Getting a bit confused with mining!

[narf poit chez BOOM]

your mineral's are probably going up from your planet's. most people use either bases or satelite's for remote mining. remote mining also lower's the value by 1% per turn in an infinite resource game. this can be turned off in the settings.txt.

[Taera]

mineral mining becomes worthwhile with destroyer+ ship sizes (read - at least 2 mining components) and on the more profitable places - asteroids go as high as 300%, use those...
With maintenance reduction + crystallurgy mining can be very profitable, if time consuming...
Dont forget tho the resources run out unless you check it off in settings.txt