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… Click to show full abstract
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.
               
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