See more from this Division: General Discipline Sessions
See more from this Session: Economic Geology
Abstract:
Albite plagioclase (An2-An5) is the dominant matrix mineral, with quartz and K-feldspar next most abundant.
Albite plagioclase being the dominant matrix mineral, plus the fine-grained nature of the ores, makes magnetite microsyenite the most common petrologic name for the ore.
Magnetite shows porphyritic textures and some phenocrysts are zoned.
Most of the magnetite and matrix minerals have typical igneous textures.
Some of the magnetite ores are finely layered which is interpreted to be of rhythmic gravitational origin.
Some of the plagioclase has an intercumulus poikilitic texture, containing included magnetite.
Calcite is a common matrix mineral and where it is dominant in small segregations within the magnetite microsyenites, the rock is considered to be a magnetite carbonatite. Where calcite is an important but not dominant matrix constituent, the rock is considered to have carbonatite affinities. Calcite is also a common constituent of sharply-bounded, late cross-cutting veins.
Hematite is present within the deposit, usually as minor late-stage alteration of magnetite or as specular hematite within late-stage hydrothermal veins or breccia fill. However, a minor part of the ore is composed dominantly of hematite, with textures indicating that it is primary igneous hematite.
Brecciation is also an important ore feature, with fragments both of host rock volcanics, and pieces of the magnetite ore itself. It is suggested that most of the breccias are intrusion-related autobreccias.
See more from this Division: General Discipline Sessions
See more from this Session: Economic Geology