Publication Date

1999

Document Type

Dissertation/Thesis

First Advisor

Walker, James Allen, 1952-

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology and Environmental Geosciences

LCSH

Geothermal resources--Guatemala; Volcanoes--Guatemala

Abstract

The chemical and isotopic composition of water and steam discharges within a 10 km radius of the Santiaguito dome complex shows that this hydrothermal system produces several types of fluids and gases that suggest the existence of different chemical or mixing processes and different flow pathways. Water chemistry suggests that four different types of water exist within the study area: (1) Acid sulfate steam-heated waters issue from a zone on the west and east sides of Rio Samala spanning the area from Fuentes Georginas to the Zunil geothermal field. The range of sulfate in these waters is 140 to 1790 ppm. (2) Most common are weak acid bicarbonate (pH values of 5.2-6.8) and neutral bicarbonate waters; the more concentrated waters are found 3km south of Santiaguito; one exception is a hot spring issuing from the west side of the Rio Samala valley within the zone outlined by the acid sulfate waters. These samples delineate a distinct trend indicating neutralization through rock hydrolysis. (3) Weakly acidic chloride water results from upflow of well equilibrated fluids from a deep zone followed by components of steam heating and interaction with host rocks. (4) Neutral sulfate-bicarbonate waters represent meteoric waters with minor mixing with acid sulfate waters. Spring samples have [lowercase delta]^13C values of -11.5%[sub o] to -8.5%[sub o] ranging between two end members: a depleted shallow meteoric water located north of Santa Maria and a series of enriched hot springs issuing from lahar deposits located <3 km south of Santiaguito. Low temperature gas emissions have [lowercase delta]^13C values of -13.86%[sub o] to -4.59%[sub o]. The foci of the [lowercase delta]^13C enrichment trend in the gas emissions lies on the Zunil fault zone at the southern end of the Zunil geothermal field closest to Santiaguito. Enriched values of [lowercase delta]^13C = -4.59%[sub o] fall within the range of magmatic CO[sub 2] indicating a magmatic source for this signature. Two distinct groups of [lowercase delta]^18O and [lowercase delta]D values occur in the water samples. Depleted springs ([lowercase delta]^18O of -12.69%[sub o] to -9.7%[sub o] and [lowercase delta]D of -96.8%[sub o] to -82.1%[sub o]) lie to the east and north of Santiaguito at elevations above 2000 masl. Enriched springs([lowercase delta]^18O of -8.79%[sub o] to - 6.3%[sub o] and [lowercase delta]D of -60.1%[sub o] to -45.4%[sub o]) occur to the south of Santiaguito at elevations below 2000 masl. The data displays a distinct elevation fractionation distribution of [lowercase delta]^18O. [lowercase delta]^37Cl data for water samples ranges from 0.39 to 1.1 and also shows an elevation fractionation distribution. Gas samples from two locations plotted on gas chemistry ternary diagrams of N[sub 2]/100-Ar-10*He lie along a tie line between air and andesitic gas, indicating some magmatic input to the Zunil geothermal field and to the Sulfur Mountain area. There are two thermal foci in this region, east of Santa Maria and south of Santiaguito, each reflecting different chemical and isotopic signatures. These manifestations from different conduits may have different magmatic sources or may solely reflect differing processes along the conduits.

Comments

Includes bibliographical references (pages [135]-140).

Extent

xiv, 166 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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