the poland Quarry I looked had a relatively short life span or likely half now; and if you assume they target the hi-grade first then get the out crop:
It supplies one of EU's best renewable Polysilicon smelter configurations; which went online 2018. But it also supplies to other glass / constructions industrial - so despite the smelter coming online 2018, the quarry itself has been shortening its life span much earlier. There was proposal by another company to build another - BUT ironically Iceland actually has energy supply crunch at the moment, part due to Crypto Miners buying capacity, but ironically less sun-light, and wind over the last twelve month, So it takes time for a further Geothermal plant to be constructed as they need to pre-allocate the capacity before commissioning, I think that was implied.
Out crop was like 91% silica, and I think it was 95% "hi-grade".
https://www.pcc.is/the-plant-technology/our-silicon-metal-plant/
Example of the mention of the other customers of the quarry:
Which leads me to believe it end of life, will probably be before 2030 or much sooner if they try fast track - but they are limited by the EU CO2 certificates pricing, if it goes up - then its unaffordable to increase production.
The largest producer is in Spain but the energy crisis demonstrates how EU is held hostage to it own "Green" values.
https://www.nasdaq.com/articles/ferroglobe-halt-two-furnaces-in-spain-due-to-high-power-prices-2021-09-28
(20min delay)