The question asks us to identify the machine used for drilling blast holes in hard rock mines from the given options. Let's analyze each option to determine the correct answer.
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Longwall shearer: Longwall shearers are primarily used in coal mining operations for the purpose of cutting and extracting coal from the coalface. They are not suitable for drilling blast holes.
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Continuous miner: This machine is also used for the purpose of cutting and gathering material (such as coal) from the seam. It is not designed for drilling blast holes, especially in hard rock mines.
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Jack hammer drill: A jack hammer or pneumatic drill is a tool used precisely for drilling holes. It is commonly used in hard rock mining to drill blast holes. Its effectiveness in breaking up hard surfaces makes it the preferred choice for such tasks.
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Belt conveyor: Belt conveyors are used primarily for material transportation rather than for drilling. They move bulk materials across considerable distances and are not suited for drilling purposes.
Based on the analysis, the correct machine for drilling blast holes in hard rock mines is the Jack hammer drill. It is specially designed to drill into hard surfaces efficiently, which is essential in mining operations for placing explosives to extract mineral ores.
Therefore, the correct option is the Jack hammer drill.