TY - JOUR

T1 - Chromite-PGM Mineralization in the Lherzolite Mantle Tectonite of the Kraka Ophiolite Complex (Southern Urals, Russia)

AU - Garuti, Giorgio

AU - Pushkarev, Evgeny

AU - Gottman, Irina

AU - Zaccarini, Federica

N1 - Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2021/11

Y1 - 2021/11

N2 - The mantle tectonite of the Kraka ophiolite contains several chromite deposits. Two of them consisting of high-Cr podiform chromitite—the Bolshoi Bashart located within harzburgite of the upper mantle transition zone and Prospect 33 located in the deep lherzolitic mantle—have been investigated. Both deposits are enveloped in dunite, and were formed by reaction between the mantle protolith and high-Mg, anhydrous magma, enriched in Al 2O 3, TiO 2, and Na 2O compared with boninite. The PGE mineralization is very poor (<100 ppb) in both deposits. Laurite (RuS 2) is the most common PGM inclusion in chromite, although it is accompanied by erlichmanite (OsS 2) and (Ir,Ni) sulfides in Prospect 33. Precipitation of PGM occurred at sulfur fugacity and temperatures of logƒS 2 = (−3.0), 1300–1100 ◦C in Bolshoi Bashart, and logƒS2 = (−3.0/+1.0), 1100–800 ◦C in Prospect 33, respectively. The paucity of chromite-PGM mineralization compared with giant chromite deposits in the mantle tectonite in supra-subduction zones (SSZ) of the Urals (Ray-Iz, Kempirsai) is ascribed to the peculiar petrologic nature (low depleted lherzolite) and geodynamic setting (rifted continental margin?) of the Kraka ophiolite, which did not enable drainage of the upper mantle with a large volume of mafic magma.

AB - The mantle tectonite of the Kraka ophiolite contains several chromite deposits. Two of them consisting of high-Cr podiform chromitite—the Bolshoi Bashart located within harzburgite of the upper mantle transition zone and Prospect 33 located in the deep lherzolitic mantle—have been investigated. Both deposits are enveloped in dunite, and were formed by reaction between the mantle protolith and high-Mg, anhydrous magma, enriched in Al 2O 3, TiO 2, and Na 2O compared with boninite. The PGE mineralization is very poor (<100 ppb) in both deposits. Laurite (RuS 2) is the most common PGM inclusion in chromite, although it is accompanied by erlichmanite (OsS 2) and (Ir,Ni) sulfides in Prospect 33. Precipitation of PGM occurred at sulfur fugacity and temperatures of logƒS 2 = (−3.0), 1300–1100 ◦C in Bolshoi Bashart, and logƒS2 = (−3.0/+1.0), 1100–800 ◦C in Prospect 33, respectively. The paucity of chromite-PGM mineralization compared with giant chromite deposits in the mantle tectonite in supra-subduction zones (SSZ) of the Urals (Ray-Iz, Kempirsai) is ascribed to the peculiar petrologic nature (low depleted lherzolite) and geodynamic setting (rifted continental margin?) of the Kraka ophiolite, which did not enable drainage of the upper mantle with a large volume of mafic magma.

KW - Chromitite

KW - Kraka ophiolite complex

KW - Low depleted lherzolite

KW - Platinum group minerals

KW - Russia

KW - Southern Urals

UR - http://www.scopus.com/inward/record.url?scp=85119338961&partnerID=8YFLogxK

U2 - https://doi.org/10.3390/min11111287

DO - https://doi.org/10.3390/min11111287

M3 - Article

VL - 11

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 11

M1 - 1287

ER -