The Occurrence and Origin
of Diamonds

By Edgar George Pye, Ph.D

Diamonds are the most beautiful, most brilliant, hardest, and most-desired of all gem minerals. The word "diamond" conjures up different things depending on one's interests and point of view. To one's fiancée or wife, a diamond is a symbol of purity and commitment to never-ending love, as exemplified by the phrase devised by De Beers "A Diamond is Forever". To the Sports Fan, a diamond is the focus of American baseball; to the gambler or bridge addict, it represents a suit of playing cards; to the more fortunate its acquisition represents wealth; to the monarchist, its beauty, rarity and durability symbolize royalty. But what is diamond? Where is it found? How does it occur in the natural environment? How was it formed? Does Canada have a future in the lucrative diamond trade? It is proposed to answer these and other questions in the following text for the curious individual whose familiarity with the gem is limited to the engagement ring and other jewelry.

Figure 1: The Aurora Collection of natural coloured diamonds. Also shown is a great variety of "cuts" found in jewelry. Courtesy of Aurora Gems, Inc., N.Y., and Alan Bronstein, Collector. (Photograph by E. Van Pelt).

The writer candidly admits to lacking any practical experience in regard to the geology and exploration for diamonds. His interest stems largely from the relatively new discoveries in Canada's Northwest Territories, a recent discovery of a diamond in the glacial drift near Wawa, Ontario; commencement of Canadian production in 1998; and from inquiries of a friend who "dabbles" in the stock market. This paper is simply the result of a review of the scientific literature on the subject so as to increase one's knowledge, heretofore sadly lacking in a Canadian geologist whose career dealt mainly with the gold and base metal deposits of the Province of Ontario, and whose concerns with exploration for diamonds were quite marginal. This review paper is not intended to present any new information; it contains nothing that has not been reported elsewhere, as in the references listed. It is presented in the hope that the reader will find it as interesting and informative as did the writer during its preparation.

The Mineral Diamond

Public knowledge of gem quality diamonds, generally is limited to scarcity and to the four "Cs"-Clarity, Carat (weight), and Colour and "Cut" (see Figure 1) - which determine value in the market place. Diamond is the world's hardest substance. Strangely, however, like the very soft mineral graphite, it is made up of only one element, carbon. Despite being of the same chemical composition, the two minerals differ widely in their physical properties. The marked contrast in colour, transparency and other features simply reflects a difference in crystal structure, that is, how the carbon atoms are arranged and packed within the crystal lattice.

Figure 2: Ball-and-stick diagrams showing the difference between the graphite structure and the cubic structure of diamond (Adapted from Jaszczak, 2001; Courtesy of Michigan Technological University).

The difference in the crystal structures of graphite and diamond are illustrated in Figure 2. Figure 2(a) is a ball-and stick representation of the graphite structure. Here the carbon atoms are arranged in sheets of six-member rings. The diagram shows three of these sheets loosely bound together. This makes graphite soft and slippery. Because the sheets of atoms are loosely bound together, they readily slide over one another. Graphite is so slippery that it makes an excellent lubricant, often substituting for grease or other products. Figure 2(b) illustrates the diamond structure, in which the carbon atoms are tightly bound by the sharing of electrons in a cubic pattern that accounts for the mineral's unusual hardness and other distinctive properties.

Occurrence of Diamonds

Diamonds were first found in India over 2000 years ago, and India was the main or only commercial source until the mineral was again discovered in Brazil in 1730. In both countries the diamonds were initially recovered from alluvial deposits of sand and gravel. The deposits are said to be "secondary", having resulted from the erosion of bedrock or "primary" sources. As recently as 1960, more than 80 per cent of world production came from alluvial or secondary sources (Levinson et al., 1992, p. 235). Important primary deposits subsequently were discovered in South Africa in the 1870s; in Russia in the 1950s; in Botswana in 1966; in Australia, (the Argyle mine, currently the World's most prolific producer), in 1979; and eventually in Canada, in 1991. Today diamonds are being produced in over 20 countries, with a total annual production of about 110 million carats by weight. It has been estimated by the US Bureau of Mines that roughly half of the diamonds marketed between 1985 and 1990 were of 'gem' or 'near-gem' quality (Levinson et al., 1992, p. 236-237).

Figure 3: Graph showing the increase in diamond production by country since 1900. (From Levinson and Cook, 2000, p.20).

Figure 3 illustrates the increase in World diamond production since 1900 and identifies the major producing countries. Most primary deposits are found in stable Precambrian Shield areas (Archons) underlain by rocks that have been dated as being over 2.5 billion years old (Figure 4). Known deposits are found either in these ancient rocks themselves or in overlying platforms of younger flat lying sedimentary rocks (Kirkley et al.,1992, p.53.). As explained later in the Section of this paper dealing with the Origin of Diamonds, this unique occurrence is thought to have been the result of a lower geothermal gradient in Shield areas than elsewhere (Mitchell, 1991, p.2).

Figure 4: Map of the World showing Archons (in purple), areas where diamond deposits are most likely to be found. (From Levinson et al., 1992, p.241, courtesy of Gems & Gemology).

In the stable Precambrian Shield areas called Archons (Figure 4), diamonds are found in pipes or "diatremes". The pipes or diatremes are also generally composed of the rock known as kimberlite, This rather unusual rock consists of olivine, serpentine, mica, ilmenite, carbonates and other minerals. It was named after its discovery at Kimberley, South Africa. An economic diamondiferous kimberlite pipe is a rare, complex lithological mix of three components: (1) kimberlite itself, which forms a matrix to (2) fragments of one or both of rocks known as eclogite and peridotite (variety, hartzburgite), and (3) pieces of sedimentary and other country rocks. The kimberlite matrix is an igneous rock that crystallized from a hot natural melt or magma generated deep within the Earth. The inclusions of eclogite, made up largely of the minerals garnet and pyroxene, and peridotite, made up largely of the minerals olivine and pyroxene, are also of deep-seated origin. While the kimberlite matrix may contain diamonds, inclusions of eclogite and peridotite may contain up to as much as 10 percent by volume. Their diamonds are primary or original constituents, however, whereas those found in the kimberlite matrix are secondary, merely inclusions like the rock fragments (Kirkley et al., 1991, p.16). Most of the World's kimberlite pipes occur as upward-expanding cones or carrot-shaped bodies (Figure 5) that represent former volcanoes.

Figure 5: Cross section through a hypothetical model of an inverted cone-shaped kimberlite pipe, showing zonal classification and interpreted surface erosion levels of various mines. Inclusions (xenoliths) may be of eclogite, peridotite, and/or country rocks. (Modified after Kirkley et al., 1991, p. 22; courtesy of Gems & Gemology).

Diamonds from the world's most productive mine, the Argyle mine in Western Australia, occur in lamproite rather than kimberlite. Lamproite is a close relative of kimberlite, but is richer in aluminum, potassium, silicon, and fluorine, generally with a much lower content of carbonate minerals (Kirkley et al., 1991, p.16). It also differs from kimberlite in that it does not form inverted cone-shaped pipes but rather ones with wider flared upper extremities where the hot magma, rising through a narrow cylindrical conduits came explosively into contact with cool near-surface ground waters (Kirkley, 1998, p.53).

In addition to their occurrence in kimberlite and lamproite, diamonds also occur as secondary deposits in alluvial sands and gravels, having resulted from the erosion of primary kimberlite or lamproite occurrences. As pointed out above, such secondary deposits are historically the most important sources of diamonds in India and Brazil. Most known deposits occur in river beds as might be expected, but in Namibia, the former German colony of Southwest Africa, rich occurrences also have been found in beach and offshore sands and gravels close to and extending north from the mouth of the Orange River. Their original source is thought to have been the bedrock deposits in the area of the river's headwaters (Levinson, 1998, p. 78-91).

Uncommon minerals found in kimberlite pipes include pyrope (a magnesian garnet generally having a having a distinctive red or purple colour, owing to the presence of iron and some chromium), bright green chrome diopside (a pyroxene), chromite, ilmenite, and, of course, diamond itself. These are often referred to by prospectors as "indicator minerals". Their unique association with diamondiferous kimberlite pipes greatly facilitates exploration for economic deposits. This is because, once released by erosion into the surface environment, careful sampling of surficial sediments may indicate "trails" that lead to the volcanic pipes or diatremes from which they originated. This method of exploration, coupled with geophysical surveys that take advantage of the magnetic or electromagnetic signature of kimberlite has been quite successful in Canada, where trails of indicator minerals have led to the discovery of the economic Ekati and Diavik diamond deposits in the Northwest Territories.

Ages of Diamonds

The radiometric ages of the emplacement of kimberlites, as determined from isotope ratios, are perhaps amongst their more interesting characteristics. Table 1 indicates that kimberlite pipes found in many localities have formed throughout most of geological history, from the Precambrian to the Eocene.

Table 1: The span of geologic and radiometric ages of the emplacement of kimberlites found in various localities throughout the World. (From Kirkley et al., 1992, p.54).

Geologic Age	Radiometric Ages of Kimberlite Emplacement (Millions of Years)	Localities
Eocene	50-55	Namibia, Africa
Eocene	52	Lac de Gras, NWT, Canada
Upper Cretaceous	65-80	Southern Cape, South Africa
Upper Cretaceous	73-81	Lac de Gras, NWT, Canada
Middle Cretaceous	80-100	Kimberley, South Africa
Lower Cretaceous	115-135	Angola, West Africa
Upper Jurassic	145-160	Eastern North America, South Africa
Middle Jurassic	172	Northwest Territories, Canada
Devonian	340-360	Colorado, Wyoming, USA
Ordovician	440-450	Siberia
Cambrian	540	Northwest Territories, Canada
Upper Proterozoic	810	Northwest Australia
Middle Proterozoic	1000-1250	South Africa, India, Mali
Lower Proterozoic	1600	South Africa

As previously stated, the diamonds of primary deposits did not crystallize from the natural melt or magma that formed the matrix of a host kimberlite body, but are merely inclusions within it, much like fragments of country rocks. They are believed to have formed deep within the Earth and transported upward toward the surface from their places of origin by the kimberlite magma (Mitchell, R.H., 1991, pp.1-3). Table 1 indicates that kimberlites formed throughout geological history. The dating of radioactive inclusions within diamonds, on the other hand, indicates that their diamonds formed early in the Earth's geologic history, in the Archean and Proterozoic, and hence to be much older than the kimberlite pipes in which they occur. As already noted, diamonds are found not only in the kimberlite matrix of volcanic pipes but also in inclusions of both eclogite and peridotite. Diamondiferous peridotite generally is thought to be a juvenile rock that crystallized at great depths very early in the history of the Earth, predating the formation of eclogite by many millions of years.

Table 2: Ages of Some Diamonds and Emplacement of Associated kimberlite Pipes found in South Africa and Australia (From Kirkley et al, 1991, p.5).

Mine	Age Dates of Diamonds (Millions of Years)	Age Dates of Kimberlite (Millions of Years)	Type of Inclusion
Kimberley	~3,300	~100	Peridotite
Finsch	~3,300	~100	Peridotite
Finsch	1,580	~100	Eclogite
Premier	1,150	1,100-1,200	Eclogite
Argyle	1,580	1,100-1,200	Eclogite
Orapa	990	~100	Eclogite

As shown in Table 2, the differences in the ages of diamonds, their kimberlite host rocks and rock inclusions within some South African and Australian kimberlites indicate (1) that diamonds in peridotite inclusions are much older than those in eclogite inclusions, and (2) that those in eclogite inclusions, in turn, are generally much older than the kimberlite pipes in which the inclusions occur. As pointed out above, diamonds did not crystallize from the kimberlite magma but are secondary constituents acquired by the magma, along with foreign diamondiferous rock matter during its upward ascent from deep below the surface. This is probably one of the most important discoveries having a bearing on the origin of diamond deposits that has come to light in recent years.

Source of Carbon in Diamonds

The source of carbon from which diamonds formed has been a matter of controversy for over a century, and has ranged from coal to carbon dioxide and methane. However, it is now generally believed that there are actually two principal sources, as determined by studies of carbon isotopes, specifically the ratio of carbon-13 to carbon-12, expressed as d13C per mil (thousand).

Figure 6: Histograms showing the distribution of carbon isotope ratios for diamonds of eclogite and peridotite origins found in many geographic locations. N indicates number of analyses. The ratios for peridotite (in purple) range from -2 to -9, whereas those from eclogites (in blue) range from +3 to -34. (From Kirkley et al., 1991, p.13; courtesy Gems & Gemology).

Figure 6 shows the distribution of the isotope ratios from many geographic localities. The histogram in purple shows the distribution in peridotite (variety, hartzburgite); that in pale blue shows the distribution of the same carbon isotope ratios in eclogite. The short range of delta values for peridotite suggests that the diamonds may have come from a single source, and probably crystallized deep within the Earth; the wide range of values for diamonds in eclogite, on the contrary, suggests multiple sources, e.g. carbonate minerals and hydrocarbons consistent with those found on the Earth's surface. Eclogitic diamonds are thought to have originated at high temperatures and pressures from surface materials that were transported deeply downward into the Earth by the process now referred to as subduction (Kirkley, 1998). To understand this process and how it may have resulted in the formation of diamonds, it becomes necessary to know something about the internal structure of the Earth and "Plate Tectonics".

Structure of the Earth

Figure 7 shows that the Earth is made up of a number of spherical cells concentric about a dense nickel-iron Core, the inner (solid) part of which is illustrated in yellow, the outer (liquid) part in red. The core is very hot, about 7,000 degrees F., residual from the creation of the planet 4.5 billion or more years ago. The core is enclosed by a Mantle (in light brown) of material rich in iron and magnesium and with its original heat maintained by the decay of radioactive elements. The central core has a diameter of 2,440 Km; the mantle, a thickness, between the outer core and the surface, of 2,870 Km; and the Crust, illustrated in dark brown ; a thickness of only 8-70 Km. The total distance from the center of the Earth to the surface is 6,370Km.

Figure 7: Schematic illustration of the Structure of the Earth. (From ROCK ON Series No.1, 1994, p.7; Courtesy of the Ontario Ministry of Northern Development and Mines).

The Earth's Mantle

The mantle, between the outer core and the crust, makes up the bulk of the planet. Its inner part , the Asthenosphere, is molten and is in slow convective overturn, with cool material in the outer parts locally sinking and hotter material close to the core rising (Figure 8). The outer part of the mantle, the Lithosphere, is quite rigid, as we know rock to be, and forms most of the Crust.

Figure 8: Schematic section through the Earth's Mantle showing assumed convection cells. Magma is created where hot rising mantle material converges. Surface eruption results in a ridge of volcanic rock, and frictional drag of lateral currents causes the crust (the lithosphere) to split and spread apart. Where two parts of the broken crust converge, one part may be pushed under another and descend into the molten asthenosphere. (Modified after Arthur Holmes; courtesy of the United States Geological Survey).

The Earth's Crust

Figure 9: Block diagram illustrating the make-up of the Earth's crust (From Kirkley, 1998, p.50).

Figure 9 illustrates the current conception of the make-up of the Earth's Crust. The cooler and solid outer part of the mantle is the so-called Mantle Lithosphere. Overlying the mantle lithosphere in the oceanic areas is a capping of oceanic volcanic rocks like those found in the Hawaiian Islands in the Pacific, and in Iceland in the Atlantic. The continental masses, of relatively low density, developed earlier in the Earth's geologic history, and similarly overlie the Mantle Lithosphere. The Crust varies greatly in thickness, from about 8 Km in the oceanic areas to about 70 Km in the continental areas.

Plate Tectonics

The Earth's Crust, as shown in Figure 10, is not a continuous unbroken shell, but rather consists of several "tectonic plates" of various sizes, and which are in constant motion relative to one another because of the drag of convection currents assumed to occur in the underlying mantle asthenosphere (Figure 8).

Figure 10: Map of the World showing the boundaries of major pieces (Tectonic Plates) of the Earth's Crust. Note the Mid Atlantic Ridge between the American Plates and the Eurasian and African Plates and the East Pacific Rise between the Pacific and Nazca plates. (Courtesy of the United States Geological Survey).

The boundaries of some plates, generally in the Earth's oceanic areas, are marked by ridges of volcanic rocks that formed above upward currents of hot material in the Earth's mantle. These ridges, which may rise several thousands of meters above the general sea floor, are split by deep central rift valleys caused by the gradual separation or divergence of the opposing plates. The most extensive oceanic ridge is the Mid Atlantic Ridge, which separates the North American Plate from the Eurasian Plate in the Northern Hemisphere, and the South American Plate from the African Plate in the Southern Hemisphere (Figure 10). Another important ridge is the East Pacific Rise, which separates the huge Pacific Plate from the Nazca Plate. The rate at which divergent plates separate from one another has been determined by geophysical studies to be of the order of a few centimeters per year. This does not seem to be much, but over a period of tens of millions of years is of great magnitude, even accounting for the separation of continents once joined as a single land mass.

Opposite a divergent plate boundary, where two plates converge and collide with one another, compression may cause the plate of higher density to turn downward and gradually disappear into the Earth's mantle over millions of years along a so-called Subduction Zone (Figure 11). It is generally thought that this subduction process, operating throughout geologic time, accounts for the formation of the rock known as eclogite from the metamorphism of oceanic basalt, and for the crystallization of diamonds from introduced carbon. It may also play a role in the development of hot fluid kimberlite magmas, which bring these diamonds and those originally occurring in mantle peridotite to the surface by volcanic action (Kirkley et al., 1991).

Figure 11: Block diagram illustrating the subduction of an oceanic plate beneath a less dense continental plate. (From Kirkley et al., 1991, p.14; courtesy of Gems & Gemology).

The Origin of Diamonds

As the lithosphere descends towards the partially molten mantle during subduction, minerals making up the oceanic crust (basaltic volcanic rocks) recombine at high temperature and pressure at depth to form the rock known as eclogite, while any carbon present (as carbonate minerals or carbonaceous matter), is transformed into either graphite or diamond depending on the pressure-temperature conditions at a particular locale. As shown in Figure 12, above a depth of about 160 kilometers, graphite is the stable form of carbon; below this depth, diamond is the stable form. It is also thought that diamonds formed locally in the upper mantle early in the history of the Earth. Such early-formed diamonds may be present locally in juvenile peridotite of the upper mantle (Kirkley, 1998, p. 57-60).

Figure 12: Graphite-Diamond Stability Diagram. (From Kirkley et al., 1991, p.21; reproduced courtesy Gems & Gemology).

It was pointed out previously that diamondiferous kimberlite pipes appear to be most abundant in areas underlain by Archean Precambrian rocks or in the world's "Archons" (Figure 4). This has been explained by the lower geothermal gradient (change of temperature with depth) in Precambrian Shield areas than in oceanic areas and elsewhere (Figure 12). It is only in Shield areas, where the geothermal gradient is lowest that the conditions of temperature and pressure are such as to favour the formation of diamond rather than graphite at a minimum depth of 150-160 Km.

As subduction proceeds (Figure 11), mantle-derived kimberlite magma, charged with carbon dioxide, of lower density than its surroundings, may begin to rise toward the Earth's surface, possibly carrying along with it any pieces of diamondiferous eclogite and/or original diamondiferous mantle peridotite that it may have picked up during its ascent. As the magma works its way upward, the eclogite and peridotite inclusions tend to disintegrate and some of their contained diamonds are carried along independently by, and become distributed throughout, the rising magma. When the magma finally crystallizes, it forms a kimberlite pipe with occasional diamondiferous inclusions of one or both of eclogite and peridotite, rare disseminated diamond crystals, and pieces of country rocks.

Where investigated in productive mines, kimberlite pipes have been found to have their roots in wide bulbous or lenticular enlargements or "blows" occurring in narrow (1-3 m wide) kimberlite "feeder dikes". These feeder dikes appear generally to be the late-formed members of several dikes that crystallized from mantle-derived magma in parallel or sub-parallel fissures of prominent fracture zones that extend upward though the continental crust from the site or sites of magma generation (Mitchell, 1986, p. 105-135). The relationship between a typical diatreme and the "blow" of a late-formed member of related kimberlite dikes in a fracture zone is illustrated in Figure 13.

Figure 13: Schematic diagram illustrating a typical cone-shaped kimberlite pipe or diatreme. The diatreme, which is younger than one (precursor) dike, has its roots in a "blow" of a younger "feeder" dike. The breccia zone of fragmented rock at and below the crater represents final hydrovolcanic explosive activity. (Modified after Hawthorne, 1975;Mitchell, 1986, p.30; and Kirkley, 1998, p. 52).

The origin of the inverted cone-shaped kimberlite volcanic pipes is a matter of considerable controversy among geologists (Mitchell, 1986, p. 83-104) and several hypotheses have been proposed. One theory visualizes that the gas-charged kimberlite magma, traveling upward in a fissure, "pools" where it meets a barrier, locally widening the confining fissure as it increases in volume, becoming increasingly enriched in gases (mainly carbon dioxide and water) streaming from below. When the external pressure falls below that of the upward magma flow, the magma suddenly effervesces with the sudden escape of carbon dioxide, in much the same way as champagne does when the bottle is uncorked (Kirkley, 1998, p.51). The magma explodes violently and forces its way upward possibly through fractures of its own making. The released gaseous mixture, with its load of inclusions and any diamonds that happen to be present, is propelled toward the Earth's surface. The volcanic conduit is reamed out and enlarged upward by the explosive and furiously swirling mixture. While some geologists consider this to be a single violent event originating about 2-3 km below the surface; others think the process may be repetitive as new barriers to magma ascent are encountered and rising gases continue to accumulate, before final eruption at the Earth's surface (Mitchell, 1986, p.99-100).

As the hot magma rises upward, it eventually contacts near-surface ground waters, and finally breaches the rock surface with explosive violence (Mitchell, Roger H., 1986, p.101-102), resulting in the volcanic ejection of magma, country rock, dust, and cinders skyward, leaving behind a crater floored by a zone of brecciated or broken rock at the top of the diatreme, in which the remaining magma eventually cools and crystallizes as kimberlite.

The volcanic crater becomes encircled by a prominent "tuff ring" of fall-back ejected or pyroclastic material. This pyroclastic material quickly falls prey to erosion and is washed back into the crater (Figure 13) and into the area surrounding the volcano. Continuing erosion over many millions of years eventually exposes the diatreme itself to the "elements" and any diamonds present may be released into the alluvial environment, to eventually become concentrated into so-called "secondary" deposits such as those of Brazil, India and Namibia. Figure 5 shows the interpreted surface erosion levels of several mines relative to the present crater zone of the Orapa pipe, which, for some unknown reason, has escaped any significant erosion (Levinson, A., personal communication).

Diamond Exploration in Canada

Early in the 19th century, a few diamonds were found in the glacial drift in widely scattered places south of the Great Lakes and it was generally believed that these diamonds had been derived by the erosion of bedrock occurrences in the James Bay Lowlands (Hobbs, 1899). In the 1960s, three geologists of the Ontario Department of Mines (Brown et al., 1967) were assigned the task of further investigating this possibility. Their study of the direction of flow of the Pleistocene ice sheets from a compilation of the orientations of glacial striae on rock outcrops confirmed Hobbs' conclusion. Subsequent private-sector exploration by several mining companies did eventually result in the discovery of kimberlite. Since 1960 numerous kimberlite bodies have been found in northeastern Ontario and northwestern Quebec. Diamonds have been discovered, but most occurrences have yet to be shown to be of economic significance. De Beers has been encouraged, however, by the discovery of the "Victor" kimberlite pipe near Attiwapiskat in northwestern Ontario. This deposit currently is being tested by bulk sampling and does present some promise.

Figure 14: Flawless diamond. This 10.22 carat diamond from the Ekati mine is valued at over $500,000. Photo reproduced from the 1999-2000 company Annual Report. Courtesy of Diamet Minerals, Ltd.

Diamond exploration by several large mining companies commenced in the 1970s in northern Saskatchewan, and over 70 kimberlite bodies have been discovered. Some of these deposits contain diamonds, but, as in Ontario, nothing of commercial significance has been announced. Exploration also began in the Northwest Territories. Here numerous kimberlite pipes have been located. The first commercial deposits were discovered, in 1990, by geologist-prospector Chuck Fipke of Diamet Minerals, in the Lac de Gras area northeast of Yellowknife. Since then, then additional deposits have been found in the area, and two discoveries, the Etaki (Figure 14) and the Diavik, under the management of Broken Hill Propriety Limited (BHP) and Rio Tinto, respectively, are economically important as sources of gem quality diamonds. The Ekati mine discovered by Fipke actually commenced production in 1998; and the start of production at Diavik mine has been scheduled for early 2003. A third deposit, at Snap Lake 225 km northeast of Yellowknife was recently purchased by de Beers Canada Mining Inc., and is scheduled for production in 2006. It has been predicted that within a few years, the mines of the Northwest Territories will account for at least 10 percent by value of the World's annual production of gem quality diamonds, putting Canada in the same league as other major producing countries. No doubt the discovery of additional commercially viable deposits will be announced in the years to come, and so add to Canada's growing importance in the diamond trade.

Acknowledgments

The writer would like to acknowledge the following for their kind assistance in the preparation of this compilation, and for their permission to reproduce their published diagrams or photographs as illustrations: Alan Bronstein, Aurora Minerals; Melissa Kirkley, De Beers Canada Mining Inc.; Alfred Levinson, University of Calgary; John Jaszczak, Michigan Technological University; George Harlow, American Museum of Natural History; and Roger Mitchell, Lakehead University.

References

1. Brown, D.D., Bennett, G., and George, P.T., 1967: The Source of Alluvial Indicator Minerals in the James Bay Lowland; Ont. Geol. Survey, Misc. Paper No.7, p. 1-35.
2. Bruton, Eric, 1978: Diamonds; 2nd Edition, Clifton Book Co., Radnore, Pa.
3. Brummer, J.J., 1978: Diamonds in Canada; CIM Bull., Vol. 71, p. 64-79.
4. Dawson, J.B., 1986: Geographic and Time Distribution of Kimberlites and Lamproites; in Ross, J., Editor, Kimberlites and Related Rocks; Proceedings of the 4th International Kimberlite Conference, Perth, Australia, Geological Society of Australia Special Publication No. 14, Vol.2, Blackwell Scientific Publications, Oxford, pp.935-965.
5. Clement, C. R., 1982: A Comparative Study of Some Major Kimberlite Pipes in Northern Cape and Orange Free State; Ph.D. thesis, University of Cape Town.
6. Frisch, Emmanuel, 1998: The Nature of Color in Diamonds; in Harlow, George E., Editor, The Nature of Diamonds, Cambridge University Press in association with the American Museum of Natural History, p. 1-278.
7. Gent, R., 1992: Diamond Exploration in Saskatchewan; CIM Bull., Vol. 85, No. 956, p. 64-71.
8. Gurney, J.J.1989: Diamonds; in Ross, J., Editor: Kimberlites and Related Rocks; Proceedings of the 4th International Kimberlite Conference, Perth, Australia, Geological Society of Australia Special Publication No. 14, Vol. 2, Blackwell Scientific Publications, Oxford, p. 935-965.
9. Harlow, George E., Editor, 1998: The Nature of Diamonds; Cambridge University Press in association with the American Museum of Natural History, p. 1-278.
10. Hawthorne, J.B., 1975: Model of a Kimberlite Pipe; in Physics and Chemistry of the Earth, Vol. 9, p. 1-15.
11. Hobbs, W.H., 1899: The Diamond Field of the Great Lakes; Journal of Geology, Vol. 7, No. 4, p. 375-378.
12. Jasczak, J. A., 1995: Graphite, Flat, Fibrous, and Spherical; in Mendenhall, A., Greenberg, A., and Liebman, J, F., Editors, Molecules and Materials, Chapman and Hall, New York, p. 161-180.
13. Jasczak, J.A., 2001: Graphite and Diamond Crystal Structures; Seaman Mineral Museum, Michigan Technical University (See www.phy.mtu.edu)
14. Kirkley, Melissa B., 1998: The Origin of Diamonds; Earth Processes; in Harlow, George E., Editor: The Nature of Diamonds, Idem., p. 48-65.
15. Kirkley M.B., Gurney, John J., and Levinson, A., 1991: Age, Origin, and Emplacement of Diamonds: Scientific Advances in the Past Decade; Gems & Gemology, Vol. 27, No.1, p. 2-25. (Also in CIM Bull. , Vol. 85, No. 856, 1992, p. 48-57.)
16. Levinson, A.A. and Cook, F.A., 2000: Geological Knowledge: A Key to the Future of the Diamond Industry; Geoscience Canada, Vol.47, No.1, p. 19-22.
17. Levinson A.A., Gurney J. J., and Kirkley, M.B., 1992: Diamond Sources and Production: Past, Present, and Future; Gem & Gemology, Vol. 28, No. 4, p. 234-254.
18. Levinson, A., 1998: Diamond Sources and Their Discovery; in Harlow, George E., Editor, The Nature of Diamonds, Idem., p. 72-104..
19. Mitchell, R.H., 1986: Kimberlites: Their Mineralogy, Geochemistry, and Petrology; Plenum Press, New York, p. 1-441.
20. Mitchell, R.H., 1991: Kimberlites and Lamproites: Primary Sources of Diamond; Geoscience Canada, Vol. 18, No. 1, p. 1-16.
21. Pell, J.A., 1998: Kimberlites of the Slave Craton, Northwest Territories, Canada; Geoscience Canada, Vol. 24, No. 2, p. 77-78.
22. Picton, J., Okoenov U., Rothwell, J.R., and Levinson, A.A., 1999: Diamond Production in the 21st Century; Gems & Gemology, Vol. 25, No. 3, p. 114-115.
23. ROCK ONTARI0 Series No.1, 1994; Ontario Ministry of Northern Development and Mines, p. 1-89.

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Copyright © 2002 Edgar G. Pye
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