and thus represent the physical and chemical conditions in the system at the time
trapping. FIAs may be composed of primary inclusions trapped during precipitation of
the host phase, or may contain secondary inclusions that are trapped along fractures in the
host phase at some time after the mineral has formed. FIAs in samples from the Veta
Madre were further classified as containing either only liquid-rich inclusions with
consistent liquid-to-vapor ratios, or containing coexisting liquid-rich and vapor-rich
inclusions with a broad range in liquid-to-vapor ratios (Fig. 6). Finally, the
homogenization temperature of the fluid inclusions was estimated based on the liquid-to-
vapor ratio in the fluid inclusions at room temperature (Bodnar, 1983) (Fig. 6).
Fluid inclusions in the Veta Madre, and in all epithermal deposits, must be
interpreted with caution because much of the host material was originally deposited as an
amorphous silica phase or as fine-grained chalcedony and has since (re-) crystallized to
produce coarse-grained quartz. Primary-appearing inclusions in such samples are unlikely
to record the original formation conditions (Bodnar et al., 1985; Sander and Black, 1988).
In this study, only secondary inclusions that clearly crosscut quartz crystal boundaries,
and therefore were trapped after the quartz (re-) crystallized, were studied in quartz that
showed textures indicative of original precipitation as an amorphous or fine-grained
phase, as described below. Similar arguments apply to fluid inclusions in replacement
minerals, such as quartz replacing lattice-bladed calcite.
Silica and calcite textures:
Previous workers have shown that silica and carbonate phases in the epithermal
environment can have highly variable and sometimes diagnostic textures (Figs. 7 and 8)