Major and trace element characteristics of biotite and chlorite as proxies for gold ore mineralization

The Archean Hattu schist belt in eastern Finland is host to several orogenic gold occurrences. One of these deposits is the Pampalo gold deposit located in Hattu, Ilomantsi. Major and trace element characteristics of biotite and chlorite were analyzed from a representative collection of rock types of different degrees of alteration from the Pampalo deposit. The main aim of this study was identifying possible correlation of changes in the elemental composition of biotite and chlorite with distance to gold ore mineralization and testing the two minerals’ use as proxies for mineralization in Pampalo. Biotite and chlorite were chosen for being represented in altered and unaltered ore and adjacent country rock units. Samples were prepared from half and quarter drill core rocks and analyzed with hyperspectral imaging, electron micro probe analysis (EMPA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). Hyperspectral imaging and thin section microscopy were used for mineral identification and mineral grain sampling. EMPA and LA-ICP-MS data found weak correlation with distance to mineralization for Mg, Al, Ti, Fe, Zn, Sr and Cs in biotites and Li, B, Mg, Al, Si, P, Sc, Ti, Mn, Fe, Ni, Zn, Ga, As and Sr for chlorite. Moderate correlation was found for Pb and Tl in biotites and Co in chlorites. Strongest correlation was found for Mn, W and Ba in biotites. These three elements all deplete in biotites with decreasing distance to mineralization. Changes in concentrations of manganese are likely variation in host rock chemistry. Tungsten concentrations seem to be linked to fluid flows, but only indirectly related to gold ore mineralization. Barium was found to be the most promising element within biotites due to its high mobility, and its depletion could indicate approaching gold ore mineralization. Changes in As concentrations of chlorites also point to two different types of chlorite grains, one of which indicate an ore mineralization event having taken place.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2018

Author dc:creator

• Kuikka, Jaro

Contributors dc:contributor

• Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Geotieteiden ja maantieteen laitos
• University of Helsinki, Faculty of Science, Department of Geosciences and Geography
• Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för geovetenskaper och geografi

Language dc:language.iso

eng

Identifier URI

URN:NBN:fi:hulib-201801251108

OAI identifier oai:identifier

oai:helda.helsinki.fi:10138/231586