It's a bug. Once your refinery fills, it starts acting odd. The bug not only keeps you from mining other minerals, it also has a couple of other effects. When the bug happens, your cargo scoop display will no longer light up when your scoop is open. You'll get the audio saying that it's open or closed, but the light will stay off. You won't be able to enter supercruise until you log off and back on. If you try, you'll keep getting the Hardpoints/Scoop deployed warning.
This is caused when your refinery and cargo hold are full. If you dump minerals from your hold, you'll see that your hold is emptying, but it continues to say it's full and you can't put anything in it unless you fire a limpet. Even if you manually empty your refinery, your number of mined minerals won't increase. It'll get stuck and any further mining won't count for Selene Jean. Check your right hand screen.
The bug will stay with your refinery, even if you sell the minerals. The next time you mine, you'll only be able to gather the number of tons that your cargo hold is rated for. If, for instance, you have a 64t hold, you'll only be able to mine up to 64 tons, even if you dump cargo before it's full.
The way to get rid of the bug is to go to outfitting and store the refinery, then put it back on your ship. (Or sell it and rebuy it). Once done, just make sure you dump unwanted minerals before your cargo hold is full. If you space it and it gets full, you'll need to store and refit it again.
I'm not sure if FD is working on it. I never opened a ticket or bug report, but others have seen this same bug.