Ratnapura alluvial gem gravel (Illam) extraction: shaft sinking and wooden winches?
What stratigraphic gravel layers (Illam) underlie alluvial paddy valleys in Ratnapura, and how do traditional miners hoist gemstone wash gravel to the surface?
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3 Answers from travellers
Gem mining in the alluvial river floodplains of Ratnapura (City of Gems) targets a rich mineral-bearing layer known as "Illam." Miners sink vertical shafts (ranging from 5 to 25 meters deep) through soft alluvial clay and sand strata until hitting bedrock where gem gravels accumulate. The shaft walls are shored up with round jungle timber framing and woven coconut frond matting to prevent collapse. Miners shovel Illam gravel into wicker baskets hoisted to the surface using manual wooden hand-winches (Yanthraya). The gravel is then washed in circular wicker baskets in nearby streams to recover corundum, spinel, and tourmalines.
Illam gravel contains rounded heavy mineral pebbles, tourmaline crystals, and quartz sand washed down from weathered Highland Complex pegmatites over millions of years.
Miners operate under strict licensing rules enforced by the National Gem and Jewellery Authority (NGJA), backfilling abandoned pits with earth after washing concludes.
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