So, for the specific situation of OP, I agree that automated mines and probably the way to go, but there is also a greater question of extrasolar colonies and what to do, when you have colonies far away. In a recent game, I tried to work towards self-sufficiency as much as possible and it actually not as difficult as I had thought. All you need to population, construction points, and minerals.
The first part is easy enough as others have already pointed out, so I'm not going to comment more on that, except to add that I had several 300 million population colonies in other systems that were well on their way to supplying their own system with mines and ground forces.
For construction points, I used to think that I needed to establish a population first, send construction factories, and then start building, but this is really a terribly slow option, especially if you cannot supply the population fast enough to service all the construction factories. Inspired by an off-hand comment in one of Steve's AAR's, I have instead started mass producing engineering brigades. This is an incredibly efficient way of servicing a frontier colony with building capability. They don't require any population and in terms of build points, they are only slighly less efficient than construction factories for the same amount of construction capacity. They use vendarite instead of duranium and neutronium, which can be an advantage if you have a crunch and I never seem to use all my vendarite. They also allow you to construct them in parallel to construction factories since they use different facilities and won't take up construction capacity to build your mines, for example. For most colonies I would probably ship around 200.000 tons of vehicles with construction modules as a start. I don't have the numbers on me right now, but this was often enough to get started. Then as I build construction factories, the engineering brigades could be redistributed to newer colonies.
But they also need minerals. If you have a specialized colony, it is easy to send the right minerals, but I always get annoyed at setting up the logistics orders to get the exact minerals needed and the amount I can hold in the mineral transports, so I tried a more universal approach. Using mineral transports with cargo capacity of 5.000 tons, I can hold 220 of each mineral type. I would set up a template to load 220 of mineral type on earth. This saves a lot of micro management, because then I would set a reserve for each mineral at the new colony (usually 1.000), unload/load to reserve level, go back to Earth to unload and refuel and set the order to cycle. This ensures a steady supply of all minerals and with the unload/load to reserve level order you also ensures that you don't just drain Earth of resources. Once the reserves have been filled, the mineral transport will only unload those minerals that have been used since last arrival.
Because construction is slow in the beginning it is easy enough to get the full reserve before getting construction up to task, but later you might want to set up a second mineral transport or just manually set up one-time deliveries of a single mineral trains fast. I had this issue multiple with boronide for fuel refineries, where I never updated the reserve level, but when I had enough construction capacity to build them, the boronide drained much faster than my mineral transports could keep up with.
Once you have colonies multiple systems, it gets a bit more tricky. The further distance away from Sol, the longer it takes the minerals to get there, which is problem when you build a lot. I haven't quite solved this. One option is simply to set up more mineral transports proportional to the distance, so the delivery relative to travelling time is the same. Another is to set up chains of deliveries, but that reduces the advantage of the template to reduce micro management, and it is a bit more tricky to make sure that the intermediary colonies get the mineral they need and that they are not just transported away immediately. If you have colonies A, B, and C and set up transport A-B and B-C to reduce travelling time, then the 220 duranium from A gets to B, but is then immediately picked up by another transport and transported to C. So you would need to set up 2 transport A-B and then one transport B-C, but I'm not sure how much more efficient this is.
None of this of course takes into account the actual minerals mined in each system, which is, after all, the main purpose.
