Ooh nice. That'll be the granite adjusting its isostatic equilibrium then!
That reminds me of an OU program on a geology course I did back in the Stone Age. I think conventional wisdom was that the granite under the Alston block was intruded after the carboniferous sedimentation, but they had a look at the Rookhope, or maybe Stanhope borehole, and I think if I remember rightly that the carboniferous beds were deposited on top of the pre-existing granite. So the mineralisation would not be due to hot granite being intruded, but maybe due to radioactive thorium, potassium and uranium heating the country rock and mobilising metal containing fluids. Lesley Judd presented it, so if I'm wrong with the above, it's her fault not mine.