The Dusi (Garba Tula) sapphire deposit, Central Kenya––a unique Pan-African corundum-bearing monzonite

Simonet, C.; Paquette, Jean‐Louis; Pin, Christian; Lasnier, B.; Fritsch, Emmanuel

doi:10.1016/j.jafrearsci.2004.02.002

Cited by 33 publications

(12 citation statements)

References 26 publications

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“…These ages only recorded in monazites are comparable with the one obtained eastward in the Galana vertical shear zone where they are associated with granulitefacies metamorphism (Hauzenberger et al 2007) or magmatic dike emplacement to the north (Simonet et al 2004). This 580 Ma event is linked to the final amalgamation of micro-continents forming Gondwana (Kuunga orogeny, Meert 2003).…”

Section: Late Neoproterozoic Metamorphic Eventssupporting

confidence: 77%

Chronological Constraints On Tsavorite Mineralizations and Related Metamorphic Episodes In Southeast Kenya

Martelat¹,

Paquette²,

Bosse³

et al. 2017

Can Mineral

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Tsavorite is exclusively hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). The gemstone mines, widespread between Kalalani (Tanzania) and Mgama Ridge (Kenya), define a continuous corridor over a hundred kilometers in length. The tsavorite is hosted by a metasedimentary sequence defined as the Kurase tsavorite-bearing metasediments (Kurase-TB metasediments) that also hosts rubies. These metasediments underwent amphibolite-facies metamorphism and are surrounded by granulitic gneisses that are also of sedimentary origin (the Kurase high-temperature gneisses). All these rocks lie below the Kasigau Group, a unit dominated by granulite-facies metamagmatic rocks.To constrain the timing of events that led to this peculiar occurrence of tsavorite, we have performed geochronological analyses of thin sections and of separated grains of zircon, monazite, and rutile using LA-ICP-MS and ID-TIMS, as well as 40 Ar/ 39 Ar of muscovite and phlogopite from various lithologies. The results show that the different terranes were metamorphosed synchronously between 620-580 Ma but under different P-T strain conditions. The Kurase-HT gneisses and the rocks from the Kasigau Group are highly strained and underwent granulite-facies metamorphism with abundant partial melting and emplacement of felsic melts between 620 and 600 Ma. Textural observations also underlined a late regional water flux controlling the occurrence of V-free muscovite and monazite mineralizations at 585 Ma. The latter event can be related to the 1 activity of the Galana shear zone, in the east. The Kurase-TB metasediments escaped strain and partial melting. They record amphibolite-facies conditions with static heating, since initial sedimentary structures were locally preserved. The age of the tsavorite mineralization was inferred at 600 Ma from metamorphic zircon rims and monazite from the closest host-rocks, sampled in the mines. Hence, tsavorite crystallization occurred statically at the end of the metamorphic event, probably when the temperature and the amount of volatiles were at maximum levels.Conversely, the ruby formed by local metasomatism of felsic dikes and isolated ultramafic bodies. The rubies are older and zircons and monazites from a ruby-bearing felsic dike (plumasite) were dated at 615 Ma. Finally, data from rutile and micas indicate a global cooling below 430 8C of the whole region between 510 and 500 Ma.

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Section: Late Neoproterozoic Metamorphic Eventssupporting

confidence: 77%

Chronological Constraints On Tsavorite Mineralizations and Related Metamorphic Episodes In Southeast Kenya

Martelat¹,

Paquette²,

Bosse³

et al. 2017

Can Mineral

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“…It is found in three main geological environments (e.g. Simonet et al 2004;Giuliani et al 2007;Graham et al 2008;Sutherland et al 2009): (1) magmatic, mainly as xenocrysts and in xenoliths of alkali basalts, syenites, monzonites, and lamprophyres; (2) metamorphic, mainly in marbles, skarns, granulites, cordieritites, gneisses to migmatite rocks, mafic-ultramafic metamorphites and as xenocrysts in basalts; and (3) secondary alluvial sedimentary deposits. In Europe, there are occurrences of sapphires in the monchiquite dike from Loch Roag, Scotland (Jackson 1984), syenite and anorthoclasite xenoliths connected with basaltic volcanism (Scotland, northern Britain, Ireland -Upton et al 1983), anorthoclasite xenoliths in trachytes at Menet, French Massif Central (Brousse & Varet 1966), syenitic pegmatites in the Southern Urals and Khibiny, Russia (Kievlenko 2003), pegmatitic albitite dikes in Urdach and Espechère, western Pyrenees, France , or in granitic pegmatite xenolith from Karpacz, Karkonosze Mts, Poland (Kozłowski & Sachabiński 2007).…”

Section: Introductionmentioning

confidence: 99%

Sapphires related to alkali basalts from the Cerová Highlands, Western Carpathians (southern Slovakia): composition and origin

Uher¹,

Giuliani²,

Szakáll³

et al. 2012

Geologica Carpathica

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Sapphires related to alkali basalts from the Cerová Highlands, Western Carpathians (southern Slovakia): composition and originBlue, grey-pink and pink sapphires from the Cerová Highlands, Western Carpathians (southern Slovakia) have been studied using CL, LA-ICP-MS, EMPA, and oxygen isotope methods. The sapphire occurs as (1) clastic heavy mineral in the secondary sandy filling of a Pliocene alkali basaltic maar at Hajnáčka, and (2) crystals in a pyroxenebearing syenite/anorthoclasite xenolith of Pleistocene alkali basalt near Gortva. Critical evaluation of compositional diagrams (Fe, Ti, Cr, Ga, Mg contents, Fe/Ti, Cr/Ga, Ga/Mg ratios) suggests a magmatic origin for clastic blue sapphires with lower Cr and Mg, but higher Fe and Ti concentrations in comparison to the grey-pink and pink varietes, as well as similar compositional trends with blue sapphire from the Gortva magmatic xenolith. Moreover, blue sapphires show similar δ18O values: 5.1 ‰ in the Gortva xenolith, 3.8 and 5.85 ‰ in the Hajnáčka placer, closely comparable to mantle to lower crustal magmatic rocks. On the contrary, pink and grey-pink sapphires show higher Cr and Mg, but lower Fe and Ti contents and their composition points to a metamorphic (metasomatic) origin.

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“…Modified from Giuliani et al (2014). (Simonet et al, 2004) and nepheline syenite (Sorokina et al, 2017b). The corundum formed by direct crystallization from the melt as an accessory mineral phase.…”

mentioning

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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The Dusi (Garba Tula) sapphire deposit, Central Kenya––a unique Pan-African corundum-bearing monzonite

Cited by 33 publications

References 26 publications

Chronological Constraints On Tsavorite Mineralizations and Related Metamorphic Episodes In Southeast Kenya

Chronological Constraints On Tsavorite Mineralizations and Related Metamorphic Episodes In Southeast Kenya

Sapphires related to alkali basalts from the Cerová Highlands, Western Carpathians (southern Slovakia): composition and origin

Geology of Corundum and Emerald Gem Deposits: A Review

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