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The minerals industry of Oman.

Keen to develop the minerals it has, Oman will shortly have a second geophysical survey carried out.

The Sultanate of Oman is the second largest country of the Arabian peninsula and covers an area of around 350,000 k[m.sup.2]. The population is just over 2 million, with over 500,000 expatriates, and more than 50% of the population under the age of fifteen. Oman has abundant resources of oil and natural gas. The revenue from the development of these reserves is being carefully and skilfully used by Sultan Qaboos to provide a modern infrastructure for the whole population. When the Sultan came to the throne in 1970 the country had no telephone, radio, TV or newspapers and just one road.

Although recognising that oil and gas will dominate its foreign earnings for the foreseeable future, Oman is enthusiastically pursuing a plan to diversify the economy. These plans will focus on Oman's principal non-oil resources, such as agriculture, fisheries and minerals. Originally, industry was directed towards import substitutes based on indigenous resources but, with a limited home market, industrial policy has been switched towards exports. Tourism is also planned to play an important role in attracting additional foreign currency. The economy continues to open up to private and foreign investment with the stock market, listing public joint stock companies, to be linked to that in Bahrain. The government plans to increase privatisation during 1994 in the gas, petrochemicals, minerals and raw materials sectors.

An international tender has been put out for a second aerial geophysical survey project. This survey will start in October 1994 and will cover a distance of 200,000 km. This follows the success of the first survey that was completed in 1992, which resulted in the discovery of several previously unknown copper deposits. It is now possible to produce 1:1,000,000-scale geological maps, as well as 1:50,000-scale magnetic and radiometric maps, to assist in mineral exploration and underground water resources.

Oman possesses the world's largest known ophiolites in a mountain range inland from the northern coastal belt of the country. Ophiolites are of particular interest to earth scientists as they are believed to represent slices of the upper mantle and be closely similar to present-day ocean floor rocks. The word ophiolite is derived from the Greek word ophis, meaning snake. Geologists use the term ophiolite to describe the suite of ultramafic rocks in which sinuous veins of serpentine are common.

The Oman ophiolite hosts minerals deposits, which include copper, chromite, manganese, nickel, iron, gold and silver. Copper mined and smelted in Oman is believed to have been exported to the Sumerian Empire in Mesopotamia some 3,000 years ago. In addition, the country hosts deposits of many non-metallic minerals, for example, large quantities of gypsum and limestone are being exploited for the production of cement, and high quality marble is quarried and sold on both the domestic and international markets. In the north there are, so far unexploited, reserves of asbestos.

Oman Mining Company

The modern mining, beneficiation and smelting of copper is the most developed of the activities of the government-owned Oman Mining Company (OMC). The $150 million Sohar copper project, which first mined ore in 1983, produces approximately 1 Mt/y from two underground mines and one open pit operation.

The major source of massive sulphide copper ore has been the underground Lasial mine, due to close in September 1994. The deposit was roughly saucer shaped, dipping 30 [degrees] to the east, with a maximum thickness of 210m. It was about 500 m long and 350 m at its widest part. The orebody is accessed by a decline with sub-level caving as the initial mining method down to the 112-m level. Below this level, all mining has been by sub-level open stoping. Electro-hydraulic equipment is used for development and stope drilling. LHDs are used to transfer broken ore to 30 t articulated diesel trucks which haul the ore to the concentrator. Ventilation is achieved by three vertical shafts at the extremities of the orebody.

The Bayda Mine is located about 8 km north of Lasail Mine. The deposit is comprised of three lenses and ore has been extracted using similar methods to those employed at the Lasail Mine. The mine is currently closed, but a southern extension to the deposit is being evaluated.

The Aarja mine is 1 km south of the Bayda Mine and commenced production in October 1989. The deposit is a roughly cigar-shaped body plunging about 30[degrees] to the south, 420 m long by 50 m wide, and 50 m at its thickest part. Production commenced as an open pit, with subsequent underground development and production based on sub-level open stoping due to continue until 1996.

With little of the geological reserves left in the three mines, extensive geophysical exploration has been conducted to identify further reserves. Several small gold/copper surface deposits (up to 10 Mt) are currently being evaluated.

The ore (0.9 - 1.2% Cu) is blended prior to feeding to the 3,000 t/d concentrator. Initially all processing was conducted in seawater (pumped 35 km from the coast), but corrosion problems have led to substitution with recycled plant water, made up with mine water.

Ore is crushed at up to 250 t/h in a 1060 mm by 1200 mm jaw crusher with a 215 mm open side setting. The discharge is conveyed to a 15,000 t capacity stockpile. The ore is recovered from the stockpile and conveyed to a 5.5 m diameter by 8.8 m long primary grate discharge autogenous mill, powered by a 2250 kW, 200 rev/min synchronous motor. The slurry discharges to a 4.1 m diameter by 5.8 m long pebble mill, powered by a 900 kW, 200 rev/min synchronous motor. Product from the pebble mill is pumped to a 1372 mm diameter by 6765 mm long spiral classifier which returns coarse material to the primary autogenous mill. The overflow from the spiral classifier is pumped to hydrocy-clones, with the overflow (65% - 45 microns) passing to froth flotation. The cyclone underflow is normally returned to the pebble mill, but can be diverted to the primary autogenous mill if necessary.

The cyclone overflow passes to conditioning ahead of flotation. From conditioning the pulp flows to a bank of ten Wemco 14.2 [m.sup.3] rougher/scavenger cells provided with overflow launders on both sides of the machines. The cells are divided into three primary roughers, three secondary roughers and four scavengers. Concentrate from the primary roughers is directed to either final concentrate or to the third cleaner cells. Secondary rougher and rougher scavenger cell concentrate when required passes to 254 mm diameter regrind hydrocyclones. The hydrocyclone underflow can be reground in a 3.0 m diameter by 4.0 m long ball mill. Regrind cyclone overflow is 80% minus 20 microns and is fed to five Wemco 4.2 [m.sup.3] first cleaner flotation cells. Concentrate from the first cleaner cells can flow to second cleaner cells or to the final concentrate thickener if it meets final grade requirements. Tailing from the first cleaners proceeds to four Wemco 42 [m.sup.3] cleaner scavenger cells. The concentrate from these cells can join the regrind hydrocyclone feed, while the tailings combines with the final plant tailings. The second, third and fourth cleaner stages of flotation are Wemco 2.8 [m.sup.3] cells, using four, three and two cells respectively. The final copper concentrate is thickened, filtered, dried and sent to the smelter.

The original target concentrate grade was 20 - 22% Cu, with a tailings grade of 0.1 - 0.2% Cu. However currently 15 - 17% Cu concentrates are produced as this gives a higher copper recovery (86 - 88% Cu) from the reduced throughput as mine production declines. In fact, the smelter still has excess capacity and this spare smelter capacity has been filled by the smelting of imported concentrates from mines in Chile, Canada, South Africa and Bulgaria.

At the smelter, the concentrate is pelletised, matte smelted in an electric furnace, converted to blister copper and cast into 99.0 - 99.5% Cu anodes. These anodes are electrolytically refined to produce 99.99% Cu cathodes and precious metal-containing anode slimes.

The company also operates two quarries, with a single mobile crushing and screening plant, for the production of around 3,360 t/week of limestone and 4,200 t/week of silica. The -25 +9 mm sized limestone is feed for the lime burning plant, capable of producing around 200 t/week of lime used for pH control in the froth flotation process. The sized silica is used in the smelter as a fluxing agent.

Gold

The Rakah gold deposit is currently being developed by Oman Mining Company LLC. Based on a small gossan occurrence, the open pit mine will feed a 300 t/day gold plant. Using grinding, cyanide leaching and CIP an estimated 500 kg of gold will be produced in 1994, rising to 750 kg/y until 2001.

Coal

Coal deposits, near Sur in eastern Oman, are being evaluated by the Ministry of Petroleum and Minerals with the technical co-operation of the United Nations Development Programme. Drilling conducted during 1992, with downhole gamma-ray analysis and core sample analysis, identified a proven coal reserve of over 40 Mt, around 2.5 Mt of which could be extracted by open-cast mining methods. Recently increased reserves of 116 Mt have been reported. The steeply inclined coal strata are some seven kilometres in length and up to one kilometre deep, with seam thickness of up to 5.5 m. The coal has a low ash (6 - 14%), low moisture (around 0.5%) and high pyritic sulphur (up to 5%) values. The high sulphur content and steeply inclined seams mean that in situ gasification or coal bed methane extraction might be the most promising exploitation technique. Recently a bulk sample has been extracted for preparation and combustion testing in the UK.

Industrial minerals

There are over 450 known small chromite lenses, representing an estimated total reserve of 2 Mt. Some of the chromite deposits in the Rajmi area in the far north of the country have been exploited by the Oman Mining Company since 1983. In addition to purchasing and marketing the chromite produced, OMC provides equipment, training and technical assistance to small scale mining and processing activities in the country.

Marble and well-crystalized limestones are found in a number of locations, along with other dimension stones, such as decorative granites. There are a number of plants, all privately owned and operated, for the cutting and polishing of such products as floor and wall tiles.

Cement is produced by two plants. The larger, in the north of the country, not far from Muscat, is owned and operated by the government-owned Oman Cement Company (OCC), while the other is in the south, near Salalah, the Raysut Cement Company. OCC has a current capacity of around 2,000 t/d of clinker from a single 56 m long by 3.8 m diameter natural-gas fired kiln. Capacity is to be increased to 3.000 t/d by a plant expansion to be funded by the issue of 15 million shares. The expansion, which was allowed for in the original plant design, will include an additional kiln, raw material and clinker grinding mills. Resources of aggregates are abundant and well distributed. A number of crushing plants operate near the major population centres producing aggregates for local construction and road building activities.

Sultan Qaboos university

Now that Oman has a developed infrastructure, with schools and medical services, a growing number of young Omanis are participating in the development of the country. The Department of Petroleum and Mining, of the College of Engineering, at Oman's only University, the Sultan Qaboos University, has graduated mining engineers for the first time this year. It has a wealth of international experience, modern facilities and can assist in research and project development.
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Article Details
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Author:Hall, Steve
Publication:Mining Magazine
Article Type:Industry Overview
Date:Sep 1, 1994
Words:2003
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