A new and effective method for quartz-feldspar separation for OSL and CRN dating

Abstract

Quartz is a preferred mineral which is widely used for optically stimulated luminescence (OSL) and cosmogenic radionuclide (CRN) dating methods. Any contamination in the sample may mislead and result in erroneous results for both the dating methods (e.g. OSL or CRN). Therefore it is essential to get pure quartz before the measurements of OSL and CRN. Presence of other minerals can introduce unaccounted luminescence signal in the case of OSL, similarly in the case of CRN unaccounted concentration of 10 Be and 26 Al may be introduced. Therefore, in order to get reliable ages from CRN and OSL, extraction of pure quartz from the sediment becomes necessary. Protocols have been developed to extract pure quartz from the sediment, e.g., the separation of quartz from feldspar and other heavy minerals can be achieved by applying 2-step density separation. This is followed by HF leaching which usually removes the feldspar contamination from the quartz (if any left). However, in some cases, this method is not successful, especially in the case of feldspar rich samples or in the samples with intergrowth of feldspar in quartz crystals. This paper reports a method that is effective in separating quartz and feldspar. A small amount of fine grained iron powder was used to make feldspar as magnetic mineral and it is separated from quartz using isodynamic magnetic separator effectively. Efficacy of the method was tested with different analytical instruments such as scanning electron microscope (SEM), OSL/TL reader and inductively coupled plasma mass spectromete (ICP-MS). The analytical tests showed that the proposed method eliminates feldspar by ~95%.