Os-rich nuggets from Au-PGE placers of the Maimecha-Kotui Province, Russia: a multi-disciplinary study |
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| Authors: | K N Malitch T Auge I Yu Badanina M M Goncharov S A Junk E Pernicka |
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| Institution: | (1) Institute of Geological Sciences, University of Leoben, Austria, AT;(2) BRGM, Orleans, France, FR;(3) All-Russia Research Institute of Geology and Mineral Resources of the World Ocean, St.-Petersburg, Russia, RU;(4) Polar Survey Prospecting Venture of Industrial Geological Enterprise “Noril’skgeologiya” of “Noril’sk Nickel”, Khatanga, Russia, RU;(5) TU Bergakademie Freiberg, Federal Republic of Germany, DE |
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| Abstract: | Summary ?Geological, mineralogical and Os isotopic data for detrital PGE-mineralization derived from the Guli and Bor-Uryah ultramafic
massifs, within the Maimecha-Kotui Province (the northern part of the Siberian Platform, Russia), are presented for the first
time. The detrital platinum-group minerals (PGM) are dominated by Os–Ir–(Ru) species, which is typical for ophiolites or Alpine-type
complexes. However, the PGM assemblage in the placers investigated is similar to that derived from zoned platiniferous clinopyroxenite–dunite
massifs (also known as Uralian-, Alaskan-type and Aldan-type massifs). The unique features of the Au-PGE placers at Guli are
(1) the dominance of Os-rich alloys over other PGM and Au, and (2) the considerable predicted resources of noble metals, particularly
osmium.
Dominant chromite, olivine and clinopyroxene inclusions recorded in Os–Ir–(Ru) alloys imply that they were derived from ultramafic
sources (e.g., chromitite, dunite and clinopyroxenite). The first in situ osmium-isotope measurements by laser ablation -
multiple collector - inductively coupled plasma mass spectrometry of different, intimately intergrown, PGM (e.g., laurite
and Os-rich alloys) in various nuggets from Guli have revealed low 187Os/188Os and γOs values. They yield a very narrow range of 187Os/188Os (0.12432 to 0.12472) and γOs (− 2.39 to − 2.07). These values are indicative of a common chondritic or subchondritic mantle
source of PGE. 187Os/188Os and γOs values of Os-rich alloys, derived from the Bor-Uryah massif, are different (i.e., γOs ranges from − 2.67 to − 1.30).
The mineral-isotopic data obtained are consistent with the conclusion that the PGM were derived from parent ultramafic source
rocks. Os-isotope model ages in the range of 495 to 240 Ma constrain the age of ultramafic protoliths in the northern part
of the Siberian Craton. The variation in 187Os/188Os values for detrital PGM, where the provenance source is unknown, is considered to be a useful technique for distinguishing
parent bedrock sources.
Received July 12, 2001; revised version accepted December 27, 2001 |
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