Robert Kane is a former staff of GIA and now a fine gemstone dealer. His views are valid today because today it's ninety five situaion: Transalation = ninety five percent of the dealers in the industry are not properly trained; only five percent is properly trained and continuously keep learning by taking refresher courses + attending seminars + workshops on new treatments, synthetics, imitations and new gem varieties. The amazing thing is most gem dealers are of the illusion that they don't need training; they are already successful by their own virtue, luck, connections, money + they think they know more about gemstones than a gemologist. The world has changed so dramatically that if you are living in the US or Europe you must always watch your back with plan B, C, or D because you don't want to get into legal problems, while in Asia, Africa and South America there are no binding consumer protection laws; at times it's like two blind walking the streeet situation. Buyer beware!
Robert Kane (President/CEO, Fine Gems International, USA) writes:
In gem treatments and synthetics, there have been more developments in the last 10 years than in the previous 50 combined. Since the 1999 Symposium, we have seen, for example, the commercial availability of (1) HPHT-treated diamonds in a variety of colors, (2) various colors of faceted synthetic gem-quality diamonds, (3) beryllium-diffused corundum, (4) poor-quality opaque corundum that has been transformed into transparent red gems by filling fractures with high-lead-content glass, and (5) diffusion ruby, which proved to be synthetic ruby overgrowth on natural corundum. It is critical that we identify and disclose these products if we are to maintain consumer confidence.
Although most of these treatments and synthetics are based on sophisticated technology, many can still be detected through precise gemological testing and observation. And when routine testing does not yield a definitive identification, major gemological laboratories can identify nearly all of them using advanced instrumentation. This presentation discusses approaches that members of the industry can take to deal with the constant influx of these new materials.
When examining a gem, the experienced gemologist systematically rules out the treatments and synthetics known for that particular stone. By running through a list of possibilities and how they are identified, one can identify the gem in question using standard observation and testing, or make an informed decision on a proper course of action, such as submitting the gemstone to an internationally respected gem laboratory for testing. The challenge is to recognize when the identification is beyond your knowledge level—to know when you don’t know.
By not facing these difficult issues, and thus buying and selling blindly, you open yourself and your company up to loss of reputation and to liability that could result in financial loss.
Gem Identify Assurance Program
One way to address these identification challenges is to develop a gem identity assurance program for your company based on gemological knowledge, trust in your suppliers, security through lab reports, and determining the level or risk that is acceptable in a given situation.
Gemological knowledge
Decades of scientific research by groups such as De Beers, GIA, and others have provided practical solutions to identification problems created by the proliferation of treated and synthetic gems. You can—and should—take advantage of this information by (1) regularly reading the gemological journals; (2) attending seminars held during trade shows such as at Tucson, Las Vegas, Basel, Bangkok, and Hong Kong; (3) taking specialized training at laboratories such as SSEF and AGTA; and (4) availing yourself of resources such as the De Beers CD-ROM Diamonds and books on specific topics—for example, GIA’s Gems & Gemology in Review: Synthetic Diamonds. There are also many educational programs available around the world to fit most needs.
There is no substitute for up-to-date gemological knowledge and solid experience. To this end, you should also consider purchasing your own gem-testing equipment, a portable lab, or-depending on your circumstances—a complete advanced gem testing laboratory.
Trust in your suppliers and financial resources
It is very important to buy gems from a trusted and knowledgeable supplier—one who will refund your money if testing reveals that the gem is not what it was represented to be. Always demand full disclosure regarding treatments and synthetics in writing on the invoice—if the seller will not comply, then find a new supplier. Buy from companies that belong to organizations such as ICA (International Colored Stone Association), AGTA (American Gem Trade Association), AGS (American Gem Society), TGJTA (Thai Gem & Jewelry Traders Association), WFDB (World Federation of Diamond Bourses), and the like. Members of such organizations must adhere to rules of ethical behavior, and the organizations can and will issue sanctions if these rules are violated.
Security through laboratory reports
Establish a company policy whereby all gems over a certain monetary value, or certain kinds of gemstones, must have a report from an internationally recognized gem lab. On expensive gems, obtain reports from at least two different labs. This is particularly important when geographic locality reports are required (because these determinations are not an exact science, the second lab may indicate a different origin, which case a third report is needed). Lab reports help protect you from future liability problems with your clients.
Risk tolerance
Determine what level of risk is acceptable. Certainly, the buying and selling of a 1ct purplish red diamond warrants an updated GIA lab report. Yet it may be reasonable to accept the word of your supplier (who knows the chain of custody and guarantees it in writing) when purchasing small amethysts, various colors of small sapphires, or parcels of emerald melee. Although you do run some risk that a mistake has been made, for most dealers the risk is manageable. Again, though, this depends on the specific situation. If a parcel of 2.0mm yellow sapphires are going into an expensive piece of jewelry featuring 200 such stones, testing (or at least spot-testing) would be required to ensure accurate representation of the entire piece.
Buying and Testing scenarios
Following are two examples of buying and testing situations.
Scenario 1
A large blue (synthetic) sapphire
A dealer is offered an 8ct superbly cut, clean, intense blue sapphire—set in an antique mounting—for $10000. However, it is not accompanied by a lab report. During very careful examination with a darkfield binocular microscope and diffused lighting, she sees subtle curved color zoning—proving that what appeared to be a magnificent natural gem was actually a flame-fusion or Verneuil synthetic sapphire. In 2005, a natural-color Sri Lankan sapphire of this size and apparent quality sold for $30000; a comparable Burmese sapphire sold for $55000. If it seems too good to be true, it probably is.
Scenario 2
A 3+ ct Unheated Mogok ruby
One gem dealer offers another a 3+ carat ruby, accompanied by a report from a gem testing stating: Burma, no indication of thermal treatment. Microscopic examination revealed inclusions characteristic of untreated Mogok rubies, such as unaltered rutile needles and small calcite crystals. It also revealed a small fracture extending from the crown facets toward the girdle. The second dealer’s prospective buyer was willing to pay in excess of $100000 for the stone, but wanted a report from a certain US laboratory. That lab reported evidence of clarity enhancement—specifically, foreign material filling the surface reaching fracture, which is typically done in an attempt to reduce the fracture’s visibility. After the stone was soaked in acetone for several days (with the first dealer’s permission), the filler was no longer present, causing the fracture to become more prominent. The client was no longer interested in the ruby, and the gem dealer lost the sale. As mentioned above, with high value gems it is good to obtain reports from two different laboratories.
Navigating the challenges ahead
To maintain vitality and confidence in our industry, it is critical that we stay up to date on technological developments in gem synthesis, treatment, and identification. Learn what is in the market, how to identify it, and when to refer a gem to a recognized laboratory for advanced analytical testing. Buy from a trusted and experienced source. With expensive gems, this can be backed up by laboratory reports. The rapid advances in technology will inevitably bring challenges to the gem and jewelry industry—some will present positive opportunities, while many others will create daunting gem identification issues. Vigilance in pursuing knowledge will insure that our industry continues to flourish.
Sunday, June 10, 2007
Major Diamond Mines Of The World: Tectonic Location, Production, And Value
Here is an insider view on the commercially important diamond deposits around the world. Many experts believe Botswana is the Kuwait of Africa, the rising super star, with no major tribal conflicts, relatively stable government except problems related to bushmen and their habitat. Canada is a newcomer with immense opportunities and difficulties due the landscape + the weather. Russia is trying to catch-up, but the politics and their way of doing business may have a lot of surprises for the diamond world. More to come.....
A J A (Bram) Janse (Archon Exploration Pty Ltd, Perth, Western Australia) writes:
The spatial distribution of the world’s major diamond mines is intimately related to the age of the earth’s crust. According to Clifford-Janse terminology, the three age-defined tectonic crustal elements are archons, protons, and tectons. At present, all diamond mines developed on kimberlite pipes are located within the boundaries of an archon, while those developed on lamproite pipes are located on a proton. Even though only one major diamond mine is underlain by lamproite pipe (the Argyle mine in Australia), several small diamond mines on lamproite pipes and other occurrences of diamond-bearing lamproites support this view. The figure also shows that major diamond mines largely cluster into three regions of the world: southern Africa, Siberia, and western Canada.
The tabulated data show Jwaneng in Botswana has the greatest current value and very high current production, followed by Udachnaya in Siberia, Orapa in Botswana, Ekati and Diavik in Canada, and Venetia in South Africa. The Argyle mine in Australia has a high production, but a low value. The most important producers for the next decade are likely to be Jwaneng, Orapa, Ventia, and Diavik, with Jubileynaya, Nyurba (Russia), Catoca (Angola), and Murowa (Zimbabwe) having slightly less importance. Argyle will continue to produce large quantities of near-gem material. The monetary values for the top six mines are in the same league as a major gold mine or a medium-sized oil field.
Date were also tabulated for seven advanced projects for which production is planned in the near future (although Jericho already commenced production in the first quarter of 2006, it is a small mine compared to Snap Lake). Victor is also small, but it has an extraordinary high value. Gahcho Kue is currently only a resource, not yet a proven reserve and only indicated reserves are available. Camafuca is an elongated pipe or the fusion of five pipes in a line underneath the bed of the Chicapa River, and it will be first operated by a five year dredging program.
The major mines of the future are Arkhangelskaya and Grib (both in Russia), but Grib’s opening is hampered by litigation. The Arkhangelskaya pipe will be the first of the Lomonosov cluster of five pipes to open in 2007.
A J A (Bram) Janse (Archon Exploration Pty Ltd, Perth, Western Australia) writes:
The spatial distribution of the world’s major diamond mines is intimately related to the age of the earth’s crust. According to Clifford-Janse terminology, the three age-defined tectonic crustal elements are archons, protons, and tectons. At present, all diamond mines developed on kimberlite pipes are located within the boundaries of an archon, while those developed on lamproite pipes are located on a proton. Even though only one major diamond mine is underlain by lamproite pipe (the Argyle mine in Australia), several small diamond mines on lamproite pipes and other occurrences of diamond-bearing lamproites support this view. The figure also shows that major diamond mines largely cluster into three regions of the world: southern Africa, Siberia, and western Canada.
The tabulated data show Jwaneng in Botswana has the greatest current value and very high current production, followed by Udachnaya in Siberia, Orapa in Botswana, Ekati and Diavik in Canada, and Venetia in South Africa. The Argyle mine in Australia has a high production, but a low value. The most important producers for the next decade are likely to be Jwaneng, Orapa, Ventia, and Diavik, with Jubileynaya, Nyurba (Russia), Catoca (Angola), and Murowa (Zimbabwe) having slightly less importance. Argyle will continue to produce large quantities of near-gem material. The monetary values for the top six mines are in the same league as a major gold mine or a medium-sized oil field.
Date were also tabulated for seven advanced projects for which production is planned in the near future (although Jericho already commenced production in the first quarter of 2006, it is a small mine compared to Snap Lake). Victor is also small, but it has an extraordinary high value. Gahcho Kue is currently only a resource, not yet a proven reserve and only indicated reserves are available. Camafuca is an elongated pipe or the fusion of five pipes in a line underneath the bed of the Chicapa River, and it will be first operated by a five year dredging program.
The major mines of the future are Arkhangelskaya and Grib (both in Russia), but Grib’s opening is hampered by litigation. The Arkhangelskaya pipe will be the first of the Lomonosov cluster of five pipes to open in 2007.
New Localities In Madagascar
Federico Pezzotta is an expert on Madagascar, and pezzottaite is named after him. The author also provides the geological landscape + the unique particularities of the gem deposits in Madagascar. Many experts believe Madagascar is vast with poor infrastructure + a virgin territory + there may be more surprises from from this island. Keep in touch.
Federico Pezzotta (Natural History Museum, Milan, Italy) writes:
Madagascar is host to an abundance and variety of gem materials as a result of its long and complex geologic history. The upper Archean to Neoproterozoic crystalline basement of Madagascar experienced locally unusual and even unique geologic conditions during several mountain-building events. Erosion of these rocks occurred during the late to post-tectonic uplift of the basement, and deposited Permian-Mesozoic sediments along the western margin of the Mozambique basin, locally forming immense paleoplacer deposits (e.g Ilakaka). More recently, the morphologic and climatic conditions of the island during the past few million years resulted in the formation of abundant secondary residual and alluvial gem deposits.
Even though research and mining of Madagascar’s gems has continued for more than a century, many large areas in the island remain poorly explored and have significant potential for the discovery of new deposits. Within the last few years, the country’s improved political situation has allowed for important developments in the scientific research, mining, and trading of gems.
Recently, two major discoveries occurred in Madagascar, both in Fianarantosa Province: (1) a series of multicolored tourmaline deposits, of both primary and residual nature, in a large area between the villages of Ambatofitorahana and Ambohimasoa, along the national road connecting the towns of Ambositra and Fianarantosoa; and (2) a multicolored sapphire deposit of residual nature located 17km south of the village of Ranotsara, southeast of the town of Ihosy.
The tourmaline deposits are related to a large rare-element miarolitic pegmatite field, surprisingly rather undocumented in the available geologic maps, that extends in a northeast-southwest direction for a distance of ~40km. Initial discoveries of tourmaline in the area were made in 1995-1996 with the mining of the primary and secondary residual deposits of Valozoro, a few kilometers southeast of Ambatofitorahana. No additional significant discoveries were made until August-September 2005 when, in the Anjoma area (located a few kilometers southwest of Ambatofitorahana), an enormous quantity of multicolored tourmaline (weighing several tones, but mainly of carving quality) was found close to the surface at Anjomanandihizna (also known as Nandihizana). Soon afterward, additional multicolored tourmaline deposits were discovered south of this area; the most important ones at Fiadanana (a few kilometers south of Valozoro), Ankitsikitsika (about 15 km south of Anjomanandihizana), and Antsengy (northwest of the village of Ambohimahasoa). Local gem dealers refer to this entire area as Camp Robin, from the name of a village in center of the district in which much of the gem trading occurs.
The new sapphire deposit, named Marosely, was discovered in October 2005. Transparent bipyramidal sapphire crystals, with colors ranging from blue to purple and, rarely, purplish red (ruby), have been recovered mainly in small size (less than 0.4 g). Larger crystals of gem quality are rare, but occasionally they exceed 2 g and produce good size cut stones. These crystals originated from the high grade metamorphic bedrock, and were concentrated in near-surface residual deposits through erosion. The total production of sapphire rough from Marosely, through June 2006 is estimated at about 500 kg.
Federico Pezzotta (Natural History Museum, Milan, Italy) writes:
Madagascar is host to an abundance and variety of gem materials as a result of its long and complex geologic history. The upper Archean to Neoproterozoic crystalline basement of Madagascar experienced locally unusual and even unique geologic conditions during several mountain-building events. Erosion of these rocks occurred during the late to post-tectonic uplift of the basement, and deposited Permian-Mesozoic sediments along the western margin of the Mozambique basin, locally forming immense paleoplacer deposits (e.g Ilakaka). More recently, the morphologic and climatic conditions of the island during the past few million years resulted in the formation of abundant secondary residual and alluvial gem deposits.
Even though research and mining of Madagascar’s gems has continued for more than a century, many large areas in the island remain poorly explored and have significant potential for the discovery of new deposits. Within the last few years, the country’s improved political situation has allowed for important developments in the scientific research, mining, and trading of gems.
Recently, two major discoveries occurred in Madagascar, both in Fianarantosa Province: (1) a series of multicolored tourmaline deposits, of both primary and residual nature, in a large area between the villages of Ambatofitorahana and Ambohimasoa, along the national road connecting the towns of Ambositra and Fianarantosoa; and (2) a multicolored sapphire deposit of residual nature located 17km south of the village of Ranotsara, southeast of the town of Ihosy.
The tourmaline deposits are related to a large rare-element miarolitic pegmatite field, surprisingly rather undocumented in the available geologic maps, that extends in a northeast-southwest direction for a distance of ~40km. Initial discoveries of tourmaline in the area were made in 1995-1996 with the mining of the primary and secondary residual deposits of Valozoro, a few kilometers southeast of Ambatofitorahana. No additional significant discoveries were made until August-September 2005 when, in the Anjoma area (located a few kilometers southwest of Ambatofitorahana), an enormous quantity of multicolored tourmaline (weighing several tones, but mainly of carving quality) was found close to the surface at Anjomanandihizna (also known as Nandihizana). Soon afterward, additional multicolored tourmaline deposits were discovered south of this area; the most important ones at Fiadanana (a few kilometers south of Valozoro), Ankitsikitsika (about 15 km south of Anjomanandihizana), and Antsengy (northwest of the village of Ambohimahasoa). Local gem dealers refer to this entire area as Camp Robin, from the name of a village in center of the district in which much of the gem trading occurs.
The new sapphire deposit, named Marosely, was discovered in October 2005. Transparent bipyramidal sapphire crystals, with colors ranging from blue to purple and, rarely, purplish red (ruby), have been recovered mainly in small size (less than 0.4 g). Larger crystals of gem quality are rare, but occasionally they exceed 2 g and produce good size cut stones. These crystals originated from the high grade metamorphic bedrock, and were concentrated in near-surface residual deposits through erosion. The total production of sapphire rough from Marosely, through June 2006 is estimated at about 500 kg.
Saturday, June 09, 2007
More On The Black Swan Concept
(via Emergic) The Guardian wrote about Nassim Taleb’s “The BlackSwan”.
“If you are aware of your own ignorance, though, you can use it to make money, as Taleb did on Wall Street, as an options trader. Options are gambles about what the market will do. To sell an option to somebody else, you need to be confident you have some kind of theory about what will happen in the future. If you're right, you make a small amount of money; if you're wrong, you lose lots. Taleb, however, realized he had no theories. So he exploited everyone else's confidence, buying options according to no particular prediction. Most days, his rivals made a small amount of money, and he lost a small amount. But the one thing he could predict was that, if he waited long enough, something unpredictable would happen. When it did, some of his rivals would lose millions, and Taleb would make millions. It happened often enough for him to turn a big profit. It takes a rebellious nature, and an iron stomach, to go against the flow for so long. It is, perhaps, the kind of mindset that comes naturally to someone who lived through the Lebanese civil war - a classic, unpredictable black swan - and then found himself living as an exile, at one remove from American society. We are not all so good at resisting the herd's way of thinking.”
Bloomberg wrote:
There's an investment strategy to profit from improbability. “Be as hyper-conservative and hyper-aggressive as you can instead of being mildly aggressive or conservative,'' Taleb advises. “Instead of having medium risk, you have high risk on one side and no risk on the other. The average will be medium risk but constitutes a positive exposure to the Black Swan.''
The hand can feed the turkey for 1,000 days until, on day 1,001; it wrings the fowl's neck for Thanksgiving. The trick is to be the butcher, not the turkey.
“A thousand days cannot prove you right, but one day can prove you to be wrong,'' writes Taleb. “I am not urging you to stop being a fool. Just be a fool in the right places.''
With risk measures at or near record lows, including volatility indexes, corporate bond defaults, credit spreads and emerging-market yields, Taleb might help you dodge the next Black Swan.
Business Week wrote:
The Black Swan is not as unprecedented as Taleb claims. You may have encountered pieces of his arguments in recent popular books by the likes of Chris Anderson, James Gleick, Paul Ormerod, Duncan Watts, Steven Strogatz, Aaron Brown, and one of Taleb's few living heroes, Benoit Mandelbrot.
Moreover, despite Taleb's best efforts to make The Black Swan a useful guide to life, we human beings aren't wired to cope well with radical uncertainty. Donald Rumsfeld, the former Defense Secretary, famously cogitated in front of the microphones about "unknown unknowns," which is precisely Taleb's concept—and look where the philosophizing got him. Still, The Black Swan is a richly enjoyable read with an important message.
Nassim Taleb’s “The Black Swan” is one of the best and most important books you will read. Go get it!
“If you are aware of your own ignorance, though, you can use it to make money, as Taleb did on Wall Street, as an options trader. Options are gambles about what the market will do. To sell an option to somebody else, you need to be confident you have some kind of theory about what will happen in the future. If you're right, you make a small amount of money; if you're wrong, you lose lots. Taleb, however, realized he had no theories. So he exploited everyone else's confidence, buying options according to no particular prediction. Most days, his rivals made a small amount of money, and he lost a small amount. But the one thing he could predict was that, if he waited long enough, something unpredictable would happen. When it did, some of his rivals would lose millions, and Taleb would make millions. It happened often enough for him to turn a big profit. It takes a rebellious nature, and an iron stomach, to go against the flow for so long. It is, perhaps, the kind of mindset that comes naturally to someone who lived through the Lebanese civil war - a classic, unpredictable black swan - and then found himself living as an exile, at one remove from American society. We are not all so good at resisting the herd's way of thinking.”
Bloomberg wrote:
There's an investment strategy to profit from improbability. “Be as hyper-conservative and hyper-aggressive as you can instead of being mildly aggressive or conservative,'' Taleb advises. “Instead of having medium risk, you have high risk on one side and no risk on the other. The average will be medium risk but constitutes a positive exposure to the Black Swan.''
The hand can feed the turkey for 1,000 days until, on day 1,001; it wrings the fowl's neck for Thanksgiving. The trick is to be the butcher, not the turkey.
“A thousand days cannot prove you right, but one day can prove you to be wrong,'' writes Taleb. “I am not urging you to stop being a fool. Just be a fool in the right places.''
With risk measures at or near record lows, including volatility indexes, corporate bond defaults, credit spreads and emerging-market yields, Taleb might help you dodge the next Black Swan.
Business Week wrote:
The Black Swan is not as unprecedented as Taleb claims. You may have encountered pieces of his arguments in recent popular books by the likes of Chris Anderson, James Gleick, Paul Ormerod, Duncan Watts, Steven Strogatz, Aaron Brown, and one of Taleb's few living heroes, Benoit Mandelbrot.
Moreover, despite Taleb's best efforts to make The Black Swan a useful guide to life, we human beings aren't wired to cope well with radical uncertainty. Donald Rumsfeld, the former Defense Secretary, famously cogitated in front of the microphones about "unknown unknowns," which is precisely Taleb's concept—and look where the philosophizing got him. Still, The Black Swan is a richly enjoyable read with an important message.
Nassim Taleb’s “The Black Swan” is one of the best and most important books you will read. Go get it!
World's Largest Available Natural Pearl To Be Auctioned
The 575 carat pearl from 12th century Mongolia was formerly owned by Chinese emperors, Persian kings, the grandson of Genghis Khan and Marco Polo. It will be up for bidding in Abu Dhabi's Emirates Palace and on the Internet, where it is estimated to raise up to US$8 million (EUR5.89 million). The real story (via AP) @ http://english.pravda.ru/news/society/02-05-2007/90823-largest_pearl-0
Prediction: DTC to send formal Sightholder Termination Notices to All 93 Clients
Chaim Even-Zohar writes about the status of new DTC (Diamond Trading Company) sightholders + existing contracts + the uncertainities @ http://www.idexonline.com/portal_FullEditorial.asp?TextSearch=&KeyMatch=0&id=27309
Geology Of Placer Gem Deposits
Here is an experts view on placer deposits and its commercial significance in gem producing countries around the world + the geological and gemological characteristics that are important in identifying the particularities of placer deposits.
James M Prudden (Prudden GeoScience Services, Nevada, USA) writes:
Placer gem depositional environments consist of colluvial, fluvial, and beach deposits. The weathering of primary gem-bearing deposits forms overlying eluvial deposits, and the down-slope migration of the residual gems by both gravity and water creates colluvial deposits. Fluvial systems range from youthful through mature and old-age sedimentological regimes with associated channel geometrics that determine the hydraulic energy and therefore the locations of gem deposition. Fluvial systems commence with straight steep-channel gradients, with low depth-to width ratios containing unsorted clasts and large gems. This evolves into to the downstream, low-energy, old-age fluvial systems with low channel gradients that host bedded, well-sorted smaller clasts deposited in a meandering fashion within a broad flood plane. Gems in this environment are smaller and more rounded. At the point where the river enters a marine or lacustrine environment, the resulting abrupt gradient change is very favorable for gem deposition. Wave energy and long shore currents further winnow and transport gems in beach environments. Alpine and continental glaciers are nature’s bulldozers and the braded fluvial streams that are fed from their melt water effectively concentrate the contained gems from the glacial rubble.
Gem characteristics such as specific gravity, hardness, shape and durability will influence their related depositional environments and survivability, thus favoring the economic concentrations of certain gems in the fluvial milling environment.
Select case histories of a variety of placer deposits illustrate the practicality of applying detailed geology and sedimentology to placer gem exploration:
1. Australian Tertiary modified paleo-colluvial type sapphire deposits, derived from the weathering of alkaline basalts, have been a major global source of sapphires.
2. Namibian long-shore diamond distribution along the Atlantic Ocean coast constitutes the world’s most valuable diamond deposit, extending westward 100km to the continental shelf edge and 200km northward. The diamonds were originally liberated from the South African kimberlites (and possibly more distant sources) by post-Gondawana erosion of the southern African craton, which commenced in the humid Middle Cretaceous with the formation of the ancient Karoo and Kalahari Rivers. Subsequent erosion of these diamondiferous placers was accomplished by the Orange River in the Miocene. Prolonged winnowing of the diamonds increased their value by about 500%.
3. Fluvial reworking of glacial sediments in British Colombia, Canada, concentrated sapphires and garnets from several cubic kilometers of glacial material.
4. A fluvial diamond deposit in China’s Hunan province was deposited on completely weathered karst bedrock, which presents challenges to sampling and mining.
James M Prudden (Prudden GeoScience Services, Nevada, USA) writes:
Placer gem depositional environments consist of colluvial, fluvial, and beach deposits. The weathering of primary gem-bearing deposits forms overlying eluvial deposits, and the down-slope migration of the residual gems by both gravity and water creates colluvial deposits. Fluvial systems range from youthful through mature and old-age sedimentological regimes with associated channel geometrics that determine the hydraulic energy and therefore the locations of gem deposition. Fluvial systems commence with straight steep-channel gradients, with low depth-to width ratios containing unsorted clasts and large gems. This evolves into to the downstream, low-energy, old-age fluvial systems with low channel gradients that host bedded, well-sorted smaller clasts deposited in a meandering fashion within a broad flood plane. Gems in this environment are smaller and more rounded. At the point where the river enters a marine or lacustrine environment, the resulting abrupt gradient change is very favorable for gem deposition. Wave energy and long shore currents further winnow and transport gems in beach environments. Alpine and continental glaciers are nature’s bulldozers and the braded fluvial streams that are fed from their melt water effectively concentrate the contained gems from the glacial rubble.
Gem characteristics such as specific gravity, hardness, shape and durability will influence their related depositional environments and survivability, thus favoring the economic concentrations of certain gems in the fluvial milling environment.
Select case histories of a variety of placer deposits illustrate the practicality of applying detailed geology and sedimentology to placer gem exploration:
1. Australian Tertiary modified paleo-colluvial type sapphire deposits, derived from the weathering of alkaline basalts, have been a major global source of sapphires.
2. Namibian long-shore diamond distribution along the Atlantic Ocean coast constitutes the world’s most valuable diamond deposit, extending westward 100km to the continental shelf edge and 200km northward. The diamonds were originally liberated from the South African kimberlites (and possibly more distant sources) by post-Gondawana erosion of the southern African craton, which commenced in the humid Middle Cretaceous with the formation of the ancient Karoo and Kalahari Rivers. Subsequent erosion of these diamondiferous placers was accomplished by the Orange River in the Miocene. Prolonged winnowing of the diamonds increased their value by about 500%.
3. Fluvial reworking of glacial sediments in British Colombia, Canada, concentrated sapphires and garnets from several cubic kilometers of glacial material.
4. A fluvial diamond deposit in China’s Hunan province was deposited on completely weathered karst bedrock, which presents challenges to sampling and mining.
Role Of Beryllium In The Coloration Of Fe and Cr-doped Synthetic Corundum
Thailand is perceived as one of the gemstone refineries of the world. The experts from GIT shares their opinion (s) on the pros and cons of beryllium treatment in natural and synthetic corundum.
Visut Pisutha Arnond, Tobias Hager, Pornsawat Wathankul, Wilawan Atichat, Jitrin Nattachai, Chakkaphant Sutthirat, and Bootawee Sriprasert writes:
X-radiation and Be-diffusion heating experiments were performed on an iron-doped (colorless) synthetic corundum and a chromium-doped (pink) synthetic corundum to evaluate the role of beryllium in causing color in the Be-Fe-Al2O3 and Be-Cr-Al2O3 systems.
The iron-doped corundum, containing around 140-170 ppm by weight of Fe with negligible concentrations of other trace elements, was irradiated with X-rays (60 kV, 53 mA) for 30 minutes, then the color was faded for one hour with a 100-watt light bulb, and finally the sample was heat treated in a crucible with ground chrysoberyl in an electric furnace at 1780ºC in an oxidizing atmosphere for 50 hours. The chromium-doped corundum, containing around 160-210 ppm by weight of Cr with negligible concentrations of other trace elements, was also irradiated with X-rays (80 kV, 4mA) for 4 hours, then faded for 4 hours with a 100-watt light bulb, and subsequently heat treated with ground chrysoberyl at unspecified conditions by a Thai treater. At each stage of the experiments, the samples were photographed and UV-Vis absorption spectra were recorded.
Both the irradiation and Be-diffusion experiments on the iron-doped synthetic corundum created defect centers that had similar UV-Vis absorption curves and produced yellow coloration. The yellow color was unstable when induced by irradiation, but was stable after Be-diffusion.
Experiments on the chromium-doped synthetic corundum produced orange coloration (and similar UV-Vis absorption patterns) by both irradiation and Be-diffusion heating methods. Again, the orange color was unstable when induced by irradiation (and quickly faded to pink), but remained stable after Be-diffusion. These results confirm that divalent Be acts as a stabilizer of defect centers or color centers in iron-doped and chromium-doped synthetic corundum. Hence, the spectrum produced by the irradiation of Fe-doped or Cr-doped synthetic corundum was attributed to metal-related unstable color centers, while that produced in synthetic corundum doped with Be + Fe + or Be + Cr was caused by Be²+ + metal-related stable color centers.
Visut Pisutha Arnond, Tobias Hager, Pornsawat Wathankul, Wilawan Atichat, Jitrin Nattachai, Chakkaphant Sutthirat, and Bootawee Sriprasert writes:
X-radiation and Be-diffusion heating experiments were performed on an iron-doped (colorless) synthetic corundum and a chromium-doped (pink) synthetic corundum to evaluate the role of beryllium in causing color in the Be-Fe-Al2O3 and Be-Cr-Al2O3 systems.
The iron-doped corundum, containing around 140-170 ppm by weight of Fe with negligible concentrations of other trace elements, was irradiated with X-rays (60 kV, 53 mA) for 30 minutes, then the color was faded for one hour with a 100-watt light bulb, and finally the sample was heat treated in a crucible with ground chrysoberyl in an electric furnace at 1780ºC in an oxidizing atmosphere for 50 hours. The chromium-doped corundum, containing around 160-210 ppm by weight of Cr with negligible concentrations of other trace elements, was also irradiated with X-rays (80 kV, 4mA) for 4 hours, then faded for 4 hours with a 100-watt light bulb, and subsequently heat treated with ground chrysoberyl at unspecified conditions by a Thai treater. At each stage of the experiments, the samples were photographed and UV-Vis absorption spectra were recorded.
Both the irradiation and Be-diffusion experiments on the iron-doped synthetic corundum created defect centers that had similar UV-Vis absorption curves and produced yellow coloration. The yellow color was unstable when induced by irradiation, but was stable after Be-diffusion.
Experiments on the chromium-doped synthetic corundum produced orange coloration (and similar UV-Vis absorption patterns) by both irradiation and Be-diffusion heating methods. Again, the orange color was unstable when induced by irradiation (and quickly faded to pink), but remained stable after Be-diffusion. These results confirm that divalent Be acts as a stabilizer of defect centers or color centers in iron-doped and chromium-doped synthetic corundum. Hence, the spectrum produced by the irradiation of Fe-doped or Cr-doped synthetic corundum was attributed to metal-related unstable color centers, while that produced in synthetic corundum doped with Be + Fe + or Be + Cr was caused by Be²+ + metal-related stable color centers.
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