@article{DesanoisLuedersNiedermannetal.2018,
  author    = {Desanois, Louis and L{\"u}ders, Volker and Niedermann, Samuel and Trumbull, Robert B.},
  title     = {Formation of epithermal Sn-Ag-(Zn) vein-type mineralization at the Pirquitas deposit, NW Argentina},
  series = {Chemical geology : official journal of the European Association for Geochemistry},
  volume    = {508},
  journal   = {Chemical geology : official journal of the European Association for Geochemistry},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0009-2541},
  doi       = {10.1016/j.chemgeo.2018.04.024},
  pages     = {78 -- 91},
  year      = {2018},
  abstract  = {The Pirquitas Sn-Ag-(Zn) deposit in northwestern Argentina is thought to be an analogue to the Miocene polymetallic epithermal Sn-Ag deposits of the southern Bolivian Tin Belt, but little is known in detail about the origin and evolution of ore-forming fluids at Pirquitas. This paper reports on a microthermometric study of fluid inclusions in quartz, sphalerite, Ag-Sn sulfides, and Ag-rich sulfosalts using transmitted near infrared and visible light, combined with noble gas isotope analyses of fluids released from mineral separates. The study focused on the vein-hosted mineralization, which formed during two major mineralization events, whereby the first event I comprises two stages (I-1 and I-2). All studied minerals exclusively contain aqueous two-phase inclusions, indicating that the ore-forming fluids did not undergo two-phase phase separation (boiling). Salinity of fluid inclusions in I-1 quartz that precipitated along with pyrite and pyrrhotite ranges between 0 and 7.5 wt\% NaCl equiv. and homogenization temperatures (Th) are between 233 and 370 degrees C. Stage I-2 is characterized by abundant Sn-Ag-Pb-Zn-sulfides and a variety of Ag-rich sulfosalts. Fluid inclusions in stage I-2 Ag-Sn sulfides have salinities up to 10.6 wt\% NaCl equiv. and Th between 213 and 274 degrees C. The deposition of stage I-2 ore is likely related to a new pulse of saline magmatic fluids to the hydrothermal system. The mineralization event II deposited the richest Ag ores at Pirquitas. Colloform sphalerite and pyrargyrite deposited during event II contain two-phase aqueous fluid inclusions with homogenization temperatures between 190 and 252 degrees C and salinities between 0.9 and 4.3 wt\% NaCl equiv. Noble gas concentrations and isotopic compositions of ore-hosted fluid inclusions were determined from crushing hand-picked ore minerals from both mineralization events. With one exception, all samples yielded He-3/He-4 ratios between 1.9 and 4.1 Ra, which is within the range of published data from the volcanic arc and somewhat higher than typical values of meteoric water-derived hot-springs in the region. This demonstrates a significant contribution of magmatic fluids to the Pirquitas mineralization although no intrusive rocks are exposed in the mine region. Taking the noble gas evidence for a magmatic fluid source, we interpret the trends of decreasing Th and salinity values in fluid inclusions from events I and II to represent waning of the magmatic-hydrothermal system and/or increased admixing of meteoric water to the magmatic fluids.},
  language  = {en}
}
@article{LunaBookhagenNiedermannetal.2018,
  author    = {Luna, Lisa Victoria and Bookhagen, Bodo and Niedermann, Samuel and Rugel, Georg and Scharf, Andreas and Merchel, Silke},
  title     = {Glacial chronology and production rate cross-calibration of five cosmogenic nuclide and mineral systems from the southern Central Andean Plateau},
  series = {Earth \& planetary science letters},
  volume    = {500},
  journal   = {Earth \& planetary science letters},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0012-821X},
  doi       = {10.1016/j.epsl.2018.07.034},
  pages     = {242 -- 253},
  year      = {2018},
  abstract  = {Glacial deposits on the high-altitude, arid southern Central Andean Plateau (CAP), the Puna in northwestern Argentina, document past changes in climate, but the associated geomorphic features have rarely been directly dated. This study provides direct age control of glacial moraine deposits from the central Puna (24 degrees S) at elevations of 3900-5000 m through surface exposure dating with cosmogenic nuclides. Our results show that the most extensive glaciations occurred before 95 ka and an additional major advance occurred between 46 and 39 ka. The latter period is synchronous with the highest lake levels in the nearby Pozuelos basin and the Minchin (Inca Huasi) wet phase on the Altiplano in the northern CAP. None of the dated moraines produced boulder ages corresponding to the Tauca wet phase (24-15 ka). Additionally, the volcanic lithologies of the deposits allow us to establish production ratios at low latitude and high elevation for five different nuclide and mineral systems: Be-10, Ne-21, and Al-26 from quartz (11 or 12 samples) and He-3 and Ne-21 from pyroxene (10 samples). We present production ratios for all combinations of the measured nuclides and cross-calibrated production rates for 21Ne in pyroxene and quartz for the high, (sub-)tropical Andes. The production rates are based on our Be-10-normalized production ratios and a weighted mean of reference 10Be production rates calibrated in the high, tropical Andes (4.02 +/- 0.12 at g(-1) yr(-1)). These are, Ne-21(qtz): 18.1 +/- 1.2 at g(-1) yr(-1) and Ne-21(px): 36.6 +/- 1.8 at g(-1) yr(-1) (En(88-94)) scaled to sea level and high latitude using the Lal/Stone scheme, with 1 sigma uncertainties. As He-3 and Al-26 have been directly calibrated in the tropical Andes, we recommend using those rates. Finally, we compare exposure ages calculated using all measured cosmogenic nuclides from each sample, including 11 feldspar samples measured for Cl-36, and a suite of previously published production rates. (C) 2018 Published by Elsevier B.V.},
  language  = {en}
}