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By M. C. Fuerstenau, J. J. Fitzgerald

Aluminum silicate hydrosol synthesis and characterization are discussed. Plausible polymeric aluminosilicate species are presented together with their effect on electrokinetics of selected minerals and flotation response of various ores. The addition of aluminosilicate hydrosol to porphyry and oxide copper ores and to a tungsten ore resulted in enhanced flotation recoveries ranging from about 1.5 to 5 percent. A significant portion of the nation's mineral resources are presently lost in the form of particles with very fine grain size. In the case of copper, for example, approximately 225 million tons of ore are concentrated by flotation per year in the United States. Total losses from porphyry ores are generally 15 to 20 percent with half of these losses being finely-divided copper sulfide minerals which do not respond to flotation. The additional 5 to 10 percent loss is the result of copper oxide minerals which are not floated. The losses of copper sulfide minerals are thought to be due in part to the lack of appropriate dispersion of the finely-divided solids less than 20 microns in size. To effect dispersion in flotation systems, sodium silicate is commonly added. Enhanced dispersion effectiveness is achieved when polyvalent metal salts are combined with sodium silicate. Since originally described by Patek (1), numerous workers have explored the utility of metal silicates. Makrousov (2), Belash et al. (3), and Eigeles (1950) (4) showed the applicability of these reagents to calcite/apatite and fluorite/calcite ores. Mercade (5, 6) reported depression of calcite in the presence of 3.33/1 mole ratio Al/Si hydrosols prepared from Type N sodium silicate (Si02/Na20 ratio 3.22/1) and 1% A12(SO4) 3•18H20 solutions. He importantly observed that the colloidal precipitates did not play a significant role in dispersion and depression but that the soluble species were responsible for this action. Patented work by this author described metal silicates used to depress calcite in scheelite flotation using 1% metal salt (FeSO4•7H2O, CoSO4•7H2O, etc.) and 5% Type N sodium silicate solutions to produce hydrosols with Si/Fe or Si/Co ratios of 8.79/1. Aluminum (III) ion systems were less effective as depressants than the iron and cobalt systems. Yang (8, 9) has studied metal silicate sols for use in the flotation of lithium and ultra-fine hematite ores. Using 10/1 Si/Fe mole ratio hydrosols prepared from 2% ferric nitrate, Fe(NO3)3.9H20, and 5% Type N sodium silicate solutions, solutions, he showed that the hydrosols either modify the slime particle surfaces or are adsorbed on the slime particles preventing anionic collector adsorption. In a subsequent patent, Yang also reported the use of these hydrosols as dispersants for beneficiation of lithium ores. Recent studies of aluminum silicate hydrosols in the flotation of chalcocite, chalcopyrite and scheelite have been reported using Si/Al dispersants prepared from 5% Type N sodium silicate and 0.1 M aluminum chloride (A1C13.6H20) solutions. Dispersant properties were shown to be dependent upon the method of synthesis, supernatant pH, and the hydrosol Si/Al mole ratio. Polymeric soluble species in these hydrosolsupernatants have been proposed as the active dispersant species. Aluminosilicate hydrosols are synthesized by the general reaction scheme presented in Figure 1. Commercial sodium silicates are available with ratios of SiO2 to Na20 of 1.60-3.25. The sample which is most frequently employed is Type N whose ratio of Si02/Na20 is 3.22/1.00. Gel filtration chromatography and NMR studies have shown that these sodium silicates contain numerous species of molecular weight from 325-2,000 gm/mole. Monomeric, oligomeric and higher molecular weight linear polymeric arrangements of these structures are found in these solutions.

Jan 1, 1989

By A. D. Davis, C. J. Webb, A. Heriba

Introduction The disposal of spent ore from cyanide heap-leach processing facilities is of concern to the mining industry, the regulatory agencies and the general public. The disposal of an additional several hundred million tons of spent ore from heap-leaching operations is planned in the western United States during the next decade, and this amount could increase if gold prices rise. In the past decade, more than fifteen million tons of spent ore have been disposed of in the Black Hills of South Dakota. The criterion for offloading spent ore was set by the South Dakota Department of Environment and Natural Resources at 0.5 ppm weak acid dissociable (WAD) cyanide. South Dakota's nitrate offloading limits vary for each mine, depending on ore type and other factors. Concentrations of nitrate in the leachate from spent ore depositories could be the result of conversion from other nitrogen-containing species. One likely source of nitrate is residual explosives from the blasting of ore. Previous work on the combustion products of nitrogen explosives has shown incomplete oxidation (Johansson and Persson, 1970). Another likely nitrate source is the degradation of cyanide to ammonia, followed by oxidation to nitrite and nitrate. A third possibility may be leaching of background nitrate from soil or rock. Objective The primary objective of this research was to investigate laboratory procedures for predicting nitrate concentrations in effluent after the disposal of spent ore at heap-leach gold processing operations. Laboratory tests were performed to define the concentrations of nitrate and nitrite in leachate as a function of time. Sources and species conversions were examined by investigating the nitrogen contributions from cyanide neutralization and from blasting with ammonium nitrate/fuel-oil (ANFO) explosives. Ore processing at cyanide heap-leach facilities Gold mines in the northern Black Hills of South Dakota normally use the following steps in their heap-leach cyanidation processing: Blasting. Surface gold mines in the Black Hills use ANFO explosives (approximately 95% ammonium nitrate and 5% fuel oil). Field evidence and studies show that explosives often fail to ignite or burn completely in shot holes. One reason is that ammonium nitrate absorbs moisture readily, which reduces blast efficiency. Ferguson and Leask (1988) cited a study conducted at the Fording coal mine in southeastern British Columbia. In that study, the total nitrogen released to surface and ground water was estimated to be about 6% of the slurry explosives. However, Ferguson and Leask (1988), in a later analysis of water quality near coal mines in the Kootenay coal fields, indicated that this is likely an overestimate of the nitrogen release. Mines that used ANFO explosives in dry conditions released 0.2% of the nitrogen from blasting. Cyanidation. At surface gold mines in the northern Black Hills, cyanide species from heap leaching can be classified into free cyanides and simple ions, weak complexes, moderately strong complexes and strong complexes (Scott and Ingles, 1981). Degradation of cyanide and disposal of spent ore. Methods of destroying cyanides include hydrogen peroxide oxidation, natural degradation and evaporation, water leaching and alkaline chlorination. Hydrogen peroxide is used to oxidize cyanides in the northern Black Hills mining area. The hydrogen peroxide oxidation reaction forms cyanate, which can hydrolyze to form ammonium and carbonate ions. After formation of ammonia or ammonium ion, further oxidation to nitrite (NO2-) and nitrate (NO3-) can occur. Spent tailings from gold processing in the Black Hills normally are disposed of in tailings facilities constructed in nearby drainages. Infiltrating rainwater with a typical pH of about 5.6 is an additional component introduced into the spent ore after disposal. Methods Field sample collection. Spent ore samples were collected from conveyor belts (or other convenient points) at heap-leach mines by personnel from the South Dakota Department of Environment and Natural Resources. The samples were placed in black plastic bags that were contained within 5-gal buckets and sealed to prevent exposure to ultraviolet light. The samples had a minimum head space to limit evaporation and contact

Jan 1, 1997

By P. E. Sperry, J. M. Duncan

INTRODUCTION The purpose of the report on which this paper is based is (1) to evaluate the potential for cost reduction of urban mass transit tunnels by use of alternative materials transport systems during the tunneling process, and (2) to identify research and development program elements to assure that the materials transport system will not become the limiting factor for the rate of excavation. The approach taken was: Review the state of the art of urban tunneling by extensive interviews with representatives of tunnel contractors, equipment manufacturers, government agencies and consultants, and by review of recent literature.

Jan 1, 1979

By J. A. Finch

The use of pneumatic methods for measuring interface level in flotation columns is analysed. It is shown that errors can vary over a wide range (e.g. 40 cm. in one industrial application) depending on bubble size, particle size, bubble loading, liquid hold-up and bulk slurry density. Accurate measurements (+ 5 cm) can be obtained by measuring intensive properties of the froth near the interface. Methods based on the measurement of temperature and conductivity are described and analysed. Control of the interface level using these measurements subject to various disturbances is demonstrated.

Jan 1, 1988

By V. Rastogi

Surfactant-based bactericides are able to control acid formation in sulfidic materials such as pyrite and sulfidic ores, thereby helping to abate acid rock drainage. Bactericides are used in the following two ways: as periodic or continuous spray treatments for the prevention of acidification of material actively handled and moved and in controlled-release form for reclamation. Site-specific bactericide treatments are designed for active sites and reclamation. Results from two active coal refuse sites show that acid production can be reduced by 88% or more. Results from reclaimed sites show that bactericide treatment can be more effective than the addition of alkaline materials such as limestone and can reduce acid production from 3,500 to <30 ppm. The controlled-release-pellets treatment outlasts the life of the pellets, as shown by a study of a site now 10 years old A single treatment sets up a change in site microbiology to replace acid-producing Thiobacillus ferrooxidans bacteria with heterotrophic bacteria and creates a stable site without the need for further treatments. A secondary beneficial effect of bactericides is on revegetation, and biomass from treated areas is almost 10 times that from areas not treated with bactericide. Depending on the application, bactericide treatment can be cost effective upfront and certainly long-term, compared to the perpetual water treatment that could be required, even after productive use of the site is completed

Jan 1, 1997

By B. K. Mishra, Partha Chakroborty

Jigs are the most important equipment used in the separation process that exploits the stratification of particulate matter under the influence of hydrodynamic and gravitational forces. Very little is known about the determined mechanisms by which particles of varying density, size, and shape stratify in a moving bed. A model is developed by using the discrete element method to understand the behavior of jig bed. This model is utilized here to study the stratification behavior of the bed and its control. The control action is based on the understanding of the physics of the stratification process within the framework of fuzzy logic. The actions suggested by the fuzzy logic controller (FLC) depend on the current degree of stratification and the existing frequency of the jig cycle. The results show that the FLC achieves efficiency in stratification with minor variations to the jig cycle.

Jan 1, 1995

By Subhash B. Bhagwat

No economic activity would take place without human ingenuity, driven by our needs and wants. Economic activity is made possible by the energy from fossil and other energy sources, our technological hardware, the buildings and infrastructure made from materials such as metals, plastics, wood, water, and numerous industrial minerals. Industrial minerals are difficult to define; however, they generally include utilitarian minerals other than metals and fuels. Some of the industrial minerals form an exception to this categorization and, as explained elsewhere in this book, belong to more than one category because of the manner in which they are used. Industrial minerals are so numerous, and their applications so ubiquitous that they often do not receive the attention given to metals or fuels. Nevertheless, without industrial minerals, many of our most fundamental economic activities such as construction of our cities and towns, control of floods, transportation of our people, the search for minerals, the smelting of metals, and the delivery of supplies of clean water would be impossible. How then do we assess the economic importance of such a variety of materials lumped together under the general designation of industrial minerals? The price per ton or the total amount consumed do not satisfactorily explain the relative value of these materials to the economy. For example, the current price of limestone is about $5/t and the price of fluorspar is about $190/t. However, nearly 1.1 Gt of limestone, valued at about $5.5 billion, are consumed in the United States annually, compared with 590 kt of fluorspar, valued at about $1 12 million. It would not, however, be accurate to conclude that the mineral with the higher total value is always more economically important. Many other questions must be answered before making judgments of this type. These questions include how many people are employed in the production, processing, and distribution of the mineral? How is the mineral used? Is it partly or entirely imported? Where do the imports come from? How is the mineral transported? Is the mineral considered critical to national security? Is there a substitute material available in case the mineral supply is interrupted? Where would the substitute be produced? What would be the basic material from which the substitute will be produced? Even when these questions have been answered satisfactorily, the economic importance of the mineral is not completely known until the consuming sectors are studied as well. For example, even though the manufacture of fighter aircraft is vital to the national security, it employs only a fraction of the number of people employed in the housing and construction industry or the automobile industry or the appliance industry. Mineral commodities consumed in these latter sectors of the economy are more significant than those consumed in the production of fighter aircraft, because nearly two-thirds of the Gross Domestic Product (GDP) depends on the purchasing power of individual consumers. In comparison, the entire defense budget accounts for only 6% of the GDP. There is no easy way to present the importance of industrial minerals to the US economy because most minerals have diverse applications and products made from industrial minerals often con- tribute to the production of other goods and services. One way of highlighting the value of a mineral would be to relate it to the GDP reported by categories such as construction, machinery, stone, clay and glass products, electrical and electronic equipment, paper and allied products, and chemicals and allied products. These GDP categories represent industries fundamental to the economy totaling $644 billion, or about 12% of the GDP in 1990. However, these categories are not convenient for discussion of the many minerals that are used in our complex economy. In a general way, minerals are the 5% of our economy that make the other 95% possible. This chapter, therefore, discusses a selected few industrial minerals to illustrate their importance to various sectors of the economy.

Jan 1, 1994

By Kourosh Shahriar

The occurrence of rock falls in underground coal mines entails detrimental effects as fatal or non-fatal injuries on workers, stoppages in mining operations and breakdown of equipment. In this paper, a risk assessment approach on the basis of a decision analysis trend is employed in order to assess the possibility of and manage roof falls. Risk is then assessed by determination of likelihood of occurrence and the cost of consequences (outcomes). In this regard, collected real roof fall data from Tabas and Kerman coal regions comprising of several underground coal mines are used. It is concluded that the annual accidents due to the roof falls occurrence in the all investigated mines are so high that it is economically feasible to improve the support systems and to implement a suitable educational program as well as an accurate supervision and other elements of safety management.

Jan 1, 2009

By M. Wasel

The Gross Rosebel gold deposits are located in theGuiana Shield of northcentral Suriname in South America. The property lies 80 km (50 miles) south of the capital city of Paramaribo. Gross Rosebel covers 170 km2 (65 sq miles) in an area of small hills covered primarily with secondary tropical rain forest, separated by discontinuous savannah (Fig. 1). The concession is accessible from Paramaribo by a 120-km (75-mile) paved and all-weather gravel road. Surficial gold was discovered in 1880 by local artisanal miners. This was followed by small-scale mechanized mining from 1885 to 1939. Placer Development carried out the first systematic exploration program from 1974 to 1977. In May 1992, Golden Star Resources optioned the property. Initial shallow reconnaissance diamond drilling of the extensive surface geochemical anomalies intersected sporadic gold mineralization with no apparent continuity between drill sections. Successive deep augering, trenching and systematic grid drilling, based on information from surface mapping, allowed the development of a preliminary geological model. Further drilling of specific structural-lithologic targets and more complete synthesis of geological data from the trenching and deep auger sampling added to the geological model and defined the multiple controls of gold mineralization. Carefully planned infill drilling on a tighter grid spacing resulted in progressive definition of reserves within six discrete gold deposits. Reserves based on $11.25/g ($350/oz) gold now stand at 35.5 Mt (39.1 million st) of 1.8 g/t (0.053 oz/st) gold, or 62.2 t (2 million oz) of gold.

Jan 1, 1998

By E. B. Johnson, G. Kjerbol, L. J. Holloway

The Mount Baker Ridge Tunnel is a major improvement of Interstate Route 90 in the State of Washington. The total length of planned underground construction is about 3,400 feet (1,040 m) of which 1,332 feet (406 m) will be constructed by a stacked-drift tunneling method. Sized for vehicular traffic on two levels, the net interior diameter will be 63 feet (19.2 m) requiring an exterior diameter of about 80 feet (24.4 m). The material to be excavated is predominantly stiff clay, and this will be the largest-diameter tunnel ever attempted in soft ground. A construction contract for the stacked-drift tunnel was awarded in late 1982.

Jan 1, 1983

By Zbigniew Hladysz

INTRODUCTION In the Polish coal mining industry, the Upper Silesian coal basin has an important position. It contributes over 98% of the total coal production of Poland which reached 193 mt in the year 1979. In view of the significant urbanized area in this region as well as the industrial potential, it is important to protect the surface by stowing the mined out underground workings. Approximately 18% of the total production is mined from longwall faces with stowing. However, caved longwall faces are most popular. In the upper Silesian coalfield, approximately 337 highly mechanized longwall faces are in operation. Out of these 337 faces, 301 longwall faces are caved. One of the main requirements for effective and safe coal extraction is a suitable method for strata control. We can divide the complex process of strata control into four steps: 1. Strata investigations 2. Selection of supports for roadways 3. Selection of supports for longwall 4. Rock bursts and other hazards protection STRATA INVESTIGATIONS Estimation of the structure and physico-mechanical properties of the rock mass surrounding the workings is an important constituent of strata control. These factors definitely influence the rock stability, support load, working conditions as well as the mining technology. Complex methods of strata investigations involve a set of indicators enabling the estimation of the stability of the roof rock, strength of the coal seam and load bearing capacity of the floor. The basis for the evaluation of roof stability for a coal seam is the classification according to the resistance to bed separation (1). The bed separation resistance is equal to the strength of the rock in tension perpendicular to the bedding plane. In order to properly classify a rock, it is indispensable to make continuous profiles of the bed separation resistance from the immediate roof up to a distance of three times the thickness of the coal seam. The profiles are developed by utilizing mine roof investigations with the hydraulic borehole penetrometer. (Fig. 1) The penetration resistance is determined by the critical pressure required to cause crushing of the rock by the penetrometer indentor (2). The classification of roof rocks and their ability to cave spontaneously during longwall mining is shown in [Fig. 2]. The measurement of the critical pressure also allows for the determination of the compressive strength of the rock, the index of workability and roof fissuration.

Jan 1, 1982

By Wei Wu

A computer-aided method for optimization of bench blast design in surface mines is presented. The design procedures basically consist of two steps. Firstly, a series of normalized, full- scale bench crater tests must be carried out in the field to find the optimum burden that produces the largest amount of acceptable fragments and other parameters that defines the effective fracture zone. Next, the locations and initiation sequence of blast-holes will be determined in such a way that each hole, at its time of firing, will be responsible for same amount of burden rock and will be in a position favorable to effective fracture of burden rock. A computer software "B.B." which can assist the second step of the design is fully introduced and its application is illustrated by an example.

Jan 1, 1992

By W. Joseph Schlitt, Donald B. Swanson

The paper provides an overview of the role that contract mining plays in the minerals industry. Particular emphasis is on contract mining and its place in the development and operation of small to medium sized precious metal mines in the western United States. The paper begins with a discussion of the mining options available to owners. This is followed by a description of contract mining organizations and the services they provide. In addition to various mining activities per se, these can include other processing functions such as crushing and agglomeration, various types of heavy civil construction, other types of technical and administrative support, and even assistance with financing. Typical equipment spreads and unit costs are presented. Final 1 y, the advantages and disadvantages of contract mining are discussed. Liberal use is made of

Jan 1, 1987

By R. C. Babcock

Exploration for mineral deposits in the western United States is increasing annually, and the data generated by this effort are increasingly complex, diverse, and abundant. It is obvious that to make full use of this data base, which is both private and public, the technology of the computer must be involved. To lay out the framework for discussion of the particular uses of computers in all steps of exploration, this chapter will discuss the various approaches to the reconnaissance program which might be considered, the types of data to be acquired, the interpretation of these data, and the generation of recommendations based on this interpretation. Where possible, some of those areas where computer technology is now used will be pointed out. The discussion will cover the extent to which the computer is now utilized in those areas or where it should be brought into the program to aid in these activities. However, this chapter will not present an exhaustive evaluation of this technology, but will stress the exploration job and its requirements, so that subsequent discussion of the technology itself can be placed in perspective.

Jan 1, 1979

By Robert F. Hauck

This chapter discusses a new technology for computer control in open-pit mine operations: the real time automatic dispatching of manually driven trucks to shovels. The monitoring of truck activity is accomplished by detection of local radio signals. Computer-operated directives are communicated to drivers by remote controlled digital display units inside the truck cab. The production objective is to maximize tonnage in a cost effective manner. The problem is formulated in the appendix and the solution method is briefly described. Side conditions such as maintaining delivered ore grade aims, balancing waste to ore volumes to keep within stripping ratio tolerances, and meeting production rate requirements temporarily established for certain shovels are also discussed. Experience with a developed event- to-event simulator applied to analyses of several North American mining operations using this technique is summarized. Complete systems employing this technology are now under- going installation at mine sites in Canada and the United States.

Jan 1, 1979

By K. Y. Haramy, B. T. Brady

A scale-invariant theory of the strength and deformability, of rock masses in static equilibrium and at incipient failure is proposed The theory provides a rationale, for designing structures in rock. This paper presents results of experiments conducted by the US Bureau of Mines and presents theoretical methods to determine and interpret the in situ strength of rock masses using the borehole shear tester.

Jan 1, 1996

By Hans von Michaelis

Metallurgists are trained to seek synergisms and to optimize trade-offs in the selection of processes and flowsheets. The subject of my paper and the focus of this entire conference is on synergisms involving more than just metallurgical recovery, but encompassing mining and environmental management too. Operators have always known that by recycling tailings water they could recover some cyanide and lime values or reduce the amount of new flotation reagent additions. The trade-offs have changed at many US mines today where concern about avian mortality necessitates that water in the tailings pond be detoxified. This is just one example of how selection of processes and technology today requires integration of environmental management. MUDDER & GOLDSTONE (1989) showed how cyanide can be recovered from tailings slurries by an acidification­volatilization-reabsorption (A VR) process which was installed in New Zealand, and which in 1992 is being commissioned also at Nerco DeLamar Silver Mine as described by OMOFOMA & HAMPDEN (1992). FRICKER (1990) and FRICKER & OWERS (1992) show how using A VR to recover cyanide from pregnant pulps ahead of gold recovery improves the yield of recoverable cyanide while improving the performance of the gold recovery step and detoxifying the tailings. This is an excellent example of the synergisms that can be achieved ,y applying a "systems approach."

Jan 1, 1992

By Richard Crawshay, Duncan Hutchison

Continuous Mining Systems Limited have developed an efficient, high-capacity, in-line loading unit capable of handling shot rock in tunnel driveages at extraction rates up to 970 tonnes (1,000 tons) per hour. A smaller 408 tonnes (450 tons) per hour loader is also available These in-line loading units called "Osciloaders"® provide a continuous flow of material from the muck pile to an anciliary conveyance eliminating the cyclic or interrupted movement noramlly associated with gathering arm or bucket type loaders. The osillating lip fluidizes the material, reduces the penetration force required and facilitates and regulates the material flow onto the adjacent conveyor. The conveyor is wide and accommodates very large material with ease, transporting and elevating it to a height suitable for a waiting conveyance at the rear of the machine. The "Osciloader"® is currently being utilized for production mining by a major company in Sudbury, Ontario. Both truck and conveyor anciliary haulage are being utilized. The paper describes the development of the loader and how it may be applied in tunnelling applications.

Jan 1, 1987

By Liyan Ren, Huayang Dai, Yingcheng Li, Enquan Wang

"Three-dimensional geological modelling of coal mines is critical to the sustainable development of the mining industry. On the basis of comprehensively analyzing 3D geological modelling methods, according to the available data of mine such as geological terrain maps, cross-sections and boreholes, we present a 3D modelling method by integrating ArcGIS and 3D GeoModeller. Our motivation is to integrate the advantages of both software modules in processing, converting, integrating and transferring geological information. Special attention has been given to the data structure and processing flow. We build a 3D geological model of the Xieqiao coal mine and successfully extract the geological framework of the strata in the 11118 workface, which is consistent with that of the actual explored geology.Introduction/Background Pertinent impediments such as a lower information degree, the out-of-date information infrastructure and the low level of information management and decision-making make it critical for there to be improvements in mines. Modern exploration technologies favour the construction of digital mine. Digital mine promotes the transformation of the mining industry by integrating information, automation and intelligence to build safe, efficient, high-yield, green and sustainable mines. Three-dimensional geological modelling and visualization of mines are at the core of digital mine. Compared with traditional 2D geological data, 3D models express the various geological phenomena completely, as well as reproduce the spatial distribution of geological units quickly, allowing for the prediction of mining subsidence, better decision-making and improved geological analysis. Modelling methods such as multi-DEM, tetrahedral grid and the generalized tri-prism that are based on borehole estimation and interpolation data are used to construct 3D models of mine geology (Chen 1995,Wang et al 2003, Wu 2004a); nevertheless, these methods cannot fully use multi-source mining data, whereas multi-source integration methods can be used to build 3D models (Kaufmann and Martin 2008, Zhao et al 2009) but require user interaction in model construction and low automation in model updates. During coal production, a plethora of geological data is accumulated. The organisation of discreteinformation under dynamic conditions and the extraction of meaningful information to better service for three-dimensional modelling is a meaningful work (Wu et al 2004b)."

Jan 1, 2017

By J. R. Dartez

The use of CCD (counter current decantat.io;1) thickeners, or; clarifiers, in the gold mining industry is quite common. Although there are a number of technologies in the industry which utilize these types of tanks, the fundamental requirement is to settle leach tailings and eventually separate gold and silver "values" from the "barren" (no values) solution. The thickener separation process varies depending upon the raw ores found in any specific mine. In mines where rudimentary, rocky ores are most common the settling process is fairly straight-forward and uncomplicated. But, for those mines with complex carbonaceous ores, usually identified by high silting, clay components, the ability to monitor and control the settled materials is quite laborious and costly. The task of monitoring and maintaining control of settled residue in clarifiers and thickeners, of any design, is difficult in any industry, but due to the added desire in the gold mining industry of leaching the values from the liquid slurry, the problem is multiplied. Other common activities taking place in the thickeners are exaggerated internal flow rates, settleable solids activity due to rake movement, and the settling activity generated by flocculents being added to the liquid medium. All of this action within the liquid column causes the continual monitoring of the interfaces within the tank close to impossible.

Jan 1, 1993