Scheelite [CaWO4] is a common accessory mineral in various kinds of rocks and ore deposits. Rare earth elements (REE) geochemistry of ore minerals may give information about the source of the ore-bearing fluid, and about the physico-chemical conditions of ore transport and/or precipitation. Luminescence spectroscopy is able to detect several of the REE3+ ions substituting for Ca2+ in the scheelite lattice; however, difficulties in the interpretation of the luminescence spectra in terms of quantifying the REE prohibited the extensive use of luminescence as an analytical method for REE in scheelite. This paper describes a new luminescence method, named thermal X-ray excited luminescence spectroscopy (XLT), which drastically increases the peak/background ratio in the luminescence spectra of scheelite. This method allows to analyse even small samples (single grains < 0.2 mm), is sensitive only to REE3+ ions replacing Ca2+ in the scheelite lattice (avoiding contamination e.g., by mineral inclusions), and is well suited for the analysis of large sample sets. Our study concentrates on 70 samples of scheelite from the Alps, but draws on a yet unpublished database of more than 2000 scheelite spectra from 350 occurrences world-wide.This work demonstrates that luminescence spectra are a powerful tool in the discussion of diverse metallogenic problems, even if they are not converted to REE concentrations. The luminescence spectra of scheelite exhibit several characteristic features which are diagnostic to the genetic type of the mineralisation. In particular, it is possible to distinguish schleelites from skarn/calcsilicate rocks, from molybdenite-veins, from stratabound metamorphic deposits, or from hydrothermal deposits. Scheelite from hydrothermal Au-deposits also often display distinctive characteristics. Different case studies illustrate the ability of the XLT method to recognise hydrothermal events at the scale of an ore province. Applied to the study of single grains from heavy mineral concentrates obtained from fluvial sediments, the XLT method enables the genetic type of the lode deposit to be recognised, thus proving to be a promisa prospecting tool.
|Number of pages||24|
|Journal||Schweizerische Mineralogische und Petrographische Mitteilungen|
|Publication status||Published - 1 Dec 1998|
- Luminescence spectroscopy