The presence of the 2250 Ma quartz-pyrite veins in both the Assynt and Gruinard terranes confirms that these crustal units were amalgamated during or prior to Inverian deformation.The absence of the veins in the Rhiconich Terrane is consistent with the suggestion that it was not finally amalgamated to the Assynt Terrane until the Laxfordian.Here we use Re-Os geochronology to show that ore-stage pyrite from the Lisheen deposit formed at 346.6 ± 3.0 Ma, shortly after host rock deposition.
In the Archaean basement rocks of the Assynt and Gruinard terranes of the mainland Lewisian Complex in NW Scotland, a regional suite of quartz-pyrite veins cross-cut regional Palaeoproterozoic (Badcallian, 1760 Ma) and later brittle faults.
Chalcopyrite typically occurs with pyrite within the breccia matrix, with Cu values generally 5 3%.
Magnetite in granitic clasts and isolated within the breccia matrix is commonly replaced by hematite, indicating that Cu precipitation was linked with redox processes and that Cu deposition was associated with hydrothermal fluid oxidation of the host-rock.
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