BIBLIOS

Document type
Journal articles

Document subtype
Full paper

Title
Occurrence and precipitation mechanism of silver in pyrite from chimney fragments in the Edmond hydrothermal field, Central Indian Ridge

Participants in the publication
Huichao Zhang (Author)
Kean Chen (Author)
Chunhui Tao (Author)
Ágata Alveirinho Dias (Author)
FACULDADE DE CIÊNCIAS DA UNIVERSIDADE DE LISBOA
Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749–016, Lisboa, Portugal
Dep. Geologia
Jin Liang (Author)
Weifang Yang (Author)
Shili Liao (Author)
Fang An (Author)
Bohao Yin (Author)
Chuanqiang Sun (Author)

Summary
The enrichment of precious elements including Au and Ag in submarine hydrothermal sulfide deposits attracts more and more attention. Previous studies indicate that Au and Ag combine distinctly different ligands under the physico-chemical conditions of submarine hydrothermal systems, therefore, the factors controlling their precipitation may be different. In general, silver mineralization has been much less studied than gold mineralization in submarine hydrothermal sulfide deposits. The Ag mineralization process and precipitation mechanism of submarine hydrothermal sulfide deposits formed at Mid-ocean Ridges are still poorly constrained. In this study, we studied the occurrence and precipitation mechanism of Ag in sulfide deposits of Edmond hydrothermal field, located on the intermediate-spreading Central Indian Ridge (CIR). Three ore-forming stages were identified in chimney fragments collected in the Edmond hydrothermal field. The corresponding minerals are (stage I) anhydrite + barite + colloidal/porous pyrite (Py1) + fine-grained sphalerite; (stage II) marcasite; (stage III) euhedral pyrite (Py2) + coarse-grained sphalerite + chalcopyrite + isocubanite. Py1, characterized by colloidal, porous, and micro-sized anhedral morphology, was usually overgrown by marcasite, which is, in turn, surrounded by euhedral-subhedral Py2, usually coexisting with coarsegrained sphalerite, chalcopyrite, and isocubanite. Compared to marcasite and Py2, only Py1 contains abundant native silver nanoparticles. LA-ICP-MS analyses suggest that Py1 contains higher Pb, Cu, Ag, Mn, Tl, Mo, Au, and lower Co as compared to Py2. In-situ LA-ICP-MS and nanoSIMS analyses indicate that Py1 with higher Ag contents (101-586 ppm) has larger variation in sulfur isotopic compositions (0.8 to 6.6%0) than those of Py2 with lower Ag contents (0.22-15.5 ppm; delta 34S values: 2.1 to 4.8%0 for Fe-rich samples and 0 to 2.8%0 for Zn-rich samples). Texture, mineral assemblage, pyrite trace element and sulfur isotopic compositions indicate a progressive decrease on the degree of fluid-seawater mixing as the temperature gradually increases during the growth of the chimneys in Edmond hydrothermal field. Phase diagram analysis indicates that the increase in pH and in particular cooling, due to the mixing of the hot hydrothermal fluid with cold seawater, can significantly decrease the solubility of Ag and be the effective mechanisms of silver precipitation. Our results suggest that mixing of hydrothermal fluid with seawater is the main Ag precipitation mechanism for submarine hydrothermal sulfide deposits formed at Mid-ocean Ridges.


Institution
FACULDADE DE CIÊNCIAS DA UNIVERSIDADE DE LISBOA

Where published
Ore Geology Reviews

Publication Identifiers
ISSN - 0169-1368

Publisher
Elsevier BV



Document Identifiers
DOI - https://doi.org/10.1016/j.oregeorev.2023.105471
URL - http://dx.doi.org/10.1016/j.oregeorev.2023.105471

Keywords
MAR SMS TRACE-ELEMENT EPRECIOUS METALS SULFiDES SILVER