pneumatolysis

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A process of rock alteration or mineral formation brought about by the action of gases emitted from solidifying magma.

from The Century Dictionary.

• noun The general process of the formation of minerals, and especially ores, along the contacts of intrusive igneous rocks with their walls, and through the agency of vapors or gases emitted by the molten magma.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geology the alteration of rocks and minerals by gases or magmatic fluid within volcanos etc