Electron spin resonance as a high sensitivity technique for environmental magnetism: determination of contamination in carbonate sediments

Abstract

Summary This study investigates the application of high sensitivity electron spin resonance (ESR) to environmental magnetism in conjunction with the more conventional techniques of magnetic susceptibility, vibrating sample magnetometry (VSM) and chemical compositional analysis. Using these techniques we have studied carbonate sediment samples from Discovery Bay, Jamaica, which has been impacted to varying degrees by a bauxite loading facility. The carbonate sediment samples contain magnetic minerals ranging from moderate to low concentrations. The ESR spectra for all sites essentially contain three components. First, a six‐line spectra centred around g= 2 resulting from Mn2+ ions within a carbonate matrix; second a g= 4.3 signal from isolated Fe3+ ions incorporated as impurities within minerals such as gibbsite, kaolinite or quartz; third a ferrimagnetic resonance with a maxima at 230 mT resulting from the ferrimagnetic minerals present within the bauxite contamination. Depending upon the location of the sites within the embayment these signals vary in their relative amplitude in a systematic manner related to the degree of bauxite input. Analysis of the ESR spectral components reveals linear relationships between the amplitude of the Mn2+ and ferrimagnetic signals and total Mn and Fe concentrations. To assist in determining the origin of the ESR signals coral and bauxite reference samples were employed. Coral representative of the matrix of the sediment was taken remote from the bauxite loading facility whilst pure bauxite was collected from nearby mining facilities. We find ESR to be a very sensitive technique particularly appropriate to magnetic analysis of ferri‐ and para‐magnetic components within environmental samples otherwise dominated by diamagnetic (carbonate) minerals. When employing typical sample masses of 200 mg the practical detection limit of ESR to ferri‐ and para‐magnetic minerals within a diamagnetic carbonate matrix is of the order of 1 ppm and 1 ppb respectively, approximately 102 and 105 times the sensitivity achievable employing the VSM in our laboratory.

Sedimentary iron cycling and the origin and preservation of magnetization in platform carbonate muds, Andros Island, Bahamas

“…Following Crook et al (2002), we assessed the relative abundance of paramagnetic Fe(III) in different samples by measuring the height of the g = 4.3 (~160 mT) peak above a baseline, which we approximated by linear interpolation between the 120 mT and 230 mT points in the derivative absorption spectra. To assess the relative abundance of Mn(II), we measured the height between the maximum and the minimum of the sixth line of the Mn(II) sextet.…”

Ferromagnetic resonance characterization of greigite (Fe3S4), monoclinic pyrrhotite (Fe7S8), and non‐interacting titanomagnetite (Fe3‐xTixO4)

“…Ferromagnetic resonance (FMR) (also termed electron paramagnetic resonance (EPR) for paramagnetic materials and termed electron spin resonance (ESR) in general) is a spectroscopic technique that has recently been applied to problems in rock magnetism and paleomagnetism. For example, it has been used to characterize intracellular magnetosome chains and detect their fossil remains in sediments [e.g., Weiss et al , 2004; Kopp et al , 2006a, 2007, 2009; Fischer et al , 2008; Faivre et al , 2010; Kind et al , 2011; Roberts et al , 2011a; Gehring et al , 2011a], to assess magnetic anisotropy and magnetic interactions [e.g., Kopp et al , 2006b; Fischer et al , 2008; Mastrogiacomo et al , 2010; Gehring et al , 2011b], to trace iron biogeochemistry in sediments [ Maloof et al , 2007], and for environmental magnetic interpretations [e.g., Pawse et al , 1998; Crook et al , 2002; Fischer et al , 2007; Roberts et al , 2011a]. Therefore, FMR analysis has the potential to become a standard tool in rock magnetic studies.…”

A laboratory study of the effect of magnetite on NMR relaxation rates

“…For all the magnetite mixtures, χ m increases with increasing magnetite concentration and is in the range of 0.70 × 10 − 6 to 15.0 × 10 −6 m 3 /kg. For the powdered synthetic magnetite mixtures there is a distinct linear relationship between χ m and magnetite concentration; this is predicted from mixture theories (Berryman, 1995;Crook et al, 2002). The error in the magnetic susceptibility measurements is below the size of the data point.…”