I tried Core mining last year before the mining nerf hit, and had the same experience as the OP. Spent an hour scanning for cores in a double hotspot before I finally found a single one, and then when I cracked it it was brommelite. I tried once more another time with similar results.
So I said screw DCM, refitted for surface mining and got excellent results with painite. When the nerf hit, I had enough money to never bother with it again.
So I said screw DCM, refitted for surface mining and got excellent results with painite. When the nerf hit, I had enough money to never bother with it again.