Search Documents

By M. B. Mansur, A. S. Guimarães, A. J. M. Santanilla, D. C. R. Espinosa, J. A. S. Tenório, R. A. Pini

The separation of Ni and Co from sulphate medium containing Mn, Mg, Cu and Ca was carried out by solvent extraction. The object of this study was to investigate the synergistic effect using phosphinic acid (Cyanex 272) and carboxylic acid (Versatic 10) and their mixtures in kerosene. The extraction percent of each metal ion was found to increase with increasing pH and extractant concentration. Co was preferentially extracted over Ni under the same extraction conditions. The separation factors of Ni/Co increased with the use of the synergistic systems investigated.

Jan 1, 2014

By Rodolfo Zanella

Au/TiO2 catalysts prepared by deposition-precipitation with NaOH (DPN) (~3 wt%) and urea (DPU) (~8 wt%) were tested in crotonaldehyde hydrogenation at atmospheric pressure. There is no differences in activity (mole.gAu -1 s-1) and selectivity between both DPU and DPN samples for a given activation treatment. This is due to the fact that DPU and DPN samples exhibit similar gold particle size distribution, although the gold loading in DPU is much higher that in DPN. The DPU samples were reduced under H2 at different temperatures (120-500 °C) or under air at 300 °C with various flow rates, to vary the average particle size within a large range, 1.7 to 8.7 nm. The selectivity to crotyl alcohol (selective hydrogenation of the carbonyl bond) is high, 60-70 %, and almost constant as a function of the particle size. The selectivity to crotyl alcohol is also constant for conversions between 10 and 50%. These results suggest that the adsorption mode of crotonaldehyde is of ?3 or ?4-type. In contrast, the TOF depends on the gold particle size, it drastically increases when the gold particle size is ~2 nm. Our results are in agreement with former studies that suggest that the gold atoms involved in the hydrogenation process are those of low coordination.

Oct 1, 2003

By S. J. Cook

The system of mining statistics for Canada, as it exists today, represents the result of long years of progress, first by the Geological Survey, later and more comprehensively by the Mines Branch of the Department of Mines, and now by the Mining Branch of the Dominion Bureau of Statistics-all supplemented by the very comprehensive reports published by the several provincial departments of mines. It is the purpose of this paper briefly to state the development and present status of Canada's statistical service, more particularly in regard to information on mineral production, and to show that in its evolution continuous progress has been made in the elimination of factors tending to duplication and overlaping, with the result that the construction of an adequate statistical service has been carried out with the least possible expenditure of .public funds. For the purpose of this discussion, the subject of mineral statistics may conveniently be considered from two points of view. The technical difficulties in obtaining satisfactory and complete data from the variety of industries represented in the mining fields of Canada must be apparent to all. Methods of record-keeping are almost as numerous as mines and even the larger concerns which maintain elaborate records for their own information, often find it difficult to compile the statistical reports required of them, because the specific form of inquiry differs from the method in use in their offices.

Jan 1, 1924

By Donald Carlisle

"IntroductionTHE OPINION is held by many persons outside the mining industry, and by some within it, that mine •operators customarily find it advantageous to mine •only the richer parts of orebodies and to leave behind, perhaps permanently, leaner material which could be mined only at a lesser profit. This opinion and the inference which might be drawn from it that 'gutting' of mineral resources is a common feruture• of the mining industry are prejudicial to the intertsts of the industry and deserve careful scrutiny. Oddly enough, a theory of mine economics which gives much support for the opinion was advanced first by members of the mining profession itself, has been repeated •several times in mining literature, and to my knowledge has never been adequately refoted.According to the theory, selective mining of the rich ore first on a large scale will yield substantial gains and these gains do not merely reflect the desire of 'money minded investors' for a quick return but derive from the logical application of compound interest rates and the concept of ;present value. W. O. Hotchkiss and R. D. Parks (1) illustrate the reasoning with a hypothetical example in which an orebody of 4,000,000 tons may be mined either in its entirety in forty years at $1.00 per ton profit or selectively with the recovery of only the richest half in twenty years at $1.50 per ton profit. They show that, with Hoskold rates of 4 and 8 per cent, the present value of profits from mining only the richer 2,000,000 tons exceeds the present value of profits :from mining the whole orebody by about 20 per cent."

Jan 1, 1953

By John N. Ludden, Maurice Rive, Hillar Pintson

"Quelques soixante-dix-sept plutons présents dans la Sous-Province de Pontiac et dans la partie centrale de la Sous-Province de I’Abitibi ont fait I ’objet d’une reconnaissance systématique. Ils ont été regroupes en huit suites plutoniques majeures et trois suites mineures à partir de critères géologiques et petro logiques. Parmi les suites majeures, quatre représentent I' activité intrusive la plus ancienne dans la région. L’une d' entre e/les est représentée par deux complexes anorthosito-gabbroi' ques lites et les trois autres comprennent les orthogneiss dioritiques a leucotonalitiques et les intrusions dons la composition varie de diurétique et granodioritique à leucotonalitique. Leur mise en place peut être pretectonique a syn ou tarditectonique; certains plutons sont synvolcaniques. Quelques data/ions U! Pb effectuées à propos de ces roches donnent des âges s' étalant entre 2 718 et 2 694 MA. Les données géochimiques indiquent la présence des deux lignées magmatiques, tholemique et calcoalcaline bien qu’il n'y ait aucune évidence de relations entre elles dans I' espace et dans le temps. Ces suites magmatiques différentes peuvent provenir soit d’une croute tholemique impliquée dans un processus de subduction soit directement du manteau.Les trois autres suites majeures comprenant des monzodiorites, des granodiorites et des monzonites ainsi que les deux suites mineures comprenant des syenites correspondent à un évènement intrusif plus jeunesse déroulant entre2 694 et2 680 MA. Ces roches sont syn, tarti a post tectoniques et sont enrichies en alcalins, Ba, Sr et terres rares legeres par rapport aux quatre suites précédentes. Leurs caractères chimiques prop res suggèrent qu' e/les proviennent d' une source différente par rapport à celle precedemment citee.La derniere suite plutonique majeure correspond a un monzogranite leucocrate, riche en pegmatite, également syn a tard tectonique, dont I' age n' est pas connu avec précision. ll représente le seul granite ""vrai"" de la région et dérive d’une anatexie soit des meta sédiments soit des granodiorites-tonalites plus anciennes. La troisième suite plutonique mineure correspond a quatre stocks de granodiorite porphyrique qui n’ont pas été étudiés en détail.ABSTRACTSevenly-sevenplutons have been identified in the east-centra/part of the Abitibi Subprovince and adjacent Pontiac Subprovince. These have been subdivided, on the basis of geological and petrological criteria, into eight major and three minor plutonic suite. Four of the major suite, which represent the oldest intrusive activity in the area, range in composition from dioritic-leucotonalitic orthogneisses to diorite-granodiorite/leucotonalite and include two layered anorthosite- gabbro complexes. Their time of emplacement ranges from pretectonic to syn-late-tectonic and some plutons are synvolcanic. U-Pb zircon ages for these rocks range from 2 718 to 2 694 Ma. Geochemical data indicate the presence of both calc-alkaline and tholeiitic magma series for these rocks although there is no evidence time and space relationships between the two. The different magma series also suggest the derivation of these rocks from two sources, either from subduced tholeiitic crust or directly from the mantle. Three major monzodiorite-granodiorite, monzonite, and two minor syenite suites comprise a younger inlrusive event ranging from 2 694 to 2 680 Ma in age. These rocks are syn-, late- to post-tectonica and, compared to the above four plutonic suites, are enriched in alkalis, Ba, Sr and light Rare Earth Elements.Their distinctive geochemistry suggests that these rocks were derived from a different source region than for the older plutonic suites. The remaining major plutonic suite consists of leucocratic, pegmatite-rich, monzogranite-granodiorite. These rocks are also syn- to late-tectonic but their ages are not known with precision. They are the only ""true"" granites in the area and were derived by the partial melting of either older"

Jan 1, 1990

By Andrew J. Freyman, George S. Barry

"Mineral endowment in northern British Columbia and the Yukon Territory was assessed on the basis of geological opinion which was gathered in a quantitative framework of subjective probabilities. The survey area encompassed 364,000 square miles and was divided into 310 cells having dimensions of one degree of longitude by one-half degree of latitude. The response solicited related to tonnage, grade and number of deposits of a particular mineral in each cell. The questionnaire sought an expression of mineral endowment down to mine-able depth as distinct from economic expectations. Details on the questionnaire and responses are presented in a series of contour maps on individual commooities, which illustrate the collective occurrence picture of the respondents. The approach is largely dependent on the cooperation of an adequate number of geologists familiar with the region being examined. This approach to an assessment of the mineral endowment of a region has a wide range of applicability, from the focusing of exploration effort to aiding government and development bodies in the formulation of regional strategies and the planning, for example, of road, rail and power facilities."

Jan 1, 1970

By B. Dubreuil, J. -M. Lalancette, D. Lemieux, C. Chouinard

The extraction of gold and silver has been examined via the use of mixed halogens: chlorine and bromine. The reaction was performed in a brine of sodium chloride with a small amount of sodium bromide at 40-50°C, in an atmosphere of chlorine, at atmospheric pressure. The process takes advantage of the very high reactivity of bromine towards gold, while the higher oxidation capacity of chlorine leads to gold chloride as end product with recycling of bromine. Fast reaction rates are observed along with gold recovery at the level of 95%. Chlorine-consuming common elements are removed prior to chlorination.

Jan 1, 2011

By G. S. Ospanova

The results of complex processing sulphide copper ore and advantages of recovery of copper by vat and heap leaching, sorption, cementation and electrolytic solutions processing and utilization of waste material after heap leaching of copper for production of building materials were investigated. The combined chemical solvents with the additives of oxidizing agents are developed at the KazNTU. The solvents are inorganic or organic chemical reagents, which form complexes of Cu, Au, Ag, Pt, Ni, Sr, Co etc. Recovery of non-ferrous metals from solutions and purification of industrial waste waters is carried out on the base of using new synthetic and natural sorbents (from local raw materials) which are able to bind ions in both cationic and anionic forms depending on type of ligands and external conditions. Optimum parameters of copper sorption were determined. The developed wasteless technologies of copper extraction from sulphide ores with usage of new non-toxic solvents and accessible sorbents with full recycling of water are tested in pilot scale heap leaching, and are recommended as the ecological, economical and practical alternative to traditional methods.

Jan 1, 2007

By K. Hawboldt, J. E. Halfyard, C. Bottaro, I. A. Harrison

"The removal of elemental sulfur from leach residues derived from massive sulfide concentrates via hydrometallurgical routes has been demonstrated in a laboratory setting by converting water-insoluble sulfur to water-soluble polysulfides. The approach was applied to leach residue from Vale's nickel hydromet demonstration plant in Argentia, Newfoundland, which contained significant amounts of elemental sulfur. This technique offers an alternative treatment protocol for residues with a sulfur component not amenable to standard flotation/hot filtration processes. The practical considerations of a proposed flow sheet will be discussed including the impact of other sulfur species (e.g. thiosulfate and sulfides) and key process variables. INTRODUCTIONPresently, large scale elemental sulfur extraction from hydrometallurgical leach residue is performed by Teck Resources using a process of sulfur flotation followed by hot filtration (Chalkley et al., 1993). As mentioned, the technique proves viable for residues derived from specific concentrations - in this case zinc - whose residues constituency is primarily elemental sulfur itself. However, problems arise when this constituency is altered as happens when, for example, a mine containing one particular concentrate is mixed or replaced with a differing concentrate from a second mine. Such cases can often strain the effectiveness of current sulfur removal processes (D'Odorico, 2004). If hydrometallurgical residue containing elemental sulfur cannot be effectively treatment by flotation, the residue is stored subaqueously as is the case in some 'grass roots' hydrometallurgical plants (those not coupled with smelting operations). Hydrometallurgical processing of concentrates involving pressure leaching is becoming increasingly common throughout the mining world, the genesis of which can be found in research performed by Sherritt in Fort Saskatchewan since the 1950’s (Ozberk et al., 1995).The investigation of elemental sulfur removal by means other than flotation includes the uses of sulfide salts (NH3S or Na2S) effecting the conversion of hydrophobic elemental sulfur to hydrophilic polysulfides. The work of Kunda et al. (1974) and Olper et al. (2007) shows that elemental sulfur can be quantitatively removed from hydrometallurgical leach residue via the formation of a mixture of polysulfides."

Jan 1, 2012

By R. Holmwood, M. Faris, P. Holloway, M. Collins

Sulphuric acid addition is a major driver of the economics in the processing of nickel laterite ores by high pressure acid leaching (HPAL). Understanding the optimal acid addition rate is essential for the success of any HPAL operation, and this is especially true at Ambatovy, where the composition of the feed tends to vary significantly on a day-to-day basis. Most studies on the effect of acid on nickel extraction in HPAL have used laboratory testwork as their basis. Although these studies are invaluable in assessing the economics of a new project, they are limited by the range of ore composition that can be tested and the differences between the operation of the laboratory equipment and the commercial plant. To enable optimization of the acid addition at Ambatovy, operating data from the HPAL operation were obtained using OSISoft’s PI system and the data from several periods were examined to develop relationships between acid addition and nickel extraction. The initial relationships from 2014 focused on the acid required to achieve a target nickel extraction of 95%, with aluminum and magnesium in ore and feed slurry solids content as the major variables. As Ambatovy ramped up through 2015 and 2016, the calculated acid requirement was further refined to address the effects of HPAL temperature and retention time, and the oxidizing/reducing characteristics of the ore, and to generate acid requirement relationships as a function of ranges of nickel extraction. These relationships supported raising the target nickel extraction to 96% and enabled the development of an economic model between acid addition and nickel extraction.

Jan 1, 2017

By Vicki Tschirhart, Bill Morris, McMaster University

A new method for mapping faults within basement rocks underlying the Thelon Formation and glacial overburden was developed and tested in the Aberdeen Sub-basin. This method utilizes newly acquired aeromagnetic data, the Blakely algorithm for defining magnetic source edges, a calculated dip-direction map, a digital elevation model (DEM) derived from the Canadian Digital Elevation Database, and the positions of identified, inferred and newly mapped faults that are within and adjacent to this sub-basin. Combining these data revealed three age groups of faults. One group is seen only on the DEM; these faults are young brittle structures that have no effect on the sub-Thelon basement unconformity, and are not visible on the dip direction map. A second group is evident on the dip direction map but not the DEM; these faults are old basement structures that did not propagate upward through the Thelon Formation. The third group is expressed on both the DEM and dip direction map; these faults are also old structures that propagated upward during and/or after deposition of the Thelon Formation. The latter group of faults may be of greatest interest for uranium exploration, with reactivation increasing their potential to serve as conduits to transport uranium-rich fluids and focus deposition at or near the unconformity surface. This methodology has promise for comprehensive mapping of basin faults and tracking the tectonic development of the whole Thelon Basin through time.

Jan 1, 2013

By Rejean Gagnon, Fernand Rochefort

"Haulage costs, in most operations, represent a large portion of total cost. Quebec Cartier Mining Company came to the conclusion t hat an electric trolley assist providing more horsepower than available from dieselgenerator sets presented the best oppor tunity for improvement. Accordingly, a testing and development program was carried out which resulted in the design, installat ion and application of a practical system. This paper describes the development of the system, the equipment used as well as the actual operation. A projection is also made to indicate further improvement in productivity. A comparison is made of truck operating data before and after activation of the trolley assist system in order to determine its economic impact."

Jan 1, 1972

By K. Bowes, M. D. Maley, R. J. Ring

The Honeymoon Uranium Project is an acid In-Situ Recovery (ISR) mine in South Australia. It was previously operated for approximately 18 months before being placed on care and maintenance in 2014, it was then acquired by Boss Resources in 2015. Boss has been performing a number of studies to plan for reopening of the mine, including a successful field leach trial (FLT) in 2017. The current configuration for uranium precipitation at Honeymoon is a batch process. Whilst this achieves effective uranium recovery, the precipitates produced are often very fine, with poor settling and solid/liquid separation characteristics. Continuous precipitation, involving recycling of solids, has reportedly been successfully utilised in other operations to increase the particle size and density of the product, leading to solids that can be more readily dewatered, dried and drummed, with less fines and dust generation. However, no operational data are available from such operations.

Jan 1, 2020

By T. Crivits

"Freeze lining technologies are used industrially to protect the integrity of furnace walls in pyrometallurgical reactors. This is achieved by solidifying a protective layer of slag on the inner furnace wall. In the current study, laboratory experiments have been undertaken to produce freeze linings in ‘Cu2232 O’-‘FeO’-MgO-SiO slags under controlled conditions using an air-cooled probe technique. Whilst most thermal models of freeze linings have assumed the freeze lining-bath interface to be at the liquidus temperature of the bulk bath and to be planar in geometry, the current research has demonstrated that this is not the case. Experiments undertaken using this high-temperature slag system have shown the interface at steady state conditions to be at subliquidus temperatures. The solid phases present at the interface do not include the primary phase and the interface is non-planar. The study indicates the need for improved understanding of the fundamentals of freeze lining formation, and of the influence of system properties and process parameters"

Jan 1, 2015

By J. C. O'Rourke

"This paper presents an overview of Alberta Oil Sands Technology Research Authority's in situ oil sands recovery project at its underground test facility near Fort McMurray. It covers the rationale for horizontal wells drilled from tunnels below the oil sands, the tunnel layout, the drilling program, and the recovery process and facilities. INTRODUCTIONThe Alberta Oil Sands Technology and Research Authority (AOSTRA) has constructed an Underground Test Facility (UTF) in the Athabasca oil sands deposit in northern Alberta, approximately 50 km northwest of Fort McMurray (Fig. 1). The facility initially is to serve as an underground laboratory from which to field test new approaches to in situ recovery of the bitumen (oil) in the Athabasca deposit.The UTF employs mine access to get at the effective exploitation of an oil reservoir. It does so, however, under conditions considerably more difficult than those faced by most other applications of the technology. Because of the unconsolidated nature of the McMurray formation, the development of drilling chambers directly in the reservoir would be prohibitively expensive. Further, mobilization of the extremely viscous bitumen requires intensive steam stimulation with the attendant concerns of large, complex well completions and potentially hazardous operations Over-all, the oil sands presents mining, drilling and operations challenges which push the technology to a new state-of-the-art. The UTF as it now exists consists of:• a 20 000 ha lease with all-weather road access;• 925 m of 5 m by 4 m tunnels in the limestone 15 m below the oil sands at roof depth of 178 m below the surface (Fig. 2);• two 3 m diameter steel lined shafts to a depth of 213 m;• administration and sur face mine support facilities from which to operate the UTF (Figs. 3 and 4);• underground piping systems to transport drill fluids, steam, produced fluids and services to and from the future well heads underground (Fig. 5);• surface steam generation and production handling facilities (Figs . 3 and 4).• a drilling rig and auxiliary systems specifically designed to drill long horizontal wells into the oil sands from tunnels in the underlying limestone (Fig. 6);• an experienced staff to engineer and operate the facility (Fig. 7)"

Jan 1, 1989

By W. Beres

Many non-commercial operators are currently faced with the need to operate fleets of legacy gas turbine engines. How long such engines can be kept in service safely, without replacing a significant portion of their aging structural components, has become a growing concern to engine life-cycle managers, due to uncertainties in the remaining lives of critical components of these engines. This paper describes the application of the damage tolerance methodology to predict safe inspection intervals (SII) for critical components of gas turbine engines, using components of a turboprop engine for a transport aircraft as examples. High temperature components of this engine are made of advanced aerospace alloys. The methods of predicting three-dimensional fatigue crack growth at the critical location of turbine discs and spacers using both commercial and in-house developed algorithms are presented. Sensitivity analyses are performed to determine the effect of variations in material parameters on the predicted safe inspection intervals. In addition, spin rig tests performed for both turbine discs and spacers are described. Finally, crack growth rates predicted by numerical analyses are compared to those obtained from spin rig testing and the damage tolerance of the turbine components is assessed.

Jan 1, 2015

By S. Bergquist

In this paper, it is investigated how different types of automation would affect the safety for workers in asphalt paving. The risk for the workers on road construction sites is consistently high in comparison to the average risk of the working population. Automation has been suggested as an alternative for improving the safety in roadside construction assuming that removing workers will inherently eliminate the risk of them being injured. In this paper, the potential for improving the safety using automation is analyzed in detail. By investigating accident statistics and understanding the type of accidents that appear, several different automated functions for increased safety are proposed and described. Based on available statistics, it is possible to estimate the safety benefit, as the reduction in fatalities, for several of the proposed functions. The highest safety benefit would be achieved by automating the road traffic driving through the work zones. This has the potential of reducing the total number of road worker fatalities with over 30 %. In addition, it would decrease the number of road traffic accidents in work zones. Automation of construction machinery and dump-trucks also has the potential to increase the safety.

Aug 1, 2013

"Ore deposits containing rare earth elements normally contain small amounts of the radioactive elements thorium (Th) and/or uranium (U). These are the naturally-occurring isotopes U238, U235, and Th232 (and associated decay-series daughter products) that are ubiquitous in nature, and that contribute a small percentage of the natural background radiation exposure encountered by humans. The presence of these radioactive materials in the ore deposit creates potential hazards to human health and the environment that must be dealt with properly in the mining, processing, and refining of the ores, as well as management of waste streams and residues. This paper presents an overview of the environmental and safety issues associated with U and Th, with particular emphasis on rare earth mining, processing, and refining projects; the regulatory approaches followed to ensure that rare earth deposits are developed, operated, closed, and decommissioned safely; and the development of information during the project predevelopment work and permitting processes that feed into the design, operation, and closure of tailings impoundments and milling/separation/refining facilities. Case studies will be presented subject to the availability of relevant public information. INTRODUCTIONNearly all ore deposits containing economically-recoverable rare earth minerals also contain small amounts of the radioactive isotopes for the elements thorium (Th) and/or uranium (U) and their associated radioactive decay products. Therefore, the handling and management of these materials in mining and mineral processing operations must be performed so that workers and the environment are protected from harm from Th and/or U (and their radioactive decay products), just as they must be protected from any other potentially harmful constituents present in the ore or introduced in processing. Examples of these might include ores with high sulfide content, which may pose a risk of acid rock drainage, or chemicals used in ore processing and metals production.The purpose of this paper is to present information on how rare earth mining and processing projects with ores containing Th and/or U can be developed, operated, and decommissioned safely according to applicable regulations intended to protect worker health & safety and the environment.It should be noted that some countries are considering developing Th as a feedstock for producing nuclear energy, which could have some effect on future development of rare earth ore deposits. To avoid confusion, that issue is not discussed in this paper."

Jan 1, 2012

By C. Samuelsson, G. Carlsson

Characterization of dust from Boliden Mineral AB’s copper-plant in Sweden was carried out using chemical analysis, X-ray diffraction analysis, energy dispersive analysis and wave length analysis using electron microprobe equipment. Dust from four different locations was characterized: the electrostatic precipitator (ESP) after the roasting furnace; the ESP after the copper smelting furnace; from the copper converter ventilation bag house filter; and from the bag house filter collecting dust from the settling furnace and tap gas ventilation. The results showed that the dust is composed of small solid and/or liquid particles from the furnace reactor which have been transported with the process gas to the dust collecting devices. This portion of the dust is mechanically formed. It also contains compounds that have been vaporized in the process and then condensed from the process gas at lower temperature, chemically formed dust. The proportion of mechanical and chemical dust varies with the process generating the dust.

Jan 1, 2001

By R. J. Allan

"CANADA HAS A GREATER LAKE AREA than any other country. Discountin the Great Lakes, this fresh-water area, mainly in the Canadian Shield, is listed as approximately 300,000 sq. mi. Densities of lakes range up to 7,500 in a 5,294-sq. mi. area of the Shield, southwest of Reindeer Lake, Saskatchewan. Five areas chosen randomly from the Shield (Figure 1) contained sufficient lakes to provide samples at a density of at least one per 10 sq. mi. Regional geochemical surveys in the Appalachian area (Nova Scotia, Boyle et al., 1958; New Brunswick, Boyle et al., 1966) and in the Cordilleran area (Yukon, Gleeson, 1965) of Canada and in many other areas of the world have relied heavily on analyses of stream sediments. These surveys show that sampling of material related to the drainage system reflects the over-all trace element content of the rocks and surficial deposits in the drainage basin. In the Shield, the classic types of dendritic (and other) stream systems found elsewhere in the world are very rare. However, impeded and disorganized stream systems that abound with lakes can provide the exploration geochemist with an ideal composite drainage system sample in the form of lake sediment. This paper attempts to demonstrate the feasibility of, and review the theory and problems involved in, the use of lake sediment as a regional geochemical exploration medium. Most of the references to field examples are taken from a regional survey using lake bottom sediment as the sample medium over 1,500 sq. mi of the Coppermine basalt group and adjacent rocks (Figure 2). During this regional survey, detailed sampling of several lakes was carried out and the results are referred to at appropriate places in the text."

Jan 1, 1971