Yep, you were reading the system correctly.
In 0.35.6 geological cores were effectively finite per field. A normal geological field gives 5 cores when surveyed, so while the map is technically infinite, in practice you had to keep finding and drilling new fields if you wanted more assay paperwork and therefore more mining equipment.
That wasn't really the behaviour I wanted. The cores are supposed to gate prospecting and mine development, not put a hard limit on how many excavators you can build.
I've changed this for 0.35.7. Geological cores are still consumed during the assay/prospecting process, but the resulting assay reports and mine-development plans are now returned when you use them to build mining machinery. So once you've done the geological work, you don't have to keep burning more cores just to expand the same mining operation.
You were also right about the Overburden Excavator. Previously the Hydraulic Excavator was basically a straight upgrade, which made spending scarce development plans on the earlier excavator feel bad.
For 0.35.7 I've reworked the roles:
• Overburden Excavator = dedicated stripping specialist. It is now faster on overburden, uses less power and produces less pollution.
• Hydraulic Excavator = flexible general-purpose excavator. It can handle overburden as well as quarry deposits and blasted hard rock, but isn't as efficient as the specialist for pure overburden removal.
So no, you weren't missing another hidden source of cores, and the feeling that you'd wasted them exposed a genuine balance issue. Thanks for pointing it out — it's fixed in 0.35.7.
