Zircons - Rare Earth Elements in Ultramafic and Mafic Rocks and their Minerals - page 166

metamorphic complexes in India were presented in the work of Murali et al . [1983].
It was ascertained that the total REE contents in the zircons from these syenites and char-
nockites are significantly higher than in the mineral from biotite migmatites (Table 4.8).
On the REE patterns of all the zircons from this collection there are weak negative Eu
anomalies, but an absence of intense positive Ce anomalies (Figure 4.12, 5.6).
Zircons from placer deposits. As already noted, due to their high mechanical strength,
zircons are able to accumulate in the terrigenous rock mass and under favorable
conditions to form the complex placer deposits. REE composition of zircons from
some of the zircon-ilmenite placer deposits in Western Siberia (Russia) is described
in the work by Rikhvanov et al . [2001] (Table 4.9). Average chondrite-normalized
La contents in the zircons from the majority of these deposits are around 100 t.ch.,
for Yb and for Lu they increased up to 3.000 t.ch. (Figure 4.13, 1-6). The authors
showed that for the colorless crystals of zircon the overall REE accumulation is lower
compared with its crystals of a yellow, brown or other type of color (Figure 4.13,
7, 8). The data on zircons from some gabbro of the Kola Peninsula (Russia) prove
this regularity [Kaulina, 2010]. Finally, we note, that Izokh et al . [2010] examined
the REE composition of zircon from Dak Nong placer deposit (Vietnam), where they
appear as individual crystals and as inclusion in crystals of sapphire. HREE contents
in these zircons are much higher then contents of LREE. The levels of accumulation
of REE in inner zones of zircon crystals are usually somewhat higher than in the outer
zones. Intense Ce positive anomalies and less intense Eu negative anomalies there are
on the patterns of REE distribution of these zircons.

4.2 COEFFICIENTS OF REE DISTRIBUTION BETWEEN
ZIRCONS AND COEXISTING PHASES

In several works along with the data on the REE composition of zircons there are
results of studies on the coefficients of REE distribution between this mineral and
melts and coexisting minerals of different composition (Table 4.10, Figure 4.14).
Among the first, the data on the values of K d (zircon/dacite matrix) and K d (zircon/
granite) were published by Nagasawa [1970], according to which the K d of all REE
for these rocks have values 1, while the values for the light elements were the first

units and for heavy elements-366-389 (Figure 4.14, 3). Later, Watson [1980] relying
on the results of physical experiments with felsitic melts executed at T

>

= 800°C and

P 2 kbar, determined that the value of K d (zircon/melt) vary within the following

ranges: La (1.4-2.1); Sm (26-40); (Ho

=

340); Lu (72-126) (Figure 4.14, 7). Data
on the REE composition of zircons from syenites and charnockites containing them
allowed Murali et al . [1983] to calculate the values of K d for some elements. For a zir-
con-syenite system they were: La

>

∼ 0.035 and Lu ∼ 100, for zircon-charnockite system:

La 2000 (Figure 4.14, 5, 6). According to the calculations made using the

estimations of REE in zircons and the basanite matrix containing them [Irving & Fray,
1984], the following values of K d (zircon/basanitic melt) were obtained: La

∼ 3 and Lu ∼

∼ 0.09,

Lu-300 (Figure 4.14, 1).
While studying the zircons from amphibole-biotite diorites of Quottoon complex
(British Columbia, Canada), the values of K d (REE) in zircon-dioritic melt system
were determined. For this purpose there were used the results of analysis of REE in