@article{fdi:010044075, title = {{G}em corundum deposits of {M}adagascar : a review}, author = {{R}akotondrazafy, {A}. {F}. {M}. and {G}iuliani, {G}aston and {O}hnenstetter, {D}. and {F}allick, {A}. {E}. and {R}akotosamizanany, {S}. and {A}ndriamamonjy, {A}. and {R}alantoarison, {T}. and {R}azanatseheno, {M}. and {O}ffant, {Y}. and {G}arnier, {V}irginie and {M}aluski, {H}. and {D}unaigre, {C}. and {S}chwarz, {D}. and {R}atrimo, {V}.}, editor = {}, language = {{ENG}}, abstract = {{M}adagascar is one of the most important gem-producing countries in the world, including ruby and sapphires. {G}em corundum deposits formed at different stages in the geological evolution of the island and in contrasting environments. {F}our main settings are identified: ({I}) {G}em corundum formed in the {P}recambrian basement within the {N}eoproterozoic terranes of southern {M}adagascar. and in the volcano-sedimentary series of {B}eforona, north of {A}ntananarivo. {I}n the {S}outh, high-temperature (700 to 800 degrees {C}) and low-pressure (4 to 5 kbar) granulites contain deposits formed during the {P}an-{A}frican orogenesis between 565 and 490 {M}a. {T}hey accompany mafic and ultramafic complexes (ruby deposits of the {V}ohibory group), skarns at the contact between {A}nosyan granites and the {P}roterozoic {T}ranomaro group (sapphire deposits of the {T}ranomaro-{A}ndranondambo district), and shear-zone corridors cross-cutting feldspathic gneisses, cordieritites and clinopyroxenites in the {T}ranomaro, {V}ohimena and {A}ndroyan metamorphic series (biotite schist deposits of {S}ahambano and {Z}azafotsy, cordieritites of lankaroka and {A}mbatomena). {T}he circulation of fluids, especially along discontinuities, allowed in-situ alkaline metasomatism, forming corundum host rocks related to desilicified granites, biotitites, "sakenites" and "corundumites". (2) {G}em corundum also occurs in the {T}riassic detrital formations of the {I}salo group, as giant palaeoplacers in the {I}lakaka-{S}akaraha area. {H}ere, sapphires and rubies may come from the metamorphic granulitic terranes of southern {M}adagascar. (3) {G}em {C}orundum deposits occur within the {N}eogene-{Q}uaternary alkali basalts from {A}nkaratra ({A}ntsirabe-{A}ntanifotsy area) and in the {A}mbohitra {P}rovince ({N}osy {B}e, {A}mbato and {A}mbondromifehy districts). {P}rimary deposits are rare, except at {S}oamiakatra where ruby in gabbroic and clinopyroxenite xenoliths within alkali-basalts probably derive from mantle garnet peridotites. {T}he blue-green-yellow sapphires typical of basaltic fields are always recovered in palaeoplacer (in karst formed {U}pon {J}urassic limestones from the {M}ontagne d'{A}mbre, {A}ntsiranana {P}rovince) and alluvial and soil placers ({A}nkaratra volcanic massif). (4) {D}eposits {O}ccur within {Q}uaternary eluvial, colluvial and alluvial concentrations, such as high-quality rubies from the {A}ndilamena and {V}atomandry deposits.}, keywords = {{M}adagascar ; {C}orundum deposits ; {M}agmatic ; {M}etamorphic ; {A}lkaline metasomatism ; {P}lacers ; {S}apphire ; {R}uby}, booktitle = {}, journal = {{O}re {G}eology {R}eviews}, volume = {34}, numero = {1-2 {S}pecial {I}ssue}, pages = {134--154}, ISSN = {0169-1368}, year = {2008}, DOI = {10.1016/j.oregeorev.2007.05.001}, URL = {https://www.documentation.ird.fr/hor/fdi:010044075}, }