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By J. J. Mulligan

Introduction Coal is found in every major geographic region through-out Alaska and in two offshore areas. Since about 1852, more than 100 small mines have opened and closed. In 1981 and 1982 production was almost entirely from one mine in central Alaska. Clearly, the utilization of Alaska's abundant coal resources presents political, economic, and technical problems that are far from solution. Location and Physical Features Figure 1 illustrates the geographical and geological similarity between Alaska and the western US. Alaska's Arctic region generally resembles Wyoming and the Dakotas. The Brooks Range is an extension of the Rocky Mountains. The central region of Alaska between the Brooks Range and the Alaska Range bears a general resemblance to the basin and range country of the western US. The southcentral and southeastern regions have a similar resemblance to the Sierra Nevadas and the West Coast. The Arctic, the central, and the southcentral regions have major coal fields. The southeast region has scattered occurrences. The topographic, climatic, and economic characteristics of each are different. These differences have a large effect on practical mining methods. Description of Alaskan Coal Coal deposits known in Alaska are almost all of Cretaceous or Tertiary age, much younger than the Carboniferous coal deposits of eastern and midwestern states. Consequently, most Alaskan coals have a higher moisture content and a lower heat value. Most Alaskan coals also have a much lower sulfur content. Low volatile bituminous, and anthracite coals occur in Alaska, but most Alaskan coals range downward in rank from high volatile bituminous to subbituminous and lignite. Alaskan coals are similar to coals of the northern Great Plains and the Rocky Mountains. Arctic Region Northern Alaska Coal Fields Northern Alaska coal fields are by far the largest group of coal deposits in Alaska (Fig. 2). Coal-bearing rocks extend from the foothills of the Brooks Range about 160 km (100 miles) northward to within about 80 km (50 miles) of the Arctic coast. The principal known occurrences are between the Colville River and the western coast. However, coal has been found eastward almost to the Canning River and westward under the Arctic Ocean. The northern Alaska coal fields are in a series of Cretaceous rocks that suggest a deltaic depositional environment. The beds tend to occur in series of up to eight or nine beds totaling 6-9 m (20-30 ft) of coal. However, beds 6-12 m (20-40 ft) thick have been reported, and beds 1-3 m (3-10 ft) thick seem to be relatively common. Including thin seams, coal in some places makes up about 10% of the stratigraphic section. However, no area has been explored in sufficient detail to block out any large body of reserves or to make reliable estimates of the total resource. Observation points in drill holes and along river and stream banks are few and far between. Coals in northern Alaskan fields tend to range in rank from bituminous, where moderately folded and faulted in the foothills, to subbittuminous in the gently folded rocks under the coastal plain. Coals toward the eastern extremities of the coal fields may be of Tertiary age and lower in rank, but the same general correlation between degree of folding and increase in rank can be expected. Some higher rank coals in the foothills belt are known to have coking properties but most, and possibly all, require

Jan 1, 1984

By Shosei Serata

Serious floor heave of up to 2.4 m in a 2.4-m high mine entry was eliminated by applying the stress control method of mining, as a last resort, at the No. 5 coal mine of Jim Walter Resources, Inc., in the Black Warrior coal basin near Birmingham, Alabama. Underground observation of the first 3-room entry created using the stress control method is discussed here. The behavior of the test entry, which eliminated the heave problem, is analyzed in relation to similar studies conducted in a salt mine under similar ground conditions by utilizing finite element analysis.

Jan 1, 1984

By R. F. Shurtz

This note calls attention to a contradiction in current eatistical theory and to corresponding difficulties in practice. These are significant concern in evaluating almost all ore deposits. The theoretical contradiction is that the commonly used spherical model for the semivariogram is not consistent with the usual definition of a "regionalized variable" as a mathematical function, the direct study of which "is excluded because its spatial variability is usually extremely erratic, with all kinds of discontinuities. . ." (Journel and Huijbregts, 1978). Specifically, this means a grade function that is too "rough" for interpolation to be useful. The practical difficulty is that the spherical semivariogram interprets the data upon which it is based in a manner that is, more often than not, demonstrably inconsistent with reality. This is attributable to the widely disregarded interaction between the sample pattern and the grade function. Each sample pattern "blurs" the grade function in its own particular way. It is as though the grade structure of the deposit were seen through a lens of poor resolution or reflected in a warped mirror, such as those found in amusement parks. The fitted spherical model embeds this sometimes dangerously blurred and distorted image in the Krige regression. A full analysis of these inconsistencies is to be presented later but, in the meantime, it seems urgent to communicate their effects so that those engaged in estimating ore reserves may be on guard. The spherical semivariogram has a sill and can be replaced by the corresponding covariogram. The equation of the spherical covariogram in normalized form, that is, variance and range both equal to one, is represented as: [ ]

Jan 1, 1984

By Thomas R. Scotese

A rock mechanics instrumentation and monitoring program was implemented during pillar extraction at Gulf Mineral Resources' Mt. Taylor Mine, the deepest uranium mine in the U.S. Three types of monitoring were employed: (1) drift convergence around stopes (using a portable tube extensometer), (2) stress changes in pillars (using vibrating wire stressmeters in horizontal boreholes), and (3) load changes in haulageways under stopes (using vibrating wire load cells in jack stands). Results include convergence-time graphs, convergence contour maps, stress-time graphs, a stress increase contour map, load-time graphs, and abutment load limit maps. Major factors influencing results include (1) size of pillars around the extraction area, and (2) presence and orientation of a major fault adjacent to one extraction area. These factors, combined with pillar extraction, produced evidence of load transfer over 120 m from a stope measuring only 55 m x 45 m. Vertical stress increases of 7 to 17 MPa (1000 to 2500 psi) within 60 m of the stope were obtained using the stress- meter manufacturer's method. The fault apparently prevented load transfer in the down-dip direction but increased load transfer in the up-dip direction. Convergence rates of up to 1.3 cm/day (0.5 in/day) were measured at two stations. Instruments were generally reliable despite adverse underground conditions. The instrumentation and monitoring program at Mt. Taylor provided a warning system against ground control problems and a characterization of ground behavior for future development and extraction of pillars. Recommendations are made for future mining and instrumentation practices.

Jan 1, 1984

By Thomas M. Tharp

INTRODUCTION Attempts to analyze the stability of slopes, foundations and underground openings in discontinuously jointed rock have generally assumed full joint continuity or ignored the role of stress concentration at the tips of discontinuous joints. The most common approach in rock slopes is to consider a failure plane consisting of coplanar, but discontinuous joints separated by intact rock. The intact rock is assumed to fail in shear as a Mohr- Coulomb material and to contribute a strength component proportional to the fraction of the failure plane that is intact rock (Jennings, 1970). An alternative approach by Stimpson (1978) applies Lajtai's (1969) theory for shear strength of discontinuously jointed rock masses to slopes. Lajtai allows tensile failure in the intact rock of a composite surface. This theory yields lower shear strength than that of Jennings (1970) except in the presence of high normal compression, however it also fails to account for the stress concentration at the tip of a discontinuous joint. For a given slope geometry, stresses increase with slope height, but in both of these models rock mass strength is independent of size. A fracture mechanics analysis shows that particularly for small slopes, rock mass strength decreases with size. A continuous stepped failure surf ace produced by propagation of preexisting joints may develop at lower shear stress than predicted by the Jennings (1970) or Lajtai (1969) models. This fracture mechanics model applied to slopes in competent rock is more realistic in its assumed failure mechanism, and for large slopes more conservative than the Jennings (1970) or Lajtai models (1969).

Jan 1, 1984

By G. Czupryna, S. Natansohn

Electrowinning is the prevalent technique for recovering silver from wastes generated in silver-tungsten electrical contact fabrication. Such scrap is placed in a permeable plastic basket, which constitutes the anode compartment, and is suspended in a larger cell where the cathode is mounted. A silver nitrate solution is used as the electrolyte and, upon application of an electric field, the silver migrates to the cathode where it deposits. At times, there is tungsten migration to the cathode compartment and consequent co-deposition with the silver. This W contamination, which may amount to several thousand mg/L (oz per gal), necessitates additional purification of the deposited Ag and its removal would, therefore, be advantageous. Eliminating the W impurity also extends the operating period of the cell with corresponding increases in the Ag output and savings in labor costs. The solution to this problem lies in the selective removal of the W from the AgNO3 electrolyte either by liquid-liquid or liquid-solid extraction. Although W extraction in the liquid-liquid mode with a quaternary amine or other reagents as extractants appears feasible, particularly in view of the low pH (about 1.5) of the system, this approach was not considered because it is essentially a batch-type process. It is a more elaborate industrial operation than extraction by ion exchange resins. Implementing the latter process consists of passing the electrolyte from the electrowinning cell through an ion exchange column which would extract the tungsten selectively and returning the tungsten-free stream to the cathode compartment. This process continues until the W extraction efficiency decreases (as a result of resin loading) below an acceptable value. The electrolyte is then directed through another, similar column while the W values are eluted off the first one and the resin is regenerated for another cycle. Thus, two columns in a parallel flow pattern provide the means for continuous processing of the electrolyte feedstock.

Jan 1, 1984

By M. T. Atwood, L. Goodfellow, S. W. Tyson

This paper reviews various methods for measuring the product output from oil shale processes. These include comparison with Fischer assay product yields, measuring conversion of feed oil shale organic carbon to volatile products, and measuring output of combustion energy in the form of product liquid and gas.

Jan 1, 1984

By Jin Zigang

In China there are more than 30 coal fields menaced by karst-confined water. In the north and east of China there are many collieries which mine coal seams of the Carboniferous and Permian Systems, which are above the Ordovician limestone (general thickness is 500-600 meters). Ordovician limestone is full of karst fissures, contains a lot of water under high pressure (15-65 kg/cm2) near the commercial coal seams (20-80 meters), the water easily infiltrates the thin lime- stone at the point of the structure crevice, so water-irruptions from the floor are the main source of water-related disasters in these coal fields. According to the statistics there were more than 300 accidents of all kinds of water-irruptions from the floor in these fields since the beginning of their development. It is of great significance in developing coal production in the eastern part of China to solve the problem of safe mining of the seams menaced by the karst-confined water of the Ordovician limestone. The research on this subject consists of three parts: (1) investigating the geological structure and hydrogeological conditions of each mine of the mining area; (2) researching the mechanism of water-irruptions from the floor and proposing reliable methods to predict and monitor; (3) improving the mining system and proposing a mining plan with safety precautions against water-caused accidents. The chief task is to research the mechanisms involved and to discover the causes and conditions of the phenomenon. The authors have obtained some findings on this subject in the last five years, making use of the comprehensive observation and research system, which will be discussed under three headings.

Jan 1, 1984

By G. T. Brookman, P. B. Katz, D. K. Martin, J. A. Ripp

With the increasing emphasis on using American fossil fuel resources, more facilities are evaluating coal conversion. In addition, those facilities now using coal are considering better coal storage procedures to minimize negative environmental impacts. For example, rainfall and snowmelt on a coal pile produce a drainage stream high in acidity, suspended and dissolved solids, iron, sulfate, and trace metals. Usually, the characteristics of the runoff stream do not allow for direct discharge to streams and lakes. Detention in a holding pond and pH adjustment are traditional methods of treating coal pile runoff before discharge. Historically, this treatment methodology has been performed inefficiently without a good data base to assess how much runoff treatment is needed to meet effluent guidelines. A model was developed to simulate runoff volume and pollutant loadings under different rainfall conditions. This model will be used to size and design treatment works for coal pile drainage. The Ohio State University (OSU) version of the Stanford watershed model was selected as the base model. The OSU model simulates overland runoff in a rural area. It includes factors such as soil moisture, depression storage, infiltration, and flow to a ground water reservoir. TRC also used the OSU co-model for acid production in coal refuse piles as the basis for qualitative modeling work. A number of modifications were made to the OSU models to make them applicable to coal storage piles. The physical/chemical reactions included in the models are described in more detail in the project report. In addition, the models were altered so that a standard NOAA magnetic tape of historical meteorological data can be used as data input instead of requiring the user to create a data file. The resulting TRC coal pile drainage model is actually two models - a quantitative model, termed H2OTRC, and a qualitative model, TRCCOAL.

Jan 1, 1984

By Bezalel C. Haimson

We have developed a new wireline hydrofracturing technique for in situ stress measurement which eliminates the need for drill rig and drill rod and renders the tripping of the straddle or impression packers continuous, fast, and inexpensive. Wireline conductors facilitate the use of downhole pressure transducers. We have confirmed the suitability of the new technique by testing it in a deep hole near the Monticello Reservoir, South Carolina. Our measurements indicate two local stress fields, one of them apparently linked to the impoundment-related induced seismicity.

Jan 1, 1984

By Gen-Hua Shi

The deformation of a discontinuous rock is a sum of individual translations, rotations, and strains of the component blocks. These produce opening and slip between blocks along the discontinuities. Rather than attempting to analyze such deformations with a mathematical model representing the geometric and stress/strain properties of all points, for the back-calculation of observed displacements we have produced a novel approach to solve the inverse problem. Using a field of displacement measurements and a map of the system of discontinuities, the method, determines the intrablock and interblock motions by a least squares formulation. In this brief paper we address only two- dimensional formulations. However, computer codes have also been developed for three dimensional problems.

Jan 1, 1984

By Douglas A. Anderson

We have instrumented well-controlled free-face blasts with six- component borehole strain gages, in order to determine the complete strain tensor as a function of time due to explosive loading. The strain tensors have been diagonalized to determine the principal strain time-histories, and further processed to determine the octahedral shear strains as a function of time. Principal strain time-histories, when compared with a computer model, indicate the arrival of various direct and reflected phases. Strong shear strains coincide with the expected arrival time of shear waves. These shear waves are probably instrumental in the fragmentation of confined rock due to explosive loading, and should be incorporated in models of the fragmentation process.

Jan 1, 1984

By M. E. Gershon

A mixed-integer formulation of the mine scheduling problem is discussed and applied for the purpose of optimizing both the mine production sequencing and the mill blending and processing problem simultaneously. Previous attempts at solving these problem separately, although successful, fail to take into account the interrelationships between these problems. Project structure selves as the outline of this paper Generalized in its organization, this concept is useful for long, intermediate, and short range scheduling. Actual applications that show the concept also is applicable to mining a variety of ore are mentioned.

Jan 1, 1984

By Neil Styler

This paper presents an analysis of measurements of inter-burden deformations above six longwall faces. An attempt is made to demonstrate some correlation between the movements at the various sites, and to examine their importance with respect to predicting caving height, disruption of overlying seams, and disruption of aquifers. This analysis demonstrates some significant differences between predicted surface subsidence, and inter-burden deformation. In addition it is shown that the caving height above a longwall face is equal to 8 to 12 times the extraction height, with a zone of fractured rock extending to approximately 50 times the extraction height above the seam.

Jan 1, 1984

By J. B. Hiskey

Heap leaching has in recent years been established as an important processing alternative for gold and silver. Currently, heap leaching accounts for about 25% of primary mine produced gold and 10% of primary silver. This paper reviews gold and silver heap leaching practice and surveys major operations in the United States.

Jan 1, 1984

By Eric L. Christiansen

A dynamic simulation model for the iron blast furnace has been developed which predicts flow rates, compositions, and temperatures of the top gas, slag, and hot metal exit streams as a function of time from specification of the time-dependent tuyere inputs and raw material charges. As a matter of convenience, a previously developed steady- state model is employed to fix furnace-dependent parameters. It also provides initial conditions for the internal states of the furnace for subsequent dynamic solution of the simultaneous differential equations which describe the local rates of chemical reaction, heat transfer, and mass transfer in the stack, bosh, combustion zone, and hearth of the furnace. The dynamic model was tested by a demonstration of its ability to relax to steady-state representations of the time-averaged data from two separate industrial blast furnaces and of its ability to follow eight days of time-dependent operating data for one of them. Simulated responses to step changes in tuyere input and burden variables have been shown to be of the correct magnitude and duration. Although complex functions of many variables, a proper description of these responses is needed for the development of optimization and control strategies . The model correctly predicts the non-minimum-phase type dynamic response observed in real furnaces in which the output variables proceed through local minima or maxima, often including inverse responses (i.e., opposite signs from their final steady-state values ) .

Jan 1, 1984

By G. J. Cardwell

The rock and mineral analyst will be called upon to determine both the major and minor constituents in materials as varied as rocks, soil, sediments, concentrates and various liquids. These analyses will have interactions requiring extraction, matrix modification, and background correction. Analytical methodologies include classical gravimetric methods, such as fire assay, emission spectroscopy, X-ray fluorescence, atomic absorption, inductively coupled plasma, and neutron activation. With these capabilities the analyst can be called on to determine three-fourths of the elements in the periodic table. How can the earth scientist pick the method best suited for his particular sample?

Jan 1, 1984

By James B. Vance, Parviz Mottahed

An extensive research program has been carried out at PCS Mining for some time into the use of high frequency microseismic emissions in the range of 30-200 kHz for roof fall warning in the mines. A laboratory investigation on loaded samples of potash has established a close correlation between acoustic emissions and the applied load. The tests also indicated the occurrence of the Kaiser effect. The positive and encouraging response from underground testing and controlled laboratory testing has lead to the extension of the investigation into correlation of the high frequency microseismic emissions and the change in stress distribution due to mining. Hydraulic borehole pressure cells were installed at different depths ahead of the advancing boring machine. The output due to the stress change and the microseismic event count was monitored by a continuous chart recorder. This paper discusses the results of this instrumentation. The results confirm the strong correlation between the two measured parameters and outlines future areas of research for the use of the high frequency microseismic emission techniques in quantifying the changes in stress distribution.

Jan 1, 1984

By James A. Soles

Concrete is a complex, multicomponent mass whose stability is dependent on three principal variables: quality of the mix, its composition, and environment of the site. The aggregate is only one component, but its constituent minerals may react in unfavorable regimes and, given sufficient time, destroy the concrete. Therefore, besides ensuring that a concrete will meet the strength requirements of a structure, the concrete engineer must be confident that the mortar and aggregates will resist destructive processes. This paper reviews the principal causes and effects of aggregate instability, notes reactions of certain phases, and suggests precautionary measures that can be taken to extend the useful life of concrete structures.

Jan 1, 1984

By R. B. Berg

Chlorite veins in the Silver Star district were of little interest to those who were mining gold and silver in the late 19th century. In 1975 unusually pure magnesian chlorite of the variety clinochlore was identified from a "talc" claim in this district. In 1977 tests by Cyprus Industrial Minerals showed that this chlorite was suitable for use in ceramics. Mining begun in that year continues. These replacement veins of chlorite in Precambrian quartzofeldspathic gneiss differ from nearby metalliferous veins to the northwest in both attitude and mineralogy.

Jan 1, 1984