Abstract
Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with pyrite and anomalous selenium content. Mineralisation here may have reflected very high heat flow in foreland basins north of the emerging Variscan orogenic front, responsible for gold occurrence in the South Wales Coalfield. At Castlecomer, gold (–platinum) is attributed to precipitation with replacive pyrite and selenium from groundwaters at redox interfaces, such as siderite nodules. Pyrite in the cores of the nodules indicates fluid ingress. The underlying Caledonian basement bedrock is mineralised by gold, and thus likely provided a source for gold. The combination of the gold occurrences in coal in Castlecomer and in South Wales, proximal to the Variscan orogenic front, suggests that these coals along the front could comprise an exploration target for low-temperature concentrations of precious metals.
Highlights
Much of the world’s resources of gold and other precious metals occur in magmatic and metamorphic “basement” rocks
Coals of the Leinster coalfield generally comprise up to 80% Total organic carbon (TOC) (Table 1), with reported 89%
[45], in a development of siderite nodules is a feature of burial diagenesis down tometres a few hundred non-marine whereenvironment, iron is deposited as carbonates
Summary
Much of the world’s resources of gold and other precious metals occur in magmatic and metamorphic “basement” rocks. The gold deposits may be located following detection of anomalies in stream sediment and water samples, especially in terrains where bedrock exposures can be very limited [1]. The mobility of gold indicated by the water-borne anomalies implies that gold is susceptible to concentration in sedimentary geochemical or hydrodynamic traps, such as in coal-forming settings [2]. Concentrations of gold-bearing Upper Carboniferous coals have been identified in the US Appalachians [9,10], Canada [11], Great Britain [12,13], France [14], Central
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