Three-dimensional structural modeling and deformation analysis of Archean magnetite quartzite from the Anshan–Benxi area, northeastern China

Abstract

The factors controlling the migration and enrichment of iron in Archean banded iron formations are important for understanding the formation of iron ore resources. Here we present, for the first time, a micro-three-dimensional modeling method that can be applied to hand specimens of iron ores. This method and petrographic observations, electron probe microanalysis, and the structural deformation characteristics of magnetite quartzite are used to assess the mechanisms of iron enrichment in such ores. The Anshan–Benxi area is located in the eastern part of the North China Craton, and is one of the most significant Archean banded iron deposits in the world. Magnetite quartzite is developed on a large scale in this area, which has experienced complex structural deformation, and thus these samples are ideal for our study. As such, we undertook micro-scale, three-dimensional structural modeling of representative hand specimens of the magnetite quartzite. Our methodology involved combined surface and internal modeling. The rock samples were sliced at fixed intervals and detailed scanned images of the slices were obtained, which enabled a three-dimensional model to be constructed of each sample. These three-dimensional models allow the deformational characteristics of the banded iron formation to be quantified on a hand specimen scale. Petrographic analysis showed that the banded magnetite quartzite has experienced brittle deformation, and electron microprobe analysis revealed iron enrichment in the fold axes. Structural deformation, such as folding and ductile shearing, has a controlling effect on iron enrichment, and the microscopic three-dimensional modeling method provides a new approach for studying the deformational characteristics of iron-bearing formations.