Characterization of vivianite from Catavi, Llallagua Bolivia

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.

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“…(Fagel et al, 2005;Sapota et al, 2006). Except for MnO, trace Mg and Zn were detected in vivianite nodules from Bolivia (Rodgers et al, 1993).…”

Section: Resultsmentioning

confidence: 93%

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

et al. 2013

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“…7) in comparison to pure vivianite that, according to Rodgers et al (1993), does not contain significant amounts of Mn. We estimate the maximum enrichment of Baikal vivianites, i.e., EFBaikal, by the ratio between the maximum measured Mn content in our samples and Mn data from the literature.…”

Section: Chemical Composition Of Vivianitementioning

confidence: 99%

“…The enrichment of both REE and U could reflect an adsorption process of large ions of lithophile trace elements (and trace metals) onto P-rich phases during diagenetic processes. (Deike et al, 1997); Bolivia from (Rodgers et al, 1993); Greece from (Stamatakis and Koukouzas, 2001). The composition of vivianite from Cameroon (MRAC collection) has been determined during the same analytical run as the Lake Baikal vivianite samples.…”

Section: Chemical Composition Of Vivianitementioning

confidence: 99%

“…A relationship between Mn and (Fe+Mg+Zn) per formula unit (p.f.u.) for selected vivianite samples from Cameroon and Greece (Stamatakis and Koukouzas, 2001), Bolivia (Rodgers et al, 1993) and Lake Baikal is shown in Fig. 8 ), responsible for the insertion of Mn into the vivianite structure.…”

Section: Chemical Composition Of Vivianitementioning

confidence: 99%

“…The concretions from the Academician Ridge display the highest measured Mn content (up to 19% Mn). The Lake Baikal samples (except one reported by Deike et al, 1997) (Stamatakis and Koukouzas, 2001), and Bolivia (Rodgers et al, 1993).…”

Section: Chemical Composition Of Vivianitementioning

confidence: 99%

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Vivianite formation and distribution in Lake Baikal sediments

Fagel

Alleman

Granina

et al. 2005

Global and Planetary Change

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In an effort to better understand vivianite formation processes, four Lake Baikal sediment cores spanning two to four interglacial stages in the northern, central and southern basins and under various biogeochemical environments are scrutinized. The vivianite-rich layers were detected by anomalous P-enrichments in bulk geochemistry and visually by observations on X-radiographs. The millimetric concretions of vivianite were isolated by sieving and analysed by X-ray diffraction, scanning electron microscope (SEM), microprobe, infrared spectroscopy, inductively coupled plasma atomic emission spectrometry and mass spectrometry (ICP-AES, ICP-MS). All the vivianites display similar morphological, mineralogical and geochemical signature, suggesting a common diagenetic origin. Their geochemical signature is sensitive to secondary alteration where vivianite concretions are gradually transformed from the rim to the center into an amorphous santabarbaraite phase with a decreasing Mn content. We analysed the spatial and temporal distribution of the concretions in order to determine the primary parameters controlling the vivianite formation, e.g., lithology, sedimentation rates, and porewater chemistry. We conclude that vivianite formation in Lake Baikal is mainly controlled by porewater chemistry and sedimentation rates, and it is not a proxy for lacustrine paleoproductivity. Vivianite accumulation is not restricted to areas of slow sedimentation rates (e.g., Academician and Continent ridges). At the site of relatively fast sedimentation rate, i.e., the Posolsky Bank near the Selenga Delta, vivianite production may be more or less related to the Selenga River inputs. It could be also indirectly related to the past intensive methane escapes from the sediments. While reflecting an early diagenetic signal, the source of P and Fe porewater for vivianites genesis is still unclear.

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