Stable isotope, chemical, and mineral compositions of the Middle Proterozoic Lijiaying Mn deposit, Shaanxi Province, China

Ore Geology Reviews
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Abstract

The Lijiaying Mn deposit, located about 250 km southwest of Xian, is a high-quality ore characterized by low P and Fe contents and a mean Mn content of about 23%. The ore deposit occurs in shallow-water marine sedimentary rocks of probable Middle Proterozoic age. Carbonate minerals in the ore deposit include kutnahorite, calcite, Mn calcite, and Mg calcite. Carbon (−0.4 to −4.0‰) and oxygen (−3.7 to −12.9‰) isotopes show that, with a few exceptions, those carbonate minerals are not pristine low-temperature marine precipitates. All samples are depleted in rare earth elements (REEs) relative to shale and have negative Eu and positive Ce anomalies on chondrite-normalized plots. The Fe/Mn ratios of representative ore samples range from about 0.034 to <0.008 and P/Mn from 0.0023 to <0.001. Based on mineralogical data, the low ends of those ranges of ratios are probably close to ratios for the pure Mn minerals. Manganese contents have a strong positive correlation with Ce anomaly values and a moderate correlation with total REE contents. Compositional data indicate that kutnahorite is a metamorphic mineral and that most calcites formed as low-temperature marine carbonates that were subsequently metamorphosed. The braunite ore precursor mineral was probably a Mn oxyhydroxide, similar to those that formed on the deep ocean-floor during the Cenozoic. Because the Lijiaying precursor mineral formed in a shallow-water marine environment, the atmospheric oxygen content during the Middle Proterozoic may have been lower than it has been during the Cenozoic.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Stable isotope, chemical, and mineral compositions of the Middle Proterozoic Lijiaying Mn deposit, Shaanxi Province, China
Series title Ore Geology Reviews
DOI 10.1016/S0169-1368(99)00014-1
Volume 15
Issue 1-3
Year Published 1999
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Ore Geology Reviews
First page 55
Last page 69