Open AccessElectron spin resonance as a high sensitivity technique for environmental magnetism: determination of contamination in carbonate sediments
Author(s) -
Crook Nigel P.,
Hoon Stephen R.,
Taylor Kevin G.,
Perry Chris T.
Publication year - 2002
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1046/j.1365-246x.2002.01647.x
Subject(s) - bauxite , carbonate , ferrimagnetism , sediment , geology , mineralogy , magnetism , analytical chemistry (journal) , chemistry , materials science , environmental chemistry , magnetization , physics , metallurgy , magnetic field , condensed matter physics , paleontology , quantum mechanics
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 Mn 2+ ions within a carbonate matrix; second a g = 4.3 signal from isolated Fe 3+ 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 Mn 2+ 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 10 2 and 10 5 times the sensitivity achievable employing the VSM in our laboratory.