WorldWide Drilling Resource

47 WorldWide Drilling Resource ® NOVEMBER 2018 Garnet is usually thought of as a gemstone, but most garnet is mined for industrial uses. Only a small number of garnets are pure and flawless enough to be cut as gemstones. They may be colorless, black, and many shades of red and green. Depending on the geologic environments, mining methods for garnet vary. At hard rock locations, such as the Barton mine in northern New York, open-pit meth- ods have been used for decades. In China, hard rock mining may consist of more primitive methods including hand mining. Garnets are extracted and processed more easily from al- luvial deposits. At the Emerald Creek mine in Idaho, backhoes or small draglines are used to cut slots and recover garnet from stream gravels. These gravels are passed through a trammel to reject the oversize, and garnet is concentrated on large wet-jigging tables. The garnet is then shipped to the mill for final processing and packaging. Beach deposits, such as those mined in Western Australia and in southern India, uti- lize low-cost earth-moving techniques. Scrapers and bulldozers are used to cut and ex- cavate benches parallel to the trend of the beach and/or bar deposit. Manual labor remains central to the operator’s community responsibility in India, so mechanized mining provides only a portion of the mine activity. The majority of garnet is ground to a variety of sizes to be used as an abrasive. The original application of this mineral was garnet sandpaper. It is also used to make a number of similar products, including sanding belts, discs, and strips. Abrasive blasting is a technique used to smooth, clean, or remove oxidation products from metals, brick, stone, and other materials. It is usually much faster than sanding by hand or with a sanding machine. It can clean small and intricate surfaces, which other cleaning methods would miss. The largest industrial use of garnet in the United States is in water jet cutting. A machine known as a water jet cutter pro- duces a high-pressure jet of water with entrained abrasive granules. When these are directed at a piece of metal, ceramic, or stone, a cutting action can occur which produces very little dust and cuts at a low temperature. Water jet cutters are used in manufacturing and mining. The World of Minerals MIN