Abstract

Cu-Fe-Mo mineralization in the Rio Pisco section of the Peruvian Coastal batholith is spatially associated with the Linga superunit, a suite of monzonitic rocks intruded into Albian volcanics. Petrochemical studies of this superunit indicate emplacement of a differentiation series at a subvolcanic level in the crust. The Cu-Fe-Mo mineralization is located principally in the Albian volcanic envelope and is essentially a low-grade porphyry copper type, although the grade is enhanced where structural controls on the movement of the ore-bearing fluids produced more sulfide-rich vein- and manto-type deposits. Alteration patterns associated with both the mineralization and the Linga superunit suggest a close, predominantly magmatic control on the nature of the hydrothermal fluids. Fluid inclusion studies of quartz from the Linga superunit support this and indicate that emplacement of magmas and mineralization took place at a depth of approximately 3 km. The characteristics of the Linga porphyry copper are compared to those of other such deposits and used to suggest a possible telescoping of geometry of the Andean model of Lowell and Guilbert (1970). Thus, in magmatic hydrothermal systems like the Linga, the deeper parts of the model are effectively brought nearer the surface.

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