<p>The Falchani Lithium Project, a volcanogenic sedimentary deposit in the Neogene Macusani Volcanic Field (Puno, Peru), hosts &gt; 5.5 Mt Li₂CO₃ resources and represents a significant potential complementary source for South American lithium production, currently dominated by Andean salar deposits of the Lithium Triangle. The ore comprises volcanogenic tuff and breccia subdivided into the Lithium-rich Tuff and stratigraphically overlying and underlying Upper and Lower Breccia units, respectively. Primary minerals include quartz, feldspars, and trioctahedral Li-F micas (zinnwaldite and lepidolite). Secondary minerals define a vertical mineralogical zonation. The Lithium-rich Tuff is characterized by abundant kaolinite and the preservation of Li-F micas, whereas the Upper and Lower Breccia are dominated by dioctahedral smectites (beidellite–montmorillonite series) with scarce, corroded relict micas. Zeolites locally occur as the predominant secondary phase in brecciated Lithium-rich Tuff samples. Lithium contents peak in the Lithium-rich Tuff (3000–4200 ppm Li), with the bulk hosted by Li-F micas, and only 7% as exchangeable Li. Conversely, the Upper and Lower Breccia units contain &lt; 3000 ppm Li predominantly in interlayer positions of smectites, yielding high exchangeable Li proportions (63–88%). This vertical variation reflects restricted fluid flow through the impermeable Lithium-rich Tuff versus pervasive alkaline hydrothermal fluid circulation through brecciated units. Falchani is unusual in having both magmatic and authigenic lithium-rich phases. These observations support a tentative classification of Falchani as a <i>mixed</i> primary mica–secondary ion-clay volcanogenic sedimentary lithium deposit, a mineralization type not previously documented.</p>

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Mixed primary mica – secondary ion-clay volcanogenic sedimentary lithium deposits in the Neogene Macusani Volcanic Field, Puno, Peru

  • Mariana Segovia-More,
  • Lisard Torró,
  • Cristina Villanova-de-Benavent,
  • Johan Ramirez-Briones,
  • Patrice Baby,
  • Ana Isabel Ruiz,
  • Jaime Cuevas,
  • Jean Vallance,
  • Loïs Monnier,
  • Oscar Laurent,
  • Stefano Salvi,
  • Joaquín A. Proenza,
  • Fernando Nieto

摘要

The Falchani Lithium Project, a volcanogenic sedimentary deposit in the Neogene Macusani Volcanic Field (Puno, Peru), hosts > 5.5 Mt Li₂CO₃ resources and represents a significant potential complementary source for South American lithium production, currently dominated by Andean salar deposits of the Lithium Triangle. The ore comprises volcanogenic tuff and breccia subdivided into the Lithium-rich Tuff and stratigraphically overlying and underlying Upper and Lower Breccia units, respectively. Primary minerals include quartz, feldspars, and trioctahedral Li-F micas (zinnwaldite and lepidolite). Secondary minerals define a vertical mineralogical zonation. The Lithium-rich Tuff is characterized by abundant kaolinite and the preservation of Li-F micas, whereas the Upper and Lower Breccia are dominated by dioctahedral smectites (beidellite–montmorillonite series) with scarce, corroded relict micas. Zeolites locally occur as the predominant secondary phase in brecciated Lithium-rich Tuff samples. Lithium contents peak in the Lithium-rich Tuff (3000–4200 ppm Li), with the bulk hosted by Li-F micas, and only 7% as exchangeable Li. Conversely, the Upper and Lower Breccia units contain < 3000 ppm Li predominantly in interlayer positions of smectites, yielding high exchangeable Li proportions (63–88%). This vertical variation reflects restricted fluid flow through the impermeable Lithium-rich Tuff versus pervasive alkaline hydrothermal fluid circulation through brecciated units. Falchani is unusual in having both magmatic and authigenic lithium-rich phases. These observations support a tentative classification of Falchani as a mixed primary mica–secondary ion-clay volcanogenic sedimentary lithium deposit, a mineralization type not previously documented.