The Rising Influence of Rising Affluence

[OakesCS]

at 1st i thought it was an interesting possibility because submarine exhalative metal deposits https://en.wikipedia.org/wiki/Sedimentary_exhalative_deposits
https://en.wikipedia.org/wiki/Volcanogenic_massive_sulfide_ore_deposit
were 1st identified in Japan and formed in somewhat similar environment.

However, after crunching some rough numbers for the area mentioned and assuming the 'mud' was 1 meter deep, then the concentration of rare earths is in the 5 ppm magnitude which is roughly the same or lower than the concentration in your backyard. The grade could be increased by lowering the thickness of the mud but then the recovery costs probably go up.

So once again, somebody is trying to sell something that only the unwitting will buy (which i see happen on a regular basis so i wouldnt rule it out).