segunda-feira, 7 de abril de 2008

THE TYPES OF DIAMOND DEPOSITS / ALLUVIAL

Angola is the third largest producer of diamonds in Africa and has only explored 40% of the diamond-rich territory within the country, but has had difficulty in attracting foreign investment because of corruption, human rights violations, and diamond smuggling.Production rose by 30% in 2006 and Endiama, the national diamond company of Angola, expects production to increase by 8% in 2007 to 10 million carats annually. The government is trying to attract foreign companies to the provinces of Bié, Malanje and Uíge. Angola has also historically been a major producer of iron ore.
1 Diamonds
2 Iron ore
3 Other minerals
4 References
Diamond mining began in 1912, when the first gems were discovered in a stream in the Lunda region in the northeast. In 1917 Diamang was granted the concession for diamond mining and prospecting, which it held until independence. Control over the company was obtained by the government in 1977. In April 1979, a general law on mining activities (Law 5/79) was enacted and gave the state the exclusive right to prospect for and exploit minerals. Accordingly, a state diamond-mining enterprise, the National Diamond Company (Emprêsa Nacional de Diamantes--Endiama), was founded in 1981 and acquired the government's 77 percent share in Diamang. UNITA, which selected the diamond mining industry as a principal target, soon crippled mining efforts, and by the beginning of 1986 the two foreign companies involved in servicing and operating the industry pulled out of Angola. By mid-1986 Diamang was formally dissolved, leaving large outstanding debts.
Attacks by UNITA on mining centers, disruption of transport routes, and widespread theft and smuggling caused diamond sales to fall to US$33 million by 1985 and to an estimated US$15 million in 1986. In late 1986, Roan Selection Trust (RST) International, a subsidiary of the Luxembourg-registered holding company ITM International, began mining in the Cafunfo area, along the Cuango River, the site of Angola's most valuable alluvial diamond deposits (see fig. 9). Mining had been halted there for more than two years after UNITA attacked the mining camp in February 1984, kidnapping seventy-seven expatriate workers and severely damaging the mining equipment. After the subsequent kidnapping of a British expatriate in November 1986, defense forces in the area were strengthened, allowing the resumption of mining operations. In 1987 production there averaged 60,000 carats, and about 120,000 carats were produced in the other two mining areas, Andrada and Lucapa. By 1987 diamond production had risen to 750,000 carats, compared with less than 400,000 carats produced in 1986. The 1987 figure, however, was still not much more than 1985 production and only a little over half of 1980 output (see table 9, Appendix A).[3]
This increase in production has benefited from the rise in the price per carat received for Angolan diamonds. The resumption of mining in the area along the Cuango River and a decline in theft of stones of higher value in the Andrada and Lucapa areas have increased the value of output. Furthermore, Endiama, which was responsible for overseeing the industry and for holding monthly sales, has benefited from a general improvement in the world diamond market as well as dealers' willingness to pay higher prices in the hope of securing favored treatment in the future. As a result, average carat value established by the monthly sales in 1987 exceeded US$110, more than twice as much as in 1985 (US$45) and at its highest level since 1981 (US$119).

In 1987 Endiama signed a two-year mining contract with the Portuguese Enterprises Corporation (Sociedade Portuguêsa de Empreendimentos--SPE), a Portuguese company that has retained a large number of Portuguese technicians previously employed by Diamang. Former Diamang shareholders founded SPE in 1979 after Diamang was nationalized. The precise terms of the contract were not made public, but it was thought that the company would undertake new prospecting, which had been at a virtual standstill since independence. Through a subsidiary, the SPE also was to help Endiama with diamond valuation, which a British company had been carrying out. In December 1987, Angola also signed an agreement with the Soviet Union to cooperate in mining diamonds and quartz. Under the terms of the agreement, the Soviet Union was to participate in mining enterprises and was to draw up a detailed geological map of Angola. In 1987 the government also began to revise the 1979 mining law to encourage new companies to invest in the diamond-mining industry, in particular to resume prospecting. Among the companies believed to be considering investing in 1988 was Britain's Lonrho conglomerate, which had taken an increasingly active interest in Angola in the late 1980s. The South African diamond-mining giant DeBeers was also interested after it lost its exclusive marketing rights for Angolan diamonds at the end of 1985 because of government suspicions that DeBeers had devalued Angolan diamonds. DeBeers has expressed interest in studying the kimberlite pipes (deep, subsurface deposits), which, because of the depletion of the alluvial deposits, were thought to represent the future of the Angolan diamond industry.
Angola is the third largest producer of diamonds in Africa and has only explored 40% of the diamond-rich territory within the country, but has had difficulty in attracting foreign investment because of corruption, human rights violations, and diamond smuggling. Production rose by 30% in 2006 and Endiama, the national diamond company of Angola, expects production to increase by 8% in 2007 to 10 million carats annually. The government is trying to attract foreign companies to the provinces of Bié, Malanje and Uíge

The Angolan government loses $375 million annually from diamond smuggling. In 2003 the government began Operation Brilliant, an anti-smuggling investigation that arrested and deported 250,000 smugglers between 2003 and 2006. Rafael Marques, a journalist and human rights activist, described the diamond industry in his 2006 Angola's Deadly Diamonds report as plagued by "murders, beatings, arbitrary detentions and other human rights violations." Marques called on foreign countries to boycott Angola's "conflict diamonds."

Iron ore
Once one of the country's major exports, iron ore was no longer mined in the late 1980s because of security and transportation problems. From the mid-1950s until 1975, iron ore was mined in Malanje, Bié, Huambo, and Huíla provinces, and production reached an average of 5.7 million tons per year between 1970 and 1974. Most of the iron ore was shipped to Japan, West Germany, and Britain and earned almost US$50 million a year in export revenue. After independence, the government established a state company, the National Iron Ore Company of Angola (Emprêsa Nacional de Ferro de Angola--Ferrangol), for the exploration, mining, processing, and marketing of iron ore. Ferrangol contracted with Austromineral, an Austrian company, to repair facilities and organize production in Cassinga. Production began to slow in 1974 as a result of technical problems at the Cassinga mine in Huíla Province and stopped completely in August 1975. The area fell under foreign control after South African forces invaded in 1975. Although South Africa withdrew its troops in early 1976, as of 1988 mining had not resumed in the area.

By 1988 the Cassinga mines had a production capacity of approximately 1.1 million tons per year. However, the railroad to the port of Namibe (formerly Moçâmedes) needed extensive repair, and since it was located only 310 kilometers north of the Namibian border, security against South African attacks could not be ensured. Furthermore, UNITA was active in the area and posed a threat to the rail line if it were repaired. Even if these problems could be resolved, production of iron ore at Cassinga would be costly in view of the depressed state of the world steel market in the late 1980s

Other minerals
In addition to diamonds and iron ore, Angola is also rich in several other mineral resources that had not been fully exploited by the late 1980s. These include manganese, copper, gold, phosphates, granite, marble, uranium, quartz, lead, zinc, wolfram, tin, fluorite, sulfur, feldspar, kaolin, mica, asphalt, gypsum, and talc. The government hoped to resume mining in the southwest for crystalline quartz and ornamental marble. It has been estimated that 5,000 cubic meters of marble could be extracted annually over a period of twenty years. A state-owned company mined granite and marble in Huíla and Namibe provinces and in 1983 produced 4,450 cubic meters of granite and 500 cubic meters of marble. Since then, the company has ceased production to re-equip with modern machinery. Quartz production, however, was suspended indefinitely because of the military situation in the areas close to the extraction sites in Cuanza Sul Province. The government established a company in 1980 to exploit phosphate deposits located in the northwest. There were 50 million tons of deposits in Zaire Province and about 100 million tons in Cabinda. Although studies of the deposits in both locations have been made by Bulgarian and Yugoslav companies, as of 1988 production had not started at either site
References
Angola: U.S. Must Strengthen Ties to Protect Strategic Energy and Security Interests
Council on Foreign Relations via AllAfrica
Angola wants foreign investors for diamond sector
July 26, 2007. Reuters Clark, Nancy. "Diamonds". Angola country study
Library of Congress Federal Research Division (February 1989). This article incorporates text from this source, which is in the public domain.
Angola to double diamond production in 2006
Afrol News , Clark, Nancy. "Iron Ore". Angola country study
Library of Congress Federal Research Division (February 1989). This article incorporates text from this source, which is in the public domain.
Clark, Nancy. "Other Minerals". Angola country study
Library of Congress Federal Research Division (February 1989). This article incorporates text from this source, which is in the public domain.
Geologic Processes
Geologic processes create two basic types of diamond deposits, referred to as primary and secondary sources. Primary sources are the kimberlite and lamproite pipes that raise diamonds from Earth's mantle, where they originate. Secondary sources, created by erosion, include such deposits as surface scatterings around a pipe, concentrations in river channels, and fluxes from rivers moved by wave action along ocean coasts, past and present. Mining of these deposits depends upon sufficient concentration and quality of diamonds.
The primary deposits, or diamond pipes, are the vertical portion. The flared top of the pipes can yield substantial quantities of diamonds, but following the narrowing pipe downward eventually becomes unprofitable. Note how erosion of the landscape moves surface minerals -- including the diamonds -- from the pipes down hills, streams, and rivers to their ultimate destination, the ocean. Because diamonds are dense they concentrate at the bottom of active zones of moving sand and gravel. These secondary deposits are eluvial &#eth; above a pipe, colluvial -- adjacent to a pipe, alluvial &#eth; stream and river transported, and marine -- along beaches that can wind up onshore or offshore with changing sea level. Secondary deposits may be found far from active means of transport, in the fossilized channels of now-vanished rivers or under fossil beaches.
Most of the diamond deposits first discovered were alluvial concentrations in streambed or riverbed sand and gravel. They are still actively exploited in many ways, from the most primitive to the highly sophisticated. The goal is relatively simple: to find a location where moving water has deposited diamonds in the bottom of a channel, possibly in a pocket or cleft. Because rivers meander and drainage can change, fossilizing a once active river, the search for alluvial diamonds requires some geological knowledge and a lot of luck. The process involves removing the overlying barren ground, digging up the bearing ground, extracting the diamonds, and, nowadays, restoring the landscape when finished.
An "independent" operation using the simplest technology: shovel, pan, water, and muscles. In the most basic, individual operations, such as in Sierra Leone or Angola, the technology involves shovel and pan, with some hand sloshing to gravitate diamond to the bottom of the pan; the eye is the ultimate sorting device. Mom-and-pop operations in South Africa involve a small claim and utilize limited technology -- shovels, buckets, jury-rigged cranes powered by small vehicles, and the like -- to load a small washing pan. The concentrate is then sieved into several size ranges, and each fraction is dumped onto a picking table, where someone checks by eye for diamonds. In the bigger operations, as shown in the model, large earth-moving equipment transports the alluvium, and the processing approaches that of the primary mines -- coarse sieving, then rotary sieving in a trommel, before loading into a large washing pan. Final processing includes concentrate sieving, a picking table, and usually a grease table. Of course, no crushing is required, as nature has already released the diamonds from the pipe rock.

There are two aspects of moving diamonds from mine to dealer. The first is the fairly straightforward but important task of separating diamonds into gem-quality, near gem-quality, and industrial-grade diamonds. The second is the more intriguing aspect: the primary diamond marketing, which has been and still is largely controlled by De Beers Consolidated Mines, Ltd. through its majority control of the Central Selling Organization (CSO). The CSO sells a large percentage of mine production to diamond dealers; independent mines sell by closed bids and through private transactions.Sorting small diamonds in a Botswanan operation. click to zoom inSorting occurs at every level of the market, from the mine to the jeweler. At the mine, the sorting depends on the sophistication of the operation and the size of production, but it is always based on grouping stones of like type. Diamonds are grouped into "sizes" -- more than one carat; "smalls" -- between 1 carat and 1/10th carat; and "sand," -- less than 1/10th carat, with some leeway for market pressures. Diamonds larger than about 15 carats are handled individually. Shape groups comprise "stones," "shapes," "cleavages," "macles," and "flats," describing characteristics familiar to the market. The ultimate purpose of sorting is to estimate an asking price for the rough diamonds. Harry Oppenheimer House is a diamond-sorting facility in Kimberley, South Africa. As in an artist's atelier, color is best judged by skylight without direct sunlight, so the windows of this building face south. Remember, South Africa is in the southern hemisphere.After great swings in diamond prices, the Diamond Trading Corporation (DTC) was set up by De Beers in 1934 to handle the actual sales of diamonds. The DTC and the Diamond Producers' Association (the mine operators) form the nucleus of the Central Selling Organization. The CSO stabilizes prices in hard times and raises them in accord with inflation and demand during good times. It needs considerable wealth and stockpiles of diamonds to maintain this position, but this "single channel marketing" system has been an effective cartel. In the United States cartels are illegal, so De Beers cannot operate here. However, the company's interests are represented by a public relations office, the Diamond Information Center, and indirectly by the diamond dealers and jewelers who sell the gems.
Alluvial Mining
Today, diamonds are mined in about 25 countries, on every continent but Europe and Antarctica (AMNH, 2006). Although most diamond mining is accomplished by large companies, in many developing countries, diamonds and other minerals are extracted by small- scale miners working in the informal sector. These small-scale miners often use simple artisanal mining techniques in alluvial deposits.
The process of alluvial diamond mining involves digging and sifting through mud, sand and gravel using shovels, sieves, or even bare hands. Typically, diamonds come from geologic rock formations called Kimberlites. Kimberlite rock formations that contain diamonds are eroded over time by rivers and streams and can deposit diamonds in the sediments carried by those streams farther downstream from the original source rocks. These deposits are called alluvial diamond deposits. The locations of these alluvial diamond deposits are controlled by the surrounding topography, drainage patterns, and the location of the Kimberlites themselves. Alluvial deposits are often mined and exploited by small-scale miners using artisanal mining techniques.
Artisanal mining techniques result in working with simple tools and equipment, usually in the informal sector, and outside the legal and regulatory framework. Artisanal operations are characterized by low productivity, lack of safety measures and high environmental impact. As a result, the majority of the artisanal miners are very poor, exploit marginal deposits with minimal returns, and are exposed to harsh and often dangerous conditions (IIED, 2006).
Artisanal and small-scale mining occurs primarily in rural areas where it represents the most promising, if not the only, income opportunity available. However, the mining activities are often viewed negatively by governments, large companies, and environmentalists. The use of child labor, the potential for environmental degradation, the high incidence of prostitution in mining camps, and the associated spread of HIV/AIDS where migrant workers are involved are major concerns in the artisanal mining sector. Further, the potential use of ASM revenue to finance conflicts and insurgencies in host countires or even regional scale conflicts is a major international concern. The use of diamond mining revenue to finance conflicts has been termed “conflict diamonds” or “blood diamonds”.
References
American Museum of Natural History. 2006. The Nature of Diamonds:
Alluvial Mining
International Institute of Environment and Development. 2006. Artisanal and Small Scale