GeoPeP 2011/2012

All sample work and measurements were carried out in laboratories of the geochemistry section of the “Geowissenschaftliches Zentrum Göttingen”. Sample preparation included a preliminary rough-crushing for those samples which were not already available in a fine-grained fraction. The fraction smaller 1 mm was sieved and afterwards milled to a fine powder.

Mineral-sensitive methods

X-ray Diffraction (XRD)
In order to get a qualitative identification of the main mineral phases, 27 powder samples were analysed using X-ray diffraction.
The XRD-Method uses the diffraction of X-rays on atomic planes of the crystal lattice. The diffraction angle is measured and can be used to calculate the distance between the atomic planes of the measured crystal. Each mineral has a characteristic distance between its atomic planes and therefore can be identified by this.
Significant mineral peaks were identified and marked in the measured XRD spectra.

Link to the Crystallography Divsion at the GZG Göttingen

Electron Microprobe (EMP)
Nine representative sediment grains from each sample with a maximum diameter of 1 mm were picked beneath a binocular and placed in an resin on a thin-section. The thin-sections were ground, polished and then analysed. In this context, compositional images (BSE) were taken and major elemental compositions of miscellaneous distinguishable mineral phases were determined using the energy dispersive system attached to the probe (EDX). The concept of EDX relies on a stimulation of the target with electrons of a uniform energy, triggering the emission of element characteristic x-ray radiation. The images also allow for conclusions concerning morphologies and textures of selected sample-specific grains.

Link to the Electron Microprobe Laboratory

Element-sensitive methods

X-ray Fluorescence (XRF)
For the XRF-analysis it is required to convert the powder to glass tablets. Therefore, a fixed amount of sample and a addition of LiF and A12 (66% di-Lithiumtetraborate, 34% Lithium metaborate) were mixed and merged into a tablet form.
X-ray fluorescence spectrometry uses secondary emitted characteristic X-rays triggered by high energetic bombardment of the prepared powder with primary X-rays. Inner shell electrons are affected by ionisation followed by de- energizing causing the characteristic radiation. The intensity, in which certain energies are detected, is proportional to the abundance of the element in the sample. Major and trace elements can be analysed with this method, providing whole rock chemistry of the rock.
In preparation the powder is ignited in order to expel volatile phases. Therefore, 5 g powder was heated for 24 h at 1050°C within a ceramic crucible in a muffle furnace in order to attain the loss of ignition (LOI).

XRF at the GZG

Inductively Coupled Plasma – Mass Spectrometry (ICP-MS)
Initially, an acid hydrolysis was carried out using 100 mg powder with the goal to destroy the silicates and oxides and to form an ionic solution. Thereby, the silicates are cracked and silicon is fixed in a SiF4-complex. Afterwards, the solutions were analysed using ICP-MS to provide data on trace elemental compositions. A 6000°C hot argon plasma is generated in a ICP torch. Elements get ionized in the plasma and enter the quadrupole analyzer where they are separated according to their mass-charge ratio.

ICP-MS at the GZG

© Christian Hansen, Andres Höweling, Kai Nitzsche, Tammo Ohlendorf 2012