Composition of magnetite trace elements in the Jõhvi magnetic quartzite in north-east Estonia as an indicator of iron mineralization processes

Abstract

The aim of this master’s thesis was to study the origin of the iron mineralisation in the crystalline basement from the Jõhvi magnetic anomaly, Estonia, using the geochemical analysis of the magnetite trace elements. Magnetite-bearing samples from the magnetite mineralisation intervals of drill cores PA-1 and PA-2 were described petrographically, and the trace element composition of the magnetite was characterised by using analytical scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry. The results of this study show that magnetite divides into different types depending on the host rock mineral composition. Compared to the previous studies on magnetite trace-element composition from various iron ore deposits, the initial origin of Jõhvi magnetite mineralization was most likely related to the formation of the banded iron formation (BIF). However, the trace-element composition of the magnetite has been changed due to orogenetic granulite facies regional metamorphism and alteration by hydrothermal fluids.