Most massive sulfide ore deposits have other portions that are not massive, including stringer or feeder zones beneath the massive parts that mostly consist of crosscutting veins and veinlets of sulfides in a matrix of pervasively altered host rock and gangue.
The term "massive sulfide" is mainly applied to the following classes of ore deposits: The main sulfide minerals occurring in both classes of massive sulfide ores are pyrite and/or pyrrhotite and variable amounts of sphalerite, galena, and chalcopyrite.
Subsequently, the term was also widely used since the 1970s for sediment-hosted ore deposits when it was realized that sediment-hosted massive sulfide (SHMS) Zn-Pb deposits could be formed from ascending and eventually venting brines that are geochemically similar to those that form MVT deposits.
One of the original definitions (1976) stated that the "term massive refers to mineralization composed of greater than 60% sulfides".
The stratiform portion may comprise up to 100% of the total sulfide present, but many deposits have a substantial component of discordant vein-type sulfide mineralization, the stringer zone, mainly in the footwall strata.