Geochemical relationship between REE and PGE in mafic and ultramafic rocks and their petrogenetic significance - Rare Earth Elements in Ultramafic and Mafic Rocks and their Minerals - page 259

10.5 LUOBUSA MASSIF (SOUTHERN TIBET, CHINA)

Luobusa ultramafic massif that is a part of ophiolite association of Southern Tibet is
a steeply dipping lenticular body having a length of 20 km and a width of 4 km. The
massif is composed of harzburgites and subordinate dunites [Zhou et al ., 2005]. Dun-
ites form a large separate body lying along a tectonic contact of the massif with host
rocks, as well as several small lenticular isolations occurring among harzburgites. In
addition, the dunites are composing narrow zones around the bodies of ore chromi-
tites localized among harzburgites.
As follows from the analysis, the content of REE in harzburgites is usually slightly
higher than in dunites, with the exception of those types of dunites that form iso-
lations among harzburgites (Table 10.10). Total REE contents in the dunites from
their large body range from 17 to 75 ppm and in those samples that compose small
isolations among harzburgites, it is higher and the average is 114 ppm. In harzburgites
the total REE content ranges from 280 to 1250 ppm. Both among the dunites and
harzburgites there are some samples with abnormally high LREE content.
Total Ir, Ru, Rh, Pt and Pd contents in ultramafites of this massif range from
16 to 29 ppb, while the configuration of patterns of PGE distribution show some
Pt deficiency in dunites. The presented graphs indicate that dunites have an inverse
relationship between total Pd, Pt and Rh contents on the one hand, and the contents
of REE on the other hand (Figure 10.21). One can also assume that in the dunites
and harzburgites from the massif there is an inverse relationship between Yb contents
and the values of Pd/Ir and Pt/Ir parameters (Figure 10.22). In general, data on the
distribution of REE and PGE in dunites and harzburgites from Luobusa ultramafic
massif do not contradict the model of their formation that occurred during the partial
melting of mantle source.

10.6 ITI AND KALLIDROMON MASSIFS (GREECE)

These two massifs that are composed of lherzolites and subordinate harzbur-
gites are a part of the ophiolite association of Central Greece [Karipi et al ., 2006].
In lherzolites from both massifs the total REE content ranges from 0.83 to 1.81 ppm,
in harzburgites - from 0.47 to 0.57 ppm (Table 10.11). Total PGE content in lher-
zolites ranges from 15.1 to 38.8 ppb, which is slightly higher than in harzburgites
(9.6-18.1 ppb). By the position of figurative points on the graphs we can assume
that in these ultramafites the contents of Sm, Eu and Gd are inversely related to the
contents of Os and that for some reason there is a direct relation between REE and Ir
(Figure 10.23). There is also an inverse relation between Yb content and the values of
Pd/Ir and Pt/Ir parameters (Figure 10.24).

10.7 KOMATIITE-BASALT COMPLEX OF NORTH-WEST
VIETNAM

During the petrological and geochemical studies of the Permian-Triassic volcanic
complex of North-West Vietnam in the composition of the residing komatiites,