Provenance of heavy minerals in the Quaternary deposits of the Lemme outcrop, Estonia, based on optical microscopy, X-ray diffractometry and scanning electron microscope microanalysis

Abstract

This paper is a methodological development, where optical microscopy, X-ray diffractometry (XRD) and microanalysis under a scanning electron microscope (SEM) were used for comparative determination of heavy minerals in Quaternary sandy sediments in the Lemme outcrop, southwestern Estonia, and for evaluation of possible provenance rocks. For comparison, samples from Devonian drill cores were analysed. Heavy minerals in the Lemme coastal deposits mostly originated from the till of the last glaciation, which contained clasts and fines from rocks of the Svecofennian Domain of the Fennoscandian (Baltic) Shield. Garnets were the dominating minerals in the Lemme samples, whereas the crystal lattice parameter of the main component was 11.535 Å. The Devonian garnets were different, with the lattice parameter of the main component being 11.610 Å. Amphiboles, ilmenite and magnetite were also important minerals in the Lemme samples, but scarce in the Devonian samples. A detailed study of magnetite revealed a Ti content of 0.3%, which is consistent with the lattice parameter 8.397 Å. The hematite content of the Lemme samples was about twice as high as that of magnetite. The Ti content of hematite grains was higher in the surface (about 5%) than in the middle section (1.6%). The XRD analysis showed that titanium in hematite grains was probably fine crystalline rutile. In the Devonian samples, the main opaque mineral was pseudorutile.

Keywords

• heavy minerals
• opaque minerals
• optical microscopy
• X-ray diffractometry
• scanning electron microscope.