Search Documents

Several years ago, North American mining companies began to realize they needed to expand their spheres to remain viable. This strategy has been successful, according to Robert W. Schafer. Today, companies from other continents have also recognized the need for an international view for long-term growth and viability, he said. Schafer is vice president for exploration with Kinross Gold. He was the program chairman and moderator of the keynote session at the 1997 SME annual meeting, held in Denver, CO, Feb. 23-27. The theme of the meeting was "Minerals - Serving the Global Community." A record attendance of more than 6,000 people participated in the meeting, which featured 415 exhibitors occupying 582 booths. The title of the keynote session was "Corporate Perspectives on a Global Minerals Industry." Each of the three keynote speakers discussed a different perspective of a global minerals industry.

Jan 1, 1997

By Stewart R. D, Lawrence W, Youl M. J

The trend towards contracting by major coal mining companies such as BHP Coal and MIM Ltd is examined. Reasons why this trend is occurring are discussed and the concept of partnering is examined. Two case studies are given: the Mt Owen Mine in the Hunter Valley, NSW and the South Walker Creek Mine in the Bowen Basin, Queensland.

Jan 1, 1997

By Kentwell D. J, Cusak C. J, Harvey-Kelly F. E L, M D. Goodz

The Morning Star Gold Mine presents an example of a prolific operation with considerable historical records, mine workings, drill hole logs and countless plans from greater than 20 adjacent mines which have now been consolidated to form the current project. Implementation of 3D computer modelling in the planning stages has provided an additional tool to integrate and refine geological models as a guide to some exploration strategies. It has allowed for a re- interpretation of the host rock units, dimensional constraints, new exploration extensions and provisional resource modelling. The initial consideration of this project was to integrate 135 years of mining history into a single database. Each historic mining area had an unrelated mine grid, often established parallel to the long axis of their main stopes; some were based on magnetic or true north. Survey plans were in chain, imperial or metric units. Through the manipulation and rotation of old grids, previously unrelated mine workings began to form continuous mineralised zones, with unmined portions still remaining in between the existing development. Furthermore the current drillhole database of >433 holes showed numerous confirmatory intersections of new mineralisation. A series of tiered tables were created within a relational database to derive guidelines for assessing data to attribute a Mineral Prospectivity Value [MPV] based on key indicators of mineralisation. Indicator logging now forms the basis of geological descriptions.

Jan 1, 1997

By Johnson N. W, Manlapig E. V, Alexander D. J, Franzidis J. P

The importance of the froth region on flotation performance is often emphasised in the literature. It is well-known that decreasing froth depth or increasing air flowrate results in increasing cell recovery at the cost of lower concentrate gra

Jan 1, 1997

By Bruington T, Perkins J, Hutton R

Natural resource developments are among the largest and most challenging projects taking place in the world. They involve capital intensive investment with long lead times and the management of geological, market, technical, operational and financial issues. A clear strategy is required to manage these projects and this strategy is underpinned by a development Philosophy.

Jan 1, 1997

By Prince R. G H, Guerney P. J, Frew J. A, Vanderkruk C. R, Wanigasekara-Mohoti D. K

This computer-aided design system for mineral processing flowsheets which are based on froth flotation, size reduction and classification combines an expert system for generating flowsheet structures with numerical models for the physical processes and the economics. Design decisions, such as specification, size and placing of process units and the destination of recycle streams, are based on clear technical and economic criteria. These decisions are controlled by user-set parameters, which allow the incorporation of industry experience and preferences and the generation of sets of good designs, from which choices may be made by further criteria, such as controllability. Liberation is now fully modelled and the early results from this extension continue to suggest potential substantial increases in added value over conventional approaches.

Jan 1, 1997

By G. L. Simmons.

Many large. low-grade (refractory) sulfide gold resources exist in Nevada and other parts of the world that are not amenable to concentration by conventional flotation practice, Over the past several years Santa Fe Pacific Gold (SFPG) has investigated flotation process options to economically treat low-grade refractory resources of this type at Lone Tree and Twin Creeks. Conventional flotation technology applied to the original high-grade gold resources at Lone Tree and Twin Creeks was initially unsuccessful. Review and analysis of auriferous (gold-bearing) iron sulfide mineralogical characteristics and flotation chemistry provided a fundamental understanding that led to the development of a new flotation process that SFPG refers to as N2TEC. This paper discusses the development of this technology and compares N2 TEC results with conventional flotation practice.

Jan 1, 1997

By Napitupulu P

PT Freeport Indonesia currently operates a concentrating complex capable of milling 127 000 metric tonnes per day of copper and gold hearing ore. The facilities consist of both a conventional crushing, ball mill and flotation circuit and a SAG, ball mi

Jan 1, 1997

By Raja V. Ramani

Worldwide, promulgation and enforcement of health and safety laws and regulations have been the primary means of ensuring minimum and uniform standards of health and safety in the mining industry. In U.S. coal mines, a new era was ushered-in in 1969 for the control of health hazards from respirable coal mine dust. Since then significant progress has been made on all aspects of the respirable dust problem-its definition, monitoring, reduction, and control. In the intervening years, our ability to monitor, analyze, and characterize the mine atmospheric environment and the health of miners has increased many fold. Also, advancements in production technology have far outdistanced enhancements in environmental control technology. Therefore, questions are continuing to be raised on the adequacy of the characterization and control measures with regard to both the airborne respirable dust in mines and the health effects of respirable dust. Late in 1995, the Secretary of Labor appointed an Advisory Committee on the Elimination of Pneumoconiosis Amona Coal " Mine Workers (Dust Advisory Committee) to review the progress towards elimination of coal worker's pneumoconiosis (CWP) and silicosis, and in the program to control respirable coal mine dust in underground and surface mines, and make recommendations including improved standards and other appropriate measures for the control of exposure to airborne coal mine dust. The Committee's report was released in October, 1996. In this paper, a summary of the recommendations of the Committee is presented. A brief discussion of the background, and the issues and findings leading to the recommendations is also presented. The Committee concluded that the progress made towards making mines safer from the health hazards of respirable coal mine dust is substantial but that it is not sufficient to achieve the intent of the 1969 Coal Act. The Committee's recommendations encompass a wide range of issues addressing permissible exposure limits (PELS), sampling, dust control plans, hazard and medical surveillances, role of miners, training, and research and development.

Jan 1, 1997

By P. Riveros, J. Binvignat, V. M. McNamara, D. Koren

The feasibility of recovering cyanide and copper from a gold mill barren solution was evaluated in a small A VR pilot plant. The campaign lasted 64 hours, during which time about 4,000 L of gold mill barren solution were processed. The results showed that A VR is an effective technology for recovering cyanide and copper from barren solutions. Under the best conditions, the copper precipitation and the cyanide volatilization attained 94% and 98%, respectively. Using 5 MNaOH as the absorbent, practically all the HCN gas was recovered in the form of a concentrated NaCN solution containing 70 g/L free CN. Basic engineering design parameters applicable to a large-scale operation were obtained, including the Henry's Law constant and the mass transfer coefficient for HCN gas.

Jan 1, 1997

By H. R. Hardy Jr., E. J. Kimble Jr., H. W. Shen

"The primary objective of this research project is to study the character of the bit-coal interaction during coal cutting and its influence on the size and shape distributions of the generated dust. Secondary objectives include the investigation of the acoustic emission technique as an indirect method for coal dust characterization and remote bit wear monitoring. The results of the project will be useful in developing efficient coal cutting techniques which significantly reduce the harmful coal dust components, and in providing methods for remote monitoring of bit condition and associated coal dust character. This paper will outline recent experiments carried out on coal under uniaxial compression, linear single-bit cutting, and cutting using a laboratory-scale, single-bit shearer. During the experiments acoustic emission and a variety of other mechanical parameters were monitored. · A commercially available artificial intelligence computer package, namely: JCEPAK (Intelligent Classifier Engineering Package), has been utilized to provide a powerful and objective means for AE waveform analysis. This program is able to evaluate a number of features of each AE event and to make objective comparisons between AE signals associated with different loading or cutting parameters. Finally, the paper will discuss the results obtained from a variety of coal breakage tests.INTRODUCTIONStudies to date clearly indicate that the reduction of the severity, and eventual elimination, of Coal Workers' Pneumoconiosis (CWP) depends on gaining fundamental understanding in a number of major areas. These include dust generation and entrainment, transportation, suppression, medical effects of dust and possible treatment. At present a project is underway by the authors to investigate the character of the bit-coal interaction during coal cutting and its influence on the size and shape distributions of the generated dust. An important aspect of this on-going project is the development of acoustic emission (AE) criteria which will make it possible to carry out remote monitoring of coal cutting operations. Suitable on-line analysis of monitored AE data would allow engineers to evaluate factors such as shearer bit condition and cutting efficiency, and to quantify the particle size and shape distribution of the generated dust. The on-going AE studies are fundamental in form and were undertaken to evaluate the general feasibility of AE monitoring techniques using simplified coal cutting procedures. This paper will outline recent experiments on coal under uniaxial compression, linear single-bit cutting, and cutting using a laboratory-scale, single-bit shearer. Additional information on these studies are presented elsewhere [4]."

Dec 1, 1996

By R. V. Ramani

"In Part 1 of this paper, published in the August 1995 issue of Natural Resources Forum, a review of several mining disasters around the world established the complex nature of their causation and their catastrophic effects. The involvement of human beings, either through acts of commission or omission, was highlighted. In Part 2, a discussion of the various approaches to disaster control, mostly as practised in the USA, is presented. A systems approach to disaster prevention incorporating elements of hazard identification, mine design, emergency response and post-emergency audit is presented.In the USA the role of government in the affairs of its citizens is continually growing. This role is intended to ensure an unimpeded pursuit of happiness and prosperity by the population and to curtail actions which are restrictive or harmful to the citizenry. The passage of a legislation is an indication that it has been decided through the established process that the activities covered by the legislation should receive appropriate consideration. The enactment of the Coal Mine Health and Safety Act of 1969 (The 1969 Coal Act), the Mine Safety and Health Amendment Act of 1977 (The 1977 Mine Act) and the Surface Mining Control and Reclamation Act of 1977 (The 1977 Surface Mining Act), was specifically intended to further the role of government in the health, safety and environmental affairs of the mineral industry.Currently, the federal government's responsibilities for mine safety and health are divided among three agencies: the Mine Safety and Health Administration (MSHA) in the US Department of Labor, the Bureau of Mines (USBM) in the US Department of the Interior and the National Institute for Occupational Safety and Health (NIOSH) in the Department of Health and Human Services (National Research Council, 1981). MSHA is responsible for issuing and enforcing mine safety and health regulations, for training miners and for responding to mine emergencies. The Bureau of Mines is responsible for conducting research on mine safety and on the technological means for reducing health and safety hazards in mines. NIOSH conducts research relating to miner health, and together with MSHA, tests and certifies devices used to detect hazardous materials in mines and protective equipment used by miners. NIOSH also plays a public health role in that its activities in mining include health hazard evalua¬tions, general mining surveillance as mandated by law and medical surveillance including coal miner X-ray and autopsy programmes. MSHA shares with the Bureau of Mines the responsibility for integrating R&D results into operational practice. MSHA implements R&D results either by incorporating them into its own operations or by rule making that requires new practices or equipment to be adopted by the mining industry. In many instances, the Bureau's R&D results have been adopted by the mining industry without rule making."

Dec 1, 1996

By R. V. Ramani, R. Srikanth, R. Zhao

"A two-pan study was conducted to understand the factors affecting respirable dust generation potential or dustiness of coal seams. In the first part, the data from three prior comprehensive laboratory studies was analyzed to establish quantitative relationships between respirable dust generation potential and coal characteristics. This analysis indicates that respirable dust generation rate is positively correlated with Hardgrove Grindability Index (HGI), fuel ratio (fixed carbon/volatile matter), Vitrinite Reflectance (VR), and Level of Organic Metamorphism (LOM). In the second part, specially-designed single breakage experiments were conducted to determine the primary dust generation potential of 17 coal samples obtained from four continuous miner sections, three longwall sections, and the Penn State Coal Data Bank. The single breakage study indicates that primary dust generation rate is positively correlated with fixed carbon content, fuel ratio (fixed carbon/volatile matter), VR, and LOM. Since VR and LOM are strongly influenced by the process of coalification, differences in respirable dust generation rates in different coal seams may be explained by the thermal metamorphism of sedimentary organic matter during subsurface burial.Mineral particles in the range of one to five microns, if inhaled in sufficient amounts, lead to a number of lung diseases generally referred to as pneumoconiosis. A priori knowledge of the mechanisms and rates of fine particle generation during mining can aid in the development of more effective technology for controlling primary dust generation. Unfortunately, the data and knowledge currently available are not adequate for this purpose. In fact, a committee of the National Academy of Sciences on the measurement and control of dust concluded that the knowledge of the fundamental mechanisms by which coal mine dust is generated and a part of it is entrained in the mine atmosphere as respirable dust is not sufficient to clarify, let alone control, the processes involved (Anon., 1980). Under a research contract from the U.S. Bureau of Mines, Stecklein et al. (1982) have identified a number of fundamental research issues for understanding the coal fragmentation and entrainment processes.Reduction of dust generation is the best means of control since fine particles are difficult to control once they become airborne. Therefore, considerable research efforts have been directed to understand the factors influencing dust generation and entrainment, including machine design, water sprays, and ventilation. Laboratory studies have been conducted on the mechanical action of bits and machine power requirements (Evans and Pomeroy, 1966; Roepke, 1984). Since the physical characteristics of coal play an important role in the process of breakage, a number of laboratory studies have been conducted to study the relationship between coal characteristics and respirable dust generation (Baafi, 1977; Moore, 1986; Polat, 1990; Thakur, 1971). Several studies have been conducted on the relationships between coal characteristics and airborne dust concentrations (Hamilton and Knight, 1958; Khair and Xu, 1991; Organiscak and Page, 1993; Page et al., 1993). A limited number of studies have also been conducted on the relationships between coal characteristics and airborne dust concentrations in mines (Organiscak et al., 1990). Yet, no reliable method has been developed to rank coal seams according to their respirable dust generation potential. The conclusions derived from previous studies can be summarized as follows:"

Dec 1, 1996

By M. A. Bussell, G. S. Camm

The study included lode zones at Wheal Pendarves, South Crofty and Rosevale tin mines. Fluid inclusion-containing microfractures are a common feature of the granites and typically show a preferred orientation over quite a large area. The close proximity of a dominant vein or fault controls their density and orientation. They are important pathways for fluids and provide a marker for palaeo-fluid flow. Overprinting provides a reliable representation of the evolution of the hydrothermal fluids in a vein system from early magmatic fluids to late-stage meteoric and basinal brine input. Measurement of microfracture orientation allows estimation of the regional stress regime during a specific hydrothermal event. Since micro- and macro-structures can generally be reliably correlated, these studies assist in modelling the detailed development of complex vein systems. Microfracture density is a good measure of palaeo-permeability, with implications for control of wallrock alteration. The determination of the location and density of microfractures can assist the mine geologist in identifying the location of potentially economic vein structures where macroscopic markers are absent

Aug 1, 1996

By Qing Wang

In this method the state of an open-pit mine is represented by the number of benches that are mined in each predesigned mining phase (or pushback). Consequently, a specific mining schedule can be represented by a sequence of states which starts with the topography of the mine site and ends with the ultimate pit. For a given set of mining phases all feasible states are first generated and sequences of states are then evaluated for technical and economical feasibility. The best sequence, which gives the maximum net present value (NPV), is found by applying a dynamic programming optimisation algorithm. The algorithm also optimises the cut-off grade which satisfies the mill feed requirement for each planning period. It was found that the algorithm can be used not only for scheduling but also as an effective tool for analysing the effects of mining and milling capacities and cut-off constraints on the mining schedule and the total NPV. The algorithm, which was programmed in C, was successfully applied to a large Au-Cu deposit

Jul 1, 1996

The following procedure was used to determine cut-off grades: define the orebody profile; plan the stope layout and quantify the work involved; formulate equipment-performance norms; calculate unit costs; input process recoveries and metal prices; and calculate the cut-off grade. Use of the method is illustrated using data from a copper mining complex in India. Results from the study led to the following conclusions for underground mines in general. Cut-off dependent costs vary significantly with the stoping method employed, orebody thickness, the degree of mechanisation and the working efficiencies of the workforce and equipment. This applies even within the same deposit. Sub-level stoping and its variants can be operated at a lower cut-off grade than cut-and-fill and its variants. Thinner orebodies affect cut-off grades adversely, but with thinner orebodies very little further reduction in cut-off grade can be achieved once a certain minimum width has been exceeded. For the same stoping method and in the same mine the cut-off grade varies with the degree of mechanisation. Labour-intensive methods require higher cut-off grades. An allowance for working efficiency should be made when calculating cut-off grades. Higher process recoveries allow a significant lowering of cut-off grades

Jul 1, 1996

By D. D. Lei, H. Sevim

Long-term production planning in open-pit mines requires the determination of cut-off grade, mining and milling production rates, a mining sequence, mine life and ultimate pit limits. Since these variables interact in a circular fashion, a genuine solution to the problem necessitates their simultaneous determination. A methodology with this capability is described. This comprises a group of heuristic algorithms and an unconventional dynamic programming algorithm. The method is demonstrated using data for a gold deposit in the western USA

Jul 1, 1996

By S. G. Beattie, N. Mojtabai

A study was carried out which aimed to: determine the effects of blasting on excavation perimeters and nearby slopes; establish a low-cost blast monitoring and field observation programme to determine peak particle velocities and blast damage; and to develop criteria for observable blast damage that are based on the peak particle velocity. Full-scale production blasts in a large open pit copper mine were monitored and studied to develop damage criteria for various rock types. Better blast designs can be achieved by correlating the results of blast monitoring with field observations of damage at the pit walls and on benches. Back-break and damage are related to blast-induced ground vibration. Peak particle velocity is accepted as a reliable measure for the prediction of ground vibration levels. Empirical models for the estimation of rock damage can be developed and used for blast design. The models are used to determine the zones of damage within the rock face. Rock damage models can also be used to design trim shots to achieve further reduction of back-break in more critical areas

Apr 1, 1996

By H. Forster, F. H. Koenemann, U. Knittel

The greenstone belt developed along the Sandawana line, an anastomosing, transcrustal shear zone. The lode gold is concentrated in veins and along brittle-ductile shear zones and other faults. Gold contents of 200 rock samples were found to be well below economically significant levels, excluding purely syngenetic deposit formation. Average gold content of unmineralised banded iron formation decreases from 7.3 ppb in the east (Manica) to 1.6 ppb in the west (Odzi), where depletion reflects hydrothermal leaching. The mineralising fluids may have been generated during deep crustal deformation, metamorphism and magmatism. Gold was hydrothermally deposited during carbonatisation and sericitisation of ultramafic and mafic rocks and during hydrothermal overprinting of banded iron formation and felsic rocks. It is present in native form and as microscopic to submicroscopic inclusions in pyrite, arsenopyrite and pyrrhotite. Argentiferous galena and other sulphides are commonly observed. Rezende, which produced over 38 t Au, is hosted by a granodiorite stock. By-product gold was produced from Cu-Ni sulphides at Mundonguara. The deposits are related to the older, but not the younger, of the granitoids intruding the belt's supracrustal sequences; the estimated age of mineralisation is 2700-2600 Ma. Odzi district, with 61 mines, has produced only 3.5 t Au as its higher-level host rocks have apparently been eroded. Mutare (formerly Umtali) district, with 133 mines and 9 placers, has produced 68 t Au (65 t from Rezende and adjacent deposits), and Manica district, with 23 mines and 8 placers, 12 t Au. Estimated reserves for the Rezende area are 20 t Au and for Manica district 4 t lode Au and 19 t placer Au

Apr 1, 1996

By P. Varona, L. Lorig, M. Board, E. Chacon

Geomechanical factors at the mine are important and will become even more relevant as the pit expands and deepens. To address these demands a team was assembled to collect geomechanical information and perform numerical analysis. The west wall is the largest and flattest of all the design sectors in the pit and rigorous studies were carried out on this wall. The wall behaviour is controlled mainly by a set of steeply dipping joints within the slope in the Fortuna Granodiorite and a weak zone, the Zona Plastica, that extends vertically near the pit bottom. These features lead to large toppling displacements in the upper portions of the wall. Two numerical models were used to reproduce the general features of failure observed in the wall. The modelling indicated that a toppling mode of failure results from shear on the steeply dipping joints. The toppling leads to slumping or landslides whereby the west wall flows slowly downslope as the Zona Plastica compresses

Apr 1, 1996