There are a lot of accessible mines in the Peak - what level of experience/technical skill are you after? Mouldridge is a good easy walk-in, Devonshire Cavern has plenty to see though routefinding off the main trail can be "fun", ditto Wapping-Cumberland. The Via Gellia has plenty to go at, or if you're experienced in SRT, Oxlow/Maskhill, odin, Water Icicle or Knotlow.
As for fluorspar mines that have been blocked up, there's only Milldam and Watersaw that have been blocked - there are a lot of others still open, like Hanging Flat?