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Through Radioactive decay, Alluvium and Sri Lanka
Chemistry
Based on color, specific gravity and composition three types of thorianite are distinguished:
- α-thorianite
- β-thorianite
- γ-thorianite
Thorianite and uraninite form a complete solid solution series in synthetic and natural material. The division between the two species is at Th:U = 1:1 with uranium possibly making up to 46.50% and thorium ranging up to 87.88%. Rare earths, chiefly cerium, substitute for thorium in amounts up to 8% by mass. Cerium is probably present as Ce4+. Complete series is known in synthetic material between CeO2 - PrO2 - ThO2 - UO2. Small amounts of Fe3+ and zirconium also may be isomorphous with thorium. Lead present is probably radiogenic.
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Varieties
- Aldanite – a variety of thorianite containing 14.9% to 29.0% UO2 and 11.2% to 12.5% PbO.
- Uranothorianite
- Thorianite Cerian
- Thorianite La bearing
Occurrence
Usually found in alluvial deposits, beach sands, heavy mineral placers, and pegmatites.
- Sri Lanka – In stream gravels, Galle district, Southern Province; Balangoda district; near Kodrugala, Sabaragamuwa Province; and from a pegmatite in Bambarabotuwa area.
- India – Reported from beach sands of Travancore (Kerala).
- Madagascar – Found in alluvial deposits of Betroka and Andolobe. Also as very large crystals from Fort Dauphin; at Andranondambo and other localities.
- Russia – In black sands of a gold placer on Boshogoch River, Transbaikalia, Siberia; in the Kovdor Massif by Kovdor, Kola Peninsula; in the Yenisei Range, Siberia.
- United States – reported from Easton, Pennsylvania; black sands in Missouri River, near Helena, Montana; Scott River, Siskiyou County, California; black sands in Nixon Fork and Wiseman districts, Alaska.
- Canada – Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca; Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario.
- South Africa – Occurs with baddeleyite as an accessory in carbonatite at Phalaborwa, Eastern Transvaal.
- Democratic Republic of Congo - Kasaï region