The origins of Kiruna-type magnetite(-apatite) [Mt(-Ap)] deposits are contentious, with existing models ranging from purely hydrothermal to orthomagmatic end members. Here, we evaluate the compositions of fluids that formed the classic yet enigmatic Mt(-Ap) deposit at El Laco, northern Chile. We report evidence that ore-stage minerals crystallized from an Fe-rich (6–17 wt% Fe) sulfate melt. We suggest that a major component of the liquid was derived from assimilation of evaporite-bearing sedimentary rocks during emplacement of andesitic magma at depth. Hence, we argue that assimilation of evaporite-bearing sedimentary strata played a key role in the formation of El Laco and likely Mt(-Ap) deposits elsewhere.
Evidence for iron-rich sulfate melt during magnetite(-apatite) mineralization at El Laco, Chile
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Wyatt M. Bain, Matthew Steele-MacInnis, Fernando Tornos, John M. Hanchar, Emily C. Creaser, Dorota K. Pietruszka; Evidence for iron-rich sulfate melt during magnetite(-apatite) mineralization at El Laco, Chile. Geology 2021; doi: https://doi.org/10.1130/G48861.1
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