Geology topics
Publications and source records attributed to Keith E. Bargar.
Hydrothermal mineralogy studies of specimens collected from nine geothermal drill holes suggest that, at the locations and depths drilled, past temperatures have been hottest (exceeding 300?C) near ring fractures on the south and west sides of Newberry Volcano.
Thirty-eight hydrothermal minerals were identified from 356 drill-core specimens that were obtained from three Scientific Observation Holes (SOH-1, SOH-2, and SOH-4) drilled along the lower East Rift Zone (ERZ) of Kilauea Volcano, Hawaii. The minerals formed during alteration of basaltic rocks and glass by hot, circulating, waters in aquifers consisting of variable mixtures of meteoric water and sea water. Several zeolites, hydrated calcium silicates, carbonates, clays, silicates, sulfates, sulfides, and other minerals were found filling open spaces of vesicles, fractures, and between breccia fragments of the recovered drill core; many specimens that originally consisted of glass are completely altered to some of these minerals, especially clays. Several hydrothermal minerals (erionite, mordenite, truscottite, smectite, chlorite-smectite, chalcedony, anhydrite, and hematite), occur in the SOH drill holes at higher measured temperatures than the same minerals are found in geothermal drill holes of Iceland or other geothermal areas, suggesting that temperatures within the ERZ geothermal system have increased since the minerals formed. Fluid-inclusion freezing data for quartz, anhydrite, and calcite from the three SOH holes show that composition of the inclusion fluids ranges from dilute meteoric water to highly modified sea water concentrated by boiling. Comparison of measured drill-hole temperatures with fluid-inclusion homogenization-temperature data indicates that only about 15% of the fluid inclusions could have formed under the present thermal conditions. The majority of fluid inclusions studied apparently formed during one or more temperature fluctuations associated with the emplacement of nearby dikes and their subsequent cooling. Bacteria-like particles at 1734.6 m depth in SOH-4 could be very significant because the particles occurred at much hotter temperatures (about 265°C) than the generally accepted 110°C limit for survival of bacteria. The presence of Cl in the particles suggests that they might have lived in a saline environment and did not result from contamination by the fresh water drilling fluids. We reccomend that future drilling and subsequent handling of drill hole specimens in the ERZ and elsewhere employ controls to minimize and(or) recognize bacterial contamination.
The purpose of this report is to make available fluid-inclusion information from drill holes in five geothermal areas: The Geysers and Long Valley caldera in northern California; Steamboat Springs, Nevada; the Ahuachapan field of El Salvador, Central America; and the Mutnovsky geothermal field, Kamchatka Peninsula, Russia. These data were produced at the request of various individuals to provide needed subsurface-temperature data for their investigations. The fluid-inclusion information presented in this report has not been previously published, and, since the author did not work in these geothermal areas, only a very minimal attempt is made at interpreting the data. Information on the location of the drill holes from which the core specimens originated ranges from very poor in the case of the Russian drill holes to very good for those in the USA. Mineral specimens from drill-core samples in the five geothermal areas were utilized as cleavage chips, thin sections polished on a single side, or double polished thin sections (polished on both sides). Fluid inclusions from all three USA geothermal areas were found in either hydrothermal or primary quartz crystals. These fluid inclusions firstly were frozen and gradually thawed to determine the final melting-point temperatures (Tm) as the last piece of ice melted and secondly, were heated to the temperature at which the vapor phase disappeared to obtain homogenization temperatures (Tn). For the El Salvador and Russian core specimens the fluid inclusions were hosted in calcite, and the order of the two procedures was reversed because calcite is a much softer mineral than quartz and there is a greater danger of the fluid inclusions decrepitating as the ice expands during freezing. A Chaixmeca microthermometry apparatus was used during studies of the Steamboat Springs and The Geysers fluid inclusions. For the remaining studies, a Linkam THM 600 heating/freezing stage and TMS 90 temperature control system were employed. Accuracy of the data generated from both instruments is similar, with values of about ±2°C for heating studies and about ±0.2°C for the freezing methods.
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The SUNEDCO 58-28 geothermal exploration drill hole was completed in 1981 to a depth of 2, 457 m near Breitenbush Hot Springs in the Western Cascade Mountains of northern Oregon. One hundred thirteen liquid-rich fluid inclusions (mostly secondary) were analyzed from drill cuttings samples of hydrothermal quartz, calcite, and anhydrite, as well as primary quartz phenocrysts. Except for one hydrothermal quartz specimen, minimum homogenization temperature (Th) measurements of fluid inclusions plot very close to the present measured temperatures for the drill hole. Fluid-inclusion data from near the bottom of the drill hole suggest that these rocks were altered by water of significantly greater salinity than Breitenbush Hot Springs water.
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Geothermal drill hole CTGH-1, located near Breitenbush Hot Springs in the Cascade Mountains of northwest Oregon, was drilled to a depth of 1463 m. The maximum reported temperature at the bottom of the drill hole was 96.4??C. The drill core consists predominantly of basalt to basaltic andesite lava flows, tuffs, and volcanic breccia. Red to orange iron-oxide stained tuffs are at least partly altered to smectite. Vesicles, fractures, and open spaces between breccia fragments are partly to completely filled by secondary minerals. All of the minerals are compatible with the present low-temperature conditions.
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Studies of secondary mineral distribution, whole-rock chemical compositions, isotopes, and fluid inclusions are being conducted on the core from Newberry Volcano drill hole 2. Rocks from the drill core are divided into 3 major intervals on the basis of their alteration pattern, which is controlled by rock permeabilities, primary lithologies, and temperatures. Incomplete alteration of pumice-rich lithic tuff layers in the upper part of the altered section and lack of self-sealing in fractures of most lava flows suggest that the hydrothermal system is young. Most of the secondary minerals could have been formed at temperatures near those present today; maximum measured temperature was 265 degree C at the bottom of the hole. Fluid inclusions indicate that past temperatures in the deeper part of the drill hole may have been as much as 100 degree C hotter than presently measured temperatures.
The approximate paragenetic sequence of hydrothermal minerals in the Y-3 U. S. Geological Survey research diamond-drill hole in Lower Geyser Basin, Yellowstone National Park, Wyoming, is: hydrothermal chalcedony, hematite, pyrite, quartz, clay minerals (smectite and mixed-layer illite-smectite), calcite, chlorite, fluorite, pyrite, quartz, zeolite minerals (analcime, dachiardite, laumontite, stilbite, and yugawaralite), and clay minerals (smectite and mixed-layer illite-smectite). A few hydrothermal minerals that were identified in drill core Y-3 (lepidolite, aegirine, pectolite, and truscottite) are rarely found in modern geothermal areas. The alteration minerals occur primarily as vug and fracture fillings that were deposited from cooling thermal water. Refs.
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CR-SB is one of three shallow (-82.0 m) heat flow holes drilled in 1976 at Mount Hood, Oregon by the Oregon Department of Geology and Mineral Industries (DOGAMI). Drill hole CR-SB was located on the southern flank of the mountain near the Snow Bunny ski lodge at an elevation of 1167.7 m (T 3 S, R 8.5 E, Sec. 25 AA) (Fig. 1). Temperatures, measured at 5.0 m intervals, and geothermal gradient data for the drill hole are given in Hull, Blackwell, and Black (1978) and are reproduced in Table 1 and Figures 2 and 3 in this report. Blackwell and Steele (1979) give an average thermal conductivity, based upon 6 samples of drill cuttings, of 4.53 (standard error =0.26) but indicated that the data obtained from the drill hole are unsuitable for heat flow calculations. Splits of the drill cuttings were obtained courtesy of J. F. Riccio (DOGAMI). The drill cuttings were wet sieved through a 200 mesh (0.074 mm) screen and both fractions were air dried and saved. Representative rock types and alteration material were hand-picked from the coarse fraction using a binocular microscope. Slurry slides of finely-ground cuttings were routinely run at 1/2°/min. from 3° to 37° 20 using unfiltered CuK radiation on a Norelco 1/ X-ray diffractometer equipped with a focusing monochrometer.
Mammoth Hot Springs, located about 8 km inside the north entrance to Yellowstone National Park, consists of nearly 100 hot springs scattered over a score of steplike travertine terraces. The travertine deposits range in age from late Pleistocene to the present. Sporadic records of hot-spring activity suggest that most of the current major springs have been intermittently active since at least 1871. Water moving along the Norris-Mammoth fault zone is heated by partly molten magma and enriched in calcium and bicarbonate. Upon reaching Mammoth this thermal water (temperature about 73?C) moves up through the old terrace deposits along preexisting vertical linear planes of weakness. As the water reaches the surface, pressure is released, carbon dioxide escapes as a gas, and bicarbonate in the water is partitioned into more carbon dioxide and carbonate; the carbonate then combines with calcium to precipitate calcium carbonate, forming travertine. The travertine usually precipitates rapidly from solution and is lightweight and porous; however, dense travertine, such as is found in core from the 113-m research drill hole Y-10 located on one of the upper terraces, forms beneath the surface by deposition in the pore spaces of older deposits. The terraces abound with unusual hot-spring deposits such as terracettes, cones, and fissure ridges. Semicircular ledges (ranging in width from about 0.3 m to as much as 2.5 m), called terracettes, formed by deposition of travertine around slowly rising pools. Complex steplike arrangements of terracettes have developed along runoff channels of some hot springs. A few hot springs have deposited cone-shaped mounds, most of which reach heights of 1-2 m before becoming dormant. However, one long-inactive cone named Liberty Cap attained a height of about 14 m. Fissure ridges are linear mounds of travertine deposited from numerous hot-spring vents along a medial fracture zone. The ridges range in height from about 1 to 6 m and in length from a few meters to nearly 300 m; width at the base of a ridge is equal to or greater than its height. In some places, such as along the northern border of Main Terrace, water from new hot-spring activity becomes ponded behind fissure-ridge barriers or dams and deposits travertine that eventually forms large flat terraces.
Volume was calculated for the 107 individual volcanic shields along the Hawaiian Ridge Emperor Seamounts chain to help fulfill the need for volume data essential to determining eruption rates, fraction of mantle melted, and other parameters. Boundaries used were based principally upon location of rift zones related to each shield. Volcanic loci shown are modified from an earlier map to accommodate changes in bathymetry. Total volumes calculated for the Emperor and Hawaiian chains are 336.3 X 10 3 km 3 and 744.9 X 10 3 km 3