We present a new quantitative model of mm-scale Fe-Zn banding in sphalerite Mississippi-Valley type ore deposits. The banded sphalerite is typically intergrown with dendritic galena in cm-scale clusters. We show that this pattern may arise due to a combined effect of geochemical reactions, crystal growth, dissolution, and ripening in far-from-equilibrium conditions. The simulated patterns are due to a self-propagating sequence of growth and dissolution events (so called coarsening wave). One of the surprising results is the geologically short time scale of the pattern formation.