Contrasting platinum-group mineral assemblages from chromitites of the Nizhny Tagil and Guli massifs (Russia): Implications for composition, sources and age |
| |
| Authors: | K N Malitch A A Efimov and I Yu Badanina |
| |
| Abstract: | The Nizhny Tagil and Guli clinopyroxenite-dunite massifs, located in the Middle Urals and Maimecha-Kotui Province, respectively,
are associated with world-class platinum-group elements (PGE) placer deposits. Both massifs contain small bodies of schlieren
to massive chromitite associated with dunite. The predominance of Pt-Fe alloys at Nizhny Tagil is consistnt with the whole-rock
“M”-shaped mantle-normalized PGE pattern of the chromitite. In contrast, the preponderance of laurite and Os-Ir alloys at
Guli is consistent with a negatively sloped PGE pattern, the latter being characteristic of ophiolite-type podiform chromitites.
The ‘unradiogenic’ 187Os/188Os values obtained for both platinum-group minerals (PGM) and chromitite are indicative of a common near-to-chondritic source
for the PGE and implies that the osmium isotope budget of chromitite is largely controlled by laurite and Os-rich alloy. Average
model 187Os/188Os ages calculated for the Nizhny Tagil and Guli massifs correspond to the late Riphean (e.g., 862 ± 48 Ma and 616 ± 8 Ma,
respectively). The compositional and isotope-geochemical results provide new constraints on the temporal evolution of ultramafic
rocks of the Uralian Platinum Belt and northern segment of the Siberian Platform. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
