on the original calcite blades during the latter stages of boiling (Etoh et al., 2002). This
type of replacement texture contains no useful primary fluid inclusions, but secondary
inclusions provide information concerning later conditions. The pseudo-acicular
replacement texture (Fig. 7P, 8I) is produced when parallel bladed calcite or rhombic
calcite is replaced by silica. An aggregate of fine-grained silica phases with anhedral to
rectangular shape replace the calcite to produce an acicular morphology (Adams, 1920;
Dong et al., 1995). This type of replacement texture contains no useful fluid inclusions.
The next most abundant texture observed in 52 samples from the Veta Madre is
massive silica (quartz) (Fig. 6J). This term refers to quartz veins that have a
homogeneous texture, show no banding, fractures or deformation (Dong et al., 1995).
This type of silica often appears milky in hand samples, owing to the abundant tiny fluid
inclusions in the quartz (< 2 µm). The massive texture represents an original growth
feature and can form during slow precipitation at relatively consistent conditions in open
space, and is not associated with boiling.
The remaining mineral textures are observed in less than five percent of the
samples. The zonal texture was observed in 23 samples. This primary depositional texture
is similar to comb texture, but with euhedral quartz crystals that show growth zoning and
which are oriented perpendicular to the vein wall (Fig. 7K). The growth zones often
contain primary fluid inclusions that record the original depositional conditions. The
crustiform texture is a primary depositional texture that has been described by Adams
(1920), Lindgren (1933), Bodnar et al., (1985) and Dong et al. (1995). The banding is
often symmetrically distributed with respect to both walls (Fig. 7L) and is formed as a
result of rapid, episodic fluctuations in temperature, pressure or fluid conditions during