Phosphate is a contaminant in iron ore, but a nutrient in agriculture.

Fine particles of ore can be a problem for handling (because of turning into dust or mud, and bunging up machinery), but they can always be sintered back together.

Chia seeds can grow fast, even in a semi-arid environment.

Open cut mines are sometimes limited in depth by the water table.

Therefore, in the end-of-life pit, turn the lowest levels into a little terraced farm, irrigated from the nearby water table, where the soil is that part of the output from the crushers that is too phosphatey to sell easily and too fine to handle easily, enriched artificially with carefully calibrated amounts of N and K.

As each little plot of iron-soil is harvested, scrape up the iron-rich dust, now lower in phosphates, sinter it together, and ship it to market.
-- pertinax, Aug 07 2024

Growing chia seeds https://www.theseed...rowguide/chia-seeds
The manure won't be a problem, because the owner of this mine also farms cattle. [pertinax, Aug 07 2024]

Fines https://www.bimco.o...0red%20to%20yellow.
The proposed idea would use only the finer fines. [pertinax, Aug 07 2024]

Beneficiation ... https://www.cdegrou...ies/simec-australia
... but this kind doesn't make food. Boo. [pertinax, Aug 07 2024]

Phosphates are precious https://www.science...e%20supply%20chain.
"Global supply of phosphate will fall below global requirement in 2040." [pertinax, Aug 07 2024]

Uptake of phosphate ... https://link.spring...20cortical%20cells.
... by roots [pertinax, Aug 07 2024]

Yes, big [+]

Years ago, I taught in prison, and we had inmates there who had been running--undetected!--a marijuana grow op in Barrie's city-centre old Molson factory for over a decade. I always though their sentence should've been to turn the old mines up north into food-secure gardens for First Nations and other northern residents: Use your powers for good, Superman!

What with the Arctic Passage being open nearly year-round (thanks Climate Disruption!), renewed interest in Canada's North means more people need more groceries. [pert], I predict a real-world uptake of your idea in 3... 2...
-- Sgt Teacup, Aug 07 2024


[+] but will they get enough light down there?
-- doctorremulac3, Aug 07 2024


In summer, they'll be glad of the relative shade; it'll be what stops them from just shrivelling up.
-- pertinax, Aug 07 2024



random, halfbakery