Temperatures estimated for the erupted rocks cover a wide range, with some exceeding . These rocks are of enigmatic origin, which may be geothermal or magmatic, with the presence of lava bombs of magnetite lava and other evidence supporting the magmatic origin theory. Other viewpoints consider the texture and chemical composition of the rocks as evidence that metasomatism of andesitic rocks formed the magnetite lavas. The role of a post-magmatic fluid phase, which was inferred from inclusions in crystals, has also been suggested. Some magnetite was oxidized to hematite,:681 probably under the influence of rainwater as indicated by isotope analysis. Only a minor amount of hematite is primary. Isotope data indicate that the formation of this magnetite magma was accompanied by the segregation of plagioclase. This plagioclase may have generated the rhyodacite lava dome. An iron-phosphate-rich magma generated the magnetite lava flows after release of volatile substances. The magma was probably bordering on forming a two-phase melt containing nelsonite and rhyolite. A favourable tectonic context associated with the compression of the magma chamber and the presence of faults helped with the eruption of the magnetite.:688-689 The magma formation probably occurred in a magma chamber. During the cooling of the magma, the ores formed. This process was probably not directed by water-rich phases, and the segregation occurred at a shallow depth. High phosphorus and volatile content may have lowered the melting point of the magma and facilitated its eruption, as well as overcoming density-based constraints on the eruption of iron-rich magmas; the magma would later have forcefully degassed within the volcano. Suggestions that anatexis of iron-rich sediments generated the iron-rich magmas appear implausible. The ultimate origin of the El Laco iron may be subducted metal-containing sediment.