Macro-to-nanoscale investigation unlocks gold and silver enrichment by lead-bismuth metallic melts in the Switchback epithermal deposit, southern Mexico
Néstor Cano, J. González-Jiménez, Antoni Camprubí, J. Proenza, E. González-Partida
{"title":"Macro-to-nanoscale investigation unlocks gold and silver enrichment by lead-bismuth metallic melts in the Switchback epithermal deposit, southern Mexico","authors":"Néstor Cano, J. González-Jiménez, Antoni Camprubí, J. Proenza, E. González-Partida","doi":"10.2138/am-2024-9388","DOIUrl":null,"url":null,"abstract":"\n Lead-bismuth (Pb-Bi) minerals of the galena (PbS)-matildite (AgBiS2) series and lillianite homologues (Pb3–2xAgxBi2+xS6) are intergrown with electrum (Au-Ag alloy) and chalcopyrite (CuFeS2) in specific bands within a colloform-banded vein at the Switchback epithermal deposit in southern Mexico. A macro-to-nano scale study revealed that these minerals fill small (<200 µm) cavities in the gangue minerals, showing curvilinear boundaries, bleb-like morphologies, and rounded nanoparticles (~100 nm). These observations are consistent with growth in a molten system from a precursor Pb-Bi melt containing Au, Ag, and Cu. Minerals in the galena-matildite series typically display Widmanstätten textures (i.e., octahedral-like or basket-weave matilditess lamellae in the galenass matrix), which have been traditionally linked to the decomposition of a high-temperature solid solution. However, galenass and matilditess show nano-scale sinuous reaction fronts and replacement relicts (“islands”) while maintaining the [011]Galena || [100]Matildite crystallographic orientation relationship. This suggests a topotaxial growth of matilditess mediated by coupled dissolution-reprecipitation reactions between galenass and the metallic melt upon cooling. A similar scenario is proposed for Pb-Bi sulfosalt intergrowths, which replace galena-matildite and electrum and grow topotaxially along (200)Galena. Collectively, these results suggest that Pb-Bi melts can exist in epithermal fluids, acting as precursors for the crystallization of ore minerals and able to sequester precious metals. This model explains abnormally high Au-Ag enrichments observed in some deposits that contain Pb-Bi ores.","PeriodicalId":2,"journal":{"name":"ACS Applied Bio Materials","volume":" 436","pages":""},"PeriodicalIF":4.6000,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Applied Bio Materials","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.2138/am-2024-9388","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATERIALS SCIENCE, BIOMATERIALS","Score":null,"Total":0}
引用次数: 0
Abstract
Lead-bismuth (Pb-Bi) minerals of the galena (PbS)-matildite (AgBiS2) series and lillianite homologues (Pb3–2xAgxBi2+xS6) are intergrown with electrum (Au-Ag alloy) and chalcopyrite (CuFeS2) in specific bands within a colloform-banded vein at the Switchback epithermal deposit in southern Mexico. A macro-to-nano scale study revealed that these minerals fill small (<200 µm) cavities in the gangue minerals, showing curvilinear boundaries, bleb-like morphologies, and rounded nanoparticles (~100 nm). These observations are consistent with growth in a molten system from a precursor Pb-Bi melt containing Au, Ag, and Cu. Minerals in the galena-matildite series typically display Widmanstätten textures (i.e., octahedral-like or basket-weave matilditess lamellae in the galenass matrix), which have been traditionally linked to the decomposition of a high-temperature solid solution. However, galenass and matilditess show nano-scale sinuous reaction fronts and replacement relicts (“islands”) while maintaining the [011]Galena || [100]Matildite crystallographic orientation relationship. This suggests a topotaxial growth of matilditess mediated by coupled dissolution-reprecipitation reactions between galenass and the metallic melt upon cooling. A similar scenario is proposed for Pb-Bi sulfosalt intergrowths, which replace galena-matildite and electrum and grow topotaxially along (200)Galena. Collectively, these results suggest that Pb-Bi melts can exist in epithermal fluids, acting as precursors for the crystallization of ore minerals and able to sequester precious metals. This model explains abnormally high Au-Ag enrichments observed in some deposits that contain Pb-Bi ores.
期刊介绍:
ACS Applied Bio Materials is an interdisciplinary journal publishing original research covering all aspects of biomaterials and biointerfaces including and beyond the traditional biosensing, biomedical and therapeutic applications.
The journal is devoted to reports of new and original experimental and theoretical research of an applied nature that integrates knowledge in the areas of materials, engineering, physics, bioscience, and chemistry into important bio applications. The journal is specifically interested in work that addresses the relationship between structure and function and assesses the stability and degradation of materials under relevant environmental and biological conditions.