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Evolution of Precambrian REE mineralization
Precambrian Research, 27 (1985) 131--151
131
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EVOLUTION OF PRECAMBRIAN
REE MINERALIZATION
TU GUANGZHI, ZHAO ZHENHUA and QIU YUZHUO
Institute of Geochemistry. Academia Sinica, Guiyang, Guizhou Province (People's Republic of China)
ABSTRACT Tu, G.-Z., Zhao, Z. and Qiu, Y., 1985. Evolution of Precambrian REE mineralization. Precambrian Res., 27: 131--151. Archaean BIF of the world generally contain only minor amounts of REE (20--30 ppm or less), but some of the post-Archaean iron-bearing and other formations of China contain several thousand ppm or even up to several percent of total REE. The following types of Proterozoic REE mineralization can be distinguished: (1) carbonate-hosted Fe--REE deposits; ( 2 ) carbonate-hosted REE mineralization; (3) REE--Fe or REE--Fe--B mineralization in metamorphosed--migmatized volcanic and volcano-sedimentary rocks; (4) REE--Fe mineralizations in clastic sedimentary beds; and (5) REE in phosphorite deposits. Large quantities of REE in sea water begin to precipitate only when the CO: content of the atmosphere drastically decreases, because the REE may occur in carbonate and phosphate minerals or isomorphically replace Ca 2. in oceanic sediments. As a CO2--N: atmosphere probably prevailed prior to the Proterozoic, the high CO: partial pressure not only restricted the precipitation of REE-bearing carbonates, but also promoted the appearance of easily soluble H:PO~. Hence, REE-rich carbonates and phosphates scarcely occur in large amounts in Archaean sediments. Only with the decrease of CO2 in the early Proterozoic did REE-bearing dolomite, REE carbonate and phosphate minerals begin to appear in noticeable quantities. The high concentration of Fe, REE and P in Proterozoic sediments seems to have evolved with geologic time. The peak of Fe accumulation appeared in the early Proterozoic, the mid-Proterozoic was favourable for REE, while large P concentrations appeared in the late Proterozoic and early Cambrian. In all of the above-mentioned types of REE mineralization, the REE distribution patterns are highly fractionated with significant light rare earth enrichment. Early Proterozoic deposits display distinct positive or no Eu anomalies, whereas middle and late Proterozoic ores show negative Eu anomalies.
INTRODUCTION In 1977 T u G u a n g z h i p r o p o s e d the t e r m " R E E - - F e f o r m a t i o n s " for the P r o t e r o z o i c F e d e p o s i t s o f C h i n a w h i c h are r i c h i n R E E , o f t h e o r d e r o f 1 0 t o 1 0 0 t i m e s t h e a v e r a g e R E E c r u s t a l c o n t e n t . L a t e r Q i u Y u z h u o e t al. ( 1 9 8 1 ) s t u d i e d t h e R E E d i s t r i b u t i o n p a t t e r n s o f R E E - - F e f o r m a t i o n s . Par-
132 ticularly the famous Baiyun Obo R E E - - Fe --N b deposits have been systematically studied in r ecent years. Based on these investigations, we summarize the principal types of Precambrian REE mineralization in China according to their geochemical and genetic features. The relationship between the REE distribution patterns and the chemical evolution of the Precambrian crust is also discussed (Taylor, S.R., 1979). ANALYTICAL METHODS Total REE contents of various ores and wall rocks were determined by chemical co lo r im e t r y with uncertainties of 10--20%. Individual REE abundances were d ete r m i ne d using an ion-exchange m e t h o d for separation and Xray fluorescence s p e c t r o m e t r y for analysis. Analytical errors for the elements o f higher concentrations were ~ 2--5%, whereas for those with lower concentrations (<1%) errors were ~ 10--20%. TYPES OF PRECAMBRIAN REE MINERALIZATION IN CHINA It has been n o t e d t hat Archaean BIF all over the world on average contain 20--30 p p m or less of the total REE concentrations {Fryer, 1977). This is in strong contrast with m a n y Proterozoic BIF formations which are much higher in REE, o f ten o f the order of thousands of ppm to several percent. The widespread Archaean Anshan-type iron deposits o f eastern Hebei and southern Liaoning are o f the Algoman-type and are related to intermediate to basic submarine volcanic activity. Table I shows their REE contents. It is clear th at th e Archaean iron formations in China rarely contain more than 100 p p m o f total REE, which is far below the crustal average of 210 ppm (Vinogradov, 1962). This is also true for Archaean BIF in ot her countries. Proterozoic R E E - - F e formations are widespread in China. The following t y p es o f R EE mineralization can be distinguished: (1) Carbonate-hosted REE--Fe deposits. These have been found in several TABLE I Total REE content of some Archaean iron formations Ore (rock) type
Location
zREE (in pprn)
Reference
Banded magnetite ore Magnetite quartzite Magnetite quartzite Hornblende magnetite quartzite Quartz--nmgnetite--amphibole banded rock Banded quartz-rich iron-fro. Carbonate facies iron-fro Banded magnetite--haematite iron-fro.
Anshan, China Anshan, China Hujiamiao, China Shuichang, China
21 78 27 20a
this this this this
N.E. Finland Wyoming, U.S.A. Michipicoten, Canada Mary River, Canada
17 11.5 9.9 14.5
Fryer (1977) Fryer ( 1977 ) Fryer (1977) Fryer (1977)
aRE203.
paper paper paper paper
133 t"e
-
l:e
-~N
f4"
-
....
It
. . . . . . . .
11 '
Fig. 1. Geological section of the Baiyun Obo R E E - - F e - - N b ore deposits, scale 1:30 000. Fe: ore b o d y ; -~: Hercynian granite; . : migmatite; H: Baiyun Obo G r o u p ; 9: black slate; 6--8: dolomite, limestone, quartzite; 5: black slate; 4: dark quartzite; 3: black slate; 2: white quartzite; 1 : conglomerate, quartzite; W: Wutai Group: gneiss, schist.
120 °
..... .
.
.
.
.
.
J
-
]
Fig. 2. Geological section of the Dianyi Fe---Cu--REE ore deposits, scale 1 : 1 5 0 0 0 . 1, argillaceous dolomite; 2, slate; 3, ore body.
356 ° ~-.,.... CK4
~>~'--. ./'/
3
o
/ i/
I ~1~
Fig. 3. Geological section of the Minsong F e - - R E E - - P ore deposits, scale 1:2500. Mar: marble; MQ: mica--quartz-schist; e: syenite; 75: granodiorite; Hch: h o r n b l e n d e quartz schist; Fe: ore b o d y ; F : fracture zone ; CK: drill hole.
134
localities such as Balyun Obo in Inner Mongolia, Dianyi in southwest China and Minsong in southeast China. Figures 1, 2 and 3, respectively, show their geologic sections. The industrial REE--Fe ore bodies occur as conformable strata in carbonate horizons which are in most cases dolomites. Ore bodies are concordant with wall rocks and are located in certain horizons. Ores are laminated to massive. Iron minerals are magnetite, haematite, Fe-dolomite and siderite. REE minerals are mostly bastnasite, monazite and REE--apatite. This type is not only enriched in REE and Fe but also in Nb. The association Fe-REE--Nb is typical for this type of mineralization. Moreover, the Dianyi deposit is rich in Cu(chalcopyrite). P is abundant in the Minsong deposit, and the REE--Fe ores are also phosphorus ores. In addition to iron ores, carbonate country rocks m a y be mineralized such as in the case of Baiyun Obo. In m a n y cases there is no indication of carbonate minerals being replaced by R E E minerals, rather both carbonate and R E E minerals seem to have been coprecipitated. Occasionally the carbonate rocks are also laminated, in comformable occurrence with other rock units. Table II lists the R E E abundances of this type. TABLE II REE and 7 abundances
of some
Chinese
S a m p l e and N o . in Figs. 6, 7, 12, 14)
Fe, Fe--REE La
ore deposits
(in ppm)
Pr
Ce
Nd
Sm
A n s h a n (Fig. 6) B a n d e d magnetite ore (2)* M a g n e t i t e q u a r t z i t e (4) Magnetite quartzite (I) Quartz plagloclase h o r n b l e n d e schist (3)
1.31 14.05 3.43 14.27
14.32 24.10 5.93 24.4
0.24 3.19 0.91 2.58
0.91 10.4 2.86 8.77
0.17 2.11 1.00 1.42
D i a n y i (Fig. 7) Banded Banded Mas~ve Banded
m a g n e t i t e siderite siderite m a g n e t i t e m a g n e t i t e Mderite m a g n e t i t e siderite
ore ore ore ore
(1) (2) (3) (4)
216.7 305.4 384.2 703.8
422.9 484.8 862.4 1378
45.4 51.6 65.5 136.7
195.1 209.0 262.4 592.5
34.3 48.9 36.8 97.7
Baiyun O b o (Fig. 12) Massive N b - - R E E - - F e ore ( M F , 7) B a n d e d N b - - R E E - - F e ore ( Z F , 9) Aegirine N b - - R E E - - F e ore ( A F , 6) D o l o m i t e N b - - R E E - - F e ore ( D F . 1) R i e b e k i t e N b - - R E E - - F e ore ( R F , 3) A e g i r i n e N b - - R E E ore ( A , 6) D o l o m i t e N b - - R E E ore ( D , 1 1 )
2171 19780 7454 294 2089 15960 8708
7166 38510 14150 1136 5755 33260 16890
1319 3745 1607 221 813 3859 1682
5061 10790 4951 1000 3265 11170 4650
567 749 349 158 313 797 329
M i n s o n g (Fig. 1 4 ) REE°bearlng m a g n e t i t e d o l o m i t e (2) R E E - b e a r i n g m a g n e t i t e d o l o m i t e (1) Biotite quartz schist (3)
747 1756 47
1371.5 2183 1320
113.5 258 10.1
397.4 869 34.9
66.9 148 6.9
135
(2) Carbonate-hosted REE mineralization. The Mongxi deposit is a good example of this type. The country rock is Proterozoic marble with some dolomite, two-mica schist and chlorite-schist, approximately in the same stratigraphic position as the ore-containing dolomite at Baiyun Obo. However, iron formation is entirely absent at Mongxi. The REE ores are rich in Nb and P. REE and Nb mineralization is expressed by monazite, nioboeschynite, columbite and apatite. There are two major ore types: marble type and biotite schist type. Both are of parallel-banded structure and are conformable with the stratification or schistosity of the wall rocks. The mineralized horizon extends for more than 10 km in length and is several metres wide, grading into the country rocks. Figure 4 is a simplified geologic sketch of the Mongxi deposit. Table III lists the REE abundances of the main ore types. (3) REE--Fe mineralization in metamorphosed--migmatized volcanic and volcano-sedimentary rocks (example Liaosheng). In many cases boron is also an important ore-forming element (example Liaowong). The country rock is usually albite granulite with biotite in appreciable amount. Important minerals are magnetite, barite and monazite, forming conformable ore bodies.
Eu
0.15 1.31 0.58 0.87
14.7 37.0 25.6 71.2
67 104 58 30 50 201 35
14.0 34 1.4
Gd
0.40 2.39 1.01 1.58
31.2 50.8 28.6 62.8
134 441 204 57 100 531 232
38.3 122 6.3
Tb
0.04 0.28 0.20 0.27
4.8 8.3 5.6 8.9
17 77 30 13 68 33
5.0 0.8
H R E E (Gd--Lu, Y)
Dy
0.50 1.77 0.89 1.99
26.5 42.6 25.8 80.9
50 150 86 24 12 197 132
32.9 61 5.3
Ho
0.04 1.01 0.82 0.50
5.0 8.6 5.8 27.0
Er
0.12 1.18 0.65 1.20
14.9 23.9 17.2 36.2
5.0 0.6
0.01 0.17 0.15 0.19
0.14 2.23 0.92 ].7
Y
2.96 13.35 8.0 18.27
100.0 216.8 140.0 536.4
28 9
16 72 28 3
64 32
67
134 372 174 79 101 466 232
9.0 21 1.9
3.3 3.5 5.8 18.0
Yb
9.9 13.7 11.5 27.1
16
31
Tm
10.0 1.0
170.O 172 17.3
RE203
LREE/ HREE
5 Eu
26 94 33 78
4.1 2.4 1.2 2.0
1.93 1.97 1.90 1.96
1350 1810 2260 4550
4.8 3.1 6.8 3.7
1.49 2.49 2.56 2.85
20000 90000 35000 3600 15000 80000 40000
44.6 62.2 49.4 16.5 54.4 49.2 40.8
0.57 0.56 0.67 0.86 0.74 0.97 0.40
3590 7800 317
10.0 14.0 7.0
0.85 0.82 0.70
136 220"
l
~
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RE hnZ~
-
40 °
I-i~'rwllf/lll/'/
1" '
A_,7i ~
" ' " '
lig..j b
Fig. 4. Geological section of the Mongxi REE--Nb ore deposit, scale 1:15 000. -~5 ~: bio tite granodiorite; 73: biotite granite; 62: metadiorite:An Z~ : marble;An Z~: two-mic;~ quartz schist; RE: ore body. S
1
2 3456
7
8
:':~:
~z"
Fig. 5. Geological section of the Liaowong B--Fe--REE ore deposit, scale 1:15000. 1: granite migmatite ; 2 : tourmaline hornblende granitic migmatite; 3: tramelite (tourmaline) albite granulite; 4,9: tramelite albite granulite; 5 : plagioamphibolite; 6: tramelite tourmaline albite granulite; 7: mineralized serpentinite; 8: ore body; 10: diopside tramelite albite granulite ; 11,12: tramelite albite granulite. T A B L E III R E E and Y a b u n d a n c e s of s o m e Chinese R E E , Fe ore d e p o s i t s (in p p m ) S a m p l e a n d No. in Figs. 8, 10, 14, 16
Mongxi
RE203
La
Ce
Pr
Nd
(Fig. 10)
Mineralized Mineralized Mineralized Mineralized
marble ( 1) schist (4) m a r b l e (2) schist (3)
286 210 433 281
68.0 54.9 100.4 79.3
104.2 77.4 169.6 121.5
7.9 6.2
32.1 18.9 54.5
310 35000
53.7 7450
104.0 13860
12.0 1320
46.7 4330
240
32.8
72.0
7. I
27.{i
2220
214.9
392.1
52.1
257.3
4400
435.2
340
58.0
128.7
500 550
88.3 75.0
173.0 181.4
L i a o s h e n g (Fig. 8) Biotite plagio-granulite (2) Monazite biotite barbite magnetite
o r e (3)
Jida (Fig. 8) Massive h a e m a t i t e ore (1) Jilin (Fig. 14) Mn-bearing c h a m o s i t e siderite h a e m a t i t e o r e (5) M n - b e a r i n g c h a m o s i t e siderite h a e m a t i t e o r e (4)
1100
138
611
J i p a n g (Fig. 8) Oolitic h a e m a t i t e ore (4)
51.0
L u s h u i (Fig. 16) Massive h a e m a t i t e ore (1) Massive m a g n e t i t e o r e (2)
17.4 19.1
63.9 75.5
137
REE occur mainly in monazite and apatite. In addition to the regular minerals magnetite and monazite, rare minerals such as ludwigite, boromagnesite and stillwellite are usually found in the REE--Fe--B association. REE minerals were possibly authigenic or partly detrital and were subjected to later metamorphism and migmatization. Monazite gave U--Pb isotopic ages of 1780--1923 Ma (Wang and Xu, 1973), probably indicating a metamorphic event. Figure 5 is a simplified geologic section, and Table III presents the REE abundances of this type of mineralization. (4) REE--Fe formation in unmetamorphosed clastic formations. 2'his refers to the late Proterozoic oolitic iron ores of NE China as exemplified by the Jilin deposit. This type of formation is generally barren in rare metals except for REE. The mineralization is of typical sedimentary origin. The Fe ore minerals are haematite, siderite, rhodochrosite and chamosite. The results of selective solution and electro-osmosis analysis have shown that the REE occur substantially in adsorbed form on Fe and Mn minerals, but small amounts of monazite and xenotime are also observed. The contents of Fe, Mn and REE are 30--40%, 5--10% and 0.1--0.5%, respectively, forming a Fe--Mn--REE association. Table III lists REE abundances. (5) REE in phosphorites. Late Proterozoic to early Cambrian phosphorite deposits are widespread in SW China. They are all marine sedimentary de-
Sm
Eu
Gd
Tb
5.4 2.7 7.8 7.6
1.7 1.0 2.4 2.3
3.8 2.5 2.5 5.6
8.1 558
1.8 163
6.7 428
6.3
4.8
7.0
63.9
19.2
73.9
148
30.4
141
9.4
2.3
5.6
13.4 18.0
3.5 3.8
12.1 17.2
Dy
Ho
Er
Tm
1.9 1.7 3.0 2.5
1.7 1.7 1.6 2.0
1.7 1.6 1.5 2.0
0.7 66
3.7 165
0.7
1.8 67
l.l
5.7
1.1
12.7 22.4
71 Ill
7.4 10.5
Y
LREE/ HREE
6Eu
0.6 0.6 0.9 0.7
9.3 5.8 12.9 9.9
11.5 11.6 15.0 9.3
1.17 1.28 1.39 1.11
0.7
1.5
16.1 719
7.1 19.2
0.79 1.08
3.1
0.4
1.8
28.2
3.1
2.43
16.1
42.2
9.7
32.6
552
1.2
0.94
23
61.6
11.6
42.5
766
2.1
0.78
3.0
1.3 1.9
Yb
1.5
1.3 1.9
3.5 4.8
1.0
0.9
9.6
12.8
0.98
3.5 2.9
28.4
6.3 4.4
0.76 0.71
138
posits. Some of them may contain REE up to thousands of ppm as in Qianzhong. REE are mainly in collophane, forming the P--REE association. GEOCHEMICAL
CHARACTERISTICS
OF PRECAMBRIAN
REE MINERALIZATION
Having briefly discussed the above-mentioned types of Proterozoic REE mineralization in China, we may conceive that they are mainly of marine sedimentary origin(both non-metamorphosed and metamorphosed). Except for the REE--Fe mineralization in unmetamorphosed oolitic iron formations, all other types of REE mineralization result from chemical deposition, regardless of the source material (submarine volcanogenic, continental or halmyrolysis). Like the Archaean and Proterozoic BIF of the world, most Chinese REE or REE--Fe formations of Proterozoic age rarely contain clastic minerals. Since most of the Proterozoic REE and REE--Fe formations in China are chemical or biochemical precipitates from sea water, the evolution of atmosphere and hydrosphere would have an important bearing on their genesis. As is now generally accepted, the Archaean atmosphere was enriched in CO2 and N: but impoverished in O2 (Hou et al., 1974; Fryer, 1977). The thenexisting abundant atmospheric CO2 prevented precipitation of large amounts of carbonate, as well as phosphate, as the latter would exist in the soluble
50
20
-,3 \
gl0
\ ,
.)
\
/:, IO
e~
o
La
Ce
Pr
Nd
Sm
Eu
(;d
Tb
D.~
[to
Er
Tm
Yb
Fig. 6. R E E d i s t r i b u t i o n p a t t e r n o f A r e h a e a n A n s h a n - t y p e Fe ore deposit. For analytical data and numbers see Table II.
139
1000 5(XI
4
t.-.
100
,)
¢,9
5o
-
10
l
1
t
I
ha Ce Pr Nd
l
1
I
I
~
I
I
I
l
Sm Eu GdTb I)y Ho Er TmYb Lu
Fig. 7. REE distribution pattern of Dianyi Fe--Cu--REE ore deposit. For analytical data and numbers see Table II.
1000500-
10(} 1
50 O
10
"o3 1
I
i
I
t
t
1
t
t
!
i
I
l
I
LaCePrNd SmEuGdTbDyHoErTmYbLu Fig. 8. REE distribution pattern of the Jida (1), Liaosheng (2,3) and Jipang (4) ore deposits. For analytical data see Table III.
140 H2PO~ form. This is the reason why the Archaean formations are depleted in REE, since the REE precipitated from sea water would either go into carbonate, isomorphically replacing Ca, or form independent REE carbonate or phosphate minerals such as monazite and bastnasite. The precipitation of large amounts of REE-bearing carbonates and REE minerals from sea water, unlikely in the Archaean, was rendered possible in Proterozoic times with the noticeable reduction of atmospheric CO2 and the increase of free O2. It must be emphasized here that the large accumulation of REE in certain Proterozoic formations such as at Baiyun Obo and at Olympic Dam, Australia, may be related to ~ow temperature metamorphism or reworking since recent experiments show that hydrous, ,(300°C media could stimulate remobilization and enrichment of REE, especially the LREE (Wood, 1976; Ludden, 1979). Ludden reported that the c o n t e n t of LREE may increase up to ten times during low grade metamorphism. The above mentioned five types of REE mineralization have the following elemental associations: Fe--REE--Nb (Baiyun Obo); Fe--REE--Nb--P (Minsong); Fe--REE--Nb--Cu (Dianyi); Fe--REE--B (Liaowong); Fe--REE--Mn (Jilin); Fe--REE (Liaosheng); REE--Nb--P (Mongxi) and P--REE (Qianzhong). The close paragenesis of REE and Fe mineralization in the Proterozoic too I
100
-~ 51) g
l0 ~3 5
1 La
[ Ce
I Nd
I 1 Sm Eu
I Gd
i Dy
1
¥b
Fig. 9. REE distribution p a t t e r ~ of granulites of the Liaowong deposit (after Li Shouyi, 1983). 1: magnetite granulit~; 2: tourmaline granulite; 3: biotite plagiogranulite.
141
may be explained by the fact that in the marine environment both tend to be soluble in acid reducing water (Archaean hydrosphere), but began to be precipitated in basic oxidizing water some 2000--2200 Ma ago. If sea water is saturated with respect to both REE and Fe, they could be coprecipitated. Not to be excluded is the process of adsorption of REE on Fe and Mn minerals. For instance, in the Jilin ores REE exist mainly in adsorbed form on haematite and rhodochrosite, with only a small a m o u n t of monazite and xenotime. Some experimental investigations gave strong evidence for the close paragenesis of REE and Fe (Balashov, 1966; Wang, Chen and Wu, personal communication, 1982). In REE-bearing solutions addition of Fe and Mn compounds can promote the REE hydrolysis. When pH is equal to 5.6 the REE hydrolysis ratio can be enhanced from 13% to 60% (Wang, Chen and Wu, personal communication, 1982). Another interesting observation is that the REE--Fe or REE mineralization results in highly fractionated REE distribution patterns (Figs. 6--16,
50{II I
I
21101
%.?\ 1 oo
•~
50
ee-.
:..)
IO
1
2
La
Ce
Pr
Nd
Sm
Fig. 1 0 . R E E d i s t r i b u t i o n p a t t e r n d a t a a n d n u m b e r s s e e T a b l e III.
Eu
(;d
l)y
IIo
Er
of the Mongxi REE--Nb
Yh ore deposit. For analytical
142
506
ZO(
"'C ,,..,
t,-,
\
m
"~,"
""-
\ .~"/ \ \
4
z, 3
lO
"'-,
l.a
(','
t'r
~:,1
~4m t.;u
I;,1
h
I~'~' Ib,
,,.-"2
Fir
f'm YI,
" I
I u
Fig. 11. REE distribution patterns of early Proterozoic metamorphic rocks in Inner Mongolia (data from Wang Yixian, personal communication, 1983). For analytical data see Table V.
Wedepohl, 1970). The L R E E / H R E E ratio is much higher than 1 {Table IV). Furthermore, the L R E E / H R E E ratio becomes greater when the total REE content increases. Thus, in Baiyun Obo the ratio reaches 40--60. The LREE enrichment is mainly due to the much higher crustal abundance of LREE over HREE. For example, this ratio may be up to 15.5 {average 7.9, Table V) in the Baiyun O b o early Proterozoic metamorphic rocks. On the other hand, the stability of complexes of LREE and H R E E may also have some effect. From the Archaean to the Proterozoic the content of CO: in the atmosphere decreased gradually, while the pH of the hydrosphere increased gradually, changing from acid to neutral and weakly basic. Experiments show that REE can form complexes with CO]- in basic solution, and the H R E E complexes are more stable than those of the LREE (Huang et al., 1981). Thus, separation of LREE from H R E E would occur with LREE even more enriched in the sediments. EVOLUTION OF PRECAMBRIAN REE MINERALIZATION
From the above-mentioned geological relationships in China, it seems that REE deposits of sedimentary genesis may reflect a time-bound development, i.e., they occurred mainly in the middle to late Proterozoic. The greatest ac-
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|.u
I.u
Fig. 12, R E E d i s t r i b u t i o n p a t t e r n s f o r d i f f e r e n t t y p e s o f o r e in t h e B i y u n O b o o r e d e p o s i t . M F = Massive N b - - R E E - - F e o r e , Z F = B a n d e d N b - - R E E - - F e o r e , A F = A e g i r i n e N b - - R E E - - F e ore, R F = R i e b e c k i t e N b - - R E E - - F e ore, D F = D o l o m i t e N b - - R E E - - F e o r e , PD = D i o p s i d e N b o r e , A = A e g i r i n e N b - - R E E o r e , D = D o l o m i t e N b - - R E E o r e . F o r a n a l y t i c a l d a t a see T a b l e II.
,v,
2
I0~ ,
10:
c~
144
1oo
\
I I
l.
I o0
.:-
I
1
I
I ~
t
I
I
I
I
1
Z
%
..x....,...,,'%,,,
o.
•.. \ .
~
".. ,,.,
I
.....
,
N~
3
10
............ \2""
""........-6 1
I
I
I
1 I
I 1
i
J
I
I
I
1
I
!
"', ,1 I
l
I.a Ce t'r Nfl SmEu Gd Vi, l.u l.a Ce Pr Nd SmEu GdT b I., Fig. 13. R E E distribution patterns in the Baiyun Obo Group, Inner Mongolia (for analytical data and abbreviations see Table VI). lc: H~c; ls: H~q; 2: H2; 3: H3; 4: H,; 5: Hs; 6: H,; 7: H~; 8: Hs; 9: Hg; 6--8: H~_~ ; G: H~_~(G); Z: H6_~ (Z).
5000I
I
5ool-
100I
1
5
10 i taCleCr,~d SlaEtuG'd'Fbl)yl~oErT'm~'bLu Fig. 14. REE distribution patterns of the MiaJong (1, 2, 3) and dilin (4, 5) ore deposits. For analytical data and numbers see Tables II and III.
145 cumulation of BIF occurred, however, in the early Proterozoic. This is the first characteristic of the evolution of Precambrian REE mineralization. The second is that the enrichment or depletion of Eu evolves with geological time. REE distribution patterns show obvious positive Eu anomalies (5 Eu > 1) for the Fe ores or wall rocks in the Archaean Anshan Fe deposit (Fig. 6). The same feature appears in the REE--Fe or REE deposits formed during the early or early mid-Proterozoic ( ~ 1 9 0 0 Ma ago) such as Dianyi, Jida, Liaosheng, Liaowong and Jipang, where REE distribution patterns of ores or wall rocks exhibit positive or no Eu anomaly (8 Eu >/ 1, Figs. 7--9). For the Mongxi REE--Nb--P deposit the REE distribution patterns show a weak positive Eu anomaly (average 6 Eu = 1.1, Fig. 10). It may have been formed during early to middle Proterozoic time according to the REE patterns although there is no isotopic age available. Early Proterozoic metamorphic rocks (gneiss and marble) in Inner Mongolia have no Eu anomalies (Fig. 11). However, different from the above-mentioned features, the REE distribution patterns show negative Eu anomalies (8 Eu < 1) for the mid to late Proterozoic REE--Fe formations. For example, different types of ores in Baiyun Obo (Fig. 12, Table VI) such as the massive type (MF), banded 2{}0
~9 t~ tc-
O
2 -
,, . . _ . a 6
1
I
I
I
l
La
Ce
Pr
Nd
Sm
I
i
Eu Gd
I
Tb
~
I
Dy Ho
I
I
I
Er Tm Yb
I
Lu
Fig. 15. (a) REE distribution patterns in rocks of the middle and late Proterozoie Jixian profile. For analytical data and numbers see Table VII.
146 200
100 50
t_
O e-
20
L~ .M 10
La
Ce Pr
Nd
Sm
Eu Gd T b
Dy
Ho
Er Tm Yb Lu
Fig. 15. (b) REE distribution patterns in rocks of the middle and late Proterozoie dixian profile. For analytical data and numbers see Table VII.
50O
100
•
o
.~ 50 L~ o
10
I
I
i
i
LaCePrNd
t
i
i
Tb I
i
t
t
SmEuGd DyHoEr
Tm I
I
I
YbLu
Fig. 16. REE distribution pattern of the Early Palaeozoic Lushui Fe-ore deposit. For analytical data and numbers see Table III.
147 TABLE IV REE geochemical parameters of some Precambrian Fe, REE ore deposits and metamorphic rocks Sample
Location, age
Iron ore Quartz plagioclase hornblende schist Iron ore Iron ore Iron ore Biotite hornblende gneiss Iron ore Granulite Mineralized marble and schist Gneiss, marble
Anshan, Archaean Anshan, Archaean
REE--Fe ore Quartzite, slate, dolomite, sandstone REE--Fe ore Biotite quartz schist Shale, sandstone dolomite Iron ore Iron ore
LREE/ HREE
8 Eu
2.6 2.0
1.93 1.96
Dianyi, Proterozoic 4.6 Jida, early--mid Proterozoic 3.1 Liaosheng, early Proterozoic 19.2 Jixian, late Archaean 4.9 Jipang, early--mid Proterozoic 12.8 Liaowong, early--mid Proterozoic 6.9 Mongxi, early--mid Proterozoic 11.9 Inner Mongolia, early Proterozoic 7.9 Baiyun Obo, mid Proterozoic 47.0 Baiyun Obo, mid Proterozoic 6.6
2.35 2.43 1.08 1.03 0.98 0.87 1.24
Minsong, Proterozoic Minsong, Proterozoic Jixian, mid and late Proterozoic Lushui, Devonian Jilin, mid--late Proterozoic
0.84 0.70 0.71 0.74 0.86
12.0 7.0 9.0 5.3 1.7
0.96 0.70 0.74
b Eu -- Eu/Eu* H R E E (Gd--Lu, Y)
t y p e ( Z F ) , aegn:ine t y p e ( A F ) , r e i e b e c k i t e t y p e ( R F ) a n d d o l o m i t e t y p e ( D F ) o f t h e R E E - - F e - - N b ores as well as t h e aegirine t y p e (A) a n d d o l o m i t e t y p e (D) o f the R E E - - N b ores, t h e d i o p s i d e t y p e (PD) o f t h e Nb ores, as well as t h e s e d i m e n t a r y r o c k s (slate, q u a r t z i t e , s a n d s t o n e , l i m e s t o n e and d o l o m i t e ) o f the J i a n s h a n - - O u l u w u l a a n d H e i n a o b a o profiles o f t h e B a i y u n O b o G r o u p (Fig. 13, T a b l e VI), possess R E E d i s t r i b u t i o n p a t t e r n s with negative Eu a n o m a l i e s (5 Eu < 1). T h e s a m e f e a t u r e is o b s e r v e d in t h e Minsong and Jilin d e p o s i t s (Fig. 14). We have a n a l y s e d t h e R E E c o m p o s i t i o n o f various r o c k s o f late P r e c a m brian to P a l a e o z o i c age. T h e Jixian profile ( 8 0 0 - - 1 9 5 0 Ma) and t h e Early Palaeozoic Fe d e p o s i t (Lushui, Ningxiang t y p e } have R E E p a t t e r n s t h a t also s h o w clear negative Eu a n o m a l i e s (Figs. 15, 16, T a b l e VII). Based o n t h e a b o v e analysis, we arrive at t h e following c o n c l u s i o n a b o u t t h e e v o l u t i o n o f P r e c a m b r i a n R E E m i n e r a l i z a t i o n . A r c h a e a n a n d early Prot e r o z o i c ores are rich in Eu; R E E p a t t e r n s display positive or no Eu a n o m a l y , while mid- to late P r o t e r o z o i c ores h a v e negative Eu a n o m a l i e s . This f e a t u r e is m a i n l y d u e to t h e c h e m i c a l e v o l u t i o n o f t h e a t m o s p h e r e and t h e h y d r o sphere. Eu o c c u r s in t w o valence states, Eu 2÷ a n d Eu 3÷. Eu existed m a i n l y in Eu 2÷ f o r m in t h e A r c h a e a n a n d early P r o t e r o z o i c b e c a u s e o f l o w e r o x y g e n
V
20.9 30.9
a S a m p l e N o . s h o w n in F i g . 1 1 .
marble Quartz biotite gneiss
40.6 83.0
62.4 94.8 117.8 161.4 243.1 116.4
gneiss (3) 25.6 Granitic gneiss 40.8 Leucogranulite 55.9 Augengnelu (4) 72.5 Biotite plagiogneiss (5) 125.3 Diol~ide marble 87.3 Phlogopite serpentine
Ce
227.1 31.7
La
of Early Proterozoic
G r a n i t i c m i g m a t i t e (1) a 1 2 9 . 6 Gabbroie gneiu (2) 13.9 Hornblende plagio-
Rock type
REE composition
TABLE
6.7 11.1
9.6 14.2 15.8 24.2 37.8 11.6
29.2 4.9
Pr
21.7 36.2
2.2 46.2 46.5 76.7 112.1 25.4
7.8 16.4
Nd
3.7 7.7
6.9 8.9 7.6 15.3 20.2 3.2
8.7 3.5
Sm
1.0 2.0
2.2 2.2 2.1 3.6 5.0 1.1
2.6 1.2
Eu
2.8 7.6
6.9 8.0 6.8 14.2 17.9 5.3
9.4 4.0
Gd
0.3 1.1
1.5 1.3 1.1 2.2 2.7 0.6
1.7 0.8
Tb
0.9 4.9
4.4 3.6 2.6 7.7 7.5 1.8
1.7 2.6
Dy
-1.0
2.2 1.3 0.7 2.5 3.1 -
1.5 1.0
Ho
0.4 2.1
2.0 1.6 0.9 3.1 2.5 0.9
0.5 1.3
Er
0.2 0.1
0.6 0.4 0.3 0.4 --
0.5 0.2
Tm
0.8 3.5
3.1 2.1 0.9 3.6 3.3 1.1
1.3 1.7
Yb
h o r i z o n s i n I n n e r M o n g o l i a (in p p m ) ( W a n g Y l x i a n o p e r s o n a l c o m m u n i c a t i o n ,
0.7
0.7 0.5 0.3 0.9 0.7 --
0.1 0.6
Lu
1983)
2.8 25.3
19.8 18.4 9.3 32.0 35.5 9.4
7.4 13.3
Y
123 262
210 293 322 504 740 317
595 117
11.5 3.7
3.3 5.6 10.9 5.3 7.8 12.8
15.5 2.8
LREE/ HREE
ERE,O3
0.98 0.87
1.09 0.87 0.95 0.84 0.91 0.91
1.02 I.II
5Eu
00
23.4 225 7.4 0.75
2.4 165 17.4 0.83
3.9 95 10.3 0.87
13.5 41.7 3.6 10.2 2.3 0.50 1.3 0.21 0.88 0.22 0.20 -0.23
H4
H~
10.5 195 9.5 0.88
25.5 93.4 6.3 16.1 3.4 0.88 0.86 0.46 1.9 0.46 0.48 -0.79
H6 9.4 19.0 2.5 7.5 16 0.42 1.9 0.25 1.5 0.39 0.52 0.06 0.61 0.11 8.3 65 3.0 0.81
H7 7.1 17.0 2.0 6.7 1.4 0.51 1.5 0.22 1.4 0.37 0.76 0.12 0.94 0.19 9.5 60 2.3 1.2
HR 21.0 41.4 5.9 19.8 4.5 0.91 5.4 0.77 4.8 1.1 2.5 0.36 2.6 0.27 29.7 170 2.0 0.63
H9 38.8 83.7 9.5 28.2 5.2 1.1 4.9 0.76 3.1 0.78 1.4 0.25 1.5 0.31 15.9 235 5.8 0.71
59.1 140.6 15.1 45.1 9.1 1.9 7.8 1.6 8.3 2.2 4.1 0.67 4.6 0.49 51.4 425 3.3 0.72
20.2 43.1 5.4 17.0 3.5 0.73 3.4 0.58 3.1 0.82 1.5 0.22 1.9 0.14 18.8 145 3.0 0.71
H5
10.4 109 4.9 0.81
13.1 45.7 3.4 9.9 2.2 0.52 1.1 0.32 1.8 0.37 0.61 . 0.76
H6_ s
15.7 316 0.8 0.58
55.9 109.7 13.9 44.4 8.0 1.3 5.9 0.86 3.9 0.83 1.1 . . 1.8
Hg
Guyang
9.0 175 9.4 0.74
23.7 81.6 5.8 16.2 2.9 0.59 1.5 0.34 1.8 0.24 0.60 . 0.52
11.2 175 6.2 0.49"
0.69
319 578 7.7 23.3 4.1 0.62 4.4 0.55 2.1 0.47 0.89
H6--R ( Z ) H6--~ ( G )
Zhurihe
G u y a n g : H~_s(G): siliceous limestone.
J i a n s h a n - - - O u l u w u l a p r o f i l e : H I c: q u a r t z c o n g l o m e r a t e , H I : q u a r t z slate, H 2 : s l a t e : H4: q u a r t z i t e , Hs: slate, H6: d o l o m i t e , H~: c a l c a r e o u s s a n d s t o n e , tis: siliceous l i m e s t o n e . H~: slate. H e i a u b a u p r o f i l e : H3: slate, Hs: slate, H6.-e: s i l i c e o u s d o l o m i t e , H9: s i l i c e o u s d o l o m i t e . Z h u r i k e : t1~-- s ( Z ) : slate.
2.0
36.5 94.1 9.4 26.4 5.7 1.2 5.2 0.91 3.8 0.87 1.8
H3
. --
43.2 52.4 7.8 21.6 4.5 1.1 3.8 0.39 0.93 ---
H2
H3
27.2 64.2 7.3 22.7 4.3 0.93 3.5 0.60 3.7 0.50 1.4
Ht
Hi c
69.6 103.7 19.7 59.2 10.5 0.85 9.2 0.98 3.3 0.49 1.3
Heiaubau profile
Jianshan--Ouluwula profile
Tm . . . Yb 1.3 1.7 Lu y 12.6 15.7 RE203 350 185 LREE/HREE 9.0 4.7 Eu 0.28 0.78
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er
Element
REE composition of Bayun Obo Group Strata (ppm)
T A B L E VI
150
fugacity. Owing to the crystal--chemical similarities of Eu 2+ with Ca `++ and the enrichment of Ca in the Archaean and early Proterozoic crust, Eu could easily get into rocks rich in Ca, giving rise to abundant Eu accumulation m this period. High oxygen fugacity resulted in Eu depletion in later times, that is, middle to late Proterozoic and Phanerozoic. TABLE VII REE c o m p o s i t i o n of Jixian Profile strata ( p p m ) Element
La
Ce Pr Nd Sm Eu Gd Tb Dy Ho
Er Tm YI) Lu Y
Changz-Chuan- Tuanzi- Dahon- Gaoyu- Yangh o u c u n lingou shan gyu zhuang ~huang (1) a (2) (3) (4l (5) (6)
Hongshuizhai
11.3 21.2 2.8 8.1 1.4 0.26 1.4 0.13 0.45 0.12 0.24
50.2 121.8 12.3 36.2 6.6 1.32 4.5 0.64 2.5 0.45 0.76
0.30
0.58
17.3 54.9 4.9 ]3.9 3.4 0.79 2.5 0.51 2.8 0.76 0.87 0.14 1.84 0.25 21.1 155 3.2 0.78
2.4
RE203 60 LREE/HREE 9.0 [Eu
0.65
11.3 300 ll.O 0.76
35.0 85.5 8.5 24.4 4.2 0.82 3.2 0.42 2.4 0.45 0.85 0.96 11.8 215 14.2 0.72
20.5 65.0 4.6 12.0 1.2 0.27 --0.56 0.12 --
3.3 130 O.81
7.0 16.2 1.9 5.6 1.1 0.19 1.2 0.17 0.85 0.23 0.38 0.06 0.50 0.15 5.8 50 3.4 0.54
8.6 45.7 2.0 4.8 0.86 0.22 -0.08 0.59 0.08 0.07 --0.15 4.2 82 12.1
(8)
Tieling
Xiama- J i n g e r y u ling (10) (9)
4.8 6.6 1.2 4.2 0.94 0.20 1.3 0.21 I.I 0.27 0.37 0.07 0.66 0.09 11.2 40 1.2 0.62
20.7 45.9 4.9 14.2 2.7 0.63 3.4 0.59 3.4 0.92 1.2 0.33 2.5 0.33 22.5 150 2.5 0.71
(7)
36.5 .97.5 8.4 23.3 J,.5 1.1 2,6 (}.65 3.0 0.46, 027 1.4 17.4 238 (;.6 0.80
Changzhoucun: quartzite; Chuanlinggou: shale; Tuanzishan: d o l o m i t e ; Dahongyu: quartzite: G a o y u z h u a n g : d o l o m i t e ; Yangzhuang: silt d o l o m i t e ; Hongshuizhai: shale; Tieling: limestone: X i a m a l i n g : sandstone; Jingeryu: s h a l e . aSample No. s h o w n in F i g . 15.
CONCLUSIONS Five types of Precambrian REE mineralization can be distinguished in China: (1) carbonate-hosted Fe--REE deposits; {2) carbonate-hosted REE mineralization; (3) REE--Fe or REE--Fe--B mineralization in metamorphosed--migmatized volcanic and volcano-sedimentary rocks; {4) REE--Fe formations in clastic sedimentary beds and (5) REE in phosphorite deposits. In these five REE mineralization types eight kinds of elemental associations can be distinguished: (1) Fe--REE--Nb; (2) Fe--REE--Nb--P; (3) Fe .... REE--Nb--Cu; (4) Fe--REE--B; (5) Fe--REE--Mn; (6) Fe--REE; (7) REENb--P and (8) P--REE. All these REE mineralizations are enriched in LREE relative to HREE. They are mainly of sedimentary origin. The composition of atmosphere and hydrosphere (particularly the contents of CO: and O2) in the Precambrian played a significant role in the evolution of these REE mineralizations. REE deposits of sedimentary genesis may reflect a time-bound development: they occurred mainly in the mid to late Proterozoic, broadly parallel
151 w i t h , b u t l a g g i n g b e h i n d t h e g r e a t e s t a c c u m u l a t i o n o f B I F in t h e e a r l y P r o t e rozoic. REE d i s t r i b u t i o n p a t t e r n s show strong L R E E e n r i c h m e n t , and the Eu cont e n t s c h a n g e d s y s t e m a t i c a l l y w i t h g e o l o g i c t i m e for all a b o v e - m e n t i o n e d t y p e s . T h e R E E m i n e r a l i z a t i o n s in t h e A r c h a e a n a n d e a r l y P r o t e r o z o i c are rich in E u (5 E u ~> 1), b u t are d e p l e t e d in E u in m i d t o late P r o t e r o z o i c dep o s i t s (5 Eu < 1). ACKNOWLEDGEMENTS We are g r a t e f u l t o t h e L a b o r a t o r i e s o f o u r I n s t i t u t e f o r a n a l y s i s o f t h e R E E c o n t e n t s . We also t h a n k W a n g Y i x i a n f o r p r o v i d i n g R E E d a t a o f m e t a morphic rocks from Inner Mongolia.
REFERENCES Balashov, Y.A. and Gorianov, N.M., 1966. Rare earth elements in the Precambrian iron ore formation of the Priimandrov region, Geokhimiya, 3 : 3 1 2 - - 3 2 2 (in Russian). Fryer, B.J., 1977. Rare earth evidence in iron-formation for changing Precambrian oxidation stage. Geochim. Cosmochim. Acta, 41: 361--367. Hou, D.F., Ouyang, Z.Y. and Yu, J.S., 1974. Evolution of the terrestrial materials in relation to nuclear energy, Science Press, pp. 47--51 (in Chinese). Huang, S.H., Zhang, Z.M., He, S.Y. and Wang, Z.G., 1981. Experimental studies on transportable forms and precipitation conditions for REE in sea water. Geochemistry, 2: 142--152. Li, S.tT., 1983. REE distribution of the boron ore in Liaoning Province, China. J. Chan~ chun College of Geology, 1 : 3 9 - - 5 2 (in Chinese). Ludden, J.N., 1979. An evolution of the behaviour of the rare-earth elements during the weathering of sea-floor basalt. Earth Planet. Sci. Lett., 43: 85--92. Qiu, Y.Z., Wang, Z.G. and Zhao, Z.H., 1981. A preliminary study of REE iron formation. Geochemistry, 3 : 1 8 5 - - 2 0 0 . Taylor, S.R., 1979. Chemical composition and evolution of the continental crust: the rare earth element evidence. In: M.W. McElhinny (Editor), The Earth, its Origin, Structure and Evolution. Academic Press, London, pp. 353--372. Vinogradov, A.P., 1962. Average contents of chemical elements in different types of igneous rocks of the crust. Geokhimiya, 7 : 555--565. Wang, X.Z. and Xu, X.Y., 1973. Genetic characteristics of Precambrian borate deposits in China. Geochemica, 1 : 12--22 (in Chinese). Wedepohl, K.H. (Editor), 1970. Handbook of Geochemistry. Springer Verlag, Berlin, vol. II/2. Wood, D.A., Gibson, I.L. and Thompson, R.N., 1976. Elemental mobility during zeolite facies metamorphism of the Tertiary basalts of Castern Icelan. Contrib. Mineral. Petrol., 55: 241--253.
131
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EVOLUTION OF PRECAMBRIAN
REE MINERALIZATION
TU GUANGZHI, ZHAO ZHENHUA and QIU YUZHUO
Institute of Geochemistry. Academia Sinica, Guiyang, Guizhou Province (People's Republic of China)
ABSTRACT Tu, G.-Z., Zhao, Z. and Qiu, Y., 1985. Evolution of Precambrian REE mineralization. Precambrian Res., 27: 131--151. Archaean BIF of the world generally contain only minor amounts of REE (20--30 ppm or less), but some of the post-Archaean iron-bearing and other formations of China contain several thousand ppm or even up to several percent of total REE. The following types of Proterozoic REE mineralization can be distinguished: (1) carbonate-hosted Fe--REE deposits; ( 2 ) carbonate-hosted REE mineralization; (3) REE--Fe or REE--Fe--B mineralization in metamorphosed--migmatized volcanic and volcano-sedimentary rocks; (4) REE--Fe mineralizations in clastic sedimentary beds; and (5) REE in phosphorite deposits. Large quantities of REE in sea water begin to precipitate only when the CO: content of the atmosphere drastically decreases, because the REE may occur in carbonate and phosphate minerals or isomorphically replace Ca 2. in oceanic sediments. As a CO2--N: atmosphere probably prevailed prior to the Proterozoic, the high CO: partial pressure not only restricted the precipitation of REE-bearing carbonates, but also promoted the appearance of easily soluble H:PO~. Hence, REE-rich carbonates and phosphates scarcely occur in large amounts in Archaean sediments. Only with the decrease of CO2 in the early Proterozoic did REE-bearing dolomite, REE carbonate and phosphate minerals begin to appear in noticeable quantities. The high concentration of Fe, REE and P in Proterozoic sediments seems to have evolved with geologic time. The peak of Fe accumulation appeared in the early Proterozoic, the mid-Proterozoic was favourable for REE, while large P concentrations appeared in the late Proterozoic and early Cambrian. In all of the above-mentioned types of REE mineralization, the REE distribution patterns are highly fractionated with significant light rare earth enrichment. Early Proterozoic deposits display distinct positive or no Eu anomalies, whereas middle and late Proterozoic ores show negative Eu anomalies.
INTRODUCTION In 1977 T u G u a n g z h i p r o p o s e d the t e r m " R E E - - F e f o r m a t i o n s " for the P r o t e r o z o i c F e d e p o s i t s o f C h i n a w h i c h are r i c h i n R E E , o f t h e o r d e r o f 1 0 t o 1 0 0 t i m e s t h e a v e r a g e R E E c r u s t a l c o n t e n t . L a t e r Q i u Y u z h u o e t al. ( 1 9 8 1 ) s t u d i e d t h e R E E d i s t r i b u t i o n p a t t e r n s o f R E E - - F e f o r m a t i o n s . Par-
132 ticularly the famous Baiyun Obo R E E - - Fe --N b deposits have been systematically studied in r ecent years. Based on these investigations, we summarize the principal types of Precambrian REE mineralization in China according to their geochemical and genetic features. The relationship between the REE distribution patterns and the chemical evolution of the Precambrian crust is also discussed (Taylor, S.R., 1979). ANALYTICAL METHODS Total REE contents of various ores and wall rocks were determined by chemical co lo r im e t r y with uncertainties of 10--20%. Individual REE abundances were d ete r m i ne d using an ion-exchange m e t h o d for separation and Xray fluorescence s p e c t r o m e t r y for analysis. Analytical errors for the elements o f higher concentrations were ~ 2--5%, whereas for those with lower concentrations (<1%) errors were ~ 10--20%. TYPES OF PRECAMBRIAN REE MINERALIZATION IN CHINA It has been n o t e d t hat Archaean BIF all over the world on average contain 20--30 p p m or less of the total REE concentrations {Fryer, 1977). This is in strong contrast with m a n y Proterozoic BIF formations which are much higher in REE, o f ten o f the order of thousands of ppm to several percent. The widespread Archaean Anshan-type iron deposits o f eastern Hebei and southern Liaoning are o f the Algoman-type and are related to intermediate to basic submarine volcanic activity. Table I shows their REE contents. It is clear th at th e Archaean iron formations in China rarely contain more than 100 p p m o f total REE, which is far below the crustal average of 210 ppm (Vinogradov, 1962). This is also true for Archaean BIF in ot her countries. Proterozoic R E E - - F e formations are widespread in China. The following t y p es o f R EE mineralization can be distinguished: (1) Carbonate-hosted REE--Fe deposits. These have been found in several TABLE I Total REE content of some Archaean iron formations Ore (rock) type
Location
zREE (in pprn)
Reference
Banded magnetite ore Magnetite quartzite Magnetite quartzite Hornblende magnetite quartzite Quartz--nmgnetite--amphibole banded rock Banded quartz-rich iron-fro. Carbonate facies iron-fro Banded magnetite--haematite iron-fro.
Anshan, China Anshan, China Hujiamiao, China Shuichang, China
21 78 27 20a
this this this this
N.E. Finland Wyoming, U.S.A. Michipicoten, Canada Mary River, Canada
17 11.5 9.9 14.5
Fryer (1977) Fryer ( 1977 ) Fryer (1977) Fryer (1977)
aRE203.
paper paper paper paper
133 t"e
-
l:e
-~N
f4"
-
....
It
. . . . . . . .
11 '
Fig. 1. Geological section of the Baiyun Obo R E E - - F e - - N b ore deposits, scale 1:30 000. Fe: ore b o d y ; -~: Hercynian granite; . : migmatite; H: Baiyun Obo G r o u p ; 9: black slate; 6--8: dolomite, limestone, quartzite; 5: black slate; 4: dark quartzite; 3: black slate; 2: white quartzite; 1 : conglomerate, quartzite; W: Wutai Group: gneiss, schist.
120 °
..... .
.
.
.
.
.
J
-
]
Fig. 2. Geological section of the Dianyi Fe---Cu--REE ore deposits, scale 1 : 1 5 0 0 0 . 1, argillaceous dolomite; 2, slate; 3, ore body.
356 ° ~-.,.... CK4
~>~'--. ./'/
3
o
/ i/
I ~1~
Fig. 3. Geological section of the Minsong F e - - R E E - - P ore deposits, scale 1:2500. Mar: marble; MQ: mica--quartz-schist; e: syenite; 75: granodiorite; Hch: h o r n b l e n d e quartz schist; Fe: ore b o d y ; F : fracture zone ; CK: drill hole.
134
localities such as Balyun Obo in Inner Mongolia, Dianyi in southwest China and Minsong in southeast China. Figures 1, 2 and 3, respectively, show their geologic sections. The industrial REE--Fe ore bodies occur as conformable strata in carbonate horizons which are in most cases dolomites. Ore bodies are concordant with wall rocks and are located in certain horizons. Ores are laminated to massive. Iron minerals are magnetite, haematite, Fe-dolomite and siderite. REE minerals are mostly bastnasite, monazite and REE--apatite. This type is not only enriched in REE and Fe but also in Nb. The association Fe-REE--Nb is typical for this type of mineralization. Moreover, the Dianyi deposit is rich in Cu(chalcopyrite). P is abundant in the Minsong deposit, and the REE--Fe ores are also phosphorus ores. In addition to iron ores, carbonate country rocks m a y be mineralized such as in the case of Baiyun Obo. In m a n y cases there is no indication of carbonate minerals being replaced by R E E minerals, rather both carbonate and R E E minerals seem to have been coprecipitated. Occasionally the carbonate rocks are also laminated, in comformable occurrence with other rock units. Table II lists the R E E abundances of this type. TABLE II REE and 7 abundances
of some
Chinese
S a m p l e and N o . in Figs. 6, 7, 12, 14)
Fe, Fe--REE La
ore deposits
(in ppm)
Pr
Ce
Nd
Sm
A n s h a n (Fig. 6) B a n d e d magnetite ore (2)* M a g n e t i t e q u a r t z i t e (4) Magnetite quartzite (I) Quartz plagloclase h o r n b l e n d e schist (3)
1.31 14.05 3.43 14.27
14.32 24.10 5.93 24.4
0.24 3.19 0.91 2.58
0.91 10.4 2.86 8.77
0.17 2.11 1.00 1.42
D i a n y i (Fig. 7) Banded Banded Mas~ve Banded
m a g n e t i t e siderite siderite m a g n e t i t e m a g n e t i t e Mderite m a g n e t i t e siderite
ore ore ore ore
(1) (2) (3) (4)
216.7 305.4 384.2 703.8
422.9 484.8 862.4 1378
45.4 51.6 65.5 136.7
195.1 209.0 262.4 592.5
34.3 48.9 36.8 97.7
Baiyun O b o (Fig. 12) Massive N b - - R E E - - F e ore ( M F , 7) B a n d e d N b - - R E E - - F e ore ( Z F , 9) Aegirine N b - - R E E - - F e ore ( A F , 6) D o l o m i t e N b - - R E E - - F e ore ( D F . 1) R i e b e k i t e N b - - R E E - - F e ore ( R F , 3) A e g i r i n e N b - - R E E ore ( A , 6) D o l o m i t e N b - - R E E ore ( D , 1 1 )
2171 19780 7454 294 2089 15960 8708
7166 38510 14150 1136 5755 33260 16890
1319 3745 1607 221 813 3859 1682
5061 10790 4951 1000 3265 11170 4650
567 749 349 158 313 797 329
M i n s o n g (Fig. 1 4 ) REE°bearlng m a g n e t i t e d o l o m i t e (2) R E E - b e a r i n g m a g n e t i t e d o l o m i t e (1) Biotite quartz schist (3)
747 1756 47
1371.5 2183 1320
113.5 258 10.1
397.4 869 34.9
66.9 148 6.9
135
(2) Carbonate-hosted REE mineralization. The Mongxi deposit is a good example of this type. The country rock is Proterozoic marble with some dolomite, two-mica schist and chlorite-schist, approximately in the same stratigraphic position as the ore-containing dolomite at Baiyun Obo. However, iron formation is entirely absent at Mongxi. The REE ores are rich in Nb and P. REE and Nb mineralization is expressed by monazite, nioboeschynite, columbite and apatite. There are two major ore types: marble type and biotite schist type. Both are of parallel-banded structure and are conformable with the stratification or schistosity of the wall rocks. The mineralized horizon extends for more than 10 km in length and is several metres wide, grading into the country rocks. Figure 4 is a simplified geologic sketch of the Mongxi deposit. Table III lists the REE abundances of the main ore types. (3) REE--Fe mineralization in metamorphosed--migmatized volcanic and volcano-sedimentary rocks (example Liaosheng). In many cases boron is also an important ore-forming element (example Liaowong). The country rock is usually albite granulite with biotite in appreciable amount. Important minerals are magnetite, barite and monazite, forming conformable ore bodies.
Eu
0.15 1.31 0.58 0.87
14.7 37.0 25.6 71.2
67 104 58 30 50 201 35
14.0 34 1.4
Gd
0.40 2.39 1.01 1.58
31.2 50.8 28.6 62.8
134 441 204 57 100 531 232
38.3 122 6.3
Tb
0.04 0.28 0.20 0.27
4.8 8.3 5.6 8.9
17 77 30 13 68 33
5.0 0.8
H R E E (Gd--Lu, Y)
Dy
0.50 1.77 0.89 1.99
26.5 42.6 25.8 80.9
50 150 86 24 12 197 132
32.9 61 5.3
Ho
0.04 1.01 0.82 0.50
5.0 8.6 5.8 27.0
Er
0.12 1.18 0.65 1.20
14.9 23.9 17.2 36.2
5.0 0.6
0.01 0.17 0.15 0.19
0.14 2.23 0.92 ].7
Y
2.96 13.35 8.0 18.27
100.0 216.8 140.0 536.4
28 9
16 72 28 3
64 32
67
134 372 174 79 101 466 232
9.0 21 1.9
3.3 3.5 5.8 18.0
Yb
9.9 13.7 11.5 27.1
16
31
Tm
10.0 1.0
170.O 172 17.3
RE203
LREE/ HREE
5 Eu
26 94 33 78
4.1 2.4 1.2 2.0
1.93 1.97 1.90 1.96
1350 1810 2260 4550
4.8 3.1 6.8 3.7
1.49 2.49 2.56 2.85
20000 90000 35000 3600 15000 80000 40000
44.6 62.2 49.4 16.5 54.4 49.2 40.8
0.57 0.56 0.67 0.86 0.74 0.97 0.40
3590 7800 317
10.0 14.0 7.0
0.85 0.82 0.70
136 220"
l
~
il " i ~ / / b
'"
/
.i.
i f +
~)2
~x/. ,l_# j
~
Y3
V ' " °
,
'
-
'
'
RE hnZ~
-
40 °
I-i~'rwllf/lll/'/
1" '
A_,7i ~
" ' " '
lig..j b
Fig. 4. Geological section of the Mongxi REE--Nb ore deposit, scale 1:15 000. -~5 ~: bio tite granodiorite; 73: biotite granite; 62: metadiorite:An Z~ : marble;An Z~: two-mic;~ quartz schist; RE: ore body. S
1
2 3456
7
8
:':~:
~z"
Fig. 5. Geological section of the Liaowong B--Fe--REE ore deposit, scale 1:15000. 1: granite migmatite ; 2 : tourmaline hornblende granitic migmatite; 3: tramelite (tourmaline) albite granulite; 4,9: tramelite albite granulite; 5 : plagioamphibolite; 6: tramelite tourmaline albite granulite; 7: mineralized serpentinite; 8: ore body; 10: diopside tramelite albite granulite ; 11,12: tramelite albite granulite. T A B L E III R E E and Y a b u n d a n c e s of s o m e Chinese R E E , Fe ore d e p o s i t s (in p p m ) S a m p l e a n d No. in Figs. 8, 10, 14, 16
Mongxi
RE203
La
Ce
Pr
Nd
(Fig. 10)
Mineralized Mineralized Mineralized Mineralized
marble ( 1) schist (4) m a r b l e (2) schist (3)
286 210 433 281
68.0 54.9 100.4 79.3
104.2 77.4 169.6 121.5
7.9 6.2
32.1 18.9 54.5
310 35000
53.7 7450
104.0 13860
12.0 1320
46.7 4330
240
32.8
72.0
7. I
27.{i
2220
214.9
392.1
52.1
257.3
4400
435.2
340
58.0
128.7
500 550
88.3 75.0
173.0 181.4
L i a o s h e n g (Fig. 8) Biotite plagio-granulite (2) Monazite biotite barbite magnetite
o r e (3)
Jida (Fig. 8) Massive h a e m a t i t e ore (1) Jilin (Fig. 14) Mn-bearing c h a m o s i t e siderite h a e m a t i t e o r e (5) M n - b e a r i n g c h a m o s i t e siderite h a e m a t i t e o r e (4)
1100
138
611
J i p a n g (Fig. 8) Oolitic h a e m a t i t e ore (4)
51.0
L u s h u i (Fig. 16) Massive h a e m a t i t e ore (1) Massive m a g n e t i t e o r e (2)
17.4 19.1
63.9 75.5
137
REE occur mainly in monazite and apatite. In addition to the regular minerals magnetite and monazite, rare minerals such as ludwigite, boromagnesite and stillwellite are usually found in the REE--Fe--B association. REE minerals were possibly authigenic or partly detrital and were subjected to later metamorphism and migmatization. Monazite gave U--Pb isotopic ages of 1780--1923 Ma (Wang and Xu, 1973), probably indicating a metamorphic event. Figure 5 is a simplified geologic section, and Table III presents the REE abundances of this type of mineralization. (4) REE--Fe formation in unmetamorphosed clastic formations. 2'his refers to the late Proterozoic oolitic iron ores of NE China as exemplified by the Jilin deposit. This type of formation is generally barren in rare metals except for REE. The mineralization is of typical sedimentary origin. The Fe ore minerals are haematite, siderite, rhodochrosite and chamosite. The results of selective solution and electro-osmosis analysis have shown that the REE occur substantially in adsorbed form on Fe and Mn minerals, but small amounts of monazite and xenotime are also observed. The contents of Fe, Mn and REE are 30--40%, 5--10% and 0.1--0.5%, respectively, forming a Fe--Mn--REE association. Table III lists REE abundances. (5) REE in phosphorites. Late Proterozoic to early Cambrian phosphorite deposits are widespread in SW China. They are all marine sedimentary de-
Sm
Eu
Gd
Tb
5.4 2.7 7.8 7.6
1.7 1.0 2.4 2.3
3.8 2.5 2.5 5.6
8.1 558
1.8 163
6.7 428
6.3
4.8
7.0
63.9
19.2
73.9
148
30.4
141
9.4
2.3
5.6
13.4 18.0
3.5 3.8
12.1 17.2
Dy
Ho
Er
Tm
1.9 1.7 3.0 2.5
1.7 1.7 1.6 2.0
1.7 1.6 1.5 2.0
0.7 66
3.7 165
0.7
1.8 67
l.l
5.7
1.1
12.7 22.4
71 Ill
7.4 10.5
Y
LREE/ HREE
6Eu
0.6 0.6 0.9 0.7
9.3 5.8 12.9 9.9
11.5 11.6 15.0 9.3
1.17 1.28 1.39 1.11
0.7
1.5
16.1 719
7.1 19.2
0.79 1.08
3.1
0.4
1.8
28.2
3.1
2.43
16.1
42.2
9.7
32.6
552
1.2
0.94
23
61.6
11.6
42.5
766
2.1
0.78
3.0
1.3 1.9
Yb
1.5
1.3 1.9
3.5 4.8
1.0
0.9
9.6
12.8
0.98
3.5 2.9
28.4
6.3 4.4
0.76 0.71
138
posits. Some of them may contain REE up to thousands of ppm as in Qianzhong. REE are mainly in collophane, forming the P--REE association. GEOCHEMICAL
CHARACTERISTICS
OF PRECAMBRIAN
REE MINERALIZATION
Having briefly discussed the above-mentioned types of Proterozoic REE mineralization in China, we may conceive that they are mainly of marine sedimentary origin(both non-metamorphosed and metamorphosed). Except for the REE--Fe mineralization in unmetamorphosed oolitic iron formations, all other types of REE mineralization result from chemical deposition, regardless of the source material (submarine volcanogenic, continental or halmyrolysis). Like the Archaean and Proterozoic BIF of the world, most Chinese REE or REE--Fe formations of Proterozoic age rarely contain clastic minerals. Since most of the Proterozoic REE and REE--Fe formations in China are chemical or biochemical precipitates from sea water, the evolution of atmosphere and hydrosphere would have an important bearing on their genesis. As is now generally accepted, the Archaean atmosphere was enriched in CO2 and N: but impoverished in O2 (Hou et al., 1974; Fryer, 1977). The thenexisting abundant atmospheric CO2 prevented precipitation of large amounts of carbonate, as well as phosphate, as the latter would exist in the soluble
50
20
-,3 \
gl0
\ ,
.)
\
/:, IO
e~
o
La
Ce
Pr
Nd
Sm
Eu
(;d
Tb
D.~
[to
Er
Tm
Yb
Fig. 6. R E E d i s t r i b u t i o n p a t t e r n o f A r e h a e a n A n s h a n - t y p e Fe ore deposit. For analytical data and numbers see Table II.
139
1000 5(XI
4
t.-.
100
,)
¢,9
5o
-
10
l
1
t
I
ha Ce Pr Nd
l
1
I
I
~
I
I
I
l
Sm Eu GdTb I)y Ho Er TmYb Lu
Fig. 7. REE distribution pattern of Dianyi Fe--Cu--REE ore deposit. For analytical data and numbers see Table II.
1000500-
10(} 1
50 O
10
"o3 1
I
i
I
t
t
1
t
t
!
i
I
l
I
LaCePrNd SmEuGdTbDyHoErTmYbLu Fig. 8. REE distribution pattern of the Jida (1), Liaosheng (2,3) and Jipang (4) ore deposits. For analytical data see Table III.
140 H2PO~ form. This is the reason why the Archaean formations are depleted in REE, since the REE precipitated from sea water would either go into carbonate, isomorphically replacing Ca, or form independent REE carbonate or phosphate minerals such as monazite and bastnasite. The precipitation of large amounts of REE-bearing carbonates and REE minerals from sea water, unlikely in the Archaean, was rendered possible in Proterozoic times with the noticeable reduction of atmospheric CO2 and the increase of free O2. It must be emphasized here that the large accumulation of REE in certain Proterozoic formations such as at Baiyun Obo and at Olympic Dam, Australia, may be related to ~ow temperature metamorphism or reworking since recent experiments show that hydrous, ,(300°C media could stimulate remobilization and enrichment of REE, especially the LREE (Wood, 1976; Ludden, 1979). Ludden reported that the c o n t e n t of LREE may increase up to ten times during low grade metamorphism. The above mentioned five types of REE mineralization have the following elemental associations: Fe--REE--Nb (Baiyun Obo); Fe--REE--Nb--P (Minsong); Fe--REE--Nb--Cu (Dianyi); Fe--REE--B (Liaowong); Fe--REE--Mn (Jilin); Fe--REE (Liaosheng); REE--Nb--P (Mongxi) and P--REE (Qianzhong). The close paragenesis of REE and Fe mineralization in the Proterozoic too I
100
-~ 51) g
l0 ~3 5
1 La
[ Ce
I Nd
I 1 Sm Eu
I Gd
i Dy
1
¥b
Fig. 9. REE distribution p a t t e r ~ of granulites of the Liaowong deposit (after Li Shouyi, 1983). 1: magnetite granulit~; 2: tourmaline granulite; 3: biotite plagiogranulite.
141
may be explained by the fact that in the marine environment both tend to be soluble in acid reducing water (Archaean hydrosphere), but began to be precipitated in basic oxidizing water some 2000--2200 Ma ago. If sea water is saturated with respect to both REE and Fe, they could be coprecipitated. Not to be excluded is the process of adsorption of REE on Fe and Mn minerals. For instance, in the Jilin ores REE exist mainly in adsorbed form on haematite and rhodochrosite, with only a small a m o u n t of monazite and xenotime. Some experimental investigations gave strong evidence for the close paragenesis of REE and Fe (Balashov, 1966; Wang, Chen and Wu, personal communication, 1982). In REE-bearing solutions addition of Fe and Mn compounds can promote the REE hydrolysis. When pH is equal to 5.6 the REE hydrolysis ratio can be enhanced from 13% to 60% (Wang, Chen and Wu, personal communication, 1982). Another interesting observation is that the REE--Fe or REE mineralization results in highly fractionated REE distribution patterns (Figs. 6--16,
50{II I
I
21101
%.?\ 1 oo
•~
50
ee-.
:..)
IO
1
2
La
Ce
Pr
Nd
Sm
Fig. 1 0 . R E E d i s t r i b u t i o n p a t t e r n d a t a a n d n u m b e r s s e e T a b l e III.
Eu
(;d
l)y
IIo
Er
of the Mongxi REE--Nb
Yh ore deposit. For analytical
142
506
ZO(
"'C ,,..,
t,-,
\
m
"~,"
""-
\ .~"/ \ \
4
z, 3
lO
"'-,
l.a
(','
t'r
~:,1
~4m t.;u
I;,1
h
I~'~' Ib,
,,.-"2
Fir
f'm YI,
" I
I u
Fig. 11. REE distribution patterns of early Proterozoic metamorphic rocks in Inner Mongolia (data from Wang Yixian, personal communication, 1983). For analytical data see Table V.
Wedepohl, 1970). The L R E E / H R E E ratio is much higher than 1 {Table IV). Furthermore, the L R E E / H R E E ratio becomes greater when the total REE content increases. Thus, in Baiyun Obo the ratio reaches 40--60. The LREE enrichment is mainly due to the much higher crustal abundance of LREE over HREE. For example, this ratio may be up to 15.5 {average 7.9, Table V) in the Baiyun O b o early Proterozoic metamorphic rocks. On the other hand, the stability of complexes of LREE and H R E E may also have some effect. From the Archaean to the Proterozoic the content of CO: in the atmosphere decreased gradually, while the pH of the hydrosphere increased gradually, changing from acid to neutral and weakly basic. Experiments show that REE can form complexes with CO]- in basic solution, and the H R E E complexes are more stable than those of the LREE (Huang et al., 1981). Thus, separation of LREE from H R E E would occur with LREE even more enriched in the sediments. EVOLUTION OF PRECAMBRIAN REE MINERALIZATION
From the above-mentioned geological relationships in China, it seems that REE deposits of sedimentary genesis may reflect a time-bound development, i.e., they occurred mainly in the middle to late Proterozoic. The greatest ac-
~:;
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|.u
I.u
Fig. 12, R E E d i s t r i b u t i o n p a t t e r n s f o r d i f f e r e n t t y p e s o f o r e in t h e B i y u n O b o o r e d e p o s i t . M F = Massive N b - - R E E - - F e o r e , Z F = B a n d e d N b - - R E E - - F e o r e , A F = A e g i r i n e N b - - R E E - - F e ore, R F = R i e b e c k i t e N b - - R E E - - F e ore, D F = D o l o m i t e N b - - R E E - - F e o r e , PD = D i o p s i d e N b o r e , A = A e g i r i n e N b - - R E E o r e , D = D o l o m i t e N b - - R E E o r e . F o r a n a l y t i c a l d a t a see T a b l e II.
,v,
2
I0~ ,
10:
c~
144
1oo
\
I I
l.
I o0
.:-
I
1
I
I ~
t
I
I
I
I
1
Z
%
..x....,...,,'%,,,
o.
•.. \ .
~
".. ,,.,
I
.....
,
N~
3
10
............ \2""
""........-6 1
I
I
I
1 I
I 1
i
J
I
I
I
1
I
!
"', ,1 I
l
I.a Ce t'r Nfl SmEu Gd Vi, l.u l.a Ce Pr Nd SmEu GdT b I., Fig. 13. R E E distribution patterns in the Baiyun Obo Group, Inner Mongolia (for analytical data and abbreviations see Table VI). lc: H~c; ls: H~q; 2: H2; 3: H3; 4: H,; 5: Hs; 6: H,; 7: H~; 8: Hs; 9: Hg; 6--8: H~_~ ; G: H~_~(G); Z: H6_~ (Z).
5000I
I
5ool-
100I
1
5
10 i taCleCr,~d SlaEtuG'd'Fbl)yl~oErT'm~'bLu Fig. 14. REE distribution patterns of the MiaJong (1, 2, 3) and dilin (4, 5) ore deposits. For analytical data and numbers see Tables II and III.
145 cumulation of BIF occurred, however, in the early Proterozoic. This is the first characteristic of the evolution of Precambrian REE mineralization. The second is that the enrichment or depletion of Eu evolves with geological time. REE distribution patterns show obvious positive Eu anomalies (5 Eu > 1) for the Fe ores or wall rocks in the Archaean Anshan Fe deposit (Fig. 6). The same feature appears in the REE--Fe or REE deposits formed during the early or early mid-Proterozoic ( ~ 1 9 0 0 Ma ago) such as Dianyi, Jida, Liaosheng, Liaowong and Jipang, where REE distribution patterns of ores or wall rocks exhibit positive or no Eu anomaly (8 Eu >/ 1, Figs. 7--9). For the Mongxi REE--Nb--P deposit the REE distribution patterns show a weak positive Eu anomaly (average 6 Eu = 1.1, Fig. 10). It may have been formed during early to middle Proterozoic time according to the REE patterns although there is no isotopic age available. Early Proterozoic metamorphic rocks (gneiss and marble) in Inner Mongolia have no Eu anomalies (Fig. 11). However, different from the above-mentioned features, the REE distribution patterns show negative Eu anomalies (8 Eu < 1) for the mid to late Proterozoic REE--Fe formations. For example, different types of ores in Baiyun Obo (Fig. 12, Table VI) such as the massive type (MF), banded 2{}0
~9 t~ tc-
O
2 -
,, . . _ . a 6
1
I
I
I
l
La
Ce
Pr
Nd
Sm
I
i
Eu Gd
I
Tb
~
I
Dy Ho
I
I
I
Er Tm Yb
I
Lu
Fig. 15. (a) REE distribution patterns in rocks of the middle and late Proterozoie Jixian profile. For analytical data and numbers see Table VII.
146 200
100 50
t_
O e-
20
L~ .M 10
La
Ce Pr
Nd
Sm
Eu Gd T b
Dy
Ho
Er Tm Yb Lu
Fig. 15. (b) REE distribution patterns in rocks of the middle and late Proterozoie dixian profile. For analytical data and numbers see Table VII.
50O
100
•
o
.~ 50 L~ o
10
I
I
i
i
LaCePrNd
t
i
i
Tb I
i
t
t
SmEuGd DyHoEr
Tm I
I
I
YbLu
Fig. 16. REE distribution pattern of the Early Palaeozoic Lushui Fe-ore deposit. For analytical data and numbers see Table III.
147 TABLE IV REE geochemical parameters of some Precambrian Fe, REE ore deposits and metamorphic rocks Sample
Location, age
Iron ore Quartz plagioclase hornblende schist Iron ore Iron ore Iron ore Biotite hornblende gneiss Iron ore Granulite Mineralized marble and schist Gneiss, marble
Anshan, Archaean Anshan, Archaean
REE--Fe ore Quartzite, slate, dolomite, sandstone REE--Fe ore Biotite quartz schist Shale, sandstone dolomite Iron ore Iron ore
LREE/ HREE
8 Eu
2.6 2.0
1.93 1.96
Dianyi, Proterozoic 4.6 Jida, early--mid Proterozoic 3.1 Liaosheng, early Proterozoic 19.2 Jixian, late Archaean 4.9 Jipang, early--mid Proterozoic 12.8 Liaowong, early--mid Proterozoic 6.9 Mongxi, early--mid Proterozoic 11.9 Inner Mongolia, early Proterozoic 7.9 Baiyun Obo, mid Proterozoic 47.0 Baiyun Obo, mid Proterozoic 6.6
2.35 2.43 1.08 1.03 0.98 0.87 1.24
Minsong, Proterozoic Minsong, Proterozoic Jixian, mid and late Proterozoic Lushui, Devonian Jilin, mid--late Proterozoic
0.84 0.70 0.71 0.74 0.86
12.0 7.0 9.0 5.3 1.7
0.96 0.70 0.74
b Eu -- Eu/Eu* H R E E (Gd--Lu, Y)
t y p e ( Z F ) , aegn:ine t y p e ( A F ) , r e i e b e c k i t e t y p e ( R F ) a n d d o l o m i t e t y p e ( D F ) o f t h e R E E - - F e - - N b ores as well as t h e aegirine t y p e (A) a n d d o l o m i t e t y p e (D) o f the R E E - - N b ores, t h e d i o p s i d e t y p e (PD) o f t h e Nb ores, as well as t h e s e d i m e n t a r y r o c k s (slate, q u a r t z i t e , s a n d s t o n e , l i m e s t o n e and d o l o m i t e ) o f the J i a n s h a n - - O u l u w u l a a n d H e i n a o b a o profiles o f t h e B a i y u n O b o G r o u p (Fig. 13, T a b l e VI), possess R E E d i s t r i b u t i o n p a t t e r n s with negative Eu a n o m a l i e s (5 Eu < 1). T h e s a m e f e a t u r e is o b s e r v e d in t h e Minsong and Jilin d e p o s i t s (Fig. 14). We have a n a l y s e d t h e R E E c o m p o s i t i o n o f various r o c k s o f late P r e c a m brian to P a l a e o z o i c age. T h e Jixian profile ( 8 0 0 - - 1 9 5 0 Ma) and t h e Early Palaeozoic Fe d e p o s i t (Lushui, Ningxiang t y p e } have R E E p a t t e r n s t h a t also s h o w clear negative Eu a n o m a l i e s (Figs. 15, 16, T a b l e VII). Based o n t h e a b o v e analysis, we arrive at t h e following c o n c l u s i o n a b o u t t h e e v o l u t i o n o f P r e c a m b r i a n R E E m i n e r a l i z a t i o n . A r c h a e a n a n d early Prot e r o z o i c ores are rich in Eu; R E E p a t t e r n s display positive or no Eu a n o m a l y , while mid- to late P r o t e r o z o i c ores h a v e negative Eu a n o m a l i e s . This f e a t u r e is m a i n l y d u e to t h e c h e m i c a l e v o l u t i o n o f t h e a t m o s p h e r e and t h e h y d r o sphere. Eu o c c u r s in t w o valence states, Eu 2÷ a n d Eu 3÷. Eu existed m a i n l y in Eu 2÷ f o r m in t h e A r c h a e a n a n d early P r o t e r o z o i c b e c a u s e o f l o w e r o x y g e n
V
20.9 30.9
a S a m p l e N o . s h o w n in F i g . 1 1 .
marble Quartz biotite gneiss
40.6 83.0
62.4 94.8 117.8 161.4 243.1 116.4
gneiss (3) 25.6 Granitic gneiss 40.8 Leucogranulite 55.9 Augengnelu (4) 72.5 Biotite plagiogneiss (5) 125.3 Diol~ide marble 87.3 Phlogopite serpentine
Ce
227.1 31.7
La
of Early Proterozoic
G r a n i t i c m i g m a t i t e (1) a 1 2 9 . 6 Gabbroie gneiu (2) 13.9 Hornblende plagio-
Rock type
REE composition
TABLE
6.7 11.1
9.6 14.2 15.8 24.2 37.8 11.6
29.2 4.9
Pr
21.7 36.2
2.2 46.2 46.5 76.7 112.1 25.4
7.8 16.4
Nd
3.7 7.7
6.9 8.9 7.6 15.3 20.2 3.2
8.7 3.5
Sm
1.0 2.0
2.2 2.2 2.1 3.6 5.0 1.1
2.6 1.2
Eu
2.8 7.6
6.9 8.0 6.8 14.2 17.9 5.3
9.4 4.0
Gd
0.3 1.1
1.5 1.3 1.1 2.2 2.7 0.6
1.7 0.8
Tb
0.9 4.9
4.4 3.6 2.6 7.7 7.5 1.8
1.7 2.6
Dy
-1.0
2.2 1.3 0.7 2.5 3.1 -
1.5 1.0
Ho
0.4 2.1
2.0 1.6 0.9 3.1 2.5 0.9
0.5 1.3
Er
0.2 0.1
0.6 0.4 0.3 0.4 --
0.5 0.2
Tm
0.8 3.5
3.1 2.1 0.9 3.6 3.3 1.1
1.3 1.7
Yb
h o r i z o n s i n I n n e r M o n g o l i a (in p p m ) ( W a n g Y l x i a n o p e r s o n a l c o m m u n i c a t i o n ,
0.7
0.7 0.5 0.3 0.9 0.7 --
0.1 0.6
Lu
1983)
2.8 25.3
19.8 18.4 9.3 32.0 35.5 9.4
7.4 13.3
Y
123 262
210 293 322 504 740 317
595 117
11.5 3.7
3.3 5.6 10.9 5.3 7.8 12.8
15.5 2.8
LREE/ HREE
ERE,O3
0.98 0.87
1.09 0.87 0.95 0.84 0.91 0.91
1.02 I.II
5Eu
00
23.4 225 7.4 0.75
2.4 165 17.4 0.83
3.9 95 10.3 0.87
13.5 41.7 3.6 10.2 2.3 0.50 1.3 0.21 0.88 0.22 0.20 -0.23
H4
H~
10.5 195 9.5 0.88
25.5 93.4 6.3 16.1 3.4 0.88 0.86 0.46 1.9 0.46 0.48 -0.79
H6 9.4 19.0 2.5 7.5 16 0.42 1.9 0.25 1.5 0.39 0.52 0.06 0.61 0.11 8.3 65 3.0 0.81
H7 7.1 17.0 2.0 6.7 1.4 0.51 1.5 0.22 1.4 0.37 0.76 0.12 0.94 0.19 9.5 60 2.3 1.2
HR 21.0 41.4 5.9 19.8 4.5 0.91 5.4 0.77 4.8 1.1 2.5 0.36 2.6 0.27 29.7 170 2.0 0.63
H9 38.8 83.7 9.5 28.2 5.2 1.1 4.9 0.76 3.1 0.78 1.4 0.25 1.5 0.31 15.9 235 5.8 0.71
59.1 140.6 15.1 45.1 9.1 1.9 7.8 1.6 8.3 2.2 4.1 0.67 4.6 0.49 51.4 425 3.3 0.72
20.2 43.1 5.4 17.0 3.5 0.73 3.4 0.58 3.1 0.82 1.5 0.22 1.9 0.14 18.8 145 3.0 0.71
H5
10.4 109 4.9 0.81
13.1 45.7 3.4 9.9 2.2 0.52 1.1 0.32 1.8 0.37 0.61 . 0.76
H6_ s
15.7 316 0.8 0.58
55.9 109.7 13.9 44.4 8.0 1.3 5.9 0.86 3.9 0.83 1.1 . . 1.8
Hg
Guyang
9.0 175 9.4 0.74
23.7 81.6 5.8 16.2 2.9 0.59 1.5 0.34 1.8 0.24 0.60 . 0.52
11.2 175 6.2 0.49"
0.69
319 578 7.7 23.3 4.1 0.62 4.4 0.55 2.1 0.47 0.89
H6--R ( Z ) H6--~ ( G )
Zhurihe
G u y a n g : H~_s(G): siliceous limestone.
J i a n s h a n - - - O u l u w u l a p r o f i l e : H I c: q u a r t z c o n g l o m e r a t e , H I : q u a r t z slate, H 2 : s l a t e : H4: q u a r t z i t e , Hs: slate, H6: d o l o m i t e , H~: c a l c a r e o u s s a n d s t o n e , tis: siliceous l i m e s t o n e . H~: slate. H e i a u b a u p r o f i l e : H3: slate, Hs: slate, H6.-e: s i l i c e o u s d o l o m i t e , H9: s i l i c e o u s d o l o m i t e . Z h u r i k e : t1~-- s ( Z ) : slate.
2.0
36.5 94.1 9.4 26.4 5.7 1.2 5.2 0.91 3.8 0.87 1.8
H3
. --
43.2 52.4 7.8 21.6 4.5 1.1 3.8 0.39 0.93 ---
H2
H3
27.2 64.2 7.3 22.7 4.3 0.93 3.5 0.60 3.7 0.50 1.4
Ht
Hi c
69.6 103.7 19.7 59.2 10.5 0.85 9.2 0.98 3.3 0.49 1.3
Heiaubau profile
Jianshan--Ouluwula profile
Tm . . . Yb 1.3 1.7 Lu y 12.6 15.7 RE203 350 185 LREE/HREE 9.0 4.7 Eu 0.28 0.78
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er
Element
REE composition of Bayun Obo Group Strata (ppm)
T A B L E VI
150
fugacity. Owing to the crystal--chemical similarities of Eu 2+ with Ca `++ and the enrichment of Ca in the Archaean and early Proterozoic crust, Eu could easily get into rocks rich in Ca, giving rise to abundant Eu accumulation m this period. High oxygen fugacity resulted in Eu depletion in later times, that is, middle to late Proterozoic and Phanerozoic. TABLE VII REE c o m p o s i t i o n of Jixian Profile strata ( p p m ) Element
La
Ce Pr Nd Sm Eu Gd Tb Dy Ho
Er Tm YI) Lu Y
Changz-Chuan- Tuanzi- Dahon- Gaoyu- Yangh o u c u n lingou shan gyu zhuang ~huang (1) a (2) (3) (4l (5) (6)
Hongshuizhai
11.3 21.2 2.8 8.1 1.4 0.26 1.4 0.13 0.45 0.12 0.24
50.2 121.8 12.3 36.2 6.6 1.32 4.5 0.64 2.5 0.45 0.76
0.30
0.58
17.3 54.9 4.9 ]3.9 3.4 0.79 2.5 0.51 2.8 0.76 0.87 0.14 1.84 0.25 21.1 155 3.2 0.78
2.4
RE203 60 LREE/HREE 9.0 [Eu
0.65
11.3 300 ll.O 0.76
35.0 85.5 8.5 24.4 4.2 0.82 3.2 0.42 2.4 0.45 0.85 0.96 11.8 215 14.2 0.72
20.5 65.0 4.6 12.0 1.2 0.27 --0.56 0.12 --
3.3 130 O.81
7.0 16.2 1.9 5.6 1.1 0.19 1.2 0.17 0.85 0.23 0.38 0.06 0.50 0.15 5.8 50 3.4 0.54
8.6 45.7 2.0 4.8 0.86 0.22 -0.08 0.59 0.08 0.07 --0.15 4.2 82 12.1
(8)
Tieling
Xiama- J i n g e r y u ling (10) (9)
4.8 6.6 1.2 4.2 0.94 0.20 1.3 0.21 I.I 0.27 0.37 0.07 0.66 0.09 11.2 40 1.2 0.62
20.7 45.9 4.9 14.2 2.7 0.63 3.4 0.59 3.4 0.92 1.2 0.33 2.5 0.33 22.5 150 2.5 0.71
(7)
36.5 .97.5 8.4 23.3 J,.5 1.1 2,6 (}.65 3.0 0.46, 027 1.4 17.4 238 (;.6 0.80
Changzhoucun: quartzite; Chuanlinggou: shale; Tuanzishan: d o l o m i t e ; Dahongyu: quartzite: G a o y u z h u a n g : d o l o m i t e ; Yangzhuang: silt d o l o m i t e ; Hongshuizhai: shale; Tieling: limestone: X i a m a l i n g : sandstone; Jingeryu: s h a l e . aSample No. s h o w n in F i g . 15.
CONCLUSIONS Five types of Precambrian REE mineralization can be distinguished in China: (1) carbonate-hosted Fe--REE deposits; {2) carbonate-hosted REE mineralization; (3) REE--Fe or REE--Fe--B mineralization in metamorphosed--migmatized volcanic and volcano-sedimentary rocks; {4) REE--Fe formations in clastic sedimentary beds and (5) REE in phosphorite deposits. In these five REE mineralization types eight kinds of elemental associations can be distinguished: (1) Fe--REE--Nb; (2) Fe--REE--Nb--P; (3) Fe .... REE--Nb--Cu; (4) Fe--REE--B; (5) Fe--REE--Mn; (6) Fe--REE; (7) REENb--P and (8) P--REE. All these REE mineralizations are enriched in LREE relative to HREE. They are mainly of sedimentary origin. The composition of atmosphere and hydrosphere (particularly the contents of CO: and O2) in the Precambrian played a significant role in the evolution of these REE mineralizations. REE deposits of sedimentary genesis may reflect a time-bound development: they occurred mainly in the mid to late Proterozoic, broadly parallel
151 w i t h , b u t l a g g i n g b e h i n d t h e g r e a t e s t a c c u m u l a t i o n o f B I F in t h e e a r l y P r o t e rozoic. REE d i s t r i b u t i o n p a t t e r n s show strong L R E E e n r i c h m e n t , and the Eu cont e n t s c h a n g e d s y s t e m a t i c a l l y w i t h g e o l o g i c t i m e for all a b o v e - m e n t i o n e d t y p e s . T h e R E E m i n e r a l i z a t i o n s in t h e A r c h a e a n a n d e a r l y P r o t e r o z o i c are rich in E u (5 E u ~> 1), b u t are d e p l e t e d in E u in m i d t o late P r o t e r o z o i c dep o s i t s (5 Eu < 1). ACKNOWLEDGEMENTS We are g r a t e f u l t o t h e L a b o r a t o r i e s o f o u r I n s t i t u t e f o r a n a l y s i s o f t h e R E E c o n t e n t s . We also t h a n k W a n g Y i x i a n f o r p r o v i d i n g R E E d a t a o f m e t a morphic rocks from Inner Mongolia.
REFERENCES Balashov, Y.A. and Gorianov, N.M., 1966. Rare earth elements in the Precambrian iron ore formation of the Priimandrov region, Geokhimiya, 3 : 3 1 2 - - 3 2 2 (in Russian). Fryer, B.J., 1977. Rare earth evidence in iron-formation for changing Precambrian oxidation stage. Geochim. Cosmochim. Acta, 41: 361--367. Hou, D.F., Ouyang, Z.Y. and Yu, J.S., 1974. Evolution of the terrestrial materials in relation to nuclear energy, Science Press, pp. 47--51 (in Chinese). Huang, S.H., Zhang, Z.M., He, S.Y. and Wang, Z.G., 1981. Experimental studies on transportable forms and precipitation conditions for REE in sea water. Geochemistry, 2: 142--152. Li, S.tT., 1983. REE distribution of the boron ore in Liaoning Province, China. J. Chan~ chun College of Geology, 1 : 3 9 - - 5 2 (in Chinese). Ludden, J.N., 1979. An evolution of the behaviour of the rare-earth elements during the weathering of sea-floor basalt. Earth Planet. Sci. Lett., 43: 85--92. Qiu, Y.Z., Wang, Z.G. and Zhao, Z.H., 1981. A preliminary study of REE iron formation. Geochemistry, 3 : 1 8 5 - - 2 0 0 . Taylor, S.R., 1979. Chemical composition and evolution of the continental crust: the rare earth element evidence. In: M.W. McElhinny (Editor), The Earth, its Origin, Structure and Evolution. Academic Press, London, pp. 353--372. Vinogradov, A.P., 1962. Average contents of chemical elements in different types of igneous rocks of the crust. Geokhimiya, 7 : 555--565. Wang, X.Z. and Xu, X.Y., 1973. Genetic characteristics of Precambrian borate deposits in China. Geochemica, 1 : 12--22 (in Chinese). Wedepohl, K.H. (Editor), 1970. Handbook of Geochemistry. Springer Verlag, Berlin, vol. II/2. Wood, D.A., Gibson, I.L. and Thompson, R.N., 1976. Elemental mobility during zeolite facies metamorphism of the Tertiary basalts of Castern Icelan. Contrib. Mineral. Petrol., 55: 241--253.