Genesis of Mg-phyllosilicate occurrences in the Middle Permian marine successions of South China

Personal adornments in West-Central Africa—the case study of a talc bead from the Kongo Kingdom (Mbanza Kongo, Angola)

“…The correlation between Zr, Hf, and Th and the total REE concentration (Fig. 5) confirms the occurrence of a small detrital contribution, likely below 2% given the similarities of the REE patterns of the type 44 bead and that of seawater (Cai et al 2019).…”

“…The slightly jagged appearance of the medium and heavy REE seen in Fig. 4 can be either the combined effect of the low abundance of these elements and the short dwell times used during the LA-ICP-MS analysis (Baldwin et al 2011) or the result of detrital input, as REE patterns of palustrine, alluvial, and mudflat Mg-phyllosilicates exhibit this feature (Cai et al 2019). Moreover, the average boron value of 5.48 (± 0.79) ppm detected in the type 44 bead (Table 1) is consistent with the boron average concentration in seawater.…”

“…Trace elements and rare earth element (REE) patterns, in particular, have been used to distinguish hydrothermal from non-hydrothermal Mg-phyllosilicates (Cai et al 2019), but also do distinguish and differentiate talc deriving from ultramafic rocks from talc associated with carbonate rocks (Baron et al 2016). Mg-phyllosilicates which precipitate from seawater enriched in silica maintain the signature of the seawater, and therefore, their REE patterns are characterized by an enrichment of heavy REE when compared to light REE, negative Ce-anomalies and positive La-anomalies; while hydrothermal Mg-phyllosilicates present an inverted "U" shaped REE pattern and high-Eu anomalies (Cai et al 2019). On the other hand, talc deriving from ultramafic rocks are enriched in metals such as Cr and Ni, with the latter two occurring in concentrations around 2000 ppm, while talc associated with carbonate rocks has low Cr and Ni values (Baron et al 2016).…”