09 Jan 2023
09 Jan 2023
Status: this preprint is open for discussion.

Structural framework and timing of the Pahtohavare Cu ± Au deposits, Kiruna mining district, Sweden

Leslie Logan, Ervin Veress, Joel B. H. Andersson, Olof Martinsson, and Tobias E. Bauer Leslie Logan et al.
  • Division of Geosciences and Environmental Engineering, Luleå University of Technology, Luleå SE-971 87, Sweden

Abstract. As part of a larger mineral systems approach to Cu-bearing mineralization in northern Norrbotten, this study utilizes structural geology to set the classic Pahtohavare Cu ± Au deposits into an up-to-date tectonic framework. The Pahtohavare Cu ± Au deposits, situated only 5 km SW of the Kiirunavaara world-class iron oxide apatite (IOA) deposit, have a dubious timing and their link to IOA formation is not constrained. The study area contains both epigenic Cu ± Au (Pahtohavare) and iron oxide-copper-gold (IOCG, Rakkurijärvi) mineral occurrences which are hosted in bedrock that has been folded and bound by two shear zones trending NE-SW and NW-SE to the east and southwest, respectively. Structural mapping and petrographic investigation of the area reveal an anticlinal, noncylindrical, SE-plunging fold geometry. The cleavage measurements mirror the fold geometry which characterizes the fold as F2 associated to the late phase of the Svecokarelian orogeny. Porphyroclasts with pressure shadows and mylonitic fabrics observed in thin section indicate S0/S1 is a tectonic fabric. The epigenetic Pahtohavare Cu ± Au mineralization sit in brittle-ductile structures that cross cut an earlier foliation and the F2 fold, indicating that the timing of the deposits occurred syn- to post-F2 folding, at least ca. 80 Myr after the Kiirunavaara IOA formation. A 3D model and cross sections of the Pahtohavare-Rakkurijärvi area and a new structural framework of the district are presented and used to suggest that the shear zones bounding the area are likely reactivated early structures that have played a critical role in ore formation in the Kiruna mining district.

Leslie Logan et al.

Status: open (until 28 Feb 2023)

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Leslie Logan et al.

Leslie Logan et al.


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Short summary
The Pahtohavare Cu ± Au deposits in the Kiruna mining district have a dubious timing of formation and have not been contextualized in the scope of an up-to-date tectonic framework. Structural mapping was carried out to reveal the deposits are hosted in brittle structures that cut a non-cylindrical, SE-plunging anticline constrained to have formed during the late Svecokarelian orogeny. These results show Cu ± Au mineralization formed more than ca. 80 Myr iron oxide-apatite mineralization.