A CASE STUDY OF THE EVOLUTION OF THE ELBAITE SUBTYPE OF RARE-ELEMENT GRANITIC PEGMATITE

• Main Authors: T. Scott Ercit, Lee A. Groat, Robert A. Gault
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: granitic pegmatite; elbaite subtype; principal components analysis; melt evolution; accessory minerals; O’Grady batholith; Selwyn plutonic suite; Northwest Territories. SOMMAIRE; Northwest Territories; Selwyn
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.542.9999; http://rruff.info/doclib/cm/vol41/CM41_117.pdf

The first confirmed Canadian occurrence of the elbaite subtype of rare-element granitic pegmatite has been encountered within the O’Grady batholith, approximately 100 km NNW of Tungsten, N.W.T. The batholith, part of the Selwyn plutonic suite, is a mesozonal, hornblende-bearing, metaluminous composite intrusion with lesser amounts of pegmatitic granite and felsitic satellite dykes. On the whole, pegmatite bodies show a mildly NYF-type geochemical and mineralogical signature (allanite- and magnetite-bearing), but in the region of the pegmatitic granite, they grade toward a distinct LCT-type signature (elbaite-bearing). The melts parental to the pegmatite bodies were more voluminous, more alkaline, less aluminous and less reduced than is the norm for melts parental to LCT-type pegmatite. Differentiation of these melts sequentially produced hornblende granite, pegmatitic leucogranite and pegmatite, as shown by major-, minor- and trace-element geochemistry of K-feldspar, plagioclase, micas, tourmaline, amphibole and a variety of accessory phases. Lithium-mineralized pegmatite is recognized by the presence of multicolored elbaite, by lepidolite, and in the diversity of characteristic accessory phases such as danburite, hambergite, stibiocolumbite, pollucite, a nanpingite-like mineral, and bismutite. The various stages of the evolution of the batholith can be well documented in similar variations in mineral chemistry, and result in one of the few well-characterized case studies of the