Description
This study investigated mineral occurrences in the Stewart pegmatite and searched for appropriate minerals in order to determine a U/Pb crystallization age for the pegmatite. Thirtythree minerals were identified by X-ray diffraction (XRD), and an additional three minerals were identified using an energy dispersive X-ray detector (EDAX) on a scanning electron microscope. Six of the minerals identified in this study represent minerals not previously identified from the Stewart pegmatite: polylithionite, foitite, analcime, clinoptilolite, epistilbite, and zircon. Five of these potentially new minerals form structural or solid-solution series with minerals previously identified. An EDAX elemental analysis was able to distinguish between schorl, green elbaite (verdelite), and pink elbaite (rubellite), and also revealed that all the SP tourmalines analyzed were enriched in fluorine. XRD work on tourmalines of varying diaphaneity also reveal replacement of tourmaline by cookeite, muscovite and illite, depending on the original tourmaline composition. Monazite was determined to present the best opportunity for U/Pb dating. The concentration of rare minerals and variations in crystal morphology throughout the Stewart pegmatite agree with previous interpretations that the core of the SP is similar to a giant pocket that lacked sufficient room to allow proper crystal growth. A comprehensive list of minerals and a reliable crystallization age are equally important to understanding the conditions of formation for the SP within the framework of the Peninsular Ranges Batholith (PRB) emplacement. This study aims to expand the known mineralogy of the Stewart Mine, a gem-bearing LCT pegmatite in the Pala Pegmatite District of San Diego County, and to potentially find minerals for U/Pb dating to correlate the geologic history of the Stewart pegmatite with the PRB.
