Geology & Mineralization
The Cerro San Pedro mining district is located in the Eastern Sierra Madre fold-and-thrust belt of east-central Mexico. The district was originally discovered by Spanish explorers during the late 16th century. The local stratigraphic section is dominated by Cretaceous age limestones that have been intruded by the San Pedro porphyry, a late Cretaceous to early Tertiary age monzodiorite intrusive body emplaced along a regional scale thrust fault. Mineralization occurs within an upper oxidized zone that hosts disseminated gold and silver associated with secondary iron oxides and a lower zone of gold-silver-zinc-lead sulphide mineralization.
Based on available historic records, between 1575 and 1950 the Cerro San Pedro district is estimated to have produced approximately 2.5 million ounces of gold, 40 million ounces of silver, 405 million pounds of zinc, 224 million pounds of lead, and 93 million pounds of copper. Nearly all of this production has come from carbonate replacement mantos, veins, and chimneys occurring in the limestones adjacent to the San Pedro porphyry, which is host to disseminated and stockwork style mineralization. More recently, open pit mining of the oxide zone has resulted in the production of approximately 1.6 million ounces of gold and 78 million ounces of silver from both limestone and porphyry ore types. When combined with historic estimates, the Cerro San Pedro district is estimated to have produced in excess of 4 million ounces of gold and 100 million ounces of silver plus associated zinc, lead, and copper.
Deposit Alteration & Mineralization – Long Section
Following the acquisition of the Cerro San Pedro Mine in 2008, New Gold initiated an exploration drilling campaign to test the potential of the sulphide zone that extends below the open-pit heap leach reserve. Exploration of the sulfide zone confirmed the continuation of both higher grade manto-style gold-silver-zinc-lead mineralization extending laterally from historic underground workings as well as lower grade mineralization hosted within the underlying San Pedro porphyry. Although the company suspended its exploration efforts at Cerro San Pedro at the end of 2012, the sulphide zone remains an attractive target for future exploration and development.