Exploration for beryllium at the Helen Beryl, Elkhorn, and Tin Mountain pegmatites, Custer County, South Dakota

Abstract

Introduction ______________________________________ _ Selection of deposits for study ___________________ _ Field and laboratory work ______________________ _ Acknowledgments ______________________________ _ Uses and production of beryllium ____________________ _ Exploration program _______________________________ _ Methods and costs _____________________________ _ ResuUs _______________________________________ _ Methods of estimating beryl content _________________ _ Tonnage of beryl-bearing units __________________ _ Grade ________________________________________ _ Sampling _________________________________ _ Spectrographic analyses ____________________ _ Grain measurements _______________________ _ Determinations of index of refraction _________ _ Comparison of methods used in determining grade ___________________________________ _ Helen Beryl pegmatite _____________________________ _ Mine workings ________________________________ _ Production ____________________________________ _ Geology ______________________________________ _ Metamorphic rocks ________________________ _ Quartz and quartz-feldspar veins ____________ _ Pegmatite ________________________________ _ Albite-quartz-muscovite pegmatite (wall zone) _______________________________ _ Granitic albite-quartz-muscovite pegmatite_ Gneissoid albite-biotite-quartz pegmatite __ _ Perthite-quartz-albite pegmatite (fracturefilling units in wall zone) ______________ _ Perthite-quartz-muscovite-biotite pegmatite (first intermediate zone) ______________ _ Perthite-quartz-muscovite pegmatite (second intermediate zone) _______________ _ Perthite-spodumene-quartz pegmatite (third intermediate zone) ___________________ _ Quartz-spodumene-perthite-albite pegmatite (core) ___________________________ _ Diamond-drilling ______________________________ _ Mineral deposits _______________________________ _

Role of Li and B bearing fluids in crystallization and alteration of granitic pegmatites, San Diego, California||Role of Li and B bearing fluids in crystallization and alteration of granitic pegmatites, San Diego, California

“…High water content in silicate melts delays nucleation and depresses the glass transition temperature hundreds of degrees, which allows significant degrees of undercooling, as shown by microthermometry studies, melt inclusion analyses, both major element and oxygen isotope partitioning among feldspars, and lack of tartan twinning in potassic feldspars (Staatz et al, 1963, Nabelek et al, 1992, Morgan and London, 1999, Webber et al, 1999, Thomas et al, 2000, and Thomas and Davidson, 2012. Thomas and Davidson (2012) suggest, based on melt inclusion analyses, that pegmatite melts can contain 10 to 50 wt.…”