Artículos de revistas
Re–Os isotopic constraints on the source of platinum-group minerals (PGMs) from the Vestřev pyrope-rich garnet placer deposit, Bohemian Massif
Fecha
2015Registro en:
Ore Geology Reviews 68 (2015) 117–126
DOI: 10.1016/j.oregeorev.2015.01.013
Autor
Pasava, Jan
Malec, Jan
Griffin, William L.
González Jiménez, José
Institución
Resumen
Mineralogical studies of the heavy fraction from a Holocene pyrope-rich garnet placer deposit at Vestřev
(Krkonoše Piedmont Basin, Bohemian Massif) have identified the presence of very rare grains of platinum
group minerals (PGM). Pt–Fe alloy grains are accompanied by Os–Ir–Ru minerals (native osmium, iridium, and
ruthenium) with inclusions of Pt–Fe alloy and hongshiite (PtCu). This mineral assemblage is typical for several
mantle settings including ophiolites. The chemistry of the Os–Ir–Ru minerals shows an enrichment of the PGM
in Ru, which is typical of ophiolites. The grain morphology of PGM and pyrope-rich garnet (mostly rounded
with numerous euhedral/subhedral grains) does not exclude a common source. In-situ laser-ablation MC-ICPMS
was used to measure the Re–Os isotopic compositions of single Os-rich grains, which show heterogeneous
subchondritic Os isotopic compositions (187Os/188Os = 0.12082–0.12505 ± 0.00003). This precludes their
low-temperature origin and indicates derivation of platinum-group elements (PGEs) essentially from mantlederived
rocks without a significant contribution of crustal Os. The mantle model age (TMA) and Re-depletion
model age (TRD) model ages range from ~0.4 to ~1.0 Ga and most likely reflect a long history of melt depletion
that affected the mantle sources of PGM.