Out of the Earth: The Mineral Industry in Canada 9781487586201

Citation preview

OUT OF THE EARTH

OUT of the Canadian earth come treasures rich and rare— gold, silver, uranium. Out of the earth come the raw materials of industry—iron, copper, nickel, and the like. From deep in the earth flows the petroleum that keeps the wheels moving in our modern economy. Coal for our fires lies under the soil of Canadian prairies, mountains, and coastal seas. From the earth come the building materials for towns and cities, roads, and bridges. From the earth come the glass and dishes for our homes, the salt for our tables, and the nylons we wear. Every Canadian uses the products of our mines. Many persons are employed in the mining industry, or in the multitude of industries dependent on its products. Many Canadians are investors in the industry, buying shares in mining companies, or processing industries, or the enterprises that sell mineral products to the public. This book is the direct result of the desire expressed by Canadians in many walks of life to know “more about mining.” It takes the interested layman on a short trip through the complex mining industry. It describes, very clearly and readably, how the minerals were formed in the earth, how they are found, how they are taken out of the earth, and how the ores are processed and the petroleum transformed to high grade gasoline. It goes farther, telling how a mine is financed, how the prospector, the engineer, the government, the mine operator, financier, and investor combine to make the great Canadian mineral industry what it is. It tells, too, about the “jobs” in the industry—about the opportunities for geologists, geophysicists, engineers, production and physical metallurgists, and many other professions that young Canadians find both challenging and rewarding.

This book gives the clue to the “language” of the mining industry—“conglomerate,” “stope,” “spudding in,” “repressuring,” “working option,” “reorganization,” “speculative risk”—to name only a few terms that are read on the financial page every day, and which the intelligent investor wants to understand clearly. Out of the Earth tells about mining as it is today. We meet not just the prospector carrying his pick, but the airborne magnetometer, which detects mineral deposits from the sky. Most readers have heard of the use of Geiger counters in locating radioactive substances, but here we read also, for example, about the seismic methods of mineral exploration, by which dynamite is fired in the earth and the shock-wave patterns calculated on instruments. Helping to make important points of the story clear are simple tables and 40 excellent line-drawings and charts. A group of photographs, chosen for informational value as well as pictorial interest, is included. Out of the Earth arose from a series of talks by leaders of the Canadian mineral industry under the auspices of the Department of University Extension at the University of Toronto. They have been put into book form by G. B. Langford, Professor of Mining Geology and Head of the Department of Geological Sciences, University of Toronto.

OUT of the EARTH THE MINERAL INDUSTRY IN CANADA

G. B. Langford

Toronto, 1954

UNIVERSITY OF TORONTO PRESS

Copyright, Canada, 1954 and Printed in Canada by University of Toronto Press London: Geoffrey Cumberlege Oxford University Press Reprinted 2017 ISBN

978-1-4875-8716 - 1 (paper)

T GIVES ME great pleasure to write a few introductory I words concerning the publication of this volume based on the series of popular lectures on the Canadian Mineral Industry delivered under the auspices of the Department of University Extension, University of Toronto. The University, and in particular the Department of Uni­ versity Extension, are much to be congratulated on their initiative, both for instituting this series of lectures-the first of their kind to be delivered anywhere in Canada-and in proceeding to their publication in book form. I have often wished for a volume such as this which I could recommend to interested inquirers. Its pages constitute a rich vein of authoritative information on various aspects of Canada's Mineral Industry. I recommend this book warmly to Canadians in every walk of life who are interested in the progress of the industry. Its appeal will not be confined to those who have direct con­ nection with actual exploration, development, production, or scientific and technical research. It will intrigue all those who have observed the rapid, adventurous expansion that the industry has made in recent years and who desire to gain a greater knowledge of its possibilities and of the beneficial influence it exerts on the economic well-being of our country.

Minister of Mines and Technical Surveys Ottawa, Canada

This page intentionally left blank

Foreword THE Evening Course on the Canadian Mineral Industry was one of the most timely courses given during the session 1950-51 and evoked widespread interest. The success of the course was due to the wholehearted co-operation which this Department received from Dr. George Langford, Professor R. E. Barrett, Dr. L. M. Pidgeon, and other members of the staff of the University; and from Federal and Provincial departments-in particular from Mr. H. C. Rickaby, Deputy Minister of Mines, Province of Ontario. Special mention should be made of the services and continued interest of Mr. V. C. Wansbrough, Vice-President and Managing Director of the Canadian Metal Mining Association. I wish to acknowledge with sincere thanks the contribution made by all the lecturers who so generously shared their knowl­ edge and experience to make the course a success, and who co­ operated in making their manuscripts available to Dr. Langford. We are also indebted to the Presidents of the companies, who, at their own expense, made it possible for many of the lecturers to travel to Toronto so that they might give the lectures in person. When, at the conclusion of the course, it was decided to publish a summary of the lectures in book form, five companies very generously came forward and contributed to the expense of carrying out this project. To them I acknowledge our indebted­ ness and express our thanks. It was most fortunate that Dr. Langford, the Course Director, was able to undertake the task of preparing this book. We are indeed grateful to him for his sympathetic co-operation and for his valuable counsel. The Honourable Dr. W. J. Dunlop, Minister of Education, Province of Ontario, was Director of University Extension during the time the course was given. His interest and encouragement in the development of this course were a stimulus at all times. vii

viii

FOREWORD

It would be most appropriate for me to record our appreciation of the assistance given so freely and in so many ways by the staff of the University of Toronto Press.

J. R. GILLEY Director, University Extension University of Toronto

Preface ON many occasions I have been asked if there were a book by which one could take a short trip through the complex Mineral Industry and return with some elementary facts and a generalized image of what goes on. The answer has always been that there was no such book. Consequently, when I was asked to prepare this volume, it seemed to be an opportunity to fill this need, and the book was written with such an objective in mind. This book is neither a complete story of the Mineral Industry in Canada-that story would fill a shelf of books-nor is it a text­ book. It is a generalized survey of the various fields of activity which constitute the industry. All that it describes is a part of the Canadian scene, and for that purpose Canadian examples are used. The lecture series, which formed the background of this volume, has been mentioned by Mr. Gilley in his Foreword. The lecturers' manuscripts have been the primary source of material for this book. It was not practical to give individual credits in the text, for the material was reorganized and condensed, as is apparent on comparing the lecture and chapter titles. I wish to gratefully acknowledge my indebtedness to the lecturers for loaning me their manuscripts and giving me carte blanche in using them. Others, whose help and advice were indispensable, but none the less gratefully received, were Miss F. G. Halpenny, Senior Assist­ ant Editor, University of Toronto Press; Miss D. Birkett who typed and corrected the MSS; and Mr. J. Ledingham who made the drawings. G.B.L.

University of Toronto

ix

This page intentionally left blank

Contents INTRODUCTION, FOREWORD,

by

by J.

THE HONOURABLE GEORGE PRunHAM

vii

R. GILLEY

ix

PREFACE

1 The Romance of the Canadian Mineral Industry,

by

v

CHARLES CAMSELL

3

2 The Geology of Mineral Deposits

10

3 Modem Methods of Prospecting

34

4 Mining and Processing of Ores

44

5 The Story of Metals

55

6 Mineral Fuels

73

7 Industrial Minerals and Rocks

88

8 Financing a Company

97

9 Government Services and the Mineral Industry 10 Canada and Her Mineral Industry,

by V. C. WANSBROUGH APPENDIX.

Mineral Production 1898-1952

104

109 115

ACKNOWLEDGMENTS

124

THE DONORS

126

xi

This page intentionally left blank

List of Illustrations PHOTOGRAPHS

u

LINE DRAWINGS

xiii

ILLUSTRATIONS

6.

19

10. 11. 12. 13.

30 31 36

14. 15.

19.

r

ym

OUT OF THE EARTH

This page intentionally left blank

1 The Romance of the Canadian Mineral Industry By CHARLES CAMSELL

FURs first led the white man into the remote and unoccupied parts of Canada. Until nearly one hundred years ago the fur trade was the pioneer industry in this country. However, it did not bring much in the way of settlement and development in its train. Indeed, it was the policy of the fur traders to discourage settle, ment and to frown upon the development of minerals or other natural resources because of the possible adverse effect upon the fur supply. The coming of the prospector, looking mainly for gold in the easily worked placer deposits, was in large measure re­ sponsible for a modification of this policy. Gold was the lure in the early days of mining and it has continued to attract men up to the present. Mining has been more instrumental than any other industry in opening up the Canadian ·hinterland, and it will continue to be so as long as we have any pioneer country left to us for exploitation. Knowledge of the mineral wealth of Canada has existed from early times. Jacques Cartier is credited with doing the first busi­ ness in metals. During his expedition of 1541 and 1542, which took him up the St. Lawrence River as far as Three Rivers, he is reported to have obtained several "casks" of gold and silver and some "quintals" of pearls and rubies. But he did no prospecting for new mineral deposits. Martin Frobisher may be said to have been our first prospector. When he returned from his expedition to Baffin Island in 1576 he was able to persuade Queen Elizabeth and others of her court to "grubstake" him for two later expeditions to the same locality, where he claimed that he had found gold. He is reported to have brought back some two hundred tons of this so-called gold ore

s

4

OUT OF THE EARTH

and was enthusiastically received by ·the Queen at Windsor. Even when the ore proved to be only iron pyrites, he did not lose the favour of the queen, who later rewarded him with a knighthood. This was probably the first occasion in Canadian mining history when "fool's gold," or iron pyrites, was the cause of excitement. It was, however, not the last. The next discovery of minerals in Canada of which we have record occurred at the beginning of the seventeenth century when iron and silver were reported to have been found at St. Mary's Bay, Nova Scotia, by an engineer attached to Champlain's expedition of 1604. Coal was first discovered on Cape Breton Island in 1672, although mining did not commence until nearly fifty years later. In 1737 the making of iron from limonite, gathered from the bogs near Three Rivers, began. This industry was to remain in almost continuous operation for the next 145 years, and cannon balls cast in the forges of the -St. Maurice district doubtless played their part in the defence of Quebec in 1759. Mining development in Canada progressed slowly in its early years, perhaps because of the greater attraction of the fur trade which afforded better opportunities to make large profits quickly and with the minimum of effort. It is interesting in this connec­ tion, for those who live in Ontario, to note that in 1686 De Troyes, while on a fur-trading expedition to the north, is said to have been shown an occurrence of silver-bearing galena on the east shore of Lake Temiskaming. What an opportunity he missed! Across the lake, only a few miles to the west, lay what were heralded more than two centuries later as the world's richest silver deposits. In February, 1836, William Lyon Mackenzie moved a resolu­ tion in the Legislative Assembly of Upper Canada providing for the appointment of a committee to report upon the need for a survey of the mineral resources of the province. The committee was named and a report made, but because of the political diffi­ culties that arose in 1837, no action was taken until the Union Parliament met in Kingston in 1841. At that session an appropri­ ation of £1,500 was made for a geological survey and in 1842 W. E. Logan, a Canadian, was appointed Director of the Geologi­ cal Survey of Canada, one of the first of such surveys to be organized in the world. It has grown to be a leading scientific institution, which has explored the little known parts of Canada, has developed the present knowledge of our mineral resources,

THE ROMANCE OF THE

INDUSTRY

5

and has been of inestimable assistance to our growing mineral industry. Of all the events which occurred in North America during the last century probably the most important was the discovery of placer gold in California in 1848. It is said that this has had a much greater influence on the lives of the people of both the United States and Canada than any event of a political nature in either of those countries. The immediate effect of the discovery of gold at Sutter Creek was that within two years 100,000 men moved to California. More far reaching was its effect in inspiring a world-wide desire for enterprise and exploration, and a migra­ tion of people away from the older centres of population. Simi­ larly, the discovery of gold in New South Wales in 1851 brought about a mass migration to Australia with consequent explora­ tion and opening-up of that country. Following the great stampede to California which commenced in 1849, prospectors and miners gradually drifted northward through what are now the states of Oregon, Washington, and Idaho into western Canada. In 1858 the placer gold which caused the first great rush to British Columbia was discovered on the Fraser River. The coming of the prospector to British Columbia was not welcomed by the Indians and for years they offered a resistance to the newcomers which was not overcome until the next decade when a small body of British troops arrived. As the resistance of the Indians declined, prospectors moved northward up the Fraser and Thompson Rivers working the gravel bars as they went until they penetrated far into the in­ terior. Soon these prospectors reached the Cariboo country, to find in its streams some of the richest placer gold deposits in the world. A wild stampede followed, which brought into British Columbia many thousands of people from all parts of the world. Lightning, Williams, and Antler Creeks are still magic names among the Cariboo old timers. To them, history only begins with the discovery of gold in that country, and indeed nothing of im­ portance has happened since. The Cariboo rush was responsible for the first highway in western Canada. The Cariboo road was built by a detachment of British sappers and miners, from Port Moody through the canyons of the Fraser and Thompson Rivers and on to Barkerville, the centre of the mining fields. Remnants of this old road may still be seen clinging to the cliffs of the Fraser canyon.

6

OUT OF THE EARTH

In the train of all the various discoveries of gold a variety of other activities began and the foundations of agriculture, fruit growing, and ranching in British Columbia were laid. Soon there came a new outlook on the part of the people of British Columbia and with it a consciousness of the meaning and consequences of mineral development. The search for minerals other than gold was stimulated and great lead, zinc, and copper deposits were discovered. For years British Columbia called herself the mining province, and she had a right to the name. Agricultural development which followed the exploitation of the mineral deposits created the need for railway facilities to support and supplement it. This led to the building, completed in 1885, of the Canadian Pacific Railway as one of the conditions of entry of British Columbia into the Canadian Confederation. Thus as a direct result of the Californian gold rush and the awakened interest in mining, by the end of the century gold, silver, lead, and zinc were being mined in British Columbia, and copper and nickel in Ontario. The farmer and the lumberman followed the prospector and the miner, and then the railroader, to lay the foundation for the modem development of the country. As if to start the cycle of events over again, in 1896 another spectacular gold strike was made in the Yukon territory, and then began perhaps the most famous rush of all-to the Klondyke. The excitement of this rush is still fresh in the minds of some people. Farmers, artisans, professional men, and people of many other classes turned their eyes northward, sold their all, and joined the trek to the new gold fields. Thousands took to the trail, the great majority without any experience in mining or any knowledge of northern travel. By 1905 gold to the value of $100,000,000 is said to have been taken from the beds of Bonanza, Eldorado, Hunker, Dominion, and Sulphur Creeks. Dawson became a city of nearly 40,000 people. The Klondyke rush has been described as one of the most romantic episodes in mining history. The region, hundreds of miles away in the northern wilderness, was reached by various routes, all of ,them difficult. Most of the Klondykers entered the country through the White and Chilcoot Passes from the Pacific coast, others travelled up the Yukon River from St. Michaels or through the Cassiar country or along the Mackenzie River route, and some made their way overland from Edmonton. All under-

THE ROMANCE OF THE

INDUSTRY

7

went great hardships. Many lost their lives through starvation, drowning, or disease. Yet, such is the appeal of a gold discovery that if a new strike were made today in any of the remote parts of Canada, thousands would Hock to the locality-this time all of them by air. With the coming of the present century the spotlight shifted from west to east. A great expansion in mining was inaugurated by the discovery of silver at Cobalt in 1903. Fortunes both per­ sonal and industrial were made from the silver mined at this world-famous camp, but, more important, a mining spirit was created which led in turn to the discovery and opening-up of the Ontario gold camps-Porcupine and Kirkland Lake. Cobalt men were also the pioneers in the discovery of the Noranda and Quebec gold fields. Here again the historical cycle was repeated. Agriculture followed close at the heels of mining, and the Temis­ kaming and Northern Ontario Railway, now the Ontario North­ land Railway, was extended to serve the communities which came into being. Just as the fortunes made at Cobalt formed a basis for the development of the Ontario and Quebec gold mines, they in turn have trained prospectors and paid for exploration in the more remote parts of the country. Northern Manitoba, the Northwest Territories, and very recently Labrador-Ungava, have become as a result the new mining areas, where deposits of gold and uranium, silver and lead, titanium and iron ore are the prizes being won. Gold has always been a lure which took men into the remote comers of the earth. The value of the gold produced in Canada has always been greater than that of any other mineral product. However, the influence of gold has been vastly greater in the Canadian economy than mere production statistics would indi­ cate. More than any other resource it has provided the stimulus for the opening-up of our northern regions. One has only to make a casual trip through the gold belt extending from Timmins in Ontario to Val d'Or in Quebec to realize how gold deposits have helped to develop this country and to make it possible for the permanent industry of agriculture to live and thrive. The coloniza­ tion of the clay belts of northwestem Quebec and Northern Ontario was made possible only because of markets for agricul­ tural produce in the mining towns and the labour opportunities of the mines. Settlers cleared and cultivated the land during the

OUT OF THE EARTH 8 summer months and sold their produce to the mines. In the winter time, when snow covered the ground, they obtained profitable employment underground in these same mines. History is being repeated today in the Northwest Territories with the development of gold mines in the Yellowknife district north of Great Slave Lake. As a consequence of the mining activity what arable land there is in the neighbourhood is being brought under cultivation. A modern townsite has been laid out and pro­ vided with schools, churches, hospitals, and modern water and sewage systems. Hydro-electric plants have been installed. Trans­ portation facilities by water, highway, and air are being improved. Indeed, all the comforts and conveniences of modem civilization are being provided at a point some 500 miles north of the nearest railway terminus, where a few years ago the only inhabitants were a sprinkling of Indians and where the most primitive con­ ditions prevailed. Yellowknife mining camp, a community of some 4,000 people, which produces annually about $7,000,000 in gold from three mines, is an outpost of civilization which is spreading its influence in ever widening circles throughout that northern country. From it planes carrying prospectors go out to the north and east to points where new discoveries of minerals are being made, some of which will probably develop into new mining camps. Yellow­ knife is thus one of rthe latest illustrations in Canada of the pioneering character of the mining industry. The discovery and development of the iron ore deposits of Labrador are so important that they have attracted the attention of the world. As transportation facilities are established, power sites developed, and the mines brought into production, an indus­ try of vast importance to North America, as well as to western Europe, will have been created. The story of that creation is a romance in itself. The Canadian Mineral Industry has come to occupy a very important place in the economy of the country, and has ,indeed brought Canada to a forward position among nations out of all proportion to her population. This has all been accomplished in the last 100 years. During ·that time the production of metals and minerals has grown in annual value from a few thousands of dollars to over one billion dollars. The industry started with an annual production of perhaps only a few pounds of copper before the coming of the white man; today it is based upon the pro-

THE ROMANCE OF THE

INDUSTRY

9

duction of over sixty minerals, metals, and mineral substances. Few other countries produce a wider range of minerals or have a mining industry so broadly based as ours. We can look to the past with pride in our accomplishments but we can also look to the future with confidence that the Canadian Mineral Industry will occupy a higher and higher place -in our economy, providing fully for our own needs as well as for the needs of many other nations. SELECTED REFERENCES

Chronological Record of Canadian Mining Events from 1604 to 1947, and Historical Tables of the Mineral Protfuction of Canada. Ottawa: Do­

minion Bureau of Statistics, 1948. GmsoN, THOMAS W. Mining in Ontario. Toronto: Ontario Department of Mines, 1937. RICKARD, T. A. The Romance of Mining. Toronto: The Macmillan Com­ pany of Canada, Limited, 1942.

2 The Geology of Mineral Deposits is the science of the earth, and geologists are a group of scientists continually probing the sec.rets of the earth to find out the how, why, and wherefore of the natural phenomena that surround us. Some of their investigations are primarily of scientific interest, but others have a very direct bearing on every-day affairs. The present chapter deals with one of these types of investigation, a most important one. However, before we can get on with our discussion, it will be necessary to become acquainted with some of the terms used by the geologist. Everyone is familiar with the word "mineral," but very few know what a mineral is. The simple classification of everything into three groups-animal, vegetable, or mineral-is well known and is a good approach to thinking about minerals. The geologist defines minerals as naturally occurring, inorganic chemical com­ pounds, which usually have a crystalline structure. The term "naturally" is used to distinguish true minerals from artificial ones; being "inorganic" they are set apart from the animal and vege­ table groups; being "chemical compounds" they are made up of elements and have a definite chemical formula. "Mineral deposit," or ore deposit, to use the popular term, means a deposit of minerals which are mined or quarried and which are put to some use, as, for example, is clay for brick making or ore for smelting into iron. Another common term, which is also little understood, is "rock." It is defined as a relatively large mass of material composed of one or more minerals. The relationship between rocks and minerals is close and the difference between them is small. A useful analogy to remember in this regard is that rocks are made of minerals as sentences ·are made of words. The crust, or outer layer, of the earth is composed of an as­ semblage of rocks, covered with a relatively thin layer of soil, sand and gravel, etc. All of this crust, including the covering GEOLOGY

10

THE GEOLOGY OF MINERAL DEPOSITS

11

material, is composed of minerals, and since they in turn are composed of chemical elements, it is of some interest to know what is the chemical composition of the earth's outer ten miles. If the crust could all be put into a beaker and analysed it would have approximately the composition outlined in Table I. TABLE I AVERAGE CoMPOSlTION OF THE EARTH'S CRUST

As we have said, most of these elements occur as compounds which we call minerals. Thus silicon and oxygen combine to form a very common substance which the chemist designates as Si02 but the geologist knows as the mineral quartz. Similarly, aluminum is frequently found as Ah0a-2H20, which is the mineral bauxite, the chief ore of aluminum, while such elements as lead and sulphur combine to form the mineral galena, PbS, the chief source of lead. A very few of the elements-platinum, silver, gold, and copper-occur by themselves as a pure metal. It is customary to think of minerals as divided into four large groups: those which form the ordin ary rocks and for that reason are called the rock-forming minerals; those from which we get our supplies of metals-the ore-forming minerals; those from which we obtain a great series of useful products ( from abrasives and asbestos, down through the alphabet past salt, sand, and sulphur, to vermiculite and zircon) and which, because of their

12

OUT OF THE EARTH

widespread use in industry, are known as industrial minerals; and lastly a most important group which, strictly speaking, are not minerals, because they are of organic origin, but which are so closely allied to them that we may include them here without any major violation of scientific ethics: the mineral fuels-coal, petro­ leum, and natural gas. The relatively small number of rock-forming minerals listed in Table II may give a surprisingly large number of rock types. This TABLE II CoMMON ROCK-FORMING MINERALS

is because the type of rock which is formed depends not only on its mineral composition, but also, and indeed primarily, on its method of origin. Some rocks are formed by the cementing together of the grains of sand or clay which occur along the shores of lakes or oceans. If the sand grains are quart�, the rock is called sandstone; if they are calcite the rock is limestone; if they are clay the rock is shale. Collectively the sandstone, limestone, and shale belong to the "sedimentary" class of rocks, because they are formed from the sediment deposited by water action. Other rocks result from the cooling of molten material, which on solidi­ fying formed interlocking masses of mineral crystals. Such rocks are classified as "igneous" rocks because they are heat formed, but each is given an individual name depending on the nature

THE GEOLOGY OF

MINERAL DEPOSITS

13

of its mineral composition. A common igneous rock is granite, which is made up of feldspar and quartz; another one is basalt, which is a form of lava containing feldspar and pyroxene. IGNEOUS ROCKS AND MINERAL DEPOSITS

As one goes down into a deep mine one is conscious of the in­ creasing temperature of the rocks. Measurements taken at many points show that the average rate of increase of temperature is 1 °F for each 60 feet of depth. On this basis it is a simple matter to calculate the depth at which the temperatures will be high enough to melt rocks. However, there is another important factor to be considered. As mines go deeper and deeper into the earth they experience increasing rock pressure. It is so great in some mines that very elabor:ate precautions are necessary to keep the workings from being crushed. At the depth at which melting temperatures prevail, it is believed that pressures are so great that the expansion, which must accompany melting, is impossible. The rocks are therefore in a superheated but solid state, awaiting only some relief of pressure to become fluid. Relief is supplied when the earth's crust is folded up into a mountain range. When this folding occurs a great volume of superheated rock becomes fluid and commences to rise under the mountain. Such a mass, called a magma, is under great pressure and will force itself into every available crack or fissure, even at times breaking through to the surface as a volcano. In addition, it melts some of the rock with which it comes in contact. A magma may be thought of as con­ sisting of a large main mass and an aureole made up of an in­ finite number of tongues or offshoots of all sizes and shapes, penetrating the covering rock ( Figure 1). All of these tongues eventually cool and form a whole series of igneous intrusive rocks-"intrusive" because they intrude into other rocks. The cooling and crystallizing process is not a simple one. The various compounds in the magma, which crystallize as minerals, do not all solidify at the same temperature. This is true of all types of solutions. A solution of common salt in water is a good example to illustrate the process. As such ,a solution is cooled it reaches a temperature where crystals begin to form. These are crystals of ice-that is, pure water-and not a mixture of salt and water. The extraction of some water as ice increases the con­ centration of salt in the remaining solution. Just such changes take place in a cooling magma. The first minerals to form will

14

OUT OF THE EARTH

have a different composition from that of the whole molten mass; their removal from solution will change the composition of the molten remainder. As this process continues we can visualize a series of minerals ( i.e., rocks) forming, and also a residual magma which becomes more and more concentrated in certain elements as the process continues. This process is called "magmatic differentiation."

FIGURE 1. Diagrammatic section through a newly formed mountain range. The sedimentary rocks have been folded and intruded by a magma which has sent up tongues into the overlying rock where they form a series of dikes.

The final residue will differ from its parent not only in com­ position, but in its physical nature. The original magma was a melt of rock-forming minerals with minor amounts of other ele­ ments, but the residual part is a hot solution in which water or steam is a major constituent, and which is capable of remaining liquid at temperatures much below the melting point of rocks. The hot aqueous solution carries the elements to form ore minerals as well as large quantities of carbon dioxide, hydrochloric and sulphuric acids. This residual solution is eventually forced up into the overlying rocks in which it seeks out every crack or opening, penetrating even farther afield than the tongues of intrusive rock. It is more mobile than its parent, and is corrosive

15 enough to enlarge cracks, thereby making its own escape routes. When the residual solution finally comes to rest and solidifies it forms mineral deposits. The type of deposit-copper, lead, zinc, gold, etc.-depends, of course, upon the composition of the original magma, and the working of the differentiation process. Sometimes the results of the entire process can be seen in a single mineral deposit. In the Falcon Lake stock in Manitoba (Figure 2) four different rocks formed in a series of roughly concentrie rings with the ore body as the small central core. A slightly different sequence is seen in the Copper Mountain area THE GEOLOGY OF MINERAL DEPOSITS

FlcURE 2. Map of the Falcon Lake intrusive, Manitoba. The magma differ­ entiated to form four different rock types, and the gold-bearing solutions were trapped as a final residue ( the small black circle} in the last-formed rock.

in British Columbia (Figure 3). Here the magma formed three different rock types, again in concentric arrangement; the ore solutions concentrated at a greater depth and were finally squeezed up into fractures in the rocks to form the mineral deposits. A more common type of occurrence is that in which portions of the differentiating magma were squeezed out from time to time into the wall rocks where they formed a series of sheet-like or lens-like intrusive rock masses. Each mass so formed was a different rock from its predecessor because the magma from which it originated was constantly changing. The Kirkland Lake gold camp illustrates this type of occurrence. It has a sequence of three quite different intrusive igneous rocks which followed each other (Figure 4). After all three had been intruded and had solidified they were themselves ruptured and into the newly

16

OUT OF THE EARTH

formed fissures were injected the gold-bearing solutions ( the last phase of the magma) to form a great system of gold-bearing veins. The association of igneous rocks and the mineral deposits that are concentrated by magmatic processes is universal. Some geologists predict that such deposits will not be found further than one mile from an igneous rock.

FxcURE 3. Map of part of the igneous rock at Copper Mountain, British Columbia. As the magma differentiated the first rock to form was syenogabbro, followed by syenodiorite and pegmatite. The ore-forming solutions were concentrated at depth and were later squeezed up into cracks either in the syenogabbro or the adjacent wall rock. STRUCTURAL FEATURES OF MINERAL DEPOSITS

The most important thing in the forming of a mineral deposit is an ample supply of ore-bearing solutions. But next in importance is a suitable place wherein the solutions can drop their mineral wealth. There must be some type of opening into which they will be forced and in which the minerals will be deposited. The size,

THE GEOLOGY OF MINERAL DEPOSITS

IT

shape, and distribution of these openings are the important structural features of mineral deposits. There are many types of rocks, and each type will have its own physical features such as porosity, strength, brittleness or ductility. Some types of rock, such as sandstone and certain lavas, may have from 10 to 20 per cent of pore space while others, such as granite, will have less than 1 per cent porosity.

F'Icmu: 4. Diagrammatic section through the Kirkland Lake area, Ontario. The conglomerate and tufE are part of the original folded mountain that was intruded by a magma. As the magma differentiated it gave off a series of intrusives as follows: (1) basic syenite, ( 2) red syenite, and ( 3) syenite porphyry. All these rocks were subsequently fractured and the ore-forming solutions came into the fractures to form a branching series of gold-bearing veins.

A rock like granite may have a crushing strength as great as 25 tons per square inch while sbales may sometimes be broken up by hand. There are rocks, such as quartzite, which are very brittle and tend to shatter when bent or folded, while some shales and limestones will undergo a remarkable amount of folding and deformation without breaking. These observations will show why we may find almost any kind of crack, break, rupture, pore space, or other type of opening in rocks.

18

OUT OF THE EARTH

Porosity in rocks is usually a result of the type of rock and the conditions under which it was formed, and we find that a rock with an unusually high porosity will be that way throughout its entire mass. Consequently if mineralizing solutions permeate such a rock we may expect to find the entire rock, or a large proportion of it, converted into an ore body. Indeed such is

Flcmu: 5. Section through the Sullivan Mine, British Columbia. The country rocks are a bed of conglomerate overlain by a bed of quartzite-both sedimentary types. Ore-forming solutions permeated a porous zone at the base of the quartzite which they replaced to form a very large deposit of lead-zinc ore. After an illustration in Structural Geology af Canadian Ore Deposits, Canadian Institute of Mining and Metallurgy.

often the case, many of the world's largest mineral deposits being formed in this manner. An outstanding example is the Sullivan Mine in southern British Columbia (Figure 5) in which a bed of quartzite was invaded by mineralizing solutions. Not only were the pores filled, but the rock itself was taken into solution and new minerals deposited in its place, until the bed had been re­ placed over a large area by ore minerals. This process is analogous to that by which petrified wood is formed. Structural conditions such as porosity, which developed when the rock was formed, are often spoken of as "primary," in con­ trast to the "second ary" structures which were developed in the rocks, as a result of some type of folding or other movement in the earth's crust. The building of mountains and intrusion of magmas always produce second ary structures. As rocks are

THE GEOLOGY OF MINERAL DEPOSITS

19

squeezed and folded the brittle or weak ones will break. The break may be a single fracture; it may be a series of parallel or branch­ ing fractures, closely spaced or far apart; it may take place as a shattering of the rock in a complex pattern like a broken window pane; or the rock may be so crushed that it is reduced to a rubble. As the mineralizing solutions fill these openings they will form a

FIGURE 6. Section through the Moneta Mine, Timmins, Ontario. A single gold-bearin g vein between two lava B.ows. After an illustration in Structural Geology of Canadian Ore Deposits.

series of ore bodies with the greatest imaginable variety in size and shape, features which are very important to the miner. There are many examples in Canadian mines of deposits formed in secondary structures. The Porcupine gold field in Ontario illustrates several types of structures, and two important ones will be discussed. The rock in this area is largely a series of very ancient lava flows that were heavily folded and now stand on edge like a series of books on a shelf. Igneous rocks called porphyry were intruded into the lavas. These rocks were then fractured

20

OUT OF

THE EARTH

by a series of almost vertical breaks, in which the ore-forming solutions deposited gold-bearing quartz to form our greatest gold­ mining area. Figure 6 illustrates a case where a single fracture developed between two lava flows, and one vein was deposited. Figure 7 shows us what happened when the rocks were broken

FIGURE 7. Map of a portion of the Hollinger Mine, Timmins, Ontario. The country rock is a series of folded lavas; these were intruded by small bodies of magma which formed stocks of porphyry. Both rock types were fractured in a series of roughly parallel breaks in which the ore-forming solutions deposited gold-bearing quartz to form a large number of rich veins. Mter an illustration in Structural

Geology of Canadian Ore Deposits.

into a series of roughly parallel fractures each of which was filled to form a vein. In this case the number of veins and their size have made this mine the largest gold producer in North America. Another interesting example is shown in Figure 8. Here the rocks of the country are ancient folded lavas which were intruded by an igneous rock, porphyry. Fracturing then took place along the contact between the porphyry and the lava and the lava, being the weaker, was most affected. It was broken into rubble

GEOLOGICAL MAP OF CANADA

Courtesy Canada Year Book

THE GEOLOGY OF MINERAL DEPOSITS

21

and the mineralizing solutions penetrated throughout the frac­ tured zone, depositing a network of small veins. In mining opera­ tions the rock fragments and vein material are all mined as a large ore body, but the ore is low grade, because of the amount of rock that is mixed with it.

FrCURE 8. Section through the Beattie Gold Mine, Quebec. The sequence of events here was: ( l) the lavas were intruded by a magma which solidified as porph yry; (2) the rock along the contact between the porphyry and the lava was shattered; and ( 3) ore-forming solutions penetrated the shattered zone to form a network of closely spaced veinlets. The large ore bodies consist of a mixture of rock and veinlets. After an illustration in Structural Geology of Canadwn Ore De posit,.

SEDIMENTARY ROCKS AND MINERAL DEPOSITS

The foregoing discussion has been concerned with mineral deposits formed as part of the process of forming igneous rocks. The following discussion will be concerned with those that are formed by the processes which build sedimentary rocks. In all probability few who read this would recognize an igneous rock, for the average person has little opportunity to observe them. However, it is different with sedimentary rocks. They are

22

OUT OF THE EARTH

the bedded or layered rocks that are so common as to evoke little interest in the casual observer. Some outstanding examples of sedimentary rocks may be seen in the gorge of the Niagara River; the Rocky Mountains of Alberta; or most spectacularly in the Grand Canyon of the Colorado River. All of these rocks had a common origin. They were formed by the weathering and erosion of older rocks, the transportation of the weathered material by water and wave action into lakes or oceans where it was deposited in layers, and its final consolidation into hard rock-clay becoming shale, sand becoming sandstone, and marl becoming limestone. The converting of a sand beach into a sandstone takes a long time, and does not begin until the sand has been buried by other sand or mud layers; the resulting pressure assists the process of solidification. The attack upon rocks by the forces and agencies of weathering is a relentless one and even the stoutest rocks finally succumb. But because some minerals decompose more readily than others there is a natural selection or concentration as the rocks begin to crumble. Very resistant minerals will be liberated as grains of sand; less resistant material will be decomposed to form a series of compounds of which clay is the most common; while soluble constituents, such as salts, are carried away in solution. The first stage in the weathering process is that of dissolving, decomposing, and carrying away the soluble minerals or elements. Under suitable conditions this may continue until there is a residue of virtually one insoluble mineral, which forms a valuable ore body. For instance, deposits of bauxite-aluminwn ore-are the final result of the weathering of certain types of igneous rocks. They form large flat-lying caps over the igneous rocks from which they developed. Concentration of ore minerals may also take place in the weathered material which is removed by erosion. This material consists of grains of sand, clay particles, and compounds in solu­ tion. The sand grains may be all of one mineral type such as quartz, in which case they will form a sand bar in a river or a beach along a shore, and be a valuable deposit of sand for build­ ing and other uses. Sometimes there are two or more mineral types in the sand. If one is heavier than the others it will not move as fast or as far as the lighter one, but will be left behind to form a deposit. Such concentrates are known as placer deposits, and much gold, platinum, and tin has been recovered from them.

THE CEOLOCY OF MINERAL DEPOSITS

23

Clay is washed into the rivers and carried to the lakes or oceans where it is spread out as a deposit of mud, to be later consolidated into shale. Beds of this sort are the source from which we get clay or shale for making ceramic products and portland cement. The soluble materials will eventually be thrown down, or pre­ cipitated, from the ·solution, but it requires rather specialized conditions to bring this about. Lakes or small seas into which rivers flow but which have no outlets, such as the Dead Sea in Palestine and many of the small lakes and sloughs in Saskatchewan and Alberta, provide examples of this process. From these seas and lakes the excess water is removed by evaporation, and the salts in solution become more and more concentrated until finally they precipitate as a layer along the shore or on the bottom. The ocean is another and even better example of this process. The rivers of the world continually carry salts into the ocean; there the water is evaporated and returned to the land as rain, but the salts remain behind. From time to time a bay or gulf, such as the Gulf of California or the Red Sea, may be cut off from the ocean. Eventually the water will dry up and a great salt deposit will remain. Common salt and gypsum are formed in this manner. From the foregoing discussion it can be seen that sedimentary ore deposits are formed in two different ways. In the first instance they resulted from a mechanical ( as opposed to chemical) con­ centration of particles, such as sand, gravel, or clay, and for that reason they are often referred to as "mechanically formed de­ posits." In the second instance they were formed by the solution and precipitation of certain compounds, and because this is a chemical process they are known as "chemically formed deposits." A convenient summary of information on the sources of the common metals is provided in Table III. It gives with their chemical formulae, the principal minerals from which we derive the metals, and indicates the most important processes by which these minerals were concentrated to form ore deposits. THE MINERAL FUELS

There is another type of sedimentary deposit which is very important to our economy: the organic sediments. These deposits are the concentrations of carbon and hydrogen which organisms have taken from the air, incorporated into their tissues, and on dying have left behind to form coal, petr-0leum, and natural gas­ the great sources of power throughout the world. Strictly speak-

TABLE III COMMON

0R.E

MINERALS: THEIR COMPOSITION AND MODE OF ORIGIN

THE GEOLOGY OF

MINERAL DEPOSITS

25

ing such concentrations are not mineral deposits, if the term "mineral" is used in its restricted sense as covering only inorganic materials. However, it is common custom to refer to them as mineral fuels, and they will be so considered here. Nevertheless it should be remembered that they are not true minerals but are organic remains. Animal and vegetable tissues are composed chiefly of three elements: carbon, hydrogen, and oxygen. The last two of these are normally gaseous and the other, carbon, is a solid. If animal or vegetable remains are left to decompose in the atmosphere they do so by reverting in large measure to their original elements, or simple combinations of them with oxygen, such as carbon dioxide (C02) and water (H20), and little is left of the former organism. If, on the other hand, air is absent, as it would be if the organic remains decomposed under water, a very different process talces place. Under such conditions the woody tissues of trees and plants disintegrate to form coal (carbon) with minor quantities of such gases -as carbon dioxide ( C02), and methane (CH.), known to the coal miners as black damp and fire damp respectively. The minute animals and plants, which are collectively called plankton, will, under similar conditions, disintegrate to form a ,series of hydrocarbons-compounds of hydrogen (H) and carbon ( C)­ that make up petroleum and natural gas. The history of the earth records great changes of all types among which varying climatic conditions have been important. There have been periods of widespread glaciation, and also periods of mild tropical climate over most of the globe. During the latter times there were extensive jungle-like forests over parts of the earth's land surface, and tremendous developments of plankton in the oceans. Many of these jungles probably flourished in swamp conditions not unlike those seen along the Amazon River today. As trees died they would gradually sink and be buried in the swamp. In this way great thicknesses of woody material were accumulated. The woody material, after it sank into the swamp and was ex­ cluded from the air, would undergo the process of transformation into coal. The first step in the process would be its breakdown in the swamp into peat-a mixture of tough woody fibres enclosed in a jelly-like mush. Where there are swamps today peat is usually forming, and in many countries these peat swamps are drained and the peat is cut into blocks, dried, and used as fuel.

26

OUT

OF THE EARTH

The great peat swamps of the past were periodically inundated by floods and the peat was covered by a layer of mud or clay. Then began the second phase of the transformation from wood to coal-a gradual change, first into lignite, often called brown coal, and later into bituminous or soft coal. This change was brought about by a continuation of the decomposition processes aided by the pressure from the overlying layers of clay. In certain areas where the coal beds have been folded by mountain-building forces the process is continued and the coal may be further changed to produce anthracite or hard coal. Today we find coal deposits as great blanket-like beds inter­ layered with clay or shale. Individual beds may extend over many square miles and be tens of feet in thickness. Mining opera­ tions may be carried on in a single bed or seam, or in several beds. Sometimes the beds are near the surface and can be mined in great quarry-like excavations, but usually they are deeply buried and must be reached by underground methods. The development and accumulation of petroleum and natural gas took place by processes somewhat diHerent from those that formed coal. They resulted from the decomposition on the sea bottom of plankton-those minute organisms which still flourish in our seas and oceans in such vast numbers that they constitute the chief food of certain species of whales. In past times they were equally plentiful, or perhaps more so, and those which were not devoured by the predatory animals of the day and died a "natural" death, sank to the floor of a shallow sea basin, where they were mixed with mud. In this way thick deposits of clay were formed, in which was incorporated a large amount of organic matter. These deposits were later buried beneath great thicknesses of other sedimentary rocks ,such as shales, sandstones, and limestones. The weight of the overlying rocks produced pressure and heat, which aided the process of changing this organic matter into a series of new compounds of carbon and hydrogen. These we call the "hydrocarbon series." Some of the compounds are gaseous, some liquid, and some semi-solids, form­ ing respectively natural gas, petroleum, and paraffin and asphalt. When the hydrocarbon compounds first formed they were dis­ tributed as minute droplets through the clay or shale. We find many such shales, which are called "bituminous" or "oil shales," and in some places they are mined and petroleum recovered from them. The bituminous sands of northern Alberta may be this type

THE GEOLOGY OF MINERAL DEPOSITS

27

of deposit. li conditions were suitable, however, the droplets of petroleum and natural gas migrated from the bed in which they developed. Their movement was due largely to the presence of sea water that remained in the clay after it was deposited: as fast as the droplets formed they would tend to rise above the water. The upward migration of the natural gas and petroleum would continue until the droplets encountered an impervious layer of rock, under which they would be trapped, or until they escaped at the surface as a seepage. The beds in which the petroleum and gas were formed are known as the "source beds"; those in which they accumulated and from which we extract them are the "reservoir beds." Shales are commonly source beds while lime­ stones and sandstones are the most common type of reservoir beds. In practice it is found ·that the natural gas or petroleum is im­ prisoned in many forms of structures or traps ( Figure 9). The

FrcURE 9. Section through a series of sedimentary rocks which have been folded into an arch or anticline. The oil and gas have risen from the source bod until they were trapped under the impervious shale. They now fill the pore spaces in the sandstone, and form a so-called pool.

28

OUT OF

THE EARTH

essential feature in each case is a tilted or folded porous layer. As the migrating droplets come to rest in the trap they segregate, the gas rising on top of the oil, which in tum rests on the salt water. These substances, though often referred to as forming gas or oil pools, do not occur in an actual pool. They occupy the pores in the rock. The size of the pores and the nature of the interconnection between them are most important features, for they determine the ease or difficulty with which the oil and gas can move to form pools, and later when a well is drilled into the pool, they influence the rate of movement of the oil and gas into the well. THE DISTRIBUTION OF

MINERAL

DEPOSITS

Metal-bearing minerals, industrial minerals, and fuels were all formed in response to definite processes which took place at specific intervals and locations during the earth's history. Conse­ quently anyone engaged in searching for them, or even interested in knowing about them, should have some appreciation of his­ torical geology, the branch of the science of geology which treats of the sequence of events in the formation of the earth and the development of animal and plant life. The oldest known rocks were formed about two billion years ago, and the records that can be derived from them are exceed­ ingly sketchy and fragmentary. However, the succeeding rocks contain an increasingly abundant store of information so that the history of the past 500,000,000 years is comparatively well known. These vast periods of time have been subdivided in a manner not unlike that which historians use, who make events, such as the Fall of the Roman Empire, the major dividing lines, and use a group of people or an individual to designate minor subdivisions, such as the Elizabethan Age. The major events of geologic time were the formation of moun­ tain systems. These events played such important roles in the ea1th's history that they are referred to as revolutions. At such times more occurred than just the formation of mountains. Usually large areas bordering them were raised from the sea floor to become new continents or major additions to old ones. Ocean and air currents were radically altered; this caused major climatic changes, which in tum affected life on land and in the seas. Within the newly formed mountains intrusive igneous rocks and

THE GEOLOGY OF MINERAL DEPOSITS

29

associated ore deposits would form. The new mountains and continents would be exposed to weathering and erosion which would slowly wear them away. In this process residual mineral deposits might be developed on the land while the eroded material from land areas would be deposited in the shallow seas to form great thicknesses of sedimentary rocks and, if conditions were favourable, deposits such as coal, petroleum, salt or gypsum. The Geological Time Chart ( Figure 10) shows the major divisions or eras-Cenozoic, Mesozoic, Palaeozoic, etc.-which are separated from each other by mountain-building revolutions. The secondary subdivisions or periods-Cambrian, Ordovician, etc.­ are separated either by small local mountain-building events, or because a continent was raised above or lowered below sea level. The periods are further subdivided ( although this subdivision is not shown), the basis being the events and life that characterized each unit of time. The economic geologist is primarily interested in those periods of geological time in which mineral deposits of economic im­ portance were formed. While we know that in mountain building times igneous rocks and associated mineral deposits were being formed, it must be emphasized that not every magma produced metal deposits nor did any one magma produce the full range of metals. Some magmas were apparently barren, others brought in lead and zinc, others copper and gold, and so forth. Similarly, during periods of sedimentation the conditions necessary for coal to form or oil to accumulate might be quite local, giving isolated coal fields or oil fields. If conditions were not favourable, none at all might be formed. The search for new mineral deposits is a fascinating game of hide-and-seek in which the individual endeavours to find where Nature has hidden her treasures. A knowledge of how and when mineral deposits were formed is of paramount assistance for it indicates where they may be. However, the final assault must be a painstaking search over the potential area. MINERAL DEPOSITS THROUGHOUT CANADA

From a geological viewpoint Canada falls into the following divisions: ( 1) the Canadian Shield; ( 2) the Interior Plains; ( 3) the Appalachian Region; ( 4) the Cordilleran Region; and ( 5) the Arctic Archipelago. These are shown in Figure 11. The Canadian Shield forms the foundation of the continent

THE GEOLOGY OF MINERAL DEPOSITS

31

for it is made up of the oldest and first formed rocks. Its great horseshoe shape extends up each side of Hudson Bay, occupying an area of 1,800,000 square miles-which is almost half of the area of Canada. The Shield is a great plain which slopes gradually up to the northeast and reaches elevations above 5000 feet in

FIGVRE 11. By courtesy of Canada Year Book.

northern Labrador. The rocky surface is hummocky and it is dotted with lakes, probably a greater number of lakes than in all the rest of the world together. The bed rocks are all of Pre­ cambrian age and include sedimentary, volcanic, and intrusive igneous types. During Precambrian time the Shield was subjected to several periods of mountain building and deep erosion. Conse­ quently its geology is very complex, and what is more important, the mineral deposits formed during these great events make it

32

OUT OF THE EARTH

one of the world's outstanding mining regions. The production of metals from the Canadian Shield has a value of over half a billion dollars annually. The mines at Sudb ury, Ontario, produce three quarters of the world's supply of nickel and half of its platinum, in addition to several other metals. Porcupine and Kirkland Lake are the most important gold-producing areas in North America, and the deposits of the famous Cobalt area were probably the richest silver veins ever found. The list o f metals produced from rt.he Shield includes cadmium, cobalt, copper, gold, iron, lead, magnesium, nickel, the platinum group, selenium, silver, titanium, tungsten, uranium, and zinc. Mines in the Shield also produce such industrial minerals as asbestos, fiuorspar, mag­ nesite, mica, nepheline syenite, quartz, talc, and sulphur. The Interior Plains are the flat-lying areas bordering the Shield on the west, north, and south, as well as along ·the coast of Hudson Bay. These Plains are underlain by flat-lying sedimentary rocks chiefly of Palaeozoic and Mesozoic age. They have not been subjected to any mountain building or igneous activities and therefore do not contain any metallic mineral deposits. They do, however, contain the great petroleum, gas, and coal deposits of Canada. In addition to these they supply great quantities of industrial minerals such as gypsum, limestone, and various types of salt. The Appalachian Region embraces that part of Canada lying south and east of the St. Lawrence River. It is an area with a complex geologic history for its rocks range in age from early Precambrian up to Mesozoic. The region is a continuation of the Appalachian mountain system of the United States, and conse­ quently the rocks, which include sedimentary and volcanic types, have been severely folded and intruded by igneous rocks. This has created a great diversity of mineral deposits. The most im­ portant production is coal from Nova Scotia, iron from New­ foundland and asbestos from Quebec. Other materials produced_ on a lesser scale are barite, copper, fluorspar, gold, gypsum, lead, natural gas, salt, silver, and zinc. Large new deposits of copper, zinc, and lead are being opened up in this area. The Cordilleran Region embraces the mountainous areas of western Canaoa from the International boundary to the Arctic Ocean. It too has a very complex geological history and a vast array of mineral deposits. The rocks of the area start with the Precambrian and range up to the late Cenozoic. All over it there

3 Modern Methods of Prospecting IF ALL ORE BODIES were exposed at the surface there would be little need for any prospecting other than looking over the ground and picking out the valuable deposits. However, vast areas of the earth's surface are covered by what is called "overburden"-sand, gravel, clay, or soil-which often bears little or no relationship to the rocks beneath, but which conceals whatever of value they may contain. In other cases mineral deposits lie beneath hundreds or thousands of feet of solid rock. The search for ore bodies that are so hidden is one of the most bafBing problems confronting the geologist. In recent years a new scientist, the geophysicist, has come to his aid. By means of newly developed techniques, the geophysicist can frequently indicate where ore bodies and petro­ leum "pools" may exist beneath the surface, or by measuring the physical properties of the rocks can give the geologist new in­ formation to aid him in the search. In the chapter dealing with the geology of ore deposits it was pointed out how minerals and rocks varied chemically. They also vary in their physical properties. For instance, a few minerals are magnetic. This property was recognized by our forbears, who made their first compasses by suspending a piece of natural mag­ net or loadstone at the end of a string. The mineral used for these crude compasses takes its name from its magnetic nature and is called magnetite. Magnetite is also an important source of iron and it is a comparatively easy thing to locate a body of this type of iron ore for it will attract a compass or a dip needle. The large ore body at Marmora in Southern Ontario was of this type and was easily located even though covered by 100 feet of lime­ stone. Other physical properties of minerals can also be helpful in the search for mineral deposits but more highly specialized equipment and techniques are required to measure them. The measuring of such properties is known as "geophysical surveying" or "geophysical prospecting." Some of the common methods used 84

MODERN METHODS OF PROSPECTING

35

in geophysical surveying and the propertie.s which they measure are given below: Method of geophysical ruroeying

Magnetic Electrical Seismic Gravitational Geiger and scintillometer

Physical property of the rocb meamred Magnetic permeability Ability to conduct electricity Ability to transmit and reflect shoc.k waves, ie., elasticity Specific gravity or density Radioactivity

It must be emphasized that geophysical methods measure one or more of the above physical properties but do not identify mineral deposits or rock types. For example, a geophysical survey may locate a hidden mass which is an electrical conductor, but since conductivity may be due to a valuable metal deposit or to worthless graphitic zones, the survey has not given specific in­ formation in terms of geology, rocks, and ore deposits. If all the rocks in a given area were uniform the geophysicist would be stymied, for the success of his work depends on finding d.iHerent physical properties, or variations in a particular property. However, no areas are uniform and the geophysicist always finds variations, which he calls "anomalies." Some people are inclined to think that anomalies mean ore bodies, and again a word of caution is in order, for the word anomaly means a variation from the normal in its technical use. After anomalies have been found and outlined they must be interpreted into terms of rocks and ore bodies. This is done by co-ordinating the geophysical data with the geology of the area, and by diamond drilling the area containing the anomaly. MAGNETIC METHODS

The earth is a large magnet, and as such it has a magnetic field covering its entire surface. We make use of this when using a compass, for the magnetic compass needle lines itself up in the direction of the earth's field. The field is not uniform over the earth's surface, since there are many rocks and mineral deposits which cause local variations or attractions. The earliest form of geophysical instrument was a dip needle, which measures tho dip of the magnetic field whereas the compass measures its direction.

36

OUT OF THE EARTH

It is a simple instrument like a compass except that its needle rotates in a vertical plane. More elaborate and sensitive devices, called magnetometers, are now used, and they measure the magnetic field with great precision. In recent years specially designed magnetometers have been mounted in aircraft. They were developed during World War II

FIGURE 12. Aeromagnetic map ( part of Despinassy Sheet, Quebec; Geological Survey of Canada). The magnetic contours show the intensity of the earth's magnetic field, expressed in gammas. A, B, C, and D are anomalies of varying degrees of intensity from high to low.

as a means of locating enemy submarines. The modem airborne magnetometer is flown along a series of parallel lines over the area to be surveyed, at a uniform height, which may be 500 or 1000 feet above the surface-the nearer to the surface the greater the amount of detail recorded. The magnetic intensity as picked up by the magnetometer is recorded on a tape so that for each

MODERN METHODS OF PROSPECTING

37

line flown there is a continuous magnetic profile. These profiles are then plotted on a map and lines are drawn through the points of equal intensity. The result is a map much like an ordinary contour map ( Figure 12). Magnetometer surveys may be made on the ground by setting up a magnetometer at a number of points. The records are plotted and the same type of map is made. The essential differ­ ence between the two types of survey is that the ground work gives greater detail. In practice, airborne surveys are used for reconnaissance, for they cover a large area in a short period of time. The slower ground work is done on those areas in which anomalies have been indicated and about which greater detail is desired. One of the earliest records of magnetic survey in Canada was that made by Thomas A. Edison in the Sudbury nickel field be­ tween 1902 and 1904. He located a strong anomaly and spent a considerable amount of money trying to sink a shaft through the deep sand and gravel that covered the bed rock. The overburden, which was more than 100 feet deep, proved to be too much for the mining methods of that day and tlie effort was abandoned. It was left to others, thirty years later, to complete the job and develop the Falconbridge nickel mine. They found that Edison's shaft was located over the widest part of the ore body. ELECTRICAL METHODS

There is often a marked difference in the electrical conductivity of ore bodies and the rocks in which they occur. Bodies of massive sulphides such as chalcopyrite, galena, or pyrite are much better conductors than rocks, while quartz veins are usually much poorer. Different types of rocks will also have different conduc­ tion values. There are many methods of geophysical surveys making use of these electrical properties of rocks and minerals, which may be grouped as follows: 1. Conductive methods (a) Using natural earth currents; ( b) Using currents introduced into the ground 2. Inductive methods Conductive methods using natural earth cu"ents. A body of sulphide minerals, which is weathering, is a natural battery, the top being the positive pole and the bottom the negative pole. A current flows through the adjacent rock from the negative to the

38

OUT OF THE EARTH

positive end of the ore body. By putting metal probes into the ground it is possible to measure the change in electric potential as one approaches the ore body. In this method of surveying readings are made at a number of points and when they have been plotted on a map and lines of equipotential drawn, the ore body will form the bull's eye of a target-like map (Figure 13 ). The method is sometimes called the self-potential method.

SECTION

FIGURE 13. Plan and section of an ore body showing the principle made use of in self-potential surveying. The ore body is a natural battery with current flowing in at its top. Measurements on the surface show a gradual increase in electric potential towards the ore body. Lines through points of equal potential outline the ore body.

This method has a limited application because of the special conditions that must be present to create a natural battery, and because errors may creep in owing to earth currents, magnetic storms, or sudden changes in temperature, all of which may cause variations in ·the flow of current. Conductive methods using currents introduced into the ground. If metal probes are stuck into the ground a current, either direct or alternating, may be made to flow between them. The path the

MODERN METHODS OF PROSPECTING

39

current follows and the drop in potential from point to point, between the probes, will depend on the resistance of the various rocks and minerals encountered by the current. It is possible, by means of suitable instruments, to determine lines of equipotential as in the previous case, and thus to outline the most conductive rocks or ore bodies. Modifications of this method are widely used, especially for investigating Hat-lying sedimentary rocks. The most popular ones are referred to as resistivity methods. The mode of operation is similar to that used in the conductive method described just above, the d.iHerence being chiefly in the methods of introducing the current into the ground, the locations of the measuring stations, and the use made of the data secured. In the resistivity method the resistance of the various rocks is calculated. By in­ creasing the distance between recording stations information can be gathered on rocks at greater depth, and it is possible to de­ termine the resistivity of rocks 2000 to 3000 feet below the sur­ face. These methods are widely used in petroleum exploration. Inductive methods. A mineral deposit which is a conductor of electricity will act as a transformer when in the presence of an alternating current, and a second ary current will be induced in it. This principle is made use of for discovering the presence of concealed conductors. In practice an alternating current is put through a loop of wire on the surface. If a conducting mineral deposit is present a second ary current will be induced which will How through the rocks, and which can be measured on the surface of the ground. In this way the presence of the conductor is indi­ cated. A modification of this method has recently been perfected which permits the entire apparatus to be mounted in an aircraft. Continuous readings can then be taken, as in the case of the air­ borne magnetometer. Indications are that this method of geo­ physical prospecting will prove as successful as other airborne operations. It is 'Often the practice to combine electrical and magnetic methods when surveying an area as one supplements the other. For instance, a large body of rock with a small amount of sulphides disseminated in it could give the same magnetic read­ ings as a much smaller body of massive ·sulphides. From a mag­ netic survey alone it would not be possible to tell which type of material might be present. An electrical survey would soon settle

40

OUT OF THE EARTH

the question for it would pick out the massive sulphides as a good conductor and the rock as a poor one. SEISMIC METHODS

Vibrations, or shock waves, may pass through solid bodies such as rocks and because they are waves they will be transmitted, reflected, and refracted according to the laws governing wave motions. Earthquakes are just such vibrations passing through

FxcURE 14. Section to illustrate the operation of seismic reflection surveying. The film record shows two shocks ( wavy lines) recorded on each detector, as the waves were reflected from the two limestone beds.

the rocks. Since the study of earthquakes is known as seismology, the method of geophysical surveying that makes use of vibrations or shock waves is known as "seismic surveying." In seismic methods waves are created by :firing a few pounds of dyn amite in a relatively shallow hole, and are recorded by a series of geophones or detectors set out at regular intervals on the ground. The vibrations picked up by the detectors are recorded on a fast-moving photographic film. Since the rate of ·travel of the film is known it is an easy matter to calculate the time it

MODERN METHODS OF PROSPECTING

41

has taken the different waves to reach the detectors, and there­ fore the distance they have travelled. There -are two types of seismic techniques. One, the refraction method, measures the velocities of shock waves through various rocks; the other, the reflection method, measures the time re­ quired for shock waves to be reflected from rock surfaces. The second method is the more widely used. It depends on the prin­ ciple that where two adjacent beds of rock have different densi­ ties, the boundary between them will act as a reflecting surface and bounce back the shock waves (Figure 14). By precisely measuring the travel time of the waves from the explosion point to the reflecting surface and back to the detector, it is possible to calculate the distance down to the rock surface. In the same manner ships use echo or radio sounding devices to determine the depth of the water. The reflection method has been used to identify the rock structures, such as folds (Figure 9), which form structural traps for oil and gas. It has proved itself to be so useful in petroleum prospecting that wells are seldom drilled without a seismic survey to indicate where the most favourable structural conditions exist. GRAVITATIONAL

METHODS

Everyone is familiar with the phenomenon of gravity or the gravitational attraction which the earth exerts. It is to every schoolboy the force which caused the apple to fall in Sir Isaac Newton's garden and which causes the tides of the ocean. This force is not the same everywhere on the surface of the earth. The variations are due largely rto differences in ·the density of the underlying rocks, the gravitational attraction being greater over rocks of higher density. By using sufficiently sensitive measuring devices it is possible to construct a map indicating by contours the variations in gravity; this map will thus outline the rocks of varying densities. Gravita­ tional surveys have been used extensively in the location of salt domes in the southern United States. These large dome-shaped masses of salt, which may measure hundreds of feet across, are easily found by 'this method of survey because of the marked difference between the density of the salt and that of the en­ closing rock. The structures in the rocks near the salt often make good petroleum traps, so they have been given very detailed study by both gravitational and seismic methods.

42

OUT OF THE EARTH

Any one of three types of instrument may be used in making gravity measurements. These are the torsion balance, the pendu­ lum, and the gravimeter, each measuring the gravitational effect in a different manner. Of these the gravimeter is most commonly used. It has the advantage of a high degree of accuracy; it is portable; and it allows measurements to be made in a short time. Gravity surveys are most useful in discovering the presence of large rock masses with densities differing from the normal Though helpful in surveys for petroleum they are of little use in locating ore bodies, for while the density of ore may differ greatly from that of the surroundip.g rock the ore bodies are usually too small to create any measurable variation in the earth's gravita­ tional field. THE GEIGER COUNTER AND THE SCINTILLOMETER

Radioactive minerals are constantly giving off small radiations of energy known as alpha, beta, and gamma rays. It is possible with suitable apparatus to detect and in some cases to measure the intensity of these emanations, and a method of prospecting for radioactive minerals using such devices has been developed within recent years. There are two types of radioactive detectors in common use today. These are the Geiger counter and the scintillation counter. The Geiger counter depends for its operation upon a special type of electronic tube which permits a pulsation of electrical current to pass through it when it is bombarded with a gamma ray. These pulsations are amplified electronically and each makes a "click" which is heard in the head phones of the counter. The rate at which clicks take place is a measure of the relative abun­ dance of the radioactive material which gives off the gamma rays. The scintillation counter in general provides the prospector with the same information as does the Geiger counter, but it has the advantage of greater sensitivity. In the scintillometer the radiations from the uranium minerals cause a glow on a screen, the intensity of which is measured electronically. Scintillation counters have been fitted to aircraft and aerial prospecting for radioactive minerals has met with some measure of success. The entire field of geophysics has developed at a remarkable rate in the past twenty-five years. It has grown from a relatively little known branch of physics to a very important separate

MODERN METHODS OF PROSPECTING

43

science which bridges the territory between physics and the geological sciences. As the mineral industry grows, so will the demand for improved methods of geophysical prospecting. It must be borne in mind, however, that a geophysical survey instrument is a piece of scientific apparatus and not a gadget for finding ore or oil. Those who operate it must be especially trained technicians. Those who interpret the results must have a knowl­ edge of both physics and geology so that the measurements of the varying physical properties of an area may be translated into terms of rocks, rock structures, and mineral deposits. SELECTED REFERENCES

Oct, C. HEwrrr. Seismic Prospecting for oa. New Yorlc: Harper & Brothen, 1952. J..u:OSKY, J. J. Exploration Geophysicl. Los Angeles, Cali£.: Times-MirrOI' Press, 1940.

4 Mining and Processing of Ores THE FINDING of an ore deposit is one problem; its conversion into a profitable mine is another. Since several million dollars of ex­ penditure on plant and development may be required before one single cent of income is received, it is necessary for the mining engineer to analyse carefully the many factors which are involved in opening up a mine. The size and grade of the ore body, the number of tons of ore to be mined daily, the initial capital re­ quired, the operating cost, the market for the material which will be produced, and the profit to be made are the outstanding considerations. Preliminary exploration work to determine the size and grade of an ore body usually begins with stripping off the overburden so that the ore can be sampled, studied, and mapped. Ore bodies do not, however, always remain constant in size or grade through­ out and it is necessary to explore them below the surface. This is conveniently done by means of a diamond drill. The drill consists of a ·tube or pipe, the end of which is set with industrial diamonds, and a mechanism by which it is rotated at a moderately high speed. The diamonds cut a ring-like or annular hole when the drill is forced into the rock. The core so formed is caught in the tube and brought to the surface; it constitutes a sample of the material being penetrated. A series of preliminary drill holes is put down which cut the ore at predetermined points, ·and in this way representative samples are secured. If the data from the surface and the preliminary diamond drill holes are sufficiently encouraging and indicate that an ore body exists, then a pro­ gramme of extensive exploration is undertaken. It may consist of many drill holes spaced not more than 100 feet apart, or of a shaft and exploratory workings. From all the surface and under­ ground data it is possible to determine the number of tons of ore in the ore body, and the amount of recoverable metal in each ton 44

MINING AND PROCESSING OF ORES

45

of ore. H the results indicate that a mining operation would be successful plans are prepared to carry it out. MINING

In order that a mine be a profitable venture there must be sufficient income from the sale of the ore to provide for operating costs, capital costs, taxes, and profit. Operating costs cover all the money spent directly in mining and preparing the ore or metal for market. They include expenditures for labour, supplies, power, and marketing. Capital costs are those sums required to repay the capital expended to acquire the property and bring it into pr