Fluid inclusion studies of rare element pegmatites, South Platte District, Colorado.

摘要

Over fifty granite-hosted pegmatites occur in the South Platte district, located in the northern portion of the 1.01 Ga Pikes Peak batholith in the Rocky Mountain Front Range of central Colorado. Many of these pegmatites are concentrically zoned and enriched in fluorite, REE, Y and Nb, relative to the host granite, and may be classified as NYF pegmatites. Rare-element mineralization principally occurs in a core-margin zone as vein and replacement assemblages comprising albite, fluorite, hematite, muscovite and a variety of rare-element minerals, including samarskite, allanite, monazite, bastnaesite and gadolinite. Laser-excited emission (fluorescence) spectra indicate early, massive, core-margin fluorite (probably magmatic) in many instances contains higher concentration of REE than later hydrothermal white, clear and purple fluorite which replace it. Fluid inclusion studies of both magmatic and hydrothermal phases reveal that four compositionally distinct hydrothermal fluid types have permeated the pegmatites. Data from primary inclusions within hydrothermal fluorite indicate that the rare-element mineralization was formed from low salinity (${u3c}10$ equiv. wt. % NaCl + CaCl$sb2$), orthomagmatic fluids at temperatures of at least 340 to 500$spcirc$C. The other fluid types occur exclusively in secondary inclusions, and post-dated the early, low-salinity fluid. (Abstract shortened by UMI.) Source: Masters Abstracts International, Volume: 37-01, page: 0211. Adviser: Iain Samson. Thesis (M.Sc.)--University of Windsor (Canada), 1997.