The shape characterization of talc and mineralogy of the Haaponen talc deposit in eastern Finland

Abstract

The Haaponen talc deposit is located at Suomussalmi municipality near Saarijärvi in the northern parts of Archean Tipasjärvi-Kuhmo-Suomussalmi greenstone complex in eastern Finland. The main aspects affecting the mineralogy and grain shape of talc, and the possibility of using macroscopic properties seen in the deposit (e.g., texture) to estimate the grain shape and size of talc were assessed. The mineralogy and the properties of talc were determined from 24 thin sections utilizing an optical microscopy and electron probe microanalyzer (EPMA). The particle characterization is determined from 27 talc concentrates using dynamic image analysis (DIA), and combining measurement obtained using Sedigraph to measurements from previous studies obtained by laser diffraction method. The particle size distribution results of talc concentrates were compared to the properties observed in 9 thin sections, which were prepared from corresponding drill cores and depths as talc concentrates.

Grain size values obtained by sedimentation method better represented the grain size variation observed in thin sections. No singular macroscopic feature (e.g., the size of carbonate porphyroblasts) can easily be used to predict the grain size or shape of talc, though they can give insight into the mineralogy, chemical composition, and the color of talc in the deposit. Additionally, certain features such as slightly elongated carbonate grains in weakly schistose samples can assist in determining more precisely the zone at which different textures change. The shape and size of talc varies in different texture types, which is also noticeable from the particle size distribution data. Although, the properties of talc cannot be easily associated with a certain feature, the overall texture could potentially be used to estimate the particle shape and size within the deposit.