MVT deposits are found throughout the world and get their name from deposits that occur in the Mississippi Valley region of the United States. The deposits are characterized by ore mineral replacement of the carbonate host rock; they are often confined to a single stratigraphic layer and extend over hundreds of square kilometres.
MVT orebodies range from 0.5 million tonnes of contained ore to 20 million tonnes and have a grade range of between 4% combined lead and zinc to over 14% combined lead and zinc. They tend to be compact, fairly uniform plug-like or pipe-like replacements of their host carbonate sequences and, as such, can be extremely profitable mines.
MVT deposits were a major source of zinc in the United States from the 19th century through the mid-20th century, where such ores were first recognised. These include the Southeast Missouri Lead District of south-eastern Missouri and deposits in north-east Iowa, south-west Wisconsin and north-west Illinois.
Irish-type carbonate lead-zinc ores such as the Lisheen Mine in central Ireland are formed in similar ways.
Tara, at Navan, now owned by Boliden – which has been producing for 35 years – was for a significant period the largest zine mine in the world, and is now the 6th largest.