Integration of local and regional structural data with gold microchemistry in the Sperrin Mountains of Northern Ireland and implications for regional exploration models

The Dalradian Supergroup in the Sperrin Mountains, Northern Ireland, hosts gold deposits at Curraghinalt and Cavanacaw, however the abundance of alluvial gold in fluvial systems across the region implies other concealed, in-situ sources may exist. This thesis informs regional exploration models by establishing the structural controls on gold mineralisation at Curraghinalt, Cavanacaw, and regionally to assess genetic relationships and variability. Paragenetic and microchemical characterisation of in-situ gold further provides a template for interpreting whether spatial variations in detrital gold microchemistry relate to known hypogene lodes and regional structures, providing insight on gold mineralisation in concealed areas.
Underground mapping reveals that the steep, WNW-ESE-striking Curraghinalt veins formed during orogen-oblique transtension linked to Late Ordovician orogenic relaxation following Grampian convergence. Grade and texture are interpreted to be controlled by permeability heterogeneities and phase separation, with episodic gold precipitation linked to distinct paragenetic stages. The low Ag and Bi-Te-bearing microchemical signature (Type 1) of detrital gold sampled from Curraghinalt Burn suggests local sourcing from veins. Type 1 is found along the Curraghinalt Trend and at Carnamurran, where veining and ore minerals comparable to at Curraghinalt are observed.
Surface mapping and historic maps show that the subvertical N–S to WNW–ESE-striking Cavanacaw veins formed progressively during ENE–WSE-striking sinistral transpression interpreted to be mid-Silurian (c. 425–430 Ma) and linked to the Scandian event of the Caledonian orogeny. Detrital gold sampled here exhibits a microchemical signature distinguishable from Type 1 through higher Ag, detectable Hg, and simpler mineral inclusions (Type 2). Type 2 spatially corresponds to a regional ’knee bend’ strike swing and veins formed during penetrative mid-Silurian deformation.
This thesis suggests two episodes of gold mineralisation occurred in the Sperrin Mountains during the Caledonian orogeny. Detrital gold microchemistry is faithful to that of local hypogene lodes and can distinguish between Late Ordovician and mid-Silurian auriferous veining.