Basement structural controls on Carboniferous-hosted base metal mineral deposits in Ireland

Abstract

Abstract Explorationists have long recognized the importance of structural control of Irish base metal deposits, but the kinematics and timing of the structures relative to the mineralization are subject to wildly differing interpretations. This paper presents a combination of structural, magnetic and gravity data that show that the fundamental structural controls are easterly to northeasterly-trending basement (Caledonian) structures which have been reactivated in dextral transtension by northeasterly to north-northeasterly extension during the Dinantian. In general, in the north of the country the ore-controlling faults dip south, while in the south of the country they dip north. The structures have evolved through a temporal kinematic history of early normal faulting, later oblique slip, and some show evidence of later reverse movements. Part of this evolution may reflect burial history, although it also reflects the transition from Dinantian transtension to Variscan (Hercynian) compression. The bulk of the mineralization appears to post-date the normal faulting, and pre-date Variscan compression. Mineralization is thought to be post-compactional and could have occurred during the dextral transtension, although some of the sulphides could post-date most of the transtensional movement.