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Investigation of trace-element distribution in detrital quartz by Electron Paramagnetic Resonance (EPR).

Abstract:

Paramagnetic defects in natural, irradiated (2 kGy, 60Co, 295 K) and etched (40% HF, 30 min, 295 K) samples of quartz grains (grain size < 0.16 mm) from quartz-sand deposits in Weferlingen, Haltern and Frechen (Germany) were investigated by EPR at 9.5 GHz and at 20, 70, and 295 K.

In all samples [AlO4]0, [TiO4/Li+]0, [TiO4/H+]0, [TiO4]-, and Fe3+ paramagnetic centres were detected.
Generally, gamma-irradiation caused a transformation of diamagnetic precursor centres into these paramagnetic centres resulting in an increase of the EPR intensity of up to five times. Samples from Weferlingen have similar trace-element contents and show only minor differences in the abundance of paramagnetic centres. In contrast, the abundance of paramagnetic centres in quartz from the different deposits may differ significantly, especially Fe3+, [AlO4]0 and [TiO4/Li+]0 centres in the irradiated quartz samples. The high concentrations of [AlO4]0 and [TiO4/Li+]0 centres in the Weferlingen quartz samples reflect higher amounts of igneous quartz than in the other deposits investigated.

These differences in quartz composition were confirmed by cathodoluminescence microscopy. Etching of quartz samples with hydrofluoric acid (ca. 30% loss of mass) followed by further EPR measurement revealed that Al centres generally show more or less homogeneous distribution pattern, whereas no Fe-centres were left in quartz after etching. This indicates that Fe centres are concentrated in the outer rim of the quartz grains.

Authors:

Götze, Jens and Plötze, Michael

Index Terms:

clastic sediments; quartz; trace-elements; cathodoluminescence; Clay; ClayGroup

Further Information:

Date published: 1997