Botryoidal arrays of banded-acicular sphalerite are intergrown with dendritic and branching galena at the Pine Point deposit, Northwest Territories. Scanning electron microscope (SEM) and electron-microprobe analyses (EMP) demonstrate that the banding in sphalerite is due to an alternation in Fe and Zn content. A time-series analysis constructed from the measurement of band widths in a doubly polished thin section is consistent with the hypothesis that the bands are self-organized as a result of the operation of a nonlinear chemical oscillator. The branching crystals of galena are shown to be another manifestation of far-from-equilibrium crystallization. Accordingly, a qualitative model is proposed that demonstrates how the interplay of reaction and diffusion kinetics can lead to the banding and branching. Models wherein the banding in sphalerite in Mississippi-Valley-type (MVT) deposits is solely considered to be an artifact of bulk chemical changes in the fluid within the system need to be re-examined.