A mineral systems-scale investigation into the Kiruna mining district and implications for the timing of ore forming processes within a regional tectonic framework

• The formation of iron oxide apatite (IOA) and iron oxide-copper-gold (IOCG) deposits and their relation to each other is currently strongly debated. Recent characterization of the polyphase Svecokarelian orogeny in the northern Norrbotten ore province provides a tectonic framework that can be used to assess the timing of IOA and IOCG genetic processes from a broader mineral systems perspective. This study combined whole rock lithogeochemistry, whole rock Sr and Nd isotopes, U-Pb zircon geochronology, and structural data to gain insight into the Kiruna mining district mineral system. Results show that the igneous intrusions range from mafic to felsic in composition and developed in an active continental margin with both volcanic arc and within-plate affinities. The intrusions have ages ranging from 1891 ± 6 Ma to 1876 ± 11 Ma. One magnetite-ilmenite gabbro gives a concordia age of 1881 ± 8 Ma. These ages indicate a thermal drive for the mineral system can be recognized occurring during an early-orogenic deformation phase (D0-D1) but remains enigmatic for a late-orogenic phase (D2). 87Sr/86Sri and εNdi data from ore-related alteration (Na-alteration and late K-Fe overprint) at Pahtohavare Cu ± Au and Rakkurijärvi IOCG deposits as well as district igneous, greenstone, and Archean rocks indicate that the deposits have distinct Sr-mixing trends and that both sourced Sr and Nd from a wide variety of protoliths. Alteration results show a prominent Na-metasomatism with certain areas showing a K-overprint. New structural analysis of the Pahtohavare area indicates the main ore-related generation of quartz-carbonate-sulfide veins cross cut foliation and were introduced during F2 folding in the late Svecokarelian (D2), suggesting that a late Cu-Au mineralization/remobilization occurred in the Kiruna mining district ca. 80 m.y. after the emplacement of the Kiirunavaara IOA deposit. In brief, our data show that IOA and IOCG systems can be of different ages and sources within the same district.

Ämnesord

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

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

Nyckelord

Kiruna

U-Pb zircon geochronology

Rb-Sr isotopes

Sm-Nd isotopes

IOA

IOCG

Ore Geology

Malmgeologi

Publikations- och innehållstyp

vet (ämneskategori)

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