Hi, nail making and mining were two major industries in Dudley (particularly in Netherton, within Dudley Borough) during the 1800s. There were apparently Nail Makers strikes around the 1840s and 1850s, I think due to increased mechanisation and the subsequent loss of jobs. It makes sense that your Grandfather would have been employed in mining, being one of the other major industries in the area, and as (I think!) there would have been few nail making jobs left in Dudley by 1900. Maybe mining in Chesterfield was similar to mining in Dudley! I'd suggest searching for 'Netherton, West Midlands' in good old Wikipedia, and under 'industry' it should give you a very brief outline of when the strikes were etc. I think it also says that the last nails to be made by hand in the area were for horse-shoes.
I hope this helps, good luck with your research.