Pegmatites are major hosts for critical materials and are thus crucial for the green technology transition. Age information and geochemical constraints are fundamental to understand pegmatite genesis and are thus highly valuable for spatial correlation of pegmatite bodies and for exploration.
Pegmatites commonly carry high Rb minerals such as white mica. These minerals are targeted for in-situ Rb/Sr LA-ICP-MS/MS dating. This ICP-MS has a reaction cell built between two mass spectrometers. Reaction gases such as N2O or SF6 can be induced into the cell to chemically separate 87Rb and 87Sr. This avoids the isobaric overlap during mass-spectrometric analysis.
LA-ICP-MS/MS Rb-Sr dating of pegmatitic mica has multiple advantages. For example, high sample throughput: the targeted minerals are main phases and rock chips or single crystals can thus be used for dating. This avoids time-consuming and contamination-prone mineral separation. In addition, pegmatitic mica often has not only high Rb mass fractions, it also has very low to neglectable common Sr. Thus, the 87Rb-87Sr age does not depend on the initial 87Sr/86Sr composition. More specifically, 87Rb-87Sr ages can be calculated without 86Sr – a main difference to the conventional 87Sr/86Sr versus 87Rb/86Sr isochron approach following Nicolaysen. This age calculation strategy will be presented in this contribution using pegmatites from the Gothenburg area (Högsbo) and Mozambique as examples.