THE EXAMINATION OF HYDROTHERMAL VEIN GROWTH SEQUENCES AND THEIR CHARACTERISTIC DISTRIBUTION OF RARE EARTH ELEMENTS IN CHEMICALLY ZONED FLUORITE AND QUARTZ IN LAKE GEORGE, COLORADO

The area of study is the Lake George Pluton located in the Pikes Peak Batholith in Lake George, Colorado. The Pikes Peak Batholith is 1 billion years old and the Lake George Pluton is slightly younger at 995 ma. The samples collected from the pluton indicate hydrothermal activity intruded its way through a granite which, according to Wobus and Epis, 1978, forms a partial ring dike.

The granite has a hydrothermal vein, consists of k-feldspar, biotite, quartz and black opaques. The samples collected consisted primarily of quartz and fluorite. The veins samples obtained were brecciated along the outer edges of the vein. The crystal growth is anhedral near the brecciated walls of the vein and the crystals become euhredral as they grow toward the center of the vein.

Thin sections were made to study the fluorite and quartz within the sample. The fluorite in the hand samples collected appeared euhedral with green, purple and blue coloration. When the fluorite was cut the coloration of the fluorite changed and turned green to dark grey. The quartz crystals in the hand sample, after the sample was cut, appears to be filling in the space around the fluorite as well as filling in the pore spaces in the brecciated walls. In thin section the fluorite was euhedral and the drusy quartz coated the fluorite cubes. Also present were quartz crystals on top of the drusy quartz. These quartz crystals grew progressively larger towards the center of the vein until they started growing into each other. The fluorite formed first and the quartz came in after the fluorite but what is unclear is whether the drusy quartz and the larger quartz crystals formed during the same episode of growth or in two different episodes of growth.

Further information needs to be obtained to determine what the crystal growth sequence of the minerals is and to find any chemical zoning in the fluorite and quartz minerals. Such information can be obtained using the scanning electron microscope (SEM). Geochemistry will be conducted to find evidence of rare-earth-element inclusions and such information will be gathered on the Lake George Pluton granite. The course of this research is to see if the inclusions were weathered out of the granite or if the fluids were bringing in the inclusions from another source other than the pluton itself.