I think this may be Craigend. I was up there the other day (Friday afternoon)with Doug45 (will write up a few thoughts later), having a look at a few things, and we confirmed three definite adits, two firmly closed, by many tonnes of large boulders, one open. Did it have barbed wire, and some recently renewed timbers? If so, it was the one and only (as far as we know) still open adit at Craigend. But I would not be surprised if there are more. My guess would be approximately grid ref NS760901 for any unknowns (I did not think to go that far), or maybe you were further south below Lewis Hill, where I do believe there has been some limestone extraction?
Or could you please give us some more description? Which side of the Bannock Burn, for instance. Any limekilns nearby?
Have a look at Cambusbarron and Murrayshall posts for some background info (more coming soon, I hope).
We may possibly have a new one here!
Best regards,
Alan