FLUID INCLUSION INVESTIGATION OF THE MIDDLETOWN DISTRICT PEGMATITE

Pegmatites are commonly divided into two main categories depending on their trace element composition. These two groups are lithium-cesium-tantalum (LCT) pegmatites and niobium-yttrium-fluorine (NYF) pegmatites. The Middletown District pegmatite in Connecticut is primarily known as an NYF-type pegmatite. Located within the Middletown District Pegmatite are the White Rocks District and the Tollgate Quarry, both of which have been actively mined since 1825 and 1927, respectively. These two granitic pegmatite quarries are well known for the mining of feldspars and micas. However, there are other accessory minerals found including garnet, apatite, tourmaline, and beryl in the White Rocks Quarry and columbite-tantalite, autunite and torbernite in the Tollgate Quarry. The samples used for this project were collected on Brooks Road south of the White Rocks District and east of the Tollgate quarry in the Middletown District of CT. These pegmatites cut across the Ordovician aged Middletown Gneiss and into the Brimfield Schist. Melts from which granitic pegmatite deposits crystallize from are commonly enriched in fluxing components such as water, phosphorus, fluorine and boron. The goal of this study is to characterize the fluids that form these deposits and to use this data to learn more about the simple type pegmatites and how they compare to NYF pegmatites as well as their geochemical similarities. General petrography of fluid inclusions in various mineral phases was conducted in order to differentiate primary and secondary inclusions. Primary inclusions are the result of fluids entrapped during crystallization while secondary inclusions result commonly from fractures which were subsequently sealed. Fluid inclusion heating and freezing experiments were carried out at a late time in order to clearly relate the fluid inclusions to one another in fluid inclusion assemblages and to characterize the general salinity of the fluid inclusions. The composition of the volatiles in the fluid inclusions was determined using Raman spectroscopy. This data was then compared to similar fluid inclusion studies on NYF pegmaties from Ontario and contrasted with simple and complex LCTpegmatites located in two different quarries in western Maine in order to determine any differences or similarities between LCT and NYF pegmatites.