The Lakeshore porphyry copper deposit, Final County, Arizona: geologic setting and physical controls of mineralization

CIM Bulletin, Vol. 83, No. 937, 1990

Holly L.O. Huyck, Department of Geology, University of Cincinnati, Cincinnati, Ohio

Disseminated hypogene sulphide mineralization in the Lake-shore porphyry copper deposit (also called the Cyprus-Casa Grande deposit) of Arizona occurs in both a granodiorite stock and associated volcanic rocks. Structural development and vein paragenesis at Lakeshore are similar to other Laramide porphyry copper deposits of the southwestern U.S. Two major structural trends are present: intrusive contacts, copper-bearing potassic alteration veins and major post-mineralization Basin-and-Range type faults trend N-NW, whereas phyllic veins and secondary post-mineralization faults trend N-NE, and deep propylitic veins trend NE-ENE. Lithologic permeabilities, caused by fracturing in all rocks and by grain size distributions in volcanic rocks, controlled the distribution of copper mineralization. Differences in chemical compositions of host rocks did not affect ore grade. Structural control, through density of chalcopyrite-rich veins, was the major control of ore grade. Fracture density of other potassic vein types did not strongly affect grade. Within volcanic lithologies, permeability, as indicated by grain size distribution, provided a second-order, but significant, control of mineralization.

Keywords: Mineralization, Copper deposits, Cyprus-Casa Grande deposit, Lakeshore deposit.