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Lithium in dyke rocks of a plutonic sequence in the Bohemian Massif (Czechoslovakia and partly in Austria)
Chemical Geology, 19 (1977) 267--276 © Elsevier Scientific Publishing Company, Amsterdam --Printed in The Netherlands
267
L I T H I U M IN D Y K E R O C K S O F A P L U T O N I C S E Q U E N C E IN T H E B O H E M I A N M A S S I F ( C Z E C H O S L O V A K I A A N D P A R T L Y IN A U S T R I A )
v
D. NEMEC
Geoindustria, Jihlava (Czechoslovakia) (Received January 5, 1976; revised and accepted June 28, 1976)
ABSTRA Or N~mec, D., 1977. Lithium in dyke rocks of a plutonic sequence in the Bohemian Massif (Czechoslovakia and partly in Austria). Chem. Geol., 19: 267--276. The Li content in 129 samples of dyke rocks derived from three different areas of the Bohemian Massis (Bohemian-Moravian Heights and Waldviertel, Eastern Sudeten, central Bohemia) has been determined. The dyke rocks investigated are partly gene~ically related to the plutonic rocks of the area and their Li content is identical to that of the comparable plutonic rocks, and they belong partly to the lamprophyre series which is in no direct genetic relation with the plutonic rocks. The Li contents of these dykes are elevated. In the calcalkaline series of the dyke rocks the Li content and the Li/Mg ratio increase with progressing differentiation, whereas in the differentiation series of mica lamprophyres, which has an alkalic trend, the Li content and Li/Mg ratio decrease. The Li content of the dykes is controlled by the Mg content of the rock, by its acidity, its content of pneumatolytic components (the grain size), the chemical composition of the constituent micas, and by the F content of the rock.
INTRODUC'rION The Li c o n t e n t has been d e t e r m i n e d in 129 samples o f d y k e r o c k s derived f r o m t h e f o l l o w i n g d y k e - r i c h areas o f t h e B o h e m i a n Massif: (I) the B o h e m i a n Moravian Heights and t h e a d j a c e n t p a r t o f Waldviertel in Austria; (H) Eastern S u d e t e n , n a m e l y , t h e m o u n t a i n ranges b o r d e r i n g the depression o f K l o d z k o ; and (III) central B o h e m i a ( F i g . l ) . In the first area, m o s t l y d i f f e r e n t p o r p h y r i e s o c c u r a n d alkalic d y k e s are rare. In the Eastern S u d e t e n , m o s t l y a m p h i b o l e spessartites and m i c r o g a b b r o s appear. Alkalic d y k e s are w i d e s p r e a d in the Orlick~ h o r y Mountains. In central B o h e m i a , in t h e Central B o h e m i a n P l u t o n , d y k e s are especially n u m e r o u s a n d p e t r o g r a p h i c a l l y variable. The d y k e s o f all the areas c o n s i d e r e d are c h a r a c t e r i s e d p e t r o g r a p h i c a l l y elsewhere (Nemec, 1 9 7 0 ; 1975a, b). As s h o w n b y B r o c k ( 1 9 4 3 ) , t h e Li c o n t e n t o f l a m p r o p h y r e s is i n f l u e n c e d b y r o c k w e a t h e r i n g . Hence, o n l y fresh r o c k s were studied. Li was d e t e r m i n e d b y emission spectral analysis, a c c o r d i n g t o t h e m e t h o d o f S u k n e v ( 1 9 6 7 ) , using a Zeiss grating s p e c t r o g r a p h PGS 2. T h e samples o f d y k e r o c k , a n a l y z e d
268
'.i;k f ".,
i2•
o
PRAHA
","\ /< , / / / • -.,
l
"\
,,"
0
2':" ,J"
,." ~ / /
!I....
. I
//
o SSNO
lOOkm
Fig. 1. S k e t c h m a p o f B o h e m i a a n d Moravia s h o w i n g t h e l o c a t i o n of areas studted,
by atomic absorption, were used as reference samples. The relative error of determination was stated to be -+ 12%. The accuracy was tested by analyses of the rock standards GM (54 ppm Li recommended, 54 ppm Li found) and Chibina (20 ppm Li recommended, 21 ppm Li found). L I T H I U M C O N T E N T IN D Y K E R O C K S
The results of the Li determinations, arranged according to individual rock types and areas, are given in Table I. In the granitic dyke rocks analysed, the [,i content varies within a broad range. The dioritic dykes studied agree as to their Li c o n t e n t with the average of diorites (20--30 ppm Li). The microgabbros an,:i microsyenogabbros and the corresponding porphyritic types occurring in the Bohemian-Moravian Heights and the Eastern Sudeten display in both areas identical average Li figures (Table I). Geochemically, they cannot be corre~ lated with gabbros. They are mostly albitized and richer in alkalis than are gabbros. Other conditions exist in central Bohemia, where the gabbro porphyries are evidently associated with gabbro massifs. There, their Li content falls withi~ the range of 10--20 ppm given by different authors as the Li average of gabbros. The case of the spessartites is the same as that of microgabbros. The spessartite~ of the Bohemian-Moravian Heights and those of the Eastern Sudeten show identical average Li contents and ranges of Li concentrations. The spessartites of central Bohemia are petrographically different. Genetically they are associated with islets of gabbros. The mica lamprophyres of the three areas compared differ in their Li contents, being, however, lower in Li than the minettes of Jersey (Lees, 1974). The samples analysed from the BohemianMoravian Heights are entirely kersantites, those from central Bohemia minettes. Alkalic minettes differ from the normal ones in the presence of alkalic amphibole, mostly richterite. In Eastern Sudeten, their Li c o n t e n t corresponds to that of normal minettes. The alkalinity of the alkalic rocks from the areas studied is due to alumina deficiency, not to lack of silica. The alkalic microgranites and microsyenites of these areas consist of K-feldspar, alkalic amphibole and quartz, sometimes also containing an admixture of aegirine. In addition to fine-grained types
20--120
10--55
10
5
25
55
44 29
14--120 12--50
10 7
130 I35 15 28
average content
9
14--280 15--235 10--23 18--38
range of contents
1
8 8*' 9"2 4
number of samples
The Bohemian-Moravian Heights and Waldviertel
5 3
10 4
7 8
number of samples
14--50 64--230
13--92 10--60
11--89 11--71
range of contents
Eastern Sudeten
*' Dykes from the environs of Nov~i Bystrice; ,2 dykes from the environs of Havlfckfiv Brod.
Leucocratic microgranites Biotite granite and granodiorite porphyries Pyroxene granodiorite porphyries Pyroxene syenite porphyries Amphibole microdiorite and diorite porphyries Amphibole microgabbros, microsyenogabbros and their porphyric types Amphibole spessartites Pyroxene minettes and kersantites Alkali minettes Alkali microgranites and microsyenites Alkali granites and syenites
Rock type
Lithium concentrations in dyke rocks (ppm)
TABLE I
27 135
31 35
41 27
average content
1
10
13--45
17--55
33--43
4 4
35--60
range of contents
5
number of samples
Central Bohemia
26 14
15 20
27
38
50
average content
270 also medium-grained alkalic dyke granites and alkalic dyke syenites appear. The latter are higher in Li than the fine-grained types and may be correlated with similar alkalic granites and syenites from Nigeria (Bowden, 1966) ov Texas (Horstman, 1957), both of wt~ich are fairly rich in Li. The fine-grained alkalic dykes from the Bohemian-Moravian Heights have Li contents strikingly similar to comparable rocks of the Orlicke hory Mountains. Irrespective of the alkalic granites and syenites, the acid': dykes of the l]mealkalic series are mostly richer in Li than alkalic ackl dykes, evidently (iue t~J the absence of micas and the richness in K-feldspar in the latter. Simitarly~ the higher Li content of mica lamprophyres as compared with that ~,t: spessartites may be attributed to the presence of micas in the former an(l ~)t Ca-amphibole, low in Li (Vorontsov and Lin, 1966; Lyakhovich, t972}, i~. the latter. From some dykes, several samples were analysed. ]'he Li amom~ts obtai~e,: sometimes are identical, sometimes they dift'er considerably. Of speciai int.ere~ are those dykes in which a heteromorphism exists: the mineral compositkm changes essentially (pyroxene m i n e t t e - amphibole spessartite; alkalic a m p h i b o microsyenite--hyperpotassic l~iotite m ierosyenite), the chemical compositio~ remaining practically constant, In similar eases, the Li content does ~ot seem to change. FACTORS CONTROLLING THE L1 DISTRIBUTION IN DYKE ROCKS Mg content of rocks
Since the pioneer work of Strock (1936) the geochemical Mg--Li cohere~c~: is a well known and crystallochemicalty well-founded fact. It is, however~ valuable only for similar rock types derived from the same area (Figs. 2 a,~d 3 L~
~m 70tJ !
#0 30 20 70
0 I
s
Fig. 2. Li--Mg plot of acid spessartites, areas II and IlL
271 LI
ppra 90 8o 1o 60 5o
3o 2o 1o
3
L/
5
6
7
8
9 %Me
Fig. 3. Li--Mg plot of mica lamprophyres, area III. However, a clear correlation between Mg and Li is not found in the mica lamprophyres from the Bohemian-Moravian Heights and from central Bohemia. R o c k acidity
The increase of Li content with rising rock acidity also is a well-known and geochemically well explainable experience {compare, e.g., Heier and Billings, 1972). This is especially evident in Table I on the samples from central Bohemia belonging to the calc-alkaline series. The Li contents increase continuously from gabbro p o r p h y r y through diorite p o r p h y r y and syenite porphyry toward granodiorite and granite porphyries. That the Li/Mg ratio increases with acidity also is a well-known fact. In this connection, the dyke of Cer(~any, central Bohemia, is of special interest. During its consolidation, the magma differentiated in the dyke so that both its marginal zones are made up of pyroxene minette which passes continuously toward the dyke centre through a pyroxene granodiorite p o r p h y r y into a biotite granodiorite p o r p h y r y (for details see N~mec, 1973). The concentrations for individual zones, from margins toward the dyke centre, are as follows, SiO~ (wt.%): 60.1, 62.6, 66.1; Mg (wt.%): 4.14, 2.78, 1.71; Li (ppm): 33, 41, 35; Li/Mg ratio × 1,000: 1.05, 1.46, 2.06. Grain size
The fine-grained alkalic dykes of the Orlick~ hory Mountains (area H) differ strikingly in their lower Li content from the coarser-grained alkalic granites and syenites. A similar case was described by Nesterenko and Frolova (1965) from the trapps of the Siberian plateau. There, the coarser-grained dolerites and the fine-grained basalts contain on the average 16 and 12 ppm Li, respectively.
272 The authors explain this fact by the escape of volatile Li-fluorides from the basalts which extruded on the surface of the earth. As a matter of fact, the alkalic granites and syenites dealt with m the present paper are essentially richer in F than the finer-grained alkalic types. The fine-grained alkalic microgranite:and microsyenites of areas I and H contain 0.23% F and 27 ppm Li (average of nine samples), whereas the alkalic granites and syenites 0.53% F and 135 ppm Li (average of three samples). Chemical co mposition o f m Was
In those rocks where mica prevails among colour minerals, the Li distributi(:~ of rocks is largely controlled by that of theii constituent micas (Kuts and Mishenko, 1963; Vorontsov and Lin, 1966). The Li contents of micas, however, evidently depend on their bulk composition. Accordingly, the Li conten*_ of rock may be correlated with the composition of the constituent micas. Similar interrelationships have been revealed only in comparing dykes of the same petrographic types derived from the same area. Fig. 4 shows the Li c o n t e n t of the rocks along with the Fe ratios [ ~/Fe/ (~2Fe + Mg) × 100] of their constituent micas for the pyroxene granodiorite porphyries of the environs of Raabs in Waldviertel and for the minettes of central Bohemia. In both cases a pronounced positive correlation exists, h~. the individual rock types the content of micas in the compared samples is approximately constant. For the pyroxene granodiorite porphyries menti(me(i the following figures were obtained, SiO2 of the rock (wt.%): 59.2, 62.0, 64.:i 63.5, 62.7; MgO of the rock (wt.%): 4.86, 2.75, 3.25, 3.27, 3.16; Li of the rock (ppm): 10, 18, 25, 31, 38; Fe ratio of biotite (at. ratio): 27, 33, 37, 40. 38. The MgO c o n t e n t was given to show that the Li content of the rocks does not show a relationship to the bulk 1VgO of the rock. ppz/7
501 I I
O
L
30ii -t
•
C, •
I¢ 6
•
::
Fig. 4. Li content of rocks and Fe ratio Q (~Fe/(~Fe + Mg)at.) of constituent micas.
Mica lamprophyres of Central Bohemian Pluton (circles) and pyroxene granodiorite porphyrie from the environs of Raabs ih Waldviertel (triangles).
273 In nature, a continuous isomorphic series exists between siderophyllite and zinwaldite (Rieder, 1970), b u t not between phlogopite and zinwaldite. However, more convincing evidence should be presented of whether this could explain the above-mentioned interrelationships. Phlogopite containing as much as 1% Li is also known (Sveshnikov and Kalentchuk, 1962), but only from metasomatic, not from magmatic rocks. The differentiation series of minettes is characterized by a continuous decrease of alumina contents, which finally causes the alkalinity of the rock. Its best indicator is therefore the Shand index (N~mec, 1973). The continuous decrease of the alumina contents with advancing differentiation is reflected in the chemical composition of micas by a progressive replacement of the siderophyllite molecule by a phlogopite one (N~mec, 1972a). As shown above, the Li content of micas probably depends on their Fe ratios, therefore it is also in relation to the rock alkalinity, as shown in Fig. 5.
9/z ,
p p m L/ 70.
3500
60
IO00
50
'500
qo.
~000 0
o
o
'bOO
30. 0
20
o o
o
t
•
0
•
.1000
0
500
Io
'6o
o.'6
a'zo
o.'75
o8o
Fig. 5. Li c o n t e n t (circles) and Mg/Li ratios (triangles) of minettes, the Central B o h e m i a n Pluton. Shand index on the ordinate.
Fluorine content o f rock
It is a well-known fact that the Li content of igneous rocks may be correlated with the F content. This is explained by the presence of F complexes in magmas (Kosteckaya and Petrova, 1966). In the dykes studied, a striking positive Li/F correlation is observable in the granite and granodiorite porphyries of the Bohemian-Moravian Heights (Fig. 6). However, it is probable that Li and F were partly introduced in some of the dykes mentioned, especially those rich in Li, by late-magmatic and post-magmatic processes. A precise linear relationship between Li and F observable in alkalic minettes of the Eastern Sudeten
274 %/z / &J
0
//
.J
0,0j/'/" /
....
i
....
@
--
~o
+--
-+.
i
0.20j
•
__ ........
0.i01 _i__.__ f . ............ 50
• I00
150
200
2J'0
p p m /;
Fig. 6. Li--F plot of alkalic minettes, area 1II 4triangles), and of acid (lykes, are~ tl (circles). (Fig. 6) results from the fact that micas prevail among the dark minerals of the rock. [It has been shown by Kosteckaya and Petrova (1966) and Tauson (1967 ~ that biotites recovered from different facies of the same massif have constant Li/F ratios.] In fine-grained biotite-free alkalic rocks from the area ~'onsidered in which an alkalic amphibole is the only dark component, no relatio~ was established between the Li and F contents. GENETIC CONCLUSIONS The dykes studied are of two different genetic types: (1) dykes genetically associated with plutonic rocks; and (2) dykes of a lamprophyre series, petrochemically independent of plutonic rocks of the area. In central Bohemia the dykes occur in the territory occupied by the Central Bohemian Pluton, p e t r ~ graphically a particularly varied intrusive body (Vejnar, 1973). The p e t r o chemical investigation of the dykes there has shown (N~mec, 1974a) that all the types mentioned in the present study, except for minettes, can be regarded as being genetically related to plutonic rocks of corresponding chemical composition. The similarity between the average Li contents o[ individual dyke types and those of the plutonic rocks (according to Vejnar, 1974) which are chemically closest to them, is striking. This is evidenced by the following data (ppm): gabbros and gabbro porphyries 15 and 15; amphibole-biotite quartz diorites (the S~izava type) and microdiorites plus diorite porphyries 25 and 27; granites (the Sedl6any type)rand microgranites plus granite porphyries 50 and 50; granosyenites (the "Certovo b}emeno" type) and the syenite porphyries 49 and 38; syenites (the T~bor type) and minettes 62 and 26, respectively. In the Bohemian-Moravian Heights and in adjacent Waldviertel, there extends an extensive m o n o t o n o u s acid massif called "the Central Moldanubim
275 % 6O 410
30 2O
~7
3O
/;
N /0
20 30
Yo
loo
250 300 p p m / / .v
o
Fig. 7. Li distribution in acid dykes from the environ of Havhckuv Brod (A) and from the environ of Pelh~imovand Nov~ Byst~ice (B), the Bohemian-Moravian Heights. massif". The basic, intermediate and alkalic dykes and lamprophyres occurring there all belong to one and the same lamprophyric intrusion, not related to the plutonic rocks of the area. The acid dykes differ genetically from the preceding group, but they also have no counterpart among the plutonic rocks of the Central Moldanubian Massif, with the exception of the leucocratic microgranites from the environs of Pelh~imov and Jindrichfiv Hradec which are high in Li (Fig. 7). Chemically these dykes are close to the granite of the Eisgarn type. Their genetic relations are also substantiated geologically. The Eisgarn granite is the latest and most acid intrusion of the Central Moldanubian Massif (Grohmann and Schroll, 1966). Among the plutonic rocks of the Central Moldanubian 5_~assifit is highest in Li (93--200 ppm). The average, 127 ppm Li, is very close to the average of leucocratic microgranites (130 ppm Li). The ~/:ykes studied in the Eastern Sudeten probably all belong to the lamprophyre series. The basic lamprophyres are assumed to have originated by contamination of tholeiitic magmas with sialic material. The Li content determined in the lamprophyres analysed corresponds with this hypothesis. The Li c o n t e n t of basaltic magmas of different types does not exceed 15 ppm (Heier and Billings, 1972). The Li content of spessartite, which among the rocks investigated most nearly resembles the basalts, is essentially higher (Table I). In different series of dyke rocks Li is distributed in two (iifferent ways, acoording to the type of magmatic ~;ifferentiation. h~ the calc-alkaline series, the Li content, as well as the Li/h~g ratio, increases. This can be observable, for instance, in central Bohemia in the gabbro porphyry--granite p o r p h y r y series (Table I). In the (;ifferentiation series of mica lamprophyres (the kersantite-minette--alkalic minette series) the alkalinity of rocks as well as their Mg/(Mg + EFe) ratio increase (N~mec, 1973) and the Li content am;. the Li/Mg ratio decrease (Fig. 5; for graphical reasons, the N~g/Li ratio instead of the Li/Mg ratio is given). REFERENCES
Bowden, P., 1966. Lithium in Younger Granites of Northern Nigeria. Geochim. Cosmochim. Acta, 30: 555--564.
276
Brock, R.W., 1943. Weathering of igneous rocks near Hong Kong. Geol. Soc. Am. Bull, 44: 717--738. Ginejko-Savicka, A., 1928. On the granite porphyry, amphibole-bearing rocks and fillings of quartz veins from the environs of Pelh~imov. Publ. Fac. Sci., Univ. Charles, Prague. No. 83 (in Czech ). Grohmann, H. and Schrolt, E., 1966. Zur Frage der Abhangigkeit der Konzentratiouen seltener Elemente yon der Altersfolge der granitoiden Gesteine der siJdlichen B6hmisch,~.~ Masse. Tschermaks Mineral. Petrogr. Mitt., 1 ] : 348--358. Heier, K.S. and Billings, G.K., ] 972. Handbook of Geochemistry (Lithium). Springer, Berlin, 37 pp. Horstman, E.L., 1957. The distribution of lithium, rubidium and cesium in igneous am] sedimentary rocks. Geochim. Cosmochim. Acta, 12: 1---28. Kosteckaya, E.V. and Petrova, Z.I., 1966. Distribution of some rare elements and mineralizer in the biotites of the Dzhiginsk granitoid complex. Geokhimiya, pp. 1057--1062 (in Russian). Kuts, V.P. and Mishenko, V.S., 1963. Distribution of lithium, rubidium and some of the minerals that contain them in the Kamennye Mogily and Yekaterinovka granites Geokhimiya, pp. 1124---11 39 (in Russian k Lees, G,I., 1974. Petrochemistry of the mica-lamprophyres (minettes) of Jersey i C.I. ) Proc. Ussher Soc., 3: 149-q55~ Lyakhovich, V.V., 1972. Rare Elements in Rock-Forming Minerals of Granitoids. Nauk, Moscow, 199 pp. (in Russian). N~mec, D., 1970. Lampro phyrische und lamproide Ganggesteine im Siidteil der B6hmisch Mghrischen Anh6he (C.S.S.R.). Tscermaks Mineral. Petrogr. Mitt., 14: 235--284. N6mec. D., 1972a. Micas of the lamprophyres of the Bohemian Massif. Neues Jahrb. Mineral., Abh., 117:196-~2:16. N6mec, D., 1972b. Ganggesteine aus der Umgebung yon Raabs (Nieder6sterreichisches Waldviertel). Verh. Geol. Bundesans. (Austria), pp. 247--262. N6mec D., 1973. Differentiation series of minettes in the Central Bohemian Pluion. J Geol., 81: 632--642. N~mec D., 1974a. Petrochemistry of the dyke rocks of the Central Bohemian Pluto~ Neues Jahrb. Mineral., Monatsh., pp. 193--209. N~mec D., 1974b. Lamprophyrische und lamproide Ganggesteine im Nordteil der B6hmiscr, Miirischen H6he. Verh. Geol. Bundesanst. (Austria), pp. 223--268. N~mec D., 1975a. Petrographie der lamprophyrischen und lanlproiden Ganggesteine im Nordostteil der B6hmischen Masse (C.S.S.R.). Z. Geol. Wiss., 3: 23--36. N~mec D., 1975b. Petrochemie und Genese der lamprophyrischen und lamproiden Ganggesteine im Nordostteil der BiShmischen Masse (C.S.S.R.). Z. Geol. Wiss., 3 : 3 7 --52 Nesterenko, G.V. and Frolova, L.P., 1965. Lithium and rubidium in trapps. Geokhimiya, pp. 343--347 (in Russian). Rieder, M., 1970. Chemical composition and physical properties of lithium--iron micas from the Kru~n6 hory Mts. Contrib. Mineral. Petrol., 27: 131--158. Strock, L., 1936. Zur Geochemie des Lithiums. Nachr. Ges. Wiss. G6ttingen, Math.--Phy.~ Kl., Fachgruppe 4, 15: 171--204. Suknev, V.S., 1967. A method for determination of low lithium contents in granitoids. Spectrochem. Anal. Geol. Geochem., pp. 187--188 (in Russian). Sveshnikova, E.V. and Kalentchuk, G.E., 1962: Lithium, rubidium and cesium in alkali rocks of Yeniseiskij Krazh. Geokhimiya, pp. 1055--1065 (in Russian). Tauson, L.V., 1967. Factors of the geochemical history of rare elements in the granite magmatic process. Geokhimiya, pp. 1310---1319 (in Russian). Vejnar, Z., 1973. Petrochernistry of the Central Bohemian Pluton. Geochem. Methods Data, No. 2. Vejnar, Z., 1974. Trace etemez~ts in rock of the Central BohemianPluton. Vgstn~ Ustr6d. Ustavu Geol., 49: 159--165. Vorontsov, A.Ye. and Lin, N.G.~ t 966. Rubidium anti lithium in the granitoids of the Bugulmin complex, Eastern ~i: ~!~,.;.(~eokhimiya, pp. 1108--1116 (in Russian ).
267
L I T H I U M IN D Y K E R O C K S O F A P L U T O N I C S E Q U E N C E IN T H E B O H E M I A N M A S S I F ( C Z E C H O S L O V A K I A A N D P A R T L Y IN A U S T R I A )
v
D. NEMEC
Geoindustria, Jihlava (Czechoslovakia) (Received January 5, 1976; revised and accepted June 28, 1976)
ABSTRA Or N~mec, D., 1977. Lithium in dyke rocks of a plutonic sequence in the Bohemian Massif (Czechoslovakia and partly in Austria). Chem. Geol., 19: 267--276. The Li content in 129 samples of dyke rocks derived from three different areas of the Bohemian Massis (Bohemian-Moravian Heights and Waldviertel, Eastern Sudeten, central Bohemia) has been determined. The dyke rocks investigated are partly gene~ically related to the plutonic rocks of the area and their Li content is identical to that of the comparable plutonic rocks, and they belong partly to the lamprophyre series which is in no direct genetic relation with the plutonic rocks. The Li contents of these dykes are elevated. In the calcalkaline series of the dyke rocks the Li content and the Li/Mg ratio increase with progressing differentiation, whereas in the differentiation series of mica lamprophyres, which has an alkalic trend, the Li content and Li/Mg ratio decrease. The Li content of the dykes is controlled by the Mg content of the rock, by its acidity, its content of pneumatolytic components (the grain size), the chemical composition of the constituent micas, and by the F content of the rock.
INTRODUC'rION The Li c o n t e n t has been d e t e r m i n e d in 129 samples o f d y k e r o c k s derived f r o m t h e f o l l o w i n g d y k e - r i c h areas o f t h e B o h e m i a n Massif: (I) the B o h e m i a n Moravian Heights and t h e a d j a c e n t p a r t o f Waldviertel in Austria; (H) Eastern S u d e t e n , n a m e l y , t h e m o u n t a i n ranges b o r d e r i n g the depression o f K l o d z k o ; and (III) central B o h e m i a ( F i g . l ) . In the first area, m o s t l y d i f f e r e n t p o r p h y r i e s o c c u r a n d alkalic d y k e s are rare. In the Eastern S u d e t e n , m o s t l y a m p h i b o l e spessartites and m i c r o g a b b r o s appear. Alkalic d y k e s are w i d e s p r e a d in the Orlick~ h o r y Mountains. In central B o h e m i a , in t h e Central B o h e m i a n P l u t o n , d y k e s are especially n u m e r o u s a n d p e t r o g r a p h i c a l l y variable. The d y k e s o f all the areas c o n s i d e r e d are c h a r a c t e r i s e d p e t r o g r a p h i c a l l y elsewhere (Nemec, 1 9 7 0 ; 1975a, b). As s h o w n b y B r o c k ( 1 9 4 3 ) , t h e Li c o n t e n t o f l a m p r o p h y r e s is i n f l u e n c e d b y r o c k w e a t h e r i n g . Hence, o n l y fresh r o c k s were studied. Li was d e t e r m i n e d b y emission spectral analysis, a c c o r d i n g t o t h e m e t h o d o f S u k n e v ( 1 9 6 7 ) , using a Zeiss grating s p e c t r o g r a p h PGS 2. T h e samples o f d y k e r o c k , a n a l y z e d
268
'.i;k f ".,
i2•
o
PRAHA
","\ /< , / / / • -.,
l
"\
,,"
0
2':" ,J"
,." ~ / /
!I....
. I
//
o SSNO
lOOkm
Fig. 1. S k e t c h m a p o f B o h e m i a a n d Moravia s h o w i n g t h e l o c a t i o n of areas studted,
by atomic absorption, were used as reference samples. The relative error of determination was stated to be -+ 12%. The accuracy was tested by analyses of the rock standards GM (54 ppm Li recommended, 54 ppm Li found) and Chibina (20 ppm Li recommended, 21 ppm Li found). L I T H I U M C O N T E N T IN D Y K E R O C K S
The results of the Li determinations, arranged according to individual rock types and areas, are given in Table I. In the granitic dyke rocks analysed, the [,i content varies within a broad range. The dioritic dykes studied agree as to their Li c o n t e n t with the average of diorites (20--30 ppm Li). The microgabbros an,:i microsyenogabbros and the corresponding porphyritic types occurring in the Bohemian-Moravian Heights and the Eastern Sudeten display in both areas identical average Li figures (Table I). Geochemically, they cannot be corre~ lated with gabbros. They are mostly albitized and richer in alkalis than are gabbros. Other conditions exist in central Bohemia, where the gabbro porphyries are evidently associated with gabbro massifs. There, their Li content falls withi~ the range of 10--20 ppm given by different authors as the Li average of gabbros. The case of the spessartites is the same as that of microgabbros. The spessartite~ of the Bohemian-Moravian Heights and those of the Eastern Sudeten show identical average Li contents and ranges of Li concentrations. The spessartites of central Bohemia are petrographically different. Genetically they are associated with islets of gabbros. The mica lamprophyres of the three areas compared differ in their Li contents, being, however, lower in Li than the minettes of Jersey (Lees, 1974). The samples analysed from the BohemianMoravian Heights are entirely kersantites, those from central Bohemia minettes. Alkalic minettes differ from the normal ones in the presence of alkalic amphibole, mostly richterite. In Eastern Sudeten, their Li c o n t e n t corresponds to that of normal minettes. The alkalinity of the alkalic rocks from the areas studied is due to alumina deficiency, not to lack of silica. The alkalic microgranites and microsyenites of these areas consist of K-feldspar, alkalic amphibole and quartz, sometimes also containing an admixture of aegirine. In addition to fine-grained types
20--120
10--55
10
5
25
55
44 29
14--120 12--50
10 7
130 I35 15 28
average content
9
14--280 15--235 10--23 18--38
range of contents
1
8 8*' 9"2 4
number of samples
The Bohemian-Moravian Heights and Waldviertel
5 3
10 4
7 8
number of samples
14--50 64--230
13--92 10--60
11--89 11--71
range of contents
Eastern Sudeten
*' Dykes from the environs of Nov~i Bystrice; ,2 dykes from the environs of Havlfckfiv Brod.
Leucocratic microgranites Biotite granite and granodiorite porphyries Pyroxene granodiorite porphyries Pyroxene syenite porphyries Amphibole microdiorite and diorite porphyries Amphibole microgabbros, microsyenogabbros and their porphyric types Amphibole spessartites Pyroxene minettes and kersantites Alkali minettes Alkali microgranites and microsyenites Alkali granites and syenites
Rock type
Lithium concentrations in dyke rocks (ppm)
TABLE I
27 135
31 35
41 27
average content
1
10
13--45
17--55
33--43
4 4
35--60
range of contents
5
number of samples
Central Bohemia
26 14
15 20
27
38
50
average content
270 also medium-grained alkalic dyke granites and alkalic dyke syenites appear. The latter are higher in Li than the fine-grained types and may be correlated with similar alkalic granites and syenites from Nigeria (Bowden, 1966) ov Texas (Horstman, 1957), both of wt~ich are fairly rich in Li. The fine-grained alkalic dykes from the Bohemian-Moravian Heights have Li contents strikingly similar to comparable rocks of the Orlicke hory Mountains. Irrespective of the alkalic granites and syenites, the acid': dykes of the l]mealkalic series are mostly richer in Li than alkalic ackl dykes, evidently (iue t~J the absence of micas and the richness in K-feldspar in the latter. Simitarly~ the higher Li content of mica lamprophyres as compared with that ~,t: spessartites may be attributed to the presence of micas in the former an(l ~)t Ca-amphibole, low in Li (Vorontsov and Lin, 1966; Lyakhovich, t972}, i~. the latter. From some dykes, several samples were analysed. ]'he Li amom~ts obtai~e,: sometimes are identical, sometimes they dift'er considerably. Of speciai int.ere~ are those dykes in which a heteromorphism exists: the mineral compositkm changes essentially (pyroxene m i n e t t e - amphibole spessartite; alkalic a m p h i b o microsyenite--hyperpotassic l~iotite m ierosyenite), the chemical compositio~ remaining practically constant, In similar eases, the Li content does ~ot seem to change. FACTORS CONTROLLING THE L1 DISTRIBUTION IN DYKE ROCKS Mg content of rocks
Since the pioneer work of Strock (1936) the geochemical Mg--Li cohere~c~: is a well known and crystallochemicalty well-founded fact. It is, however~ valuable only for similar rock types derived from the same area (Figs. 2 a,~d 3 L~
~m 70tJ !
#0 30 20 70
0 I
s
Fig. 2. Li--Mg plot of acid spessartites, areas II and IlL
271 LI
ppra 90 8o 1o 60 5o
3o 2o 1o
3
L/
5
6
7
8
9 %Me
Fig. 3. Li--Mg plot of mica lamprophyres, area III. However, a clear correlation between Mg and Li is not found in the mica lamprophyres from the Bohemian-Moravian Heights and from central Bohemia. R o c k acidity
The increase of Li content with rising rock acidity also is a well-known and geochemically well explainable experience {compare, e.g., Heier and Billings, 1972). This is especially evident in Table I on the samples from central Bohemia belonging to the calc-alkaline series. The Li contents increase continuously from gabbro p o r p h y r y through diorite p o r p h y r y and syenite porphyry toward granodiorite and granite porphyries. That the Li/Mg ratio increases with acidity also is a well-known fact. In this connection, the dyke of Cer(~any, central Bohemia, is of special interest. During its consolidation, the magma differentiated in the dyke so that both its marginal zones are made up of pyroxene minette which passes continuously toward the dyke centre through a pyroxene granodiorite p o r p h y r y into a biotite granodiorite p o r p h y r y (for details see N~mec, 1973). The concentrations for individual zones, from margins toward the dyke centre, are as follows, SiO~ (wt.%): 60.1, 62.6, 66.1; Mg (wt.%): 4.14, 2.78, 1.71; Li (ppm): 33, 41, 35; Li/Mg ratio × 1,000: 1.05, 1.46, 2.06. Grain size
The fine-grained alkalic dykes of the Orlick~ hory Mountains (area H) differ strikingly in their lower Li content from the coarser-grained alkalic granites and syenites. A similar case was described by Nesterenko and Frolova (1965) from the trapps of the Siberian plateau. There, the coarser-grained dolerites and the fine-grained basalts contain on the average 16 and 12 ppm Li, respectively.
272 The authors explain this fact by the escape of volatile Li-fluorides from the basalts which extruded on the surface of the earth. As a matter of fact, the alkalic granites and syenites dealt with m the present paper are essentially richer in F than the finer-grained alkalic types. The fine-grained alkalic microgranite:and microsyenites of areas I and H contain 0.23% F and 27 ppm Li (average of nine samples), whereas the alkalic granites and syenites 0.53% F and 135 ppm Li (average of three samples). Chemical co mposition o f m Was
In those rocks where mica prevails among colour minerals, the Li distributi(:~ of rocks is largely controlled by that of theii constituent micas (Kuts and Mishenko, 1963; Vorontsov and Lin, 1966). The Li contents of micas, however, evidently depend on their bulk composition. Accordingly, the Li conten*_ of rock may be correlated with the composition of the constituent micas. Similar interrelationships have been revealed only in comparing dykes of the same petrographic types derived from the same area. Fig. 4 shows the Li c o n t e n t of the rocks along with the Fe ratios [ ~/Fe/ (~2Fe + Mg) × 100] of their constituent micas for the pyroxene granodiorite porphyries of the environs of Raabs in Waldviertel and for the minettes of central Bohemia. In both cases a pronounced positive correlation exists, h~. the individual rock types the content of micas in the compared samples is approximately constant. For the pyroxene granodiorite porphyries menti(me(i the following figures were obtained, SiO2 of the rock (wt.%): 59.2, 62.0, 64.:i 63.5, 62.7; MgO of the rock (wt.%): 4.86, 2.75, 3.25, 3.27, 3.16; Li of the rock (ppm): 10, 18, 25, 31, 38; Fe ratio of biotite (at. ratio): 27, 33, 37, 40. 38. The MgO c o n t e n t was given to show that the Li content of the rocks does not show a relationship to the bulk 1VgO of the rock. ppz/7
501 I I
O
L
30ii -t
•
C, •
I¢ 6
•
::
Fig. 4. Li content of rocks and Fe ratio Q (~Fe/(~Fe + Mg)at.) of constituent micas.
Mica lamprophyres of Central Bohemian Pluton (circles) and pyroxene granodiorite porphyrie from the environs of Raabs ih Waldviertel (triangles).
273 In nature, a continuous isomorphic series exists between siderophyllite and zinwaldite (Rieder, 1970), b u t not between phlogopite and zinwaldite. However, more convincing evidence should be presented of whether this could explain the above-mentioned interrelationships. Phlogopite containing as much as 1% Li is also known (Sveshnikov and Kalentchuk, 1962), but only from metasomatic, not from magmatic rocks. The differentiation series of minettes is characterized by a continuous decrease of alumina contents, which finally causes the alkalinity of the rock. Its best indicator is therefore the Shand index (N~mec, 1973). The continuous decrease of the alumina contents with advancing differentiation is reflected in the chemical composition of micas by a progressive replacement of the siderophyllite molecule by a phlogopite one (N~mec, 1972a). As shown above, the Li content of micas probably depends on their Fe ratios, therefore it is also in relation to the rock alkalinity, as shown in Fig. 5.
9/z ,
p p m L/ 70.
3500
60
IO00
50
'500
qo.
~000 0
o
o
'bOO
30. 0
20
o o
o
t
•
0
•
.1000
0
500
Io
'6o
o.'6
a'zo
o.'75
o8o
Fig. 5. Li c o n t e n t (circles) and Mg/Li ratios (triangles) of minettes, the Central B o h e m i a n Pluton. Shand index on the ordinate.
Fluorine content o f rock
It is a well-known fact that the Li content of igneous rocks may be correlated with the F content. This is explained by the presence of F complexes in magmas (Kosteckaya and Petrova, 1966). In the dykes studied, a striking positive Li/F correlation is observable in the granite and granodiorite porphyries of the Bohemian-Moravian Heights (Fig. 6). However, it is probable that Li and F were partly introduced in some of the dykes mentioned, especially those rich in Li, by late-magmatic and post-magmatic processes. A precise linear relationship between Li and F observable in alkalic minettes of the Eastern Sudeten
274 %/z / &J
0
//
.J
0,0j/'/" /
....
i
....
@
--
~o
+--
-+.
i
0.20j
•
__ ........
0.i01 _i__.__ f . ............ 50
• I00
150
200
2J'0
p p m /;
Fig. 6. Li--F plot of alkalic minettes, area 1II 4triangles), and of acid (lykes, are~ tl (circles). (Fig. 6) results from the fact that micas prevail among the dark minerals of the rock. [It has been shown by Kosteckaya and Petrova (1966) and Tauson (1967 ~ that biotites recovered from different facies of the same massif have constant Li/F ratios.] In fine-grained biotite-free alkalic rocks from the area ~'onsidered in which an alkalic amphibole is the only dark component, no relatio~ was established between the Li and F contents. GENETIC CONCLUSIONS The dykes studied are of two different genetic types: (1) dykes genetically associated with plutonic rocks; and (2) dykes of a lamprophyre series, petrochemically independent of plutonic rocks of the area. In central Bohemia the dykes occur in the territory occupied by the Central Bohemian Pluton, p e t r ~ graphically a particularly varied intrusive body (Vejnar, 1973). The p e t r o chemical investigation of the dykes there has shown (N~mec, 1974a) that all the types mentioned in the present study, except for minettes, can be regarded as being genetically related to plutonic rocks of corresponding chemical composition. The similarity between the average Li contents o[ individual dyke types and those of the plutonic rocks (according to Vejnar, 1974) which are chemically closest to them, is striking. This is evidenced by the following data (ppm): gabbros and gabbro porphyries 15 and 15; amphibole-biotite quartz diorites (the S~izava type) and microdiorites plus diorite porphyries 25 and 27; granites (the Sedl6any type)rand microgranites plus granite porphyries 50 and 50; granosyenites (the "Certovo b}emeno" type) and the syenite porphyries 49 and 38; syenites (the T~bor type) and minettes 62 and 26, respectively. In the Bohemian-Moravian Heights and in adjacent Waldviertel, there extends an extensive m o n o t o n o u s acid massif called "the Central Moldanubim
275 % 6O 410
30 2O
~7
3O
/;
N /0
20 30
Yo
loo
250 300 p p m / / .v
o
Fig. 7. Li distribution in acid dykes from the environ of Havhckuv Brod (A) and from the environ of Pelh~imovand Nov~ Byst~ice (B), the Bohemian-Moravian Heights. massif". The basic, intermediate and alkalic dykes and lamprophyres occurring there all belong to one and the same lamprophyric intrusion, not related to the plutonic rocks of the area. The acid dykes differ genetically from the preceding group, but they also have no counterpart among the plutonic rocks of the Central Moldanubian Massif, with the exception of the leucocratic microgranites from the environs of Pelh~imov and Jindrichfiv Hradec which are high in Li (Fig. 7). Chemically these dykes are close to the granite of the Eisgarn type. Their genetic relations are also substantiated geologically. The Eisgarn granite is the latest and most acid intrusion of the Central Moldanubian Massif (Grohmann and Schroll, 1966). Among the plutonic rocks of the Central Moldanubian 5_~assifit is highest in Li (93--200 ppm). The average, 127 ppm Li, is very close to the average of leucocratic microgranites (130 ppm Li). The ~/:ykes studied in the Eastern Sudeten probably all belong to the lamprophyre series. The basic lamprophyres are assumed to have originated by contamination of tholeiitic magmas with sialic material. The Li content determined in the lamprophyres analysed corresponds with this hypothesis. The Li c o n t e n t of basaltic magmas of different types does not exceed 15 ppm (Heier and Billings, 1972). The Li content of spessartite, which among the rocks investigated most nearly resembles the basalts, is essentially higher (Table I). In different series of dyke rocks Li is distributed in two (iifferent ways, acoording to the type of magmatic ~;ifferentiation. h~ the calc-alkaline series, the Li content, as well as the Li/h~g ratio, increases. This can be observable, for instance, in central Bohemia in the gabbro porphyry--granite p o r p h y r y series (Table I). In the (;ifferentiation series of mica lamprophyres (the kersantite-minette--alkalic minette series) the alkalinity of rocks as well as their Mg/(Mg + EFe) ratio increase (N~mec, 1973) and the Li content am;. the Li/Mg ratio decrease (Fig. 5; for graphical reasons, the N~g/Li ratio instead of the Li/Mg ratio is given). REFERENCES
Bowden, P., 1966. Lithium in Younger Granites of Northern Nigeria. Geochim. Cosmochim. Acta, 30: 555--564.
276
Brock, R.W., 1943. Weathering of igneous rocks near Hong Kong. Geol. Soc. Am. Bull, 44: 717--738. Ginejko-Savicka, A., 1928. On the granite porphyry, amphibole-bearing rocks and fillings of quartz veins from the environs of Pelh~imov. Publ. Fac. Sci., Univ. Charles, Prague. No. 83 (in Czech ). Grohmann, H. and Schrolt, E., 1966. Zur Frage der Abhangigkeit der Konzentratiouen seltener Elemente yon der Altersfolge der granitoiden Gesteine der siJdlichen B6hmisch,~.~ Masse. Tschermaks Mineral. Petrogr. Mitt., 1 ] : 348--358. Heier, K.S. and Billings, G.K., ] 972. Handbook of Geochemistry (Lithium). Springer, Berlin, 37 pp. Horstman, E.L., 1957. The distribution of lithium, rubidium and cesium in igneous am] sedimentary rocks. Geochim. Cosmochim. Acta, 12: 1---28. Kosteckaya, E.V. and Petrova, Z.I., 1966. Distribution of some rare elements and mineralizer in the biotites of the Dzhiginsk granitoid complex. Geokhimiya, pp. 1057--1062 (in Russian). Kuts, V.P. and Mishenko, V.S., 1963. Distribution of lithium, rubidium and some of the minerals that contain them in the Kamennye Mogily and Yekaterinovka granites Geokhimiya, pp. 1124---11 39 (in Russian k Lees, G,I., 1974. Petrochemistry of the mica-lamprophyres (minettes) of Jersey i C.I. ) Proc. Ussher Soc., 3: 149-q55~ Lyakhovich, V.V., 1972. Rare Elements in Rock-Forming Minerals of Granitoids. Nauk, Moscow, 199 pp. (in Russian). N~mec, D., 1970. Lampro phyrische und lamproide Ganggesteine im Siidteil der B6hmisch Mghrischen Anh6he (C.S.S.R.). Tscermaks Mineral. Petrogr. Mitt., 14: 235--284. N6mec. D., 1972a. Micas of the lamprophyres of the Bohemian Massif. Neues Jahrb. Mineral., Abh., 117:196-~2:16. N6mec, D., 1972b. Ganggesteine aus der Umgebung yon Raabs (Nieder6sterreichisches Waldviertel). Verh. Geol. Bundesans. (Austria), pp. 247--262. N6mec D., 1973. Differentiation series of minettes in the Central Bohemian Pluion. J Geol., 81: 632--642. N~mec D., 1974a. Petrochemistry of the dyke rocks of the Central Bohemian Pluto~ Neues Jahrb. Mineral., Monatsh., pp. 193--209. N~mec D., 1974b. Lamprophyrische und lamproide Ganggesteine im Nordteil der B6hmiscr, Miirischen H6he. Verh. Geol. Bundesanst. (Austria), pp. 223--268. N~mec D., 1975a. Petrographie der lamprophyrischen und lanlproiden Ganggesteine im Nordostteil der B6hmischen Masse (C.S.S.R.). Z. Geol. Wiss., 3: 23--36. N~mec D., 1975b. Petrochemie und Genese der lamprophyrischen und lamproiden Ganggesteine im Nordostteil der BiShmischen Masse (C.S.S.R.). Z. Geol. Wiss., 3 : 3 7 --52 Nesterenko, G.V. and Frolova, L.P., 1965. Lithium and rubidium in trapps. Geokhimiya, pp. 343--347 (in Russian). Rieder, M., 1970. Chemical composition and physical properties of lithium--iron micas from the Kru~n6 hory Mts. Contrib. Mineral. Petrol., 27: 131--158. Strock, L., 1936. Zur Geochemie des Lithiums. Nachr. Ges. Wiss. G6ttingen, Math.--Phy.~ Kl., Fachgruppe 4, 15: 171--204. Suknev, V.S., 1967. A method for determination of low lithium contents in granitoids. Spectrochem. Anal. Geol. Geochem., pp. 187--188 (in Russian). Sveshnikova, E.V. and Kalentchuk, G.E., 1962: Lithium, rubidium and cesium in alkali rocks of Yeniseiskij Krazh. Geokhimiya, pp. 1055--1065 (in Russian). Tauson, L.V., 1967. Factors of the geochemical history of rare elements in the granite magmatic process. Geokhimiya, pp. 1310---1319 (in Russian). Vejnar, Z., 1973. Petrochernistry of the Central Bohemian Pluton. Geochem. Methods Data, No. 2. Vejnar, Z., 1974. Trace etemez~ts in rock of the Central BohemianPluton. Vgstn~ Ustr6d. Ustavu Geol., 49: 159--165. Vorontsov, A.Ye. and Lin, N.G.~ t 966. Rubidium anti lithium in the granitoids of the Bugulmin complex, Eastern ~i: ~!~,.;.(~eokhimiya, pp. 1108--1116 (in Russian ).