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A 40Ar/39Ar age of 16.94 ± 0.34 Ma on hypogene alunite from the La Virgen sedimentary and volcanic rockhosted Au deposit and new ages of 16.06 ± 0.11 to 15.58 ± 0.12 Ma on porphyry Cu-Au deposits at Minas Conga confirm the existence of early Miocene and earliest middle Miocene mineralization in the eastern part of the Miocene metallogenic belt of northern Peru. A new K-Ar age of 15.3 ± 0.3 Ma for the Magistral porphyry-skarn Cu-Mo deposit extends the belt of known early and middle Miocene deposits southeast of La Virgen. A 40Ar/39Ar age of 20.02 ± 0.15 Ma is reported for a late intrusive phase at the Michiquillay porphyry Cu deposit.

A 40Ar/39Ar plateau age of 15.61 ± 0.12 Ma on alunite from the San Pedro Sur zone at the La Zanja epithermal Au district is consistent with the location of the district within the middle Miocene Quiruvilca-Pierina subbelt of the Miocene metallogenic belt. 40Ar/39Ar mineralization ages of 20.79 ± 0.10 and 21.78 ± 0.11 Ma have been obtained on mineral deposits of the Malvas and Huinac districts in the Cordillera Negra to the south. Together with a published age of 18.7 ± 0.6 Ma on the Churropampa Au prospect in the eastern part of the Cordillera Negra and a new Re-Os age of 18.15 ± 0.06 Ma on the Pachagón porphyry Cu-Ag prospect northeast of Trujillo, an early Miocene mineral activity in the western part of the metallogenic belt is indicated. The new ages show that clearly magmatically related mineralization was formed at the same latitudes in both the eastern and western parts of the Miocene metallogenic belt during early Miocene and earliest middle Miocene times.

The deposits of the giant Yanacocha Au district, which were formed at about 11 Ma, are younger than deposits to the west and to the east. Deposits of the Hualgayoc district to the north, which have yielded mineralization ages from 12.4 ± 0.4 to 14.4 ± 0.2 Ma, may overlap in time with those of Yanacocha. These districts, which are located within large coeval volcanic fields, could reflect a younger episode of magmatic activity of late middle Miocene age.

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