Early Jurassic arc related magmatism associated with porphyry copper mineralization at Zafranal, Southern Peru unraveled by zircon U-Pb ages

Abstract

Early Jurassic arc-related igneous rocks host porphyry copper prospects and gold-bearing quartz vein deposits in southern Peru. Ten new zircon U-Pb ages for wall rocks of gold-bearing quartz veins, Jurassic rocks and copper-mineralized porphyry bodies in Zafranal porphyry copper, together with published ages for Jurassic rocks, reveal a continuous magmatic evolution of the early Jurassic arc. The Jurassic rocks and gold-bearing quartz vein systems in the western flank of the Western Cordillera are hosted by Paleo- and Meso-proterozoic orthogneisses of the Arequipa Massif (1.75-1.44 Ga) that underwent Grenville-age metamorphism ~1 Ga. The early mafic magmatism is recorded between 199.6-193.2 Ma, and was followed by dominantly felsic magmatism from 184.1-174.9 Ma. Both magmatic events have formed the thinnest intrusive belt (<15 km wide) of the Coastal Batholith in southern Peru. The last magmatic event of the early Jurassic (181.0-174.9 Ma) is represented by several phases of porphyries associated with copper mineralization in the Zafranal porphyry copper deposit. The published ages indicate that the magmatic arc migrated along eastern limit of the Arequipa Massif during Middle Jurassic. In the late Jurassic (~146 Ma) the magmatic locus returned near early Jurassic intrusion. Overall, the plutonic intrusive rocks and porphyry bodies with copper mineralization represent the oldest magmatic events of the Coastal Batholith of Peru formed during the early Jurassic.