Coal Exploration, Mine Planning & Development

COAL EXPLORATION, MINE PLANNING,AND DEVELOPMENT

"Coal in truth stands not beside but entirely above all other commodities. It is the material energy of the country-the universal aid-the factor in everything we do. With coal almost any feat is possible or easy. Without it we are thrown back intothe laborious poverty of early times."

JEVONS

COAL EXPLORATION,MINE PLANNING,

AND DEVELOPMENT

by

Roy D. MerrittAlaska Division of Geological and Geophysical Surveys

Fairbanks, Alaska

NOYES PUBLICATIONSPark Ridge. New Jersey. U.S.A.

Copyright 1986 by Roy D. MerrittNo part of this book may be reproduced in any formwithout permission in writing from the Publisher.

Library of Congress Catalog Card Number: 8525869ISBN: 08155-1070-5Printed in the United States

Published in the United States of America byNoyes PublicationsMill Road, Park Ridge, New Jersey 07656

10987654321

Library of Congress Cataloging-in-Publication Data

Merritt, Roy D.Coal exploration, mine planning, and development.

Bibliography: p.Includes index.1. Coal mines and mining. 2. Prospecting.

3. Mineral industries. I. Title.TN803.M457 1986 622'.334 85-25869ISBN 0-8155-1070-5

Preface

Coal Exploration, Mine Planning, and Development provides a new andinnovative overview of issues related to these rapidly-evolving fields. It sum-marizes methods now in wide application and explores new trends for the fu-ture. Methods discussed include field exploration and mapping; drilling; geo-physical techniques; depositional modeling; logistical planning; basinal analysis;resource modeling; sampling and analysis; data acquisition and projection;data synthesis and interpretation; graphical presentation; reference, informationcompilation, and literature review; premine planning; and environmental base-line assessment and environmental resource protection.

The organization of the book is relatively straightforward. An introductorychapter is followed successively by a chapter reviewing world coal resources;chapters dealing with analysis of methods; a concluding chapter looking to thefuture; an expansive glossary of terms related to coal geology, exploration,mining, and technology; and an extensive bibliography.

The book is fairly simple in concept, format, presentation, and expression.As such, it is hoped that it will serve the interests and needs of a broad audienceboth within and outside the coal industry. No single volume can include an ex-haustive account of the diverse and specialized topics covered herein. Thegeneral purpose adopted from the outset was to give a practical and broad-stroke synthesis and description of the main techniques in vogue. As always,any omissions, errors in interpretation, or shortcomings of any nature are thesole responsibility of the author.

Fairbanks, AlaskaJanuary, 1986

v

Roy D. Merritt

Acknowledgments

Many individuals have assisted either directly or in-directly with the preparation of this book and I wouldlike to take this opportunity to acknowledge their con-tributions. It should be noted that the contents of thebook summarize the findings of many coal scientistsworking in the fields of coal exploration, mine planning,and development over the past decade. An attempt hasbeen made to extend credit to these researchers through-out the text.

Dr. Ross G. Schaff, Alaska's state geologist, is recog-nized for his continuing support. I also appreciate theinterest and encouragement extended by other friendsand coworkers at the Alaska Division of Geologicaland Geophysical Surveys. Mr. Alfred Sturmann of theAlaska Division of Mining assisted in preparing thegeological illustrations for this volume.

In addition, the author would also like to thankthose organizations (cited in the book) that grantedreprint permissions for certain figures and tables.

vii

About the AuthorRoy D. Merritt, a coal geologist directs the Coal Field InvestigationsProgram of the Alaska Division of Geological and Geophysical Surveys,Fairbanks. Prior to his current position, he worked in geological con-sulting, for industry, and research institutions. Besides conducting re-mote coal exploration projects in Alaska, he has worked in the Appala-chian, Eastern Interior, and Powder River coal basins.

ix

General Units and Conversion Factors

TO CONVERT TO MULTIPLY BY

acre hectare 0.4047centimeters inches 0.3937feet meters 0.3048gallons liters 3.7853grams pounds 0.0022grams kilograms 0.001hectare acre 2.471inches centimeters 2.540kilograms grams 1000.0kilometers miles 0.6214Ib/acre ppm 0.5liters gallons 0.2642liters milliliters 1000.0miles kilometers 1.609milliliters liters 0.001millimeters meters 0.001meters feet 3.281meters millimeters 1000.0ounces li ters 0.0296pounds grams 453.6ppm Ib/acre 2.1)section (mi2) acres 640.0temperature:

.oFc 5/9 (OF-32)

c of (9/5 C) + 32

xi

Contents

GENERAL UNITS AND CONVERSION FACTORS xi

1. INTRODUCTION TO COAL AND COAL ISSUES 1

2. COAL DEPOSITS OF THE WORLD 20

3. EXPLORATION AND MAPPING METHODS 33

4. METHODS IN LOGISTICAL PLANNING 69

5. DEPOSITIONAL MODELING METHODS 74

6. METHODS IN BASINAL ANALYSIS 117

7. METHODS IN RESOURCE MODELING 129

8. SAMPLING METHODS 147

9. METHODS OF ANALYSIS 163

10. METHODS IN DATA ACQUISITION AND PROJECTION 227

11. METHODS IN DATA SYNTHESIS AND INTERPRETATION 241

12. METHODS IN GRAPHICAL PRESENTATION OF COALINFORMATION 249

13. METHODS IN REFERENCE, INFORMATION COMPILATION,AND LITERATURE REVIEW 263

14. METHODS IN PREMINE PLANNING 266

xiii

xiv Contents

15. METHODS IN ENVIRONMENTAL BASELINE ASSESSMENTAND ENVIRONMENTAL RESOURCE PROTECTION 292

16. FUTURE METHODS 315

GLOSSARY 317

BIBLIOGRAPHY 412

SUBJECT INDEX 447

1Introduction to Coal and Coal Issues

Coal is the black diamond of the earth and the gem of the

lithosphere. It is the most abundant fossil fuel on earth (Fig-ure 1-1), and the oldest of the mineral fuels. Geologically,some coal deposits on earth are known to be over 400 million

years old. The earliest occurrences of land plants and coal

are from the Silurian Period of the Paleozoic Era. However,

there exist several Precambrian coal-like occurrences, but

these have been metamorphosed to graphite, and were probably

originally of algal or fungal origin. The first extensive coal

seams of economic value are of Mississippian age. By Pennsyl-

vanian time, land floras were well-developed and peat forma-

tion was common.

Most bituminous and anthracite coal occurs within strata

of the Carboniferous Period (about 350 to 270 m.y.B.P.), a geo-logic time division recognized by European geologists. In the

United States, this time interval has been divided into the

Mississippian and Pennsylvanian periods. This era was dominated

by coal formation worldwide, and hence is often referred to as

the 'First Age of Coal.'

The paleolatitude distribution of world coal fields (asrelated to plate tectonic theory) has led to their divisioninto two main groups---a low paleolatitude group consisting

1

2 Coal Exploration, Mine Planning, and Development

Figure 1-1. Coal is the most abundant fossil fuel on earth.In outcrops, coal appears as dark-colored bands of rock with-in lighter colored interbedded strata.

primarily of Carboniferous coals of western Europe and NorthAmerica and a high paleolatitude group consisting mainly of

Permian and younger coals from Canada, Siberia, and the south-ern continents (McElhinny, 1973; Figure 1-2). Each group con-tains a distinct fossil flora that lends evidence for the gene-

tic heritage of the plant materials forming them.

The prolific growth and widespread development of land

floras at this time resulted from the prevalent warm humid

climatic conditions. Paleobotanists have identified over 3000

species of plants that inhabited the earth and were preserved

as constituents of coal. Among the Carboniferous species are

Lepidodendron, Sigillaria, and Calamites. The class Filicineaeor the ferns first appeared during the Devonian period, and be-

came abundant during the Mississippian period. Tropical ferns

reached heights of forty feet. Shrubs and rushes grew to 100

Introduction to Coal and Coal Issues 3

------------ --- -- - ----------

/30

Suggestedper!>lsten1 endzone 120 - 30

.,-"

E"z

o

Figure 1-2. Equal-area latitude histogram of world's coal de-posits. Paleolatitude values have been plotted irrespectiveof sign. Deposits have been divided into two large groups---Carboniferous coals, Permian and later coals---near the equa-tor and poles respectively. (From Irving, Paleomagnetism andits application to geological and geophysical problems, 1964;reprinted by permission of John Wiley & Sons, Inc.)

feet high. Figure 1-3 shows various plant species in relationto geologic age, climatic influences, and types of coal depo-

sits ultimately formed.Historically, the Greeks, Romans, and Chinese were early

users of coal. Theophrastus (371-288 B.C.) made reference to

PALEOPHYTIC MESOPHYTIC CENOPHYTIC- 'f I'

PALEOZOIC I MESOZOIC I CENOZOIC

ANGIOSPERMS

VEGETATION

;Subfropl-TROPICAL Ic.' And

ITlmp.rate-'Warm Clima',IIII: IBROWNI COALI\,,(Q.\\~- :",n _-

---

I

::-R-t--

- - --I

I

--:.1~

Tlmp.r-.to-ColdClimat.

P80,,.-..............;

HUMIC ROCKS

ConifersCycad" Ginkol

Slid Feme 8Cordoi'ol..rna IClub Mo,

Calamitl.Sphonophyili. 0

LApidodendra,SigdlariCM

P,i1ophy tI,

.. 0 ....

FungiAlg.o

GYMNO-SPERMS

PTERIDO-PHYTES

~

(')oe:.MX'00-...

P>....o::l

~5'"

'"ii>::l::l5

'!"lP>::l0-t:l'"Rank C Colo. 25.8 31.1 38.4 4.7 0.3 6.3 50.0 0.6 38.1 8,580 ;:l

0-Lignite N. Dak. 36.8 27.8 30.2 5.2 0.4 6.9 41.2 0.7 45.6 6,960 (")

0e:.-rnrn

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rn

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stances, but they are most difficult to remove from coal. Oil

and gas can be stored without breaking down, but low-rank coals

particularly are subject to slacking and spontaneous combustionwhen stored over extended periods.

Table 1-2. Sulfur content in weight percent of variousmaterials (from Meyer, 1977).

Material Content

Crust of the earth 0.052

Coal 1.0-14.0

Oil 0.1-14.0

Gas 0.1-40.0

Gypsum 18.6

Soil 0.01-0.05

Coal can be used as a source material for the production

of mass quantities of synthetic petroleum substitutes. It can

be converted to a sulfur- and ash-free clean fuel---a deriva-

tive gas, liquid, or reconstituted solid energy product.

The particular characteristics of a coal, such as impuri-

ties and volatile-matter content, determine its end use. In

turn, a coal's economic value depends on this end use. For ex-

ample, a high-quality coal is needed to produce a high-grade

coke for metallurgical uses. Coking coal must be low in impuri-

ties, highly reactive, and capable of withstanding the high

pressures common in blast furnaces. Although the electricity-

supply industry's requirements are not as stringent as those

for the metallurgical industry, a low sulfur, ash, and mois-

ture coal is preferred. This is due to the environmental re-

strictions during combustion, such as those for SOx and NOxemissions.

The important resource factors which determine the useful-

ness of a coal deposit are: 1) coal quality; 2) overburden


thickness and quality; 3) the thickness and continuity of theseam(s), as well as the overall size of the deposit; 4) thegeologic structure of the basin; and 5) the strategic locationof the deposit with respect to transportation facilities and

potential markets (Table 1-3). Among the major factors thatinfluence coal planning and development are: 1) reserve quan-tity and quality; 2) mining, production, and transportation;3) the availability of critical resources; 4) appropriate la-bor participation; 5) sufficient equity assistance; and 6) re--search and development (Schmidt, 1979; Figure 1-8).

Table 1-3. General types of resource factors.

A. LOCATION--Appalachian, Interior, Western, Alaska

B. COAL TYPE--Anthracite, Bituminous, Subbituminous, Lignite

C. COAL CHARACTERISTICS--Heat content, Sulfur, Ash, Moisture,Chlorine, Sodium

D. SIZE OF DEPOSIT--Large, Significant, Small

E. ACCESSIBILITY--Rail, Tidewater, Barge, Highway, IsolatedF. MARKETS--World, Interstate, Local

Coal quality, reserve tonnage, environmental conditions,and geological engineering determine the economic rninabilityof a given coal deposit. The physical features related to coaldeposits that influence production methods include: 1) the po--sition of the coal relative to the earth's surface; 2) thethickness of seams; 3) attitude; 4) degree of fracturing; and5) continuity.

The chief participants and affected parties related tocoal production are: 1) electric utility coal consumers; 2)mine owners; 3) labor; 4) the local mining community; 5) en-vironmentalists; and 6) government. In general, there are fourmain categories of coal-mining communities: I) integrated com-panies that mine coal largely for their own use---captive mines;

2) interstate corporations operating mines in several areas of


FACTORS INFLUENCING PLANNING AND DEVELOPMENT

Vla:0I-U.....

... ~0 VIW

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of coal production and utilization technologies exists where

each level represents many alternative methods or approaches(Schmidt, 1979; Table 1-4).

Primary technologies are involved in the development andextraction of coal from geologic deposits. Secondary technolo-gies are limited by the nature and physical properties of theraw coal and includes coal preparation. Tertiary technologiesare involved in attempting to modify the chemical and physico-chemical properties of coal influencing utilization. Tertiary

processing of coal, as in blending to meet emission control re-quirements, may be required in certain cases because of a spe-cific coal's properties, necessary utilization conditions, andconsumption regulations. Quaternary technologies involve allfactors related to coal utilization including the chemical pro-perties of ashes and other combustion products as sulfur and

nitrogen. Coal extraction technologies exert strong influenceon preparation, blending, and utilization (Schmidt, 1979).

Since the world has such vast resources of coal, it is on-ly logical that we develop these in response to our presentneeds and future demands. The demand for coal should graduallybut steadily increase the remainder of this century as petro-leum reserves continue to dwindle. Thermoelectric power plantsand other large industrial customers will continue to convertfrom oil to coal usage. Applications of coal to liquefactionand gasification technologies should expand. More and largermines will be needed to meet these increased future demands.However, many of the high-quality, easily mined seams have al-ready been exploited in some areas. Greater demand for coalmay eventually increase the economic feasibility for developingsome formerly unminable and unprofitable seams.

Steam-coal production will become increasingly importantin the next decade, and exploration and evaluation of coal re-sources of this type will resultantly also increase. Since eas-ily surface-minable reserves of high-quality coking coal areapproaching full development, exploration activity related to


Table 1-4. Hierarchy of coal development technologies (fromSchmidt, 1979).

Class*

1. Primary

2. Secondary

3. Tertiary

4. Quaternary

Description

Extraction from natural deposits; deter-mination of size consist and noncombusti-ble content.

Preparation; use of physical propertiesto beneficiate extracted coal and sepa-rate noncombustibles.

Blending; mixing of coals with differentproperties to achieve a desired productin terms of heating value, ash, and sul-fur content.

Utilization; actual use of coals in plantor process applications (with or withoutfinal treatment or additives).

*Classes reading down indicate decreasing opportunity to altercoal characteristics but increasing importance of chemicalproperties as compared to physical properties.

underground production potential should rise (Svenson, 1979).Substantial growth in future coal production in many parts

of the world will directly influence market prices and there-fore force it to become more selective. Certain coal-qualitycriteria will assume increased significance at that time. Re-search related to the petrographic and physical characteristicsand chemical composition of coals will be indispensable during

exploration phases and afterwards to determine market prospects

(Orheim, 1979).Evidence of this future trend can already be witnessed in

the types of coal research currently being pursued and also in

the training of coal geologists. Current coal research is cen-

tered in four key areas: I) depositional environments as ap-plied to the prediction of coal continuity and lateral extent,seam quality variations, roof-rock conditions, and geochemis-

try; 2) coalification processes---rank changes, chemistry, and


utilization; 3) coal uses---prediction of combustion behaviorand coking suitability; and 4) petrology---coal properties andreactions during combustion. The training of coal-explorationgeologists has broadened to include the social, economic, en-vironmental, and engineering aspects of the exploration and ex-traction of coal as well as the reclamation of mined lands(Mathewson, 1979).

In order for coal usage to be increased substantially ona worldwide basis, it needs to be economically competitive withother energy sources such as oil and gas. In the past, the sol-id fuels were gradually replaced by oil, gas, and other moreconvenient forms of energy. Coal use in the United States needsto be substantially increased in order to further reduce ourpresent dependence on imported oil. This can be accomplishedin several ways: 1) direct conversion of coal to oil and gas;2) increase industry's use of coal for process heating; andperhaps most importantly 3) use coal to replace the oil and gascurrently inefficiently used for electricity generation.

Another important factor in increasing coal usage world-wide will be necessary improvements in transportation facili-ties for coal, which are currently inadequate. This includesboth rail and port facilities. In order for the exports of coalto be increased significantly in the United States, these faci-lities must be improved and expanded.

Regardless of existing technological, production, develop-ment, and transportation problems, coal is destined to assumea far larger share of the future global energy mix and alsoplay a far greater role as a substitute for oil in the petro-chemical industry.

Coal is the most abundant fossil fuel in the United States,in total accounting for over 90 percent of our current energyreserves. It plays a major economic role in several states ofthe United States, particularly in the Appalachian, Midwestern,and Western regions of the country. The ten states of the Uni-ted States holding the largest resources of coal are Alaska,


North Dakota, Montana, Illinois, Wyoming, Colorado, West Virgi-nia, Pennsylvania, Kentucky, and New Mexico.

Coals of the eastern and western United States differ in

several significant ways. Geologically, eastern coals are older

being about 300 million years old compared to 100 million yearsfor western coals. Eastern coals are typically relatively thin

seams from 4 to 6 feet, while western coals are 10 to 30 feetthick or more. In general, eastern coals, which have been com-paratively more deeply buried, have been subjected to more in-tense tectonic stress and are more completely formed than wes-

tern coals. Eastern coals are commonly indurated and compact,

while western coals are porous and friable. Eastern coals us-

ually have relatively high heating values (10,000-12,000 Btu/Ib or higher) compared to western coals (7,000 to 9,000 Btu/lb).Eastern coals often have a sulfur content from 2 to 3 percent

or higher, while western coals have a sulfur content less 1percent. Eastern coals are primarily deep-mined while western

coals are primarily surface-mined (Schmidt, 1979).While most states of the United States have been fairly

thoroughly explored for coal resources, exploration will conti-nue to be important in western states. The ultimate resourcebase of the state of Alaska alone may eventually equal or sur-pass that of all the 'lower 48' states combined. Alaska isstrategically situated to take advantage of expanding Pacific-rim coal needs. Export of Alaska coal to South Korea began in

1984 and is expected to increase markedly in the future. Coaltrade, other commerce, and the continued rapid industrializa-tion of Far-Eastern countries, promises to make the 21st cen-tury the 'Age of the Pacific (Figure 1-9).' Continued improve-ments in coal technology and facilities, and expansion in ex-

ploration, mine planning and development should bode well for

future coal trade and utilization throughout the world.

...... ....~ '..

Figure 1-9. Estimated round-trip ocean freight distances in nautical miles from vari-ous coal-exporting sites to Japan on the Pacific rim (after Swift and others, 1981).

.....

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o(')oe?.l>l::l0..(')oe?......

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2Coal Deposits of the World

Coal is the most widely distributed fossil fuel on earth(Figure 2-1). It is known to occur in over 2000 sedimentarybasins worldwide (Ross and Ross, 1984). Estimates of worldcoal resources are substantially larger than for oil or natu-ral gas. Although coal is a finite fuel resource, based on

present and expected future rates of consumption, it has beenconservatively estimated that the supply will last at least200 years.

Coal has been found on every continent including Antarc-tica. Two-thirds of the world's coal is located in the UnitedStates, the Union of Soviet Socialist Republics (USSR), andthe People's Republic of China. The estimated total coal re-sources of the USSR are 12.5 trillion short tons. The UnitedStates contains an estimated 9.5 trillion short tons of coalwith up to 5.5 trillion tons of this in Alaska alone. The Peo-ple's Republic of China contains about 5.0 trillion tons ofcoal. Total world coal resources are estimated to be about 35trillion short tons.

Geologically, nearly one-half of explored coal resourcesformed during Carboniferous time (particularly the Pennsylva-nian Period)---the so-called 'First Coal Age (Figure 2-2).'Late Permian and Triassic coals are widespread in Antarctica,

20

Figure 2-1. Locations of significant world coal resources and trade move-ments of major world coal-exporting countries (modified from Crabbe andMcBride, 1978).

eo.1 ~lrportor.

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--USA--c.ll(Idl__ussn----PoleNi-Austr.ll.

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Subbitwni Hlel> Hiet> 1.0....Bro"" Bro"" Black Medium vol.til~eoo1 Iianite lienit DO" volatile vobtile volatile and "mi AnthraciteA.B C. B A anthraciu

Qua"'n

Coal Deposits of the World 23

England, 48, 153, 155, 158, 157, 180, 182; France, 53, 165,166, 168; East Germany,S, 21, 22, 23, 90, 121, 137, 106,143; West Germany, 24, 49, 61, 63, 62, 64, 2, 27, 57, 59,127,150; Greece, 75,86; Hungary, 30, 35, 42, 44, 74, 95,130; Italy, 18,45,83; Poland, 6, 138, 149, 151; Ruhr dis-trict, 148; Romania, 17,129,162; USSR, Russia, 117, 177,124, 126, 179, 184, 185; Scotland, 120, 181; Spain, 160;Spitzbergen, 76, 178, 79, 82, 84, 107, 108; Switzerland, 4,87,154; Turkey, 58; Yugoslavia, 10, 11, 12, 13, 15,50,34,51,52,39,40,41,47,54,56,60,85,99, 142, 156. NorthAmerica/ Canada, 68,116,104,110,176,112,113,115; Mex-ico, 141; United States, 43, 77, 92, 65, 66, 67, 69, 70, 71,80,96, 97, 103, 101, 102,88, 105, 140, 173, 174, 175.South America/ Brazil, 145; Peru, 46, Ill, 109, 114.

Australia, India, South Africa, and South America. Jurassiccoals are predominantly found in central Asia, Australia,Madagascar, South Africa, and Antarctica. The so-called 'SecondCoal Age' includes the Cretaceous and Tertiary periods. Creta-ceous coals are widespread throughout the world and are espe-

cially common around the Pacific rim; they are second only toCarboniferous coals in the total amount of resources. Tertiarycoals place third in the amount of world resources; they aremainly of subbituminous and lignite rank and hence have resul-tantly been less explored. Perhaps two-thirds of Tertiary coalresources are in the western plains of the United States (Fig-ure 2-3) and in Alaska; other occurrences are in Europe, Aus-tralia, and parts of Asia.

Most areas of the world contain more than one coal seam.In fact, most coal basins contain numerous seams of coal. Forexample, in West Virginia of the Appalachian basin, there areat least 120 named seams. In northern Alaska, there are manymore than this but most are unnamed and have not been correla-ted. The coal seams of the world range in thickness from lessthan an inch to several hundred feet.

Exploration for new coal deposits is continuing at a slowpace, but should accelerate in the future as existing suppliesare depleted. However, a number of known coal deposits are not


. .--

Figure 2-3. Thick seam of Tertiary subbituminous coal in Wyo-ming's Powder River basin.

now being developed or are producing at lower than maximum ca-pacities. Current geological research on world coal depositscenters on the depositional environments and coalificationhistory of coal since these areas have practical applicationsrelated to minability and utilization (Ross and Ross, 1984).

Countries of the world with the largest coal resourcesare listed in Table 2-1. The USSR, the world's largest coalproducer, contains the largest amount of geological coal re-sources, but half to two-thirds of these resources are foundin little explored areas above 60 latitude far from highlyindustrialized European sectors of the country (Figure 2-4).The deposits of the USSR occur in at least 10 important coalfields and in a similar number of smaller fields. The depositsvary widely in age, rank, and structural complexity. Theyrange from Paleozoic to Cenozoic in age, with the main coalbasins decreasing in age toward the east. Paleozoic coals arefound in the Urals and Siberia; Mesozoic coals are centered in


Table 2-1. World coal resources on a percent total resourcebasis. Data evaluated from various sources including Wilson(1980) and reflects a magnitude percentage of the total only.

GEOLOGICALCOUNTRY RESOURCES

1. Soviet Union 40.02. People's Republic 16.0

of China

CURRENTTECHNICALLY AND ECONO-

MICALLY RECOVERABLERESERVES

16.515.0

3. Contiguous UnitedStates

15.0 15.0

4. Alaska 15.0 10.0..........................................................

U.S. Total 30.0 25.0

5. Australia 4.5 5.06. Canada 2.5 0.57. Federal Republic 2.0 5.0

of Germany8. United Kingdom 1.5 6.59. Poland 1.0 8.0

10. India 0.5 2.011. Republic of 0.5 6.5

South Africa12. Other countries 1.5 10.0

World Total 100.0 % 100.0 %

the Far East of Siberia but are also found in central Asia andthe Urals; and Cenozoic coals are mainly located in the Uralsand the Ukraine (lEA Coal Research, 1983).

The United States probably holds 30 percent of world coalresources, with perhaps as much as half of this amount concen-trated in the state of Alaska alone (Figure 2-5). Coal has beenmined in 27 of the 50 states. There are recoverable reserves inat least 35 states and appreciable deposits in 32 states. Wes-tern U.S. coal accounts for about 75 percent of the country'ssurface-minable reserves, and for two-thirds of our total coal


, EII.blhh.d '.,.""o Eilimiled ft'If"Nn

Figure 2-4. Locations of coal resources in the Middle East, USSR,and Asia (modified from Crabbe and McBride, 1978).

resources. Coal beds here may be 60 to 100 or more feet thickand may be covered by less than 200 feet of overburden. The de-posits of the United States vary widely in age, rank, and struc-tural complexity. They range from Paleozoic to Cenozoic age.Paleozoic bituminous coals are predominant in the Appalachianand Eastern Interior basins. Cenozoic subbituminous coals andlignites are abundant in the northern Great Plains. Cretaceousand Tertiary bituminous and subbituminous coals account for

Coal Oeposits of the World 27

EII"bllllu:-dretf''I"Q Elllmlt~'fetel'Ytt

Figure 2-5. Locations of North American coal resources (modi-fied from Crabbe and McBride, 1978).

most of Alaska's coal resources.Coal deposits underlie approximately 5.5 percent of Chi-

na's land area (Figure 2-4). Pennsylvanian-, Permian-, andJurassic-aged coals make up 95 percent of the resources andthe remainder are Tertiary. The country contains an estimated5 trillion tons of coal resources of which over 700 billiontons are estimated to be recoverable. Pennsylvanian coals arehigh in sulfur, Permian coals are low in sulfur but high inash, and Jurassic coals are of best quality with both low sul-


fur and ash. Tertiary coals are of subbituminous and ligniteranks. Thirty percent of China's coals are low-rank bituminous,28 percent subbituminous, 9 percent anthracite, 8 percent mid-dle-rank bituminous, 8 percent lignite, 6 percent high-rankbituminous, and 11 percent mixed coals. The People's Republicof China is the third largest coal producer in the world with628 million tons mined in 1981. Most of the coal is used domes-tically but increasing tonnages will be available for export inthe future (Aughenbaugh and others, 1982).

Australia contains the fourth largest resource of coal inthe world, but is the second largest exporter of coal, mostgoing to Japan. The country contains as many as 30 coal-bearingbasins; the more important of these basins are shown in Figure2-6. Bituminous coals are mainly located in three sedimentarybasins on the east coast---Bowen, Gippsland, and Sydney. Thedeposits range in age from Paleozoic to Cenozoic. Paleozoiccoals are mostly bituminous but also include some subbituminousand anthracite. Mesozoic coals, mainly subbituminous, are lessabundant than Paleozoic coals. Cenozoic coals are subbituminousand lignite.

Canada contains the fifth largest resources of coal in theworld (Figure 2-5). Only a small percent of these resourcesfall in the measured category. The deposits range from Paleo-zoic to Cenozoic in age, and vary widely in rank and structuralcomplexity. The main coal-bearing region occupies a belt acrosssouthern Saskatchewan, Alberta, and British Columbia (Figure2-7); here, Cenozoic and Mesozoic subbituminous coals and lig-nites are found in the plains, and Mesozoic bituminous coalsare found in the mountains of northeastern and southwesternBritish Columbia. Paleozoic bituminous coals are found in botheastern and western Canada. There are also numerous northernCanadian occurrences of coal.

Western Europe contains relatively small resources in sev-eral countries (Figure 2-8). In addition, thick Carboniferousseams extend beneath the North Sea. The Federal Republic of


Coal RankBituminous

WESTERNAUSTRALIA

Q'V

~:).J I

- III NORTHERN I I "-I TERRITORY I \. BowenI , "\~"H'y Po,",: : QUEENSLAND~, ...~I I \ ,0 GladstonerSOUTH-AUSTR;UA; "I II 0l.. Leigh I J. BrisbaneI \') Creek ... - - - - - - - ?II Arcka"nga G 'NEW SOUTH .-

~Bas,n 'WALES- St. Vincent's Basin .Collie =:=:?;..-- ~ 7} ~~urrav Basin NewcastleBasin . .0, ..., . Sydney

Port Adelaide I 'r~ ,Port Kembla~ 'VICTORIA ~ I

AIBacchus Marsh. ~~trobe Valley and Gelliondaletona and Anglesea D ~

TASMAr;;;:] F;ngal Valley\-0 Hobart

Subbituminous

200 400Lignite o! , , ( I

Scale 01 Mjles

Figure 2-6. Major coal-resource locations and supply regionsof Australia (from Swift and others, 1981).

Germany (West Germany) and the United Kingdom contain most ofthe western European resources. About a quarter of West Ger-many's coal is used in coke production. Paleozoic coals occupylarge areas in the western part of the country and minor depo-sits in the south; these coals are mainly bituminous with less-er anthracite. Mesozoic coal deposits are limited to the west

Rhine district and southeastern sector of the country; these

coals range from subbituminous to anthracite rank. The UnitedKingdom contains over 200 billion tons of coal resources con-centrated in 6 important coal fields. These deposits are mainlyof Paleozoic age. Minor Mesozoic-aged bituminous deposits arefound in Scotland, and Cenozoic lignite in Devon. Lesser quan-


h----~I Saskatchew.n II I1 ,

IJ,IIIIJIIII,I,III

Coal RankBituminous

Subbituminous F11JLignite [J

400I

"....I ' ....(". -' ...... , ...................

, ................~f) ) - ............t.w ~ BritiSh COlumbi: ...... - ............IVan ,I

...... "'1)'0. "~\J ;

(} .~ Prince Rupert([~ ~~ Bowron R;ver

\", \(Q ~

(0 /"

,o:~!.~?~".,',...\\'L \~~ "'({"nceton and\

Vancouver~ \2) Tulameenlr:'-....J~~ --S'p~~~E~STERN

Scale of Mileso 100 200 300b

Figure 2-7. Major coal supply regions of western Canada(from Swift and others, 1981).

tities of coal resources are located in other western Europeancountries (lEA Coal Research, 1983).

Poland is a major world coal producer and coal-exportingcountry, and contains the largest resources in eastern Europe(Figure 2-8). Paleozoic deposits of bituminous coal are foundin several basins in the southwest and eastern parts of thecountry. Mesozoic bituminous and subbituminous coals are foundin the southern part of the country, and Cenozoic subbitumi-nous coals and lignites occupy extensive areas of western,central, and southern Poland.

India contains at least 10 important coal basins and oth-


"

UK

..... _ ...0-~..I~

".' ., r-'.

E$lilIJllihe(J Ie""",.~ Ellimiue


BOTSWANASOUTH WEST AFRICA

(NAMIBIA)

CAPE PROVINCE

"

INDIAN OCEA;'Ir,I

c, R.nk JBi1Uml"~UI .",-::1 ~Anrh'lc.te ..

Figure 2-9. Major coal-resource locations and supply regionsof South Africa (from Swift and others, 1981).

age, but there are minor Mesozoic deposits.

There are other deposits of coal in several third-world

countries that may assume increased importance in the future.

These include countries in Latin America, Africa, and south-

east Asia. However, these nations will not likely playa majorrole in the world coal trade picture for many years to come.

3Exploration and Mapping Methods

A field coal exploration program is a multi-faceted endea-

vor that involves several phases. Among the more important of

these are: 1) permitting and pre-field logistical coordination;2) field exploration itself; and 3) report and mine plan prep-aration.

When a coal exploration program begins, it is very impor-tant to determine the present land status. State and federalagencies are contacted and any required permits are obtainedthat are necessary to carry out the proposed investigations.Sometimes private property may be involved, and it is just asnecessary to contact these parties to obtain permission forthrough access to sites concerned.

Characterization of property geology includes a review ofliterature, assimilation of in-house data, delineation of gene-ral traits, and graphical analysis of property (Figure 3-1).Projects in areas of limited coal exposures and poorly knowngeology are largely exploratory in nature. Investigation proce-

dures in such areas should be selected with care to allow foraccurate data acquisition and permit a realistic evaluation of

coal geology~ resources~ reserves, quality and development of

viable mine plans should the deposits prove economically ex-tractable.

33


GEOLOGICAL EVALUATION

I CHARACTERIZE PROPERTY GEOLOGY I

1 1LITERATURE ASSIMILATE IN-HOUSE

REVIEW DATAUSGS Drill DataState GS F laid Obs8r'vationsExisting Mines Geophysical Info

I I

DELINEATE GENERAL TRAITS

Seem ConsistencyNo. of SeamsPotential OutcropsGeneral Overburden Characteristics

GRAPHICALLYANALYZE PROPERTYGenerate X-Sectlons orFonce DiagramsDerive Overburden/CoalVolumes

Calculate Strip Rstlos

Layout Crude Strip RatioIsopach

GEOLOGICAL EVALUATION

Figure 3-1. General flow chart illustrating the ma-jor methods involved in the geological evaluationof a mine property (modified from Loy, 1983).

Diverse coal exploration problems are encountered in re-mote, mountainous, coal-bearing regions in many parts of theworld. Among the development restrictions that apply to these

areas are: 1) physical terrain; 2) climate; 3) highly disturbed

Exploration and Mapping Methods 35

geological structure; 4) environment; and 5) government re-straints (Beresford, 1979).

Air photos aid the interpretation of the structural frame-work on such coal-bearing tracts and can help to focus explora-tion for optimum performance and results. High-altitude, falsecolor infra-red photography particularly is useful to delineateobservable structural trends and features in the region.

During the initial reconnaissance survey of a suspectedcoal-bearing area, geological mapping should be completed. Map-ping involves compiling detailed field notes, measuring coal bedthicknesses and lateral extent, taking strikes and dips of beds,plotting contacts between varying rock units, and locating faultsand other structures affecting rock strata (Figure 3-2). Coaloutcrops and other characteristic localities should be documen-

Figure 3-2. A field geologist maps the location and notesthe characteristics of an outcropping coal seam prior tosampling.


ted by section descriptions and photographs (Figure 3-3). Allstreams and gullies are usually searched for outcrops or coalfloat and holes or trenches can be dug in critical locations.Ultimately. a geologic map is produced that shows in plan viewthe areal distributions of various rock units (Figure 3-4).

During reconnaissance geologic field investigations, map-ping aids in establishing the prevalent structural conditions.Based on the mapping results. the drilling and geophysical pro-gram can then be modified to best fit site conditions. Integra-ted geological mapping and geophysical orientation surveys areused in areas of known coal exposures and deposits, and are usedas a guide to subsequent exploration drilling programs.

When first reaching a field exploration site and early inthe program. trenching can be used locally to rapidly assess thelithology and structure and plan drill-hole locations. However.a backhoe or Caterpillar tractor will be required to excavatetrenches. The use of trenching as a method of exploration de-pends on the availability of equipment.

The surface locations of proposed drill holes must be sur-veyed by stadia and transit. After drilling. sites are markedpermanently with a cement plug. metal post and engraved metaltag with hole identification.

Figure 3-5 details full-sequence exploration and table 3-1summarizes activities and methods associated with the four mainphases of an exploration project. Among the geologic factorsthat should enter into a preliminary evaluation of a coal pros-pect are the following: 1) preparation and review of surface-geologic maps and surface-sample data including all analysesand test work on coal samples; 2) review of all previous explo-ration. maps. reports, well and drillhole data, history of theprospect if previously explored or mined. and determination ofreason for cessation of previous mining; 3) review of drill pat-tern for its adequacy and representativeness. review of drilllogs to determine the nature and physical properties of over-burden. interburden, and seatrock; 4) plotting of all geologic


Figure 3-3. The modern coal explorationist is concerned withmany aspects related to the geology of coal deposits. Theseinclude resource base, coal character and quality, field re-lations, coal petrology and depositional environments, mina-bility, and coal utilization.


EXPLANATIO NQOATJ:R.HAATIQ1.bu Ty~ 01 0 .-,-

~::S1Id.0

_,

Sbtl.-t"IIJIlllbCoDurl_

~ ~pSockEn ::~ DabrilLl ~~o.~,-

TUTlA.-.T:Eo"II.

l:~.:.-JE:l :~..~.,- R_.1~ ;;:;. '.--

{~ ~~u ,._...

Figure 3-4. Mapping of unconsolidated surficial andbedrock materials is important for applications bothto exploration and premine feasibility studies.


RECONNAISSANCE. TARGET INVESTIGATIONI , , ,

STAG!. No.1 STAGE No.2 STAGE No. 3 S,TAGE No."----

rl REGIONAL r DETAILED H ~ DETAILED DETAILED I ECOHOM'C IAPPRAISAL ~ECONNAJSSAI'lC SURFACE HREEDIMENSIONAL MINERALOF FAVORABLE r APPRAISAL 0" SAMPLING AND DEPOSIT! AREAS TARGET AREA PREL1MIr-tARYr EVALUATION, I :, , I,I

jI

,

:,r II : II I Ir I ,:1REG'OH HOT I- : r-- I TARGET ARU r

.:r

AREA REMAtNS . UNECONOMIC, HOTATTRACTIVE _ .' FAVORABU .---'. ATTRACTIVE .- MINERALAT THIS TIME BUT NOT ATT"'STI"'1.DEPOSIT

ATTRACTIVE"T TKIS TIM!

REJECT:

I~,~ECTI r NOTAlUG ION MINERALNP'''VORAIIU - NormaJ ExploralJoQ $equ,aoe DEPOSIT0(-------- R~)'clinc Af1er Temporvy RejecuoD~ Ke,. :zpIOllllloD o."OQ,l

Figure 3-5. Flow chart illustrating the four main stagesinvolved in the typical full-sequence mineral explorationproject (modified from Bailly, 1972).

data on maps, review of maps and cross sections, review of geo-logic interpretations relating to the structure of the coal de-posit, estimation of the overburden/coal (stripping) ratio, andcalculation of the coal reserves; 5) review of all coal-qualitydata and interpretations as to the type of run-of-mine coal thatcan be produced; and 6) evaluation of the total reserves of thedeposit, projection of annual production rates, and establish-ment of mine life. Furthermore, review and study of core orsamples obtained in a previous exploration program is used forfamiliarization with general stratigraphy and to assess the use-

fulness of conducting different tests on the cores. Evaluationof all these factors will lead to a decision as to whether fur-ther exploration is warranted or mine development is currentlyviable (Sundeen, 1972).

The basic factors that should be taken into account duringthe preliminary evaluation of a surface coal-mine prospect in-


Table 3-1. Main activities and methods used during the fourstages of exploration previous to a decision that a profita-ble coal surface mine can be opened. At the end of each stageall results are integrated and the area of interest redefined(modified from Bailly, 1972).

STAGE

#l

#2

#3

14

PHASE

Regionalappraisal

Detailedreconnaissance

Detailedsurfaceinvestigationof targetarea

Detailedthree-dimensionalphysicalsamplingof targetarea

ACTIVITIES AND METHODS

O---Geologic compilation for"marketing" area*

F---Field check of sectionscontaining coal seams*

F---Reconnaissance drillingfor stratigraphy andcoal thickness

F---Chemical and calorificcheck of outcrops ordrill samples

F---Detailed helicopter-borne or ground survey

F---Detailed mapping ofoutcrops

F---Drilling and logging*L---Mineralogical, chemical

analyses and physicaltests on samples, cores,and cuttings*

F---Down-hole geophysicalsurveys

L---Amenability tests oncoal quality

O---Reserves computations*O---Preliminary valuationF---Investigation of water

problems and water availa-bility for plants*

F---Investigation of suitabilityof ground for plant, tailings,dump and town sites

F---Shaft sinking, tunneling, ortrenching to obtain bulksamples

L---Coal bulk tests

LEGEND: F= field investigation; L= laboratory tests; 0= officestudy; * = activity or method thatis judged indispensable.


elude: 1) geography; 2) legal status of the land and miningrights; 3) historical, political, and sociological factors;4) geology; 5) mining conditions; 6) coal preparation re-quirements; and 7) economic analysis (Sundeen, 1972).

Several distinct phases of further work and evaluation fol-

lows the project review and positive appraisal of outcrop andsurface data collection efforts. These phases include: 1) ad-ditional surface surveys and sampling; 2) diamond drilling onwide-spaced pattern and testing of the coal and other core sam-

ples; 3) diamond drilling on close-spaced pattern and testingof the coal and other core samples; 4) bulk coal sampling andtesting; and 5) final feasibility study (Sundeen, 1972).

Project geologists perform all necessary geologic reconnais-sance at the project site to obtain an understanding of the geo-logy. An experienced geologist must log all borings made in thefield. Driller's logs are inherently crude, vague, and too gene-ralized for purposes of making valuable geologic interpretations;

an example of a driller's log is cited in table 3-2. All samplesand core are visually classified in the field and special careis taken in preparing coal samples for transport. All boringsdrilled are located on air photos and enlarged topographic maps

of the sites. The project geologist guides the field explorationprogram by modifying boring locations as new information is gene-rated by geophysical methods and completed borings. He continual-ly reassesses the exploration program in order to obtain thenecessary geologic information on the coal beds in the most eco-nomic and efficient manner.

Among the most often occurring weaknesses of coal explora-

tion projects are problems related to management control, per-sonnel experience, and financial constraints. Planning-stage

problems include lack of appreciation of project tasks and pro-gram objectives and lack of technical capabilities of personnel.Management control of an exploration program is required from

the calling-of-bid stage to final move-out of drill rig andsite reclamation (Wallis, 1979).


Table 3-2. Example of coal driller's borehole log.

DH 50-ADEPTH THICKNESS( feet) STRATA (feet)

loose rock 2.02.0 clay, sandy 6.08.0 clay wI burn 10.0

18.0 shale, sandy 11. 529.5 burn 10.840.3 smut 1.742.0 shale, dark 1.043.0 shale, dark 4.247.2 shale, dark 4.852.0 coal, soft 2.454.4 shale, dark 7.061.4 shale, brown 24.485.8 rock, hard 1.086.8 shale, brown, sandy 2.088.8 shale, gray 47.3

136. I coal 3.5139.6 shale, dark 0.4140.0 coal 5.9145.9 shale 0.1146.0 coal 30.8176.8 shale, dark 0.7177.5 coal 65.8243.3 shale, dark 0.5243.8 coal 1.5245.3 shale, gray 25.5270.8 rock, hard 0.5271.3 shale, gray 9.5280.8 rock, hard 0.6281.4 shale, gray 4.4285.8 rock, hard 1.2287.0 T.D.

Project management coordinates exploration planning byholding meetings with drilling contractors and geophysical con-tractors including mobilization, execution, and demobilizationof each party's personnel and equipment. On an extended explo-ration project, monthly reports should be provided to projectmanagement that includes information as to work accomplishedto date, the current status with regard to the project time-table, a general summary of data gathered, changes or additionsmade to the planned program, and suggested comments to improve


ultimate project output.Budgeting includes prefield mobilization costs, field costs,

and associated personnel costs to synthesize and interpret data(Table 3-3). Overall project costs should include expenses ofall subconsultants and subcontractors. Project costs can be es-timated based on daily drill rates, drill-crew standby rates,

geophysical crew rates, and including fixed wing and helicopter

support and camps. Most projects include at least basic expendi-tures for drilling, logging, and personnel (Table 3-4). Pre-ex-ploration drilling plans that outline a proposed field program

can be drawn up to facilitate scheduling, organization, and fol-lowthrough once on site (Table 3-5).

Among the problems encountered in preparing a time-explora-

tion budget are estimating completion dates, data interpretation,

and planning phase activities. Staff supervision, communication,and documentation are important aspects of a typical exploration

budget. Simple formatted data sheets can be used to provide nec-essary documentation. Field management personnel can provide thedesired degree of control of projects by on-site supervision.Cost-limited, time-constrained, and specific-objective explora-tion projects influence and determine program planning (McNulty,1979).

The primary method for acquiring subsurface data in a coal-exploration program is a rotary drilling program combined withgeophysical logging of the boreholes. At a minimum, core drill-ing is implemented where necessary to obtain coal-quality data.

The nature and extent of the overburden and coal is deter-mined by drilling boreholes from the surface through the ore de-

posit. The data sought during test drilling for coal include thefollowing: 1) the configuration of the coal seam(s), for example,the dip; 2) core samples for evaluation of coal and overburdenquality and quantity; 3) character of mine roof and floor ma-terials; and 4) existence and nature of geologic conditions af-fecting continuity. The latter include faults, washouts, clayveins and clastic dikes, concretions, shale partings and splits,


Table 3-3. Major categories for budgetary expenditures at atypical coal exploration project in North America (afterMcNulty, 1979).

A. Rotary drillingB. Core drillingC. Geophysical loggingD. Coal analysesE. Topographic mapping and hole location surveysF. TransportationG. CommunicationH. Staff supervisionI. Geologic mappingJ. SubsistenceK. Documentation

Table 3-4. Sample budget for relatively small drilling pro-gram in western United States, 1980 estimated costs.

COSTI. Drilling

A. Main holes1. Coring , 35,025.002. Plugging ' 4,950.00

B. Pilot holes (plugging) 6,700.00C. Standby ......................................... 4,000.00D. Preparation and setting casing

(four hydrology wells) 700.00E. Reaming holes (for hydrology wells) 650.00F. Per diem (drill crew) 3,150.00G. Mobilization costs 120.00H. Supplies l l,700.00I. Contingency2(estimated at 10% of drilling

costs) 5,850.00II. Geophysical logging

A. 300 hours 8,250.00B. 5,700 ft logging 3 1,425.00C. Mileage 4 .......................................... 600.00D. Per diem 1,200.00

III. GeologistA. Salary .............................. 9,600.00B. Field technician/assistant 5,100.00C. Expenses ........................................ 3,600.00D. Mileage 1,600.00

TOTAL ESTIMATED BUDGET 95,720.00

lIncludes casing, packers, caps, connectors, core boxes, plastictubing for samples, etc.

2Includes unanticipated extra costs as for scoria drilling; delaysdue to drilling through hard rock bands; drill bits, soap, andwater costs; drilling or coring in excess of predicted intervals.

3Includes natural gamma, caliper, resistivity, and density.4Includes mobilization and decommissioning only.


Table 3-5. Drilling plan for supplementary exploration, coalquality, and hydrologic conversion program by company in Wyo-ming's Powder River Basin.

PILOT ROUS l'V,IM IfOL~ESTllUTtD TOT..... TOTAL

SnKATtO ESTIl'tATD ItYOItOLOGIC TOTAL n. EST. EST.KOLE NO. T'QTM. DEPTH COAL DEPTH 0 80U5 Co.l '00

" "10 1.145.720 424.')60 '00 85-195 Coa.l '00"

uo

U 1.)43.2)0 414.720'"

llS-tJO Co.. 1'"

llO U,

IZ I,Hl,090 423.aoo'"

45-145 Co.1 1>0 >0 100

"1,343.]20 427,OJO '05 ~OO-lOO Co.l lO' 10' 100

LI LHS.920 418. Ho 270 160-265 Coal 270 16> 105

"I.H8.040 427 ,ala

'"HQ-nO Ovb.' Coal

'"10 n,

16 l.HI.OOO 419.620 1lO ~OO-lO5 Coal no 10' 10'17 1.350."80 429 ,180 140 90-1)5 Coal 200

"..

IS 1,H9.360 00.690 '10 'O-lOS Coal 210"

U,

.. 1.H8.'10 4]1.120'"

1)';-140 Coal'"

1

~cr>

CHANNELS FAULTS

No coal missing; seam is merely displaced

:s:5'C1l

'"ii>;:l;:l5'Tll>l;:l0-t::lC1l


gathered on coal seams and subsurface geology during mine plan-ning may preclude problems for a mine operator. This becomesincreasingly important as more and more of the high-quality,easily minable coal is produced, and remaining coal propertiesmay support only economically marginal operations (Chironis,1982) .

All drilling is conducted with modern equipment and drill-ing methods. The major components of a typical core-drill riginclude: 1) a mounting platform; 2) a derrick; 3) a drill andpower unit; 4) hoisting element; 5) controlled-feed rotary drillhead; and 6) a water or mud pump (Figure 3-7). Units can be skid-

Typical diamond-drllllng rig tor explorationBoll & clevis

Double shea ve

WIre ~ne

Variabledisplacement

Courtesy Acker Drill Co

Figure 3-7. Schematic illustration of asimple drilling rig formerly used wide-ly in coal exploration. These units arenow being replaced by hydraulic drillingrigs. (From Chironis, 1982, Coal Age,v. 87, no. 10, copyrighted McGraw-Hill,Inc.)


mounted, tractor-mounted, or truck-mounted. Hydraulically-driv-en diamond drills are the newest major innovation in explora-tion equipment. These drills are capable of producing strong

downward thrusts and driving torques, and although more expen-

sive, allow for significantly more rapid exploration operations

(Chironis, 1982). In some countries, oilfield drilling equip-ment has been adapted for drilling deep boreholes and recover-ing acceptable coal seam core at considerable depths (Pidskal-ny, 1979).

There are various types of diamond-boring bits in use forcoal exploration in the United States. There are several differ-ent crown shapes for diamond bits, and the number and quality

of the contained bortz diamonds also varies widely. In general,

drillers select the particular type and configuration of dia-mond bit that best suits their specific drilling operation. The

diamonds are usually bonded into a tungsten carbide or othermetallic matrix or base. By impregnating and mixing the diamondfragments with the finely ground metal, they are pressed andsintered into the bit. The diamonds are set in the surface ofthe bit and cover its entire crown. A new type of impregnateddiamond bit can be used and discarded after the diamonds aredestroyed. However, the diamonds on conventional bits are usual-ly returned to the manufacturer for replacement (Chironis, 1982).A typical tricone roller rock bit (Figure 3-8) is often used incoal exploration to drill through overburden to the depth atwhich coring begins.

A truck-mounted type drilling rig is pictured in figure

3-9. Drilling rigs that are capable of producing a coal coresize of at least 2.5 inches (HQ-size core barrels; Figure 3-10)are recommended. Larger diameter core than standard HQ usuallywill enhance core recovery substantially. Core samples cut by

a diamond bit are recovered and retained in an inner core bar-

rel and are subsequently brought to the surface. In general,the use of this method requires the entire drill string of rods

be removed from the hole to retrieve the core barrel containing


Figure 3-8. Typical tricone roller rock bit commonly used incoal drilling operations.

the cored rock column. The wireline diamond-drilling method per-mits the removal of an inner tube containing the rock core froman outer core barrel that retrieves it as it is cut by the bit.The inner tube is lowered through the string of thin-walled rodsand locked into position to receive the core and eventually liftit to the surface. This method has a much higher core producti-vity than the conventional method where about 70 percent of rigtime is used in tripping (that is, pulling and lowering rods).With the wireline diamond-drilling method, the rods have to beremoved only when changing a bit or upon hole completion (Chi-ronis, 1982).

Generally, core holes should constitute at least 20 percentof the total drill holes on a mine prospect. With prudent pre-mine planning and the use of calibrated geophysical logs to sup-plement the core hole information, a mine plan can be developed

that will minimize coal recovery and quality fluctuations (Ab-shier and others, 1979). Oftentimes, at least one borehole (a


Figure 3-9. A drilling rig complete with its accessorytools and equipment set up and ready to begin drillingoperations. Photo courtesy A. Banet.


Figure 3-10. Core barrels holding continuous sections of rockcore penetrated in a drill hole. Coring is the accepted meth-od for obtaining fresh and representative samples of coal foranalysis of inherent properties.

pilot hole) can be drilled to greater depths early in the explo-ration program and used as a guide to the depths and locationsof other holes. Square grid and square-offset grid patterns areused in many coal exploration drilling programs (Figure 3-11).In order to maximize the area tested by drilling, a parallelo-gram-grid pattern, is used with lines of holes intersecting at

60. Older exploratory holes can be twinned with a new core holeto compare and correlate logs and analytical results. Holes arelocated near any potentially-exploitable coal beds observed in

outcrops to test continuity, attitude, and provide core samplesfor analyses.

Core recovery is one of the chief factors related to a suc-

cessful coal exploration project. Double and triple inner tubesand larger core diameter size are valuable in increasing corerecovery. In general, core recovery percentages expected and re-


Square qr Id Square offset

0 0

., . 0 0 0u

.r/' .1 ./ 0 0

0 0 0

0 0

Example 1\ Example B

Figure 3-11. Examples of the use of squaredrilling grids: A) square pattern with holesplaced on d centers; B) offset pattern wherecenter distance is d,.f'2. (Reprinted from Mc-Nulty and Ball, in Considine, 1977, Energytechnology handbook, fig. 3, p. 1-46, copy-righted McGraw-Hill, Inc.)

quired of contractors should be specified in drilling contracts.Geophysical logs are indispensable for determining the exactlocation of core loss and reversed coal core in the driller's

core box (Wallis, 1979).Perhaps the most important factor relating to core recovery

is the relative strength of the material (Table 3-6). Severalsteps should be followed to maximize core recovery in relative-ly soft coal-bearing formations and to minimize caving, bridg-ing, and washout problems in frozen material. The hole shouldbe penetrated and completed as rapidly as possible reducing theamount of time that the relatively warm circulating fluid is in

contact with the frozen ground. This will prevent major changesin the thermal state that is inherently responsible for the

bonding and stability in the material. Specially-developed poly-mer muds are useful in preventing the drilling fluid from chemi-

cally interacting with and saturating the coal and frozen ground.

The actual volume of circulating fluid should be kept to an ab-solute minimum during the drilling process.

Compressed air and biodegradable foam injection can be usedin rotary drilling programs. Or depending on subsurface condi-


Table 3-6. Suggested strength classification for weak, non-brittle materials for core logging in coal exploration (fromStimpson and Ross-Brown, 1976).CLASSIFICATION DESCRIPTIVE

SYMBOL NAME

VW Very weak

W Weak

F Firm

VF Very firm

H

VH

EH

Hard

Very hard

Extremelyhard

CHARACTERISTICS

Easily molded or crumbledbetween fingers.Core easily penetrated tofull thickness of knifeblade.Knife blade penetrates butnot easily to full length.

Knife blade can only bepenetrated to full lengthwith considerable diffi-culty.Knife blade will partiallypenetrate and can cutgroove on core surface.Knife blade will not pene-trate core and will onlyscratch core surface. Corecould probably be pointload tested.Competent, brittle mater-ials that can be pointload tested.

tions, water-based, polymer type, biodegradable drill fluidscan be used including Drilltrol, Quik Trol, Clear Mud, etc.Compressed air-drilling systems are generally impractical inarctic areas where permafrost conditions prevail. Water andpolymer-based mud drilling circulation medium is practical inpermafrost strata.

All core should be packed and transported in wooden coreboxes that have been carefully marked as to the hole number andfootage interval. Cores are sealed in plastic sleeves for ship-ment. Any significant minerals, fossils, or other features areflagged. The cores are photographed and described in the field


as to petrology, mineralogy, bedding, jointing, paleontology,and recovery factors.

Chip sampling and augering are usually unreliable methodsfor acquiring representative samples. However, when cuttings

,

from rotary drilling are collected, they are sampled on five-

foot intervals. A special cyclone sample-cuttings retrieval

system is used on the drill rig of figure 3-12. Sample cuttings

have commonly been used in the past for overburden characteri-

zation, assessment of roof and floor conditions, and lithologic

and geochemical analysis. Descriptions of lithology, hole con-

ditions, drilling time, and fluids and muds used are data that

must be supplied for each hole.

Figure 3-12. Truck-mounted drill rig and ancillary equipmentat remote coal exploration site showing special cyclone sam-ple retrieval system for drill cuttings.


Selective coring and rotary/auger programs augmented withground and borehole geophysical surveys will provide necessarysubsurface information regarding a coal deposit, its quality,

associated sedimentary rock types, permafrost conditions (as incertain areas of Alaska), and structural conditions for resourceevaluation and mine design consideration.

Downhole geophysical logging provides independent, conti-

nuous, objective, and precise in-situ records of rock stratapenetrated and intercepted in a borehole. In areas with coreloss, down-hole electric-logging is mandatory. Down-hole toolspermit coal evaluations to be made in open holes, cased holes,and through drill rods. Basic data on lithology identification

and characterization, correlation, individual seam identifica-

tion, true seam thickness, and approximate coal quality can be

obtained under nearly all drill-hole conditions.Several geophysical tools and instruments can be used in

combination with rotary drilling to scan and analyze the char-acter and composition of borehole walls. A sonde or cylindricaltool that has been lowered into the borehole is winched to thesurface at a fixed speed and forwards information from its mea-surements to the surface for chart recording. There are several

different types of logs that are commonly used in coal explora-tion including natural gamma, gamma-gamma, bulk density, neu-tron density, electrical resistivity, and electrical conducti-vity by an induction log or laterolog (Chironis, 1982).

Utilization of an extreme high-resolution (EHR) densityprobe now allows for better definition of coal seams and part-ings. In addition, it provides for improved delineation of im-pure benches, accuracy in thickness determinations, ash-content

determinations, and seam correlations (Fishel and Mayer, 1979).Coal companies today are demanding more information from

their exploration expenditures. As a result, geophysical methods

are receiving increased emphasis for supplementing and some-times replacing expensive coring programs. The calibrated geo-

physical borehole logs are used in determining coal quality,


rock strength of roof and floor materials, and overburden exca-

vation characteristics (Abshier and others, 1979).Geophysical logging programs should be integrated with

drilling to provide a log of the hole immediately upon its com-

pletion. Permanent survey base points may be established in re-

mote areas to tie all drill holes for future reference, cross-section preparation, and mine planning. All hole locations are

plotted both on topographic maps and air photographs.Rotary and core holes are geophysically logged by a train-

ed technician and immediately evaluated by the project geologistto insure maximum quality. Site evaluation allows for relogging

at different calibrations or conditions to obtain optimal re-sults. The required suite of logs are natural gamma, gamma-

gamma density, and caliper logs (Table 3-7). Resistivity andspontaneous potential logs require uncased, fluid-filled holesand usually are not of significant additional value over therequired suite.

At the beginning of the geophysical logging program, logresponse should be tested in the local coal-bearing strata todetermine if resolution and contrast are suitable for the geo-physical log. If not, necessary adjustments can be made to maxi-mize the amount of data that can be obtained from the suite oflogs.

The main determinant in obtaining a useful geophysical logis careful tool calibration before each logging run. The geolo-

gist should ascertain that the calibration checks have beenmade by the logging technician. In addition, all electronic and

recording systems on the logging device must be checked for

proper setting and function and that logging responses are nor-

mal. All logs for a specific hole should be started at the same

depth and logging speed should be the same for all holes---typi-cally about 20 ft per minute. Greater detail can be achievedby slowing down the speed through zones of particular interest(Abshier and others, 1979).

In some cases, quantitative curves can be developed rela-


Table 3-7. Coal thickness determination methods (fromAbshier and others, 1979, Coal Age, v. 84, no. 9, copy-righted McGraw-Hill, Inc.)

METHOD

Resistance

Focussedresistivity

Naturalganunaray

Ganuna-ganunadensity(includingLSD and BRDlogs)

Neutrondensity

Sonicvelocity

RESPONSE

Highresistance

Highresistivity

Lowganunaray

Lowdensity

Lowdensity(highapparentporosity)

Very lowvelocity

BED BOUNDARYINDICATOR

Midpoint ofcurve deflec-tion

Midpoint ofcurve de-flection




Midpoint ofcurve de-flection.

INVALID WHEN:

Highly resistant bedis adjacent to coalbed.

Highly resistant bedis adjacent to coalbed. Bed is thinnerthan electrode spacing.

Very clean sand isadjacent to coalbed. Coal bed isuranium acceptor.

Caving shale is ad-jacent to coal bed.Hole size is erratic.Bed is thinner thantool spacing. Rockaround drill hole isbadly fractured.

Caving shale or wetclay is adjacent tocoal bed. Hole sizeis erratic. Bed isthinner than toolspacing. Rock arounddrill hole is badlyfractured.

Very loose sand isadjacent to coalbed. Hole size iserratic. Bed isthinner than toolspacing. Rock arounddrill hole is badlyfractured.

ting coal quality to the geophysical response (Figure 3-13).Cross-plots can also be constructed showing the relationshipand correlation of coal-core quality parameters with the cali-brated logging tool response. Examples of specific plots in-clude density versus ash or heating value and neutron densityversus heating value. The relationships are derived by regres-


90

80

70

60

~ 50II;/I

~.s::.

-i 40~

30

20

10

00 60 70 80Gemma radiation, counts/second

Figure 3-13. Typical plot of natural gamma ra-diation versus coal ash content. (From McNultyand Ball, in Considine, ed., 1977, Energy tech-nology handbook, fig. 2, p. 1-45, copyrightedMcGraw-Hill, Inc.)

sion analysis and can be represented by either simple straight

or complex curved lines.In general, it is more effective to log boreholes open.

After casing, the reception of signals is significantly de-

creased, and often it is so highly degraded that it may bedifficult to determine even the lithology. Down-hole geophy-sical surveys should be conducted immediately after borehole

completion to prevent loss of information because of hole cav-

ing.

Geophysical hole surveys are analyzed, reviewed, and in-


terpreted immediately by the project exploration geologist inconcert with the geophysical technician to ascertain the needfor modifications in the proposed drilling program. The geophy-sical log is compared and correlated with the lithologic logprepared by the project geologist. Examples of geophysical logsin combination with corresponding lithologic logs for threedifferent coal-bearing sections are presented in figures 3-14to 3-16.

It has been found that using a combination of logging meth-ods is advantageous during coal exploration. Gamma ray and den-sity logging are used to identify the type of coal. Density,gamma ray, resistivity and caliper logs are used to determineseam thickness accurately. The character and condition of roofand floor materials can be determined by sonic and density logs.The following descriptions of the various types of borehole logsused are abstracted from Chironis (1982):

1) Natural gamma ray. This method measures the naturalgamma rays emitted by isotopes of uranium, thorium,and potassium. Coals and lignite are usually low inradioactivity, whereas the adjacent rocks are usual-ly high in potassium-rich clay and sometimes uraniumminerals. Occasionally, however, uranium mineralsfrom ground water precipitate in the coal beds, mak-ing the beds less apparent on the log.

2) Bulk density (gamma-gamma density). Interaction be-tween induced gamma rays and electrons in the ma-terial surrounding the borehole is measured. Porousmaterials with light elements, such as coal and lig-nite, have a low apparent density on the gamma-gammadensity log. This log alone may be used to identifythickness and structure of coal seams, but is moredefinitive when used in combination with a caliperlog showing changes in hole size.

3) Neutron density. This method involves measurementssimilar to bulk density, except that the neutrontool emits a stream of high-energy neutrons thatinteract with hydrogen atoms. Because coal and lig-nite are hydrogen-rich and porous, and the poresusually are filled with water, which is hydrogen-rich, these beds have a porosity index on neutronlogs.

4) Sonic (acoustic) velocity. This method measures the


0

10

20

30

40

50

60

70

80

90

I()()

~ 110"ga 120

130

140

150

160

170

180

190

125 cps ----Gommo roy

-_._._-._-

,

,_ ... J

Figure 3-14. Gamma ray and density log curves fora western U.S. drill hole. (Reprinted from McNultyand Ball, in Considine, 1977, Energy technologyhandbook, fig. 1, p. 1-44, copyrighted McGraw-Hill, Inc.)

velocity of the compressional wave component ofan acoustic signal between a transmitter and areceiver. The interval transit time is usuallyhigher for coal than for surrounding rock. Themore highly compacted coals have lower transittimes. Lignite's range is 130 to 150 microsecondsper ft, while anthracite's is 120 or less. Ac-curacy is affected by variations in hole sizeand condition.

GAMMA RAY DENSITYAPI Unrts grams/cc

o


LITHOLOGIC LOG

LIMeSTONE

SHAI.E

COAL

SANDSTONE

Figure 3-15. Five geophysical logs from a coal explorationdrill hole from the Eastern Interior basin of Illinois. Thegamma ray, density, neutron, acoustic velocity (sonic), andlateral logs show their respective responses to bituminouscoal and limestone of Pennsylvanian age (from Wood andothers, 1983, after modification from Bond and others,1971).

5) Resistivity (electrical). These measurements involvedetermining the current flow between an electrodein the logging tool and another electrode in theground at the surface. Because coal is a poor con-ductor of electric current, it exhibits high resis-tivity values. Tight sandstone or limestone beds,however, may be confused for coal. Also, the iden-tity and thickness of a coal bed may not show upaccurately, depending on the electrode spacing withrespect to bed thickness. Newly developed focussedresistivity tools can measure true coal seam resis-tivity and thus provide better resolution.

6) Laterolog (electrical conductivity, induction log).This method measures the electrical conductivityof a bed, sending out the signal horizontally. High-rank coals exhibit low conductivity; poorer qualitycoals vary with ash content. Bed boundaries arelikely to be more accurate than on the resistivitylog but, as with the resistivity log, results from


SiltB Clay~

CALIP~RU1..JC'--

Ind'l~,

NATURAL SPONTANEOUSGAMMA POTENTIAL

ISandO

RESISTANCEGAMMA-GAMMA

DENSITY116 U1 186I g"VC( I I

Cool.

1,62I

Figure 3-16. Example of correlation of lithological and geo-physical data from a coal-exploration drill hole (from Irvine,1981).

this log can cause confusion when comparing coalwith tight sandstone or limestone beds.

Areal geophysical surveys are sometimes useful in identi-fying coal beds in the subsurface and tracing the beds for per-sistence and identification of faults, washouts, and rolls.

The surveys are more valuable where the coal-bearing stratahave been identified by other methods. Although many types ofsurveys are appropriate for determining the tectonic relation-ships of a coal-bearing unit, they often are not cost-effec-'tive compared to other modes of exploration. Electromagnetic,gravity, high-resolution seismic, magnetic, and gradiometricsurveys are the most commonly used methods of areal geophysi-cal surveys.


Surface geophysical and geologic information obtained dur-

ing exploration programs must be integrated, analyzed and plot-

ted on a daily basis in the field. Geophysical data are proces-sed using field computers. This daily integration and analysisof data will allow for the most cost-effective direction to

future surveys and subsequent drilling.Under ideal conditions, surface geophysics can be utilized

to ascertain the lateral continuity of and depth to subcrop

coal; delineate structural irregularities as faults, rolls, and

washouts; and to reduce the need for expensive in-fill or defi-

nition drilling. The application of geophysical methods in coalexploration is generally dependent upon the resolving power ofthese methods in terms of boundaries between lithologic units

encountered in the field. A specified method to be used at alocation has to be selected on the basis of site-specific geo-logy (for example, lithology, depths of interest, bedding, at-titude, etc.).

The following factors must be evaluated in selecting sur-

face versus down-hole geophysical methods: 1) respective costs;2) field survey problems; 3) data retrieval delays; 4) compli-cated multi-site logistics; 5) permafrost complications (ifany); and 6) confidence in method. In some cases, additionaldefinition drilling, down-hole geophysics, and interpretativegeology may be more appropriate in accurately evaluating coalresources and preparing viable mine plans.

Because of budgetary constraints associated with most coalexploration projects, geophysical methods adopted should befield-proven, state-of-the-art, and capable of generating im-

mediate on-site definition of coal-seam geology. In certainlow-budget programs, surface geophysical methods may not be

practical because: 1) the information gained might be of limit-ed value for mine-planning purposes; 2) time constraints; and3) budget constraints.

Permafrost conditions in arctic areas complicate the


selection of appropriate geophysical equipment because the in-terstitial ice and ice lenses affect the acoustic impedance ofindividual beds and the velocity contrasts of reflecting strata

interfaces.

Surface seismic geophysical techniques have been introdu-ced into the coal exploration field over the past several years

and are gaining broad acceptance as an important tool in inte-

grated coal exploration programs for both new and known coaldeposits (Peace, 1979; Figure 3-17). Seismic investigations atan exploration site may involve reflection and refraction. Stra-tigraphic and structural results from previous exploration canbe used to assess the potential of these geophysical methods to

accurately determine the thickness, extent, and geometry of a

coal-bearing unit. Seismic reflection can be employed in loca-ting and characterizing the presence and mode of faulting, and

refraction can be used for velocity determinations. In areas ofsteeply dipping strata, it is difficult to apply reflection

techniques.Shallow-reflection high-resolution seismic methods have

been applied in coal exploration and mine planning to locateand delineate coal-seam discontinuities, channel fills, andold mine workings. The chief advantage of this technique isthat it provides continuous subsurface information as opposed

to point-source information supplied by borehole geophysicallogging methods. In general, this method is more economicalthan conventional drilling methods for locating coal-seam dis-

continuities and for correlation purposes (Chironis, 1982).Seismic waves produced by a small explosion or other pro-

pagation agent travel downward through the different stratabased on their individual rock properties. When a rock ofstrongly contrasting physical properties is encountered, a

signal is reflected and refracted back to a set of geophones

or electromechanical transducers that detect a specific seis-mic pattern. A tandem seismograph senses the voltage change and

records the diagnostic pattern in reference to the initial time


FINAL SECTION ) + --BOREHOLE DATA~ .0 ~o ~ ~ ,6 ~ ~ 1'0 IlO I

INTEGRATED EXPLORATIONPROGRAM

~

u.-

.1-

.=

ACCURATE 3DGEOLOGY INTERPRETATION

~~~~

+LOCAL

KNOWLEDGE

Figure 3-17. General data flow for an integrated coal explora-tion program. An accurate three-dimensional interpretation ofa mining prospect incorporates prevailing geologic knowledge,borehole data, and seismic cross sections. (From Peace, 1979,in Argall, Coal exploration, v. 2, p. 243, copyrighted MillerFreeman, Inc.)

of exploration (Chironis, 1982).Seismic refraction geophysical methods can provide abun-

dant reconnaissance data and can be used to define relative


small-scale features in addition and at reasonable explorationcosts. The method supplies data along a generally continuous

line and to flexible mining depths. When used to support drill-

hole information, it can be cost-effective locally. Seismic re-fraction can provide: 1) structure information---locate and mapfaults and fracture zones; 2) depth to coal; 3) thickness ofcoal beds; 4) maps of coal-bed tops; 5) location and delinea-tion of channel sands, burn areas, and beds or lenses of hardsiderite; 6) ground water potential data; and 7) premine-plan-ning information relating to rock mechanical properties, poten-tial slope failure, and rippability.

During seismic refraction surveying, a sound wave is crea-

ted near the surface above the exploration target site. Thesound wave travels downward through the various rock layerswith a velocity that is dependent upon the elastic properties

of the rock layers intersected. Rock layers of differing elas-tic properties provide an acoustical interface along which partof the wave energy is refracted. At this site, upward-traveling

wavelets are generated that are detected at the surface by sen-sors.

Seismic refraction geophysical surveys provide a means formapping subsurface rock interfaces in terms of velocity units.These units are three-dimensional and because of their elasticproperties, they propagate seismic waves at a characteristicvelocity or velocity range. The seismic velocity is relateddirectly to the relative consolidation or competence of the

rocks. More competent rocks produce higher seismic velocities.Seismic refraction data is processed in the field by re-

cording the times of arrival of the refracted seismic energywaves to surface sensors. The data is plotted typically on a

time-distance graph. Velocities for given rock layers are cal-

culated and a depth section is computed. Seismic refractiondata can serve as an initial guide in directing future drillingoperations. In general though, some drilling is necessary for

velocity and lithologic control in an area prior to using seis-


mic refraction methods. Seismic profiling can sometimes elimi-

nate the need for elaborate coring and other geophysical pro-grams.

Magnetic and gravity geophysical methods generally rely ondifferences in the magnetic susceptibility and density of under-lying lithologies. Hence, they are normally utilized to delin-eate horizontal (With vertical) variations within the underly-ing material, that is, profiling techniques for horizontal chan-ges in defining physical properties.

Magnetometer surveys at a coal exploration site may be use-ful in locating suspected faulting and defining igneous intru-

sions in a coal-bearing unit and to assess its geometry. Magne-tometer survey lines can be paired with EM survey lines when

initial data reveals a correlation. Although magnetometers are

effective in helping to map structure, they cannot directly lo-cate coal seams. Ground magnetometer geophysical explorationsurveys are generally fast and relatively inexpensive.

In areas with flat-lying coal-bearing strata and some con-ductive zones, electromagnetic (EM) methods can show variationsin depth and thickness or the absence of the coal seam. An EMunit uses a combination of coil spacings and measurement fre-

quencies at given survey stations to determine the depth ofcoal. Generally speaking, a few orientation surveys can be usedto choose ideal coil separation and frequencies to maximize pro-duction rates and interpretation capabilities. EM investigationsat a site can involve both traverses and soundings. Boring dataat a site provides control and can be used to accurately eval-uate the general performance of this technique. Some systems

are capable of yielding data at significantly deeper penetration

depths, so the different systems available should be investiga-

ted. Traverses can be made along a grid pattern.Coal can sometimes be mapped based directly on the resis-

tivity contrast between the coal and the enclosing strata. Theresistivity of the coal is usually considerably higher thanother rock units in the geologic section. Both direct current


resistivity and electromagnetic methods respond to the same gene-

ral physical contrasts, and thus make complimentary geophysical

tools.

DC resistivity measurements can be taken along a surveyline to provide information on changes in trend or for depth

soundings. A greater number of parameters can be changed with

the DC method to 'fine tune' the system for depths and resis-tivity contrasts for the detection of the coal seam. Resisti-

vity surveys are slower than electromagnetic surveys and re-

quire electrical contact with the earth.

Vertical electrical sounding (VES) methods can be used toestablish true-layer resistivities and depth. VES may be used

to make local models of coal occurrence and in concert with the

EM method to adjust horizontal profiles in a vertical manner.However, down-hole geophysics may obtain this information more

rapidly and less expensively.

Subsurface radar geophysical methods are particularly use-

ful and effective on some exploration projects. This techniqueoffers high mobility, rate of production and potential aerial

survey extent. Subsurface radar can be considered an electro-

magnetic method based on the transmission and reception of an

electromagnetic wave at a known frequency. Variations in the

resistivity of underlying materials create modification of the

return time of the electromagnetic wave. In this sense, it is

analogous to seismic reflection methods except that it is based

upon the electrical property of the underlying material. The

depth of penetration for subsurface radar is directly affected

by the electrical resistivity of overlying layers. In general,

as the electrical resistivity decreases, the effective depth of

penetration of subsurface radar also decreases.

The

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Coal Exploration, Mine Planning & Development