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textures described above are thought to be produced as a result of boiling. At

temperatures =340°C, the solubility of quartz decreases with both decreasing pressure

and decreasing temperature (Fournier, 1985). Shallow hydrothermal systems such as

those associated with epithermal deposits often experience repeated episodes of sealing

and fracturing during the lifetime of the system, as evidence by abundant brecciation and

broken crystals in epithermal systems. Hydraulic fracturing and the concomitant pressure

drop may cause the fluid to boil (or “flash” to steam). When this occurs the temperature

also decreases owing the large heat of vaporization of water. As a result, the originally

silica-undersaturated fluid may achieve high degrees of silica supersaturation, leading to

the precipitation of amorphous silica with a colloform texture. With time, the amorphous

silica may recrystallize to chalcedonic silica and/or quartz (Fournier, 1985) to produce

many of the textures observed in this study. For example, jigsaw texture quartz,

characterized by equant, anhedral interlocking grains is thought to indicate crystallization

from gelatinous amorphous silica that precipitated from a solution very supersaturated in

silica (Fournier, 1985).

Those textures observed here that are thought to be produced directly by

precipitation from supersaturated solutions, or by crystallization of chalcedony or quartz

from original amorphous silica, include jigsaw (Fig. 7A), feathery (Fig. 7B), flamboyant

(Fig. 7C), plumose (Fig. 7D), colloform (Fig. 7G), colloform banded plumose (Fig. 7H),

colloform banded jigsaw (Fig. 7I), crustiform quartz (Fig. 7L), moss (Fig. 7N) and ghost-

sphere (Fig. 7R). Similarly, lattice bladed calcite (Fig. 7F), lattice-bladed calcite replaced

by quartz (Fig. 7Q) and pseudo-acicular quartz after calcite (Fig. 7P) are also textures

associated with boiling fluids. In each sample, the presence of these textures has been


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