POLYMODAL FAULT PATTERNS IN THE NORTHWESTERN SECTOR OF PACHUCA RANGE, HIDALGO, MEXICO: IMPLICATIONS FOR TECTONIC AND STRUCTURAL EVOLUTION OF PACHUCA-REAL DEL MONTE DISTRICT

The Pachuca Range (PR) is ~ 37 km long and ~15 km wide, NW-SE trending mountain range in the eastern part of the Trans-Mexican Volcanic Belt (TMVB). It is composed of Oligocene-Miocene volcanic sequence of andesite, dacite, rhyodacite and rhyolite rocks grouped into various formations of the Pachuca Group, which is covered discordantly by the Zumate Formation and Plio-Quaternary rocks of the TMVB.

The Pachuca-Real de Monte Mining District (PRMD) is in the PR, and has been mined for more than 500 years as it contains more than 100 epithermal Au-Ag veins of intermediate sulphidation. A great amount of mining and geological studies had been done in the PRMD that remains unpublished or exists in the form of technical reports of Mexican Geological Survey. However, studies about structural geology are scarce and old as many of these were based on the classic analysis of faulting in two-dimensional with two sets of faults.

In this work we recognize multiple deformation events through field geologic mapping and structural analysis (kinematic analysis) in an area located 15 km to the west of the PRMD, between Actopan city and the mining area of San Jose Tepenene-Capula-Santa Rosa.

The fault patterns reveal the existence of multiple deformations and complex faulting with more than four sets of faults in the studied area. A minimum of three deformational phases were identified, an WNW-ESE oblique lateral faulting (phase 1), polymodal faulting (phase 2) and N-S extensional phase (phase 3). The structural results obtained are important to understand the tectonic evolution, spatial distribution of hydrothermal alterations and mineralization in the western part of Pachuca range.