Elsevier

Ore Geology Reviews

Volume 150, November 2022, 105130
Ore Geology Reviews

In-situ trace element and Sr isotope signature of apatite: A new key to unravelling the genesis of polymetallic mineralisation in black shales of the Early Cambrian Niutitang Formation, Southern China

https://doi.org/10.1016/j.oregeorev.2022.105130Get rights and content
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Highlights

  • This study focuses on apatite in the Niutitang formation.

  • Petrological and geochemical in-situ study helps deciphering its genesis.

  • A hydrothermal contribution is evidenced.

  • Element sources are better constrained.

Abstract

The Early Cambrian Mo-Ni-PGE sulphidic black shale in the Niutitang Formation on the margin of the Yangtze Craton (Southern China) is known for its extremely high metal concentrations. It is also very rich in phosphate that formed contemporaneously with the sulphides. Detailed petrological as well as in-situ trace element and Sr isotope analyses of authigenic apatite revealed new information on the metallogenesis of this enigmatic rock unit. In the ore bed, apatite forms nodules or is found in phosphatic (phoslithoclasts) and sulphide clasts. In the latter, the replacement of organic matter and sulphides by apatite microspherules suggests a microbially mediated phosphogenesis. Enrichment in middle rare earth elements emphasizes the role played by Fe-oxyhydroxides and organic matter in element scavenging. Moderately reducing conditions are supported by a lack of Ce and Eu anomalies. The trace element signature of apatite and its initial 87Sr/86Sr (0.7032–0.7190), which is - for a group of analyses - well below the signature of Lower Cambrian seawater, points to some contribution from mafic rock-sourced hydrothermal brines. This effectively explains the exceptional enrichment of Ni and PGE in the sulphides. Seawater remains, however, the preferred source for other elements such as P and Mo.

Keywords

Phosphorite
Ni-Mo-PGE sulphide ore
Rare Earth Elements
Mafic affinity
Hydrothermal brines

Data availability

No data was used for the research described in the article.

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