Mineralogy of the Stewart Mine LCT Pegmatite, Pala, California
Krishangi Groover
B.S. Candidate
Department of Geological Sciences
San Diego...
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Mineralogy of the Stewart Mine LCT Pegmatite, Pala, California
Krishangi Groover
B.S. Candidate
Department of Geological Sciences
San Diego State University
Advisors Dr. David Kimbrough
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ABSTRACT
Pegmatites of the famous Pala District in the Peninsular Ranges batholith are intruded as a subparallel swarm that dips gently to the west. The Stewart pegmatite mine is the thickest dike in the swarm ranging between 25 to 60 meters thick. The purpose of this study was to investigate mineral occurrences in the Stewart pegmatite and hopefully find zircon in order to determine a U-Pb crystallization age for the pegmatite.
Thirty-four 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. Four of the minerals identified in this study represent minerals not previously identified from the Stewart Mine: polylithionite, analcime, foitite, and epistilbite. The use of XRD to distinguish major structural differences between different colored tourmalines was unsuccessful, though an EDAX elemental analysis revealed that all Stewart Mine tourmalines samples analyzed were enriched in fluorine. XRD work on tourmalines of varying diaphaneity also reveal replacement of tourmaline by cookeite and illite. The search for zircon proved inconclusive.
Samples collected from a small area of the mine dubbed the “Glory Hole” by mine owner Blue Sheppard are of particular interest in terms of mineral assemblages. Minerals from this area range from large blocks of lepidolite to a complex mix of fine- and coarse-grained albite, quartz, schorl, elbaite, lepidolite, beryl, garnet, and Mn-oxides, while much simpler mineral assemblages surround the Glory Hole. The Glory Hole is postulated to represent a large potential pocket that did not have adequate room to crystallize gem quality minerals (cf. Jahns, 1979).
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