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By S. E. Phillipson

Underground mine mapping is a critical component of understanding the controls on ground instability. Many relatively localized examples of ground failure are associated with geologic features, such as faults, joints, compaction zones, or sedimentological transition zones. In contrast, long-running, directional roof falls are associated with regionally directed horizontal stress fields, which are induced by tectonic plate interactions in the earth?s crust. When stress-related features are distinguished from geological features, underground mapping can be an effective method for inferring the direction of horizontal stress at individual mines. Comparisons with data compiled in the World Stress Map confirm that underground mapping can be a valid method for determining the orientation of maximum principal horizontal stress at a variety of scales, ranging from individual mines to an entire mining district or coal basin. Comparisons are presented between the maximum horizontal stress directions inferred by MSHA?s Roof Control Division through underground mapping and the azimuths of maximum horizontal stress in the World Stress Map database for North America?s Pennsylvanian-aged Appalachian, Illinois, Black Warrior, and Arkoma Basin coal fields. The comparison indicates that azimuths are similar for both data sets, even where variations in the direction of horizontal stress are present. It is interpreted that inconsistencies in direction are attributable to near-surface affects such as deeply incised stream valleys, or to fault zones that represent heterogeneities in the crust.

Jan 1, 2009

By A. S. Ibrado, D. W. Fuerstenau

The adsorption of the cyano complexes of Ag(I). Cu(l), Hg(II), Cd(II), and Zn(II) on activated carbon was investigated as a function of pH and correlated with the speciation diagram for each metal. The results show marked changes in uptake with pH, closely resembling the predominance profiles of their neutral and singly charged cyano complexes. Multicharged negative complexes are repelledby the negatively charged carbon surface. The sensitivity of activated carbon to the charge of the adsorbing species indicates that silver adsorbs as an anion, not chemically bound to the coadsorbing counterions. For the same reason, activated carbon is selective to metals that preferentially form neutral and singly charged cyano complexes, namely gold and silver.

Jan 1, 1990

By Petr Salak, Adrian St. John, Angelos Gakis

"INTRODUCTIONCrossrail will provide London and the South East of England with a world class, high-capacity railway to ease congestion on London’s public transport system and enable better access between business, residential and entertainment districts. At the heart of this £14.8bn scheme lies Farringdon Station, which will form a major interchange between Crossrail, Thameslink and London Underground. The £400m Farringdon Crossrail station was awarded to a joint venture of BAM Ferrovial Kier (BFK) in 2011, and comprises two ticket halls, two platform tunnels and a multitude of connecting tunnels all constructed using open face sprayed concrete linings (SCL). BFK appointed Dr. Sauer & Partners (DSP) as their specialist SCL designer. As the main contractor for both C300/C410, the Western Running Tunnels and Station Caverns, and also for C435 Farringdon Station, BFK were in a unique position to develop strategies to reduce cost, time and risk for the Client. One such innovation involved the continuation of the TBM drives for the running tunnels right through the length of the new Farringdon platform caverns. This created large diameter precast concrete pilot tunnels for the subsequent platform enlargement using SCL. The benefits of such an approach are described in detail by St.John et al 2015. BFK also introduced another alternative strategy to reduce cost, time and risk, by proposing to abandon the TBMs in the ground (“Turn & Bury”) permanently rather than recovering them through the ticket hall shafts. This de-risked the programme, enabling critical ticket hall construction to proceed unhindered. However, one consequence of this revised strategy was an area of increased underground congestion, with two SCL tunnels (RTE2 and ES2) and a bored tunnel (complete with abandoned TBM) in close proximity to a ticket hall excavation (see Figure 1) and a sensitive, listed railway structure. Faced with this complex geometry, and combined with challenging geotechnical conditions (Gakis et al 2015), the team chose to install enhanced monitoring to study the behavior of tunnel RTE2 and provide additional assurance that the tunnels were performing as predicted. Applying advanced 3D numerical modelling and taking into account the residual tensile strength of the SCL helped avoid unnecessary reinforcement installation in primary lining and/or early installation of a secondary lining in RTE2 prior to ES2 construction."

Jan 1, 2016

By Jacek Kolacz, Knut Lyng Sandvik

Fine grinding in an air swept and a grate discharge ball mill working in closed circuit with a forced vortex air classifier has been investigated in continuous laboratory scale. Minerals with different physical properties were ground down to 40, 20, and 10 micron top size. The shape of the product particle size distribution curve was investigated and specific surface (BET) was measured. During production of material with top size of 40 microns in an air swept mill, the capacity was up to 25% higher when compared to a grate discharge mill. This difference dropped to 180A during production of 10 micron top size material. A corresponding decrease in power consumption was observed. An important finding is that by regulation of the air flow rate through the mill, it is possible to achieve products with different specific surfaces and particle size distribution curve steepness. During production of the 10 pm material, the specific surface could be varied in the range 3 to 4.5 m2/g. Such powders could hardly be produced in a grate discharge mill because fine particles coated the grinding media and the lining. On the other hand the internal classification in the air swept mill kept the size distribution of the mill content relatively free of fines. This prevented a similar slowing-down of the air swept grinding process.

Jan 1, 1995

By A. J. Benham, H. Kessler

In the UK a high proportion of land-won sand and gravel is extracted from sub-alluvial gravels and river terrace gravels located within river valleys. However, extraction from deposits of this type is increasingly proving to be less acceptable. Quarries within river valleys often have a high visual impact and the cumulative impact of these operations in close proximity to each other can be high (figure 1). River valley operations are almost always restored to open water. Whilst these may be attractive for nature conservation and provide leisure activities, they can also have a serious impact on the natural hydrology of the flood plain. Wet restoration of quarries located close to airports or airfields can also lead to concerns regarding increased risk of bird strike on aircraft. The Civil Aviation Authority recently suggested that an exclusion zone of 13 km be applied around all airports and airfields to reduce the potential for bird strikes on aircraft. This action is likely to have a serious impact on the availability of potential sand and gravel extraction sites in river valleys.

Jan 1, 2005

By K. Sample

Slope stability analysis plays an integral role in the design of various mining applications including waste dumps, heap leach piles, solution ponds, and tailings dams. Generally, limit equilibrium analysis using one of the several prevalent approaches is considered adequate. The density, saturation, and shear strength parameters of the materials forming the slope affect the failure mode and the calculated factor of safety (FS) against sliding. These parameters are generally based on laboratory tests. Field practices and construction procedures are often not completely simulated in the laboratory for various reasons (e.g. equipment limits, time and budget restraints, etc.). This paper presents a holistic assessment of slope stability analysis as practiced in mining applications, using example data from multiple heap leach projects. A sensitivity analysis is presented for variations in material properties, data interpretation, and computation methods. For each step in the design process, the possible variations in parameter values were identified and then used to perform traditional and probabilistic stability analyses. This simple, cradle-to-grave-type approach is used to evaluate the reliability of an example design, and the combined impact of multiple uncertainties on the factor of safety. Example Study The issue of addressing uncertainty in geotechnical design has been discussed in depth by numerous authors (Duncan 2000; Christian 2004; Whitman 1984; Christian et al. 1993). One may ignore the uncertainties involved in a design, take a conservative approach, rely on observational methods (Peck 1969), or attempt to quantify the uncertainty. Geotechnical projects in general, may include a combination of these methods. For important structures, such as heap leach pads, it is critical that sources of uncertainty in the stability analysis be acknowledged early on and considered in the overall design approach. As with any project, economics and other physical constraints, such as space limitation, often do not always allow for an overly-conservative, robust design. In an effort to quantify uncertainty and provide a sense of level of confidence in the safety and reliability of a design, probabilistic methods have been developed and implemented in many slope stability software packages. Reliability methods are often used in the design of open pit mine slopes, but not as commonly in designing heap leach pads and waste dumps. As an example, the stability analysis of a copper heap leach project is presented here to evaluate the effects of multiple sources of uncertainty and differing methods of data interpretation. Some of the parametric values, or the variation therein, are assumed on the basis of actual data from multiple heap leach projects, included in the paper as well. A generic representation of the example case study is shown in Figure 1. As depicted in the cross-section, the ultimate height of the design is 114 m (measured from the crest to the toe). The overall slope of the heap leach pad is 1.88 horizontal to 1 vertical (1.88H:1V), or 28°. The slope benches are considered in the overall slope. The example leach pad is founded on alluvial, colluvial and residual soils overlying weathered limestone. The ore to be placed on the pad is characterized as poorly graded gravel (GP) with average fines content (percent passing #200 sieve) of 4%. The liner subgrade is low permeability (fine) soil. The cover or the drainage material, placed directly above the geomembrane (between the liner and the ore), is crushed ore in this case. The phreatic surface was assumed to be 1 m above the base liner, which is what the collection system over the liner is typically designed for. [ ] In heap leach pads, typically, Linear Low Density Polyethylene (LLDPE) or High Density Polyethylene (HDPE) is used as the base liner. The decision is based on the elongation, strength and other requirements of the application as well as economic considerations. In this example study, the base liner was 80-mil single-side textured LLDPE. FIELD INVETIGATION AND SAMPLING When selecting appropriate values for the input parameters of the stability analysis, the level of uncertainty in the data and the assumptions that are made must be clearly identified and considered in the design. This concept has been emphasized through an extensive number of publications regarding geotechnical uncertainty and reliability (Christian et al. 1994; Duncan 2000; Christian 2004). The primary source of uncertainties involved in slope stability analysis for mining applications is inadequate geotechnical investigation, often lacking in a thorough assessment of in-situ material characterization and sampling disturbances. To emphasize this point, some background information is presented here. The tradeoff between the costs of a thorough site investigation versus the risks of design uncertainty has long been a challenging management decision in geotechnical projects. For mine sites, significant investment is typically made in exploration and estimating mineral resources and the geology of a mine site is often more thoroughly documented than other types of geotechnical projects. Nevertheless, the engineering properties of the soil and rocks relevant to slope stability receive less emphasis. Baecher and Christian (2003) observed that the areas of geotechnical concern, such as slopes and waste disposal facilities, are usually associated with mine costs rather than revenue, and therefore, significantly less money is devoted to their site characterization and laboratory testing. The expenditure for site investigations varies significantly from project to project, with higher levels of uncertainty and, therefore, the

Jan 1, 2009

By David K. Ingram

The objective of this U.S. Bureau of Mines investigation was to characterize overburden response due to longwall mining. Subsurface strata and surface deformations were monitored during the mining of two adjacent, 900 ft wide longwall panels in southeastern Ohio. The panels were separated by a five entry, four pillar system (about 350 ft wide). The overburden thickness in the study area ranged from 214 to 280 ft, and the extraction thickness averaged 70 in. To delineate the geology of the overburden, six coreholes were drilled along a profile line extending across the two longwall panels. Multi-point borehole extensometers (MPBX) with eight-anchors were installed in six boreholes to measure subsurface displacements. The MPBX units were continuously monitored using a data logger. During the mining of the first panel, displacement occurred in a radiating pattern beginning just above the extracted area in the center of the panel and extending upward and outward towards the surface and margins of the panel. Overburden deformation did not project over the gate road entries. During the mining of the second panel, the MPBX's showed almost simultaneous displacement, indicating that the overburden began to move as a whole unit. Again, overburden deformation was confined to the immediate panel area. At both panels, overburden movement began when the longwall face was approximately 55 ft beyond the line of MPBX boreholes. Moreover, all ground movement was complete when the longwall face was approximately 200 ft beyond the line of MPBX boreholes. This paper discusses the results of the study and identifies the characteristics of overburden deformation.

Jan 1, 1986

By J. O. Marsden

The Candelaria copper-gold mine is located approximately 25 km south and east of Copiapo in Region III, Chile. The original concentrator was designed to treat 28,000 t/d (30,800 stpd) of chalcopyrite-bearing ore through a circuit consisting of a single 11.0 m (36 ft) diameter SAG mill, two ball mills, conventional rougher and scavenger flotation, column cell cleaner flotation, and ceramic disc filtration. The plant was commissioned in August 1994 and quickly reached capacity and expected levels of metallurgical performance. In May 1996, a decision was made to double the capacity of the concentrator by the addition of a second line of equipment. The expanded facilities were commissioned in October 1997, less than 18 months after the decision to proceed, and well within the budget. The original concentrator facilities were replicated or duplicated as much as possible, however, a number of important equipment changes were made to take advantage of industry developments since the original concentrator was designed. These included the use of Eimco 120 m3 (4,200 ft3) cells for rougher and scavenger flotation and the installation of a Svedala VTM -800 Vertimill for regrinding. This paper describes the rationale behind these changes and explores the reasons for the success of the project.

Jan 1, 1999

By Wilbur C. (Original by) Helt

Throughout the history of mankind, the principal use of coal has been to produce heat through combustion. The heat is used in many ways: to warm air space for our comfort; to provide heat or energy to power industrial processes, such as cement and steel production; and to produce electricity. Because it is our nation's most abundant fossil energy fuel, coal in the late 20th century is on the threshold of becoming a significant source for synthetic liquids and gas energy fuels for this country. This is made possible by conversion processes which can change solid coal into various synthetic gases and liquids. These coal-derived fuels are nearly identical to the processed fuels and chemicals provided by natural gas and crude oils, which presently provide almost all the petrochemical feedstocks and energy fuels needed for the residential, light commercial, and transportation markets. A revolution is beginning to take place, not only in the United States, but in many other countries with a return to a coal-based energy economy. Also, new combustion and conversion technologies which are compatible with national health and environmental goals are rapidly emerging. These technologies will allow coal's use to be expanded not only in its traditional markets, but also to supply markets held by natural gas and crude oil. With the worldwide decline in natural gas and crude oil reserves, coal is being-looked upon to meet the energy demand. Because of these new coal conversion technologies, coal will no longer be only a combustion fuel, but a valuable raw material for production of a variety of clean fuels and chemicals.

Jan 1, 1981

By S. A. K. Forson, Newton A. Amegbey

In order to investigate production decline in Tarkwa Goldfields Ltd., located in a tropical rain forest, amongst other areas, a health survey was conducted with the aim to see 1. The health status of the workers. 2. Which parameters carry the most information about the health situation and which of them can be applied easily during screening programmes. 3. What steps could be taken to improve the situation. In all 249 workers were investigated. A non-invasive method involving taking of body weight and arterial blood pressure was used. All subjects were required to answer a questionaire. Emphasis was placed on the history of malaria and diarrhoea within the last six months. Both management and workers co-operated fully. Another set of 110 workers from a neighbouring tyre factory were also investigated for control. Among the underground workers, the percentage body weight loss during a shift increased with decreasing body weight. Dehydration levels could be as much as 4 to 5% of body weight. This could be attributed to the fact that workers took insufficient or no water during the shift. The health status of the mine workers was generally poor and in our opinion malnutrition combined with malaria severely threatens the health and well-being of the workers. Hypertension is also a problem. An improvement in production is intimately linked with the well-being of the workers.

Jan 1, 1989

By Günter Strappler, Max John

When tunneling through karstic terrain, diverse and complex karst structures are to be expected. By means of drilling ahead of the face using drill jumbos, these structures can be detected to such a degree that by applying proper support measures both open karst cavities and karst holes surrounded by boulders embedded in soft rock can be mastered without causing any break-outs. Support measures such as spiles ahead of excavation, sealing off cavities, back?lling with sand, etc. have to be planned schematically and adapted to the dimensions and formations of the karst structures on site. An essential requirement for a smooth excavation procedure is the availablility of all necessary tunneling equipment for excavation by drill and blast as well as for excavation of soil, with experienced tunnel engineers being in charge of any adaptions on site.

Jan 1, 2003

By E. Viet Howard

During the recent expansion of precipitate copper production at the Chino Mines Division of Kennecott Copper Corporation, Santa Rita, New Mexico, local studies of the dump leaching process were intensified. As these studies progressed it became apparent that a reliable method for locating leach solutions within the dump was required, since the contact between leach solutions and the copper-bearing material would determine, in great part, the recovery of values. In the past, the problem of determining leach solution contact has been attacked by various methods, including destructive testing (dump dissection), indirect observation (such as chloride or dye tracers), and mathematical or laboratory model studies. These methods have not proved completely satisfactory for the studies now being developed. Investigation of methods for in situ observation of leach solutions led to consideration of radiation logging in drill holes, which are petro¬leum exploration and development techniques for locating fluids and measuring porosity in the subsurface. Standard oil field logging equipment was leased, modified, and tested. After successful testing, the equipment was purchased for additional studies. Applications and results of the methods are described in this paper.

Jan 1, 1968

By G. Argyris

A number of important studies, ongoing environment monitoring efforts and mining and road construction projects in the lignite based electrical power production area of Amyntaio ? Ptolemais in North West Greece require an accurate and up to date model of the topography. In recognition of the importance of such a model, a project was initiated by the Laboratory of Mining Information Technology and GIS Applications in the Department of Geotechnology and Environmental Engineering of the Technological Educational Institute of Western Macedonia. A massive surface triangulation model was generated from vector data using an optimized Delaunay based method. Combined with aerial and satellite imagery, the triangulation model provides a complete 3D terrain model of the area characterized by high levels of accuracy, detail and realism. The generated model is easy to modify with new data in order to improve its detail and keep it up to date with ongoing earth moving and development operations in the area.

Jan 1, 2008

By Chas. F. Jackson

INTRODUCTION This paper is one of a series dealing with mining methods and costs, prepared and published under the sponsorship of the US Bureau of Mines (USBM) and made possible through the cooperation of many mining companies in the US and foreign countries. The data presented have been obtained from papers previously published by the Bureau dealing with indi¬vidual mines, from the technical press, and from infor¬mation furnished by the mining companies. DEFINITIONS Top Slicing The term top slicing is commonly applied to that method of mining in which the ore is extracted by a series of timbered slices, beginning at the capping; the slice is caved, bringing down the capping to the floor of the slice; the succeeding lower slices are mined up to the overlying mat or gob, consisting of an accumulation of timber from the upper slices and broken capping, which follows the mining progressively downward (Fig. 1). The term has also come to be applied to the mining of ore bodies only one slice thick, by a series of tim¬bered slices one beside the other. The timbers are blasted out, bringing the capping down to the floor, suc¬ceeding slices being driven alongside those already caved (Fig. 2). In USBM classifications of mining methods, top slic¬ing has been placed under the heading caved stopes. The method differs fundamentally, however, from the cav¬ing methods of mining in which the breaking of the ore itself is accomplished by caving action induced by undercutting. In top slicing the ore is broken by the ordinary methods of drilling and blasting, and only the capping is broken up by caving. Main Levels or Haulage Levels Main or haulage levels are the main extraction levels on which the ore is hauled to the shaft. These levels and the shaft constitute the preliminary development of the mine.

Jan 1, 1982

By Y. J. Wang

This paper describes a procedure for solving the generalized system of n network equations in n unknowns considering the following ventilation variables and parameters: (a) air quantities, (b) pressure losses or gains caused by the control devices (i.e., fans or regulators), (c) resistance factors, (d) natural ventilation pressure, and (e) fan pressures (as a function of air quantities). The air quantities and pressure losses for all branches in the network are grouped into dependent and independent variables. The branches with an independent quantity are contained in a chord set, and the branches with a dependent pressure loss are contained in a chord set. In addition to the problem formulation, the solution procedure, applying the Newton method, is discussed and illustrated with a numerical example.

Jan 1, 1989

By J. Richard Kyle

Salt domes, their cap rocks, and the adjacent sedimentary strata represent a major economic resource in the Gulf of Mexico basin. Gulf Coast salt diapirs formed in response to sediment loading of the "mother" Louann evaporite sequence of middle Jurassic age, an effect that is caused by the buoyant nature of the lower density salt. Halokinesis progresses from nonpenetrative deformation that creates broad "pillow" structures into discrete high-amplitude diapirs. Because of its buoyancy, the top of the salt diapir remains near the land surface or the seafloor during much of its history as the basin floor subsides. The salt within the Gulf Coast diapirs is deformed complexly and commonly shows subvertical banding that represents modified sedimentary layers with different contents of nonhalite components. The most abundant impurity is anhydrite, which occurs as individual millimeter-scale crystals or as deformed clasts that generally form about 5% of most salt stocks. Many mature salt diapirs are mantled by a "cap rock" that consists of a lower anhydrite zone and an upper calcite zone, commonly separated by a discontinuous gypsum-bearing zone. The anhydrite zone forms as accreted layers of anhydrite grains and clasts that are left after episodes of halite dissolution. The calcite zone is a product related to petroleum destruction accompanying bacterial reduction of aqueous sulfate. Calcite-cemented siliciclastic strata occur above or alongside diapirs. The mineral resources of the salt-dome setting are remarkably diverse. Major economic products of the salt-dome environment are salt and cap-rock-hosted native-sulfur deposits, as well as petroleum resources that occur on the dome flanks and in the cap rock. Native sulfur forms as a result of bacterial sulfate reduction accompanying petroleum destruction to form hydrogen sulfide, which is subsequently oxidized to elemental sulfur, major amounts of which have been produced by the Frasch process from Gulf Coast salt-dome cap rocks. Some cap rocks have produced limestone, gypsum, and anhydrite for a variety of construction uses. Although traditional industrial-mineral resource production from Gulf Coast salt domes is shrinking, some cap rocks host potentially commercial concentrations of celestite and barite, as well as the metals Zn, Pb, and Ag. Furthermore, caverns, excavated within the salt stocks, serve as major storage facilities for crude oil (including the Strategic Petroleum Reserve), liquefied petroleum gas, and natural gas. These resources are products of fundamental geologic processes that are integral to the evolution of the Gulf of Mexico basin. Whereas production of some industrial-mineral resources, such as elemental sulfur, has declined in recent years, ample reserves of salt will allow production to continue into the foreseeable future. Further, there is potential for other mineral-resource production from cap rocks under favorable economic circumstances. Expanded use of caverns, excavated in the salt masses for material storage and disposal, is likely to continue into the next century.

Jan 1, 1999

By John A. DesLauriers, Hans J. Broennimann

INTRODUCTION The early record of tunnel excavating machines in hard rock tunneling has not been one to particularly brag about. We have all heard the stories of major difficulties when trying to break hard rock with machines at promised advance rates of several times that of conventional drill and blast. Unfortunately, sometimes this has not happened. It has been through this trial of the past generations disappointments that today's TBM's have evolved to their present high level of performance in a wide range of ground conditions. Today's machines offer much increased reliability and durability. This translates into high availability to the tunnel contractor. Although there still are occasional disappointments being reported, the state of the art is that reliable and predictable machine excavation of rock now is both a reality and well founded expectation. The most recent editions of Atlas Copco's MINI/MIDI Fullfacer, we feel, make a strong contribution to the reliable performance of todays TBM's---especially in small-size rock tunnels. This report will, 1.) explain the equipment and effect of rock both on the cutting technique and machine performance; 2.) list advantages of the non-circular shape, during and after construction; 3.) list applications in civil and mining industries; 4.) discuss North American experiences, performance and costs; 5.) list advantages over drill and blast and; 6.) discuss briefly lease arrangements.

Jan 1, 1979

By Scott G. Britton

Traditionally, water removal has taken a backseat to many other coal mining functions. However, it is a vital part of the total mine support system. In many US coal mines, more tons of water are removed each year than tons of coal. An excellent discussion of general drainage characteristics can be found in Chapter 8 of Elements of Practical Coal Mining, published by SME-AIME. This chapter is organized into three major sections. These are: designing effective drainage systems; constructing the main mine pumping station (static system); and constructing a portable pumping station (dynamic system). Each topic presents a separate discussion of the elements a construction foreman or engineer should consider for effective installation and operation of the mine drainage system. In addition, a list of pumping equipment manufacturers is available to interested persons and follows these sections.

Jan 1, 1983

By P. A. Meyer

The Tenmile Range is a north trending zone of high relief within the central Colorado porphyry-mineral belt, located between Leadville and Breckenridge. (Figure 1, the Index Map of the area surveyed.) The Climax mineralized zone is located at the southern end of the range on the northwest side of the Continental Divide. This portion of the total area surveyed will be discussed in detail today. A fixed wing aeromagnetic survey was flown over this range and mineralized zone in the fall of 1957. The survey was run as an experiment to see if a useful geophysical tool could be applied in the exploration for similar type deposits. The purpose of this paper is to describe the results of this survey and the approaches used to aid in the interpretation of the total intensity data.

Jan 1, 1968

By R. Bhaskar

The results of an experimental and theoretical research study into the spatial and temporal behavior of dust in mine airways is summarized in the paper. Experiments were performed in mine airways under both controlled and normal operating conditions. The controlled experiments included the documentation of the concentration and deposition patterns for two types of dust under three different velocities. Real-time dust concentration data were obtained using Real-time Aerosol Monitors (RAM-I) to determine the dispersion coefficient in a mine airway. On the theoretical front, a convection-diffusion model of the dust flow phenomenon in mine airways was developed considering dominant mechanisms affecting dust transport and deposition in mine airways. Mechanisms modeled include turbulent and gravitational deposition, coagulation, and dispersion.

Jan 1, 1988