Mexican epithermal deposits can be broadly grouped into two types based on their contained metals, distribution, associated
igneous rocks and fluid inclusion compositions. Silver-gold deposits (e.g. Tayoltita) mostly occur in the western part of
northern Mexico where host rocks consist of Eocene, intermediate composition volcanic and intrusive rocks; fluid inclusion
studies indicate that mineralizing fluids were <300 c and dilute (53 eq. wt. % nacl ). in contrast, silver-lead-zinc deposits>
(e.g. Fresnillo) mostly occur in the central part of northern Mexico where they are temporally associated with Oligocene- Miocene volcanic rocks and intrusions of felsic composition, but commonly hosted within underlying Paleozoic-Mesozoic
sedimentary rocks; fluid inclusion studies indicate that mineralizing fluids ranged from 200 to 400 C and were saline (>_10
eq. wt. % NaCl). The distribution of these two deposit types, crosscutting major major crustal sutures, and the close
spatial-temporal relationships between mineralization and magmatism, together suggest that magmatic processes were more
important in the formation of mineralizing solutions, as a source of both ligands and metals, than the segments of crust
hosting deposits.