Aurcana´s Shafter Property is host to the historic Presidio Mine and the newer Shafter Silver mine, both of which are located at the eastern end of a seven mile long trend of lead, zinc, and silver prospects.
The Shafter deposit is the northeastern, down-dip extension of the previously mined Presidio mine workings. Silver mineralization at Shafter and the historical Presidio mine is hosted within the Permian Mina Grande Formation limestone.
The silver deposits at Shafter are in the form of “oxide mineralization,” thought to be the result of prolonged exposure of the original sulphide bodies to meteoric groundwater. The mineralization occurs as flat-lying mantos and steep-standing veins within a silicified carbonate host-rock, usually less than 15 metres from an overlying contact with much younger sandstone and shale. Mineralization is often associated with igneous dykes and northeast-striking faults and fractures that relay between stronger east and north-striking normal faults.
Silver minerals of economic interest in the oxide mineralization include native silver and acanthite, while minor hypogene silver occurs primarily with galena. Acanthite leaches readily in cyanide and the silver is recovered by the Merrill-Crowe process.
The silver deposits at Shafter have been classified as a carbonate replacement deposit (CRD) and is similar to many of the world's largest CRDs which occur in adjacent northern Mexico. Mineralization has occurred as part of a long lived system with early anomalous lead and zinc mineralization found along silicified sections of the north-south-trending Mina Grande Fault. A second phase consists of higher grade silver mineralization found along east-west trending structures with varied levels of silicification. These east-west structures form the Presidio and Shafter Deposits. The east-west Herculano Fault separates the Presidio and Shafter Deposits and may have focused the flow of mineralizing fluids rising from depth.
Aurcana´s exploration at Shafter commenced in April 2011, starting with the creation of an updated database that includes Gold Field´s exploration data from between 1977 and 1983, followed by drilling in 2012. Exploration at Shafter was conducted independently from mining development activities.
The main exploration activity has been geophysical surveys, geological mapping and structural analysis, as well as a core drilling campaign focused on the near mine environment that totaled 11,000 metres in twenty-nine holes.
Most of the pure exploration holes were long angled holes designed to bend under known mineralization seeking evidence of a plumbing system and to look for additional potential in previously untested, deeper, limestone units. Major regional and mine structures were targeted. Eleven holes intersected mineralization in the Shafter and Presidio Mine horizons and provided additional data for the mine model.
The potential to increase silver resources at Shafter through exploration drilling is good. Successful in-fill drilling within the area of the current block model may link some of the currently isolated zones of mineralization that were detected by earlier, widely-spaced drill holes. Step-out drill holes may extend the zone to the east, and several holes with interesting silver and gold intercepts suggest potential exists to the southwest, beyond the historic Presidio Mine workings.