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Introduction to the Gold Mining Process for Tabular Ore Bodies
There are a number of different methodologies used to conduct mining operations. One of these methods are discussed in this article.
The gold bearing ore is in situ in the reef band where it was deposited millions of years ago. It requiers drilled and blasted to free it from the country rock. According to Nell (1984:95) this process is called stoping. He defines stoping as:
the actual mining of ore by means of breaking ground in stopes to a size suitable for handling and processing for the recovery of the mineral content.
The breaking of the country rock includes drilling blast holes and blasting it. This is followed by cleaning, supporting and the providing of the infrastructure to the stope faces.
The provision of infrastructure includes the maintenance and managing of:
• in stope water and air services that is necessary for the drilling and dust allaying process
• travelling ways to and from the stope necessary for creating access ways for people and material
• scatter walls to contain the blast rock in a conveniently concentrated muck pile for the cleaning crew,
• material and people handling appliances including monorail, mono rope and chairlift devises
• double drum winches and scraper scoops for the moving of blasted rock
• pumping and pump installations to ensure sufficient water pressure and or clear out the accumulation of excess water from low lying areas.
• rail tracks for the locomotives and trains that transports workers, material and broken rock pover long horizontal distances underground.
• Safety devices that include tips and grizzlies to prevent inadvertent access of people down these near vertical excavations.
• Blasting equipment that includes remote blasting system cables and ventilation sensor equipment in the intake and return air passages.
• Ventilation systems that consists of various sizes of columns, temporary and permanent ventilation brattices, -walls, -holings and fans.
• Electricity and electric equipment required for the use during the mining process.
With reference to figure 1 a three dimensional mining layout of a typical gold mine can be viewed here. The figuredepicts the basic components, in three dimensions, used to explain the mining layout of a typical gold mine.
The broken ore is typically scraped on dip, down a 30 meter stope face into a strike gully, by means of a double drum winch and scraper scoop once it is blasted from the country rock.
Another double drum winch and scraper scoop is used to scrape the broken rock on strike to an orepass or boxhole, situated in the original raise. This boxhole can be situated up to 90 meters from the face where the blasting took place. The broken rock now cascades down this steeply inclined excavation (boxhole or orepass) to a crosscut on a lower level.
In the crosscut a train, normally with ten eight ton hoppers are used to transport the broken rock to the shaft. The shaft can be kilometres away from the point of mining. At the shaft the train tips it's cargo down the shaft orepass system, where it again cascades down to the shaft loading station near the bottom of the shaft. The broken rock are hoisted up a 2000 meter vertical shaft in rock skips with a typical capacity of 12 tons by means of a rock hoist to surface, in the case of a surface shaft, or to just above the loading station of the surface shaft in the case of a sub - shaft.
On surface the broken ore is transported to the metallurgy plant by means of a conveyor belt. In the metallurgy plant the ore is milled, screened, and chemically treated in order to allow separation of the gold from the gold bearing ore. The slime residue is pumped to a tailing dam and the gold concentrate is further treated. The gold concentrate is smelted and the 89% pure gold is poured into gold bars weighing about 31 kilograms each.
These gold bars are then transported to a Refinery where the silver is removed and the gold refined to 99.99% purity. It is this pure gold that is sold on the world gold markets.
© 2009 Carl Marx
Dennis Wilkinson