The Zacatecas Mining District covers an area of over 700 square kilometres in north central Mexico known for its rich epithermal and mesothermal vein deposits containing silver, gold with varying amounts of copper, lead and zinc. The dominant features responsible for the localization of precious and base metals are believed to be Tertiary age and are likely related to a volcanic caldera complex and to a set of northerly trending basin and range fault structures. The following description was obtained from Price (2008) and further condensed from Ponce and Clark (1988). “The district is located at the transition of the eastern flank of the southern Sierra Madre Occidental province and the north-western limit of the Mesa Central physiographic province. The Sierra Madre Occidental province, one of the most extensive volcanic fields of the world, is a massive pile of nearly horizontal volcanic rocks that underlies a vast plateau, composed largely of siliceous volcanic rocks of the upper volcanic series that rest discordantly either on the lower volcanic series, which are composed mainly of intermediate lavas, or on metamorphic rocks of Precambrian or Palaeozoic age and igneous or sedimentary rocks of the Mesozoic era (the Pimienta series).
Local Geology and Mineralization – San Acacio area (on the main Veta Grande) The San Acacio concession is underlain by the early Cretaceous Chilitos Formation. Rock types include a variety of different submarine andesitic volcanics with textures commonly pillowed, massive, porphyritic or brecciated in nature. Minor clastic sediments are intercalated with this dominant volcanic package.
Regional Mineralized Vein Systems – Zacatecas Area Precious and base metal veins in the Zacatecas area can be divided into three distinct vein systems depending on mineral assemblage, age and general orientation. These are briefly described below in sequence of importance, partially condensed after Price (2008). A detailed account is discussed in Ponce and Clark (1988).