High-temperature thermomagnetic properties of vivianite nodules, Lake El'gygytgyn, Northeast Russia

Abstract

Abstract. Vivianite, a hydrated iron phosphate, is abundant in sediments of Lake El'gygytgyn, located in the Anadyr Mountains of central Chukotka, northeastern Russia (67°30′ N, 172°05′ E). Magnetic measurements, including mass-specific low-field AC magnetic susceptibility, field-dependent magnetic susceptibility, hysteresis parameters, temperature dependence of the induced magnetization, as well as susceptibility in different heating media, provide ample information on vivianite nodules. Electron microprobe analyses, electron microscopy and energy dispersive spectroscopy were used to identify diagnostic minerals. Vivianite nodules are abundant in both sediments of cold (anoxic) and warm (oxic) stages. Magnetic susceptibility of the nodules varies from 0.78 × 10−6 m3 kg−1 to 1.72 × 10−6 m3 kg−1 (average = 1.05 × 10−6 m3 kg−1) and is higher than the susceptibility of sediments from the cold intervals. Magnetic properties of vivianite are due to the respective product of oxidation as well as sediment and mineral inclusions. Three types of curves for high-temperature dependent susceptibility of vivianite indicate different degrees of oxidation and inclusions in the nodules. Vivianite acts as a reductant and reduces hematite to magnetite and masks the goethite–hematite transition during heating. Heating vivianite and sulfur mixtures stimulates the formation of monoclinic pyrrhotite. An additive of arsenic inhibits the formation of magnetite prior to its Curie temperature. Heating selective vivianite and pyrite mixtures leads to formation of several different minerals – magnetite, monoclinic pyrrhotite, and hexagonal pyrrhotite, and makes it difficult to interpret the thermomagnetic curves.

Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approach

“…The occurrence of vivianite nodules in a recent and unlayered sediment horizon distinguishes the vivianite finding described here from Lake Groß-Glienicke from the vivianite deposits regularly detected in palaeolimnetic core records (e.g. Brauer et al, 1999;Sapota et al, 2006;Minyuk et al, 2013).…”

“…5). Considering the range of a factor of two for the mass-specific magnetic susceptibility of vivianite (Minyuk et al, 2013), the vivianite contents determined by both the chemical digestion and the FeS-corrected paramagnetic susceptibility methods match acceptably.…”

“…The vivianite content (c vivianite [weight as % of total]) in high-density samples was estimated by comparing the measured paramagnetic mass-specific susceptibility of a highdensity sample (MS sample [m 3 kg −1 ]) with the value given for vivianite, of MS vivianite = 1.05 × 10 −6 m 3 kg −1 (Minyuk et al, 2013). The MS sample values were calculated from the slope of the linear increasing part of the hysteresis loops after magnetic saturation of ferrimagnetic minerals.…”

“…The mineral is a regularly found deposit in sedimentary cores (e.g. Brauer et al, 1999;Fagel et al, 2005;Sapota et al, 2006;Minyuk et al, 2013). Since P is only a minor constituent in sediments, the direct identification of vivianite is difficult.…”

Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approach

“…Organic P originates from settled organic material which is refractory or not yet mineralised by microorganisms. Inorganic phases include P sorbed onto the surface of iron(oxy)hydroxides, aluminium hydroxides, clays and calcite (Moosmann et al, 2006). P associated with Fe(III) minerals have been found in anoxic marine and estuarine sediments, indicating a resistance towards reductive dissolution of these compounds, at least under nonsulfidic conditions (Hyacinthe and Van Cappellen, 2004;Lehtoranta et al, 2009).…”