• High REE (∼2000 ppm) Dzhurzhivka phosphorites challenge age-based prospectivity. • Terrigenous contamination indicated by low Y/Ho ratio. • MREE enrichment during early diagenesis, LREE depletion during late diagenesis. • Positive Eu anomalies indicate upwelling of hydrothermally-influenced, P-rich waters. • Sediment diagenesis, not seawater composition, led to REE phosphorite endowment. Late Ediacaran–early Cambrian sedimentary phosphorites offer insights to seawater geochemistry and phosphorus cycling during a pivotal evolutionary period, and have also recently attracted attention for their potential Rare Earth Element (REE) enrichment. In the Moldova-Podillya Basin (southwestern Baltica), such deposits remain poorly geochemically characterized. This study focuses on the Dzhurzhivka Beds (Nahoryany Formation, Mohyliv-Podilsky Group), which contain reworked phosphorite clasts in conglomerates. Two varieties, phosphorite clasts and phosphatic matrix, were analyzed using bulk-rock (ICP-MS, XRF) and microanalytical techniques (SEM-EDS, EPMA, LA-ICP-MS) to constrain the minerals hosting phosphorus and REE. The phosphorite conglomerates are markedly REE-enriched, with average concentrations of 2053 ppm (clasts) and 1572 ppm (matrix), with a distinctive, diagenetic MREE-enriched ‘hat-shaped’ pattern. Based on a criticality assessment, these concentrations classify the conglomerates as a promising, secondary source for REE. LA-ICP-MS trace element data for apatite indicate similar MREE-enriched patterns, with average concentration of 5257 ppm. While a significant contribution from continental weathering to the oceans in the late Ediacaran is likely, the primary source of phosphorus was probably upwelling of P-rich, marine deep waters, as suggested by the positive Eu anomalies in the apatite (Eu/Eu* = 1.35–1.61), with P enrichment and subsequent apatite precipitation potentially coupled to organic matter remineralization. Strong correlation between ΣREE and P 2 O 5 confirms fluorapatite as the primary REE host. Geochemical and textural data indicate that phosphorite clasts are phosphate-cemented sandstones with terrigenous components, reworked and embedded within an argillaceous matrix. Low Y/Ho ratios (28–37) reflect terrigenous contamination and minor hydrogenous influence. MREE enrichment is attributed to uptake of clay-derived REE released during early diagenesis, thereby overprinting original seawater and early pore-water REE signature. Subsequent burial, and late diagenetic recrystallization led to LREE depletion. Comparison to other, major Ediacaran phosphorite deposits in China and Brazil highlights the Dzhurzhivka Beds phosphorite conglomerates as a distinct end-member of the Ediacaran phosphogenic event.
Francovschi et al. (Wed,) studied this question.