Pegmatites and granites of probable anatectic origin (anatexite) are abundant. Faults are numerous. Clastic sediments of Tertiary and Quaternary ages cover most of the area; thus, outcrops of the Precambrian rocks are sparse. Trenches and pits have exposed mineralized zones as much as 10 m wide at some localities within the region. A layer of apatite at least 1 ½ m thick is exposed in a trench at Lagoa do Mel. At Rio do Peixe, vertical shafts have penetrated a mineralized zone, to a depth of as much as 13 m, of which about 25 percent is apatite. Apatite is massive or forms minute crystals, stringers, and disseminated grains in alkalic host rocks. At Apolinario, euhedral crystals of apatite are as much as 50 cm long and 30 cm in diameter. Associated minerals include vermiculite, biotite, scapolite, opal, chalcedony, epidote, montmorillonite, chlorite, kaolinite, sericite, magnetite, and limonite. Apatite is everywhere intimately associated with pyroxene-rich rocks, alkalic syenite pegmatites, and alkalic granite pegmatites. At Panelas-Retiro, apatite is associated with pegmatites, crystalline calcite (vein calcite), vermiculite, and pyroxene-bearing rocks. Analyses of samples show that the apatite is radioactive and rare-earth-bearing. Traces of vanadium and titanium were detected by spectroscopic analysis. The apatite was probably derived from phosphatic zones in the original Precambrian sedimentary rocks and has been crystallized and some mobilized by high-temperature regional metamorphism (higher amphibolite facies) into veins, pegmatites, and along certain preferred beds and fractures. Radiometric and geophysical surveys, in addition to conventional geological investigations, are planned to further investigate the nature and economic potential of the deposits.

Jan 1, 1972

By F. D. Fox

Abandoned mill tailings deposits can be found scattered throughout the Northern Black Hills of South Dakota, indicative of past mining activities that originated during the great gold [ERRATA SHEET RESTORATION OF GOLD MILL TAILINGS, BLACK HILL, SOUTH DAKOTA 84-119 F. D. Fox Under subtitle Prospects Related to Present and Future Tailings Disposal Practices, include reference No. 12 in paragraph seven after "construction of the Grizzly Gulch tailings disposal project,"12 Reference 12 should read: Jeffries, Lawrence F. and Tczap, Andrew, "Homestake&apos;s Grizzly Gulch Tailings Disposal Project," paper presented at 1978 International Mining Show, October 11, 1978.]

Jan 1, 1984

By James R. Aggson, Verne E. Hooker

GENERAL CONSIDERATIONS The design of a mine or any underground opening in rock is similar to the design of any other structure, such as a building or a bridge, in one important way. This similarity lies in the fact that the stability of the structure is a function of the loads that will be applied during the structure&apos;s expected lifetime. In the case of an underground opening, the applied load is the product of the existing in situ stress field and the concentration of this field that is produced by the extraction of a load¬bearing material. Thus, a knowledge of the in situ stress field is considered a basic requirement in the design process and essential to the eventual stability of the underground structure (Duvall, 1976; Obert, 1972; Merrill and Peterson, 1961; Dahl and von Schonfeldt, 1976; Hedley and Wilson, 1975). The in situ stress field can be used along with the physical properties of the rock masses involved, the ge¬ometry of the various rock types, the geometry of the openings involved, and a failure criterion to evaluate structural stability of a planned mine by theoretical or numerical techniques. This same information can be used to investigate ground control problems in existing mines. In situ rock stress determinations can be separated into three categories: the determination of applied stress, also called the absolute or field stress; the deter¬mination of concentrations of the field stress near open¬ ings; and the determination of changes in rock stress as load-bearing material is removed. The applied stress field is more difficult to determine than are stress changes. Various instruments and techniques have been developed to determine applied rock stress and stress changes in rock. ABSOLUTE OR FIELD STRESSES Theoretical Considerations In the absence of actual measurements, it is often assumed that at any point, the vertical stress is equal to the weight of the overlying material. [ ] where S„ is vertical stress, S is average weight density of overburden rock, and h is depth from the surface. This is normally consistent with actual experience. The horizontal stresses are assumed to be equal and related to the vertical stress through the Poisson effect. [] where Sh is horizontal stress, S„ is vertical stress, and v is Poisson&apos;s ratio. The derivation of Eq. 2 is dependent on lateral con¬finement of the rock mass. An increasing amount of information is rapidly becoming available which indi¬cates that the in situ stress field at a particular location cannot simply be assumed to be a gravity-induced stress distribution in which the secondary principal stresses in the horizontal plane are due to confinement and Pois¬son&apos;s effect. Rather they can be a complex function of gravity loading, regional stresses, structural features, ex¬cavation geometries, and variations in surface and/or possibly basement rock topography. Furthermore, the underground principal stress dis¬tribution is not necessarily vertical and horizontal as is often assumed. The deviation of the three-dimensional stress distribution from vertical and horizontal can be due to a combination of both topographic (Hooker, Bickel, and Aggson, 1972) and structural features.

Jan 1, 1982