The Peg Claims spodumene pegmatites, Maine

Abstract

The Peg Claims pegmatites are located SW. of Rockland in the towns of Warren and Cushing, Knox County, Maine. These pegmatites are representative of a group of zoned, granitic, Li-bearing pegmatites in which spodumene is present nearly from wall to wall. The pegmatites are discordant, steeply dipping, tabular bodies in the Penobscot quartz-mica schist near the Waldoboro granite. A narrow quartz- tourmaline-muscovite-apatite aureole is commonly developed around each of the pegmatites and around inclusions of country rock in the pegmatites. The pegmatites are zoned, and each may be subdivided into: 1) a narrow quartz-muscovite border zone; 2) a narrow albite-quartz-muscovite wall zone; and 3) an albite-quartz-spodumene-perthite core that constitutes most of the pegmatite. Cross-cutting, fine-grained, quartz-albite-spodumene-muscovite lenses are found within pegmatite cores. The bulk mineralogy and variations in the mineralogy from zone to zone of the largest body (Dike 1) were determined by megascopic mineral point-counts. There is a decrease of albite, quartz, and muscovite and an increase of spodumene and perthite from the border and wall zones into the core. The alkali contents of Dike 1 and of each of its zones were determined by flame photometer and X-ray fluorescence analyses. The amount of Na 2 O decreases and the amounts of K 2 O, Li 2 O, Rb 2 O, and Cs 2 O increase from the border and wall zones into the core. Estimated bulk compositions of Dike 1 and of each of its zones were computed. It is concluded that the distribution, structural features, bulk chemistry, and the mineralogical, chemical, and textural zoning of the pegmatites are consistent with development by fractional crystallization of a pegmatitic fluid in a restricted system.