Hi Peter,
I'm a little bit confused by your reply. This may be because I do not know
the Combe Martin occurrences myself so please bear with me!
You cite Scrivener as saying they are syngenetic "with the Devonian seabed".
That, if they are veins, is clearly a contradiction in terms. If these
deposits are indeed syngenetic then they are sed-ex layers folded with the
parent sedimentary sequence. From what I know this seems unlikely, but
perhaps more info on the mineralisation and its relationship with the strata
will clear that up.
Additionally, tetrahedrite may well be as common as indicated in the report
by Trevor's colleague - and the same thing goes for mines like Cwmsymlog -
if you have a lump of steel-ore in your hand you will not see the mineral.
However, as Trevor wisely had done, get a petrologist to section & polish a
sample and then the reality of the ore mineralogy becomes rapidly clear.
Although tetrahedrite was (before the madcap "reclamation" schemes in the
Cwmerfin valley) common in hand specimen, in centimetre-sized masses, the
greater significance was in the fact that bog-standard galena from those
mines was stuffed with inclusions of it. OK - only 5-500 microns across, but
loads of them. That's where the Darren Mines silver came from!
To recap, I think that the Combe Martin mines worked epigenetic veins in
which the galena had an interesting (and fortuitously
argentiferous)inclusion assemblage. Rob (Ixer) - have you ever examined any
of these ores?
All the best - John
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