Llanberis mine is also of some mineralogical interest. The lodes it worked
contain a similar mineral assemblage to the mines around Cwm Pennant,
Nantlle and Bethesda i.e. the chalcopyrite is accompanied by a lot of
arsenopyrite and pyrrhotite. These mines all have another thing in common -
they are at a lower stratigraphic level (some of them in Cambrian strata)
than the mines up on Snowdon e.g. Lliwedd, Brittannia etc, hosted by Middle
Ordovician volcanics. In the latter mines, common pyrite, sphalerite and
galena acompany the chalcopyrite; conversely arsenopyrite and pyrrhotite
are rare or absent.
The lodes in all of these mines occupy structures related to caldera
development in Caradoc times, and are texturally pretty similar in all
cases. Hence, this may well be a case of mineral zonation, although as
ever, more research is needed!
Cheers - John
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