SEDEX deposits form on the seafoor as metaliferous fluids exit onto the seafloor within fault controlled sedimentary basins. The zinc-lead-silver mineralization is commonly banded as indicated in the following photo. The formation of the deposits on the seafloor commonly provides for strong lateral continuity of mineralization with thinning and thickening dependent on structural and sedimentary facies variation.
The following photo of Howard's Pass ores illustrates fine sedimentary banding of sulphides with later recrystallization and deformation structures. Interestingly and favourable from a metallurgical perspective is that the mineralization at Howard's Pass is typically very low in pyrite (an iron sulphide mineral). The lack of pyrite is very important as it makes the separation of zinc and lead sulphide minerals easier during flotation and results in favourable metallurgy. The other positive feature of the ores, from a metallurgical, geotechnical and environmental perspective, is the abundance of carbonate in the host shale strata.
High grade laminated zinc-lead mineralization - low pyrite content makes for good metallurgy