GEOCHEMICAL FLUID VARIATIONS OF CLOSE-PROXIMITY PEGMATITES IN OXFORD CO. MAINE

Pegmatites are coarse-grained intrusive bodies that form rapidly and generally represent fluid drainage of larger granitic bodies. Large mineral sizes indicate uniform distribution of material for nucleating crystals to grow as well as potentially liquid-liquid immiscibility (i.e. silicate melt-hydrothermal fluid). Pegmatites are economically important storehouses of gemstones (such as beryl and tourmaline), industrial minerals (such as quartz, muscovite, and feldspar), and REE-bearing phases (such as columbite, tantalite, and pollucite). This project focuses on examining the fluids of rare-earth type granitic pegmatites. Rare-earth pegmatites are typically categorized into NYF-type (Niobium, Yttrium, and Fluorine) and LCT-type (Lithium, Cesium, and Tantalum) pegmatites. The primary goal of this study is to examine geochemical variation within the pegmatite fluids over short distances within different “quality” quarries. Samples were collected from three geographically adjacent pegmatite quarries located in Oxford County, Maine. The quarries include Noyes (Harvard), Waisanen, and Tamminen quarries. These quarries belong to the Oxford pegmatite field, are within a 1 km radius, and are categorized as LCT-type pegmatites. Previous pegmatite work in this area has focused more on the descriptive mineralogy and/or geochemical analysis of specific minerals rather than on overall composition and fluid evolution. Fluid inclusions trap important information regarding geochemistry, and formation conditions. Therefore, fluid inclusions represent the exact fluid composition from which the host crystal formed. This study discusses fluid geochemistry and petrogenesis of fluids trapped in quartz, apatite, and tourmaline crystals collected from these pegmatites. Homogenization experiments were used to determine minimum trapping temperatures, and the fluid salinity/general composition. The major and trace element composition was determined using laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS). The apatite geochemistry was determined using electron probe microanalysis (EPMA).