PETROGENETIC EXAMINATION OF LCT TYPE PEGMATITES, AUBURN, ME

Pegmatites are intrusive igneous rocks that contain interlocking crystals that are two centimeters or larger that form in the final stages of solidification of a magma chamber. Therefore, the geochemistry of the minerals and contained fluid inclusions offer valuable data for the formational environment in which the pegmatite crystallized. Pegmatites are important for their economic value as industrial and gem resources. The first type of pegmatites is the lithium-cesium-tantalum (LCT) type which corresponds to the Mount Apatite (Maine Feldspar Aggregates) and Havey (also known as Berry) quarries, and many other pegmatites in Maine. The second type of pegmatites is the niobium-yttrium-fluorine (NYF) type, which is commonly found in New Hampshire and Ontario, Canada. Samples from this study will be compared to previously obtained data regarding NYF type pegmatites. The focus of this study is to investigate the petrogenesis of the pegmatites in the Mount Apatite and Havey quarries located in Auburn, Maine. The Mount Apatite quarry was originally mined for feldspars. During exploration, the gem minerals apatite, beryl, garnet, quartz, and green and pink tourmaline were discovered as well. The Havey quarry lies in close proximity to Mount Apatite approximately 1 mile to the south and is also part of the Auburn District. This quarry was also originally a feldspar quarry, and is most famous for being the “type-locality” of watermelon tourmaline. Fluid inclusions were examined to address the question of how does the crystallizing fluid change over time and space. As such, primary fluid inclusions were examined petrographically and then subjected to thermometric experiments using a freezing-heating Fluid Inc. stage at Stockton College. The overall composition of the fluid inclusions were determined by laser ablation- inductively coupled plasma mass spectrometry at Virginia Tech. Finally, the compositions of apatite crystals were examined by electron probe microanalysis at the American Museum of Natural History to also monitor small-scale changes during crystallization.