Peter,

Yes, tetrahedrite group minerals typically occur as primary phases in
mid-temperature ore deposits. The images Trevor has obtained show galena
with a tetrahedrite-chalcopyrite-ullmannite-millerite inclusion assemblage -
a typical primary association from such deposits.

Supergene (or secondary) tetrahedrite can form under certain ciecumstances,
but the material Trevor has is definitely primary.

I've had a look in Dines (1956) Volume 2 pp. 757-758, regarding Combe Martin:

"Devonian slates, dipping steeply south-south eastwards, are traversed by
veins, lenses and small lodes, generally following the bedding planes of the
slates, but, in places, crossing them at acute angles. The veins and lenses
consist of white quartz and siderite with small veinlets and scattered
crystals of galena and, occasionally, crystals of zinc blende. Other
minerals present are chalcopyrite and, in the gossans, the secondary copper
ores covellite, malachite and azurite, and filaments of native silver. Some
minerals of rare occurrence in the veins are antimonite [=stibnite - JM] and
millerite. The silver content of the galena ranged up to 168 oz. per ton."

This description (almost certainly based on hand specimen mineralogy rather
than pretrology) suggests to me that the mineralisation was probably
emplaced after the end-Carboniferous Variscan folding that gave the host
rocks their steep dip. Tensile stresses that would permit fracturing and
thus vein emplacement would readily exploit any pre-existing weaknesses in
the strata, and in a steeply dipping sequence as we have here, bedding
planes would offer such a weakness for exploitation, so that
bedding-parallel fractures would readily develop.

I wonder, then, if these deposits are indeed part of the Permian and younger
SW England Orefield, and if they in fact represent a development of
mineralisation at a point rather distal from the "centres" where the
Cornubian Batholith comes to the surface? It would be interesting to get a
handle on the sulphur isotope compositions at Combe Martin.

Your point regarding rich ore being discarded applies similarly to the
Darren and Cwmerfin mines, where prior to the reclamations, chunks of quartz
with multi-centimetre masses of tetrahedrite could be found quite easily. If
that was what they threw away, what was the really good stuff like???

Also agree with Trevor when he says there should be more cross-cooperation
between the disciplines. There is much that mineralogy can offer to the
mining archaeologist especially with complex old mines like the one being
discussed. Getting funding for such work is the tricky bit, though!

Cheers for now - John