The cassiterite makes up some fraction of the standard sand and river silt there.

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The Canal and River Trust said silt would be "hoovered" up from the bottom of the docks.

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But by the time it was completed in 1598, the Guadalquivir River had begun to silt up, causing all New World trade to move to Cadiz and the building became a rather opulent filing cabinet instead.

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Work has begun on removing several tonnes of silt from the River Nene in Northamptonshire.

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The silt will be removed from the river using an excavator on a barge.

BBC: River Nene: Silt removal aimed at improving navigation

The river swirls away, white-crested and silt-laden, racing to the nearby border with Pakistan.

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The river is a khaki-colored wash of silt and snowmelt that flows out of the mountain range to the north, past mud-walled family compounds.

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"This resulted in a 33km stretch of the brook, the River Cledan, the River Irfon and the Wye being polluted with silt, impacting on water quality, " said an agency spokesperson.

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Those glorious inundations moved massive quantities of sediment through the Grand Canyon, wiping the slate dirty, and making a muddy mess of silt and muck that would make modern river rafters cringe.

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