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Hard Rock
Hard RockUnlike the many alluvial gold operations on the West Coast, hard rock open pit mining is a large scale and complex operation. OceanaGold's new Globe Progress open pit mine near Reefton is an excellent example of a modern large scale mining operation.

Open pit mining is used to access gold bearing rock that usually occurs in reef systems well below the surface. Often there will be no 'surface expression' at all and comprehensive drilling programmes must be undertaken to 'prove' the resource. Once the operators are confident that the resource is economic and can be physically accessed, plans are drawn up to address and mitigate any social, cultural or enviroenmental issues and a consent is applied for under the Resource Management Act.

In a typical open pit mine operation topsoil and plant material are removed from the surface and stockpiled to provide access to gold-bearing rock called ore. The ore is excavated and transported by large mining trucks to a crusher. Here it is reduced in size then moved by conveyor to a large grinding mill. The mill is a large rotating cylinder, the ore is ground to a fine consistency and then passed through a series of holding tanks in which chemical processes remove the gold-bearing material and form a slurry. At the Globe Progress Mine the slurry is then dewatered to form a 'dry' concentrate which is transported by rail to OceanaGold's processing plant at their Macraes Mine near Dunedin for further processing. The ground up rock that remains is called tailings it is piped as a slurry to a purpose-built tailings dam. In the dam the tailings settle and consolidate. As mining in each area is the completed the area is contoured and the stockpiled topsoil and plant material is returned. The area is planted with native trees and shrubs to complete the rehabilitation. When mining is completed the tailings dam will also be rehabilitated.
 
Hard Rock
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