Abstract
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.
Highlights
The origins of Kiruna-type magnetite(-apatite) [Mt(-Ap)] deposits are contentious, with existing models ranging from purely hydrothermal to orthomagmatic end members
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
Summary
The origins of Kiruna-type magnetite(-apatite) [Mt(-Ap)] deposits are contentious, with existing models ranging from purely hydrothermal to orthomagmatic end members. We characterize the ore-forming fluids at El Laco by detailed analyses of inclusions hosted in ore-stage diopside-magnetite-anhydrite veins from the Pasos Blancos orebody (Fig. 1; Table S1 in the Supplemental Material1). We focus on assemblages of primary inclusions, and our results show that an Fe-rich sulfate melt was present during magnetite deposition.
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