Mica geochemistry, and paired in situ [superscript87]Rb/[superscript87]Sr and in situ [superscript40]Ar/[superscript39]Ar geochronology of the Brazil Lake Li-Cs-Ta pegmatite, Nova Scotia, Canada

Abstract

<p><span>The timing of critical mineral deposit formation is challenging to determine, particularly in areas with a complex tectono-thermal history. We apply <em>in situ</em> ⁸⁷Rb/⁸⁷Sr geochronology to investigate the emplacement timing of the Brazil Lake pegmatite Lithium-Cesium-Tantalum deposit, Nova Scotia, Canada. The novel <em>in situ</em> method for ⁸⁷Rb/⁸⁷Sr geochronology is compared with the more established ⁴⁰Ar/³⁹Ar method. Six mica types were identified in and around the pegmatite. Geochronology of the pegmatite is dictated by the initial mineralization age, determined from the oldest ⁸⁷Rb/⁸⁷Sr date of 390.9&plusmn;1 Ma, and the maximum resetting/re-equilibration age ca. 330-320 Ma. Quartz-hosted fluid inclusions indicate post-solidus temperatures were sufficient to reset ⁴⁰Ar/³⁹Ar, but not ⁸⁷Rb/⁸⁷Sr systematics. Re-equilibration was driven by a combined thermal-fluid event recognized in the BLP and southern Nova Scotia.</span></p>