Saturday, November 13, 2010

Exploration, Mining, Milling, Gemology & Uses of Diamond


Raw diamonds from Arkansas (photo from Glenn Worthington).






Kimberlite pipes erupt as violent volcanoes - the magma, as it weathers, releases diamonds and tracer minerals such as chromian diopside, pyrope garnet, picroilmenite, chromite, etc. into streams where they can be panned and traced back to the source rock. While panning for these indicator minerals, sometimes other valuable minerals are found including diamond, gold, ruby, sapphire.

EXPLORATION
Cost figures for annual diamond exploration amounts to tens of millions of dollars. Capitalization costs for the development of the Ekati diamond mine in the Northwest Territories were more than $800 million. When an exploration program is initiated, priority is given to areas of highest favorability and best access for finding ‘traditional’ diamondiferous host rocks. For example, commercial diamondiferous kimberlites are considered to be restricted to cratonic regions that have been relatively stable for 1.5 Ga (billion years). Janse (1984, 1994) suggested that cratons be separated into areas of favorability. He suggested separating these regions into Archons,Pprotons and Tectons. This method for outlining regions of favorability provides an excellent first option priority list that has withstood through time.


Archons (Archean basement stabilized >2.5 Ga ago) are considered to have high potential for discovery of commercial diamond deposits hosted by kimberlite and possibly by lamproite and lamprophyre.  Protons (Early to Middle Proterozoic [2.5–1.6 Ga] basement terrains) have moderate potential for commercial diamond deposits in kimberlite and high potential for commercial diamond deposits in lamproite and possibly lamprophyre. Tectons (Late Proterozoic [1.6 Ga–600 Ma] basement terrains) are considered to have low potential for commercial diamondiferous host rock. Unconventional diamond deposits (such as high-pressure metamorphic complexes, astroblemes, subduction-related complexes and volcaniclastics) may occur in tectonically active terrains, but the methods for exploration for these are not well defined, nor are the parameters that identify high from low priority established.

Following selection of a favorable terrain, topographic and geological maps, aerial and satellite imagery, and aerial geophysical data are examined. Unusual circular depressions, circular drainage patterns, noteworthy structural trends and vegetation anomalies are noted. For example, Hausel (2009a,b) identified several targets using available software on the Internet including Google Earth, Virtual Earth and others. Geophysics is used to search for distinct (“bull’s eye”) conductors and magnetic anomalies. Geochemical data are examined for Cr, Ni, Mg, and Nb anomalies.

Stream sediment sampling. One of the primary methods used in diamond exploration is stream sediment sampling programs designed to search for ‘kimberlitic indicator minerals’ (pyrope garnet, chromian diopside, chromian enstatite, picroilmenite, chromian spinel, and of course diamond).  Diamond targets are small and may range from diatremes of several acres to narrow dikes and sills.  Diamond-bearing kimberlites and lamproites typically contain abundant soft serpentine with resistant mantle-derived xenocrysts and xenoliths.  The serpentine matrix tends to decompose releasing distinct mantle-derived ‘kimberlitic indicator minerals’ into the surrounding environment.  The indicator minerals may be carried downstream for hundreds of yards, or a few or many miles depending on the climatic and geomorphic history of the region.  Diamonds however, are thought to be carried considerable distances – in some cases, hundreds of miles.  The indicator minerals may provide a trail leading back to the source.

Panning for diamonds at undisclosed location in Wyoming
In the planning stages of stream-sediment sampling, proposed sample sites are initially marked in prominent drainages on a topographic map using a sample spacing designed to take advantage of the region.  In arid regions, sample spacing should take advantage of relatively short transport distances of the indicator minerals.  In subarctic to arctic areas (i.e., Canada, Sweden, Russia, etc) sample density may be considerably lower owing to the greater transport distance and the logistical difficulties of collecting samples.  Anomalous areas are then re-sampled at a greater sample density.

The traditional kimberlitic indicator minerals are rare to non-existent in lamproite, thus other minerals (zircon, phlogopite, K-richterite, armalcolite, priderite) may be considered that unfortunately have low specific gravity, poor resistance, and are potentially difficult to identify. The better indicators for diamondiferous lamproite have been diamond and magnesiochromite. 

To take advantage of the dispersion of kimberlitic indicator minerals, the size of samples are determined based on the environment.  For example, where there is a general lack of active streams, much larger samples are taken compared to regions with active drainages.  In areas with juvenile streams, samples are often panned on site to recover a few pounds of sample concentrates.  Recovered indicator minerals are tested for chemistry using an electron microprobe to identify those that have higher probability of originating from the diamond stability field.  The data are plotted on maps to facilitate evaluation.

Geomorphology. Kimberlite and olivine lamproite are often pervasively serpentinized, making outcrops the exception rather than the rule.  In many cases, geomorphic expressions of pipes are subtle to unrecognizable. The Kimberley pipe in South Africa was expressed as a slight mound, but nearby pipes (i.e., Wesselton pipe) were expressed as subtle depressions. Others produced subtle modifications of drainage patterns (Mannard 1968). In the subarctic, where glaciation has scoured the landscape, some kimberlites produce noticeable depressions filled by lakes. In the semi-arid region of Wyoming and Colorado, a few kimberlites are expressed as slight depressions, but most blend into the surrounding topography and may or may not have a subtle vegetation anomaly.

Depressioin over Maxwell diamondiferous kimberlite, one
of a few hundred untested diamond pipes in Colorado,
Wyoming and Montana.
In the Ellendale field, Western Australia, serpentinized diamondiferous olivine lamproites lie hidden under a thin layer of soil in a field of well-exposed leucite lamproite volcanoes. The Argyle lamproite and diamondiferous lamproites in the Murfreesburo area of Arkansas were also hidden by a thin soil cover.

Lineaments. Many kimberlites and lamproites are structurally controlled (Hausel and others, 1979; 1981; Macnae, 1979, 1995; Nixon, 1981; Atkinson, 1989; and Erlich and Hausel, 2002).  Controlling lineaments and fractures may be indicated by alignment of a cluster of intrusives or by the elongation of a pipe. In Lesotho, South Africa, Dempster and Richard (1973) reported a close association of kimberlite with lineaments: 96% of kimberlites were found along WNW trends, and many pipes were located where the WNW trends intersected WSW fractures.


During recent exploration, I was able to identify more than
300 cryptovolcanic structures in and surrounding the State
Line district. Many of these are likely kimberlites, but remain
untouched, such as these depressions in Colorado that sit
on distinct lineaments and adjacent to diamondiferous
kimberlites.
Lamproites in the Leucite Hills, Wyoming are found on the flank of the Rock Springs uplift where distinct E-W fractures lie perpendicular to the axis of the uplift (Hausel and others, 1995). In the West Kimberley province of Western Australia, some lamproites are spatially associated with the Sandy Creek shear zone, a Proterozoic fault. In the Ellendale field, several lamproites lie near cross faults perpendicular to the Oscar Range trend, even though the intrusions do not appear to be directly related to any known fault. The Argyle lamproite to the east has an elongated morphology suggestive of fault control, and intrudes a splay on the Glenhill fault (Jaques and others, 1986).

Remote Sensing. Kingston (1984) reported remote-sensing techniques are widely used to search for kimberlite: these include conventional and false color aerial photography, LANDSAT multispectral scanner satellite data, and airborne multispectral scanning.  Multispectral scanning data is used to identify spectral anomalies related to Mg-rich clays (i.e., montmorillonite), carbonate, and other material with silica deficits.  Image enhancement techniques (contrast enhancements, ratios, principal components and clustering) produce images that are optimum for discrimination of kimberlite and olivine lamproite soils. These and other photo images can be used to search for vegetation and structural anomalies. Airborne multispectral scanning provides higher resolution than LANDSAT, and can also be used to measure reflectance qualities of clay in soil.

Many pipes and dikes possess distinct structural qualities or vegetation anomalies that may allow detection on aerial photographs. Mannard (1968) reported kimberlites in southern and central Africa were identified on aerial photographs on the basis of vegetation anomalies, circular depressions or mounds, and/or tonal differences. Low-level aerial photographs (both conventional and false color infrared) have been used to locate kimberlite in the USSR (Barygin 1962) and in the US (Hausel and others, 1979, 2000, 2003).
Geophysical Surveys. Geophysical exploration has been successful in the search for hidden kimberlite and lamproite (Litinskii 1963a, b; Gerryts 1967; Burley and Greenwood 1972; Hausel and others, 1979, 1981; Patterson and MacFadyen 1984; Woodzick, 1980), particularly in districts where kimberlites have previously been discovered.  Contrasting geophysical properties are often favorable for distinguishing kimberlite, lamproite and minette from country rock.
INPUT™ airborne surveys are effective in identifying both serpentinized and weathered kimberlite owing to the combination of conductivity and magnetics used in INPUT™.  Rock exposures of kimberlite may yield magnetic signatures but are poorly conductive, while deeply weathered kimberlites are conductive but poorly magnetic.


Geonics EM31 worked very well over
buried and exposed weathered
conductive kimberlite.
Because of the relatively small size of the diamond host rock, close flight-line spacing is necessary. In an airborne INPUT™ survey over the State Line district, Wyoming, a flight-line spacing of 640 feet (200 m) effectively detected several kimberlites and identified distinct magnetic anomalies interpreted as blind diatremes (Patterson and MacFayden 1984). An aeromagnetic (200–400m line spacing) survey flown over parts of northeastern Kansas identified several anomalies, some of which were drilled resulting in the discovery of previously unknown kimberlites (i.e., Baldwin Creek, Tuttle, and Antioch kimberlites) (Berendsen and Weis, 2001).  Flight line spacings of 160 to 320 feet (50-100 m) were used for INPUT™, magnetics and radiometrics in the Ellendale field, Australia (Atkinson 1989; Janke 1983; Jaques and others, 1986). The olivine lamproites yielded distinct dipolar magnetic anomalies.

In the Yakutia province, Russia, ground magnetic surveys were used where differences between the magnetic susceptibility of kimberlite and the carbonate sedimentary country rock was high.  Anomalies as great as 5,000 gammas were also successfully detected from airborne surveys (Litinskii 1963b).  In Mali, West Africa, the magnetic contrast between kimberlite and schist and sandstone country rock resulted in 2,400-gamma anomalies over kimberlite (Gerryts 1967). In Lesotho, anomalies over kimberlite were comparable with those in the Yakutia province (Burley and Greenwood 1972).

Fipke and others (1995) indicated that barren peridotite phases in Arkansas yielded magnetic highs, but the diamondiferous phases were not detected.  In northeastern Kansas, Brookins (1970) reported large positive (550 to 5,000 gamma) and negative (0 to –2,800 gamma) anomalies over some kimberlites emplaced in regional sedimentary rocks. The sedimentary rocks had relatively low magnetic susceptibility making magnetic surveys an effective method for exploration.

Most kimberlites in the Colorado–Wyoming State Line district yielded small complex dipolar anomalies in the range of 25 to 150 gammas, with some isolated anomalies of 250 and 1,000 gammas (Hausel and others, 1979). Blue ground kimberlite tends to mask magnetic anomalies. In the Iron Mountain district, where much of the kimberlite is relatively homogeneous, massive hypabyssal-facies kimberlite, only weak to indistinct magnetic anomalies were detected (Hausel and others, 2000).

Gem-quality diamonds recovered from Wyoming kimberlite in 1979. Largest stone is about 1 carat.
Magnetite is replaced by hematite during weathering masking near-surface magnetic affinity. Clay produced during weathering promotes water retention, thus weathered blue ground over kimberlite may produce vegetation anomalies that are susceptible to detection by electrical methods.  For example, resistivity surveys in the Colorado–Wyoming State Line district detected apparent resistivity of 25 to 75 ohm-m over weathered kimberlite, compared with 150 to 2,250 ohm-m in the country rock granite (Hausel and others, 1979).

Resistivity of weathered lamproite may be lower than that of country rock, owing to the conductive nature of smectitic clay relative to illite, kaolinite and other clay minerals (Gerryts 1967; Janke 1983).  However, the Argyle olivine lamproite yielded moderate to strong resistivity anomalies (40-100 ohm/m) compared to the surrounding country rock (200 ohm/m) (Drew 1986).

Biogeochemical and Geochemical Surveys. Kimberlite and lamproite are potassic alkalic ultrabasic igneous rocks with elevated Ba, Co, Cr, Cs, K, Mg, Nb, Ni, P, Pb, Rb, Sr, Ta, Th, U, V and light rare earth elements (LREE).  The high Cr, Nb, Ni, and Ta may show up in nearby soils (Jaques 1998), but dispersion of these metals in soils is not extensive.  Stream-sediment geochemistry generally is not useful due to efficient dispersion of most metals in streams.  In the Colorado–Wyoming State Line district, Cominco American outlined several known kimberlite intrusives on the basis of Cr, Nb, and Ni soil geochemical anomalies.  However, dispersion patterns were restricted and of little use in exploration in this terrain.


Classical indicator minerals used to find kimberlite include picroilmenite,
chromite, chrome diopside, and spessartine and pyrope garnets. The
purple garnets are typical G10 (diamond-stability) peridotitic garnets
and the yellow orange are characteristic eclogitic garnet.
Gregory and Tooms (1969) found that Mg, Ni, and Nb anomalies did not extend farther than 0.36 mile (0.6 km) from the Prairie Creek lamproite, Arkansas.  Haebid and Jackson (1986) noted that soil geochemical anomalies (Co, Cr, Nb, Ni) were detected in sand and soil immediately above lamproite vents in the West Kimberley province, Australia.  Such anomalies could prove useful in the search for hidden olivine lamproites.  Gregory (1984) used lithochemistry to distinguish olivine lamproite from leucite lamproite on the basis of Mg, Ni, Cr, and Co ratios.

Bergman (1987) suggested that olivine lamproites are generally enriched in compatible elements relative to leucite lamproites as a result of the abundance of xenocrystal olivine in the former. Barren lamproites contain elevated alkali and lithophile contents (K, Na, Th, U, Y, and Zr) relative to diamondiferous (olivine) lamproites.  Diamondiferous lamproites possess twice the Co, Cr, Mg, Nb, and Ni, and half the Al, K, Na and as barren lamproites (Mitchell and Bergman, 1991), and lamproites have anomalous Ti, K, Ba, Zr, and Nb compared to most other rocks.  These components may favor the growth of specific flora or may stress local vegetation (Jaques 1998). The Big Spring vent, West Kimberley, Australia, is characterized by anomalous faint pink tones that reflect the growth pattern of grass on the vent (Jaques and others, 1986).

Many kimberlites in the Colorado–Wyoming State Line district will not support growth of woody vegetation resulting in open parks over kimberlite in otherwise forested areas.  These same kimberlites may support a lush stand of grass delineating the limit of the intrusive.  Distinct grassy vegetation anomalies over kimberlites in the Iron Mountain district were used successfully to map many intrusives (Hausel and others, 2000). The anomalies are especially distinct following a few days of rain in the late spring.

Some Siberian kimberlites support denser stands of larch (Larix dahurica) and abundant undergrowth of shrub willow (Salix) and alder (Alnus) compared to surrounding Cambrian carbonates. In central India, trees over the Hinota pipe are healthier, taller, and denser than those in the surrounding quartz arenite. This may be attributed to greater availability of K, P, micro-nutrients and water.


Vegetation anomaly followed over kimberlite at Iron Mountain, Wyoming.
The kimberlite underlies the thicker vegetation to the left and granite to the
right. We also noticed the presence of carbonate in the soil (left), with
periodic indicator minerals and also abundant diamondbacks (rattlers).
Vegetation over the Sturgeon Lake kimberlite in Saskatchewan was tested for 48 elements; the kimberlite showed a consistent spatial relationship with Ni, Sr, Rb, Cr, Mn and Nb, and to a lesser extent with Mg, P and Ba, and relatively high Ni concentrations occurred in dogwood twigs. In hazelnut twigs, Cr levels were greater than 15 ppm near the kimberlite but only 5 to 8 ppm elsewhere, and Nb was higher in hazelnut twigs.  Sr and particularly Rb were relatively enriched in some plant species on kimberlite. The Sr was probably derived from the carbonates associated with the kimberlite, whereas the Rb was derived from phlogopite.  Ni, Rb and Sr distribution and Cr enrichment associated with Mn depletion in the twigs could be used to identify nearby kimberlite.

MINING & MILLING

Economic diamond deposits depend on the average price of stones, the amount of waste material removed, mining methods, company politics, socioeconomics of the area, and many other factors. For example, a diamond deposit may be mined at a comparatively lower cost in a third world country due to the availability of an inexpensive labor force, although constructing an infrastructure in such an area could offset some of these benefits. Whereas in the US, high labor and mining costs require higher-value ore for commercial operation, however, an infrastructure may already be available nearby.


Lost Lake volcanoclastic structure (circular depression with structural
control and white carbonate-rich soil in center.
More than half of the world’s natural diamonds is mined from kimberlite and lamproite and the rest are mined from placers. Economic cutoff grades are typically >0.10 carats/tonne (Jaques 1998), but the grade is highly dependent on mining costs and the value of the recovered diamonds. Thus the economic cutoff grade will vary after considering these factors. Average ore grades range from a high of 6.8 carats/tonne for Argyle to a low of about 0.15 carat/tonne for Prairie Creek, Arkansas. Some of the rich crater facies lamproite mined at Argyle yielded grades as high as 20 carats/tonne. Most economic deposits yield >30% gem-quality diamonds.

Commercial deposits include narrow dikes to pipes of 100 to 5000 feet (30-1,500 m) across. Pipes range in surface area from 2.5 to 370 acres (1-150 ha) averaging about 30 acres (12 ha) (Jaques 1998). Diamond mines possess resources in the neighborhood of >10 million to 350 million tonnes of ore and the richest deposits contain reserves measured in the hundreds of millions of carats that are valued in the billions of dollars.

One of the first grease tables we constructed at the Wyoming Geological
Survey for my diamond projects. Diamonds are non-wettable and
will stick to grease. Other minerals will wash over the grease. We constructed
this using an old Wilfley table (we actually found in the trash on the UW
Campus) drive because the state was too cheap to give us any money
even though they were taking in $100s of millions in mineral taxes.
Open pit diamond mines are typically designed to recover as little as 100,000 tonnes to more than 10 million tonnes of ore per year.  Annual diamond production may range from several thousand carats to a few million carats.  For example, the Finsch mine, South Africa, produced about 5 million carats annually between 1981 and 1991, whereas annual diamond production for the extremely rich Argyle lamproite reached a record 39 million carats during the height of operation.

Even so, the average weight of diamonds from the Argyle lamproite was small (only <0.1 carat), and those from Ellendale lamproites are only 0.1 to 0.2 carat (Mitchell and Bergman 1991). The largest reported diamond from the Prairie Creek lamproite is 40.42 carats (Hausel 1998).  However, diamonds from some kimberlites are extraordinary: the largest diamond ever recovered was fist size and was mined from the Premier kimberlite, South Africa, and weighed 3,106 carats.



Diamond Extraction mills were constructed in the Colorado Wyoming State
Line district at the Sloan kimberlite and on the Kelsey Lake kimberlite
(above). Another portable mill was constructed on a trailer used at
Kelsey Lake and a fourth was built along the northern edge of Ft. Collins
by Cominco American. None of these were well designed and all rejected
many diamonds. This problem was documented at Kelsey Lake when a
company interested in purchasing the mine tested mill rejects. The first sample
processed yielded several diamonds (including a 6.2-ct stone).
This problem was serious as it basically resulted in questions as to what the
actual diamond grades of kimberlites were. How many
 macrodiamonds were lost? Other gemstones (chrome diopside and pyrope
were all rejected at all four mills.
To evaluate a potential commercial diamond deposit, they must first be bulk sampled.  If favorable, additional bulk samples are used to assist in establishing ore grade maps to assist in a mine planning. Samples are taken on the surface and from drilling in order to achieve a three dimensional view of ore grades. If the pipe is considered to be economic, planning is completed for an initial open pit design and a mill placed near the pipe. Open pit mining typically proceeds from a spiral road developed from the rim of the pit toward the center of the pipe. As mining proceeds, the country rock is cut back in steps to aid in supporting the highwalls of the open pit. Mining in the pit may occur in an oval pattern, or in a polygonal pattern (Bruton 1979).

As mining continues and the pipe narrows at depth, the open pit will shrink to smaller and smaller diameters. Mining operations may ultimately continue underground using bulk recovery by block caving. However, less than 30% of diamond mines are continued underground. And to do so, the diamond ore must be relatively high value, because the cost of underground mining is considerably higher and the amount of ore recovered is considerably lower. Some kimberlites in Siberia and South Africa have been mined to depths of 3,540 feet (1,080 m). Open pits may have mine lives of 2 to 50 years (Jaques 1998).

Following recovery of rock mined from open pit operations, the ore is crushed and screened. Screening separates midsize from larger material rejects and from material too small to contain commercial diamonds. Decisions on the maximum screen size must weigh the cost of processing additional material with the loss of potentially priceless large diamonds.

The typical diamond mill has a basic flow sheet that begins with primary milling and continues to primary gravity concentration, secondary concentration, magnetic separation, attrition milling.  The final diamond extraction stage uses grease table, electrostatic separation, and/or x-ray fluorescence extraction (Bruton 1979). 

Placer mines are different. The size of a placer mine will vary from a small one-man operation to a full-scale mine using bulldozers, scrapers and/or dredges.  Paystreaks are identified in streams or beaches: mining is then completed using small-scale or large-scale earth moving equipment (Bruton 1979).

GEMOLOGY

The primary monetary value for diamond is as gemstones. Diamond prices vary considerably. There are approximately 5,000 diamond categories with prices that vary from $0.5/carat up to several tens of thousands of dollars/carat (for large uncut or colored “fancy” diamonds) (Miller 1995).  Many faceted diamonds are worth many times an equivalent weight in gold or platinum.  Rough gemstone diamonds have values as high as 100 or more times that of industrial diamonds. After the diamonds are faceted, the value of the gem can increase another 10 to 100 fold, and the final placement of a stone in jewelry will again add another increase in the value of the stone. Thus any mining operation should consider not only recovery of the gems, but also the fashioning of the gems and marketing.


14.2 carat diamond recovered at Kelsey Lake (Photo
courtesy of Howard Coopersmith.
Diamonds include some of the more valuable gemstones on earth, and arguably are the most valuable of all commodities based on weight. For example, some Argyle pink diamonds have sold for as much as $1 million (US) per carat (one carat weighs only 0.2 grams [0.007 ounce]). Thus, an equivalent weight in gold would only be worth $2.80 (at $400/ounce)!  The extreme value of diamond is due to its mystique, rarity, extreme hardness, high refractive index and dispersion that can result in brilliant gems with distinctive “fire” when faceted and polished.

Four general types of natural commercial diamonds are recognized. These are gem (well-crystallized and transparent), bort (poorly crystallized, gray, brown translucent to opaque), ballas (spherical aggregates formed of many small diamonds), and carbonado (opaque, black to gray, tough, and compact). Gem diamonds are further subdivided into gem and near-gem (low-quality gemstones).

The fashioning of diamond “rough” into a finished gem may require up to six steps that include marking, grooving, cleaving, sawing, girdling, and faceting (Hurlbut and Switzer 1979). Whether or not all of these steps are used depends on the size, shape, and quality of the rough stone. There are three traditional types of cuts: step-, rose-, and brilliant-cut (Milashev 1989).

620 carat diamond from African Craton.
The value of finished gem diamonds is judged by the “four C’s” known as cut, clarity, carat weight, and color. The cut of a diamond can increase its value tremendously, and the better proportioned, polished and faceted, the greater its value. When the girdle (base) and table of the diamond are proportioned correctly, the diamond will exhibit greater fire and brilliance.

Diamonds may be graded using the Gemological Institute of America’s color grading system.  This ranges from D (colorless) to X (light yellow). Each letter of the alphabet from D to X shows a slight increase in yellow tinge that is generally not apparent to the untrained eye (Hurlbut and Switzer 1979).  Fancy diamonds are separated from colorless diamonds into groups based in color and intensity (Bruton 1978).  Clarity is determined by the presence or absence of blemishes, flaws, and inclusions. One typical grading system ranges from Fl (flawless) to I3 (imperfect) with intermediate grades of VVS1 (very, very slightly imperfect), VVS2, VS1, VS2, SI1, SI2, I1, and I2.

USE
The diamond industry is a multi-billion dollar mega-industry. The unique physical and optical properties of diamond also make it indispensable and irreplaceable for many industrial uses in addition to personal adornment in jewelry.

Due to its extreme hardness, industrial and synthetic diamonds are used extensively as abrasives in grinding, drilling, cutting and polishing.  Diamond also has chemical, electrical, optical and thermal characteristics that make it the best material available for wear and corrosion resistant coatings, special lenses, heat sinks in electrical circuits, wire drawing, drilling, and many other advanced technologies. One significant future application will be in computer chips due to their unmatched thermal conductivity and resistance to heat, since a tremendous amount of heat can pass through diamond without causing damage.


Wyoming diamond with distinct trigons on its surface.
Today's speedy microprocessors run hot - upwards to 200oF, and microprocessors can't run much faster without failing. Diamond microchips would be able to handle much higher temperatures allowing them to run at speeds that would liquefy ordinary silicon. But manufacturers have not considered using the precious stone, because it has never been possible to produce large diamond wafers affordably.  The Florida-based company Gemesis and the Boston company Apollo Diamond plan to use the diamond jewelry business to finance attempts to reshape the semiconducting world.

At room temperature, diamond is the hardest known material with the highest thermal conductivity of any material. Even though diamond is more expensive than competing abrasive materials such as garnet, corundum, and carborundum, diamond has proven to be cost effective in several industrial processes as it cuts faster and lasts longer than rival material. Synthetic industrial diamond is superior to natural industrial diamond in that it can be produced in unlimited quantities and tailored to meet specific applications. Consequently, manufactured diamond accounts for more than 90% of the industrial diamonds used in the US.

According to the US Geological Survey, much synthetic industrial diamond produced domestically was used as grit and powder. The major use was in machinery (27%), mineral services (18%), stone and ceramic products (17%), abrasives (16%), contract construction (13%), transportation equipment (6%), and miscellaneous uses (3%). Industrial diamonds are consumed in the production of computer chips, in construction, in the manufacture of machinery, for mineral and energy exploration and mining, stone cutting and polishing, in transportation (infrastructure and vehicles). Stone cutting along with highway construction and repair are some of the largest users of industrial diamond.

Diamond has one significant limitation in industrial use: it reacts with iron at high temperature causing the diamond to revert to graphite resulting in high rates of wear. In an iron rich environment, diamond may be uneconomical to use in comparison to other conventional abrasives, i.e., aluminum oxide, silicon carbide, and boron nitride. Even though these are considerably softer than diamond, they are suitable as high performance abrasives on ferrous work-pieces.

Diamond use has increased in both jewelry and industrial applications. One reason for the increase is due to the development of diamond synthesis technology making it possible to produce diamond abrasives for specific applications. In the past the only option was to use natural diamond, which had to be sorted by size and crushed, or by surface treatment such as rounding.  However, synthetic diamond abrasives can now be produced under a controlled environment such that the shape of the crystal can be made irregular and sharp.

Diamond has many potential exotic applications. For example, the Venus probe was fitted with a transparent diamond window since diamond was the only material transparent to infrared light which could withstand the extreme cold and vacuum of space and the extreme high temperatures and atmospheric pressures of Venus’s atmospheric (temperatures as high as 920°F, and pressures a hundred times that of earth) (Ward, 1979). Another exotic use gives a whole new meaning to the family jewels. LifeGem in Illinois started manufacturing diamonds from cremated human ashes for jewelry for surviving relatives. The cost for a family jewel is reported to be more than $2000 for a 0.25 carat stone.

Arkansas diamonds (photo from Glenn Worthington).
Diamond has applications in high-energy physics. Diamond windows are used in high-power lasers due to the high thermal conductivity, low absorption coefficient and a low value of temperature coefficient of refractive index.  Diamond anvils are used in high-pressure research, where pressures in excess of 4 megabars are needed.  Such ultra-high pressure research can simulate conditions in the core of the earth and planets. 

Diamonds are also used in dental drills and surgical blades, and provide cutting edges that are many times sharper than the best steel blades.  Since diamond has the greatest thermal conductivity of any material, pinhead size gold-coated diamonds are used in high capacity miniature transmitters that carry television and telephone signals.

Synthetics. Synthetic gem diamonds and simulants are becoming more common on the marketplace. These include cubic zirconia and mossainite. Mossainite has twice the fire of natural diamond, is doubly refracting (unlike diamond and cubic zirconia which are singly refractive) and has a hardness of 9.25 –thus both mossainite and cubic zirconia can easily be scratched by diamond. Double refraction is detectable in mossainite when viewing the front of the stone.  The back facets will appear to be duplicated due to the double refraction –except when viewing down the optic axis where light is singly refractive. The optic axis is usually perpendicular to the table of mossianite, thus one must observe the back facets through another facet to see evidence of double refraction.

Synthetic gem-quality diamonds may be produced in about 24 hours. Some stones weighing up to 3 carats have been produced for a few hundred dollars (uncut). Most are yellow, but some Russian stones are clear. In 1971, facet quality synthetic diamonds were grown by General Electric that is nearly colorless (0.3 and 0.26 carats).   

The colorless gemstones caused concern in the jewelry trade. Diamond simulants can be detected by a simple thermal conductivity test, but most jewelers were unprepared to distinguish faceted synthetic diamond from natural faceted diamond. Thus, DeBeers developed a diamond verification instrument known as DiamondView which uses ultraviolet fluorescence to distinguish colorless natural diamond from synthetic diamond. In addition, many synthetic diamonds examined by GIA contain metallic inclusions in high enough abundance that they are able to attract a magnet. Non-faceted synthetic diamonds exhibit a unique crystal habit of a cuboctohedron with a flat base. Synthetic diamonds also exhibit unusual dendritic and striated surface patterns.  According to Shigley and others (1997), because of the technological challenges and high cost of production, it is unlikely that fashioned gem-quality diamonds larger than 25 points will impact the gemstone industry in commercial quantities. 

FUTURE OF THE DIAMOND INDUSTRY
Diamonds have intrinsic value because of unique hardness, transparency and thermal conductivity. Diamonds will be needed as long as we have industrialized nations. Without any foreseeable major economic disasters, the future of the diamond industry should remain strong. 

As science and industry advance, additional applications will likely be found for diamond in the electronics industry. Demand for diamonds for drilling in exploration for oil, gas, and minerals, as well as in the construction industries is anticipated to increase.  Some technological advances will demand both natural and synthetic diamond in the future. 

However, the continual decline in new mines and decline in mineral and oil and gas exploration in the US will undoubtedly affect demand for industrial diamonds, but this decline will probably be more than offset by progressive nations where environmental extremism is not rampant.  In particular, the economic boom in China will result in increased demand for diamonds for industrial and engineering applications. 

For many years, the gem diamond industry was controlled by DeBeers: a monopoly so powerful that the diamond industry and DeBeers were thought by many to be the same. But the discovery of significant diamond resources outside of Africa has diminished DeBeers’s monopoly. 

The first real threat to the monopoly occurred with the discovery of significant gem-diamond deposits in the USSR in the 1950s, but communistic bureaucracy could not compete with South Africa, and the Soviet diamonds did not greatly affect the market (Erlich and Hausel, 2002). A major diamond discovery (Argyle) in Western Australia in the 1980s started the real first erosion of the monopoly.  However, the Argyle deposit, though rich in diamonds was dominated by industrial stones, and the gemstones recovered from the mine were small. Even so, the Australian company Ashton Mining, decided to market their own production.   

Some gemstones produced by Argyle included rare pink diamonds.  Marketing strategies by the Australians were brilliant, resulting in the Argyle Pinks becoming some of the more valuable gemstones on earth.  A large population of the Argyle diamonds was also brown to greenish brown that had been considered by the jewelry trade as industrial or near gem.  These were marketed as burgundy and cognac diamonds, and the marketing strategy effectively resulted in these stones becoming highly sought gemstones. Even so, many of the Argyle diamonds were small, and required special cutting skills taken up gem cutters in India and Sri Lanka.

The next major diamond discoveries were made on the North American Craton.  This is the largest Craton with the largest Archon core in the world. Based on the shear size of the craton, and the many finds of detrital diamonds in glacial moraines, this craton should have been a high-priority target for diamond exploration groups.  But for many years, the North American craton was ignored. 

The discovery of economic diamond deposits in this craton was the result of unrelenting prospecting by geologist Chuck Fipke. The discovery set off the greatest rush in modern history, and resulted in the development of a diamond industry in Canada. 

Part of a day's diamond recovery from Argyle, Austraila in 1986
Diamond production began in Canada following the capitalization of BHP’s Ekati mine at more than $700 million. A few other mines have now been developed and in April 2004, the value of diamond production from Canada surpassed that of South Africa! This occurred in 6 short years. In the future, we can expect many more discoveries of diamondiferous kimberlite in the North American Craton. To date, as many as 500 kimberlites and some unconventional host rocks have been identified in Canada –nearly 50% contain diamonds; thus the North American craton could easily become the number one source of diamonds in the near future. 

The North American craton extends across the Canadian border into the United States where several diamond deposits have been found.  Even so, much of the terrain in the US has not been prospected, or only partially explored for diamonds. Many exploration targets remain inexplicably unexplored. To date, only two deposits have been mined for diamonds in the US – one in the Colorado-Wyoming State Line district, and another near Murfreesburo, Arkansas.  Little is expected to be done in the US because of the current political climate and widespread environmentalism.

Diamond in matrix of Chinese kimberlite (GemHunter collection).
Diamond exploration in the near future will continue to focus on Canada, where the geology and political climate is favorable.  In addition to discoveries of diamonds in kimberlite and some lamproites, one might anticipate additional diamond discoveries in some unconventional host rocks such as minettes, alnoites, other lamprophyres, komatiites, and in particular, subduction zone related breccias.

One concern that has risen is the production of relatively inexpensive gem-quality diamonds.  However, gem-quality natural diamonds are also relatively inexpensive until they are faceted and mounted in jewelry.  Overall, the synthetic gemstones may cost less, but the price difference may not great.  And it is human nature to want an original, or the real thing, rather than an imitation.  Gem-quality synthetic diamonds will probably not affect the jewelry market.

CONCLUSION
With the current trend of investment, exploration and progressive pro-mining atmosphere, it is anticipated that Canada will be a leading diamond producer for decades to come. The shear size of the North American Craton allows one to predict Canada to become the world’s primary source for diamonds in the future. Unless there is a major change in attitude of the US government and population, little is expected to be produced in the US, even though parts of the US (i.e., Superior and Wyoming Provinces) are underlain by this craton. The importance of the North American Craton in the future of the diamond industry has resulted investments of hundreds of millions of dollars in exploration in North America.



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Diamond Deposits: Distribution & Production

DISTRIBUTION & PRODUCTION
Diamond Production
Diamonds are mined from at least 20 countries; the leading producers of natural diamond are Australia, Botswana, Canada, South Africa, Russia and Zaire. The World Diamond Council estimated that natural diamond production in 1999 was more than 111 million carats valued at $7.4 billion (US). In 2000, diamond production was estimated at 110 million carats valued at $7.9 billion (US), and in 2001, the Mining Journal estimated that 110 million carats were mined with an estimated value of $7.3 billion (US).  The Northern Miner (v.90, no.1) reported rough diamond sales in 2003 for the Diamond Trading Company (DeBeers Marketing Arm) was $5.52 billion.  It is extraordinary to note that Canada ranked 6th in diamond production during this period and was expected to surpass South Africa in the second quarter of 2004, particularly when it is realized that prior to 1998, Canada did not have a diamond industry.  This is one of the great exploration success stories of the 20th century (Krajick, 2001).

Industrial diamonds have considerably less value than gem diamond and much industrial production is synthetic. In 2001, nearly 70% of the total natural and synthetic industrial diamond production came from Ireland, Russia, and the United States: 92% was synthetic (Olson, 2001). According to the US Geological Survey, world production of natural industrial diamond totaled 48 million carats in 2001 and 48.9 million carats in 2002. Over one-third of the world’s natural diamond production was classified as industrial. However, this represented only a very small percentage (~1%) of the total monetary value of natural diamond production. Australia led the market in recovery of natural industrial diamonds and has averaged 22.1 million carats per year; however, declining reserves at the Argyle mine resulted in Australian industrial diamond production of only 13.1 million carats in 2001 and in 2002 (Olson, 2003)

The World Diamond Council reported that the US was the largest producer of synthetic industrial diamonds with 125 million carats manufactured in 1999. The US Geological Survey reported that domestic synthetic industrial diamond production for 2002 was 310 million carats.  The total industrial output worldwide was estimated to be in excess of 800 million carats in 2001 valued at more than $600 million (Olson, 2001).  Domestic synthetic diamonds were produced by two companies: GE Superabrasives in Ohio and Mypodiamond, Inc., in New Jersey.

Natural diamond production was dominated by southern African countries with a significant contribution by Russia and Australia. Nearly all of the Australian diamond production was from the Argyle mine, which accounted for more than 20% of world’s diamonds. However, the relatively low quality of the Argyle diamonds rendered the production to be less valuable than some smaller operations elsewhere (Table 1). 

Table 1: Estimated 2001 World Diamond Production*
Country                             Carats (x 103)      Value ($ millions)
Botswana                                 26,416                         2,194
Russia                              20,500                         1,650
South Africa                     11,301                         1,145
Angola                                         5,871                           803
D.R. Congo                      19,637                           496
Canada                                        3,685                           531
Namibia                             1,502                           322
Australia                                   26,070                           294
Guinea                                            754                           128
Sierra Leone                                 375                             68
Central Africa Republic            614                             92
Venezuela                                      325                             41
Tanzania                                        191                             28
Brazil                                              550                              22
Liberia                                           155                              23
Ivory Coast                                 145                              17
China                                             150                              15
Ghana                                            450                              11
Lesotho                                           20                                4
Guyana                                             20                               2
Total                           110,176                        7,253
*Source: Mining Journal, London, August 23, 2002

Diamond Distribution
Although there are hundreds of known diamond occurrences around the world, commercial diamond deposits are rare. In the richest, diamond occurs in concentrations of much less than 1 part per million (Lampietti and Sutherland, 1978). The few commercial diamond deposits are hosted by kimberlite, lamproite, and placers derived from these host rocks. These are all associated with Archean cratons and cratonized Proterozoic belts. However, the discovery of several unconventional host rocks in recent years, some with very high ore grades, suggests that other rock types and geological environments will become diamond targets in the future (Hausel, 1996; Erlich and Hausel, 2002).

The world’s natural diamonds are produced from a small group of deposits, which typically have operating lives of 20 to 30 years. A notable exception is the Premier mine (South Africa), which potentially could operate for more than 100 years (Levinson and others, 1992).

Table 2: Diamond Production of Major Mines in 2001**
Country                                  Carats             Tonnes                        US$/carat        Value
(‘000)              (‘000)                                      ($ m)
Canada
            Ekati                            3,685                 3,685                             144                  531

Botswana

            Jwaneng                       12,339              8,920                               110                1,357
            Orapa                           13,056            15,779                                50                    653
            Letlhakane                     1,021               3,625                              180                   184

South Africa
            Venetia                         4,977               4,602                                85                    423
            Namaqualand                   808               6,083                              180                    145
            Finsch                           2,465               4,768                                70                    173
            Premier                         1,637               3,102                                75                    123
            Kimberley                       550                3,766                              110                      61
            Baken                               65                5,835                              400                     26
            Koffiefontein                   145                2,299                              225                     33

Russia
            Udachnaya                     11,500             9,000                               85                    978
            Jubilee                              5,500             9,100                               65                    358

Australia
Argyle                            26,000             15,100                             11                    286
            Merlin                                  70                  270                           110                       8

Namibia
            Namdeb Onshore               1,385            21,867                             220                  305

**Source: Mining Journal, London, August 23, 2002

Africa
The Orange River basin with its many tributaries drain a region with more than 3000 known barren and diamondiferous kimberlite pipes that include some of the richest pipes in the world. The principal diamond producing countries in Africa include Angola, Botswana, Central African Republic, Congo Republic (Zaire), Ghana, Guinea, Namibia, Sierra Leone, South Africa and Zimbabwe. In total, Africa accounts for nearly 50% of the world’s diamond production.

Atlantic Coast. Erosion of diamond pipes and dikes in the Orange River basin resulted in the concentration of millions of diamonds in the basin and along the Atlantic Ocean shoreline. Stream sediments in the basin and beach sands along the West Coast of Africa extending from Port Nolloth, Namaqualand to Luderitz, Nambia, contain placer diamonds. The powerful energy generated by wave action along this coast resulted in large numbers of poor-quality stones being destroyed (or broken) while gemstones remain untouched.

Congo Republic. The Congo Republic accounts for about 18% of the world production and in recent years, has been the second largest producer by weight next to Australia. However, only 6% of the Congo diamonds are gem quality with another 40% near-gem, resulting in the Congo being the 4th ranked producer based on value. According to the American Museum of Natural History, the Mbuji-Mayi mine in the Congo has been a prolific source for diamonds with recent annual production of about 5 million carats. 

Botswana. DeBeers discovered three world-class kimberlite pipes (Orapa, Letlhakane and Jwaneng) in Botswana between 1967 and 1973.  The Orapa pipe was found in 1967 and production began in 1972. It is the second largest producer of diamonds in the world and yielded more than 13 million carats in 2001 (Table 2).  The Jwaneng pipe was discovered in 1973 under the sands of the Kalahari Desert and mining began on the property in 1982: it has been the third most productive diamond mine by weight and first by value.  Two smaller pipes known as the Letlhakane 1 and 2 were discovered in 1968. 

Botswana’s diamond reserves are immense. Total production in 2001 was a record 26.3 million carats as compared to 21.26 million carats in 1999 and 19.8 million carats in 1998.  Output from the mines was 13 million, 1 million, and 12 million carats from Orapa, Letlhakane and Jwaneng, respectively (Table 2). A fourth mine, Tswapong, produced 10,100 carats in 1999. Application for a fifth mine at Gope in the Central Kgalagadi Game Reserve was under review in 1999, and Debswana Diamond Company Ltd (formed by the Botswanna government and South Africa's DeBeers in equal partnership) applied for a license to mine diamonds from four small kimberlite pipes known as the B/K pipes near the Orapa mine. Mining was scheduled to begin in 2001.

South Africa. Diamonds were initially reported in South Africa in the 1860s, and between 1870 and 1871, a great diamond rush occurred along the Orange River resulting in discovery of several deposits (Wagner, 1914). South Africa is the fifth largest producer of diamonds (by value) with annual production of million carats.  In 2001, the South African mines produced 10.65 million carats.  The region has produced more than 500 million carats since the 1860s. A high percentage of these have been gem and near-gem, and has included some of the largest diamonds found in history.

The diamonds occur in kimberlite pipes and dikes and in associated alluvial placers. The largest pipe in South Africa is the 133 acre (54 hectare) Premier. The Premier Mine has been the source of some of the world's largest diamonds including the Cullinan, Premier Rose, Niarchos, Centenary and Golden Jubilee. The largest diamond ever found, the fist-size (3,106 carats) Cullinan, was recovered from the Premier.

The Finsch mine covers an area of 44 acres (17.9 ha) and lies 92 miles (160 km) northwest of Kimberley.  It is one of DeBeers’ seven South African operations. Discovered in 1961, the deposit was initially developed by open pit.  Since 1991, underground mine operations continued beneath the abandoned pit. Production from the mine in 2001 was 2.46 million carats from 4.8 million tonnes of ore (51.7 ct/100 tonnes).

Diamond-bearing gravels were discovered as early as 1903 close to the Limpopo River, 20 miles (35 km) northeast of the present location of the Venetia mine in South Africa. In 1969, De Beers launched a reconnaissance sampling program to locate the source of the alluvial deposits, and kimberlite pipes were discovered upstream in 1980. Mine construction began in 1990, and the Venetia mine opened in 1992 with full production in 1993. This mine represents one of De Beers’ single largest investments in South Africa. Situated 50 miles (80 km) from Messina in the Northern Province, the property required a capital investment of $400 million. The mine produced 4.98 million carats from 4.6 million tonnes of ore in 2001 (108 cts/100 tonnes).

There are 12 kimberlites in the Venetia cluster. Of the 11 pipes and one dike, only two kimberlites, K1 and K2, are currently being mined. Some of the pipes were formed by multiple intrusive events resulting in a variety of kimberlite facies. The kimberlites are clustered over approximately 2 miles (3 km), while the total surface area of kimberlite is 69 acres (28 ha). Venetia is being mined by conventional open-pit. Surface mining is expected to continue for 20 years. The current targeted pit depth is 1,280 feet (400 m).

Australia.
New South Wales (NSW). Alluvial diamonds were initially reported in NSW in 1861; later found in Queensland (1887) in South Australia (1894), and in Tasmania (1899).  From 1884 to 1922, 167,548 diamonds (with stones weighing as much as 8 carats) were recovered from alluvium in the Copeton field, NSW.

The diamonds were found in gravel buried by Tertiary basalt in an active tectonic environment similar to that of the Urals in Russia, the West Coast of the United States, and in some Archean greenstone terrains in Canada (Erlich and Hausel, 2002; Ayer and Wyman, 2003; Kaminsky and others, 2003).  It is thought that the diamonds were derived from phreatomagmatic volcaniclastics and tuffs associated with lamprophyre pipes (Atkinson and Smith 1995). Diamonds in such geological terrains provide signatures suggesting derivation from a relatively shallow mantle (<80 km) (Ayer and Wyman, 2003).

Northern Territories. Decades after the diamond discoveries in NSW, Ashton Exploration discovered diamonds near Mt. Percy, West Kimberley by following a trail of kimberlitic indicator minerals in 1976.  The mineral trail led to diamondiferous lamproite in the Ellendale field (Tertiary).  In August 1979, diamonds were found in Smoke Creek, more than 350 km to the northeast.  In October 1979, the Argyle lamproite (1.2 Ga) was discovered (Atkinson and Smith, 1995).  Both lamproite fields are located within Proterozoic mobile belts cratonized around 1.8 Ga and were tectonically active until the Devonian or later (Jaques et al. 1982, 1983; Atkinson and others, 1984).  Presently, about 450 lamproites, kimberlites and lamprophyres have been identified in Australia of which more than 180 are diamondiferous.  Some of the recently discovered kimberlites yielded minor to significant diamond grades (Berryman and others, 1999).

 
Production began in the mid-1980s at the Argyle mine resulting in Australia becoming a leading diamond producer.  At full production, the mine yielded more than 30% of the world’s annual production. Further development of the open pit continued into 2001, and the current operator (Rio Tinto) reported plans to expand operations underground.

Diamonds were recovered from the Normandy Bow River placer mine in the lower reaches of Limestone Creek, 12 miles (20 km) northeast of the Argyle.  This deposit was discovered in the early 1980's and mined by Poseidon/Freeport and Normandy from 1988 until late 1995 (Biggs and Garlick, 1987).  The plant was inactive at the end of late 1995, after nearly 7 million carats were produced from 24 million tonnes of gravel.

Kimberley Diamond Company acquired the Ellendale leases previously held by Argyle Diamond Mines.  Initial bulk sampling results from Ellendale 4 and 9 revealed higher ore grades near the surface.  The company reported the Ellendale 4 resource at more than 2 million carats to a depth of 450 feet (140 m) (23 million tonnes at 0.088 carat/tonne), which included a higher-grade zone (444,000 tonnes at 0.261 carats/tonne) to a depth of 9.6 feet (3 m). The near-surface enrichment zone was part of the mining target for 2002.  Primary diamond resources of Ellendale 4 and 9 were estimated at more than 2.6 million carats. 

For the first three years of operation, 2.2 million tonnes of ore is expected to be mined from the top 9.6 feet (3 m) of enriched material on both Ellendale 4 and 9.  The ore is estimated to average 0.15 carats/tonne.  The company also reported the discovery of 11 previously unknown lamproite pipes in the area (Shigley and others, 2001; MiningNews.net, January 10, 2002).

The Merlin mine, which was developed on a group of 12 diamondiferous kimberlites in northern Australia, yielded the country’s largest diamond, the 104.73-carat Jungiila Bunajina (“star meteorite dreaming stone”) white diamond.  Merlin is located 50 miles (80 km) south of Borroloola.  After 6 years, it was announced that the mine would close at the end of the 2002 due to marginal ore.

Australia’s total diamond production in 2001 was 26.2 million carats, a decrease of 0.4 million carats from the previous year.  The Argyle mine (26.1 million carats) accounted for nearly all of the Australian production. The Merlin mine in the Northern Territory produced 55,000 carats making it the second largest Australian producer in 2001.

Brazil
A diamond rush occurred in Brazil in 1725, and by the end of 1729 several diamond placers had been found in eastern Brazil in the region of Diamantina (“diamond city”).  Placers were also found along the Sao Francisco, Parana, Goyas, and other streams in southeastern Brazil. In 1844, rich diamond placers were found in another region of Brazil—the state of Bahia to the north. During the first 120 years of mining, about 10 million carats were recovered, including some weighing more than 100 carats.

The primary source of the diamonds has not been found, and it was initially assumed that a rock referred to as itacolumite (micaceous sandstone) was the source. This assumption was based on the presence of middle Proterozoic diamondiferous conglomerates that have supported some small mining operations in the Diamantina area.

The large number of diamonds found in placers suggests that major primary diamond deposits will be found in Brazil some day.  Since 1967, a systematic exploration program identified more than 300 kimberlite, lamproite, kamafugite, and melilitite intrusives, none of which contain economic amounts of diamond (Bizzi et al. 1994; Meyer et al. 1994).  A total of about 55 million carats have been recovered from Brazil with annual production averaging about 1.2 million carats.

China
Diamond deposits in the Liaoning Province of China are associated with kimberlite.  More than 100 kimberlites are found in this region including the Jingangshi kimberlite, which contains commercial amounts of diamond (Sunagawa, 1990).  At another locality, the Changma mine in the Shandong Province near Mengyin, about 500 km southeast of Beijing, is China’s largest diamond producer.  This deposit was initially mined as open pit over the past several decades and converted to underground mining in 2002 with an expected life of another 30 years.  The Changma deposit consists of a couple of kimberlite diatremes and a dike that all merge at 40 m below the surface.  The kimberlite has been drilled to depths of 600 m.  Production from the mine during the past 30 years included 1.6 million carats recovered from ore that averaged 1.27 carats/tonne: the largest diamond was a 119 carat stone. The property has an indicated resource of 1.4 million tonnes of ore at a grade of 0.92 carat/tonne with an inferred resource of 1.5 million tonnes of 0.63 carat/tonne.  The Changma property includes 9 diamondiferous kimberlites with a total measured and indicated resource of 9.7 million tonnes at an average grade of 0.055 carat/tonne (Beales, 2004).
India.
Diamonds were initially reported in the Golconda region of India from medieval time to the 19th century.  Golconda was actually the market place, and the actual source of the Indian diamonds were placers in the Penner, Karnool, Godvari and Makhnadi rivers in the Krishna Valley, and possibly in the Panna diamond field to the north in south-central India (Mathur 1982).  Many of the better diamonds ended up in the royal treasuries of sultans and shahs of India and Persia. Total production is estimated at about 12 million carats (Milashev 1989).
The majority of the diamonds was found in placer deposits (Sakuntala and Brahman 1984), although diamonds were also found in the Majhagawan lamproite as early as 1827.  After kimberlite was described in South Africa in 1877, intensive exploration in the ancient diamond-producing areas of India resulted in the discovery of what was thought to be kimberlite in areas adjacent to many placers (e.g., Majhagawan and Hinota near the Panna placer district, and the Wajakurnur and other intrusives in the Anantpur district).  Years later, petrographic studies of some Indian ‘kimberlites’ confirmed that many were actually olivine lamproite (e.g., Majhagawan and Chelima) (Scott-Smith 1989; Middlemost and Paul 1984; Rock et al. 1992). Diamonds recovered from the pipes are mostly transparent and flawless, with dominantly octahedral and dodecahedral habits.  About 40% are gem quality (ore grade ~ 0.01 carat/tonne).
Mitchell and Bergman (1991) indicate there are several other lamproites, kimberlites, and peridotites in this region, and Rock and others (1992) also report several olivine lamprophyres and minettes of potential economic interest occur in eastern India.  Known kimberlites in India are primarily Proterozoic in age and include diamondiferous kimberlites in the Wajrakarur field in the Andra Pradesh of the southern kimberlite province and kimberlites in the Raipur field in southeastern Madhya Pradesh in the central province (Middlemost and Paul 1984).

Many of the Indian deposits were depleted by the 19th century and new deposits were discovered in the mid 20th century, including placers in the Junkel region and Koel Valley, and in the Simla region near the Himalayas (which were originally described in Sanskrit texts). Total historical production is estimated to be between 14 to 21 million carats. Currently, about 20,000 carats are produced each year.

North America
There is little doubt that Canada, which has become a major diamond producer, will remain in the forefront of diamond production and exploration for decades to come. Recent exploration in Canada has resulted in the discovery of more than 500 kimberlites (including some unconventional host rocks) of which nearly half are diamondiferous (Kjarsgaard and Levinson, 2002).  Some of the unconventional host rocks include lamprophyre (including minette) and actinolite schist at Wawa, Canada, that is interpreted to represent metamorphosed komatiite. 

The North American Craton is the largest craton in the world. The Cratonic basement rocks of Canada continue south into the US and underlie large regions of Montana-Wyoming and the Great Lakes region.  However, exploration in the US has been relatively minimal.  Even so, more than 100 kimberlites, lamproites, and lamprophyres have been identified in the southern extension of the North American craton in Colorado, Wyoming and Montana. Approximately half of the kimberlites found in Colorado and Wyoming are diamondiferous, only one in Montana has yielded diamonds to date. The presence of several hundred kimberlitic indicator mineral anomalies, several diamonds, along with some geophysical and remote sensing anomalies support that the Wyoming Craton has been intruded by a major swarm of kimberlitic and related intrusives, most of which remain undiscovered. In that a large part of the Wyoming craton remains unexplored for diamonds, additional discoveries are expected. In the Great Lakes region, a group of about 30 kimberlites are reported in the Michigan-Illinois area (8 of which contain trace amounts of diamond) (Hausel, 1998).

One of the great exploration success stories of the 20th century was the discovery of diamonds in the Northwest Territories of Canada, which sparked the largest claim staking rush in history (Krajick, 2000).  A group of diamondiferous kimberlites were found nearly 300 km northeast of Yellowknife under a group of shallow lakes in the Lac de Gras region.  Within a few years following the discovery, Canada’s first diamond mine was commissioned by BHP in late 1998 (Figure 9).  This mine, known as Ekaki, is a world class mine. The mine property includes a group of 121 kimberlite intrusives, and to date, commercial mineralization has been identified and reserves established for the Fox, Leslie, Misery, Koala, Koala North, Panda, Beartooth, Sable and Pigeon kimberlites on the Ekati property: the other kimberlites are being evaluated for reserves. The mine is anticipated to have a minimum life of at least 25 years. 

In 2001, Ekati produced 3.7 million carats totaling about 6% of the world’s diamond value. In 2003, production increased to 6.96 million carats (EMJ, 2004).  The open pit operation on the Panda kimberlite reached its maximum economic depth in 2003, five years after mining was initiated. However, the declining production from the Panda open pit was replaced by production from the nearby Misery and Koala open pits. Evaluation showed that the Panda kimberlite mine life could be extended using underground mining techniques, thus the remaining kimberlite is being developed using sublevel retreat mining. Underground mining was previously initiated at the adjacent Koala North pipe in 2002. The Panda underground mine is expected to produce 4.7 million carats over an operating period of 6 years, with production scheduled to begin in 2005, followed by full production in 2006.  The Ekati production for the first quarter of 2004 totaled 1.27 million carats of diamonds, which was a 40% decline from the previous quarter.  For the first 9 months of fiscal year 2004, the Ekati mine produced more than 5.3 million carats.

Ore reserves at the Ekati mine are substantial. On June 30th, 2003, the Ekati mine reported 47.7 million tonnes of ore reserves graded at 0.8 carat/tonne (36.6 million carats of recoverable diamonds) based on a 2 mm cutoff size.  Measured, indicated, and inferred kimberlite resources stood at 127.9 million tonnes of ore containing an estimated 171.2 million carats (Robertson, 2004)!  As exploration continues on the property, these reserves will increase.

A few other commercial properties have been identified in the Northwest Territories. In addition, numerous other properties being explored or evaluated for reserves. These include Snap Lake, Diavik and Jericho. Production at the Diavik mine began in 2003. The Diavik pipes located in the Lac de Gras region east of Ekati, are being mined by Diavik Diamond Mines based out of Yellowknife (Figure 9). Diavik Diamond Mines is a subsidiary of London-based Rio Tinto, and the mine is a joint venture between Rio Tinto (60%) and Toronto-based Aber Diamond Mines (40%). Rio Tinto assumed operating responsibility from their subsidiary, Kennecott Canada Exploration.  The mine is estimated to contain 138 million carats of diamond and includes four kimberlites (A154S, A154N, A418, A21).  The A154S kimberlite is one of the richest kimberlites in the world and contains a reserve of 11.7 million carats at an average grade of 5.2 carats/tonne.  The property is anticipated to yield 6 to 8 million carats/year when in full production and has reserves that will sustain the operation for 16 to 22 years.  The property lies on a 20 km2 island known as East Island, 300 km northeast of Yellowknife. The Diavik kimberlites (55 Ma) intruded the Precambrian basement complex (2.5 – 2.7 Ga).

 
The Snap Lake mine is located in a kimberlite dike about 100 km south-southeast of Ekati and 220 km northeast of Yellowknife.  Snap Lake will be DeBeers’ first mine developed outside of southern Africa and is anticipated to begin production in 2006, or possibly as late as 2008.  The kimberlite will be mined entirely underground.  The kimberlite is estimated to host 38.8 million carats with an average ore grade of 1.46 carat/tonne. 

Toronto-based Tahera Diamond Corporation is the operator of the Jericho project located about 150 km north of Ekati near Echo Bay’s Lupin Gold mine. This property includes six diamondiferous kimberlites within the Nunavut Territory located 170 km north of Ekati.  When placed into production, the property would produce about 6 million carats over a mine life of 8 years. Reserves of 2.6 million tonnes of ore averaging 1.2 carats/tonnne have been established.  The mine is expected to begin development in 2004 and production scheduled for 2005 (EMJ, 2004).

Another project of DeBeers Canada - the Victor Project, lies in the James Bay Lowlands of northern Ontario, approximately 90-km west of the coastal community of Attawapiskat. De Beers anticipates a decision regarding mine development in mid-2004.  Victor is one of 18 kimberlite pipes discovered on the property, 16 of which are diamondiferous. The Victor kimberlite has a surface area of 15 hectares and consists of two pipes that coalesce at the surface known as the Victor Main pipe and Victor Southwest pipe. The Victor kimberlite is a complex pipe consisting of pyroclastic crater and hypabyssal facies kimberlite and has highly variable diamond grades.  If a decision is made to put the property in production, the open pit mine will have a life of 12 years and total project life of 17 years.  The mine will be supported by a processing plant designed to process 2.5 million tonnes per year.

DeBeers is also involved in the Kennady (Gahcho Kue) Lake project located about 100 km east of Snap Lake near Ft. Defiance and southeast of Ekati.  Kennady Lake is currently under exploration by a joint venture between Mountain Lake Resources and DeBeers.  The property includes the 5034, Hearne, and Tuzo kimberlites. Initial sampling of the 5034 and Hearne pipes yielded an average ore grade of 1.67 carats/tonne.   If this project receives a go-ahead, it is expected that permitting will require 2-3 years followed by another 3 years of mine development (EMJ, 2004).

Many other deposits have been found in Canada since the 1990s in the Northwest Territories, Nunavut, Alberta, Ontario, Quebec, and Saskatchewan (Olson, 2001). 

According to EMJ (2004), Canada is currently supplying about 15% of the world’s diamonds and is expected to show dramatic increases in the future.  In 2002, the Canadian diamond industry produced nearly 5 million carats. In 2003, production increased to 11.2 million carats, and it is estimated that essentially 50% of the world diamond exploration funding is focused on Canada.
Russia
The official discovery of kimberlite in Russia occurred in 1954 at what later became known as the Mir pipe (Erlich and Hausel, 2002).  In 1957, development was initiated on placers associated with the Mir pipe and was followed by open pit operations in the kimberlite.  Years later, operations ceased at a depth of 1090 feet (340 m).  The average ore grade was high in the upper mine levels (4.0 carats/tonne) but decreased near the bottom of the pit (1.50–2.0 carats/tonne).  The Mir had high gem to industrial diamond content and was the source of several large gems including the Star of Yakutiya (232 carats) and the Diamond of 26th Party Congress (342.57 carats).  Annual output from the mine was 6.0 million carats (Miller 1995).
The Udachnaya pipe was found in 1955 and mining began on the associated placers in 1957, followed by open pit operations in the pipe.  Udachnaya has been the most productive diamond mine in Russia with more than 14.4 million carats mined of which 80% were gems.  By 1956, over 500 kimberlites had been discovered in the USSR.  During the next 30 years, Russia became the third largest producer in the world: nearly all its production came from mines within the northern Siberian platform.

In 1960, the Aikhal pipe was discovered in Yakutiya: mining began in 1962 and ceased sometime between 1981 and 1988, presumably due to overproduction from other sources. Production resumed after 1988, and by 1995 the pit reached a final depth of 770 feet (240 m).  Annual production at the peak of mining was 600,000 carats at an average grade of 1.0 carat/tonne (Yakutalmaz 1999).

Another commercial pipe, known as the Sytykanskaya was discovered in 1955. Open pit mining began in 1979, and 600,000 carats/year were produced (average grade of 0.60 carat/tonne).  The mine was scheduled to close in 2001 (Yakutalmaz 1999).  Another commercial diamond mine, the Internatsional’naya pipe, was found in 1969.  Mining began in 1971 and the open pit was developed to a depth of 900 feet (280 m) by 1980.  Open pit operations ceased but plans were made to resume mining underground.

The 23rd Party Congress pipe was discovered in 1959: mining began in 1966 on this very rich pipe. The ore averaged 6.0 carats/tonne and the open pit reached a depth of 395 feet (124 m) after 15 years of operation.  The Jubilee (Yubileinaya) pipe was discovered in 1975.  Following the removal of 225 to 320-ft (70–100-m) of basalt overburden, open pit mining began: the Jubilee was anticipated to replace production from the declining Udachnaya pipe.  

During the 1970s, other diamondiferous kimberlites were discovered within the Russian platform.  At about the same time, several kimberlitic pipes were discovered northeast of the city of Arkhangel’sk, which included the Lomonosov diamond deposit. Currently, Russia is the 4th largest producer of diamonds in the world (by weight).  The American Museum of Natural History reported that the country has produced a total of 332 million carats and currently has an annual production of 10 to 12.5 million carats.

Venezuela
In 1890 and 1901, secondary placer deposits were discovered in Venezuela and Guyana, and near the end of the 1960s, a placer deposit was found on Caroni River in southeastern Venezuela.  To mid-1969, 1.3 million carats had been mined; the largest stone weighed 12 carats.  In September 1971, near the town of Salvacion in the state of Bolivar, another significant placer was discovered.  Within a short period, monthly diamond production from the Salvacion region reached 50,000 carats but the source of the diamonds remains unknown.

Other Cratons
Several diamondiferous pipes have been reported in other cratons such as in the Greenland region, and also in Kazakstan.  Kazakstan also has the added attraction of having some very unusual and very rich unconventional metamorphic diamond deposits – but most of the diamonds are low-value industrial stones (Erlich and Hausel, 2002).