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Open AccessReview

Ruby Deposits: A Review and Geological Classification

1
Géosciences Environnement, Université Paul Sabatier, GET/IRD et Université de Lorraine, C.R.P.G./C.N.R.S., 15 rue Notre-Dame-des-Pauvres, BP 20, 54501 Vandœuvre, France
2
Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
3
Isotope Geosciences Unit, Scottish Universities Environmental Research Centre (S.U.E.R.C.), Rankine Avenue, East Kilbride, Glasgow G75 0QF, UK
4
Georessources, Université de Lorraine, UMR 7539 CNRS-UL, BP 70239 Vandœuvre, France
5
Field gemmologist & Consultant at VP Consulting, Manama, Bahrain
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(7), 597; https://doi.org/10.3390/min10070597
Received: 30 March 2020 / Revised: 22 June 2020 / Accepted: 23 June 2020 / Published: 30 June 2020
(This article belongs to the Special Issue Mineralogy and Geochemistry of Ruby)
Corundum is not uncommon on Earth but the gem varieties of ruby and sapphire are relatively rare. Gem corundum deposits are classified as primary and secondary deposits. Primary deposits contain corundum either in the rocks where it crystallized or as xenocrysts and xenoliths carried by magmas to the Earth’s surface. Classification systems for corundum deposits are based on different mineralogical and geological features. An up-to-date classification scheme for ruby deposits is described in the present paper. Ruby forms in mafic or felsic geological environments, or in metamorphosed carbonate platforms but it is always associated with rocks depleted in silica and enriched in alumina. Two major geological environments are favorable for the presence of ruby: (1) amphibolite to medium pressure granulite facies metamorphic belts and (2) alkaline basaltic volcanism in continental rifting environments. Primary ruby deposits formed from the Archean (2.71 Ga) in Greenland to the Pliocene (5 Ma) in Nepal. Secondary ruby deposits have formed at various times from the erosion of metamorphic belts (since the Precambrian) and alkali basalts (from the Cenozoic to the Quaternary). Primary ruby deposits are subdivided into two types based on their geological environment of formation: (Type I) magmatic-related and (Type II) metamorphic-related. Type I is characterized by two sub-types, specifically Type IA where xenocrysts or xenoliths of gem ruby of metamorphic (sometimes magmatic) origin are hosted by alkali basalts (Madagascar and others), and Type IB corresponding to xenocrysts of ruby in kimberlite (Democratic Republic of Congo). Type II also has two sub-types; metamorphic deposits sensu stricto (Type IIA) that formed in amphibolite to granulite facies environments, and metamorphic-metasomatic deposits (Type IIB) formed via high fluid–rock interaction and metasomatism. Secondary ruby deposits, i.e., placers are termed sedimentary-related (Type III). These placers are hosted in sedimentary rocks (soil, rudite, arenite, and silt) that formed via erosion, gravity effect, mechanical transport, and sedimentation along slopes or basins related to neotectonic motions and deformation. View Full-Text
Keywords: ruby deposits; classification; typology; magmatism; metamorphism; sedimentary; metasomatism; fluids; stable and radiogenic isotopes; genetic models; exploration ruby deposits; classification; typology; magmatism; metamorphism; sedimentary; metasomatism; fluids; stable and radiogenic isotopes; genetic models; exploration
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Giuliani, G.; Groat, L.A.; Fallick, A.E.; Pignatelli, I.; Pardieu, V. Ruby Deposits: A Review and Geological Classification. Minerals 2020, 10, 597.

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