Location: Central Ashanti region of Ghana in West Africa.
ReservesProven: 18.4Mt graded at 1.4g/t Au; Probable: 37.2 Mt graded at 1.1g/t Au.
Geology: TypeIntensely folded and faulted birimian flysch-type metasediments of the Paleoproterozoic age.
Mineralization Type: Narrow quartz veins within granite structures.
Production Scheduled: 2011
Estimated Mine Life: 10.2 years
The Central Ashanti gold mine is located approximately 57km south-west of Obuasi town and 195km north-west of Ghana’s capital Accra. Formerly known as Ayanfuri gold project, the mine has produced in excess of 300,000oz of gold between 1994 and 2001. It is owned by Central Ashanti Gold Limited, a wholly owned subsidiary of Perseus, which owns 650kmÂ² of tenements on the Ashanti gold belt.
The project is currently in the planning stage with a detailed feasibility study completed in July 2009. Production is scheduled to begin in 2011. The life of the mine is estimated to be approximately ten years.
Gold Mine Reserves
The mine contains an estimated 18.4Mt of proven reserves graded at 1.4g/t Au and 37.2 Mt of probable reserves graded at 1.1g/t Au. Measured and indicated resources total 29.9Mt graded at 2.1g/t Au. Inferred resources have been estimated to be 62.1Mt at 2.2g/t.
Gold Mine Geology
The deposit is hosted within the Man Shield of the Precambrian aged West African Craton. The deposit flanks the western end of the Ashanti greenstone belt along the Obuasi-Akropong gold corridor.
Intensely folded and faulted birimian flysch-type metasediments of the Paleoproterozoic age overlie the entire project area.
These sediments are metamorphosed to upper greenschist faces and include dacitic volcaniclastics, greywackes and argillaceous (phyllitic) sediments.
The sediments are intruded along multiple regional bodies by a number of small basin-type or Cape Coast-type granite structures.
The intrusions vary in size and shape from 200m to 400m long and 40 to 150m wide egg-shaped plugs, to longer and narrower sills and dykes that measure more than 2,000m in length and between 50m and 100m in width.
Regionally, the deposit hosts minor amounts of cherty and manganiferous exhalative sediments. Graphitic schists coincide with the main shear (thrust) zones. Parallel to partially parallel cleavage and bedding follow the regional trend of the 50Â° striking, steep to near vertical, southeast and north-west dipping Akropong structures.
Gold mineralisation at the mine is found primarily within granite structures. Two or three generations of several, narrow quartz veins host the mineralisation. The quartz veins are associated with nearly 3% pyrite, minor arsenopyrite and lesser amounts of sphalerite, chalcopyrite, galena and rutile.
Gold observed at or near the margins of the veins, occurs as fine grains along the boundaries of sulphide grain or in sulphide fractures. Coarse visible gold is hosted within the quartz. Mineralisation also occurs in shear zones that host the classic Ashanti-style sediments.
mining and processing
The deposit will be mined using hydraulic excavators ranging in size between 120 and 200t, with a backhoe configuration. Depending on the swell, flitches averaging 2 x 2.5m will be used.
Ore and waste will be excavated and loaded within the marked boundaries, thereby ensuring maximum ore recovery with minimum contamination.
Due to the intact strength of the rocks, fresh rocks will be blasted heavily. Control blasting techniques including pre-splitting, buffer rows and trimming will be used to minimise the impact of blasting on the slopes.
Mining will be carried out to support a mill feed rate of 5.5Mtpa of high grade primary ore. Processing will be carried out in a 5.5Mtpa gold processing plant that will include a primary jaw crusher , single stage SAG mill, gravity circuit, flotation circuit, regrind ball mill, concentrate CIL circuit and elution circuit.
A mining operations contract is yet to be awarded. The scope of the contract will include site preparation, construction and maintenance of haul-road, loading and transportation of ore to the ROM pad and hauling of waste material to the waste dump.
Perseus will undertake the technical services of the project including planning the mining activities, scheduling of production, grade controlling and ore blending.
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Cement production introduction
Cement is one of the most essential materials (bonding agent) in the building industry. It can be produced in a simple process and at reasonable cost, the finished product is not harmful to the environment, and it can be recycled.
There has been a significant increase in the utilization of cement over the past few years. The demand is expected to increase further in the future as, especially in Asia and Latin America, infrastructure measures and housing will be intensified. There are double-digit growth rates in cement production mainly in China, but also in India, Indonesia, Malaysia and the Philippines. Several Middle East and African countries are also increasing their cement production.
FAG, as a rolling bearing manufacturer, has to prepare for the growing demand for bearings used in machines for cement production.
The most essential materials for cement production are:
â€¢ limestone (Ca0) ca. 65 %
â€¢ clay (Si02 ca. 20 %; AL203 ca- 5 % and Fe203 ca. 3 %)
â€¢ additives (small amounts)
Cement producer plants are usually erected near huge limestone deposits. If the geological structure of the limestone is not homogeneous, additives must be admixed during the preparation process.
Limestone deposits are virtually unexhaustible so that the availablity of this raw material for cement in the future is ensured.
Crushing limestone, alumina etc.
Limestone, alumina etc. are quarried or mined in quarries or pits and subsequently reduced to sizes ranging from 12 to 80 mm.
The following machines are mainly used for crushing these materials:
â€¢ Jaw crushers (see section 1.2.1)
â€¢ Cone crushers (see section 1.2.2)
â€¢ Hammer crushers (see section 1.2.3)
in addition, tertiary crushers can be used, in combination with vibrating screens, for crushing/grading.
The material broken in the crushers is taken to drying plants by truck or belt conveyors. In the drying process the moisture is reduced to approx. 8 to 15 %, depending on the further size reduction process. During the drying process, additives can already be admixed. The material is then put in intermediate storage.
State-of-the-art coarse grinding systems are usually vertical roller grinding mills (see section 1.2.4) or roller presses (see section 1.2.5). Due to their slighter energy consumption, these systems are gradually replacing ball tube mills (see section 1.2.6) which are still used, in combination with an impact mill or as independent units for coarse grinding. In the coarse-grinding process the final grain sizes of approx. 0.1 mm required for the further cement production process are produced.
Burning the raw meal/cooling the clinkers
In so-called cyclone preheating plants and succeeding rotary kilns the raw meal is continously heated from ambient temperature to approx. 1500 Â°C and discharged as granulated cement clinker.
The burning of raw meal to clinker constitutes a complex process. It consists of precisely defined steps and is constantly monitored. Large rotary kilns today can be approx. 6 m across and 100 m long, reaching throughputs of up to about 10,000 t per unit and day.
The energy carriers used for preheating and heating in preheating plants and for “burning” the material in rotary kilns are coal, oil and natural gas. Which of these fuels are ultimately used depends on their price and availability.
Where coal is used as energy carrier, coal crushers are frequently used in cement plants for size reduction and fine grinding. Generally, these coal crushers are smaller vertical rolling mills similar to those used for grinding raw meal. As a rule, several machines are run in parallel operation, grouped into units.
As the roller grinding mills have to cope with extremely adverse ambient conditions the bearings frequently fail due to wear so that there is a constant demand for new bearings. There is also a constant demand for bearings for beater wheel mills which are used for coal crushing.
Rotary kilns are usually radially supported in hydrostatic bearings. However, for some years now, support roller units with rolling bearings have also been used, fig. 22. The FAG product Programme includes such units. Axial support of the rotary kiln is always effected by support rollers (fig. 23) which in turn are supported in rolling bearings.
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April 28, 2012
Industry Description and Practices
The preparation of cement includes mining; crushing and grinding of raw materials (principally limestone and clay); calcining the materials in a rotary kiln; cooling the resulting clinker; mixing the clinker with gypsum; and milling, storing and bagging the finished cement. The process results in a variety of wastes, including dust, which is captured and recycled to the process. The process is very energy-intensive and there are strong incentives for energy conservation. Gases from clinker cooler are used as secondary combustion air. The dry process, using preheaters and precalciners, is both economically and environmentally preferable to the wet process because the energy consumption (200 joules per kilogram (kg) is approximately half of that for the wet process.
Certain solid waste products from other industries, such as pulverized fly ash (PFA) from power stations, Slag, roasted pyrite residues, and foundry sand can be used as additives in cement production.
The generation of fine particulates is inherent in the process, but most are recovered and recycled. Approximately 10-20% of the kiln feed can be suspended in the kiln exhaust gases, captured, and returned to the feed, other sources of dust emissions include the clinker cooler, crushers, grinders, and material handling equipment. When the raw materials have high alkali or chloride content, a portion of the collected dust must be disposed of as solid waste, to avoid alkali buildup. Leaching of the dust to remove the alkali is rarely practiced. grinding mill operations also result in particulate emissions. Other materials handling operations, such as conveyors, result in fugitive emissions.
Pollution Prevention and Control
The priority in the cement industry is to minimize the increase in ambient particulate levels by reducing the mass load emitted from the stacks, from fugitive emissions, and from other sources. Collection and recycling of dust in kiln gases is required to improve the efficiency of the operation and to reduce the atmospheric emissions. Well designed, operated and maintained units normally can achieve less than 0.2 kilograms (kg) of dust per metric ton (kg/t) of clinker using dust recovery systems. NOx emissions should be controlled by the use of proper kiln design, low NOx burners and use of an optimum level of excess air.
The NOx emissions from a dry kiln with preheater and precalciner is typically 1.5 kg/t of clinker compared to 4.5 kg/t for the wet process. The NOx emissions can be reduced further to 0.5 kg/t of clinker by after burning in a reducing atmosphere and energy of the gases recovered in a preheater/precalciner.
Monitoring and Reporting
Frequent sampling may be required during start-up and upset conditions. Once a record of consistent performance has been established, sampling for the parameters listed above should be as detailed below.
Equipment for continuous monitoring of opacity levels (or particulates in the stack exhaust whichever is cost-effective) should be installed. Sulfur content of raw materials , Direct measurement of particulate, SO2 and NO2 levels at the plant boundary levels should be carried out at least annually. When operational upsets occur, the opacity of kiln and clinker cooler exhaust gases should be measured directly and corrective actions taken to maintain the opacity level of the stack gases below 10% (or an equivalent measurement).
The pH and temperature of the wastewater effluent should be monitored on a continuous basis. Suspended solids should be measured monthly if treatment is provided.
Monitoring data should be analyzed and reviewed at regular intervals and compared with the operating standards so that any necessary corrective actions can be taken. Records of monitoring results should be kept in an acceptable format. These should be reported to the responsible authorities and relevant parties, as required, and provided to MIGA if requested.
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crusher offers you with a large choice of crushers with different capacities used in raw materials crushing for cement production. Introduction of crushing and prehomogenization process for cement plant.
Cement is pulverized with the mixture of limestone, clay, and iron ore powder in proportion. At this time the mixture is called raw materials. Followed by calcination, the general temperature is of 1450 degrees. After calcination, the product is called clinker. Then according to a certain percentage, the clinker is mixed with gypsum. The mixture is then grinded to the required fineness. Here you have produced cement. This is only a general description. Here you can learn about the whole process in detail.
Cement Crushing And Prehomogenization Details
1. Crushing machines– jaw crusher , impact crusher, cone crusher and vertical shaft impact crusher
During cement production process, the majority of raw materials such as clay, limestone, iron ore and coal etc should be crushed into small size. Limestone is the most used raw material for cement production. Since the limestone after mining is of big particle size, high hardness, limestone crushing occupies a more important position in cement plant.
Crushing process is more economy and convenient than grinding process, so a reasonable choice of crushing equipment is very important. Before that the material is sent into grinding equipment, large materials should be crushed into small, uniform particle size as far as possible, in order to reduce the load of the grinding equipment, and improve cement production. Material crushed, you can reduce the materials segregation phenomenon during transportation and storage of different particle, which is good to make uniform components and improve the accuracy of raw ingredients. crusher offers you with a large choice of crushers with different capacities used in raw materials crushing, such as jaw crusher , impact crusher, cone crusher and vertical shaft impact crusher, etc. we will recommend you the right one according to the raw materials’ different particles and hardness for cement production. Please feel free to contact us if you are interested in our crushers.
2. Raw material prehomogenization equipment– material piling machine
Prehomogenization refers that during the storing and using of materials, we use advanced technology to realize preliminary homogenization of raw material.
Raw material prehomogenization’s basic principle is that when piling the materials, material piling machine is used to range the material continuously into overlap coal layer of same thickness. Material taking in perpendicular to the direction of coal layer, as far as possible while cutting took all material layers. When taking the materials, you cut the pile in perpendicular direction of coal layer as far as possible, taking all material layers at one time.
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April 27, 2012
Calculation of Power for a Hammer Mill
Hammer mills are machines that grind large, solid materials into smaller pieces. Hammer mills are used in many different types of industry, most notably in agricultural and industrial manufacturing such as the manufacturing of paper and seeds. When operating a hammer mill, it may become important to determine the power the mill exerts on the material contained within, as this may help identify inefficiencies in the crusher.com”>equipment. The power of a hammer mill can be calculated in a few short steps.
Hammer Mill Instructions
1. Find the square root of the mill circuit product size, and find the inverse of the result. As an example, if the mill circuit product size is 16 micrometers, the square root of this is 4, and the inverse of this number is 0.25. Call this result A.
2. Find the square root of the mill circuit feed size, and find the inverse of the result. For example, if the mill circuit feed size is 25, the square root of this is 5, and the inverse of that number is 0.2. Call this result B.
3. Subtract result B from result A. In the example used here, 0.2 subtracted from 0.25 gives 0.05. Call this result C.
4. Multiply result C by the work index of the hammer mill and the number 10. For example, if the work index is 3 metric tons, then multiplying this number by 10 and 0.05 gives 1.5 kilowatt-hours per metric ton. This is the power of the hammer mill.
cement ball mill classifier
phosphogypsum grinding machine
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April 26, 2012
Brief introduction to sandstone production line
Sandstone production line is a kind of specialized equipment for standstone of building material and stones, which is 50% advantage than traditional vertical shaft impact crushers in energe-conservation. It can make all kinds of rocks, sandstone, cobbles into sand for building purpose with outstanding features of perfect standy granularity, and very high compression strength, that performs better in meeting the requirement of building than natural sand and the stand produced by common hammer blasting machine, capable of improving the quality of construction. This equipment has the following features: reliable performance, reasonable design, easy to handle, high working effeciency. Manual sandstone production line gets suitable different specification stone by crushing, viberating and screening through feeding machine and jaw crusher , finished stand will be obtained by high effect sand washing machine.
Sandstone production line is defined according to discharging type, manufactured products including building stones and artificial sand,also called building stones production line, to be equivalent to the combination of building stone production line and sand machine. It often needs a shared sand and stone production line in raw material factory for road building and construction site. This set of sandstone production line equipment can fully meet the requirment of producing the building stones and artificial sand.
Following is the introduction to process of sandstone production line:
The stones is conveyed from viberation feeding machine to jaw crusher to make rough crush, the material after rough crushing is sent by belt conveyor to sand machine for further crushing, the precise crushing material is transported to viberation screen for screening, and then the material which have reached the granularity requirement of finished products is carried to sand washing machine for cleaning, after cleaning the finished products comes off the conveyor; those not meeting the granularity requirement will be reworked back from viberation screen to sand machine, forming a closed manifold cycles. The granularity of finished products can be combined and classified according to customersâ€™ requirement. If choose to use dry manufacturing techniques, coarse powder and fine powder splitter, and dust-removing equipment can be prepared.
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April 25, 2012
BR1000JG-1 mobile crusher Introduction
Various debris from construction work some dozen years ago: Concrete debris from demolished buildings, etc. Asphalt debris from road repairing work. Natural rocks from civil engineering work.
BR1000JG-1 Mobile Crusher
The debris was transpor ted to disposal sites. Environmental and economic problems occurred due to rising disposal costs from a shortage of disposal sites and transpor tation of debris and new aggregates by dump trucks.Under such social circumstances, in 1992 Komatsu introduced mobile crusher BR60 equipped with an impact crusher for the purpose of “on-site treatment of miscellaneous debris from the demolition of wooden houses”. In 1993, Komatsu developed BR200J-1 with increased capacity and equipped with a jaw crusher capable of disposing of large masses in large-scale demotion and civil engineering work to promote on-site recycling method.
Later the workability was improved by applying a three-way loading structure and a conveyor with increased discharge height. A vibratory feeder to remove muck, and automatic feeding control was installed to increase production. In August last year, Komatsu began the sale of BR380JG-1 equipped with a crusher of improved maintainability and operability through its own development. This machine continues to sell steadily.
On the other hand, separate from the field of disposal by crushing of debris from construction work , the following method has been conventionally adopted in the quarry field where the jaw crusher was originally used:
. After blasting, blasted rocks are collected by a bulldozer.
. Rocks are loaded on a dump truck by a hydraulic excavator or wheel loader and transported to a crushing plant.
At some sites where the benches height is large, an open chute method is adopted to drop blasted rocks with the bulldozer. As exploitation proceeds, however, distance between the working face and the aggregate production plant becomes greater causing the hiking of blasted rock transportation costs to the plant. To cope with the circumstances, a new method has been adapted by which a mobile crusher is arranged near the working face as the primary crushing equipment, and the primarily crushed rocks are transported by either a conveyor or a 10-ton dump truck to the secondary crushing plant and onward. At Komatsu we can carry out primary crushing at the working face, then transport the primarily crushed rocks over the conveyor with a combination of a mobile crusher BR1600JG and mobile conveyor BM2014C.Moreover, Komatsu proposed the following systems using mobile crushers in the quarry field:
New quarry development system
Enables efficient development of a new quarry by a combination of a mobile crusher and a loader, requiring no electric power supply or foundation work for fixed type crushing plant. Thus, primar y crushing can be done in a narrow space, and crushing site can be moved according to the quarry site formation after stripping.
Working face on-site production system
Enables production of aggregate in the working face and product delivery directly from there. mobile crushers perform primary and secondary crushing and crushed rocks are sorted with mobile screens within the working face. These mobile machines allow flexible movement from one working face to another. In addition, aggregate products can be transported in a 10-ton dump truck which requires minimum road construction, contributing to environmental load reduction.
Under those proposals, Komatsu has developed and marketed the large-type mobile crushers, BR500JG-1, BR550JG- 1, and BR1600JG-1. We have also developed and begun marketing BR1000JG- 1 equipped with a jaw crusher of the 48-inch class which is predominant in the quarry field.
Introduction of achievement methods
(1) The largest jaw crusher in this class A 50-inch hydraulic driven jaw crusher provides a large production capacity , largest in this class (inlet size of 1,260 x 1,000 mm)
(2) Large hopper and wide crusher discharge port Equipped with a large folding type hopper having a capacity of 8.2 m3, it enables loading using a hydraulic excavator of the 3 to 4 m3 bucket capacity class.
(1) Hydraulic lock cylinder is installed on the crusher Adoption of a special-structured lock cylinder has added the following functions:
. Automatic discharge clearance adjustment function Clearance adjusted by extending the cylinder (reducing clearance) or retracting (increasing clearance)
. Toggle plate protection function when the crusher is clogged with foreign material When clogged with foreign material, the cylinder piston forcibly slides to open the discharge clearance to release the load.
(2) BR1000JG-1 can reduce or increase clearance by controlling the lock cylinder in the crusher structure shown in Fig. 3. This can be effected by operating the monitor switch in the control panel operable from the ground. Since the discharge clearance detected by the sensor is displayed on the monitor, no discharge clearance adjustment jig is needed to check the clearance. This enables the operator to adjust the discharge clearance from the ground without riding on the machine.
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April 24, 2012
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Continental Belt conveyor Systems equipment offers many safety features, some of which are standard, while others are optional and specified by the user based on conditions under which the equipment will be operating. Good common sense is the key when working on any equipment and must be used while observing or servicing equipment.
Belt Conveyor Safety
Employees and operators must be protected from moving belts, pulleys, shafts, chains, gears etc. CBCS offers belt guards, chain guards, nip guards, skid resistant catwalk with toe boards, safety railing, emergency stop switch with safety pull cord, belt covers, and many other safety items some of which may be optional and were not purchased nor included as a part of your equipment. In the absence of any such safety apparatus having been specified by you on your order, it is up to you to provide whatever such devices are deemed necessary to comply with your current and existing requirements.
Employees, maintenance personnel and operators must be made aware of the type of equipment and how it operates and of the power required to operate this equipment. Basic conveyor safety begins with the design of the equipment that avoids foreseeable hazards. Company management must provide training in the proper operation and maintaining of the equipment. Management must insist on good housekeeping and safety procedures.
These are some of General Safety Guidelines
1. Lockout/tag out all energy sources to the belt conveyor, conveyor accessories, and associated process equipment before beginning any work â€“ whether it is construction, installation, maintenance, or inspection that is directly associated with the equipment you are involved with. The use of lockout device with one key for each piece of equipment should be used. The person actually doing the work should be the only person with the key to the lockout device.
2. Operating and maintenance personnel should become familiar with the material being handled in the system along with the location and purpose of the safety devices before being allowed to operate or work on the equipment.
3. A belt conveyor safety training session should be a portion of a comprehensive safety program provided by the company to all employees that will be required to operate or maintain the equipment.
4. All safety devices should be in good working condition, properly maintained and easily accessible. Emergency stop switch with safety pull cords should be mounted at the proper height.
5. The equipment should be operated at its design capacity and speed. Overloading belt conveyors results in spilled material and hazardous working conditions and premature failure of components.
6. During and after maintenance on the equipment a safety â€œwalk aroundâ€ is recommended as a precaution for leaving tools or work material prior to staring the equipment.
7. A formal maintenance and inspection schedule should be developed and followed for the equipment and associated safety devices.
8. Required personnel safety equipment such as hard hats, safety glasses, steel toe shoes should be worn when in the area of the equipment to provide any type service or work.
Manual inspection, maintenance or repairs must be done at a time the can be taken out of service, properly lockout and tagged. In NO case should belt conveyors or any operating equipment be serviced while in operation. Only visual inspection can be done during operation and care must be taken to be at a safe distance and not be wearing loose clothing. Inching drives provide an excellent method of visually inspecting the belting.
Companies must constantly observe the working conditions, and if doubt exists, as to whether you deem your equipment safe enough for your employees welfare, call in a qualified safety engineer to advise you as to whether or not your equipment satisfies current safety regulations and requirements of any federal, state, municipal or other duly constituted regulatory agency to whom you might be responsible.
It is also the responsibility of your company to properly train your personnel in the correct use of this equipment. Should there be any question as to the safe manner of its operation you should first contact Continental Belt Conveyor Systems. Keep in mind that what might be considered an open and obvious danger to the most experienced plant operator could be completely ignored and overlooked by an inexperienced or less perceptive employee.
The information contained in this manual is be used as a guideline only, any company policies, local or state regulation should be adhered to. The recommendation on service and maintenance are general in nature and any technical information from the manufacture on particular parts should be used.
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