I realise I'm answering my own post, well at my age that's okay, but I realise i was a bit cryptic with the last. A slightly more detailed explanation although the graphics aren't great.
🔗LAVRIO-Silver-Mine-User-Album-Image-015[linkphoto]LAVRIO-Silver-Mine-User-Album-Image-015[/linkphoto][/link] Operation of a Helicoidal washery
(Note: the name comes from the word helical - from helix i.e. spiral - as the water slowly spirals down towards the ground as it runs round the washery circumference)
Water is initially transferred from the cistern (top right) into the washery tank via an elevated channel. A hole in the side of the washery tank (3) allows water to meet the unwashed ore being shovelled into the start of the circular washery (2). As the water/ore mixture progresses round the circular channel (a 20 cm level difference from start to finish) the heavy lead ore drops onto the depressions while the unwanted impurities are carried round to the primary sedimentation tank at the end of the channel & removed by shovel. The clarified water from the secondary sedimentation tank (12) is bucketed back into the washery tank for reuse.
The past is a foreign country: they do things differently there.