The deposit consists of a north-south zone of large and small lenses of massive sulfide that grades northward into coarse disseminated sulfide ('impregnation ore'). Ore minerals are pyrite, chalcopyrite, and sphalerite. The country rock is greenstone, commonly amygdular, ranging in composition from spilitic metabasalt to keratophyre. The greenstone may be massive or schistose, but is schistose adjacent to ore. The ore lenses are grossly conformable, cross-cutting in detail. Analysis of 292 samples of wall rock and impregnation ore suggests that the ore-forming process led to strong leaching of Na and Ca, and some leaching of Si, whereas Mg and possibly K were added. Regional mapping of the distribution of spilitic rocks might help in selecting areas for detailed prospecting, and aureoles enriched in Na may surround ore deposits to provide more specific targets.