Whitby & tourism more generally is the long-term cash cow & employer in those parts, not a mining venture with a finite lifespan. Bringing huge freight trains into or close to Whitby or along the coast or the Esk Valley would never be a viable or desirable option?
Regardless of that though, I'd guess it would be hopelessly inefficient & unsuitable to a large scale venture. Even the two carriage Middlesbrough to Whitby Northern Rail service takes half a lifetime down the Esk Valley line. Couldn't guess how long a heavy freight train would take, even with massive line improvements?