Characterization and zircon SHRIMP U-Pb geochronology of the subvolcanic rocks from Yarumalito Porphyry System, Marmato District, Colombia

Abstract

The mining District of Marmato, located in the Central Cordillera, is considered one of the oldest gold districts in Colombia and its exploration dates back to the Inca’s times, being exploited regularly for more than a thousand years. Inserted in this context lies the Yarumalito porphyry system (YPS), characterized to concentrate ore in structure related veins and stockworks. The YPS is related to the Miocene magmatism of the Combia Formation. In this paper, the subvolcanic rocks directly associated with the mineralized zones were described in order to obtain U-Pb ages in zircon to the intrusions. Selected samples from two fertile intrusions, one andesitic (more abundant in the area) and other dioritic (more restricted), were carefully described and dated by SHRIMP. The results points to a very restricted interval for the ages, with weighted average ²⁰⁶Pb/²³⁸U varying from 7,00 ± 0,15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results constrain the Yarumalito system to the final stages of the Combia magmatism and suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and in the Marmato District.