In my blog on 29 January 2011 entitled “Navigational challenges on featureless plateau” I mentioned that we began our walk by following a bulldozed track that at one time serviced a quarry situated at a height of 900m (now disused), and that although I did not know what was being quarried here I hypothesized that it must have been something special to justify the challenging location.
Well, I now have the answer to what was being quarried. One of our friends, Roy, who is both a very keen mountaineer and amateur mineralogist / geologist, and actively follows our progress on-line, has provided me with the answer [thank you Roy].
Roy has sent me a copy of a scientific paper authored by R. H. S. Robertson and published in 1973 in the Scottish Journal of Science covering the analysis of the rock excavated at this quarry [Robertson73]. Robertson’s paper notes that the quarry was an investigation into the scale and viability of a vein of high-grade quartz that had been observed protruding around a stream-bed and first documented by J. G. C. Anderson in a paper in 1945 [Anderson45].
The general observation of Anderson was that the seam was very pure and uniform in quality, at least at the protruding outcrop and on the rock surface elsewhere in areas where the peak was scrapped back.
There were several reasons that this outcrop received further investigation by Robertson almost three decades later:
- The quality of the quartz on show;
- The perceived size of the seam (dyke-like reef);
- The fact that it was only overburdened by peat (and not by other rock);
- The route to get to the seam, although at 900m, began at Dalwhinnie (some 400m elevation) and the incline of the hillside to climb was reasonably modest.
However, the investigation outlined in Robertson’s paper shows that the quality of the vein quartz was not uniform with depth and samples extracted using a diamond-tipped drill showed that just below the surface (100mm deep) the quartz was “found to be no longer brilliantly white but dull grey, like mutton fat in appearance”. This reduction in quality at depth, plus the fact that bulldozed excavation of the top-layer of peat showed that the area of quartz was smaller than initially anticipated, meant that there was insufficient quantity of high-grade quartz to make extraction commercially viable.
I guess that my own hypothesis that it must have been something “special” (high-quality quartz) being quarried was sort of correct.