Magmatism and Related Au-Cu Mineralization in the Hualgayoc Mining District, Northern Peru

Abstract

The Hualgayoc district in the Cajamarca region in northern Peru hosts the Cerro Corona Au-Cu porphyry deposit, the Tantahuatay high-sulfidation epithermal Au deposit, and the AntaKori skarn Cu-Au project, plus other Au, Cu, Ag and base metal prospects. Herein the author presents a comprehensive geochemical study and U-Pb dating of igneous rocks associated with mineralization as well as barren intrusions and volcanic rocks in the Hualgayoc district. Bulk rock geochemistry, electron-probe analysis of amphibole grains, and laser ablation ICP-MS analysis of zircon were conducted in order to define the magmatic history of the district and characterize the magmas associated with Au-Cu mineralization. Zircon U-Pb ages indicate that the magmatic activity in the district occurred in the Miocene from 14.8 to 9.7 Ma. The Cerro Corona porphyry Au-Cu deposit formed in a short period of time at around 14.5 Ma. Most igneous rocks hosting the Tantahuatay high-sulfidation Au epithermal deposit formed later at around 13.7-11.5 Ma, and are contemporaneous to the high sulfidation epithermal mineralization. Several barren intrusions and volcanic rocks were emplaced contemporaneously. Bulk rock, zircon and amphibole composition show that all magmas in the Hualgayoc district originate from an amphibole rich source, and are oxidized and water-rich regardless of the presence of mineralization. The magma conditions are conducive for the formation of porphyry and high-sulfidation epithermal deposits. The absence of mineralization in some intrusions suggests that other factors, such as intrusion shape and depth of emplacement, are required for the formation of a deposit. It has been shown that zircon in igneous rocks associated with porphyry deposits have high positive Ce anomalies and low negative Eu anomalies reflecting the oxidized nature of their parental magmas. Igneous zircon from the Hualgayoc district show that the magnitude of Ce and Eu anomalies is independent of the association with mineralization. The result suggests that zircon composition cannot identify specific intrusions associated with mineralization. However, it remains useful in recognizing areas containing oxidized, hydrous magmas, some of which may be associated with porphyry or high-sulfidation epithermal deposits