Rubies and Sapphires from Winza, Central Tanzania

Schwarz, Dietmar; Pardieu, Vincent; Saul, John M.; Schmetzer, Karl; Laurs, Brendan M.; Giuliani, Gaston; Klemm, L.; Malsy, Anna-Kathrin; Erel, E.; Hauzenberger, Christoph; Toit, Grizelda du; Fallick, A.E.; Ohnenstetter, Daniel

doi:10.5741/gems.44.4.322

Cited by 40 publications

(47 citation statements)

References 22 publications

(28 reference statements)

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“…3a) defined in the FeO-Cr 2 O 3 -MgO-V 2 O 3 vs. FeO + TiO 2 + Ga 2 O 3 classification diagram proposed by Giuliani et al (2014). (a1) The field of sample CO1 overlaps the plots of rubies from Andriba in Madagascar hosted in ultramafics , the Winza deposit in Tanzania located in amphibolite and metagabbro (Schwarz et al, 2008), high-grade Proterozoic orthoamphibolites of the Bamble area in Norway (Hutchinson et al, 2004), and ultrahigh pressure ruby-rich garnetite layers from garnet lherzolite in the Sulu terrane of China (Zhang et al, 2004); (a2) The field of sample CO2 is correlated to the very high Cr 2 O 3 content of ruby up to 4.6 wt% (Fig. 3b).…”

Section: The Rubies From Mbuji-mayimentioning

confidence: 99%

Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China

Giuliani¹,

Pivin

Fallick

et al. 2015

Comptes Rendus. Géoscience

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Section: The Rubies From Mbuji-mayimentioning

confidence: 99%

Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China

Giuliani¹,

Pivin

Fallick

et al. 2015

Comptes Rendus. Géoscience

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“…At the Winza deposit in central Tanzania (Peretti et al, 2008;Schwarz et al, 2008), gem corundum crystals are embedded in dark amphibolite. The corundum is locally associated with areas of brown to orangy garnet ± feldspar, with accessory Cr-spinel, mica, kyanite, and allanite.…”

Section: Geology and Genesis Of Metamorphic Corundummentioning

confidence: 99%

Geology of Corundum and Emerald Gem Deposits: A Review

Giuliani¹,

Groat²

2019

G&G

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The great challenge of geographic origin determination is to connect the properties and features of individual gems to the geology of their deposits. Similar geologic environments can produce gems with similar gemological properties, making it difficult to find unique identifiers. Over the last two decades, our knowledge of corundum and emerald deposit formation has improved significantly.The mineral deposits are classically separated into primary and secondary deposits. Primary corundum deposits are subdivided into two types based on their geological environment of formation: (1) magmatic and (2) metamorphic. Magmatic deposits include gem corundum in alkali basalts as in eastern Australia, and sapphire in lamprophyre and syenite as in Montana (United States) and Garba Tula (Kenya), respectively. Metamorphic deposits are divided into two subtypes (1) metamorphic deposits sensu stricto (in marble; mafic and ultramafic rocks, or M-UMR), and (2) metamorphicmetasomatic deposits characterized by high fluid-rock interaction and metasomatism (i.e., plumasite or desilicated pegmatites in M-UMR and marble, skarn deposits, and shear zone-related deposits in different substrata, mainly corundum-bearing Mg-Cr-biotite schist). Examples of the first subtype include the ruby deposits in marble from the Mogok Stone Tract or those in M-UMR from Montepuez (Mozambique) and Aappaluttoq (Greenland). The second subtype concerns the sapphire from Kashmir hosted by plumasites in M-UMR.Secondary corundum deposits (i.e., present-day placers) result from the erosion of primary corundum deposits. Here, corundum is found in the following types of deposits: eluvial (derived by in situ weathering or weathering plus gravitational movement), diluvial (scree or talus), colluvial (deposited at the base of slopes by rainwash, sheetwash, slow continuous downslope creep, or a combination of these processes), and alluvial (deposited by rivers). Today, most sapphires are produced from gem placers related to alkali basalts, as in eastern Australia or southern Vietnam, while placers in metamorphic environments, such as in Sri Lanka (Ratnapura, Elahera) and Madagascar (Ilakaka), produce the highest-quality sapphires. The colluvial Montepuez deposit in Mozam bique provides a huge and stable supply of clean and very highquality rubies. Primary emerald deposits are subdivided into two types based on their geological environment of formation: (1) tectonic-magmatic-related (Type I) and (2)tectonic-metamorphic-related (Type II). Several subtypes are defined and especially Type IA, hosted in M-UMR, which accounts for about 70% of worldwide production (Brazil, Zambia, Russia, and others). It is characterized by the intrusion of pegmatites or quartz veins in M-UMR accompanied by huge hydrothermal fluid circulation and metasomatism with the formation of emerald-bearing desilicated pegmatite (plumasite) and biotite schist. Type IB in sedimentary rocks (China, Canada, Norway, Kazakhstan, and Australia) and Type IC in granitic rocks (Nigeria) are of minor importance.T...

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“…A: Polarized absorption spectra of four sapphires from different deposits (Notari and Grobon, 2002) showing bands corresponding to chromophores. B: Polarized absorption spectra of Winza ruby (Schwarz et al, 2008) and orangy pink sapphire from Madagascar (Peretti and Günther, 2002). The spectrum of ruby shows the well-known Cr 3+ absorption bands at [405][406][407][408][409][410]and the Cr "doublet" at presence of Cr and V in the beryl structure causes a red fluorescence that enhances the luminosity of the blue-green color, but if Fe 3+ is present in the emerald crystal, this effect is suppressed (Nassau, 1983).…”

Section: Characteristics Of Emeraldmentioning

confidence: 99%