You could also have separate Miner Base and Tanker ships. Which then leaves you the question of having your ISRU converter on the Base and tankering fuel or putting your ISRU converter on a space station and tankering up ore. Ore tanks have the best wet/dry fraction of all tanks IIRC, so the theoretically the most efficient system would be a fixed, engineer manned miner base in a high concentration spot, a Tanker lander carrying Ore with just enough Dv to land empty of ore, fill with ore from the miner (via KIS/KAS pipes or EVA Transfer or a rover with a klaw etc etc.) Then to ascend and rendevous with the converter/fuel depot space station to deposit ore and refuel. This would get you: 1. Constant mining of ore with high efficiency (the higher experience the engineer the better 2. Best payload fraction Tanker 3. ISRU converter with reliable Solar power and easy access for passing ships to refuel. In terms of Zero amounts, I am not sure. With Karbonite (Roverdude's original ISRU mod which was the basis for the current Ore system) it was possible to have areas of Zero concentration. Each biome had an average concentration with a variation either side of that e.g. on my 0.90 Minmus had an average of 5% concentration in its highlands biome with variation down to 3.7ish and up to 7.2. However this was right next door to slopes biome, which has 0% concentration. I would have to check the Ore default generation aettings to see if its possible for a 0% ore to be generated. P.S. if you want an ISRU option with smaller converter/drilling options or want to be able to find resources in space, in oceans, or in atmosphere as well as on land then I can recommend Karbonite as an option, although a few of the included parts could be considered OP by some.