The Nui Chua layered peridotite-gabbro complex as manifestation of Permo-Triassic mantle plume in northern Vietnam

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The Nui Chua layered peridotite-gabbro complex as manifestationof Permo-Triassic mantle plume in northern Vietnam

G.V. Polyakov a, R.A. Shelepaev a, Tran Trong Hoa b, A.E. Izokh a,*, P.A. Balykin a,Ngo Thi Phuong b, Tran Quoc Hung b, Bui An Nien b

a Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russiab Geological Institute of the Vietnamese Academy of Sciences and Technologies, Hanoi, Vietnam

Received 31 July 2008; accepted 24 October 2008

Abstract

New data on the age, composition, formation conditions, and ore-geochemical specialization of the Nui Chua layered peridotite-gabbrocomplex are reported. They evidence that the complex resulted from the Permo-Triassic mantle plume activity in northern Vietnam (southernframing of the Yangtze Platform). Two series of mafic and ultramafic rocks differing in ore productivity—layered (PGE-Cu-Ni) and pegmatoid(Fe-Ti-V)—have been recognized within the complex. The first estimates of the composition of their parental melts have been obtained.© 2009, IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Keywords: layered peridotite-gabbro complex; Permo-Triassic mantle plume; layered and pegmatoid series; parental melts; ore-geochemical specialization; Vietnam

Introduction

The well-studied Nui Chua pluton is part of the Nui Chuacomplex of layered peridotite-gabbro intrusions in northernVietnam (Nui Chua, Khao Que, Tri Nang, Nui Yen Chu, etc.).The geologic position of these massifs is schematically shownin Fig. 1. Earlier they were united with the Pia Bioc granitesinto the complex Late Triassic Ban Sang–Pia Bioc ultrabasite-gabbro-granite series (Dovzhikov et al., 1965; Nguyen VanChien, 1963). The Rb-Sr age of gabbroids of the Nui Chuapluton obtained at the early stage of its study (195 Ma) (BuiQuang Luon et al., 1985) corresponds to the Late Triassic.But it was obtained by a single and not highly reliabledetermination, which was not reproduced later. Until recently,the Nui Chua pluton, like the Nui Chua complex of layeredintrusions as a whole, has been assigned to Late Triassicigneous formations related to rift structures of Mesozoictectonomagmatic activity.

With SHRIMP zircon dating, we obtained a new age ofgabbronorites of the Nui Chua massif, 251±3.4 Ma (TranTrong Hoa et al., 2008). Close ages were obtained for the BanSang and Kim Boi granites of the Pia Bioc complex,250.5±1.0 (Ar-Ar dating) and 242±2 Ma (U-Pb dating),

respectively. These mutually consistent dates correspond tothe Permian–Triassic boundary, the second stage of evolutionof the Emeishan igneous province (Yangtze Platform), andevidence that the Nui Chua complex is a derivate of theEmeishan mantle plume that acted in the south of the Chinesecraton, including the North Vietnamese structures of itsframing, in the Permian-Triassic (Zhu Bing-Quan et al., 2005;Borisenko et al., 2006; Izokh et al., 2005; Polyakov et al.,2006; Tran Trong Hoa et al., 2004, 2008; Zhong et al., 2007;Zhou et al., 2005). In North Vietnam, the bimodal volcanicseries of the Song Hien zone formed at this time boundary.The age of rhyolites from this rock association in the CaoBang region is 248 Ma (Tran Trong Hoa et al., 2008). Thus,the Nui Chua pluton, like the Nui Chua complex as a whole,can be considered a product of the Permo-Triassic within-platemagmatism in North Vietnam.

Geologic position, composition, and internal structureof the pluton

The Nui Chua pluton, the largest (55 km2) and mostrepresentative massif of layered peridotite-gabbro intrusionsin North Vietnam, is localized in the south of the Phu Ngustructure composed of Paleozoic deposits. It occurs mainlyamong the Ordovician–Silurian quartzites, siliceous-sericiticschists, quartz porphyry, and tuffstones of the Phu Ngu unit

Russian Geology and Geophysics 50 (2009) 501–516

* Corresponding author.E-mail address: [email protected] (A.E. Izokh)

1068-7971/$ - see front matter D 2009, , Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.IGM

doi:10.1016/j.rgg.2008. .0010 2

and makes contact with Devonian schists, limestones, andsandstones along a fault in the northeast. In the west, theintrusion is overlain by Triassic molasse sand-shaly andcoarse-clastic deposits (Fig. 1).

The pluton is cut by faults into several blocks and has anintricately differentiated internal structure (Balykin, 2002;Balykin et al., 1996; Hoang Huu Thanh, 1994; Polyakov etal., 1984, 1986, 1996). All blocks are mainly layered rocks:olivine gabbros, olivine gabbronorites, and troctolites withinterbeds and horizons of plagiowehrlites, lherzolites, oliv-inites, olivine melanogabbronorites, leucogabbros, and anor-thosites (Fig. 2). Some interbeds and horizons of this seriesbear sulfide-disseminated PGE-Cu-Ni mineralization (Polya-kov et al., 1984, 1999). The magmatically layered trachytoidstructures (plane-parallel) are of NE concordant strike andsteep dip in the central and southwestern blocks. In thenortheastern block, where the structural center of the plutonseems to occur, similar layered structures are of more gentlereverse dips. Correspondingly, the exposed rocks of the upperpart of the massif are less melanocratic.

In the layered series forming the base of the intrusion, smalllenticular and dike-like bodies of coarse-grained pegmatoidrocks are ubiquitous. The rocks vary from olivine-free, oftenleucocratic gabbros and gabbronorites to olivine-free melano-gabbronorites and plagiopyroxenites. In the extreme southwestof the massif, such rocks are more abundant, and in the easternblock, where layered rocks prevail, they are associated withcompositionally similar taxitic and coarse-grained gabbroidsand pyroxenites with titanomagnetite-ilmenite mineralization(Cay Cham deposit). A similar rock association also occurs,

though to a lesser extent, in other parts of the intrusion,including the western block.

Mineralogy and geochemistry of the layered and pegmatoid rocks

The layered and pegmatoid rocks have a stable composi-tion. The most distinctive feature of the mineral compositionof the layered rocks is a predominance of olivine, which variesin f value from chrysolites (f = 27.8%) in ultramafites tohyalosiderites (f = 40.3%) in gabbroids and is characterizedby low contents of Ni (230–1100 ppm) (Balykin, 2002;Poliakov et al., 1996). Most of the pegmatoid rocks lackolivine. They contain inverted pigeonites with fir-like exsolu-tion structures bearing diopside lamellae. Taxitic gabbronoritesand pyroxenites often bear large palmate poikilitic orthopy-roxene crystals with similar exsolution structures. In thesoutheast of the massif, pigeonite grains are scarce in therocks. In the layered olivine gabbronorites, pigeonite occursas intricate intergrowths with diopside and, more seldom, asindividual euhedral crystals. The pegmatoid rocks also aboundin inverted pigeonite exsolved into diopside (f = 23–31%) andorthopyroxene (f = 38–65%). Analysis of the composition ofthe main rock-forming minerals (Tables 1–4) showed that theclino- and orthopyroxenes (Tables 2 and 3) of the pegmatoidgabbronorites and pyroxenites are more ferruginous than thepyroxenes of the layered rocks but less aluminous, and theplagioclases are more potassic, as evidenced from their highnormative content of orthoclase (Table 4). The compositional

Fig. 1. Schematic geologic structure of the Nui Chua massif (a) and tectonic scheme of North Vietnam (b). 1–6, structure-formational complexes of different ages: 1,Proterozoic; 2, Late Proterozoic–Early Paleozoic; 3, Paleozoic; 4, Early Mesozoic; 5, Late Mesozoic; 6, Cenozoic; 7, disjunctions; 8, layered periodite-gabbrointrusions of the Nui Chua complex: 1, Nui Chua, 2, Khao Que, 3, Tri Nang, 4, Nui Yen Chu; 9, layered rocks of the massif; 10, pegmatoid rocks; 11, fine-grainedbiotite gabbros and monzodiorites; 12–14, enclosing deposits: 12, Upper Triassic strata; 13, Devonian essentially carbonate deposits; 14, Ordovician–Siluriansandstones and schists; 15, geologic boundaries: a, established; b, supposed. A–B, Section profile (see Fig. 2).

G.V. Polyakov et al. / Russian Geology and Geophysics 50 (2009) 501–516502

variation of plagioclase, olivine, and pyroxenes is shown inFig. 3.

The different and discrete compositions of the layered andpegmatoid rocks have been revealed by comparing theirpetrochemical features. The comparison was based on morethan 200 chemical analyses, about 170 on the layered rocks

and more than 30 on the pegmatoid rocks. Table 5 lists theaveraged compositions of different rock groups of both series.

In the multidimensional space of petrogeochemical fea-tures, the rocks of both series are separated by the nonlinear-discrimination method (VADIC program (variance analysis,discrimination, and clustering) designed by V.V. Khlestov,

Fig. 2. Compositions of plagioclases (a), pyroxenes and olivines (b) and volume proportions of minerals in rocks (c) along the A–B section profile (d) running throughthe eastern block of the Nui Chua massif (Fig. 1). 1, interbeds of peridotites and pyroxenites; 2, layered gabbroids with a predominance of olivine meso- andmelanogabbroids; 3, layered gabbroids with a predominance of meso- and leucogabbroids; 4, gabbros and gabbronorites; 5, pegmatoid pyroxenites and gabbroids;6, ore minerals (sulfides, magnetite, and ilmenite); 7, olivine; 8, pyroxenes; 9, plagioclase; 10–12, f value of: 10, olivines; 11, orthopyroxenes; 12, clinopyroxenes;13, content of the anorthite end-member in plagioclases.

Table 1Average chemical composition of olivines from layered rocks of the Nui Chua massif

Component 1 2 3 4 5 6 7 8 9 10

x s x s x x s x s x s x s x s x s x s

FeO*, wt.% 28.65 2.26 26.7 0.91 27.8 28.4 2.19 27.99 1.32 29.19 1.56 30.36 1.88 29.21 1.81 30.19 2.28 30 0.71

MgO 34.23 2.49 35.17 1.26 33.56 34.19 0.84 35.39 1.54 33.96 1.49 31.8 1.88 34.44 1.5 33.38 1.18 31.99 1.09

CaO 0.04 0.04 0.02 0.01 0.02 0.02 0 0.02 0.01 0.02 0.01 0.03 0.02 0.02 0.01 0.02 0.01 0.04 0.03

NiO 0.09 0.02 0.07 0.01 0.06 0.06 0.03 0.08 0.02 0.08 0.03 0.09 0.02 0.08 0.03 0.07 0.02 0.1 0.05

Ni, ppm 707 170 509 84 462 453 195 597 165 593 211 686 164 629 200 516 139 786 360

f, % 31.3 2.5 30 1.18 31.6 31.8 2.02 30.6 1.69 32.5 1.71 34.9 2.65 32.3 2.04 33.6 2.32 34.3 1.29

Note. 1–10, layered rocks (n, number of analyses): 1, lherzolites and olivinites (n = 6); 2, melanotroctolites, olivine melanogabbros, and melanogabbronorites(n = 5); 3, ore-bearing olivine melanogabbronorites (n = 2); 4, ore-bearing melanogabbroids (n = 4); 5, mesocratic troctolites, mesocratic olivine gabbros, andgabbronorites (n = 36); 6, olivine-bearing mesocratic gabbronorites (n = 30); 7, ore-bearing gabbronorites (n = 16); 8, leucotroctolites, leucocratic olivinegabbros, and gabbronorites (n = 14); 9, olivine-bearing leucogabbronorites (n = 5); 10, ore-bearing leucogabbroids (n = 3). Hereafter, x, average value; s, variance;*, total iron as FeO.

G.V. Polyakov et al. / Russian Geology and Geophysics 50 (2009) 501–516 503

Table 2Average chemical composition of clinopyroxenes from different rock groups of the Nui Chua massif

Component 1 2 3 4 5 6

Kr6378 x s x s x s x s x

SiO2, wt.% 52.39 52.31 0.61 52.18 0.85 52.27 0.52 52.34 0.95 52.08

TiO2 0.85 0.82 0.13 0.82 0.1 0.78 0.17 0.76 0.11 0.65

Al2O3 2.6 2.48 0.08 2.55 0.4 2.34 0.3 2.08 0.44 1.78

Cr2O3 0.29 0.3 0.04 0.25 0.12 0.27 0.07 0.08 0.1 0.11

FeO* 6.86 6.51 0.86 7.48 1.32 7.38 0.97 9.28 0.93 9.6

MgO 15.7 15.59 0.53 15.74 0.87 15.06 0.56 14.42 0.65 14.21

CaO 21.13 21.02 1.11 20.2 1.99 21.37 0.81 20.04 2.17 20.54

Na2O 0.46 0.31 0.06 0.35 0.06 0.31 0.07 0.23 0.07 0.28

Wo, % 45.5 42 3.42 40.7 5.96 43.7 3.23 38.8 5.67 43

En 44.4 46.9 2.05 46.3 3.7 44 2.07 43.8 2.61 41.3

Fs 10.1 11.1 1.58 13 2.72 12.3 2.08 17.4 3.55 15.7

f 18.4 19.9 1.64 20.2 1.99 21.9 3.08 28.3 3.45 27.6

Note. 1–4, layered rocks (n, number of analyses): 1, plagiolherzolite (n = 1); 2, melanocratic olivine gabbros and gabbronorites (n = 6); 3, mesocratic olivinegabbros and gabbronorites (n = 16); 4, leucocratic olivine gabbros and gabbronorites (n = 7); 5, 6, pegmatoid rocks: 5, plagiowebsterites (n = 4); 6, melano-and mesocratic gabbronorites (n = 2).

Table 3Average chemical composition of orthopyroxenes from different rock groups of the Nui Chua massif

Component 1 2 3 4 5 6

x x s x s x s x x

SiO2, wt.% 53.7 54.58 0.47 53.91 0.84 54.11 0.63 53.94 52.83

TiO2 0.37 0.32 0.05 0.35 0.12 0.35 0.16 0.2 0.32

Al2O3 1.16 1.38 0.11 1.38 0.13 1.2 0.38 1.12 0.98

Cr2O3 0.12 0.07 0.05 0.14 0.11 0.15 0.11 0.08 0.1

FeO 16.58 16.44 1 17.83 1.72 16.53 1.29 20.17 22.15

MgO 27.17 26.16 1.13 25.54 1.3 25.91 2.42 23.11 23.12

CaO 1.05 1.72 0.61 1.34 0.58 1.91 2.03 2 0.94

Na2O 0.01 0.02 0.03 0.04 0.05 0.06 0.08 0.01 0.02

Wo, % 2.1 5.1 1.91 3.4 2.18 4.2 1.57 4.7 1.9

En 73 70.2 3.31 69.5 3.32 70.4 3.92 63.6 63.8

Fs 24.9 24.7 1.99 27.1 3.29 25.4 1.59 31.7 34.3

f 25.6 26.7 1.88 28.41 2.78 26.6 1.57 33.2 35.1

Note. 1–4, layered rocks (n, number of analyses): 1, plagiolherzolites (n = 2); 2, olivine melanogabbronorites (n = 7); 3, mesocratic olivine gabbronorites(n = 9); 4, olivine leucogabbronorites (n = 5); 5, 6, pegmatoid rocks: 5, plagiowebsterites (n = 2); 6, mesocratic gabbronorites (n = 2).

Table 4Average chemical composition of plagioclases from different rock groups of the Nui Chua massif

Component 1 2 3 4

x s x s x s x s

CaO, wt.% 13.82 0.45 13.59 0.35 13.51 0.57 13.45 0.72

Na2O 3.52 0.3 3.61 3.19 3.74 0.32 3.79 0.21

K2O 0.05 0.03 0.1 0.01 0.06 0.04 0.12 0.02

FeO 0.1 0.08 0.05 0.05 0.05 0.05 0.06 0.05

An, % 68.6 2.11 67.5 2 66.6 2.5 66.5 2.7

Ab 31.1 2.3 32 2.8 33 2.6 32.8 2.6

Or 0.3 0.2 0.5 0.2 0.4 0.2 0.7 0.1

Note. 1–3, layered rocks (n, number of analyses): 1, olivine melanogabbronorites (n = 4); 2, mesocratic olivine gabbronorites (n = 10); 3, olivine leucogabbroids(n = 5); 4, pegmatoid rocks: melanogabbronorites (n = 3).


Sobolev Institute of Geology and Mineralogy, Novosibirsk)with an error of 2% (Fig. 4). The MgO–Al2O3, MgO–TiO2,MgO–Fe2O3 diagrams reflecting the correlation between rock-forming and trace elements are different for the layered andpegmatoid rocks (Fig. 5). Note that the element trends for bothrock series are mainly subparallel, approaching the Ol–Pl,Cpx–Pl, and Opx–Pl fractionation trends to different extents.This is best seen on the MgO–Al2O3 diagram (Fig. 6), wherethe composition points of the layered rocks are arrangedbetween the Ol–Pl fractionation lines, whereas the composi-tion points of the pegmatoid rocks are shifted toward theOpx–Pl and Cpx–Pl fractionation trends. The pegmatoid rocksare richer in Fe2O3, TiO2, and V2O5 (Fig. 7) than the layeredones; the average compositions of both rock series are listedin Table 5.

The two rock series have specific patterns of trace andrare-earth elements. The layered rocks (Table 6) show aweakly fractionated positively sloped REE pattern, withchondrite-normalized contents of LREE varying from 2 (La)to 10 (Eu) and those of HREE, from 5 to 7. Lherzolites andolivine melanogabbronorites have a flattened element patternwith variations of primitive-mantle-normalized contents of Cs,Th, U, Pb, Sr, and P from 1 to 300 (Cs) and 2 to 5 (otherelements) (Balykin, 2002). The patterns show negative Nb,Ta, La, Ce, and Zr and positive Cs, U, Pb, Sr, and P anomalies.

Ore minerals in the layered rocks are mainly sulfides(pyrrhotite, pentlandite, and chalcopyrite) and sulfoarsenides

(Table 7). Oxide minerals magnetite, titanomagnetite, andilmenite are scarcer. Linneite, polydymite, heazlewoodite, andcobalt and nickel arsenides and sulfoarsenides are of episodicoccurrence. Sulfide dissemination prevails in the layered rocksof the main pluton body. Borehole LK 2, drilled in the uppersection of the layered rocks of the eastern block, exposed ninesulfide-enriched horizons. Regular fine sulfide disseminationincluding high-Ni (up to 1.0%) pyrrhotite (50–70%), high-Co(up to 4%) pentlandite (10–30%), and chalcopyrite (10–30%)is the most widespread. Mixed oxide-sulfide mineralizationconsisting of syngenetic pyrrhotite, pentlandite, and chalcopy-rite dissemination superposed by later magnetite, titanomag-netite, and ilmenite occurs less frequently. Analysis of theolivines and host layered rocks showed their commensurateNi contents. This indicates that in sulfidized gabbroids Niconcentrates mainly in the ore (sulfide) fraction, which ensuresa Ni potential of the layered rocks. In the pegmatoid taxiticand coarse-grained gabbroids and pyroxenites, fine ore dis-semination usually accompanies nest-like and schlieric segre-gations of chalcopyrite, magnetite, titanomagnetite, andilmenite, which locally reach their commercial concentrations(Cay Cham deposit).

The PGE mineralization revealed in the layered rocks(Polyakov et al., 1984, 1999) consists of sperrylite, paolovite,sobolevskite, michenerite (Table 8), and other rare Pt and Pdminerals. We revealed PGE mineralization in sulfide-enrichedgabbroids and lherzolites from the deep horizons of the layered

Fig. 3. Distribution of the compositions of plagioclases (n = 131) (a), olivines (n = 123) (b), and clino- and orthopyroxenes (n = 30) (c) from the Nui Chua massifrocks. Pyroxene compositions were recalculated in the coordinates Wo(Di–Hd)–En–Fs by Lindsley’s (1983) method. Isotherms are given for P = 5 kbar. n, numberof runs.


Tab

le 5

Ave

rage

che

mic

al c

ompo

sitio

n of

dif

fere

nt r

ock

grou

ps o

f th

e N

ui C

hua

mas

sif

(wt.%

) co

nver

ted

to a

vol

atile

-fre

e ba

sis

Para

met

erSi

O2

TiO

2A

l 2O

3Fe

O*

MnO

MgO

CaO

Na 2

OK

2OP 2

O5

Roc

k, n

umbe

r of

run

s (n

)

Lay

ered

roc

k se

ries

x41

.29

0.22

5.06

22.6

70.

2724

.66

5.22

0.27

0.16

0.06

1. P

lagi

olhe

rzol

ites

and

oliv

inite

s, n

= 3

s1.

100.

110.

831.

470.

060.

471.

980.

320.

110.

04

x38

.92

0.20

3.82

26.2

60.

2726

.84

3.34

0.25

0.07

0.04

2. O

re-b

eari

ng p

lagi

olhe

rzol

ites,

weh

rlit

es,

and

oliv

inite

s, n

= 9

s3.

210.

121.

471.

890.

061.

381.

460.

210.

090.

03

x40

.50

0.21

3.94

23.7

40.

2727

.03

3.88

0.28

0.10

0.05

3. U

ltram

afite

s (a

vera

ge):

1 +

2,

n =

12

s2.

010.

111.

472.

550.

062.

231.

690.

030.

030.

03

x45

.11

0.22

13.4

113

.32

0.20

17.2

39.

011.

080.

300.

124.

Mel

anot

roct

olite

s an

d ol

ivin

e m

elan

ogab

bron

orite

s, n

= 5

s1.

520.

071.

021.

980.

021.

271.

340.

340.

330.

11

x48

.03

0.42

10.3

012

.69

0.21

15.8

811

.28

0.98

0.13

0.06

5. M

elan

ogab

bron

orite

s, n

= 5

s1.

100.

091.

690.

690.

030.

611.

240.

210.

070.

08

x42

.70

0.23

10.7

219

.73

0.23

18.2

67.

130.

880.

080.

066.

Ore

-bea

ring

mel

anot

roct

olite

s, o

livi

ne m

elan

ogab

bron

orite

s,

and

gabb

ros,

n =

10

s2.

710.

142.

973.

260.

045.

412.

420.

330.

090.

07

x45

.28

0.28

11.4

515

.16

0.22

17.6

58.

760.

970.

150.

087.

Sub

ultr

amaf

ites

(ave

rage

): 4

+ 5

+ 6

, n

= 20

s2.

800.

142.

623.

820.

045.

992.

590.

310.

190.

08

x44

.41

0.21

16.1

914

.76

0.17

12.5

010

.05

1.50

0.13

0.09

8. M

esoc

ratic

tro

ctol

ites,

oliv

ine

gabb

rono

rite

s, a

nd g

abbr

os,

n =

24

s8.

030.

094.

234.

040.

054.

102.

440.

570.

090.

08

x48

.63

0.34

16.3

69.

990.

1710

.60

12.0

71.

590.

160.

099.

Mes

ocra

tic g

abbr

onor

ites

and

gabb

ros,

n =

45

s1.

430.

091.

741.

780.

032.

011.

880.

410.

080.

07

x47

.55

0.32

16.9

511

.63

0.16

9.47

12.0

61.

570.

160.

1210

. O

re-b

eari

ng m

esoc

ratic

oliv

ine

gabb

roid

s, n

= 2

5

s1.

310.

061.

771.

260.

021.

851.

050.

470.

150.

08

x48

.37

0.30

17.1

59.

590.

1710

.63

11.9

01.

630.

160.

1011

. M

afite

s (a

vera

ge):

8 +

9 +

10,

n =

94

s1.

640.

101.

851.

820.

022.

041.

580.

430.

100.

08

x47

.77

0.18

22.3

97.

420.

117.

9811

.73

2.09

0.25

0.06

12.

Leu

cotr

octo

lites

, le

ucoc

ratic

oliv

ine

gabb

rono

rite

s, a

nd g

abbr

os,

n =

15s

1.17

0.07

1.17

0.86

0.02

1.07

0.82

0.29

0.08

0.07

x49

.28

0.35

20.3

88.

060.

147.

3111

.76

2.30

0.30

0.12

13.

Leu

coga

bbro

nori

tes

and

leuc

ogab

bros

, n

= 11

s1.

400.

320.

761.

310.

020.

851.

310.

560.

340.

12

x48

.95

0.45

24.3

07.

490.

123.

3311

.94

2.63

0.69

0.10

14.

Ano

rtho

site

s, n

= 8

s1.

500.

423.

161.

680.

052.

551.

200.

150.

480.

09

x48

.19

0.24

20.2

010

.58

0.13

6.70

11.6

02.

000.

290.

0715

. O

re-b

eari

ng o

livin

e le

ucog

abbr

os,

n =

6

s1.

170.

061.

122.

290.

030.

711.

320.

240.

200.

07

x47

.71

0.25

27.0

87.

490.

081.

5312

.31

2.26

0.84

0.09

16.

Ore

-bea

ring

ano

rtho

site

s, n

= 3

s0.

640.

141.

300.

710.

050.

611.

430.

250.

450.

09

x48

.91

0.30

22.2

27.

110.

136.

7011

.94

2.25

0.35

0.09

17.

Leu

coba

site

s (a

vera

ge):

12

+ 1

3 +

14 +

15

+ 16

, n

= 43

s1.

410.

282.

331.

600.

032.

271.

060.

420.

310.

09


Tab

le 5

(co

ntin

ued)

Para

met

erSi

O2

TiO

2A

l 2O

3Fe

O*

MnO

MgO

CaO

Na 2

OK

2OP 2

O5

Roc

k, n

umbe

r of

run

s (n

)

Peg

mat

oid

rock

ser

ies

x49

.85

0.49

10.2

713

.15

0.25

15.0

49.

830.

960.

100.

0718

. W

ebst

erite

s an

d m

elan

ogab

bron

orite

s, n

= 4

s2.

010.

151.

022.

140.

061.

060.

870.

290.

080.

06

x47

.63

0.71

6.79

17.8

90.

2615

.53

10.1

90.

700.

140.

1619

. O

re-b

eari

ng w

ebst

erit

es a

nd m

elan

ogab

bron

orite

s, n

= 7

s2.

330.

333.

593.

140.

043.

374.

220.

350.

120.

22

x49

.37

0.64

8.19

14.5

70.

2615

.64

10.2

60.

810.

130.

1320

. Su

bultr

amaf

ites

(ave

rage

): 1

8 +

19,

n =

11

s2.

100.

313.

343.

040.

052.

753.

410.

340.

100.

18

x49

.99

0.48

14.9

111

.62

0.18

9.70

11.4

41.

390.

140.

1521

. M

esoc

ratic

gab

bron

orit

es a

nd g

abbr

os,

n =

7

s0.

900.

152.

802.

580.

022.

091.

200.

580.

070.

03

x47

.96

0.41

15.1

518

.05

0.20

8.25

8.51

1.24

0.14

0.10

22.

Ore

-bea

ring

gab

bron

orite

s an

d ga

bbro

s, n

= 4

s2.

050.

083.

132.

260.

053.

534.

060.

720.

100.

08

x50

.56

0.47

15.3

611

.90

0.20

9.36

10.5

31.

350.

140.

1323

. M

afite

s (a

vera

ge):

21

+ 22

, n

= 11

s1.

600.

142.

602.

940.

052.

522.

670.

600.

080.

06

x48

.56

0.98

15.4

112

.91

0.20

7.46

12.2

41.

620.

370.

2424

. G

abbr

oids

of

endo

cont

act

faci

es,

n =

9

s1.

751.

031.

933.

790.

052.

432.

520.

350.

370.

26

Table 6Petrogeochemical composition of some types of layered rocks from the NuiChua massif

Component Kr6404A T180 B6115 T175

1 2 3 4

SiO2, wt.% 42.44 — 48.52 48.95

TiO2 0.26 — 0.36 0.32

Al2O3 5.35 — 16.73 15.74

FeO* 19.26 — 7.72 9.46

MnO 0.25 — 0.17 0.17

MgO 26.36 — 11.35 12.39

CaO 5.53 — 13.02 11.44

Na2O 0.47 — 1.96 1.47

K2O 0.05 — 0.00 0.03

P2O5 0.02 — 0.16 0.03

Ni, ppm 1021 1792 190 149.4

Co 140 179.5 46 45.04

Sc 30 18.19 37 22.16

Cu 1038 1074 57 52.95

Cr 580 174.1 595 555.5

V — 117 — 199

Rb 0.8 0.96 0.3 1.5

Sr 39 27.71 159 106

Y 6.2 6 9.1 5.89

Zr 4.4 5.15 10.5 4.7

Ta 0.02 0.01 0.02 0.02

Nb 0.2 0.14 0.2 0.3

Cs 1.4 1.84 0.3 0.76

Ba — 5.12 — 13.18

La 0.35 0.41 0.8 0.58

Ce 1.1 1.09 2.4 1.33

Nd 1 1.05 2.2 1.12

Sm 0.35 0.44 0.84 0.43

Eu 0.2 0.2 0.54 0.46

Gd 0.6 0.69 1.2 0.68

Tb 0.15 0.11 0.24 0.11

Yb 0.66 0.59 0.95 0.58

Lu 0.1 0.1 0.15 0.09

Hf 0.2 0.2 0.3 0.2

Th 0.1 0.05 0.3 0.1

U 0.2 0.02 0.3 0.03

Dy — 0.92 — 0.91

Ho — 0.21 — 0.21

Er — 0.57 — 0.57

Pb — 2.39 — 1.31

Pr — 0.18 — 0.2

Tm — 0.09 — 0.1

Note. 1–4, layered rocks: 1, 2, plagiolherzolites; 3, 4, olivine melanogab-bronorites. Analyses were carried out by: 1, 3, neutron activation method,Institute of Geology and Mineralogy, Novosibirsk (Poliakov et al., 1996);2, ICP MS, Department of Geosciences, Franklin and Marshall College, USA;4, ICP MS, Department of Geosciences of National Taiwan University, Taipei(Hoang Huu Thanh et al., 2004). Dash, no determination.


rocks in the eastern block of the massif, exposed by BH-LK 2(near the peak of Mt. Nui Chua) at depths of 418 and438–440 m. Sperrylite occurs as cubic crystals up to 15 mmin size in paragenesis with nickeline, Co sulfoarsenides, and

michenerite. Palladium minerals were found as intergrowthswith Co and Ni sulfoarsenides and arsenides and as fineinclusions in these minerals. High contents of Pd and Sb weredetected in maucherite, Co and Ni sulfoarsenides, and pent-landite; in breithauptite their contents reach 3.15%.

The above geological data and mineral and geochemicalcompositions of the Nui Chua rocks show that they belong totwo successively formed associations: layered and pegmatoidseries (the latter is compositionally similar to the endocontactfacies rocks). These rock series are of different ore speciali-zations: sulfide PGE-Cu-Ni (layered rocks) and oxide Fe-Ti-V(pegmatoid rocks). The compositions of these series, includingthe specific mineralogical and geochemical features, evidencetheir consanguinity and, at the same time, stable significantdifferences, which suggests their different parental melts.Based on the available representative petrochemical data onthe recognized rock series, we have obtained preliminaryestimates of the possible compositions of their parental melts.

Estimated compositions of parental melts for the layered and pegmatoid rock series and their ore-geochemical features

Challenging problems of petrology are to determine thecompositions of parental melts for complex ultramafic-maficplutons with magmatic layering and to model their formation.

Fig. 4. Nonlinear discrimination of layered (black points) and pegmatoid (lightsquares) rocks. Bold line is a discriminant.

Fig. 5. Correlations between rock-forming and trace elements in the layered (1) and pegmatoid (2) rocks.

508 G.V. Polyakov et al. / Russian Geology and Geophysics 50 (2009) 501–516

In our case, the problem is complicated by the presence ofmafic and subultramafic pegmatoid rocks in the Nui Chuapluton and other massifs of this complex. As shown above,these rocks played a significant role in the pluton formation.Basic pegmatoids are of crucial importance not only inpetrological but also in ore-geochemical models of the forma-tion of layered plutons (Barnes and Campbell, 1988; Konnikovet al., 2002; MacDonald et al., 1989; Zolotukhin, 1997).

Taking into account the consanguinity and phase proportionsof the layered and pegmatoid series of the Nui Chua massif,we made separate estimations of the compositions of theirparental melts and then compared them and discussed theresults.

The composition of parental melts of layered series isusually estimated from the average or weighted averagecompositions of the layered massifs as a whole or theirseparate, most complete rhythms. Sometimes, data on thecomposition of the quenched facies of corresponding intru-sions are invoked. We estimated the validity of the composi-tions thus obtained using the Pluton software designed at theSobolev Institute of Geology and Mineralogy, Novosibirsk(Lavrenchuk, 2004).

The model calculations are based on the data on thesequence of the appearance of liquidus minerals and theircomposition, the depth of the intrusion formation, and thewater content in the melt.

For the layered rocks of the Nui Chua massif, the followingsequence of the appearance of liquidus minerals was estab-lished: Ol–Pl → Px. A specific feature of these rocks is thepresence of orthopyroxenes and invertible pigeonite withexsolution structures. The formation pressure for the layeredseries does not exceed 2 kbar, because the endocontact zonecontains hornfelses and the enclosing rock complex consistsof weakly metamorphosed facies. The parental melt, mostlikely, contained water, as indicated by the presence of minorcontents of hornblende and phlogopite as accessory minerals.

If we take the average composition of the layered andpegmatoid series of the Nui Chua massif as a parental melt,we obtain the sequence of their model compositions shown inFig. 8. In this case, the model and real compositions of therocks differ significantly in all main components. The samegreat difference is obtained in the model calculations based

Fig. 6. Al2O3–MgO composition diagram for the Nui Chua massif rocks con-verted to a dry base. 1, layered rocks: plagioclase lherzolites and olivinites,melano-, meso-, and leucocractic olivine gabbros, gabbronorites, and troctolites,olivine leucogabbronorites and anorthosites; 2, pegmatoid rocks: pla-giowebsterites and melanogabbronorites, meso- and leucocratic gabbros andgabbronorites; 3, gabbroids of endocontact facies. The diagram shows thecompositional variations of the main rock-forming minerals: Ol, olivine, Pl,plagioclase, Cpx, clinopyroxene, Opx, orthopyroxene. Solid bold lines mark thecomposition trends of layered (1), pegmatoid (2), and endocontact (3) rocks, andthin lines, the Ol–Pl, Opx–Pl, and Cpx–Pl fractionation trends.

Fig. 7. Histograms of TiO2 and V distribution in the Nui Chua massif rocks. Rocks: 1, layered; 2, pegmatoid.


Table 7Chemical composition of sulfides and sulfoarsenides from the Nui Chua rocks and ores (wt.%)

No. Sample Fe Ni Co Cu As Sb Se S Total

1 LK2-167 59.12 0.55 0.08 0.01 N.f. N.f. — 39.02 98.782 LK2-439 60.02 0.27 0.07 N.f. N.f. N.f. — 38.23 98.593 P9 61.94 0.21 0.05 0.01 0.1 — 0.01 37.52 99.84

4 P12 61.07 0.34 0.12 N.f. 0.09 — 0.03 38.07 99.725 P14 60.66 0.68 0.03 0.06 0.1 — 0.06 38.84 100.43

6 P25B 61.18 0.04 0.06 0.01 0.08 — 0.03 37.62 99.027 B5036 59.24 1.01 0.08 0.01 0.12 — N.f. 38.77 99.23

8 G1141 59.68 0.74 0.02 0.05 0.05 — 0.02 38.86 99.429 G1444 59.29 0.57 0.21 N.f. N.f. — N.f. 39.37 99.44

10 G1153 60.07 1.08 0.08 0.02 N.f. — N.f. 38.93 100.1811 G1154 59.08 0.57 0.08 0.02 0.02 — N.f. 39.35 99.1312 LK2-167 31.83 28.51 4.79 0.04 N.f. N.f. — 33.55 98.72

13 P9 31.7 32.23 2.46 0.07 0.01 — 0.1 32.72 99.2914 P12 32.33 31.66 2.21 0.07 0.03 — 0.01 32.42 98.43

15 P14 30.33 33.32 2.13 N.f. 0.15 — 0.06 32.45 98.4416 P25B 31.19 30.48 4.03 0.05 0.09 — 0.04 32.64 98.52

17 Kr6404A 34.42 29.51 1.96 0.13 0.07 — 0.04 32.65 98.7818 G1141 29.96 33.95 2.34 N.f. 0.02 — 0.05 33.06 99.3819 G1144 28.74 22.65 13.4 0.16 N.f. — N.f. 34.89 99.84

20 G1153 29.01 34.28 2.92 0.03 0.03 — N.f. 33.01 99.2821 G1154 27.71 34.25 3.49 0.05 0.02 — 0.06 33.14 98.72

22 P9 30.79 0.03 0.06 34.49 0.07 — 0.07 34.89 100.423 P12 30.58 0.64 0.1 33.18 0.07 — N.f. 34.42 98.99

24 B5036 30.94 0.01 0.03 34.35 0.06 — 0.06 34.62 100.0725 Kr6404A 40.94 0.1 0.06 22.6 0.12 — 0.03 35.06 98.91

26 LK2-438 30.43 0.15 0.08 33.64 N.f. N.f. — 34.47 98.7727 LK2-439 30.27 0.03 0.02 34.41 N.f. N.f. — 34.05 98.7828 LK2-167 4.99 11.37 19.67 N.f. 47.53 0.01 — 17.94 101.51

29 LK2-438 4.95 12.55 18.11 N.f. 46.14 0.62 — 18.43 100.830 P25B 3.43 2.49 30.88 0.01 44.57 — 0.2 19.46 101.04

31 LK2-167 0.51 42.5 0.87 0.07 54.44 0.36 — 0.24 98.9932 LK2-438 1.16 50.77 0.4 0.06 48.39 0.06 — 0.04 100.88

33 LK2-439 40.54 0.01 0.05 23.27 N.f. N.f. — 34.66 98.53

Note. 1–11, pyrrhotite; 12–21, pentlandite; 22–27, chalcopyrite; 28–30, cobaltite; 31, 32, nickeline; 33, cubanite. Samples 28 and 32 have high contents of Pd(0.12 and 0.14 wt.%, respectively). Analyses were carried out on a Camebax Micro probe at the UIGGM, Novosibirsk (analysts O.N. Maiorova andO.S. Khmel’nikova). Dash, no determination. N.f., not found.

Table 8Composition of PGE minerals from the Nui Chua rocks and ores (wt.%)

No. Sample Pt Pb Ni As Sn Sb Te Bi Total

1 LK2-418 51.45 0.54 2.4 43.86 — 0.56 — — 98.81

2 The same 52.56 0.67 1.14 43.34 — 0.69 — 0.04 98.44

3 The same — 64.25 — — 36.74 0.59 — — 101.58

4 The same — 63.9 — — 36.77 0.84 — — 101.51

5 The same 0.08 25.37 0.1 — 0.03 1.87 30.77 44.04 102.26

6 The same — 25.32 0.1 — 0.04 2.13 31.55 43.55 102.49

7 The same 51.89 1.1 1.59 43.68 0.02 0.41 — 0.12 98.81

8 The same — 65.11 — — 35.28 2.41 — — 102.8

9 The same — 3.09 29.3 0.32 0.03 65.2 0.35 0.04 98.33

10 The same 0.03 3.15 29.29 0.31 0.02 66.4 0.4 — 99.6

11 LK2-439 — 64.12 — — 37.02 0.65 — — 101.79

12 The same — 64.64 — — 37.19 0.6 — — 102.43

13 The same 0.08 38.3 — — 0.1 7.11 14.72 41.76 102.07

14 The same 0.06 38.55 — — 0.09 7.18 14.69 41.72 102.29

Note. 1, 2, 7, sperrylite; 5, 6, michenerite; 3, 4, 8, 11, 12, paolovite; 13, 14, sobolevskite; 9, 10, breithauptite. Analyses were carried out on a Camebax Microprobe at the UIGGM, Novosibirsk (analyst O.S. Khmel’nikova). Dash, no determination.

510\ G.V. Polyakov et al. / Russian Geology and Geophysics 50 (2009) 501–516

on parental melt of composition similar to the averagecomposition of the layered rocks.

Better results are obtained when medium-Ti basalts (M001)from the Permo-Triassic volcanic complex of the Song Hienzone neighboring the Phu Ngu zone are taken as a parentalmelt. These basalts are comagmatic to the layered Nui Chuamassifs, as evidenced from their close ages and similargeochemistry. Analysis of the trace-element and REE patternsof Permo-Triassic basalts from the Song Hien zone andlayered rocks from the Nui Chua massif showed their similar

geochemical features: enrichment in LILE and depletion in Taand Nb (Figs. 9 and 10).

The obtained data evidence that the Song Hien zone basaltsand layered rocks of the Nui Chua massif belong to the sametype of basites with suprasubductional geochemical features.The Song Hien basalts show negative Sr and Eu anomalies,and the Nui Chua gabbroids are characterized by the positiveanomalies of these elements. This complementary distributionof elements might be due to the plagioclase fractionation inintermediate chamber, e.g., in the Nui Chua massif, wheregabbroids are enriched in cumulose plagioclase. The Song

Fig. 8. Compositions of the Nui Chua rocks. 1, layered series; 2, pegmatoid series; 3, rock compositions obtained on the Pluton software modeling of the intrachamberdifferentiation of the average massif composition (both rock series).


Hien zone basalts can be considered residual melts effusedfrom the intermediate chamber. The parental composition ofmagma in this chamber is likely to be intermediate betweenthose of the Song Hien basalts and early cumulates of thelayered Nui Chua massif.

The model calculations of the fractional crystallization ofmelt compositionally corresponding to basalt M001 (its chemi-cal composition and composition of parental melt calculatedfrom the latter are given in Table 9) show the following

sequence of the appearance of liquidus phases: Ol + Pl →Pl + Px. By our observations, this sequence is typical of therocks of the middle and upper parts of the Nui Chua massif.For using this melt composition for the whole layered seriesof the Nui Chua massif, it is necessary to add 10% olivine(the earliest cumulose mineral) with Mg# = 70–75%. Thisassumption is likely to be valid given a high probability of an

Fig. 9. Primitive-mantle-normalized (Sun and McDonough, 1989) multielemen-tal patterns for basalt M001 from the Song Hien zone and gabbroids of thelayered series from the Nui Chua massif. 1, gabbroids; 2, basalts. Fig. 10. C1 chondrite-normalized (Henderson, 1984) REE patterns for basalt

M001 from the Song Hien zone and gabbroids of the layered series from the NuiChua massif. For designations, see Fig. 9.

Table 9Chemical composition of medium-TiO2 basalt from the Song Hien zone and tentative composition of parental melts calculated from it for the layered andpegmatoid rock series of the Nui Chua massif (wt.%)

No. SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5

1 49.35 1.14 15.53 10.68 0.20 8.70 10.71 2.11 1.45 0.132 38.38 0.00 0.00 25.37 0.00 36.25 0.00 0.00 0.00 0.003 48.25 1.02 13.98 12.15 0.18 11.46 9.64 1.90 1.31 0.114 49.08 1.40 14.22 13.89 0.00 6.59 10.74 2.18 1.73 0.15

Note. 1, medium-TiO2 basalt (M001) from the Song Hien zone; 2, composition of early-cumulose olivine; 3, tentative composition of parental melt for thelayered rock series (M001 basalt + 10% olivine); 4, tentative composition of parental melt for the pegmatoid series (M001 basalt + 10% olivine compositionfractionated to a degree of 30%).

Table 10Average compositions of the layered and pegmatoid rock series from the intrusions of the Nui Chua complex (wt.%)

Massif Series Parameter SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 n

Nui Chua A x 47.89 0.29 17.11 10.01 0.17 11.50 11.07 1.65 0.22 0.09 165

s 7.71 0.03 26.92 20.92 0.00 34.99 7.51 0.45 0.06 0.01

B x 50.59 0.73 14.22 10.75 0.21 10.19 11.76 1.16 0.24 0.16 24

s 5.69 0.63 21.56 13.20 0.00 16.09 6.39 0.32 0.14 0.01

Khao Que A x 47.62 0.28 16.35 5.67 0.15 12.52 15.98 1.01 0.22 0.20 98

s 2.55 0.05 23.07 9.68 0.00 33.79 8.09 0.31 0.04 0.00

B x 46.77 1.28 14.41 9.94 0.17 5.50 16.66 1.73 0.91 0.35 18

s 5.29 0.56 14.53 8.91 0.00 6.17 17.77 0.96 0.54 0.03

Tri Nang A x 48.43 0.23 18.13 5.80 0.15 11.50 13.76 1.60 0.24 0.16 118

s 5.76 0.02 25.64 9.17 0.00 41.93 9.74 0.68 0.06 0.00

B x 49.16 0.53 13.11 6.79 0.15 10.07 16.00 1.39 0.20 0.21 16

s 3.56 0.08 28.98 4.76 0.00 5.81 11.57 0.57 0.02 0.01

Nui YenChu

A x 45.40 0.24 17.40 6.69 0.15 15.98 12.86 0.84 0.25 0.19 47

s 7.58 0.04 43.77 6.11 0.00 124.01 22.95 0.26 0.07 0.01

B x 50.72 0.38 11.40 9.70 0.18 11.45 12.48 1.41 0.59 0.20 9

s 5.21 0.01 10.59 5.59 0.00 11.08 14.76 0.59 0.16 0.01

Note. Series: A, layered; B, pegmatoid; n, number of runs.


increased part of ultramafites at the unexposed deep levels ofthe massif.

We have established that with the model melt of thiscomposition, the formed sequence of rocks has almost thesame petrogenetic characteristics as the real associations oflayered rocks of the Nui Chua massif (Fig. 11). The modelcompositions of minerals are similar to the real ones in themassif rocks. Olivine has f = 28–41% (calculated f = 20–35%);plagioclase bears 65–75% An (calculated value is 70–77%An). The above calculations evidence that the intrachamber

fractionation of magma of this composition should be accom-panied by the accumulation of residual melts enriched inalkalies. Correspondingly, the crystallization products of thesemelts and the late cumulates should approach monzodioritesby composition. Note that such rocks were found in smallersatellite intrusions in the western endocontact of the Nui Chuamassif, including the studied Son Dau massif. Rocks corre-sponding in chemical composition to monzodiorites are alsopresent in pegmatoid series in some other massifs of the NuiChua complex (Khao Que, Nui Yen Chu, etc.), which is

Fig. 11. Compositions of rocks from the Nui Chua and Son Dau massifs. 1–3, Nui Chua massif: 1, layered series; 2, pegmatoid series; 3, rock compositions obtainedon the Pluton software modeling of the intrachamber differentiation of parental melt compositionally corresponding to basalt M001 + 10% olivine (Table 9); 4, SonDau massif.


reflected in the average compositions of these pegmatoid series(Table 10). The calculations also showed that such a differ-entiation should lead to the enrichment of residual melts andlate cumulates with Ti, which explains the formation of theCay Cham titanomagnetite-ilmenite deposit related to thetaxitic and pegmatoid rocks of the eastern block of the NuiChua massif.

We attempted to model the formation of pegmatoids in theNui Chua massif. As noted above, these rocks differ from thelayered rocks of the massif in having no olivine. The modeling

of the sequence of formation of the layered rocks showed thatolivine disappears when the degree of fractionation of parentalmelt of the above composition reaches 30%. The obtained setof rock compositions is far from that of the real pegmatoidrocks by SiO2, FeO, and K2O and is very similar to it byCaO, MgO, Na2O, and TiO2 (Fig. 12).

Thus, the model constructions confirm the genetic relation-ship of the Nui Chua pegmatoid series with the layered oneand permit it to be considered derivates of late residual meltsevolved toward their enrichment in alkalies and Ti. This is

Fig. 12. Compositions of rocks from the Nui Chua and Son Dau massifs. 1, layered series of the Nui Chua massif; 2; 3, rock compositions obtained on the Plutonsoftware modeling of the intrachamber differentiation of parental melt compositionally corresponding to basalt M001 + 10% olivine fractionated to a degree of 30%(Table 9): 2, rocks; 3, residual melts; 4, Son Dau massif.


evidenced from the appearance of monzonitoids in pegmatoidsof some massifs of the Nui Chua complex (Khao Que, NuiYen Chu, etc.). In the pegmatoid gabbronorites of the NuiChua massif, high alkalinity is expressed as the enrichment ofplagioclases in orthoclase. Probably, the pegmatoid series ofthis massif can be associated with biotite gabbros andmonzodiorites of small satellite intrusions (Son Dau, etc.) onthe western flank of the Nui Chua massif, which wererecognized and first described by E.P. Izokh and Nguyen VanChien (Dovzhikov et al., 1965).

As shown above and in our previous works (Poliakov et al.,1996; Polyakov et al., 1984, 1999), the layered rock series ofthe Nui Chua massif, particularly at deep unstripped levels, iscertainly productive as to sulfide and low-sulfide PGE-Cu-Nimineralization. The products of the late stage of its formation,including the pegmatoid rocks (derivates of residual melts),are rich in Ti and V. In the eastern block of the Nui Chuamassif (Cay Cham deposit), these rocks bear titanomagnetite-ilmenite mineralization. In our opinion, it is highly topical toestimate the V productivity of this mineralization. Similarmineralization might be expected in pegmatoid biotite gabbrosand monzodiorites on the less denuded western flank of themassif. The ore potential of the Nui Chua massif might bestill higher in view of the fractionation of parental melts inlarge deeper-seated intermediate chambers.

This work was supported by grants 07-05-00825 and08-05-90304-V’et-a from the Russian Foundation for BasicResearch, grants NSh-2715.2008.5 and MK-5023.2007.5 fromthe Scientific School, and Integration Project 6.11 from theSiberian Branch of the RAS.

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Editorial responsibility: A.S. Borisenko


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The Nui Chua layered peridotite-gabbro complex as manifestation of Permo-Triassic mantle plume in northern Vietnam