Publication Date:
2011-01-01
Description:
The formation age of platinum-group minerals (PGM) in placer deposits has traditionally been difficult to constrain. We have applied the Pt-Os and Re-Os isotope systems to this problem by analyzing a suite of PGM from a placer deposit in southeastern Borneo that are derived, by mechanical processes, from chromitites of the Meratus ophiolite. Published subduction and emplacement ages and biostratigraphy of pelagic sediments of the ophiolite sequence define a minimum age for genesis at a spreading ridge. However, igneous components of the ophiolite have previously been undateable. Alluvial PGM grains (n = 260) from the Pontyn River, which drains the Meratus Mountains, were analyzed by laser ablation-multicollector-inductively-coupled mass spectrometry (LA-MC-ICPMS). Re-Os data do not show any isochronous relationship. Despite a significant range in 187Os/188Os (0.122-0.141), 187Re/188Os values show a very narrow range (0.000005-0.002980). In contrast, the PGM have a wide range in both 186Os/188Os (0.119801-0.120315) and 190Pt/188Os (
Print ISSN:
0361-0128
Topics:
Geosciences
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