adj. Formed underground, (often by ascending solutions).
the GNU version of the Collaborative International Dictionary of English
adj. Formed or crystallized at depths beneath the earth's surface; -- said of granite, gneiss, and other rocks, whose crystallization is believed of have taken place beneath a great thickness of overlying rocks. Opposed to epigene.
The Century Dictionary and Cyclopedia
Produced or formed under or below (the earth's surface); netherformed; specifically, in geology, said of rocks which have assumed their present form and structure beneath the surface; Plutonic: a term applied more especially to the granitic rocks: opposed to epigene.
Word Usage
"The underlying sulfide portion of the deposit, known as the hypogene project, is currently in the commissioning phase."