@article{fdi:010048271,
  title = {{P}roximal and distal styles of pegmatite-related metasomatic emerald mineralization at {I}anapera, southern {M}adagascar},
  author = {{A}ndrianjakavah, {P}. {R}. and {S}alvi, {S}. and {B}{\'e}ziat, {D}. and {R}akotondrazafy, {M}. and {G}iuliani, {G}aston},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he {I}anapera emerald deposit is located in the {N}eoproterozoic {V}ohibory {B}lock of southern {M}adagascar. {T}he local geology consists of intercalated migmatitic gneissic units and calcareous metasedimentary rocks, containing boudinaged metamorphosed mafic/ultramafic lenses, all intruded by pegmatite veins. {T}hese units occur near the hinge of the tightly folded {I}anapera antiform, within a few kilometers of the {A}mpanihy shear zone. {E}merald mineralization is hosted by metasomatic phlogopite veins, and bodies developed within the mafic/ultramafic rocks. {B}ased on field and textural relationships, we distinguish proximal and distal styles of mineralization. {P}roximal mineralization occurs at the contact of pegmatite veins with mafic/ultramafic units; in the distal style, pegmatites are not observed. {T}hree types of emeralds could be distinguished, mainly on the basis of color and mineral zoning. {S}ome of these emeralds have the most {A}l-depleted and {C}r-rich composition ever recorded. {A}nother characteristic feature to the {I}anapera deposit and, to our knowledge, yet unreported, is the association of some emeralds with scapolite in metasomatised mafic rocks. {M}ineral inclusions are common in most emeralds and include phlogopite, carbonates, barite, {K}-feldspar, quartz, pyrite, zircon, monazite, bastnaesite, phenakite, plus {F}e and {C}r oxides. {H}owever, feldspar and rare earth element-bearing minerals occur predominantly in proximal emeralds, which also have a more incompatible trace-element signature than distal emeralds. {W}e propose a model related to syn- to post-tectonic magmatic-hydrothermal activity. {P}egmatitic bodies intruded units of the {I}anapera antiform probably during tectonic relaxation. {E}xsolution of fluids rich in halogens and incompatible elements from the cooling pegmatites caused hydrothermal metasomatism of {C}r-bearing mafic/ultramafic rocks in direct contact with the pegmatites. {L}ocal fracturing favored fluid infiltration, permitting the formation of distal mineralization. {E}merald composition was controlled by the chemistry of the host rock. {T}he presence of carbonate mineral inclusions in the emeralds and the high {F}-activity indicated by elevated {F}-contents in newly formed minerals suggest transport of {B}e as a fluoride-carbonate complex. {I}t seems likely that beryl formation was triggered by precipitation of {F}-rich phlogopite, which removed the complexing ligand from the fluid.},
  keywords = {{E}merald ; {B}eryl ; {P}egmatite ; {P}hlogopitite ; {I}anapera ; {M}adagascar},
  booktitle = {},
  journal = {{M}ineralium {D}eposita},
  volume = {44},
  numero = {7},
  pages = {817--835},
  ISSN = {0026-4598},
  year = {2009},
  DOI = {10.1007/s00126-009-0243-5},
  URL = {https://www.documentation.ird.fr/hor/fdi:010048271},
}