Relationships between the tectonic evolution of an orogen and the formation of polymetallic vein deposits

The Caledonian-Appalachian Belt (CAB) hosts several economic and sub-economic polymetallic vein systems and is, therefore, an excellent natural laboratory to study the variations in the characteristics of ore deposit and the timing of their formation, within an orogenic belt. We present some of the preliminary outcomes of a large-scale study on the variability of the vein-hosted mineralisation within the CAB, covering c. 20 different polymetallic vein systems within the Grampian Terrane and its equivalents in Scotland, Northern Ireland, Ireland and Newfoundland.

The multi-disciplinary study combines structural data, age determinations, vein textural mapping and paragenetic interpretation, gold geochemical characterisation, and stable isotope data to show that although the occurrences show many superficial structural and mineralogical similarities, there are significant differences between the structural styles, mineralogy and timing of the mineralisation in different areas (see [1] and [2] for the first publications coming from this work). At least three, possibly four, distinct mineralisation stages are identified between Ordovician and Early Devonian, each associated with a characteristic structural style that can be linked to the overall tectonic evolution of the Grampian Terrane. The tectonic evolution of the orogen in time and space therefore greatly influenced both the timing and the style of mineralisation.

References:

[1] Shaw J, Torvela T, Cooper M, Leslie G, Chapman R (2022). A progressive model for the Cavancaw Au-Ag-Pb vein deposit, Northern Ireland, and implications to the metallogeny and evolution of the Grampian Terrane. J. Struct. Geol. 161, https://doi.org/10.1016/j.jsg.2022.104637.

[2] Chapman R., Torvela T, Savastano L (2023).  Insights into regional metallogeny from detailed compositional studies of alluvial gold: An example from the Loch Tay area, central Scotland. Minerals 13, doi.org/10.3390/min13020140.