Petrology, geochemistry and structure of the host rock for the Printzsköld ore body in the Malmberget depositReport as inadecuate

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2010 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Abstract [en] : The Malmberget deposit is one of the largest apatite iron ore (Kiruna type) in the world, located in northern Norrbotten, 70 km north of the article circle and this area is one of Sweden’s major ore-producing regions. The apatite iron ores in the Kiruna area occurs in an early Proterozoic continental setting. It is related to a Paleoproterozoic succession of greenstones, porphyries, and clastic metasediments that rest uncomformably upon a 2.8-2.7 Ga Archaean basement. The ore bodies are hosted by mafic to intermediate volcanic rocks and is intruded by felsic and mafic rocks. The area has experienced at least two metamorphic events: the first at 1.88 Ga and the second at 1.80 Ga. The present work is a petrochemical and structural geological study of the host rock of the Printzsköld ore body in the central part of the Malmberget deposit. The aim is to clarify if there are any petrographical and chemical differences between the footwall and the hanging wall of the Printzsköld ore body and to make clear the importance of local structural geology for the ore body geometry. Moreover it implies to identify the original character of the leptites which host the Printzsköld ore body. Seven drill cores were logged in order to outline the spatial distribution and character of rock types and the variation in alteration. Two of them have been sampled for analysis. Analytical methods that were used are whole rock geochemistry and optical microscopy. The structural geological studies were carried out both on the drill core and through underground mapping. The host rock is composed of strongly altered rock types, which are intrusive felsic rocks of aplitic and pegmatitic character, intrusive mafic rocks and extrusive mafic to intermediate metavolcanic rocks. The intrusions occur widespread both in the hanging wall and in the footwall. The common alteration minerals are biotite, albite, amphibole, K-feldspar, sericite and chlorite. Amphibole alteration strongly affects the aplites and extends into the adjacent mafic to intermediate metavolcanic rocks. The K- feldspar alteration is developed both in the footwall and in the hanging wall which will affect both the aplites, the pegmatites and the metavolcanic rocks. The K-feldspar alteration is overprinting the amphibole alteration. The biotite alteration is widespread in the metavolcanic rocks and may result in the formation of biotite schist. The hanging wall contact and the footwall contact of the ore are marked by strong amphibole alteration and biotite enrichment respectively. The strong alteration and metamorphism makes the use of mobile element for rock characterisation difficult. These alterations also affect other elements and only few high field strength elements (Zr, Ti) are not mobile in the system and can be used to characterise the different rock types. The geochemical results show that the mafic rocks have basaltic character and the intermediate rocks have andesitic character. The rare earth elements show large variations in their concentrations and are consequently affected by alterations. The host rock show geochemical similarities with the Kiruna Porphyry Group. The large scatter patterns of most element plots indicate that the felsic and mafic intrusions, the basalts and the andesites surrounding the Printzsköld ore body are affected by a varying degree of alteration and metamorphism. The character and distribution of the alterations is more controlled by the rock type than the location either in the hanging wall or in the footwall. Comparing the regional foliations with the foliation in the host rock of Printzsköld, we notice a significant difference of strike and plunge. The Printzsköld ore body does not follow the general structure of the ore horizon. These observations could be the result of either a folding event or a W-E oriented shear zone which might controls the host rock geometry and is the cause of the steep NE-SW foliation. The structural geology study needs to be extended in Printzsköld and to the host rock of the others ore bodies in order to give conclusions on the control of the geometry for all the ore bodies.

Place, publisher, year, edition, pages: 2010.

Keyword [en] : Life Earth Science, Printzsköld, apatite iron ore, Kiruna Porphyry, host rock, alterations, metamorphism, foliation, intrusions, aplite, basalt, andesite, mobility

Keyword [sv] : Bio- och geovetenskaper

Identifiers: URN: urn:nbn:se:ltu:diva-48400ISRN: LTU-PB-EX--10/052--SELocal ID: 5d984fad-88e9-4b93-9a55-22f1cd0bca55OAI: diva2:1021742

Subject / course: Student thesis, at least 30 credits

Educational program: Geosciences, master's level

Supervisors : Martinsson, OlofLund, Cecilia

Note: Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

Author: Debras, Céline


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