Structural analysis of the Velardeña mining district, Mexico: a faulted Au–Ag-rich hydrothermal system

Abstract

Epithermal Au–Ag veins of the Velardeña mining district (north-central Mexico) correspond to narrow, fault-controlled, high-grade structures that are continuous along strike for several kilometres. The veins converge toward the Guardarraya intrusion where carbonate-hosted deposits are found at the contact with surrounding limestones. The mineralized structures are cut by Basin and Range normal faults showing apparent vertical displacement up to 320 m. Paleostress reconstructions in the Velardeña mining district suggest that mineralized structures formed during a NNE-directed extensional event that predated the Basin and Range faulting event (ENE-directed). Basin and Range normal faulting is responsible for surface exposures of various Au–Ag mineralizations formed at different crustal depths, thus enabling studies of the entire hydrothermal system—from low-grade breccia zones in the volcanic cover rocks to deeper base-metal-rich deposits.