Magnetite bombs at El Laco volcano, Chile

Abstract

The origin of apatite iron ores of the Kiruna type remains controversial, especially the formation of almost pure magnetite that constitutes large parts of major deposits. The best preserved ores of this type occur on the flanks of El Laco, a Plio-Pleistocene volcano in the Chilean Andes. Based on recent studies a group of workers argues that the El Laco deposits were formed by hydrothermal fluids. However, existence of ballistic volcanic bombs composed of radiating porous aggregates of magnetite crystals in some of the orebodies, demonstrates that apatite iron ores can form directly from a melt.