Outside of your home system, larger concentrations of minerals will generally have a lower accessibility.
Noticed that ...
Eden-A I
Duranium 432 180 000 Acc: 0.1
Neutronium 220 522 500 Acc: 0.1
Corbomite 198 810 000 Acc: 0.1
Boronide 116 640 000 Acc: 0.1
Uridium 166 410 000 Acc: 0.1
Gallicite 20 250 000 Acc: 0.1
Eden-A II
Duranium 30 186 450 Acc: 0.1
Neutronium 67 076 100 Acc: 0.1
Corbomite 24 354 220 Acc: 0.1
Tritanium 43 758 220 Acc: 0.1
Mercassium 8 037 225 Acc: 0.1
Uridium 3 186 225 Acc: 0.1
Corundium 27 562 500 Acc: 0.1
Eden Prime - my first colony ( i didn't bother with colonizing mars - only put some mass drivers and auto-mines )
Duranium 10 396 690 Acc: 0.1
Corbomite 2 547 106 Acc: 0.1
Tritanium 14 439 890 Acc: 0.1
Boronide 47 830 940 Acc: 0.1
Mercassium 23 658 250 Acc: 0.4
Vendarite 33 362 060 Acc: 0.1
Sorium 47 830 940 Acc: 0.1
Uridium 976 032 Acc: 0.1
Corundium 5 550 625 Acc: 0.1
Gallicite 23 658 380 Acc: 0.1
Eden-A IV
Duranium 156 800 Acc: 0.9
Neutronium 784 Acc: 0.5
Boronide 1 192 464 Acc: 0.3
Sorium 200 704 Acc: 0.8
Uridium 240 100 Acc: 0.7
Gallicite 451 584 Acc: 0.5
I'm gonna make it a nice nigh-impervious system