A progressive model for the development of the Cavanacaw Au-Ag-Pb vein deposit, Northern Ireland, and implications for the evolution and metallogeny of the Grampian Terrane

摘要

Deformed vein systems may exhibit complex geometries with kinematics that are not always easily reconciled within the overall tectonic framework and interpreted palaeostress fields. In ore exploration and mining, the misinterpretation of complex vein geometries as polyphase deformation, as opposed to progressive deformation, may be detrimental to developing effective exploration strategies or geometric models for ore bodies. An example of this is the Cavanacaw Au-Ag-Pb vein deposit in Northern Ireland which has previously been interpreted to have had a polyphase deformation history linking economic mineralisation to span both the Caledonian and Variscan orogenies. Here, we present structural analysis to demonstrate that the geometries and kinematics of the broadly N to WNW-striking vein system is more easily explained with a single progressive kinematic model incorporating overall sinistral shearing along Silurian ENE-WSW-striking transcurrent faults during the Scandian event of the Caledonian orogeny. This progressive deformation further accounts for a regional, abrupt 'knee bend' strike swing in Dalradian Supergroup rocks that is probably related to the wider mineralisation and penetrative mid-Silurian deformation in the area. Our analysis additionally implies that Cavanacaw is younger than the nearby Late Ordovician Curraghinalt deposit which is related to the Grampian event, but is also slightly older than the Early Devonian Cononish deposit in Scotland that similarly links to the Scandian event. This study ultimately demonstrates how an understanding of progressive deformation can have key scientific and economic implications by informing regional and tectonic deformation models and exploration strategies, respectively.