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List of Figures

Figure 1. Schematic diagram showing the relationship between fluid inclusion types, boiling and gold and base metal mineralization in epithermal deposits. (modified from

Cline et al., 1992).

37

Figure 2. Location map of the Guanajuato Mining District showing locations of the three major veins (La Luz, Veta Madre and Sierra) and various mines in the district. (modified

from Church, 1907 and Taylor, 1971).

38

Figure 3. Solubility of gold as a function of pH and oxidation state (log fH2 or log fO2). The solubility is calculated at a temperature of 250°C, total sulfur (S) activity of 0.01, potassium ion (K+) concentration of 5 x 10-3 molal and magnesium ion (Mg2+) concentration of 4 x 10-5 molal. Illite-adularia equilibria calculated from data in Helgeson

  • (1969)

    and amorphous silica and quartz solubilities from Gunnarsson and Arnórsson

  • (2000)

    . Maximum gold solubility is represented by the yellow circle, and gold solubility

contours (in ppb) are shown by dashed lines. (modified from Henley and Brown, 1985,

and Shenberger and Barnes, 1989).

39

Figure 4. Stratigraphic column of the Guanajuato Mining District adapted from Echegoyen-Sanchez (1964), Buchanan (1979) and Randall et al. (1994).

40

Figure 5. (Top) Plan view of the Veta Madre showing surface sample locations and general geology (modified from Stewart, 2006). Tvbx: Veta Madre vein exposed at surface; TEanbx: Tertiary (Eocene) volcanic breccia derived from the massive lava flows: TEanfl: Tertiary (Eocene) massive andesite lava flows overlain by volcanic breccia; TEss: Tertiary (Eocene) monomictic to polymictic conglomerates, breccias, sandstones and ash tuffs; Kqfp: Cretaceous rhyolite, quartz porphyry dikes and small plugs; Ksh: Cretaceous mudstone, slate, muscovite schist, pyllite, sandstone, quartz arenite, limestone interbeds; Kanfl: Cretaceous andesite lava flow. (Bottom) Cross section showing location of all 855 samples, including drill core samples,

projected onto the Veta Madre. No vertical exaggeration.

41

Figure 6. Fluid inclusion textures observed at Guanajuato, Mexico. Schematic diagram of the FIAs containing consistent liquid-to-vapor ratios (top, left) and inconsistent liquid-to- vapor ratios indicating boiling (top, right); Photomicrographs of FIAs containing consistent liquid-to-vapor ratios (middle, left) and inconsistent liquid-to-vapor ratios indicating boiling (middle, right); Schematic representation of the liquid-to-vapor ratios of aqueous inclusions at room temperature as a function of temperature of

homogenization.

42

Figure 7. Summary of silica and calcite textures observed in the epithermal environment (modified from Bodnar et al., 1985; Sander and Black, 1988; Dong et al., 1995). A) Jigsaw texture quartz; B) Feathery texture quartz; C) Flamboyant texture quartz; D) Plumose quartz; E) Rhombic calcite; F) Lattice bladed calcite; G) Colloform texture silica (quartz); H) Colloform-banded plumose texture quartz; I) Colloform-banded jigsaw texture quartz; J) Massive quartz; K) Zonal texture quartz; L) Crustiform texture quartz;

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