The tiles are just atomic units of land. One player will be given, like, 20 or 100 of them, initially?
Or more precisely, player can claim the number of tiles corresponding to what his economical status allows, those initial 20 or how much is just the basis.
Minerals - there's enough of minerals everywhere, it's just that the profitability of mining becomes lower after you exploit the easy sources. It will need a better tech for it, ore enriching etc. For some materials the technology will be only available at Mothership, that will trade with you.
There should be way of determining the quality of the ore, the percentage of precious stuff contained within it. Technically, if you filter a ton of common dirt you'll still be able to extract some small amount of metals from it, but of course you'll be motivated to find a better source. The distribution of these richer ores will be determined by fractal, and you will have to make measurements and infer the location of deposits from them.
There will be mines that can be built, upgradable by enrichers so that it's possible to reduce the volume needed to be ferried to the base where the separator is stationed ..