You wouldn't believe the system I just found...
There was a little jump point way out in Sol that I had previously ignored (#6, I had explored the other 5 and a bunch of other jumps out past them) and I decided to send my new exploration vessel through it. Wow...
Two stars, star B only orbiting 15.9b KM from the main one. The B star is relatively cruddy, with no mineral content - but it does have 3 worlds with decent gravity and enough temperature to eventually terraform to 0.
The A star, on the other hand, is just amazing. It's orbited by a bunch of massive worlds. The first one has about 50 million minerals distributed between 9 types, all of which are above 0.5 accessibility (three are .9), it's too hot but I think I can get it to 0 cost with anti GHG like I did mercury. The second world is immense with way too much gravity, but it has 153 million minerals in 7 types with fair accessibility (couple .1s, others are .7, .8, .9). Third world is a huuuuge gas giant with 10 million Sorium at 0.4 orbited by a bunch of moons, 2 of which are about 1 gravity with atmospheres at 0 and 0.01 colony cost. Both of them have massive mineral content - 105 million on one, 175 million on the other. The larger one has alien ruins. Between the worlds orbiting this star I have access to every mineral at 0.9 accessibility with tonnage in the tens of millions.