The seller's notes claims all three are pertain to Welsh gold mining and state 'they came from a collection of slides relating to gold mining in Mid Wales and slate quarrying in North Wales'.
The nice group photo looks to be about 1900-1905 to judge from the hats. The proprietorial old gent with the splendid beard is very distinctive. All the men look well scrubbed - the company must have asked them to come in on an off day specially for the photo! Looks to be a re-equipping and reopening of an existing mine.
The three-throw pump powering a generator looks quite advanced for the time and the place - assuming its the same date and of the same mine as the group photo. There is a notable amount of brick in the wall and vault housing the pump which is very untypical of Welsh metal mining and slate quarrying regions. The incoming water supply pipe on the left looks recently crudely inserted through the wall; what appears to be an older pipe can be seen in the centre of the wall to its right, suggesting the machinery show had replaced an older installation (which may have performed a different function). All the machinery looks brand-new.
The last photo, captioned on the mount 'Section of Boulder Clay, B-Y-Coed GJW' suggests a location in Gwydyr if pertains to a mine and consequently creates doubt whether all three are of the same location: if all three are from the Betws y Coed area then it'll be a lead-zinc mine; alternatively, if two are Merioneth gold mine images then the third is unrelated. Other permutations are also possible of course. However the specific use of the term 'section of boulder clay' and the detail of the photo gives me the strong impression that this photo is a geological one, probably not closely related to the subject matter shown in the other two, so these may three photos of quite different locations.