Carbonate Hosted Lead Zinc Ore Deposits - Mineralogy and Alteration

Mineralogy and Alteration

Ore minerals in carbonate replacement deposits are typically lead sulfide, galena, and zinc sulfide sphalerite. Weathered equivalents form anglesite, cerussite, hydrozincite and secondary galena and sphalerite within the supergene zone.

MVT and Irish type deposits are commonly associated with a 'dolomite front' alteration, which manifests as a yellow-cream wash of dolomite (calcium-magnesium carbonate) within calcite-aragonite assemblages of unaltered carbonate formations.

Most ore bodies are quite sulfidic, and most are very low-iron, with pyrite-marcasite contents typically below 30% of the mass of sulfides. This makes MVT lead-zinc deposits particularly easy to treat from a metallurgical view. Some MVT deposits can, however, be very iron-rich and some sulfide replacement and alteration zones are associated with no lead-zinc at all, resulting in massive accumulations of pyrite-marcasite, which are essentially worthless.

There is sometimes an association with quartz veining and colloform silica, however silicate gangue minerals are often rare.