First occurrences of PGE mineralization in ultramafic rocks of the Middle Kraka massif, the Southern Urals

In the South Urals, we have identified and investigated two platinum-bearing formations – ophiolite chromitebearing complexes, and the Khudolaz differentiated mafic-ultramafic complex with sulfide Cu-Ni mineralization. The ophiolite chromite-bearing complexes include fragments of the upper mantle and lower crust of the Paleouralian Ocean, which were induced by collision onto the edge of the East European platform. The origin of the Khudolaz complex is related a mantle plume activity. Here, we review and compare the main features of platinum-metal mineralization (PMM) in these two formations.The article presents the results of mineralogical and geochemical studies of PMM associated with chromite and sulfide Cu-Ni ores. In association with chromitites, two types of PMM are distinguished: (1) predominating refractory platinoids in chromitites of the mantle unit of the section, and (2) predominating platinum and palladium in chromitites of the transitional wehrlite-clinopyroxenite complex. Compositions of platinum group minerals (PGM) and relations between their elements and host minerals suggest that the minerals of the ophiolite chromite-bearing complexes are of a restite origin, while the Khudolaz complex results from a combination of magmatic processes and solid-phase redistribution of material. Palladium (michenerite, froodite, merenskyite, borovskite, sudburyite) and platinum (sperrylite, moncheite) minerals are found in magmatic sulfide ores of the Khudolaz complex, which were subjected to hydrothermal metasomatization. Texture observations using electron microscope and optical (reflected light) images, as well as LA ICP MS analyses of sulfides suggest late- and post-magmatic crystallization of PMM in three phases: (1) immiscible metalloid or highly fractionated residual sulfide melts trapped in sulfides; (2) segregation of isomorphic impurities of platinum group elements (PGE) and chalcogenide elements from sulfide solid solutions; and (3) interaction of hydrothermal fluids with soluble sulfides.Prospective for PMM are extended bodies of disseminated chromitites in marginal dunites of the Kraka and Nurali massifs, and wehrlite-clinopyroxenite complexes of the same massifs containing PGE (above 500 ppb). In the Khudolaz complex, promising PMM bodies are low-metasomatized parts of sulfide ore bodies (1 ppm of ΣPGE and above) located in the largest massifs, Severny Buskun and Zapadny Karasaz. Exocontact zones of these intrusions are also promising for PMM.

show abstract

Section: минералогия эпг офиолитовых хромититовunclassified

“…Note. 1-14 -Kraka, 15-24 -Nurali; some data from [Saveliev et al, 2014[Saveliev et al, , 2015 значимые количества ЭПГ, в частности иридия, платины, осмия, родия и рутения.…”

Section: минералогия эпг офиолитовых хромититовunclassified

Platinum Metal Mineralization of the South Urals Magmatic Complexes: Geological and Geodynamic Characteristics of Formations, Problems of Their Genesis, and Prospects

Рахимов

Савельев

Вишневский

2021

Geodin. tektonofiz.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Modal and geochemical prevalences of the refractory Os, Ir, and Ru (IPGE) over the low-melting Rh, Pt, and Pd (PPGE) result in the typical negative slope of chondritenormalized PGE patterns that distinguish the PGE mineralization in ophiolites from the Pt-specialized mineralization of Ural-Alaskan type [22][23][24][25][26][27][28][29]. There are, however, significant differences in total PGE content and PGM mineralogy between ophiolitic chromite deposits, showing total PGE concentrations up to more than 1 ppm or low PGE contents not exceeding a few hundred ppb.…”

Section: Introductionmentioning

confidence: 99%

“…The chromitites in the deposits of Bolshoi Bashart (BB) and Prospect 33 have been objects of exploitation since the middle of the last century [4]. They have to be distinguished from veinlets of high-Fe chromitite recently described in the wehrliteclinopyroxenite cumulates of the Middle Kraka massif, which were found to contain scattered Pt-PGM [29], but are not big enough for ore deposits. The deposits investigated in this work occur in the mantle-tectonite unit of the Kraka ophiolite: one (Bolshoi Bashart) occurs inside massive harzburgite of the upper mantle transition-zone; the other (Prospect 33) is at depth in the lherzolite mantle unit [30,31].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

View full text Add to dashboard Cite

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 Al2O3, TiO2, and Na2O compared with boninite. The PGE mineralization is very poor (<100 ppb) in both deposits. Laurite (RuS2) is the most common PGM inclusion in chromite, although it is accompanied by erlichmanite (OsS2) and (Ir,Ni) sulfides in Prospect 33. Precipitation of PGM occurred at sulfur fugacity and temperatures of logƒS2 = (−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.

show abstract

First occurrences of PGE mineralization in ultramafic rocks of the Middle Kraka massif, the Southern Urals

Cited by 2 publications

References 1 publication

Platinum Metal Mineralization of the South Urals Magmatic Complexes: Geological and Geodynamic Characteristics of Formations, Problems of Their Genesis, and Prospects

Platinum Metal Mineralization of the South Urals Magmatic Complexes: Geological and Geodynamic Characteristics of Formations, Problems of Their Genesis, and Prospects

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

Contact Info

Product

Resources

About