Tectonophysical study of an epigenetic Cu-Fe mineralisation in northern Sweden

• A tectonophysical study has been performed on the Tjårrojåkka Cu-Fe mineralisations, WSW of the city of Kiruna, northern Sweden. The bedrock is characterized by intermediate to mafic meta-volcanites, mafic dykes and monzo-dioritic intrusions, with ages of c. 1.9-1.88 Ga. The epigenetic copper and iron mineralisations occur within the meta-andesitic rocks. The aim of the study is to define structures that may have controlled the deposition of the mineralisations using combined geophysical and petrophysical data. Magnetic, gravity and VLF (Very Low Frequency) datasets have been analysed for the delineation of geophysical domains and lineaments. Subsequently, in spite of the glacial sediments, a number of outcrops along a profile, that intersects major structures, has been sampled for petrophysical studies. These also include Anisotropy of Magnetic Susceptibility (AMS) measurements that are used for the tectonic interpretation. 21 outcrops were drilled in the Tjårrojåkka area, for a total of more than 150 samples. We defined three major geophysical domains reflecting different rock types: meta-basalts, meta-andesites and an intrusive body. Geophysical lineaments of tectonic significance, striking E-W, SW-NE, NW-SE, occur in the area and at least one of them (SW-NE) seems to be related to the mineralisations. Examination of ground-geophysics datasets gives a SW-NE strike for the major mineralised bodies. The small number of structural elements visible in outcrop makes the analysis of AMS necessary for a comprehensive tectonic study. Magnetic foliations and lineations, defined for both meta-volcanic and intrusive rocks, confirm the trends obtained from other geophysical and geological observations and allow more detailed information about the character of the different geophysical lineaments and domains. Besides, magnetic foliations defined for meta-andesitic rocks, weakly Cu-mineralised, in proximity of the major Cu-deposit, mark two major tectonic events, one of them parallel to that defined for the orebodies. This result reinforces the thesis of a tectonic control on Cu-Fe mineralisations, reflected by a petrophysical inprint of this tectonic episode.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geofysik (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geophysics (hsv//eng)

Nyckelord

Tillämpad geofysik

Applied Geophysics

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vet (ämneskategori)

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