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By Thomas D. Kaufmann, Robert C. Drury

Few factors are as important as fluctuations in aggregate economic activity and exchange rates in determining the profitability of mineral investments. Macroeconamic theory explains how the two factors are interconnected in today's world and in tomorrow's. We can use macro¬economic theory to lessen some of the risks in mineral investments. And in the current state of the world the risks are high. The above paragraph summarizes our argument. Our goal in this paper is to examine the nature of contemporary business cycles so as to explain their implications for the metal industries, particularly the implications for capacity. Thus, our first section examines the workings, causes, and history of the recent economic fluc¬tuations. In doing so we must understand how current world economy is interconnected, that is, how economic events in one country are trans¬mitted to the rest of the world. Our view is that governments and central banks are key actors in the creating of economic fluctuations. Then, in section two, we work out the implications of section one for the metal industries focussing on comparative advantage, trade, and capacity decisions. Over the last fifteen years the world economic system has had slow overall economic growth and has had strangely unpleasant recessions. While future business cycle will not repeat the de¬tailed pattern we have seen, there will be similarities. The similarities need to be under¬stood before investment occurs. The slow growth in the world economy since the early 1970s has aggravated the problems from business cycles, created its own problems, and has partially hidden the effects of other events. Major realignments of currencies are likely to take place over a business cycle. The nature of the causes of the cycle will determine the direc¬tion of change in the exchange rates. For example, whether a USA recession will be accompanied by a weaker or a stronger dollar will be determined by the cause of the recession. The realignment of currencies over a business cycle leads to a realignment of comparative advantage in the metal industries. Thus, not only will world metal consumption vary over the business cycle but the impact on various countries' metals industries will differ consi¬derably. Competitiveness often depends more on the value of the dollar than it does on inherent efficiency and wage rates. Capacity decisions are inherently riskier due to the country specific nature of exchange rate risk. A realignment of currencies changes the pattern of trade if and only if the country with the cheaper currency also has idle capacity. The importance of our topic is indicated by Table 1 which shows the impact of cyclical and exchange rate shocks on the USA metal industry. In the cyclical downturn, from the peak of 1979 to the trough of 1982, consumption dropped by a fifth to a third. Metal price moved in the same

Jan 1, 1989

By Georgios Kafantaris, Carsten Bonde, Nataša Katic

Within the investigation works for the Copenhagen Cityring metro, Geo/CMT have carried out 90 geotechnical boreholes. Together with the previously available investigation, this resulted in more than 15 km of vertical drillings and several thousands of laboratory tests. The design is made for 17 stations, four shafts and two parallel 16 km long tunnels. The geotechnical investigation and design have been carried out in several stages comprising appropriate refinement of structural design and design of excavation operations, including TBM break-in and launching operations at each station shaft. Acceptance of the solution and / or refinement of the investigation and design schedule in the next stage were based on the geological conditions, area availability at surface level, planning and cost-control criteria. The applied recursive design refinement is presented herein with an example of the Østersøgade shaft location.

Jan 1, 2016

By Ted Budd, Vladimir Goubanov

The East Central Interceptor Sewer, commonly known as the ECIS Project, is the largest public works construction project awarded by the City of Los Angeles. The complexity of this $240 million project, together with the challenge created by the mandated 1,000 calendar days for construction completion, make this project a major interest for the tunneling industry. This paper will describe the ECIS tunnel project, currently under construction by the Joint Venture of Kenny (Sponsor) / Shea / Traylor / Frontier-Kemper. Mining of the18.5 km (about 11 miles) long and 4.7 m (15ft-4in) diameter tunnel is underway with four Tunnel Boring Machines mining at the same time. Details on the mining machines, muck handling systems, innovative construction sequence, together with mining progress will be given.

Jan 1, 2003

By S. C. Westerfeld

The original patent for the gyratory crusher was granted to Philetus W. Gates in 1881. This first crusher was used by the Buffalo Cement Co. At the time these early gyratory crushers were developed all mining and quarrying, either underground or open pit, was done by hand; tonnages generally were small and product specifications simple and liberal. Likewise plants were small and demands for small product sizes practically nonexistent. In addition to substantial amounts of hand labor, the available material handling equipment was small, simple, and not suited to handling large run of mine ore. Mine can, cable ways, or belt conveyon transporting crushed material to the mill had limited capacity per hour. At the turn of the century the largest Gates crusher, the No. 9, had a receiving opening of 21 x 48 in. with a three-arm spider and a 21 x 80-in. opening with a two-arm spider. The steam shovel began to change the entire picture of open pit quarrying. As a result of the use of steam shovels around 1910 crushers with 48-in. receiving openings were built; thus it can be seen that the basic gyratory crusher was developed prior to World War I. The improvement of the internal combustion engine and the use of pneumatic tires created a new set of operating conditions. Early mines were small, using shrinkage stoping and small mine can. The capacity of material handling was small, limiting the size of the largest piece and the feed rate. Improved material handling resulted in more and more large open pit mines with large shovels and a tremendous increase in the size of off road or mine haul trucks or rail can. Primary gyratory crushers also increased with receiving openings as large as 60 in. and connected hp of 1,000.

Jan 1, 1985

By J. W. Leonard, C. L. Jiang, B. K. Parekh, X. H. Wang

The selective depression of pyrite from the Kentucky No. 9 coal seam was systematically examined using various kinds of inorganic and organic chemicals. Most of the organic chemicals tested showed little selectivity in pyrite depression. It was found that both orthophosphate and pyrophosphate were effective for the selective depression of coal pyrite in coal flotation using fuel oil as a collector. At substantially low concentrations of pyrophosphate, the flotation of coal pyrite was completely depressed over a wide pH range, while the coal flotation remained unaffected. The mechanism of the selective depression of pyrite by phosphates was explained with the help of thermodynamic calculations of iron-phosphate-water systems and zeta-potential measurements. It was shown that pyrophosphate reacts strongly with the iron ions of pyrite to form stable hydrophilic iron pyrophosphate complexes on pyrite surfaces.

Jan 1, 1999

By K. Severin, B. Flanigan, P. Marion

"Plutonic-related" gold deposits in Interior and SW Alaska (Tintina Gold Belt) vary significantly in size, grade, vein/deposit morphology, depth of emplacement, distance from causative pluton and metal association. Metal associations such as Au-Bi and Au-As- (Sb-Hg) are a good empirical indicator of the depth of emplacement and distance from causative pluton. These associations have been used successfully in exploration. Results from several analytical techniques also suggest a phenomenological cause for these metal associations. Gold and bismuth have paired mineralogy at high temperatures and, thus, are best correlated at deposits that are deep and/or close to causative intrusions.

Jan 1, 2003

By Andrew L. Mular

Methodology to model, simulate and optimize full scale mineral pro- cessing circuits in production environments is reviewed and evaluated. Strategies for data acquisition and adjustment are considered along with techniques to fit models to adjusted data. Examples are considered for clarity.

Jan 1, 1989

By Changhong Huang, Y. J. Wang

This paper describes the formulation of mine ventilation network optimization as a standard nonlinear programming problem and the solution of the problem using the generalized reduced gradient (GRG) method. In general, the GRG method is regarded as one of the most effective and efficient methods for solving large-scale nonlinear programming problems. The variables considered in the network optimization include air quantity, regulator pressure loss, and fan pressure for each branch. Each of the variables is constrained by lower and upper bounds. This facilitates proper assignments of ventilation requirements and provides a great flexibility to include various situations encountered in mine ventilation. The objective of the network optimization is to minimize the overall air power consumed by or supplied to the network; whereas the constraints are, in addition to the variable bounds, the two fundamental network laws: Kirchhoffs voltage law and Kirchhoffs current law. A computer program has been developed based on the GRG method for the network optimization. An example of network with 18 branches, 8 regulators and 3 fans is included for illustration.

Jan 1, 1993

By L. M. Yokum

Tremendous strides have been made in front end loaders in the last fifteen years. Fifteen years ago a 2; cubic yard front end loader was the largest standard machine you could purchase. Today there are two commercially available 15 yard front end loaders and many 10 yard front end loaders. The estimated total worldwide market for all front end loaders over one cubic yard has increased to over 30,000 units yearly. The trend for front end loaders, in general, and for the mining market, in particular, is to larger and larger loaders. Today there are 18 cubic yard and a 24 cubic yard front end loader in prototype form. It is not inconceivable that within another fifteen years that there will be front end loaders in the 50 cubic yard class with design features quite different from today's. These larger loaders are being designed at the demand of the mining industry and the design criteria are being directed at this market area. The costs of these larger loaders will be greater per unit of capacity, and it is the intent of the various manufacturers that they will be more reliable, be easier to service, give greater availability, live longer, and cost less to maintain, than previous loaders. It is also the intent of the manufacturers to compete directly with the large mining shovel as the front end loaders become appropriately larger and more reliable. There has been some trend in this direction in the past with smaller shovels and loaders. In Figure No. 1 are data for U.S. production of front end loaders (5-6 cubic yard class and 10 cubic yard class) and U.S. production of cable operation, crawler mounted power shovels, draglines and cranes (1; to 5 cubic yard class) for the years 1965 and 1970. (Source: Bureau of Census, U.S. Department of Commerce.)

Jan 1, 1972

By Christophe Bragard, Rebecca Reeve

The Regional Connector Transit Corridor (RCTC) Project is a 1.9-mile-long metro light-rail extension project that traverses the historical core of downtown Los Angeles, California. This project aims to improve mobility throughout downtown LA with fewer transfers for riders. It is designed to connect two existing rail lines for a more seamless travel. The project consists of twin bore tunnels, three new stations, and is scheduled to be completed in 2022. The design-build contract was awarded to the Regional Connector Constructors (RCC) in 2014, a joint venture of Skanska and Traylor Bros, Inc. with Hatch Mott MacDonald as the designer. One of the challenging aspects of the project was the construction of a crossover cavern in a narrow public right-of-way surrounded by historical structures. RCC used Sequential Excavation Method (SEM) to construct the crossover cavern measuring 287 ft long by 58 ft wide by 36 ft tall. The initial lining of the cavern featured a 12 in. fiber reinforced shotcrete lining. The initial lining was separated from the final lining by a hydrocarbon resistant membrane, as specified by the standard requirements of Metro. The cavern features a cast-in-place final lining with a thickness of 5 ft 9 inches in the invert and 18 inches in the crown and walls. The structure also features a nonload bearing plenum slab and interior walls for ventilation.

Jun 13, 2021

By James R. Arnold, John G. Mansanti

BACKGROUND Gold Fields Mining Corporation started their Chimney Creek operation in late 1987. The dump leaching operations commenced in October and the mill startup took place during the last half of November. The milling process at Chimney Creek is almost a conventional CIP plant with the major exception being the installation of a second thickener as a washing stage prior to CIP12 ' A simplified flow sheet is shown in FIGURE 1. Most of the gold in the mill is liberated by grinding in cyanide. After grinding in a conventional SAGball sill circuit, the cyclone overflow reports to the thickeners. The thickener overflow from the first thickener is pumped through 5 stages of carbon columns for gold adsorption. Slurry from the thickener underflow is leached, washed, re-thickened and pumped to CIP. After approximately 6 hours of retention time in CIP, the slurry is pumped to tailings for final deposition. The carbon from CIP is transferred to the third stage of carbon adsorption and then advanced as normal through the columns and strip circuit. Loaded carbon is stripped at approximately 1500C (3000 F) and 55 kPa (80 psi). After 4-5 hours of stripping, the grade of four tons of carbon is reduced from 5,140-6,860 g/t (150¬200 oz/ton) to typically 17 g/t (0.5 oz/ton). Zinc precipitation is used to recover the gold from the pregnant solution. After a water wash, the stripped carbon is transferred to acid wash or to the kiln feed tank for reactivation. All strip lots are acid washed in 3.0% HC1 and all stripped carbon passes through the kiln for thermal reactivation. Then the carbon is quenched, sized and stored in tanks or bins for transferral to CIP or to the carbon columns. Loaded carbon from the dump leach circuit is treated in a circuit consisting of five carbon columns which are parallel to the mill circuit. No distinction is made between the mill or dump leach carbon once the gold has been stripped from them. CARBON FINES HANDLING Once the carbon has been transferred from the carbon columns, every effort is made to minimize carbon attrition and to recover the carbon fines that have been generated in the process. Wemco Hidrostall pumps are used for transferring all carbon in

Jan 1, 1990

By Robert L. Randall

The mineral industries have a continuing need for market forecasting and analysis for a variety of purposes, among which are organization and control of the sales effort, financial and corporate planning, and evaluation of the anticipated revenue from investment in proposed projects. For anything beyond the simplest extrapolation, some kind of economic reasoning or analysis is called for, which may or may not be incorporated into a formal or quantitative model. The principles described here apply to most of the commercially significant minerals and metals. The examples are drawn largely from the copper market, as it is the one with which I have the most practical experience. Practical forecasting is the process of analysis and synthesis from three categories of knowledge: facts and statistics, theory, and practical knowledge and informed opinion. Although many attempts have been made to build forecasts on only one of these three pillars, none has been successful as an operating procedure because of the lack of balance. There are no facts about the future-only about the present and the past. Facts can illuminate the future, but the future can be described only in terms of probability or more or less likely states of affairs-not as a continuous extension of the past and present. Likewise, theory, although useful as an organizing discipline and for providing a methodology of analysis, is inadequate for the complexities of reality. This is especially so when there is feedback between plans and forecasts to produce a new outcome and when there are significant elements of unpredictable free will, such as presidential jawboning or foreign policy considerations. Such elements are difficult to accommodate in neat theories, although they must certainly be reflected in the forecasts. Pure opinion frequently suffers from both a lack of-disciplined reasoning and the presence of biases or self-interest. While the future is unknown, it tends to cast its shadow before it; hence, forecasting is the art and science of positioning oneself so that the shadow becomes visible to the forecaster.

Jan 1, 1979

By I. Kapageridis

The mining industry worldwide has recognized in the past the need to apply specific rules and guidelines in the reporting of mineral resources and reserves. The high financial investment and risk associated with any mining project and the ever stricter environmental and social controls were the forces behind this recognition. For years the industry experienced the development and enforcement of several codes for reporting accepted by different countries. The implementation of any code can be a confusing task as the guidelines are sometimes general and open to different interpretation. The use of computers in the estimation and reporting of mineral resources and reserves is necessary, particularly when trying to implement particular code guidelines. This paper discusses ways to implement a reporting code in a computerised resource/re-serve estimation study. The implementation is demonstrated using a gold deposit project as an example. The effects of mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors are taken into consideration. This paper also discusses well established reporting codes and the possibility of reaching a single, universally applied code that could be used by Greek mining companies.

Jan 1, 2007

By John A. Cordes, John J. Schanz

INTRODUCTION The economic structures of industrialized countries require a continuous supply of reasonably priced and appropriately processed nonfuel minerals. As a result, national policy makers are sensitive to real or perceived threats to the effective operation of these commodity markets. Their most persistent concerns can be subsumed into the related political economy issues of supply availability and marketplace stability. These concerns are not new. For over a century the "global struggle" for mineral resources has influenced national policies and international relations (Eckes, 1979). During the past two decades the complexity of these issues, if not their place on national political agendas, has increased. Dramatic changes in the structure of mineral industries and in the nature of international economic relations have redefined policy needs and response options. This paper focuses on how selected OECD countries have responded to nonfuel mineral industry issues over the past twenty-five years. Particular emphasis is placed on the impact these policy decisions have had on the size and location of productive capacity and its utilization rates. The results, perhaps, are not surprising for this group of market- oriented economics. While individual cases of significant impact are easy to identify at various times in most countries, the overall importance of policy decisions has not been great. This is especially true for the past decade when excess capacity reached unusual highs of magnitude and duration. Macroeconomic forces and market structure changes played much more important roles. PERSPECTIVES ON THE ISSUES OECD nations dominate the international nonfuel minerals marketplace as producers, consumers and traders. In 1986, these twenty-four countries accounted for 75 percent of the Western world's export trade value in minerals, ores and metals. They imported 88 percent of the total value. During 1966, the respective percentages were 70 and 94. Japan was the world's largest importer in 1986 followed by the US, FRG, UK and France. The same five countries led the 1966 list except that, then, Japan was ranked fourth. Table 1 ranks the fifteen largest Western exporting nations in the two specified years. It also indicates the growth in current export dollars earned in 1986 compared to 1966.

Jan 1, 1989

By Christopher Hebert, Michael R. King, Mehdi Ghazi

The Inland Feeder project is a critical component of Southern California’s water delivery system, relying on a strategic plan of water transfer and storage to enable the delivery of an additional 650 million gallons of water a day. The Arrowhead West and Arrowhead East tunnels form part of this system, comprising the construction of nearly13 km (8 miles) of bored tunnel under the San Bernardino National Forest. This paper describes the design and manufacture of the 4.88 m (16 ft) diameter precast segmental primary lining that will be used in these tunnels to resist rock loads, and up to 275 m (900 ft) of external hydrostatic head.

Jan 1, 2003

By Zhen-xing Diao, Feng Zhao, Ya-dong Xue

"Two important aspects of excavation performance of TBM are advance rate and cutter replacement/ring consumption, which is closed to the cost and construction duration of the project. To achieve this, a database of TBM parameters and the geological-geotechnical conditions during the excavation of Yinhanjiwei was compiled and analyzed. Relationships between different geological and TBM operational parameters were investigated. Results of analyzes show that there are qualitative correlation between Field Penetration Index (FPI) and rock geological parameters. And strong relationships between FPI and operational parameters are suggested. In this study, the cutter replacement and ring consumption were analyzed using statistical method for preliminary estimation in similar conditions. 1. ITRODUCTION Hard rock TBM is widely used in tunneling project nowadays because of its advantages to conventional drilling and blasting, especially in long tunnels. The biggest advantage is its high advance rate. However, rock conditions of tunnels are complicated. So TBM performance becomes a primary topic in tunneling engineering, which includes of rate of penetration, utilization, daily advancement, cutter consumption and so on. Many prediction models have been developed to estimate the TBM performance in the project planning phase. The most widely accepted and used models around the world are semi theoretical CSM model (Rostami and Ozdemir, 1993; Rostami, 1997) and the empirical NTNU model (Blindheim, 1979, Bruland, 1998).With increasing uses of TBMs in different ground conditions, an increasing number of researchers have developed new models in order to predict the performance of TBM more accurately in similar geological conditions.(Gong and Zhao, 2009; Hassanpour et al.,2009, 2010, 2011, 2014; Delisio et al., 2013; Delisio and Zhao, 2014)"

Jan 1, 2016

By Charles A. Beasley, Vince Joyce, David E. Beasley, Orlando A. Gallegos, David A. Shuman, Mehmet H. Erten

COAL CHARACARISTICS AND PREPREPARATION REQUIREMENTS Preparation and Market Specifications The national ambient air quality standards (NAAQS) established by the Environmental Protection Agency in 1977 require that when coal is burned, the environmental degradation should be a minimum. For this reason, even coal containing low ash and sulfur must be used in compliance with the NAAQS. The most important pollutants resulting from the combustion of coal are ash, SO2, and NOx gases, and the particulate matter escaping with the combustion gases. The ash is the residue left after complete combustion of coal. It results from the inorganic mineral matter existing in the coal before it is burned. The SO2 results from the combustion of inorganic and organic sulfur associated with the coal. The inorganic sulfur may occur as pyrite, marcasite, or as sulfate sulfur of mostly iron and calcium. The authorities disagree in the definition of organic sulfur in the coal. However, according to ASTM Standard D2492-77,1 the organic sulfur is that sulfur occurring in the coal after subtracting the sum of pyrite and sulfatic sulfurs from the total sulfur in the coal. The NOx gases are produced from high temperature oxidation of nitrogen in the coal that is released into the atmosphere. The particulate matter may consist of fly ash and unburned coal. Selective Mining The cleaning of coal from included ash and sulfur-bearing materials should start at the working faces of surface or underground mines. This can be done by (1) mining only those seams which meet certain quality standards, (2) not mining sections of the seams which may cause deterioration in overall quality of the mined coal, and (3) using a mining method that allows selective mining of coal areas or horizons either underground or on the surface. Since these steps improve the coal quality before the coal reaches the preparation plant, they can be considered to constitute precleaning of coal. During the exploration and development stage of a mine, core and channel samples taken from the coal seam are used to determine (1) petrographic analysis and physical properties,2 (2) character of roof and floor of the seam, 3,4 (3) character and quality of impurities,5 (4) proximate and ultimate analysis, and (5) washability characteristics. However, all of these parameters are subject to considerable variation even within the same seam during the advance of the coal face. This creates a problem in meeting the market demand for coal quality if the coal is to be shipped directly from the mine. If the mining operation is large enough, special blending silos or mechanical blending systems may have to be used to provide uniform quality to the market. However, even if the coal is shipped from a coal preparation plant, prepreparation

Jan 1, 1991

By Richard L. Gordon, William A. Vogely

ENERGY POI.ICY-PRINCIPLES AND THEIR PRACTICE Persistently, at least since the end of World War 11, governments have intervened broadly, deeply, and incoherently in major energy markets. If we take a broad definition of energy that encompasses gas distribution and electric power, we can observe regulations of even older vintage. This trend, of course, is not unique to energy. Expansion of government controls has occurred in many areas. The relevant basic question about energy regulation, therefore, is not why is energy special, but whether any general principles exist to explain the wisdom of existing regulations. This review takes place at a time, the middle 1980s, in which a massive onslaught is being undertaken against government regulation. However, the present chapter is influenced primarily by my observations of the failures of energy regulations and not by any inspiration from those ideologically opposed to government intervention. Several subquestions arise in policy appraisal. A primary need is to establish clear objectives and determine the consistency between these goals and the policies imposed. Thus, the first step is to set objectives. The next is to outline ways to attain these goals. However, it should be recognized that many apparently distinct options are economically equivalent. When the goal is to charge producers or consumers for something, it is possible to attain the same result through either government ownership or taxing private transactions. The tax can raise the price to the level the government would have charged if it were the owner. Creation of a Department of Energy is not necessarily any different from having separate energy agencies well coordinated by some small supervisory body. Thus, a distinction should be made between substance and form in policymaking. The critical substance concerns such matters as whether the government imposes financial penalties, incentives, or rules to attain a goal. Then, there can be many equivalent ways to implement the basic policy form. The second prior illustration suggests that one favorite question is how to attain proper integration of policy. At various times, voices on either (or even both) sides of the Atlantic have called for a coordinated energy policy. The U.S. Paley Commission made this a primary goal for future policy. The western European governments that were the founding members of the Coal and Steel, Economic, and Atomic Energy Communities spent much time in the middle fifties and much of the sixties trying futilely to agree on an energy policy. (See Gordon, 1970 for an annotated review). The energy price rises of the 1970s rekindled United States interest in coordination. However, astute observers of the problem such as O. C. Herfindahl of the United States and Maurice Allais (1 962) in France warned the discussions confused form with substance. The crucial issues were what were the goals and what were the best types of policies to attain such goals. Policy suffered, not from poor organization, but from discord about the goals and how to attain them. All this suggests that we need principles to guide policy appraisal. The branch of economic theory known as welfare economics concentrates on providing guidance about the problems of policymaking. The theory examines both what

Jan 1, 1985

By Frank F. Aplan, Edward C. Jr. Dowling, Richard R. Klimpel

Thirteen kinetic models that mathematically describe the flotation process have been statistically evaluated for the flotation of copper, lead and zinc ores. Comparisons have been made for a variety of circuits involving roughing, cleaning, scavenging and regrind followed by cleaning. Variations in collectors, frothers, depressants and activators have been considered. Based on the statistical criteria used for the evaluation, and the reagent, circuit and ore variations studied, the most reliable flotation models have been identified and subsequently used to characterize the metallurgical results.

Jan 1, 1986

By Yunsheng Yao, P. Golledge, A. D. S. Gillies

In order to investigate the explosibility of sulphide mineral dusts, sulphide ore samples were collected from five underground metalliferous mines in Australia. The mineralogical and chemical composition of the dust samples was analysed by X-Ray Powder Diffraction and Atomic Absorption techniques. Simulated post detonation fumes were produced and used in dust explosibility tests to examine the influence of the fumes on sulphide dust ex- plosions. These tests were conducted in a 20 Litre Siwek Explosion Chamber with measurement and control system that is regarded as a standard testing system worldwide for dust explosion studies. The dust mineralogical composition and dust explosibility tests indicated that the content of sulphur can not accurately predict the explosibity of the sulphide dust. The percentage content of pyrite in the sulphide dust can be a relatively reliable diagnostic criterion in evaluating the risk of sulphide dust explosions in the mining of a massive sulphide orebody. The hybrid explosion tests demonstrated that the post detonation fumes from ANFO not only decrease the lower explosion limit of the sulphide dusts, but also increase the severity of the dust explosions. The explosion pressure reaches its peak value when the fumes content in the explosion chamber is about 20 per cent by volume

Jan 1, 1997