If you are using gcps properly I don’t understand why you wouldn’t be getting good enough accuracy for mining? How large an area are you flying? What size are the stockpiles?
If you don’t mind spending the $2,000 then Topodrone is a great kit and will provide L1/L2 GNSS but for $600 you could get the M+ instead of the M2 and the Tuffwing kit. L1 only is fine for a drone because it is in the air and free of obstructions. You can still use your RS2 as a base. You just turn off L2 when you PPK. Another advantage of the Tuffwing is that it is a snap-On snap off so you can take it off whenever you don’t need it. Either way I would still use gcps just for horizontal map alignment if you are trying to do flight to flight deltas.