Interstitial Brines Research Articles

Formation of cryolite and other aluminofluorides: A petrologic review

Petrologic reviews are provided for 17 confirmed localities of cryolite, and for occurrences of 19 other aluminofluorides. Four environments can be recognised: granitic, carbonatitic, volcanic and aqueous. Cryolite, partly replaced by other aluminofluorides, forms at the post-magmatic stage of granite evolu­tion in alkali granite pegmatites, albitised riebeckite granites and hydrothermal bodies. The associated magmatic granites are post- or non-orogenic, late intrusions often associated with regional faulting. They are rich in Na and F, poor in Ca, and low in normative anorthite, acmite and sodium silicate. High contents of Rb, Zr, Nb, REE and Li are characteristic. They equilibrated at 1-2 kb P H20 in agreement with their epizonal setting. Experiments in the granite-HlO-HF system develop aluminofluorides in coexisting dense vapours. Equivalent fluids cooled to multi-phase inclusions in the Volyn pegmatites, Ukraine, and contain cryolite and elpasolite. Post-magmatic autometasomatism extracts and then redeposits F, Na and other elements probably via fluids containing fluoriferous complex ions. Quartz-feldspar metasomatites in E Siberia are related to regional metamorphism and deep faulting. Rare carbonatites and silico-carbonatites with high contents of Na concentrate Fin late hydrothermal solutions and produced cryolite at Goldie, Colorado and Francon quarry, Montreal. Ralstonite is widely reported, and elpasolite and weberite. rarely reported, from · fumaroles and HF-metasomatised lavas of basic to intermediate volcanoes. Deposition occurred at 300-100°C. Thermal springs and surface runoff froin volcanoes carry relatively high F contents and occasionally form gearksu­tite and creedite by reaction with aluminosilicate materials. Cryolite is a rare authigenic mineral in sediments of the Green River Formation, W USA. F-rich interstitial brines, developed as in the modem Lake Magadi, Kenya, probably reacted with the host aluminosilicate sediments. Gearksutite and creedite, plus five other recently discovered aluminofluorides, occur within or just. below the oxidation zones, or in the weathering crusts, of some F-rich mineral deposits. Low-temperature precipitated aluminofluorides have been produced synthetically but are un­known in nature. The only economic aluminofluoride, cryolite, was present as several million tons at Ivigh1t, S Green­land. Fluorine was concentrated immediately below the sealed roof of a narrow granite pipe.

Water-Rock Interaction During Clastic Diagenesis in Both Open and Closed Systems: ABSTRACT

Studies have shown that the composition of ocean water may be controlled by reactions with clay minerals which act as solid phase buffers. The compositions of interstitial brines are subject to similar controls, but at least two boundary conditions can be established. In permeable sandstones (open system) it has been proposed that reactions of the form (1), clay mineral + dolomite + H2O ^rarr chlorite + calcite + CO2, produce large quantities of CO2 as a vapor which may migrate, causing production of secondary porosity during later diagenesis. In this case the mineralogy is clearly controlled by the composition of interstitial waters. In a closed system, represented by over-pressured shales from the Gulf Coast, published water compositions can be correlated with mineral reactions inferred from X-ray diffraction. Equilibria of the form (2), kaolinite + K+ ^rlhar2 clay mineral or feldspar + H+, can be used to document the path of fluid phase compositional buffering with increasing depth. Theoretical phase relations End_Page 726------------------------------ predict a decrease in the concentrations of K+, Na+, and CA++ such that K+ < Na+ < Ca++ in buffering capacity. This phenomenon is actually observed. Reactions such as from (2) also provide a mechanism to produce H+, lowering pH, and perhaps also forming secondary porosity during later diagenesis of clastic rocks. Both examples demonstate that authigenic mineral assemblages, not the appearance or disappearance of single minerals, must be documented to relate diagenetic changes to burial depth. Also, diagenetic mineral assemblages are strongly controlled by water compositions in open systems and these are not a simple function of burial depth. This also implies that any disturbance of fluid compositions during drilling or well completion may profoundly affect mineralogy. End_of_Article - Last_Page 727------------

Sulfur and Oxygen Isotope Geochemistry of Abu Dhabi Sabkha: ABSTRACT

Sulfur and oxygen isotope data vary in a laterally systematic manner across the sabkha at Abu Dhabi. At least three different mechanisms are required to explain the variation of ^dgr34S and ^dgr18O of sulfate in evaporite minerals and interstitial brine. Gypsum is precipitating in the seaward zone, and extensive postcrystallization exchange maintains isotopic equilibrium between bulk gypsum and dissolved sulfate. Anhydrite is the dominant sulfate mineral in the central zone where bacterial sulfate reduction results in heavier ^dgr34S and ^dgr18O values. In the landward zone both minerals and brine reflect mixing with the isotopically distinct sulfate of continental brines. Laterally systematic isotopic variation supports Patters n's chemical discrimination between seaward, mixed and landward hydrologic regimes, and is consistent with vertical variation of ^dgr34S demonstrated by Butler et al for this regressive sedimentary sequence. Gypsum-anhydrite transitions do not have significant effects on the isotopic composition of sulfate. Some ancient marine evaporite formations consisting mainly of dolomite and anhydrite may have formed in environments similar to the seaward and central zones of the Abu Dhabi sabkha; considerable isotopic variation would probably accompany subaerial deposition of laterally extensive marine evaporites. End_of_Article - Last_Page 505------------

On the possible primary precipitation of atacamite and other metal chlorides in certain stratabound deposits

The discovery of atacamite (Cu 2 (OH) 3 Cl) in close association with algal remains in Red Sea core 95G from Atlantis II Deep raises the possibility that base (and/or precious) metals are often precipitated, and in some cases preserved as halides, in certain stratabound deposits. Calculations indicate that atacamite could form in the interstitial brines of Atlantis II Deep under conditions of exceedingly low concentrations of H 2S aq and HS −. Atacamite and/or the dimorph paratacamite might be early diagenetic phases but are rarely preserved due to subsequent replacement by sulphides. Organic material, particularly algae, evidently play an important role in initially concentrating Cu 2+ (also Pb 2+ and Zn 2+) by 'sorption, but it seems clear that some minerals, e.g. carbonates, act in a similar capacity. Scattered reports in the literature tend to confirm that base (and/or precious) metals occur as chlorides in, and/or near, certain metallic mineral deposits.

Diagenesis in tertiary sandstones from Kettleman North Dome. California—II. Interstitial solutions: Distribution of aqueous species at 100°C and chemical relation to the diagenetic mineralogy

Interstitial brines from the Temblor and the McAdams sandstones at Kettleman are essentially NaCaCl solutions with subsidiary SO 4 and the total salinities are roughly 30,000 and 10,000 ppm, respectively. Activities of H + and all other aqueous species have been calculated for 100°C (the in situ temperatures of the brines) from chemical analyses of the brines and 100-degree dissociation constants alone. The brine alkalinities measured at surface temperature appear to be too low when comparing them against alkalinities calculated from the measured pHs of the brines. Consequently, alkalinities calculated for 25°C were substituted for the measured ones in the calculation of the distribution of aqueous species at 100°C. Although the brines are nearly neutral (pH 6·3–d7·9) at surface temperature, their pHs calculated for 100°C range from 8·1 to 8·7 (± 0·35). These pHs and the 100-degree activities of the other aqueous species permit graphic representation of the brines on activity diagrams. Most brines fall at or near the boundaries between the stability fields of quartz, albite, microcline, mica, montmorillonite and anhydrite. Because these minerals are present as authigenic phases in the sandstones, the calculations suggest that the minerals are in stable equilibrium with the brines. By contrast, the calculations suggest that the brines are supersaturated by about three orders of magnitude with respect to calcite, also present in the sandstones. One possible explanation for this is kinetic inhibition of calcite crystallization by Mg 2+ and SO 4 2− ions in the brines. Phosphatic pellets, glauconite and probably dolomite, pyrite and some kaolinite are early authigenic minerals preserved in the sandstones and they are not now in equilibrium with the brines, which are supersaturated with respect to dolomite and pyrite. The chemical relationship between the brines and the diagenetic minerals laumontite and sphene, also present in the Temblor Formation, cannot be assessed reliably until the thermodynamic properties of laumontite and of aqueous titanium complexes are well known.

TRANSIENT AND STEADY‐STATE SALT TRANSPORT BETWEEN SEDIMENTS AND BRINE IN CLOSED LAKES1

A diffusional transport model for Lake Abert, Oregon, predicts the rates of salt transport from pore fluids into lake waters. In a lake without outflow dissolved salts may migrate across the sediment‐water interface in response to a concentration difference between lake and interstitial brine. Transport of salt upward is transient; its direction can be reversed by external input of salt or by depletion of salts stored in the sediments, and a steady‐state concentration in lake water is not attainable. Downward transport can be a stationary process if the sedimentation rate is rapid compared with molecular diffusion of salt in interstitial brine, but characteristic rates arc too slow to lead to steady‐state concentrations within the lifetime of a closed lake. In Lake Abert, diffusional flux upward was much more important than input of salt from other sources; 45% of the salt of lake brine in 1963–1964 was added from the sediment pore space during the preceding 25 years, only 0.1% from external inflow. The sediment source will dominate input during high water level. Such models permit comparison of salt transport across the sediment‐water interface with other input sources at different times of the lake’s history.

Crenulation Cleavage and Faulting in an Artificial Salt-Mica Schist

A synthetic foliated material made of mica flakes and NaCl has been compressed normal to the foliation, in plane strain, with and without interstitial brine, at room temperature. The experiments have employed confining pressures to 2,070 bars, and strain rates from $$10^{-4}sec^{-1} to 10^{-6}sec^{-1}$$. Specimens deformed with brine are weak and ductile compared with specimens deformed dry. A specimen run with kerosine shows intermediate strength. The deformed specimens are traversed by conjugate sets of planar discontinuities, the character of which is sensitive to strain rate, confining pressure, and nature of the pore fluid. In wet specimens deformed at medium strain rate typical discontinuities are morphologically identical with natural crenulation cleavage. In comparable specimens run dry or with kerosine, typical discontinuities are more faultlike. A transition from faulting toward cleavage development is effected in dry specimens by increasing confining pressure and can be obtained in wet specimen...

Zonal Arrangement of the Triassic Rocks of the Western Carpathians: A Contribution to the Dolomite Problem

ABSTRACT The Triassic of the Western Carpathians consists of hypersaline sequence in the north, grading southwards into dolomite and then limestone. This zonal arrangement was due to the development of algal reefs (banks) in the south, with subsequent hypersaline lagoonal evolution in the back-reef (bank) area. It is proposed that the dolomites within the lagoonal sequence originated by a very early diagenetic replacement of an aragonite mud, with clay minerals serving as charged net membranes or seeds for penetrating interstitial brines with high Mg/Ca ratios. It is also proposed that these brines were squeezed out from the lagoonal sequence into the porous algal reefs (banks) during later stages of diagenesis, causing dolomitization of the lagoonal side of the reefs (banks).

Interstitial brines in playa sediments

Study of several closed drainages in the Great Basin has shown that the interstitial solutions of shallow, fine-grained playa deposits store a large quantity of dissolved solids and are often more concentrated than associated lakes and ponds, except in peripheral zones of stream or ground-water inflow. These interstitial fluids, when compared with local runoff, impoundments, or spring waters, commonly have a distinctive ionic composition which sometimes cannot be explained by either simple mixing of surface and subsurface inflow or by evaporative concentration. At Abert Lake, Oregon, the interstitial solute concentrations increased with depth to values as much as five times greater than the lake, except where springs indicate significant ground-water input. Where Na +, Cl, and CO 2 species constitute more than 90% of the solutes, Na + Cl − ratios in the lake water are lower than in interstitial solutions of bottom cores and higher than in playa fluids. At the same time, Na + K + ratios are highest in the fluids of lake bottom muds and lowest in playa interstitials. In deeper playa profiles, interstitial Na + Cl − tended to decrease with depth (5 ft. maximum). In the Abert Lake area, as in other parts of the western Great Basin, Na + Cl − ratios are indicative of total CO 2 in solution and the effects of organic decay in surficial sediments. These ratios, coupled with data on silica and bulk density, show that higher P CO 2 accompanying decay promotes silicate dissolution and hydrogen ion exchange, stripping alkalis from sediment which had preferentially adsorbed K + when entering the lake. On subsequent loss of pore fluid in the playa regime, silica initially released to solution in the lake environment is readsorbed on dissolution products.

Modern Evaporite Deposition and Geochemistry of Coexisting Brines, the Sabkha, Trucial Coast, Arabian Gulf

ABSTRACT Near Abu Dhabi, Trucial Coast, diagenetic evaporite minerals are developed within an accumulation of detrital Pleistocene sands and Recent carbonate sediments which form a supratidal flat (sabkha) 8 miles wide. Field studies were carried out by the author and his co-workers of Imperial College in 1964. A further visit to the Trucial Coast was made by the author in 1967 under the auspices of the Dry Lands Research Institute, Riverside. A study of 260 interstitial brine samples showed that the distribution of the evaporite minerals, which include gypsum, anhydrite, dolomite, and balite, is largely controlled by the hydrology of the area. Interstitial brines within the sabkha sediments are replenished with sea water by abnormally high tides and storm surges. These surface waters, which soak down into the sediments, are concentrated both by solution of soluble salts and by evaporation. The subsequent equilibration between brines and host sediments leads to precipitation of aragonite, gypsum, and halite; alteration of gypsum to anhydrite, and dolomitization of carbonate sediment. A direct correlation exists between the frequency and extent of flooding, the mineral phases developed, and the chemical composition of interstitial brines. Flooding of a 2- to 3-mile wide belt roughly concentric to lagoon margins, occurs at monthly or longer intervals. In this belt, a surface gypsum crystal mush up to 12 inches thick is present which, landwards, is overlain and progressively replaced by anhydrite. Dolomitization is extensive toward the landward margin of this zone. From the lagoon laterally across the 2- to 3-mile wide belt to its landward margin, chlorinity increases from 44 to 155; sulfate concentration rises from 6 to 17 gm/kg and then falls to less than 3 gm/kg; the Mga2+/Ca2+ mole ratio increases from 5.3 to 35 and then decreases to about 4. Concentration of these components decreases with in reasing depth below the sediment surface. Gypsum is the stable calcium sulfate mineral in contact with brines of chlorinities less than 145 and anhydrite at chlorinities greater than 145. An additional 5-mile wide zone is flooded only at 4- to 5-year intervals. The original gypsum crystal mush in this zone is completely replaced by up to a 12-inch thick layer of chicken-wire mesh structure anhydrite, and the carbonates are highly dolomitized. Interstitial brines are Saturated with NaCl at chlorinity 160 and specific gravity 1.20. These brines contain less than 1 gm/kg sulfate and have Mg2+/Ca2+ mole ratios of about 4. In this zone, constant Mg2+/Ca2+ values with increasing magnesium concentration suggest that there has been an approach to mutual equilibrium between brines and evaporite-carbonate minerals. The remaining 1 to 2 miles at the landward margin of the sabkha are underlain by Pleistocene sands and are not flooded by marine waters. Ground waters in this zone are in part terrestrial in origin. Inland across this zone, chlorinity decreases from 160 to 107; the sulfate concentration is 2 gm/kg and the Mg2+/Ca2+ mole ratio averages 3.5. Locally, anhydrite is hydrated to gypsum where brine chlorinity is less than 145. Processes of gypsum precipitation and dolomitization are essentially restricted to the 2- to 3-mile wide belt close to the lagoon margin. In the mid-sabkha, equilibrium conditions probably prevail between brines, diagenetic minerals, and host sediments. Diagenesis at the landward margin of the sabkha is in part retrogressive. Both a progressive and a retrogressive diagenetic facies can be visualized as moving out with the progradation of the shore line. The similarity between the stratigraphy and mineralogy of some Ordovician, Silurian, Pennsylvanian, and Jurassic evaporite sequences and the sabkha on the Trucial Coast suggest that evaporites of supratidal origin may be more common in older evaporite rocks than previously realized.

Thermodynamic and Geochemical Characteristics of Salton Sea Geothermal System: ABSTRACT

The Salton Sea geothermal area is in a rift valley of the San Andreas fault system in southern California. The geothermal reservoir consists of more than 2,000 ft of arkosic sandstone containing interstitial concentrated NaCl-CaCl2-KCl brines. No steam is present underground. The sandstone is overlain by shale from the surface to a depth of 2,000-3,000 ft. The temperature in the subsurface exceeds 300°C at 3,000 ft and 360°C at 7,000 ft. Thermal convection of pore fluids in the sandstone appears to be the primary mechanism of heat transfer in the reservoir. The salinity and temperature of the pore fluids decrease outward from the center of the geothermal reservoir. The enthalpy of the brines in the reservoir ranges from 220 to 275 cal/g, which is 45-9 cal/g less than the enthalpy of pure water at equivalent temperatures and pressures. Although the origin of the brines is obscure, it appears likely that they formed by evaporation of Colorado River water originally trapped in the pore spaces of the reservoir sands. Thermodynamic calculations indicate that reaction of the interstitial brines with the sediments in the geothermal reservoir (which is below 3,000 ft) has resulted in substantial mass transfer (more than 40 g/1,000 g of water) during metamorphism. Geochemical considerations suggest that the reservoir fluids in the geothermal system are in chemical equilibrium with the mineral assemblage in the enclosing rocks. Chemical reactions between the original pore fluid in the rock and the sedimentary mineral assemblage have led to a relatively low pH and enrichment of K, Ca, Fe cations, and other constituents in the aqueous phase. The total dissolved solids in the brine have been concentrated by removal of water from the system. End_of_Article - Last_Page 563------------

Structure of Winnfield Salt Dome, Winn Parish, Louisiana

Megascopic structural features were mapped of that part of the Winnfield, Louisiana, salt dome exposed in the Carey Salt Company's mine, located 811 feet below the surface and about 400 feet below the flat top of the dome. Layering of the salt is visible throughout the mine. White to dark gray beds of halite and anhydrite, 1 inch to 1 foot in thickness, are intricately folded. Both the bedding layers and fold axes dip and plunge steeply toward the center of the dome. The increased intensity of layering and the concordancy near the boundary of the dome show the close relation between the structural attitude of the plastically deformed original salt layers and the edge of the salt dome. Pencil-shape aggregates of anhydrite, as long as 18 inches, parallel the fold axes; most of them plunge steeper than 70° inward toward the dome and support the interpretation of upward and outward movement of the salt during its diapiric emplacement in the surrounding rocks. The structural data also suggest the possibility that the dome overhangs the enclosing sedimentary rocks on the south and west. Structurally the Winnfield dome is similar to the Jefferson Island, Louisiana, and Grand Saline, Texas, domes as mapped by Balk. Special features in the Winnfield dome include the emanation of interstitial brine and CO2 into the mine. Blowouts which result in cavities up to 100 feet in length have occurred in parts of the mine near the salt-dome boundary. Microscopic examination and chemical analyses of the salt indicate the blowouts probably are due to instability caused by high CO2 pressures in numerous small gas-filled cavities close to a free-air surface.

Displacement of Oil from Porous Media by Water or Gas

Abstract Laboratory apparatus has been devised which permits study of the displacementof oil from cores by water and by gas. The cores used contained interstitialbrine as well as oil. Experiments were run to determine the comparative effect of varying theproperties of the fluids used. No great effect was noted on the maximumdisplacement achieved. This observation made it unnecessary in initial work touse fluids in their exact reservoir conditions. Consequently, the displacementswere run at near-atmospheric pressure in Pyrex glass equipment, using strippedcrude oils. Introduction and Theory The chief object of this work has been to determine the efficiency of gasand water as primary agents for displacing oil from reservoir rock underlaboratory conditions in which capillary phenomena were predominant. To thisend the maximum displacement of oil from cores has been ascertained. Thismaximum displacement may not be equal to the maximum displacement from areservoir; but it will he a close approximation to it sometimes, and othertimes the laboratory information will be useful in reservoir engineeringpredictions. It is believed that the laboratory experimental maximum representsthe upper limit for the reservoir recovery. The experiments were carried out by obtaining cores of interest from thereservoir, and filling the pores with interstitial brine and oil with therestored state technique. Then the oil was displaced from the core as describedlater, either by brine from below, or by gas from above. The former type ofdisplacement suggests analogy to production by water drive, but not to waterflooding, for reasons discussed below. The latter type of displacement isbelieved to simulate production by gas cap displacement. The displacements were performed by what may be termed thecapillary-pressure method. The cores are placed in capillary contact with anoil-wetted membrane which has very small pores (about I micron in diameter).Pores of this size will transmit oil hut prevent the passage of gas or water, unless the pressures used are higher than the capillary pressures employed inthis work. Accordingly, use of the membrane makes it possible to apply acapillary pressure differential between the displacing phase and the oil in thecore. T.P. 2433