Siderite formation

Postma D (1982) Pyrite and siderite formation in brackish and freshwater swamp sediments. Amer J Sci 282 1151-1183... 

Thus, to apply the findings of Mozley (1989a), it is important to determine precisely the diagenetic regime of siderite formation. 

In summary, equilibrium calculations based on pore-water composition indicate that Fe carbonate or phosphate are unlikely to form below the top few centimeters of sediment and that siderite formation is unlikely generally. Undersaturations by a factor of A, p/IAP —100 are found. The presence of solid-phase sulfide is evidence for the formation of Fe sulfides. However, pore waters are not always saturated with respect to the common Fe-sulfide minerals and under-or supersaturations by a factor of —10 are calculated. These deviations may be due to such problems as organic complexing or cumulative analytical and sampling errors, but the possibility that other phases are influencing Fe concentrations cannot be excluded on the basis of these data. 

In fully marine systems siderite formation is probable to occur below the sulfate reduction zone where dissolved sulfide is absent, if reactive iron is still present and the Fe/Ca-ratio of pore water is high enough to stabilize siderite over calcite (Berner 1971). The coexistence of siderite and pyrite in anoxic marine sediments was shown by Ellwood et al. (1988) and Haese et al. (1997). Both studies attribute this observation to the presence of microenvironments resulting in different characteristic early diagenetic reactions next to each other within the same sediment depth. It appears that in one microenvironment sulfate reduction and the formation of pyrite is predominant, whereas at another site dissimilatory iron reduction and local supersaturation with respect to siderite occurs. Similarly, the importance of microenvironments has been pointed out for various other processes (Jorgensen 1977 Bell et al. 1987 Canfield 1989 Gingele 1992). 

Ellwood, B.B., Chrzanowski, T.H., Hrouda, F., Long, GJ. and Buhl, M.L., 1988. Siderite formation in anoxic deep-sea sediments A synergetic bacterially controlled process with important implications in paleomagnetism. Geology, 16 980-982... 

Calcite and siderite (27) are used occasionally because of their solubiUty in hydrochloric acid which offers a method of removing mud filter cake deposited on productive formations. Calcite and siderite are used most frequently in workover or completion fluids when a nondamaging fluid is required, ie, one that can be removed by acidising at a later time. 

Shikazono, N. (1977b) Composition of siderite and the environments of formation of vein-type deposits in Japan. Econ. Geol, 72, 632-641. 

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

In the wetlands of Idaho, the formation of an Fe(III) precipitate (plaque) on the surface of aquatic plant roots (Typha latifolia, cat tail and Phalaris arundinacea, reed canary grass) may provide a means of attenuation and external exclusion of metals and trace elements (Hansel et al, 2002). Iron oxides were predominantly ferrihydrite with lesser amounts of goethite and minor levels of siderite and lepidocrocite. Both spatial and temporal correlations between As and Fe on the root surfaces were observed and arsenic existed as arsenate-iron hydroxide complexes (82%). 

The effect of the partial pressure of oxygen and of CO2 is also very important for the decomposition behaviour of siderite and rhodochrosite. The formation of the iron oxides was followed by TG and by high temperature X-ray diffraction. Below 10-6 mm Hg oxygen pressure only Fe304 was formed. 

Figure 21. Plot of the measured 6 Fe value of pairs of magnetite and siderite layers from Banded Iron Formations. Data from Johnson et al. (2003a) and C. Johnson and B. Beard unpublished.

Figure 10. Comparison of isotopic fractionations determined between Fe(II)aq and Fe carbonates relative to mole fraction of Fe from predictions based on spectroscopic data (Polyakov and Mineev 2000 Schauble et al. 2001), natural samples (Johnson et al. 2003), DIR (Johnson et al. 2004a), and abiotic formation of siderite under equilibrium conditions (Wiesli et al. 2004). Fe(II)aq exists as the hexaquo complex in the study of Wiesli et al. (2004) hexaquo Fe(II) is assumed for the other studies. Total cations normalized to unity, so that end-member siderite is plotted at Xpe = 1.0. Error bars shown reflect reported uncertainties analytical errors for data reported by Johnson et al. (2004a) and Wiesli et al. (2004) are smaller than the size of the symbol. Fractionations measured on bulk carbonate produced by DIR are interpreted to reflect kinetic isotope fractionations, whereas those estimated from partial dissolutions are interpreted to lie closer to those of equilibrium values because they reflect the outer layers of the crystals. Also shown are data for a Ca-bearing DIR experiment, where the bulk solid has a composition of q)proximately Cao.i5Feo.85C03, high-Ca and low-Ca refer to the range measured during partial dissolution studies (Johnson et al. 2004a). Adapted from Johnson et al. (2004a).

Although the majority of attention in discussions on the origins of BIFs has been on the oxide facies, siderite facies rocks are equally important in many BIF sequences. Reaction of Fe(II)aq and dissolved carbonate with hematite to form siderite and magnetite has been hypothesized to be an important diagenetic process in marine basins during formation of some BIFs if sulfate contents were low (e.g., Klein and Beukes 1989 Beukes et al. 1990 Kaufman 1996 Sumner 1997). In Figure 18 we assume that Fe(II)aq was derived either from MOR sources or DIR, or a combination of the two, which reacted with ferric oxide precipitates to form magnetite or dissolved carbonate to produce siderite. 

Magnetite that has 5 Fe values near zero might reflect formation during slow (equilibrium) reduction rates, whereas the lowest 5 Fe values might reflect rapid Fe(III) reduction and kinetic isotope fractionation (Fig. 19), or multiple reduction cycles. The correlation between Magnetite-siderite 8 Fe of magnetite observed in BIFs therefore probably reflects changes in... 

Mozley PS, Carothers WW (1992) Elemental and isotopic compositions of siderite in the Kuparuk formation, Alaska effect of microbial activity and water/sediment interaction on early pore-water chemistry. J Sed Pet 62 681-692... 

Postma D (1981) Formation of siderite and vivianite and the pore-water composition of a recent bog sediment in Denmark. Chem Geol 31 225-244... 

Pye K, Dickson JAD, Schiavon N, Coleman ML, Cox M (1990) Formation of siderite-Mg-calcite-iron sulphide concretions in intertidal marsh and sandflat sediments, north Norfolk, England. Sedimentology 37 325-343... 

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