Enrichment and Mineralization Patterns of P–F–Sr, Li, Zr–Ta, and REY in the Early Permian Coal Seams from the Qinshui Basin, Northern China

Coal seams can host numerous critical metals (e.g., lithium
and
rare earth elements), which are of great significance to modern industry.
An Early Permian coal seam from the Qinshui Basin (northern China)
was investigated and is characterized by an unusual enrichment of
P–F–Sr, Li, Zr–Ta, and REY (rare earth elements
and yttrium). Integrated petrological, geochemical, and mineralogical
analyses were used to elucidate the enrichment mechanisms of several
characteristic elements and critical metals in coal. The results show
that these coal samples are significantly enriched in F (560 μg/g
on average, coal basis) and Sr (602 μg/g on average, coal basis).
Apatite is found to be the main carrier of P and Sr. Geochemical indicators
(e.g., Sr/Ba) indicate peat deposition under marine-influenced conditions,
which promoted early diagenetic precipitation of apatite and Sr-phosphates.
The positive correlation between Li and paragonite (r = 0.68), together with strong correlations of Ta with Zr and Hf,
suggests a mixed derivation from felsic volcanic materials. Moreover,
the geological background, mineral assemblages, and discrimination
diagrams, such as Al2O3/TiO2–Nb/Yb
and Al2O3/TiO2–Zr/TiO2, indicate episodic deposition of felsic volcanic ash combined
with detritus derived from weathering of the Yanshan and Qinling Orogens,
which are dominated by granitic and felsic volcanic rocks. Scanning
electron microscope observations further suggest that hydrothermal
activity subsequently redistributed these metals within the coal seam,
as evidenced by the occurrence of vein carbonates (Sr-ankerite) and
diaspore. This multistage history explains the concurrent P–F–Sr,
Li, Zr–Ta, and REY enrichment in coal. This also highlights
the potential of this coal seam as a critical-metal resource and offers
a framework for exploring similar deposits.