In this work, we present and validate a physically-based model to predict the chemical distribution resulting from LPBF of physically mixed powders of different compositions. We demonstrate that mixing of powders with different compositions can be used to generate a deliberately controlled, mesoscale chemical heterogeneity in LPBF that allows the formation of multiphase microstructures and delivers new microstructural complexity to LPBF. The model describing the chemical distribution in the consolidated build has also been extended to describe remelting effects and exploited for the design of spatially varying microstructures. This provides a path towards generating architectured materials from random mixes of initial powders.