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Citation link: https://doi.org/10.26092/elib/3246

Publisher DOI: https://doi.org/10.1016/j.apgeochem.2006.12.021
Lazareva_Pichler_Naturally occurring arsenic in the Miocene Hawthorn Group southwestern Florida_2007_accepted-version.pdf
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Naturally occurring arsenic in the Miocene Hawthorn Group, southwestern Florida: Potential implication for phosphate mining


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Lazareva_Pichler_Naturally occurring arsenic in the Miocene Hawthorn Group southwestern Florida_2007_accepted-version.pdf4.65 MBAdobe PDFView/Open
Authors: Lazareva, Olesya 
Pichler, Thomas  
Abstract: 
To understand the mineralogical association, concentration, and distribution of arsenic (As) in the Hawthorn Group, the chemical and mineralogical composition of 362 samples that were collected from 16 cores in southwestern Florida were examined in detail. In the study area, the Hawthorn Group consisted primarily of a basal carbonate unit (the Arcadia Formation) and an upper siliciclastic unit (The Peace River Formation). The Peace River Formation contains appreciable amounts of phosphate and is currently being exploited for phosphate ore. Samples were taken from cores of each formation at intervals of 7.5 m. In addition, to the interval samples, sections likely to have high As concentrations, such as zones with pyrite crystals, hydrous ferric oxides, green clays, and organic material, were collected and analyzed. Bulk As concentrations were determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) after digestion with aqua regia (3:1 HCl and HNO3). The elements Fe, Al, Si, Mg, Ca, S, and P were measured on the same solutions by inductively coupled plasma optical emission spectrometry (ICP-OES). The identification of discrete minerals was aided by scanning electron microscopy (SEM) and chemical compositions within the sample matrix and in individual minerals were obtained by electron-probe microanalysis (EMPA).

This detailed mineralogical and geochemical study demonstrated that: (1) As in the Hawthorn Group varied from formation to formation and was mostly concentrated in trace minerals, such as pyrite; (2) average As concentrations significantly changed from 8.8 mg/kg (σ = 8.6 mg/kg) in the Peace River Formation to 3.0 mg/kg (σ = 3.7 mg/kg) in the Tampa Member of the Arcadia Formation. Arsenic concentrations for all Hawthorn samples varied from 0.1 to 69.0 mg/kg; (3) pyrite, with one exception, occurred as framboids and was unevenly distributed throughout the Hawthorn Group; (4) pyrite framboids were located inside a francolite (carbonate fluorapatite) matrix with As concentrations as high as 3730 mg/kg and as a trace mineral in the sediment matrix concentrations varying from <1 to 8260 mg/kg; (5) hydrous ferric oxides (HFO) contained As concentrations as high as 540 mg/kg; (6) francolite, organic material, and clays contained substantially less As than pyrite; (7) thus, the release of As from pyrite could pose a potential problem for the phosphate industry.
Keywords: Miocene Hawthorn Group; Florida; Arsenic; phosphate mining
Issue Date: May-2007
Publisher: Elsevier Science
Project: Southwest Florida Water Management District grant 
Journal/Edited collection: Applied Geochemistry 
Issue: 5
Start page: 953
End page: 973
Volume: 22
Type: Artikel/Aufsatz
ISSN: 1872-9134
Secondary publication: yes
Document version: Postprint
DOI: 10.26092/elib/3246
URN: urn:nbn:de:gbv:46-elib82129
Institution: andere Institution 
Appears in Collections:Forschungsdokumente

  

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