J.S.
Mason - Central Wales
Orefield: Electrum
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Electrum (above):
a bright yellow grain,
less than 100 microns long, and big for Central Wales. This sample is
from Eaglebrook mine, and the electrum (Au:Ag = 60:40) occurs embedded
in galena, associated with the extremely rare mineral tucekite (buff)
and chalcopyrite (yellow). A little pyrite (high relief) is also
present.
Samples of this assemblage from Eaglebrook assay up to ca. 0.7g/t Au,
and you need to make dozens of polished blocks to find one auriferous
grain! Gold is widespread in Central Wales, but always in academic
rather than economic terms. There were quite a few claims of gold
discoveries at lead mines in the 19th century but these always proved
be signs that the mines were running out of lead ore, and were hopeful
attempts to cheer up shareholders. Compare it with the high-grade
specimen from Clogau Mine in the Dolgellau Gold Belt (below).
For some reason, gold in Central Wales is invariably associated with
Co-Ni-Sb minerals. Maybe this says something about the source-terrain
from which the ore-forming fluids scavenged their metallic payload. One
wonders if the Gold-belt strata underlie Central Wales at great depth -
but persuading anyone to drill a hole to find out carries as much hope
these days as winning the lottery! |
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