@article{PAR00029881,
  title = {{N}anoscale characterization of chrysocolla, black chrysocolla, and pseudomalachite from supergene copper deposits of {A}tacama {D}esert in northern {C}hile},
  author = {{K}ahou, {Z}. {S}. and {S}eydoux-{G}uillaume, {A}. {M}. and {Z}anetta, {P}ierre-{M}arie and {D}uch{\^e}ne, {S}. and {B}richau, {S}t{\'e}phanie and {C}ampos, {E}.},
  editor = {},
  language = {{ENG}},
  abstract = {{W}e present the first textural and chemical characterization at nanometer scale of chrysocolla [({C}u2-x{A}lx){H}2-x{S}i2{O}5({OH})4<middle dot>n{H}2{O}], black chrysocolla (a {M}n-rich variety of chrysocolla), and pseudo-malachite [{C}u5({PO}4)2({OH})4] from two distinct supergene copper deposits from {A}tacama {D}esert in northern {C}hile. {T}hese minerals are the most common copper minerals found in the supergene deposits associated with copper porphyries from {A}tacama {D}esert. {H}owever, the lack of nanoscale morphological information prevents a deeper understanding of their formation process. {N}anoscale characterization using transmission electron microscope ({TEM}) imaging allows further characterization of the structural states of chrysocolla, black chrysocolla, and pseudomalachite, offering valuable insights into their genesis. {C}hrysocolla and black chrysocolla are not single crystals but assemblages of {C}u nanoparticles embedded in an {S}i-rich amorphous matrix. {S}canning {TEM} ({STEM}) images reveal that chrysocolla consists of rounded {C}u-rich nanoparticles embedded in an amorphous matrix, while black chrysocolla consists of rounded {C}u-rich nanoparticles with few needle-shaped {M}n-rich particles, all embedded in an amorphous matrix. {T}he richness in nanoparticles defines a layering that mimics the colloform texture observed in optical microscopy. {I}n contrast, pseudomalachite is a massive polycrystalline mineral consisting of a juxtaposition of large nanocrystal grains of similar to 500 nm. {T}he {STEM}-electron energy loss spectrometry ({EELS}) spectra show that copper in chrysocolla and black chrysocolla is in a reduced state. {T}his suggests that chrysocolla and black chrysocolla form under reducing conditions, probably just below the water table. {A}lternatively, it could be that water table oscillation allows for the cyclical precipitation of {C}u0-rich nanoparticles and oxidized copper-rich silicates. {C}onversely, pseudomalachite crystallization requires oxidative conditions. {T}he oxidation state variations, from chrysocolla ({C}u0) to pseudomalachite ({C}u2+), certainly occur during the episodic switch of the water table linked to tectonic events or climatic changes. {T}he findings also have implications for the {U}-{P}b dating of supergene copper deposits, since black chrysocolla and pseudomalachite can incorporate significant {U} contents. {T}he different structural states of the three minerals may explain their different behaviors regarding {U} and {P}b mobility and, therefore, the preservation of the {U}-{P}b chronometric signal.},
  keywords = {{C}hrysocolla ; black chrysocolla ; pseudomalachite ; transmission electron ; microscope ; nanoscale characterization ; {CHILI} ; {ATACAMA} {DESERT}},
  booktitle = {},
  journal = {{A}merican {M}ineralogist},
  volume = {110},
  numero = {8},
  pages = {1329--1339},
  ISSN = {0003-004{X}},
  year = {2025},
  DOI = {10.2138/am-2024-9300},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00029881},
}