Donald E. White

THERMAL WATERS OF VOLCANIC ORIGIN

Waters of widely differing chemical compositions have been considered at least in part volcanic in origin, and are commonly associated with each other in the same area. Do any or all of these types contain volcanic components, and if so, how are the different types derived? To determine the probable characteristics of volcanic waters, the writer has selected hot-spring groups that are particularly high in temperature and associated heat flow, are associated with late Tertiary or Quaternary volcanism, and are therefore most likely to contain some water and chemical components of direct volcanic origin. Of the different types of water that occur in these groups, one of the most common is characterized chemically by a dominance of sodium chloride. Isotopic evidence indicates that the contribution of water of direct volcanic origin is not large and is probably no more than 5 per cent in typical sodium-chloride springs. The compositions of volcanic waters are believed to be determined by: [1] type of magma and stage of crystallization; [2] temperature and pressure of the emanation at different stages during and after departure from the magma; [3] chemical composition, relative quantity, and depth of penetration of mixing meteoric water and water of other origin; and [4] reactions with wall rocks. Although the type of magma and its stage of crystallization are of major interest and have been emphasized in the past, the outstanding characteristics of volcanic emanations at and near the surface of the earth seem to be controlled for the most part by the other factors. Nonvolatile compounds are slightly to highly soluble in steam at high pressure, and high-density steam has solvent properties similar to those of liquid water. In the volcanic sodium-chloride waters, the high ratio of lithium to sodium and potassium is shown to indicate that alkalies were transported as alkali halides dissolved in a dense vapor. This in turn demands a deep circulation of meteoric water for steam to condense at high pressure and for the halides to remain in solution. The depth of circulation of meteoric water in the sodium-chloride spring systems is believed to be in the order of 2 miles. Where circulation of meteoric water is shallow, the vapors rise and expand at low pressure, which does not permit transport of substances of low volatility; some type of water other than the sodium-chloride type is formed. The common volcanic sodium-chloride waters are therefore concluded to be the diluted product of high-density emanations, modified by reactions with wall rocks and by precipitation of the less soluble components. Emanations at high temperature and relatively low pressure consist almost entirely of steam and volatile components. Their compositions are therefore relatively simple, and their ability to transport matter of low volatility is very limited. The sodium-chloride type is probably gradational into acid-sulfate-chloride waters. There is some evidence that, under conditions not well understood, sulfur may be emitted as SO 2 , SO 3 , or other sulfur species of intermediate valence, rather than as H 2 S or S. Other major types of volcanic waters are called sodium bicarbonate, acid sulfate, and calcium bicarbonate; the first two tend to be distinct, but the calcium-bicarbonate type clearly grades into the sodium-chloride type. The writer concludes that, in general, all these are derived from the sodium-chloride waters as a result of physical environment or of reactions with wall rocks.

Active Metamorphism of Upper Cenozoic Sediments in the Salton Sea Geothermal Field and the Salton Trough, Southeastern California

The Salton Sea geothermal system is entirely within Pliocene and Quaternary sediments of the Colorado River delta at the north end of the Gulf of California. At the time of deposition, these sediments consisted of sands, silts, and clays of uniform original mineralogic composition, but under the elevated temperatures and pressures of the geothermal system they are being transformed to low-grade metamorphic rocks of the greenschist facies. We have studied these transformations by X-ray, petrographic, and chemical analyses of cuttings and core from deep wells that penetrate the sedimentary section. Temperatures within the explored geothermal system range up to 360° C at 7100 feet. The wells produce a brine containing over 250,000 ppm dissolved solids, primarily Cl, Na, Ca, K, and Fe, plus a host of minor constituents. The original sediments consisted of detrital quartz, calcite, K-feldspar, plagioclase, montmorillonite, illite, dolomite, and kaolinite. Discrete montmorillonite is converted to illite at temperatures below 100° C, and illite-montmorillonite is completely converted to K-mica at temperatures below approximately 210° C. Ankerite forms by the conversion of calcite, dolomite, or both, at temperatures as low as 120° C, possibly as low as 80° C. Dolomite, ankerite, kaolinite, and Fe ++ (probably from the brine) react to produce chlorite, calcite, and CO 2 at temperatures as low as 180° C and possibly as low as 125° C. At temperatures greater than approximately 290° to 310° C, iron-rich epidote and K-feldspar become abundant, calcite disappears, and K-mica is sporadic. Detrital Na-Ca plagioclase persists throughout the explored system, and at depth exists out of equilibrium with metamorphic albite. The most common metamorphic assemblage at temperatures of 300° C and above is quartz + epidote + chlorite + K-feldspar + albite ± K-mica. Pyrite, sphene, and hematite are also sporadically present. Similar metamorphism occurs in the sedimentary section penetrated by the Wilson No. 1well, drilled to a depth of 13,433 feet 22 miles south-southeast of the geothermal field. The lower-temperature reactions observed in the Salton Sea geothermal field also occur in Wilson No. 1, but at much greater depths owing primarily to the lower temperature gradient. Temperatures in this well reach only 260° C, insufficient for the formation of epidote and the destruction of calcite and K-mica. The mineralogical transformations taking place in the Salton Sea geothermal field are metamorphic responses to the elevated temperatures and pressures. Some transformations such as the reaction of dolomite, ankerite, and kaolinite to produce chlorite, calcite, and CO 2 are regional in extent and pose no metasomatic requirements other than that the system be open to H2 O and CO 2 . Other relationships, such as the destruction of calcite and K-mica and the complementary formation of epidote, may involve interchange of elements with the brine. The Salton Sea geothermal system displays a continuous transition from sediments through indurated sedimentary rocks to low-grade metamorphic rocks of the greenschist facies. This transition encompasses transformations commonly considered as diagenetic, and takes place without the formation of zeolites.

Silica in hot-spring waters☆

Abstract The silica in hot-spring waters and in a few cold waters was studied by moans of the colorimetrie ammonium-molybdate method of analysis. Murata found in 1947 that only a part of the total silica in aged samples of high-silica waters was determinable by the colorimetric method. Weitz , franck And schuchard later showed that ammonium molybdate reacts readily with the monomeric form of silica (probably H4SiO4) but very slowly with polymeric silica. If the colorimetric measurement is completed in two or three minutes, only the monomer is determined. Nearly all silica of hot springs is in the monomeric form. Solubility equilibrium exists between dissolved (monomeric) and amorphous silica. For the hot springs that were studied, the solubility is about 315 p.p.m. at 90°C and 110 p.p.m. at 25°C, which is very similar to Krauskopfs experimental data. Monomeric silica polymerizes so slowly to colloidal silica that many waters are supersaturated with respect to amorphous silica. The rate of polymerization is influenced by pH, temperature, degree of supersaturation, presence of previously formed colloidal and gelatinous silica and contact with opal and other substances. Supersaturated acid waters and alkaline waters with less than 100% supersaturation tend to remain supersaturated almost indefinitely, with little or no change. Precipitation of colloidal silica is favoured by high temperature and contact with opal. Many connate and other ground waters, including some thermal springs, are much below saturation with respect to amorphous silica, probably because low-solubility quartz and chalcedony have been precipitating. Quartz is favoured by relatively high temperature, slow rale of precipitation, and low degree of supersaturation, and is believed to form by deposition of monomeric molecules. Chalcedony is probably deposited when the degree of supersaturation is moderately high and the rate of deposition is relatively fast. The ranges of temperature over which quartz and chalcedony deposit no doubt overlap, but, if other factors are equal, quartz is favoured by high temperature. Opal is favoured by relatively low temperature and rapid rate of precipitation. Although opal has probably been deposited at temperatures as high as 140°C, it is unstable and is slowly converted to chalcedony or quartz. Water that is saturated with respect to opal is highly supersaturated with respect to quartz. Opal is probably formed from monomeric or more probably, the smaller polymeric molecules of silica, retaining some of their water content. Evidence is lacking for the direct conversion of gelatinous silica to opal. Some differences in solubility probably exist between amorphous opal and opal that shows X-ray patterns like that of cristobalite. The suggestion is made that clay minerals form by combination of monomeric silica and a comparable form of monomeric alumina, which must have very low solubility in waters within the pH range of 5 to 9. Because of the abundance and relatively high solubility of silica, the proposed reaction, dissolved alumina + dissolved silica ⇌ clay, is ordinarily displaced strongly to the right in hydrothermal alteration and in ordinary soil formation. With removal of free silica, aided by tropical rainfall and temperatures, the reaction may be displaced to the left by dissolution and removal of silica from the system. Alumina, because of its very low solubility, remains as bauxite.

MAGMATIC, CONNATE, AND METAMORPHIC WATERS

Some major types of water of “deep” origin are believed to be recognizable from their chemical and isotopic compositions. Oil-field brines dominated by sodium and calcium chlorides differ markedly from average ocean water. In general, the brines are believed to be connate in origin (“fossil” sea water) with a negligible to high proportion of meteoric water. Many brines, particularly in pre-Tertiary rocks, are much higher in salinity than sea water and are greatly enriched in calcium as well as sodium chloride. Brines near the salinity of sea water are generally higher, relative to sea water, in bicarbonate, iodine, boron, lithium, silica, ammonium, and water-soluble organic compounds, and lower in sulfate, potassium, and magnesium. Many changes take place after sea water is entrapped in newly deposited marine sediments: (1) Iodine, silicon, boron, nitrogen, and other elements have been selectively concentrated in organisms that decompose during and after burial in sediments. Many of the elements may redissolve in the interstitial water. (2) Bacteria are active in the sediments and reduce sulfate to sulfide and produce methane, ammonia, carbon dioxide, and other products. (3) Some elements have been selectively removed from sea water by inorganic processes, such as adsorption on clays and colloidal matter. When this matter is reconstituted by diagenetic and other changes, some components are redissolved. The abundance of lithium and possibly boron and other elements may be controlled to a considerable extent by these inorganic processes. (4) The interstitial water may react chemically with enclosing sediments and produce dolomite, reconstituted clays, and other minerals. The high loss of magnesium relative to calcium in most connate waters is probably caused by such reactions. Volcanic hot-spring waters of different compositions have been discussed in an accompanying paper (White, 1957). The most significant type is believed to be dominated by sodium chloride, and is best explained as originating from dense gases driven at high temperature and pressure from magma and containing much matter of low volatility that is in solution because of the solvent properties of high-density steam. This dense vapor is condensed in and greatly diluted by deeply circulating meteoric water. Most other types of volcanic water are believed to be derived from the sodium-chloride type. Volcanic sodium-chloride waters are similar in many respects to connate waters but are believed to be distinguishable by relatively high lithium, fluorine, silica, boron, sulfur, CO2, arsenic, and antimony; by relatively low calcium and magnesium; and by lack of hydrocarbons, water-soluble organic compounds, and perhaps ammonia and nitrate. Relatively high boron and combined CO2 are alone not reliable indicators of a volcanic origin. During compaction, rocks lose most of their interstitial high-chloride water; much additional water may then be lost during progressive metamorphism, and the content changes from about 5 per cent in shale to perhaps 1 per cent in gneiss. This expelled water is here called metamorphic. Because of pressure and permeability gradients, it must normally escape upward and mix with connate and meteoric water. Even though large quantities must exist, no example of metamorphic water has been positively identified. Some thermal springs in California are high in salinity and relatively low in temperature and apparent associated heat flow. Some are clearly connate in origin. Other springs are characterized by very high combined carbon dioxide and boron, relative to chloride. Their compositions are considerably different from known connate and volcanic waters and are believed to be best explained by a metamorphic origin. Although some major types of deep water seem to be recognizable, there is much danger of oversimplifying the problems. Many waters are no doubt mixtures of different types, and some of high salinity result from dissolution of salts by meteoric water.

Hydrothermal Explosion Craters in Yellowstone National Park

Hydrothermal explosions are produced when water contained in near-surface rock at temperatures as high as perhaps 250°C flashes to steam and violently disrupts the confining rock. These explosions are due to the same instability and chain reaction mechanism as geyser eruptions but are so violent that a large proportion of solid debris is expelled along with water and steam. Hydrothermal explosions are not a type of volcanic eruption. Although the required energy probably comes from a deep igneous source, this energy is transferred to the surface by circulating meteoric water rather than by magma. The energy is stored as heat in hot water and rock within a few hundred feet of the surface. At least ten hydrothermal explosion craters, ranging in diameter from a few tens of feet to about 5000 ft, have been recognized in Yellowstone National Park. Eight of these craters are in hydrothermally cemented glacial deposits; two are in Pleistocene ash-flow tuff. Each is surrounded by a rim composed of debris derived from the crater. Juvenile volcanic ejecta are absent, and there is no evidence of impact. Geologic relations at the Pocket Basin crater establish that the explosion there took place during the waning stages of early Pinedale Glaciation. This association with ablating ice suggests that an ice-dammed lake existed over a hydrothermal system at the Pocket Basin site and that the hydrothermal explosion was triggered by the abrupt decrease in confining pressure consequent to sudden draining of the lake. Most of the other explosion craters in Yellowstone Park could have been triggered in the same manner. Calculations of energy available in Yellowstone hot-spring systems and of energy required to form craters indicate that the proposed mechanism is reasonable. The sizes of craters expected in various rock types correspond with those observed.

Geothermal brine well: Mile-deep drill hole may tap ore-bearing magmatic water and rocks Undergoing Metamorphism

A deep geothermal well in California has tapped a very saline brine extraordinarily high in heavy metals and other rare elements; copper and silver are precipitated during brine production. Preliminary evidence suggests that the brine may be pure magmatic water and an active ore-forming solution. Metamorphism of relatively young rocks may also be occurring within accessible depths.

VIOLENT MUD-VOLCANO ERUPTION OF LAKE CITY HOT SPRINGS, NORTHEASTERN CALIFORNIA

During the night of March 1 and 2, 1951, an inconspicuous group of hot springs and small mud volcanoes in northeastern California burst into spectacular eruption, unequalled by other known mud volcanoes. The eruption cloud of steam, gases, and mud particles rose several thousand feet in the air and distributed fine debris to the southeast for a distance of at least 4 miles. More than 20 acres of the hot-spring area was intensely disturbed and greatly modified by the eruption, estimated to involve at least 6 million cubic feet or 300,000 tons of mud. Several days after the eruption, the area was barely active. The eruption appears to be unique in the history of the springs. The hot-spring system is in deep fine-grained clastic sediments immediately east of the Surprise Valley fault bounding the Warner Range. The sediments of the spring area are saturated with near-neutral hot saline water. Previous temperatures and geothermal gradient of the area were probably high. Mud volcanoes exist in similar physical environment near Gerlach in Washoe County, Nevada, and on the southeast shore of Salton Sea, Imperial County, California. Other mud volcanoes occur in acid thermal areas and are characterized by abundant volcanic gases and near-surface alteration by sulfuric acid; their eruptions involve only surficial material and not underlying competent bedrock. Eruptions in deep fine-grained basin sediments are attribured to unstable or metastable temperature-depth relations existing in many high-energy thermal systems. Vapor pressure at depth may equalor exceed hydrostatic pressure. Great energy is stored in a thermal system of this type, but ordinarily is released slowly. A mud-volcano origin is possible for some eruption deposits classed as phreatic or cryptovolcanic. Although near-boiling hot springs are considered phases of volcanism, true volcanic eruptions are distinct from mud-volcano eruptions. The former derive their energy directly from new volcanic rocks or magma, but the latter are caused by sudden release of energy stored in near-surface hydrothermal systems and do not involve direct release of energy from new volcanic magma. The energy of true volcanic eruptions, however, may be increased by release of energy from previously existing hydrothermal systems, for example in the Rotomahana phase of the great Tarawera eruption of 1886 in New Zealand. Language: en

Halogen acids in fumarolic gases of Kilauea volcano

The water-rich condensates of fumarolic gases, obtained from degassing lavas of the 1959–60 eruption of Kilauea volcano, contain unexpectedly high concentrations of hydrofluoric and hydrochloric acids, and thereby suggest that halogens are significant constituents of basaltic magmas. Vents on the pumice hill of Kilauea Iki yielded one sample that contained, in parts per million, 21,000 HF (1.1 N) with 2,920 HCl, and another sample, 20 HF with 70,500 HCl (2.0 N). Samples from vents elsewhere on the volcano had from one-fortieth to one-thousandth as much of the two acids.A rough correlation exists between the temperature of the fumaroles (range 110 to 820°C) and the total concentration of the halogen acids. This correlation is mainly due to progressive dilution of the magmatic halogen acids by water of probable meteoric origin in fumaroles of lower temperatures.Variations in the HF/HCl ratio (range 0.0003 to 7.2) may be explained by means of two different processes whose relative importance cannot be assessed with the data at hand (1). In their migration to the surface, the acid gases may have reacted with the lava to a variable extent owing to the widely different configurations of the several vents (steaming areas in glassy pumice, glowing cracks, and drillhole in lava lake). In the reaction, relatively more HF could have reacted at temperatures around 300°C with the glassy pumice (2). There is some indication that the HF/HCl ratio increases with time,suggesting that the crystallizing lava may have released HCl early, with HF concentrated in the later exhalations.The Br/Cl ratio ranges from 0.0036 down to 0.0014, as compared to 0.0034 of seawater.

Deep geothermal brine near Salton Sea, California

A well drilled for geothermal power near Salton Sea in Imperial Valley, Calif., is 5,232 feet deep; it is the deepest well in the world (1962) in a high-temperature hot spring area. In the lower half of the hole temperatures are too high to measure with available equipment, but are at loast 270°C, and may be as much as 370°C. For comparison, maximum temperature heretofore reported at depth (1962) for hot spring areas is 295°C.The well taps a very saline brine of Na-Ca-K-Cl type (about 185,000 ppm Cl) with exceptionally high potassium, and with the highest content of minor alkali elements known for natural waters; Fe, Mn, Zn, Pb, Cu, Ag, and some other metals are also exceptionally high. This brine may be connate, but present evidence favors a source in the magma chamber at depth that supplied late Quaternary rhyolite domes of the area. If the latter is correct, the brine is an undiluted magmatic water that is residual from the separation of a more volatile phase high in CO2, H2S, and with some alkali halides. Elsewhere, the hypothesized volatile phase may account for near-surface hot spring activity of most thermal areas of volcanic association. The residual brine of high salinity may ordinarily remain relatively deep in the volcanic systems because of high specific gravity and low content of volatiles, seldom appearing at the surface except in a greatly diluted form.The hot springs of Arima, Japan, may be a rare example of this type of magmatic water discharging at the surface in moderate concentration (Cl as much as 42,000 ppm). Independent evidence from fluid inclusions in minerals of high-temperature base-metal deposits also favors the existence of magmatic water high in Na, Ca, and Cl, and low in CO2 and other volatile components.During a three-month production test several tons of material precipitated in the horizontal discharge pipe from the well. Amorphous silica with iron and manganese, and bornite are the dominant recognized components. This material contains the astonishingly high contents of about 20 percent copper, 2 percent silver, and notable sulfur, arsenic, bismuth, lead, antimony, and some other minor elements. Total quantities of all elements in the original whole brine are not yet known, but calculated amounts corresponding to 1 to 3 ppm of copper and 0.1 to 0.3 ppm of silver were precipitated from the brine to form the pipe deposits. The brine, therefore, may be man’s first sample of an « active » ore solution.Equally fascinating to many geologists is the possibility that in the lower part of the hole temperatures are so high and pressures are sufficient for young sedimentary rocks to be undergoing transformation into rocks with mineral assemblages of the greenschist facies of metamorphism. Drill cores from 4,400 to 5,000 feet in depth contain chlorite, albite, K-feldspar, epidote, mica, and quartz, with some indication of increase in metamorphic grade downward. Regional geological and geophysical studies favor a depth of about 20,000 feet to pre-Tertiary basement rocks in the general area. A shallow basement or local upfaulting of old metamorphic rocks are not likely possibilities for the thermal area.