Acicular sphalerite enriched in Ag, Sb, and Cu embedded within color-banded sphalerite from the Kokanee Range, British Columbia, Canada

Sphalerite from the Kokanee Range, British Columbia, displays color banding ranging from light to dark brown. Sphalerite forms massive layers with a dark base enriched in Fe and Cu. Layers have sharp boundaries that can be planar or undulating. The base of the sphalerite layers commonly contains articular crystals of sphalerite oriented perpendicular to the layer boundary. Acicular sphalerite is enriched in Sb, Ag and Cu, which substitute for Zn in the structure. The base of the layers is commonly marked by chains of complex inclusions of chalcopyrite, galena, pyrargyrite and freibegite, which mimic color banding. The layer thickness displays a lognormal distribution ascribed to a random process; it is interpreted to be dependent on the amount of hydrothermal fluid introduced within a fracture prior to precipitation of a layer. The acicular sphalerite probably inverted from rapidly precipitated wurtzite formed from a solution enriched in Cu, Fe, Ag and Sb, an inference that is supported by chains of sulfides and sulfosalts at the base of ferroan sphalerite layers. The precipitation of acicular wurtzite would have depleted the solution in Cu, Ag, Sb, the acicular crystals becoming embedded in Zn-rich sphalerite. Under those conditions, the color banding of sphalerite is controlled by local conditions, which prevents its use for correlation (sphalerite stratigraphy) from one vein to the other.