GEOCHEMICAL INVESTIGATION OF ZONED LCT PEGMATITES, BARBERVILLE, RI

The Narragansett Pier Granite (NPG) is a large Permian-age plutonic body that developed 275 Ma in present-day Rhode Island and eastern Connecticut. It is characterized as a pink to pale-gray, medium-grained equigranular granite that is primarily composed of microcline, oligoclase, quartz, and accessory minerals such as monazite, biotite, magnetite, and zircon. The pluton is cut by a series of pegmatites and aplites that are similar in composition to the host granite but vary in crystal size, mineralogy, and mineralogical zonation. One of the best localities that displays different zonation patterns is found at a sequence of roadcuts on a small road off I-95 in Barberville, RI. The pegmatites along this roadcut have intruded the Hope Valley Alaskite Gneiss of the Avalonian terrane. The NPG pegmatites along this road-cut have been classified as LCT type, meaning that they have higher concentrations of lithium, cesium, and tantalum (Li, Cs, and Ta). The intruding pegmatite dikes contain quartz, potassium feldspar, plagioclase, biotite, magnetite, hornblende, and fluorite. The pegmatites along this road cut vary in terms of mineralogy, zonation type (sodic or potassic), and grain size despite being confined to a quarter-mile long stretch of outcrop. Fluid inclusions were examined to address the question of how does the crystallizing fluid change within the relatively small studied area. The changes in mineralogy, mineralogical zonation, and fluid inclusions were determined through mineralogical and fluid inclusion studies at the Richard Stockton College of New Jersey.