J.S. Mason - Central Wales Orefield: Electrum

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!