Diamonds from the Espinhac Ëo Range Minas Gerais, Brazil) and their redistribution through the geologic record M.L.S.C. Chaves a, * , J. Karfunkel a , A. Hoppe b , D.B. Hoover c a Institute of Geosciences and Natural History Museum, Federal University of Minas Gerais, Belo Horizonte MG 31270-901, Brazil b Hessisches Landesamt fu Èr Bodenforschung, Leberberg 9, Wiesbaden D-65193, Germany c Hoover Associates, Spring®eld, MO 65803, USA Received 31 March 1999; revised 30 June 2000; accepted 31 October 2000 Abstract Diamond-bearing deposits from the Espinhac Ëo Range are associated with three distinct periods in the geologic record. During a Precam- brian magmatic period $1.75 Ga), diamondiferous rocks were introduced into the crust; the location of these rocks remains an enigma. During a second period, diamonds were eroded from the primary rocks and deposited in the Mesoproterozoic Espinhac Ëo basin  ù 1.75± 1.70 Ga), where several generations of reworking and diagenisis are suggested. The third period is the Phanerozoic, during which several more episodes of reworking occurred. The ®rst was during the Eocretaceous uplift of the range, when Precambrian conglomerates were partially eroded and diamonds redeposited in ¯uvial systems. These deposits have little economic signi®cance because of overlying Tertiary laterites. Renewed upheaval at the Neogene formed diamondiferous fanglomeratic deposits as a result of the pronounced relief. Quaternary climate cycling developed colluvial deposits on earlier formed occurrences. Fanglomeratic and colluvial deposits are worked where the adjacent Proterozoic or Cretaceous sources produced widespread diamond-bearing gravels. Finally, recent river systems have reworked all theearliersourcestoproduceeconomicgravelsinsomeplaces.Althoughtheserecentgravelsarelowgrade,theyareamajordiamondsource because of the large reserves. The mineralogical characteristics of these diamonds re¯ect the long history and repeated reworking of the source deposits, and the geologic history of the region points towards an extra-basinal source area, probably to the west within the Sa Äo Francisco Craton. This repeated reworking has resulted in a natural selection of the diamonds that eliminated low-quality stones in the journey to their ®nal resting place. q 2001 Published by Elsevier Science Ltd. Keywords: Precambrian magmatic period; Espinhac Ëo Range; Conglomerate Resumo Os depo Âsitos diamantõ Âferos da Serra do Espinhac Ëo podem ser relacionados a tre Ãsperõ Âodos de evoluc Ëa Äogeolo Âgica.Umperõ Âodo magma Âtico, Pre Â-Cambriano $1,75 Ga), cuja a Ârea fonte do diamante permanece como um enigma. Durante um segundo perõ Âodo, os diamantes foram depositados na bacia Espinhac Ëo, de idade mesoproterozo Âica  ù 1.75±1.70 Ga). Um terceiro perõ Âodo ocorreu no Fanerozo Âico; em conse- qu Èe Ãncia do soerguimento juro-creta Âcico da serra, os conglomerados antigos foram erodidos e os diamantes redepositados no Eocreta Âceo em sistemas ¯uviais entrelac Ëados. Tais conglomerados sa Äo anti-econo Ãmicos devido a cobertura laterõ Âtica espessa. Um novo levantamento durante o Neo Âgeno permitiu a formac Ëa Äo de fanglomerados nas bordas serranas. No decorrer do Quaterna Ârio, oscilac Ë o Ä es clima Âticas levaram a Á sedimentac Ëa Äodecolu Âviosdiamantõ Âferos.Osdiamantesdessesdepo Âsitossa Äolavradosquandosituadosnasproximidadesdosconglomerados pre Â-cambrianose/oucreta Âcicos.Osdepo Âsitosaluvionaresrecentes,apesardosbaixosteoresemdiamante,representamatualmenteaprincipal fonte do mineral devido a Ás imensas reservas. As caracterõ Âsticas mineralo Âgicas dos diamantes, em combinac Ëa Äo com os aspectos geolo Âgicos, re¯etem os diversos ciclos de retrabalhamento, indicando para eles uma a Ârea fonte extra-bacia, provavelmente localizada no Cra Âton do Sa Äo Francisco. Essas caracterõ Âsticas sa Äo consequ Èe Ãncia da selec Ëa Äo natural que eliminou os diamantes de baixa qualidade durante a evoluc Ëa Äo da histo Âria geolo Âgica. q 2001 Published by Elsevier Science Ltd. 1. Introduction The Espinhac Ëo Range is a mountain chain extending on the south from the Quadrila Âtero Ferrõ Âfero Iron Quadrangle) nearthecapitalofMinasGeraisState,BeloHorizonte,north Journal of South American Earth Sciences 14 2001) 277±289 0895-9811/01/$ - see front matter q 2001 Published by Elsevier Science Ltd. PII: S0895-981101)00024-4 www.elsevier.com/locate/jsames * Corresponding author. Tel.: 155-31-499-5447; fax: 155-31-499-5410. E-mail address: mchaves@igc.ufmg.br M.L.S.C. Chaves).