Abstract

Field data and chemical analyses do not support the intrusive-magmatic theory for the formation of the iron ores of the Kiruna Field. The following observations provide convincing arguments against the theory:(1) Abundant fragments and balls of Kiruna-Luossavaara ore are found in the hanging wall of these deposits. It is highly unlikely that these fragments were derived from older ores, because iron ores of the Kiruna type have not been found in rocks which are older than the Kiruna Keratophyres (previously called porphyries).(2) In places, the Per Geijer Ores show a continuous gradation upward into quartz-banded ores.(3) At Luossavaara, a conglomerate unit containing abundant ore fragments identical to the main ore is found in the hanging wall.(4) The so-called ore breccia at Luossavaara---which is not a breccia in the usual sense but rather a framework of ore veins---differs chemically and texturally from the main ore.(5) Geochemical studies do not support the intrusive-magmatic theory.(6) The form of the orebodies suggests that they represent sedimentary units.(7) The composition of the rocks above and below the ores indicates that the ores were deposited in a volcanic-marine environment.The sedimentary nature of the Kiruna iron ores must be stressed in their classification. The volcanic environment also suggests an important role for exhalative processes in the formation of the ores. Based on the present study, it is proposed that the ores be renamed Kiruna-type exhalative-sedimentary apatite iron ores.

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