Geochemistry and mineralogy of the felsic porphyries at Hanhimaa, Kittilä in the central Lapland belt, northern Finland

• Main Author: Ohvo, V. (Viivi)
• Format: Master Thesis
• Language: English
• Published: University of Oulu 2020
• Subjects: Hanhimaa; Kellolaki; Kittilä; Lisma; Siskeli; Northern Finland; Lapland
• Online Access: http://jultika.oulu.fi/Record/nbnfioulu-202003181289

Abstract. Several small gold occurrences are identified along the Hanhimaa shear zone, located in the Central Lapland belt, northern Finland. Gold occurrence are hosted by the mafic volcanites of the Kittilä suite. In addition, felsic porphyric rocks are common within these occurrences. However, their association to the gold mineralisation is not known. In this thesis, petrography and geochemistry of the felsic porphyritic rocks occurring in the gold occurrences are used to characterize them and compare them appearance to the other known felsic porphyries within the Central Lapland belt. 55 samples are collected from the drill cores, representing eight exploration targets: Lisma, Kellolaki, Kiimalaki, Siskeli, Väli-Kiima, Kiimakuusikko, Kousa and Kapsa. Three of them; Kellolaki, Kiimalaki and Kiimakuusikko are identified gold mineralisation hosted by the Kittilä suite mafic volcanic rocks along the Hanhimaa shear zone. The rest are early stage exploration targets and cannot be called as gold occurrences at this stage. Methods used are geochemical whole rock assay, microscopical study of thin sections and electron microprobe study of selected, representative thin sections. Results show that the felsic porphyries are ranging from rhyolitic to andesitic in composition. Based their textures in drill cores, petrographical studies and geochemical characteristics, they can be divided into the known felsic porphyry types, the Veikasenmaa (2.02–2.01 Ga) and the Nyssäkoski type (1.92 Ga). Locally, elevated gold is found from the felsic porphyric rocks belonging to the younger, Nyssäkoski type. This type is known to host gold in other occurrences within the Kittilä suite. The results may be used as an additional information at the exploration activities ongoing at the Hanhimaa area.Tiivistelmä. Keski-Lapin vyöhykkeeltä, Kittilän alueelta Hanhimaan hiertovyöhykkeeltä tunnetaan useita kultaesiintymiä. Nämä esiintymät sijoittuvat geologisesti Kittilän sviitin mafisiin metavulkaniitteihin, joiden yhteydessä esiintyy ...