Skip to Main Content
Skip Nav Destination

Magmatic-hydrothermal processes produced significant metasomatic alteration of country rock, with resultant metal transport and deposition of low-Ti magnetite bodies, during the intrusion of late granitic magmas in the Adirondack Highlands of the Grenville Province. Manifestations of these ore-forming systems occur as sillimanite-bearing quartz-rich rocks within ca. 1040 Ma Lyon Mountain leucogranites in the southwestern Adirondack Highlands. Field and petrographic relationships demonstrate that emplacement of quartz-sillimanite and bull quartz veins into granite was accompanied by leaching of feldspar and other labile minerals from the granite to produce aluminum- and silica-rich residua. These relationships, coupled with fluid inclusion and stable isotope data from quartz in the host granite, in quartz-sillimanite veins, and in massive quartz veins, suggest that crystallization of granite released acidic magmatic fluids that resulted in high-temperature hydrolytic leaching of feldspars. These fluids also transported and redeposited silica and, locally, alumina to form a quartz-rich sillimanite-bearing carapace near the margins of the granite pluton. Later low-temperature hydrothermal processes mobilized silica and altered sillimanite to illite and diaspore. Zircons exhibiting U-Pb ages overlapping those of the host granite are abundant in the leached quartz-rich rock and are interpreted as residual grains incorporated from the granite. The spatial relationship of both high-temperature and low-temperature hydrothermal features relative to the intrusive Lyon Mountain leucogranite strongly suggests that emplacement of granitic magmas drove the hydrothermal system during progressive unroofing and cooling of the Adirondack orogen.

You do not currently have access to this chapter.

Figures & Tables





Citing Books via

Close Modal

or Create an Account

Close Modal
Close Modal