The Linchburg mine, in the Magdalena district, is typical of the pyrometasomatic group of deposits, differing only in its lack of a known intrusive rock to which the pyrometasomatic mineralization can be related. The ore deposit consists principally of sphalerite, galena, and sparse chalcopyrite in a gangue of andradite, hedenbergite, and hematite. The ore body has been controlled by a major fault on which some 500 ft. of dip slip has placed Paleozoic limestones in contact with the Precambrian complex of the Magdalena Mountains. Related to the major fault are tension breaks along which the ore fluids ascended to replace favorable beds of the Kelly formation (Mississippian) Distinct zoning of hydrothermal minerals has taken place spatially related to controlling faults. Geometry of the ore body, zoning, and paragenetic data indicate that control of the ore body is not directly related to tectonic shattering of early silicated beds. Deposition of metallic and gangue minerals appear to have been essentially contemporaneous and related to factors other than tectonics. Experimental evidence is cited to show that the hydrothermal deposition could have been closely related to a reaction gradient that may have been only slightly influenced by temperature but was closely related to a variation in pH and changes in the environment of deposition.