Unique trace element geochemistry of pyrometamorphic apatite-supergroup minerals: a case study of fluorellestadite from burnt coal (Poland) and shale (France) post-mining waste heaps, with emphasis on boron, germanium, aluminium and titanium

Abstract

Apatite-type structure is known for its flexibility towards accommodating numerous ions of different crystallographic affinities. Two samples of fluorellestadite from two pyrometamorphic rocks (slags) from burned waste heaps (BWH) from France (LdS) and Poland (RDT) were studied in terms of their trace element composition using Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Boron shows an evident, persistent enrichment in both the samples, with average/maximum levels of 497/1040 and 49/106 ppm, respectively. So is true for magnesium (884/16766 and 404/6251 ppm, i.e., respectively) and sodium (512/697 and 249/370 ppm, respectively). Germanium is clearly enriched in the first sample (29/40 ppm) and, to a lesser degree, in the second one (34 ppm on average). The LdS sample is also clearly enriched in Al (888/1238 ppm), K (385/697 ppm), Ti (515/943 ppm), V (172/347 ppm), and Cu (16/1369 ppm).  The RDT sample is also rich in As (105/120 ppm) and Sr (1072/6592 ppm). An interesting feature of both samples concerns their REE pattern: Nd is the dominant element of the group, with the respective Nd/ΣLREE and Nd/(Ce+La) values of 0.43 and 0.90; and 0.37 and 0.66. In order from highest to lower average concentrations, aluminium, magnesium, titanium, boron, potassium, and germanium may be essential substituents in the BWH apatites.