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By Ivan E. Goodner, Charles H. Fulton

The subject of the constitution of copper-iron mattes has received considerable attention in recent years by Keller,' Belles,2 Hofman,3 and Gibb and Philp.4 Still more recently Friedrich, Röntgen, Wiedmann, Heyn and Bauer, and Leroux have published, in some instances, elaborate researches on the various systems of the sulphides, and the snlphides and their respective metals, which enter into the constitution of mattes, and have added very greatly to the knowledge of the subject. The work of Friedrich has been especially fruitful. But to' date no effort has been made to correlate the data obtained in the latter researches and apply them to the study of the product called " matte," which is made in such large quantities by copper- and lead-smelters. In this paper we propose to determine, by metallographic and chemical means, the constitution of copper-iron and copper-lead-iron mattes in the light of the recent data above mentioned. We do not discuss copper-nickel mattes or speisses (artificial arsenides). The paper is divided into three sections: I. A review and discussion of the various binary systems of the metallic sulphides, and the binary systems of various metals and their respective sulphides entering into the constitution of mattes; also a discussion of the physical properties of these sulphides. II. A description of the results obtained from the chemical and microscopic examinations of the samples of copper-iron and copper-lead-iron matte obtained from various plants.

Jan 1, 1909

By George H. C. Norman

A NUMBER of methods have been developed for the determination of the dust concentration in air, some of which have been reported as very efficient and for research may be more satisfactory than the method about to be described. In practical mine use, however, the accurate research equipment is unwieldy and requires a high degree of technical skill to manipulate it. Also, it gives less general practical information to the operator in the same length of time than the method described here. Moreover, it is doubtful whether at the present stage of affairs the results obtained from the precise methods have any more practical significance than those obtained with simpler and more portable apparatus, which can rapidly give a sufficiently reliable indication of the relative dust hazard. HISTORY OF DUST DETERMINATION IN ONTARIO The first record of mine-dust determination in Ontario is given in an article by Dr. J. H. Elliott,' in which he records a few dust counts made with the Palmer spray apparatus. There were insufficient data from which to draw any definite conclusions or reasonably compare with present-day counts using the konimeter. The first konimeter dust sampling was started in the Porcupine district in 1926, using light-field counting without adhesive and with no sample treatment before counting. A method of semidark-field counting was used from about 1928 to 1931 and dark-field illumination was adopted permanently about December 1931. The konimeter has been continued as the principal means of dust sampling in the mines of Ontario, where South African practice has been adopted because in South Africa most careful study has been given the problem of silicosis, and very complete records of work done there are

Jan 1, 1937

By St. John, JOHN Ancel

AT THE New York meeting of the Institute of Metals Division in February, 1927, Jeffries and Tarasov presented a paper on Tungsten and Thoria,1 in which the experimental facts were interpreted in accordance with the prevailing point of view that the thorium is present as the oxide, thoria. In discussing that paper the writer of this article stated that his own investigations, which had been unavailable to Messrs. Jeffries and Tarasov, showed that the so-called "thoriated" tungsten filament failed to disclose any sign of the oxide when subjected to X-ray diffraction analysis, but did give plenty of evidence of the presence of metallic thorium and, in certain cases, of a material believed to bean alloy of tungsten in thorium. Since these results were completely at variance with the results reported in the paper under discussion and with other papers which had preceded it from time to time in the past, it was felt that further discussion should be withheld until the new evidence could be presented adequately. Arrangements were therefore made to present that evidence at this meeting. MATERIAL EXAMINED The material examined was high-emission filament such as is used in radio tubes, supposed to contain about 0.75 per cent. thoria. The actual analysis was not stated.

Jan 1, 1927

As bizarre an example of competitive salesmanship to be imagined took place last June in Western Australia. A half dozen world renowned mining groups received a Japanese iron and steel investigatory mission. Geologists, engineers and businessmen, all specialists in iron ore, representing elements of the Japanese government and steelmakers, politely grilled each iron ore group for technical information and plans for property development. At stake were sales contracts with Japan for many millions of tons of iron ore. Since approximately two dozen visitors were involved, it was necessary to divide them into four groups for dispensing information, transportation and accommodations at the remote exploration camps. In a continent noted for its wide open spaces, the hinterland of Western Australia is spectacularly lacking in settlements. The state has better than one third of Australian land and statistically 0.8 persons per sq mile. In reality, however, over 400,000 of the 800,000 population reside in Perth. Under such circumstances, properly receiving and feting these important visitors would seem to be difficult but the competing exploration groups vied ingeniously to outdo each other in hospitality.

Jan 10, 1964

By Julius Pohlman

The history of Niagara Falls, as currently told, is simple, and by that very simplicity it has been rendered plausible. AS the story runs, the Falls were once situated at Lewiston, 7 miles to the north of their present site; and, since all the rocks in this section are alternate hard and soft strata, the waters acting readily upon the soft shales caused their removal, and the overlying hard lagers, deprived of support, broke down under the weight of the large volume of water that rushed over them; and this erosive action has sent the edge of the fall more and more southward, until it now has excavated the seven-mile gorge between Lewiston and the village of Niagara Falls. (See Fig. 1.) As early as 1790" we find this theory advanced in a description of this region; and it has been practically endorsed by subsequent observers, the most prominent of whom was Prof. James Hall, the State Geologist of New York, who surveyed the Falls in 1841, and gave the most exact description of their surroundings in the publications of the State Survey.? Not until 1883 was the correctness of the accepted theory of the Falls questioned.‡ The geology of the basins of the Great. Lakes, as elucidated by Newberry,§ Speneer,ll and others, has added largely to a clearer understanding of the life-history of the Falls. The investigators have shown us that Lake Erie, as a lake, is, geologically speaking, quite young; that its valley was excavated in pre-glacial times by a series of rivers; and that the Maumee, Sandusky, Cuyaboga, Alleghany and other rivers carried the drainage of the surrounding

Jan 1, 1889

By George F. Comstock

It has been known for many years that the alloy containing 90 per cent. copper and 10 per cent. aluminum can be hardened, like steel, by quenching from a suitable temperature, and that the hardened alloy can be softened again by annealing or drawing the temper. It does not seem to be generally appreciated, however, that the effect of the first slight reheating after quenching is actually increased hardness, the softening effect not taking place until a certain temperature of "drawing" has been exceeded. This paper gives the results of a few experiments on various specimens of cast 10 per cent. aluminum bronze, quenched for maximum hardness, and subsequcntly annealed at different temperatures. The hardness measurements were made with both a scleroscope and a standard Swedish Brinell machine; some peculiarities of the scleroscope test on this material are described. The author is not aware of many previous investigations of the hardness of this alloy when quenched and drawn, but two important papers on the subject should be mentioned. The earliest was by Portevin and Arnou,1 in which it was stated that tempering quenched 10 per cent. aluminum bronze at 400" C. increased the hardness as compared with the quenched untempered alloy and that reheating above that temperature ' was necessary to obtain any softening effect. A later paper was by Seidell and Horvitz,2 who mentioned Portevin and Arnou's work, but did not report any increase in hardness obtained

Jan 1, 1925

By Dan G. Cojocariu, E. Ene-Danalache, I. Huber-Panu

A general model which represents not only batch but also continuous flotation in multi-cell machines is presented. This model considers both the size distribution and the distribution of flotabilities in a size class for valuable mineral particles in the pulp. The general expression is shown to reduce to several previously reported models. In addition, a number of new models are found to arise for different specific assumptions concerning the flotability distribution and/or the size distribution of the particles undergoing flotation. Several of these new models are tested experimentally using laboratory-scale batch and pilot-scale continuous data. Model parameters are estimated from this data and a comparison of calculated recoveries and those experimentally determined are presented. Finally, the influence of the feed rate, aeration rate and valuable mineral content of the feed on the recovery is examined.

Jan 1, 1976

By W. H. Herrnstein, J. B. Clark, E. C. Utley, A. J. McEvily

The ratio of the endurance limit (10' cycles) to tensile strength of age-hardened aluminum alloys is approximately 0.3, whereas the ratio for annealed alloys is about 0.5. The lower value for the age-hardened alloys has been associated with the instability of coherent precipitate during cyclic loading, but it has not been definitely established whether this instability is due to overaging or reversion during cyclic loading. The results of the present investigatzon support the reversion viewpoint. In this work specimem of 2024-T4 aluminum alloy were aged for 16 hr at 150°C after cycling for 10 pct of the life at 25.000 psi. These specimens were then tested to failure and exhibzted a marked increase in fatigue life. It is proposed that during the early stages of fatigue in this alloy dislocations cut through the coherent precipitate and bring about the reversion of the precipitate. Subsequent aging at 150ºC induces reprecipitation in the precipitate-free zones so that the weakened regions are strengthened and the fatigue life is extended. It Is recognized that the fatigue strengths of precipitation hardened aluminum alloys are unusually low relative to their tensile strength.'-= This feature is illustrated in Fig. 1 where it can be seen that age-hardened alloys have lower fatigue ratios (the ratio of the fatigue strength to the tensile strength) than those in the annealed or cold worked state. Further, as shown in Fig. 2, the more an alloy is dependent upon precipitation hardening for its total strength, the lower is the ratio of the fatigue strength to the tensile strength. This state of affairs has been associated with an instability of the metastable metallurgical structure of precipitation hardened aluminum alloys during cyclic loading. Evidence2 in support of this view is that the fatigue ratio increases in these alloys as the test temperature is lowered, thereby indicating that thermo-mechanical instability, rather than some other factor such as a non-uniform distribution of precipitate, is the factor responsible for the low fatigue ratio at room temperature. Two mutually exclusive proposals have been ad- vanced to account for this instability. Hanstock has proposed that overaging takes place during cyclic loading, and in support of this view, Broom et a1.2 have indicated that an overaging process might be promoted by the large numbers of vacancies which are created during cyclic loading. The creation of vacancies by radiation4 has been shown to lead to rapid overaging. Hanstockl obtained visual evidence of overaging in an aluminum alloy after cyclic loading, but in this instance it has been pointed ou? that because of the high frequency used (60,000 cpm) the observed effect may have been due to normal high temperature precipitation around energy dissipating cracks. Efforts to discern visual evidence of overaging in this alloy at lower test frequencies were not successful.3 The alternative postulate3 is that reversion takes place during cyclic loading and leads to localized soft spots at which fatigue cracks are readily initiated. Evidence for this process has recently been provided by Polmear and Bainbridge5 who demonstrated metallographically that regions depleted of precipitate were created during cyclic loading of an aluminum alloy. Inasmuch as precipitate particles bordering the depleted region had not grown in size, it was concluded that the solute atoms which had constituted the missing particles had gone back into solution. No mechanism for the reversion process was presented. The present study was undertaken to investigate further the conditions leading to instability during cyclic loading, and to determine whether reversion or overaging had taken place as a result of cyclic loading. BACKGROUND AND TEST PROCEDURE In order to differentiate between the processes of reversion and overaging, rest periods at an elevated temperature, which ordinarily would insure additional precipitation, were used in this investigation. It was expected that after a period of cyclic loading an elevated temperature rest period would result in a decrease in the remaining life of the specimen if overaging were occurring during cyclic loading, whereas in the case of reversion, reprecipitation would occur and the fatigue life would be extended. Such an expectation is based on the assumption that the crack-nucleation phase is a significant portion of the total fatigue life, and that such a treatment is of influence in the crack-nucleation stage and is relatively unimportant thereafter.

Jan 1, 1963

By M. L. Holzworth, Philip R. Sperry, Paul A. Beck

INTRODUCTION THE basic work of Z. Jeffries1,2,3 has long ago established the main features of grain growth in the presence of a dispersed second phase. Working with sintered specimens of initially fine grained tungsten, to which various amounts of thoria have been added, Jeffries found that grain growth was inhabited, that is, practically prevented, up to a certain annealing temperature. When this temperature, which increased with the thoria content, was exceeded, extremely large grains developed abruptly from the fine grained matrix. Such a "coarsening temperature" was later found by Gross mann13,14 in certain types of steel, while Bain showed" that in other steels grain growth was gradual, without inhibition and abrupt coarsening. Later work16,17,18,19,21 demonstrated the connection between coarsening and aluminum additions. The viewpoint that the direct cause of inhibition and coarsening in aluminum killed steels is a fine dispersion of aluminum oxide21 appears to be held quite generally, although some doubts have been voiced even very recently.20 In steels with Ti additions the titanium carbide phase is considered responsible for the inhibition effects found.20 The coarsening temperature increases, with the titanium content. That coarsening may occur, as a result of certain heat treatments, even in low carbon rimmed sheet steel, was shown by Samuels,22 He also detected coarsening in a steel ingot of similar composition, after giving it the same heat treatment as that used by him for the sheet material, In this instance the identity of the inhibiting phase has not been determined, However, Tangerding found 23 that even the few small carbide particles, which occur in carbonyl iron, have a very marked inhibitive effect. As a result of an oxidizing anneal at 850°C, large grains begin to form at the surface of the carbonyl iron specimen, and gradually grow inward as the subsurface oxidation of the carbide particles progresses and eliminates the obstruction, The carbide particles can be removed also by annealing in hydrogen, with similar results. But if the oxidizing anneal of 10 hr at 850°C in air, is followed by annealing in hydrogen for 75 hr at the same temperature, grain growth is more spectacular; usually the whole specimen is transformed into a single crystal (approx. 1,5 cm X 5 cm). The reversed procedure, that is, hydrogen annealing followed by oxidizing annealing leads to smaller grains. Tangerding arrived at the logical conclusion that there must have been in his specimens some additional obstruction to grain growth resulting from a minor impurity, other than carbon. It seems likely that this obstruction was caused by an oxide formed during the oxidizing anneal and gradually reduced during the subsequent hydrogen-annealing. Other instances of grain growth inhibition of varying severity, associated with a dispersed second phase, have been described by several authors. Notable examples: lead with 0.06 pct Cu or Ni,24 cartridge brass with 0.12 pct Cr,25 or with up to 0.15

Jan 1, 1948

By H. G. Doll

A new logging method, called induction logging, is described; it measures the conductivity, or resistivity, of the strata traversed by a bore hole. The apparatus, which is briefly described, comprises a coil system coupled with the ground by induction, so that there is no need for direct contact with the mud, or with the formations. For that reason, the method is particularly useful in oil base mud, and it was first applied to that case. A discussion concerning the respective contribution of each region of ground in the vicinity of the coil system is given. Through the concept of a geometrical factor, it is demonstrated that the total signal, which measures the apparent conductivity, is the summation of the partial products — geometrical factor by conductivity — for the different regions of the ground under consideration. It is thus possible to establish, for each type of coil arangement, investigation characteristic as well as departure curves and correction charts for beds of various thicknesses. This should greatly facilitate the quantative interpretation of the field logs, even in cases where such interpretation would have been difficult on electric logs taken with electrodes. It is also shown that focussing combinations of coils can be used, which give, directly on the recorded log, a value close to the true conductivity, even for fairly thin beds, thus eliminating in most cases the need for corrections. These focussing systems also give a sharper definition of the boundaries between successive strain.

Jan 1, 1949

By C. A. Czako

INTRODUCTION In recent decades sintering and pelletizing of finely divided materials have become the primary tonnage producing modes of agglomeration. This statement is especially true in the iron and steel industry and, to a lesser degree, in the nonferrous, chemical and non-metallic minerals processing industries. In every industry the main objectives in agglomerating fines are essentially the same, namely to convert ores, minerals and chemicals of undesirable fineness into agglomerates characterized by a size consistency desirable for subsequent use or processing. Depending on the type of agglomeration process selected and the conditions maintained during agglomeration, the physical process of increasing size is complemented by a number of other unit processes. These processes can occur simultaneously, consecutively or in an overlapping manner. Some of these additional unit processes are incidental to the agglomeration operation, but at the same time can be critical, depending upon the subsequent use of the product. Accordingly, during processing, conditions have to be controlled to either suppress or enhance the extent of completion of these unit processes. The purpose of this report is to review laboratory testing as the basis for engineering modern sintering and pelletizing plants. Considering that most typical applications are for the iron and steel industry, agglomeration of ferrous materials is reviewed and discussed. When these total processes are adapted to suit non- ferrous materials, chemicals, or non-metallic substances, the over- all approach remains the same; only the processing parameters are affected as necessitated by the different nature of the materials.

Jan 1, 1977

By Michael A. Devane, Neil Duncan

Inclines and tunnels can extend from ground surface to considerable depths traversing a wide range of lithologies. The strata encountered may be affected by loosening and induced stresses at different locations along the route. It is suggested that Phase I of the pre- driving assessment process should include study of the geology, hydrogeology, rock material and rock mass characteristics. A rock mass disruption factor is used to express the ratio of the unconfined strength of intact rock material to the unconfined strength of in situ rock mass. It is suggested that there is a relationship between in situ (secondary) permeability values and the disruption factor, since the permeability of the rock mass is governed by parameters which influence strength. In Phase I1 of the pre-driving assessment, consideration should be given to the prediction of primary loosening which results largely from disturbances to the rock mass arising from the driving process. Also in Phase 11, preliminary assessments are made of the effects of induced stresses and of the geodurability characteristics of the rocks. In Phase 111, the mechanics of various secondary loosening pro- cesses are considered along with their relevance to estimates of stand up time and support requirements. Yield-line analysis is introduced for the study of plastic and brittle type bending deformations. Stand up time and support characteristics are also assessed. In Phase IV, the effects of induced stresses are analysed. It is suggested that even for broken rock in the Yield Zone, the rock mass disruption factor may not often increase above lo which is equivalent to an in situ permeability of 10-1 m/s.

Jan 1, 1983

By William B. Phillips

The concentration of natural magnetites has been carried on in this country for several years, and more or less information has been collected on the subject. Various inventors, availing themselves of the magnetism which is inherent in such ores, have devised machines for separating the impurities from the ore by means of the electric current; and a greater or less degree of success has rewarded their painstaking and persevering efforts. We are now fairly in position to judge of the value of the process as applied to such material. It is not my purpose to speak of this matter further than may be required by the emergencies of the case. I shall assume that most engineers and metallurgical chemists are already acquainted with what has been done at the Chateaugay mines, at Mineville, at the Benson mines, at the Weldon and Ogdensburgh mines, and at Cranberry; although, at this latter place, there has not been so much done as we could wish. I shall not now speak of the various types of separators. From the time of William Fullarton, to whom was granted an English patent, in 1792, for separating iron-ore by the application of magnetic attraction, down to the present time, a great. many devices have been suggested, and a great many patents taken out for this purpose; but it is not necessary now to enter upon a discussion of their merits. Perhaps, at some future meeting of the Institute, after we shall have experimented further with some of the machines on the market, there may be an opportunity to contribute something to the current knowledge of the efficiency and economy of separating-machines. In this paper I propose to give, as briefly as possible, the results already reached in converting a non-magnetic ore into magnetic ore, and then concentrating it over a magnetic separator of the alternate-polarity type. I am aware of the work

Jan 1, 1896

By H. G. Doll

A new logging method, called induction logging, is described; it measures the conductivity, or resistivity, of the strata traversed by a bore hole. The apparatus, which is briefly described, comprises a coil system coupled with the ground by induction, so that there is no need for direct contact with the mud, or with the formations. For that reason, the method is particularly useful in oil base mud, and it was first applied to that case. A discussion concerning the respective contribution of each region of ground in the vicinity of the coil system is given. Through the concept of a geometrical factor, it is demonstrated that the total signal, which measures the apparent conductivity, is the summation of the partial products — geometrical factor by conductivity — for the different regions of the ground under consideration. It is thus possible to establish, for each type of coil arangement, investigation characteristic as well as departure curves and correction charts for beds of various thicknesses. This should greatly facilitate the quantative interpretation of the field logs, even in cases where such interpretation would have been difficult on electric logs taken with electrodes. It is also shown that focussing combinations of coils can be used, which give, directly on the recorded log, a value close to the true conductivity, even for fairly thin beds, thus eliminating in most cases the need for corrections. These focussing systems also give a sharper definition of the boundaries between successive strain.

Jan 1, 1949

By J. D. Wright

INTRODUCTION The Endako deposit was first explored in 1926, but development waited until the early nineteen sixties. It first came under the control of Placer Development in 1963, and early in 1964 a decision to bring it into production was reached. The deposit is located near the geographic center of British Columbia, and is served by an east-west communication system including a paved highway, mainline railway and good telephone, teletype, and computer facilities. The plant area is shown in Figure 1. The operation is known as the Endako Mines Division of Canex Placer Limited of Vancouver. First production was achieved in June, 1965, at a nominal rate of 10,000 tons per day, but it soon was closer to 15,000 tons per day. In 1967, two new grinding and flotation, sections brought capacity to the present rate of approximately 27,000 tons per day. With mill heads of around 0.15 percent MoS2, production is about 14,000,000 pounds of molybdenum per year. A flowsheet of the operation is given in Figure 2. A legend for this flowsheet is given in Table 1. Published ore reserves are estimated at 214,500,000 tons at an average grade of 0.143 percent MoS2. PRIMARY CRUSHING The 85 or 100-ton haulage trucks dump over a grizzly into a 42 inch x 65 inch C.A.C. (Canadian Allis Chalmers) gyratory crusher. The

Jan 1, 1976

Jan 1, 1897

Domestic: Middle West-,11.. B. Newcombe Eastern District-J. French Robinson1 Kansas-Henry A. Ley 2 Oklahoma-Henry A. Ley 3 Texas, except Gulf Coast and Panhandle-M. G. Cheney 5 Texas Panhandle-W. E. Hubbard and H. E. Crum 6 Gulf Coast-L. P. Teas 7 South Arkansas, North Louisiana and Mississippi-H. K. Shearer 8 Foreign Mexico-V. R. Garfias and C. 0. Isakson 9 Canada-Line M. Farish 10 Venezuela-C. W. Hamilton 10 Colombia-J. T. Duce 12 Peru-O. B. Hopkins 12 Trindad-Williaim J. Millard 13 Dutch East Indies-Fred B. Ely 13 Rumania-I. I. Gardescu . .. . 14 India-Eric J. Bradshaw 14

Jan 1, 1931

By G. W. Poling

Chemical and physical properties of thiol collectors are re-examined to compare the prospects,of heavy metal-thiolate or disulphide surface reaction products acting as actual collector species. Recent evidences for the existence and importance of each of these types of adsorbed species on sulphide minerals are also discussed. A conclusion is reached that partial coverage by chemisorbed heavy metal thiolate is often sufficient to confer practical levels of hydrophobicity and floatability. Only on a few highly conducting and "noble" sulphides does adsorbed disulphide-type collector oxidation product appear to be significant.

Jan 1, 1976

By Betty M. Miller

INTRODUCTION In September 1974 the Resource Appraisal Group of the Branch of Oil and Gas Resources, U. S. Geological Survey, was asked to aid the Federal Energy Administration (FEA) in its legal responsibility to generate by June 1975 an independent appraisal of the undiscovered oil and gas resources of the United States, both onshore and offshore. As a result, the Resource Appraisal Group accelerated its ongoing efforts to develop sound appraisal methods and procedures that would permit the systematic collection and evaluation of basic data from petroleum provinces throughout the Nation. The results of this independent appraisal of the Nation's conventional oil and natural gas resources were published by the U. S. Geological Survey as Circular 725, June 1975 (1). The estimates in this report of undiscovered recoverable oil and gas resources for the United States were made: (1) by carefully re- viewing a large amount of geological and geophysical information gathered on more than 100 different provinces by over 70 geologists within the Survey; (2) by applying a variety of resource appraisal techniques to each potential petroleum province; and (3) by application of subjective probability procedures to group appraisals for each petroleum province. These methods provide a range of estimates which are summarized in terms of low, high and mean values for the various provinces and groups of provinces, or regions. The basic data and procedures used are documented and are being incorporated into a dynamic, data- intensive system that can be upgraded, updated and reevaluated periodically. These data are open to public inspection. In this study, the primary emphasis was placed on conventional crude oil and natural gas in the onshore provinces and the provinces on the continental shelf out to water depths of 200 metres; estimates

Jan 1, 1977

By G. J. Saulnier, K. E. Goddard

The US Geological Survey has developed mathematical modeling techniques to assess potential impacts on the hydrologic system resulting from mining of coal and oil shale in northwestern Colorado. Potential impacts of oil shale mining on groundwater hydrology have been simulated using a quasi-three-dimensional, finite-difference model. The model has been used to simulate hypothetical mine dewatering operations at two proposed oil shale mines. Dissolved-solids distribution and solute transport were simulated with a three-dimensional, finite-difference model that was used to evaluate the effects of flooding in hypothetical abandoned mines. The potential impacts of coal and oil shale mining on water-sheds were investigated using a digital watershed model. This deterministic physical-process model predicts responses of the hydrologic system to modifications resulting from mining in basins having snow as the major source of runoff and recharge. Potential impacts of coal development on surface water quality were investigated using a river quality assessment model. The models developed by the US Geological Survey have been useful in defining the potential effects of mining in northwestern Colorado. They are an important first step in analyzing the existing data base and in predicting impacts and new data needs. The models may not be totally applicable on the local scale but are very meaningful on the regional level.

Jan 1, 1983