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crossed-polars, the colloform texture sometimes shows an evolution from fine-grained

silica to coarse-grained quartz with a plumose texture (Fig. 7H) along a traverse from the

vein wall to the center of the vein. Similarly, colloform texture silica sometimes shows a

jigsaw texture characterized by banding of fine-grained silica near the wallrock contact,

with the size of grains increasing towards the vein center, and is most easily recognized

when the sample is viewed under crossed polars (Fig. 7I). Henley and Hughes (2000)

suggest that this texture is generated during rapid opening of a fracture that produces a

pressure drop and rapid cooling. Colloform texture silica is a primary depositional texture

that has been interpreted to indicate rapid, low temperature deposition of chalcedonic

silica in open space in shallow epithermal systems to produce the rhythmic banding

(Roedder, 1984; Bodnar et al., 1985; Fournier, 1985). This type of silica contains no

useful fluid inclusions (Bodnar et al., 1985).

Lattice bladed calcite is observed in 120 out of 855 samples from the Veta Madre.

This classification includes bladed calcite that is still calcite today (Fig. 7F, 8E,F), as well

as bladed calcite that has been replaced by quartz (Fig. 7F, 8G,H), and calcite with an

acicular texture that has been replaced by quartz (Fig. 7P, 8I). Simmons and Christenson

(1994) described the close association between bladed (platy) calcite and boiling in

geothermal systems and attributed this morphology to the rapid growth of calcite as

carbon dioxide is lost to the vapor phase during boiling. The presence of coexisting

liquid-rich and vapor-rich inclusions in the calcite often confirms that the fluids were

boiling during bladed calcite formation (Simmons and Christenson, 1994; Simmons et al.,

2005). Often quartz completely replaces the bladed calcite and this is thought to occur in

the presence of non-boiling fluids, after precipitation of small quartz and adularia crystals


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