Hydrothermal metasomatism and solid-phase transfer in petrogenesis of listvenite: the Meso-Tethyan ophiolite, central Tibet, China

Chen, Ji; Zhang, Kai-Jun; Yan, Lilong

doi:10.1007/s00410-022-01988-5

Cited by 5 publications

(1 citation statement)

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“…Furthermore, the chemical composition of surface water around Dujiali Lake evolved from the rock-weathering-type waters of T1 (Ca-Mg-HCO 3 water type) to more concentrated sodic waters of T2 (Na-SO 4 -Cl water type) due to evaporation [54,61]. Therefore, the high-temperature circulating groundwater in Kamado may have had the ability to take much magnesium from ultrabasic or/and magnesium-rich carbonate rocks into the surface lakes [62]. In contrast, the exceedingly low REE contents of banded ores and massive ores may crystallize at lower temperatures [63,64], and aqueous solution conditions for plateau lakes with alkalinity (pH > 7) [65] support the obvious assumption that Mg 2+ is derived from ultramafics, which are poor in REEs [27,66,67].…”

Section: Magnesium Sources Of the Kamado Magnesite Depositmentioning

confidence: 99%

Genesis of the Large-Scale Kamado Magnesite Deposit on the Tibetan Plateau

Yu,

Hu,

Chen

et al. 2023

Minerals

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Lacustrine strata-bound magnesite deposits associated with Alpine-type ultramafic rocks are hydrothermal in origin. The magnesite ores of the Kamado deposit are unconformably underlain by mid-Jurassic marine carbonate and ultramafic rocks of the Bangong-Nujiang ophiolite suite and are in fault contact with hanging wall rocks composed of siliceous sinter. Three types of cryptocrystalline magnesite ores can be identified in Kamado: (1) strata-bound massive magnesites, representing the main ore type in the upper part; (2) banded ores in the lower part; and (3) some vein and stockwork ore in the ultramafic wall rocks. Integrated scanning electron microscopy, C–O isotope analysis, and geochemical analyses were carried out on the Kamado deposit. The results indicate that: (1) the orebody is composed of magnesite, with accessory minerals of aragonite, opal, and chromite; (2) the siliceous sinter and relatively high B (32.0–68.1 ppm) and Li (14.7–23.4 ppm) contents of the magnesite ores reflect long-term spring activity in Kamado; (3) the light carbon (δ13CV-PDB: −4.7 ± 0.3‰ to −4.1 ± 0.6‰) and oxygen isotopic compositions (δ18OV-SMOW: +12.3 ± 0.3 to +16.3 ± 0.1‰) of the stockwork ores in the foot wall rocks indicated that the carbon in fractures in the ultramafic rocks is from a mixture of marine carbonate and oxidized organic-rich sedimentary rocks, reflecting a typical “Kraubath-type” magnesite deposit; and (4) the relatively heavy carbon isotopic (δ13CV-PDB: +8.7 ± 0.4‰ to +8.8 ± 0.3‰) composition of the banded magnesite ores in the lower segment may have formed from heavy CO2 generated by anaerobic fermentation in the lakebed. Additionally, the carbon isotopic (δ13CV-PDB: +7.3 ± 0.3‰ to +7.7 ± 0.7‰) composition of the massive magnesite ores in the upper segment indicates a decline in the participation of anaerobic fermentation. As this economically valuable deposit is of the strata-bound massive ore type, Kamado can be classified as a lacustrine hydrothermal-sedimentary magnesite deposit, formed by continuous spring activities under salt lakes on the Tibetan Plateau, with the Mg mainly being contributed by nearby ultramafic rocks and the carbon mainly being sourced from atmosphere-lake water exchange, with minor amounts from marine carbonate strata.

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