Rubies are crystals of aluminum-oxide containing trace amounts of chromium. While there are some practical applications, as in lasers and high-precision bearings, the stones have been prized for their beauty for millenia. Trade of rubies along the Silk Road existed as early as 200 BCE. Because the supply of rubies is so heavily concentrated in Myanmar (formerly Burma), the techniques by which most of them are mined are those used in that country.
Most mining operations around the world are carried out using heavy equipment. However, the totalitarian regime controlling Myanmar has opted for a very insular foreign policy and thus limited its own ability to procure machinery. The extensive use of modern equipment was never previously instituted, so its loss as an option was negligible. The Burmese simply continue to mine the gems as they have for centuries. In any case, procurement of precious stones is economically tolerant of less efficient operations, and the cost of labor in Myanmar is only a fraction of that in industrialized nations.
In the pit mining technique, workers use a large metal tube to bring up a core of gem-bearing gravel. They typically extract a core from three to twenty-four meters deep. Because the rubies are extremely hard, the mother-rock is then eroded away from around them and, thus freed, they wash downstream. Pit mining is performed in river deltas or areas that were once deltas. Once material is dug up, it is thoroughly irrigated, washing away less dense materials like soil and sand, while the denser gemstones remain in the pan or sluice box.
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In hilly areas, open-trench mining is employed, using a high-pressure stream of water to wash away material from the slope. Again, the denser rubies tend to remain in place, while lighter debris is washed away. This method leaves smaller quantities of material to be transported for processing than does pit mining, though, obviously, it can only be employed on sloping ground.
This system involves the excavation of shafts into gem-bearing earth. Gravel containing rubies, that has washed downstream, often accumulates in caves formed when limestone is dissolved by subterranean streams. This method does not compare to the extensive caverns and deep shafts that can be worked using modern equipment in bedrock, but still remains a viable method in areas that can provide a high yield. These operations' most persistent problem is accumulation of groundwater in the shafts, which must be pumped out. These operations are usually abandoned during the monsoon season.
Fully mechanized operations, also known as quarrying, are only possible with heavy equipment and high explosives. While this represents the minority of operations in Myanmar, it does exist on a limited scale. The investment in expensive equipment and training is significant, but mechanization offers the advantage of being able to harvest stones from the mother-rock. While some operations must be suspended during the monsoons, thoroughly mechanized operations have the equipment to evacuate water from the shafts on a continuous basis.