Pore waters minerals

Fig. 3. Pore-water mineral saturation indices calculated with PHREEQC (Parkhurst Appelo 1999) using the llnl.dat database.

Chlorine has two stable isotopes, Cl and Cl, and one radioactive isotope, C1 (half-life = 0.301 Ma). The stable isotopic composition of chloride in geologic materials is reported in the conventional del notation as S Cl. Seawater, which is used as the isotopic standard, has a S Cl of 0%c. Most natural waters have S Cl values between —l%o and +l%o. However, values of —8%c have been measured in marine pore waters. Minerals in which chloride substitutes for OH at high temperatures have S Cl values as high as 7%c (Banks et al., 2000). 

Cochran JK, Krishnaswami S (1980) Radium, thorium, uranium and °Pb in deep-sea sediments and sediment pore waters from the north equatorial Pacific. Am J Sci 280 849-889 Cochran JK, Masque P (2003) Short-lived U/Th-series radionuchdes in the ocean tracers for scavenging rates, export fluxes and particle dynamics. Rev Mineral Geochem 52 461-492 Colley S, Thomson J, Newton PP (1995) Detailed °Th, Th and °Pb fluxes recorded by the 1989/90 BQFS sediment trap time-series at 48°N, 20°W. Deep-Sea Res 42(6) 833-848... 

Even where it is not occluded, the mineral surface may not be reactive. In the va-dose zone, the surface may not be fully in contact with water or may contact water only intermittently. In the saturated zone, a mineral may touch virtually immobile water within isolated portions of the sediment s pore structure. Fluid chemistry in such microenvironments may bear little relationship to the bulk chemistry of the pore water. Since groundwater flow tends to be channeled through the most permeable portions of the subsurface, furthermore, fluids may bypass many or most of the mineral grains in a sediment or rock. The latter phenomenon is especially pronounced in fractured rocks, where only the mineral surfaces lining the fracture may be reactive. 

Fig. 25.1. Mineralogical consequences of mixing the two fluids shown in Table 25.1 at 60 °C in the presence of microcline, muscovite, quartz, and dolomite. Results shown as the volume change for each mineral (precipitation is positive, dissolution negative), expressed per kg of pore water.

Haswell, S.J., P. O Neill, and K. C Bancroft. 1985. Arsenic speciation in soil-pore waters from mineralized and unmineralized areas of south-west England. Talanta 32 69-72. 

Leaching and desorption of As from its associated mineral surfaces such as iron, aluminum and manganese oxides under the influence of the aquifer complex geochemistry, largely take part in its transport from sediment to aquifer pore-water. Adsorption has widely been considered as the retardation of As transport (Smedley 2003). 

Interactive Version 2.15.0 (Parkhurst Appelo 1999). The llnl.dat database distributed with PHREEQC was used for all calculations. Geochemical modeling was used to speciate the components of the tailings pore-water at discrete depths and to investigate the thermodynamic stability of mineral phases through out the tailings. 

Geochemical speciation calculations suggest that Sb occurs predominantly as Sb(lll) throughout the tailings pore-waters and that Sb concentrations are limited by the precipitation of common Sb(lll) minerals, such as sernamontite (Sb203, reaction 1). 

The tailings comprise 5-10 wt. % pyrrhotite a highly reactive sulfide mineral that releases protons and Fe3+ into adjacent pore waters on oxidation. Further, the concentration of carbonate minerals in the tailings is low providing little buffering capacity above pH 5. Therefore, the tailings continued to acidify until they reach the pH of AI(OH)3 (pH 4-4.5) and Fe(OH)3 (pH 2.5-3.5) buffering. 

Figure 16. Depth profiles from three ODP Sites, showing Li isotopic composition variations in pore waters (open symbols) and associated sediments (filled symbols), (a) Site 918, Irminger Basin, north Atlantic (Zhang et al. 1998) (b) Site 1038, Escanaba Trough, northeastern Pacific (James et al. 1999) (c) site 1039, Middle American Trench off of Costa Rica (Chan and Kastner 2000). The average composition of seawater is noted on each profile with dashed line (note different scales). Whereas sediments have relatively monotonous compositions, pore waters have compositions reflecting different origins and processes in each site. Interpretations of the data are summarized in the text under, Marine pore fluid-mineral processes. ...

Croal LR, Johnson CM, Beard BL, Newman DK (2004) Iron isotope fractionation by anoxygenic Fe(II)-phototrophic bacteria. Geochim Cosmochim Acta 68 1227-1242 Curtis CD, Coleman ML, Love LG (1986) Pore water evolution during sediment burial from isotopic and mineral chemistry of calcite, dolomite and siderite concretions. Geochim Cosmochim Acta 50 2321-2334... 

A significant amount of seawater is trapped in the open spaces that exist between the particles in marine sediments. This fluid is termed pore water or interstitial water. Marine sediments are the site of many chemical reactions, such as sulfate reduction, as well as mineral precipitation and dissolution. These sedimentary reactions can alter the major ion ratios. As a result, the chemical composition of pore water is usually quite different from that of seawater. The chemistry of marine sediments is the subject of Part 111. 

Phosphate is remineralized during the oxidation of organic matter and dissolution of hard parts, such as bones and teeth, that are composed of the minerals hydroxyapatite and fluoroapatite. Unlike the other products of remineralization, pore-water phosphate concentrations are regulated only by mineral solubility, such as through vivianite (iron phosphate) and francolite (carbonate fluoroapatite). Redox reactions are not significant because phosphorus exists nearly entirely in the h-5 oxidation state. 

Diagenesis and catagenesis can alter the evaporite minerals after burial. For example, high temperatures, pressures, and pore-water salinities characteristic of deep burial lead to the conversion of gypsum into anhydrite. Thus, evaporite mineralogy reflects not only the environmental conditions under which the evaporite was formed, but also those under which diagenesis and catagenesis occurred. 

The actual density of clay minerals is 2.7g/cm. but these solids are surrounded by pore waters as they accumulate in the sediments. An average wet density of marine sediments is estimated at 1.6g/cm ... 

A summary of the observed natural chlorine isotope variations is presented in Fig. 2.23. Ransom et al. (1995) gave a natural variation range in chlorine isotope composition of about 15%c with subduction zone pore waters having S Cl values as low as —8%c whereas minerals in which Cl substitutes OH have 5 Cl values as high as 7%c. 

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