A K-feldspar breccia from the Mo-Cu stockwork deposit in the Galway Granite, west of Ireland

A K-feldspar breccia, spatially associated with the Mo-Cu mineralization of a stockwork in the Late Caledonian Galway Granite at Mace Head, is described. The breccia is clast-supported and is composed of sub-angular fragments of perthitic K-feldspar granite and microgranodiorite clasts set in a matrix of quartz, biotite granite clasts were brecciated and silicified as they were carried (to the present structural level) by hydrous K- and SiO₂-rich fluids. The residue of these fluids crystallized to form the breccia matrix. The formation of the breccia predates the mineralized quartz veins of the Mo-Cu stockwork. It is concluded that the breccia formation is genetically related to ore-forming processes in the Galway Granite. -from Authors