I think "massive" has a specific meaning to geophysicists. It means the mineralisation (i.e. the sulphide mineral grains) are interconnected so that it forms a conductor.
This results in different electromagnetic properties than for, for instance, desseminated sulphides (e.g. as in a porphyry copper deposit) which has specific electrical properties enabling a different geophysical technique to be used for exploration.
Cheers, Gung
