Origins of the Ediacaran Doushantuo High-Grade Primary Phosphorites at Kaiyang, Guizhou Province, China.

The Ediacaran Doushantuo phosphate deposit in Kaiyang, Guizhou Province, China, contains thick phosphate ores. Most of the ores are reconstituted phosphorite, and there have been few studies of the primary phosphorites, which has led to controversy regarding the origins and nature of mineralization of these phosphate-rich deposits. We identified high-grade primary phosphorites in the Kaiyang area and undertook a stratigraphic, petrological, sedimentological, geochemical, and isotopic study of these rocks. Moving up-section, the Longshui phosphate ore deposit comprises granular, micritic, stromatolitic, honeycomb, and sandy phosphorites. The first four types of phosphorite contain abundant biological structures, such as spherical, lobe-like, and amorphous forms. These are mainly fossils of benthic multicellular red algae, along with other types of algae. These fossils comprise >70% of the phosphorites, indicating that these are protist phosphorites. The ores are massive, unstratified, and contain numerous layered cavity structures, indicating that the ore bed was originally a reef. The phosphorites have P2O5 contents of 38.6-40.2 wt %, with an average of 38.9 wt %. The Al2O3 + TiO2 values are 0.02-0.44 wt %. The δ18O values of the samples vary from 13.76 to 16.57‰, with an average of 14.60‰, and δ13C values range from -15.789 to -8.697‰, with an average of -13.133‰. The samples exhibit rare-earth element patterns that are enriched with middle rare-earth elements and have strongly negative Ce anomalies. The geochemical features show that the reef was deposited in clear and oxidized waters. The discovery of this high-grade protist phosphorite shows that the involvement of algae was key to the formation of the Kaiyang phosphate-rich deposit.

Studies on geochemical characteristics and biomineralization of Cambrian phosphorites, Zhijin, Guizhou Province, China.

Phosphate rocks, an important ore resource in Guizhou Province, China, are mainly hosted within the Sinian Doushantuo Formation and the Cambrian Meishucun Formation. In addition, the phosphate rocks of the Cambrian Meishucun Formation are rich in biological fossils. Although numerous studies investigating the genesis of phosphate deposits have been performed, the relationship between biological activity and the formation of phosphate deposits in the lower Cambrian Meishucun Formation has not been convincingly explained. This study focuses on the biological fossil assemblage, the characteristics of phosphorus, and the relationship between biological and phosphorus enrichment of the lower Cambrian phosphorites. The primary objectives of our study are to analyze the role of organisms in the formation of phosphorites, restore the phosphorus-formation environment of the Cambrian Meishucun Formation, and construct a sedimentary model of the phosphorites in the Meishucun Formation. The results indicate that there is a significant positive correlation between biological activity and the deposition of phosphorites, that is, the higher the degree of biological enrichment and differentiation, the stronger the deposition. The geochemical analysis of several profiles in the Zhijin phosphorite block shows that the phosphorite block was deposited in an oxygen-rich environment and was affected by a high-temperature hydrothermal fluid. Upwelling ocean currents supplied abundant phosphorus and other nutrients, which provided the conditions for small shells and algae to flourish. Biochemical activity was a crucial factor in the deposition of the phosphorite.

Anomalous concentrations and environmental implications of rare earth elements in the rock-soil-moss system in the black shale area.

Nowadays, rare earth elements (REEs) pollution caused by anthropogenic activities has aroused great attention, but the contribution of natural geological sources remains unclear. In this study, parent rocks, corresponding soil, and overlying moss (Pohlia flexuosa Harv. In Hook) were collected to identify the release, transportation, and environmental exposure of REEs in the black shale areas. The results showed that black shales had elevated REEs levels (245 ± 124 mg kg-1) and served as a geogenic source of REEs. The released REEs were temporarily enriched in the acidized soil (327 ± 91.8 mg kg-1, pH 4.87 ± 0.810) and were still highly bioavailable, thereby resulting in REEs accumulated up to a high level in moss P. flexuosa (86.2 ± 64.3 mg kg-1). Hence, the ecological risks of REEs in black shale areas were assuredly enhanced. The shale-normalized results of REEs concentrations in the parent rock - soil - moss system followed a remarkably identical pattern and were characterized by strong enrichment in HREEs (LaN/YbN 0.520 ± 0.274), indicating that geogenic input was responsible for the concentration and composition of REEs in mosses. Moreover, REEs were readily preserved and not easily fractionated in moss P. flexuosa due to its special morphological features, indicating the lithological signatures of REEs in black shales were readily inherited by moss P. flexuosa, and underwent only minor losses. Overall, moss P. flexuosa could be used as a powerful tool to reflect the content and composition of REEs in black shale areas.