Occurrence and Geochemistry of Khondalite Series in the Shandong Peninsula, China

RESOURCE GEOLOGY, 44(1), 39•`49, 1994

Haizhang JI*, Hidehiko SHIMAZAKI*, Shouxi Hu** and Yiying ZHAO**

Abstract: The Jingshan Group of early Proterozoic era in the Shandong Peninsula of China, consists of highly metamorphosed rock assemblages, and is firstly recognized as one of typical khondalite series. The Group is characterized by economic graphite, magnesite, phosphorus and iron deposits. The metamorphic grade reached amphibolite to granulite facies. The original rocks in the Jingshan Group can be divided into four types such as alumina-rich rock, quartzo-feldspathic rock, calc-silicate rock and carbonate rock. Major and rare earth element data of these rocks show that the original clastic sediments were mainly derived from nearby Jiaodong greenstone belt of Archean era. The rock assemblages suggest a shallow-water depositional environment on the margin of stable continent in early Proterozoic era. The thick accumulation of alumina-rich clastic sediments, large-scale biogenic graphite and magnesite deposits demonstrate that the paleoclimate was warm and damp in that time.

located in the central part of the Peninsula. Early 1. Introduction Proterozoic metamorphic rocks of amphibolite to The Shandong Peninsula, Shandong Province, granulite facies, named the Jingshan Group, occur China, is widely occupied by Archean and Prot- surrounding the southern half of the Jiaodong erozoic rocks. The Archean rocks named the greenstone belt, as shown in Fig. 1. Those rocks Jiaodong Group occur as greenstone belt, and are are intruded by later granitic rocks of various

Fig. 1 Geological map of the Shandong Peninsula. 1. khondalite series (Jingshan Group), 2. greenstone belt (Jiaodong Group), 3. granite, 4. late Proterozoic to Phanero- zoic sediments.

Received on April 19, 1993, accepted on September 10, 1993 * Geological Institute, University of Tokyo, Hongo, Tokyo 113, Japan ** Department of Earth Sciences, Nanjing University, Nanjing 210008, China Keywords: Khondalite series, Jingshan group, Shandong Peninsula, China

39 40 H. JI, H. SHIMAZAKI, S. Hu and Y. ZHAO RESOURCE GEOLOGY:

ages, mainly of Mesozoic. wet chemical method, and REE analysis by the The word "khondalite " was used for the first atomic absorption spectrometry. About two hun-

time by WALKER(1902) to describe garnet-graph- dred thin sections were examined to establish ite-sillimanite schists in the southwestern part of mineral assemblages of the metamorphic rocks. the Kalahandi region in India. At present, most geologists define khondalite as metamorphosed alu- 2. Occurrence of the Jingshan Group mina-rich metasediment series of early Protero- The Jingshan Group consists of highly meta- zoic age, along with marbles and quartzites. morphosed, well-bedded sedimentary rocks, and Khondalite represents special rock associations is mainly distributed at south of the Archean

rather than a new rock type, thus a term "khondal- greenstone belt in the Shandong Peninsula (Fig. ite series" is commonly used. The diagnostic min- 1). The available radiometric ages (zircon U-Pb) eral assemblage of khondalite series is garnet - sil- of original rocks concentrated at 2.4 - 1.8 Ga (LIN limanite - graphite - quartz - K-feldspar (DISSA- and Yu, 1988). According to the data obtained by NAYAKEand MUNASINGHE,1984). Cordierite, JIN et al. (1987) using geothermometries and geo- kyanite, staurolite, plagioclase and biotite com- barometries of opx-cpx, opx-hb, cpx-hb, hb-pl, monly exist. In the case of calc-silicate rocks, scapolite-pi and Fe-Ti oxides, the temperature of mineral assemblage is diopside-scapolite-tremo- the principal metamorphic phase was estimated as lite-plagioclase-hornblende. Hypersthene, allanite 720 - 810•KC, the pressure as 0.5 GPa. Thus the and epidote frequently appear in the assemblage. metamorphic rock series belong to upper amphi- Chemical composition of khondalite series is bolite facies to lower granulite facies (JIN et al., characterized by high silica and alumina. The 1987). maximum content of Al2O3reaches above 30 wt According to LIN and Yu (1988), the Jingshan

%. The content of alkali is low, and usually K20 Group is classified into three Subgroups: the >Na2O and MgO>CaO. Khondalite series are Lugezhuang, Yetou and Douya, each of which can markedly characterized by economic graphite, also be subclassified into two Members. The total magnesite, phosphorus and iron deposits (JIANG, thickness reaches 2940 m. Lithology and mineral 1990). In India and Sri Lanka, khondalite series assemblage of representative specimens of each contain manganese ore deposits (RADHAKRISHNAmember are examined in the present study, and and NAQVI,1986). The metamorphic grade gener- summarized in Table 1. The dominant metamor- ally reaches amphibolite to granulite facies. The phic rocks are: sillimanite - cordierite - graphite reason of high-grade metamorphism was con- gneisses, quartz - K-feldspar gneisses, diopside - nected with A-type subduction (continent-conti- hypersthene granulites, tremolite - diopside nent) by CHACKO et al. (1987) and BARBEY et granulites along with marbles and quartzites. al. (1982). Their protoliths were estimated from the min- The present study describes the occurrence and eral assemblages, and were grouped into four chemical characteristics of the Jingshan Group. types as follows: alumina-rich, quartzo-felds-

Based on these data, the Group is for the first time pathic, calc-silicate and carbonate rocks. Mineral recognized as typical khondalite seires. Then ori- assemblages observed in each type are listed in gin and depositional environment of protolith of Table 2. The following is a brief description of the the Jingshan Group will be discussed. four protholiths and associated mineral deposits The studied area has been investigated in detail including quartzite. by some Chinese geological teams. Following the 2. 1 Alumina-rich rocks suggestions by the member of the 4th Geological Alumina-rich rocks occur as gneisses, schists Team of Shandong Province of the Ministry of and granulites with porphyroblasts of aluminous Metallurgy, the field survey in the present study minerals such as garnet, sillimanite, kyanite, was carried out intensely in several selected areas. cordierite and staurolite. Typical mineral assem-

The chemical analyses of the collected samples blage is sillimanite - cordierite - graphite - garnet - were carried out at Nanjing University. Major quartz - K-feldspar. These rocks are mainly rec- component analysis was made by the traditional ognized in the lower part of H, and whole se- 44(1), 1994 Occurrence and geochemistry of khondalite series in the Shandong peninsula, China 41

Table 1 Stratigraphic sequence and lithologv of the Jingshan Group.

Table 2 Mineral assemblages of rock types. quence of H3 Subgroup of the Jingshan Group (Table 1). Sillimanite shows flow texture around garnet crystals. Various amounts of granitic gneisses regularly occur, and are interlayered with alumina-rich rocks. The total thickness of the alumina-rich rocks is generally large. 2. 2 Quartzo-feldspathic rocks Granitic gneisses and biotite granulites com- prise this rock type. Quartz and feldspar are major minerals. The mineral assemblage is quartz - or- thoclase - microcline - plagioclase - biotite. Mus- covite is often recognized in thin sections. This rock type occurs as interlayers with alumina-rich rocks. 42 H. Ji, H. SHIMAZAKI,S. Flu and Y.ZHAO RESOURCE GEOLOGY:

2. 3 Calc-silicate rocks 2. 7 Phosphorus deposits These rocks mainly occur in the lower part of Three phosphorus deposits occur also in the H2 Subgroup of the Jingshan Group, and are char- lower part of H2 Subgroup near Laizhou City. The acterized by mineral assemblage of hornblende - wall rocks are metamorphosed calc-silicate rocks diopside - tremolite - plagioclase. Hypersthene, such as amphibolites and tremolite-diopside gran- allanite, epidote and scapolite often occur. The ulites. The mineral assemblage of ores is apatite - content of ferromagnesian minerals is high. The homblende - diopside - tremolite - plagioclase.

major rock types include tremolite-diopside 2. 8 Magnesite deposits granulites, plagioclase amphibolites and hyper- Magnesite deposits of various sizes occur in the sthene - diopside granulites. Phosphorus and iron upper part of H2 Subgroup including the Laizhou deposits are associated with this rock type, and mine, which is the second largest magnesite pro- occur exclusively in the lower part of H2 Sub- ducer in China. The ore bodies are stratiform, and group. the relict of cross-bedding can be seen in the ores. 2. 4 Carbonate rocks As will be discussed later, magnesite deposits are Carbonate rocks in the Jingshan Group are all thought to be of evaporation-sedimentation origin metamorphosed to marble. Dolomitic marble is followed by hydrothermal enrichment. Besides major and calcitic marble is relatively rare. magnesitization, the associated alterations include Quartzites intercalated in marbles are always pure desilication, talcization and dolomitization. in composition. Typical mineral assemblage of 2. 9 Quartzite

marbles is dolomite - calcite - diopside - forsterite Quartzite beds are observed as interlayers in - phlogopite. In thin sections, serpentine always marbles and alumina-rich gneisses. They contain replaces forsterite crystals with relict texture. The various amounts of feldspar, and vary from pure

amount of magnesian minerals such as forsterite quartzite to feldspathic quartzite. Usually pure and phlogopite is variable even in a single bed. quartzites are observed as thin layers in carbonate This seems to reflect MgO contents of original rocks. At the lower part of H3 Subgroup of the carbonates. The amount of magnesian minerals Jingshan Group, feldspathic quartzites occur in decreases from Hi to H2 horizons, and also prob- alumina-rich gneisses as many thin layers with ably shows the decrease of Mg/Ca ratio in carbon- constant thickness of 0.5-1 m. Because feldspar is ate rocks. easily weathered, quartzites appear in cellular 2. 5 Graphite deposits form in these beds. The lower part of H3 Subgroup is more or less graphite-bearing, and is continuously traced for 3. Geochemistry of the Jingshan Group about 50 km from west to east. The Nansu mine is 3. 1 Geochemistry of alumina-rich rocks a well-known graphite deposit in this horizon. Table 3 shows some representative analyses of Graphite occurs usually as coarse scaly crystal in major components of alumina-rich rocks in the most gneisses of this horizon. Sulfides are com- Jingshan Group. One remarkable feature is high monly associated. content of Al2O3 average of which reaches up to 2. 6 Iron deposits 19.06 wt.%. It is also notable that K2O is more Two subeconomic magnetite deposits at Xitiefu enriched than Na2O, and that CaO content is rela- and Niniuzhuang are embedded in the lower part tively low. SiO2 contents, although they are vari- of H2 Subgroup. The iron ore bodies are conform- able from 50 to 73 wt.%, mostly lie in a narrow able to the surrounding rocks. The maximum range of 55•}5 wt.%. Fig. 2 illustrates the behavior thickness of the iron formation is about 25m. The of Al2O3, EFeO+MgO, and K2O against SiO2 for wall rocks of iron ore bodies are calc-silicate alumina-rich rocks. Both Al2O3 and EFeO+MgO rocks with hornblende, tremolite, diopside, scapo- contents show marked negative correlations lite, apatite and sulfides. In the Xitiefu deposit, against SiO2. BARBEY et al. (1982) also found four sulfide minerals, mainly pyrite, are genetically as- elements such as Al, Fe, Mg and Ti had negative sociated with magnetite, and occur in dissemi- correlations with silica for alumina-rich rocks in nated form. the khondalite suite of Lapland (Fennoscandia). 44(1), 1994 Occurrence and geochemistry of khondalite series in the Shandong peninsula, China 43

Table 3 Analysis of major components in alumina-rich rocks (wt. %).

1-sillimanite gneiss, 2-garnet-graphite gneiss, 3-granitic gneiss, 4-garnet gneiss, 5-graphite schist, 6-plagioclase gneiss, 7-plagioclase gneiss, 8-sillimanite schist, 9-biotite schist, 10-garnet -biotite gneiss. The data of samples 5-10 are taken from LIN and Yu(1988).

Through detailed geochemical studies, BARBEY et al. (1982) reached the conclusion that the alumina-rich rocks were originally mixtures of quartz and clay minerals, and that the Al2O3contents are controlled by the amounts of clay minerals and SiO2 contents are by quartz. Following their conclusions, it is reasonable to suppose the original rocks of alumina-rich rocks in the Jingshan Group were mixtures of quartz and clay minerals. Figs. 2 (B) indicates that iron and magnesium behaved together with aluminum, and were brought to the sediments in clay minerals in the original sedimentary rocks. Fig. 2 (C) shows that K2O has a positive correlation with silica. The reason may be the addition of K-feldspar as a detrital component. The presence of K-feldspar in the sediments suggests a highly fractionated continental crust as the provenance for the detritals (DISSANAYAKEand MUNASINGHE,1984). Thus the mineral composition in the original rocks was probably clay minerals, quartz and K-feldspar. The protolithof alumina-richrocks was probably pelite and/or siltstone. The Niggli parameter al-alk was calculated for each analyzed specimen. The obtained values of generally 20 - 40 indicate that Al2O3 was brought to the original sediments as clay minerals and micas rather than as feldspar. Because the param- Fig. 2 Al2O3, ‡”FeO+MgO, K2O variation with SiO2 for eter al-alk in albite and K-feldspar is zero, and de- alumina-rich rocks. (A) Al2O3 against SiO2, (B) ‡”FeO trital anorthite-rich feldspar is excluded by the ab- +MgO against SiO2, (C) K2O against SiO2 44 H. JI, H. SHIMAZAKI, S. Hu and Y. ZHAO RESOURCE GEOLOGY.

Fig. 3 Al-alk, SiO2 variation with TiO2 for alumina-rich rocks. (A) TiO2 against al-alk, (B) TiO2 against SiO2

sence of a positive correlation between al-alk and CaO. Consequently plots against al-alk show which components were dominantly added to the sediment in clay minerals and micas (SENIOR and LEAKE, 1978). Figs. 3 (A) and (B) show a marked

positive relation between TiO2 and al-alk, and a negative relation between TiO2 and SiO2 , respectively. These compositional relation strongly sug- Fig. 4 Chondrite-normalized REE patterns of meta-sedi- gests that titanium was attributable to clay minerals in the original sedimentary rock. If TiO2 was ments in the khondalite series. (A) for alumina-rich rocks, (B) for quartzo-feldspathic rocks, (C) for calc- provided as Ti-minerals, the points would be scat- silicate rocks tered in Fig. 3. In fact, VAN DE KAMP et al. (1976)

pointed out that a characteristic feature of most mina-rich rocks have negative Eu-anomaly, high sediments that contain clay minerals is a marked ‡” REE and low LREE/HREE ratio. positive correlation of TiO2 and al-alk, because The high ‡”REE could be explained by relative substantial amounts of TiO2 can enter into the enrichment of clay fraction in the original sedi- structure of sheet silicates. ments, because the bulk of REEs in eroded materi- ƒÂ Eu, ‡”REE and LREE/HREE ratio are the most als is mainly contained in clays (ROALDSET and important three parameters which can represent ROSENQUIST, 1971). The obtained patterns shown the characteristics of REE patterns in sediments, in Fig. 4 (A) are similar to those of North Ameri- and indicate the genesis of rocks. During the can shale composite (NASC) (GROMET et- al., metamorphism, REEs are known to be relatively 1984), they are also similar to the patterns of post- immobile (HEIER, 1973), and they could be used Archean terrigenous sediments which are inter- to infer the original nature of metamorphic rocks. preted as being derived from K-rich granitic plu- Table 6 and Fig. 4 show the REE characters of tons (TAYLOR et al., 1986). In the Shangdong metamorphic rocks in the Jingshan Group. Fig. 4 Peninsula, however, Archean K-rich granitic plu-

(A) shows that the sedimentary materials of alu- tons have not been observed. The source materi- 44(1), 1994 Occurrence and geochemistry of khondalite series in the Shandong peninsula, China 45 als of alumina-rich rocks in the Table 4 Analysis of major components in quartzo-feldspathic rocks (wt.%). Jingshan Group will be discussed later. 3. 2 Geochemistry of quartzo- feldspathic rocks The data of major components of quartzo-feldspathic rocks are shown in Table 4. They have high Si02 (average 68.01 wt. %) and Al2O3 (average 13.94 %) contents . Na2O and K2O contents are also high (average

3.95% and 2.95%, respectively), but CaO reaches up to only 1.94%. Al- though not shown in figures, the re- lations of Al2O3 and ‡”FeO contents versus SiO2 contents are similar to 1. granitic gneiss, 2. quartz gneiss, 3. quartz gneiss, 4. gneiss, 5. feldspar gneiss, 6. plagioclase gneiss. The data of samples 4-6 are taken from LIN and YU (1988), those for alumina-rich rocks, and and column 7 is the average greywacke by PETIITOHN(1969, p. 260). have high negative correlation coefficients of 0.7 and 0.9, respectively. Thus it may Table 5 Analysis of major components in calc-silicate rock (wt. %) be reasonable to assume that quartz, feldspar and clay minerals were the major constituentsof the protolith of quartzo-feldspathic rocks as well as alumina-rich rocks. The only remarkable difference between the two rock types is the ratio of quartz and feldspar to clay minerals. Table 4 shows that quartzo-feldspathic rocks are more depleted in ‡”FeO+MgO and Al2O3 contents than alumina-rich rocks with a few exceptions. These figures indicate that the clay fraction was much less in the original sediments of quartzo-feldspathic rocks than in those of alumina-rich rocks. Relatively high Na2O and K2O contents in quartzo-feldspathic gneisses clearly 1.tremolite diopsidite, 2,3,4 and 6. plagioclase amphibolites, indicate that the fraction of feldspar instead of 5. hornblende diopsidite. clay minerals was enriched in their original sedi- The data of samples 4-6 are taken from Lua and Yu (1988) ments. Thus quartz and feldspar components in- felsic volcanism in early Proterozoic. Based on crease at the expense of clay mineral fraction in these data, it could be concluded that the original quatzo-feldspathic rocks compared with alumina- rocks of quartzo-feldspathic rocks had at least two rich rocks. types, greywackes and felsic volcanics. In Table 4, average composition of quartzo- Fig. 4 (B) shows REE patterns for quartzo- feldspathic rocks is listed with the average chemi- feldspathic rocks. They have relatively low ‡”REE cal composition of greywackes given by and LREE/HREE values, and lesser Eu depletion PETTIJOHN (1969). The similarity between them compared with those for alumina-rich rocks. The is obvious. Thus the original rocks of quartzo- low FREE is due to high concentration of quartz, feldspathic rocks were probably typical grey- and the lesser Eu depletion is probably caused by wackes. In addition, LIN and Yu (1988) analyzed high feldspar fraction. These features are consis- major components of quartzo-feldspathic rocks in tent with the estimation given above that quartz the Jingshan Group, and stressed that some and feldspar fractions were high in the original quartzo-feldspathic rocks were derived from sediments. 46 H. JI, H. SHIMAZAKI, S. Hu and Y. ZHAO RESOURCE GEOLOGY:

Table 6 REE analysis of metasediments in khondalite rocks (ppm).

1. sillimanite gneiss, 2. garnet-graphite gneiss , 3. granitic gneiss, 4. granitic gneiss, 5. quartz gneiss, 6. plagioclase gneiss, 7. plagioclase amphibolite, 8. tremolite diopsidite.

3. 3 Geochemistry of the calc-silicate rocks Table 5 shows the data of major components for 4. Discussion calc-silicate rocks. These rocks have high CaO 4. 1 Characters as khondalite series (average10.50 %) and Al2O3(average 14.09 %) As stated before, khondalite is understood by contents. Thecontents of SiO2are about 50 %. It most geologists as alumina-rich metasediment se- is necessary to know whether iron and magne- ries of early Proterozoic age, which have associa- sium are contained either in clay minerals or in tions of schists, gneisses and granulites along with carbonate phases. ‡”FeO and MgO contents are marbles and quartzites. All khondalite series'in moderately correlated to Al2O3 contents with high the world have the same characteristics, including correlation coefficients of 0.64:and 0.69, respec- Inari complex of northern Finland (HORMANNet tively. Thus iron and magnesium are thought to al., 1980), Mt. Aloysius granulites of Central Aus- have been brought by clay minerals to the original tralia (GRAY, 1977), Highland Series of Sri Lanka sediments of calc-silicate rocks. If this is the case, (COORAY, 1962; DISSANAYAKA and MUNA- large portion of calcium should be present as a SINGHE,1984), and Kerala and Madras Khondalite form of CaCO3, because the possibility of dolo- Belt in the southern part of India (CHACKOet al., mite and/or ankerite is denied by above consider- 1987; WEAVER and TARNEY, 1978). The present ation. CaO contents have no positive correlation study clearly shows that Proterozoic metamorphic with Al2O3 contents as clearly seen in Table 5, in- rocks of the Jingshan Group in the Shandong Pen- dicating no possibility of calcic plagioclase as a insula also have the same features cited above, major carrier of calcium into the sediments. and belong to khondalite series. In the Jingshan Na2O and K2O contents do not display any cor- Group there are economic graphite, magnesite, relation with other oxide contents. They are pos- phosphorus and iron ore deposits. These features sibly added by small fraction of alkali feldspars. also indicate that the Jingshan Group belongs to The proportion of detrital quartz may be limited typical khondalite series. because the content of SiO2 is only about 50%. In China, there are five areas so far known Thus it is possible to consider that the original where khondalite series metamorphic rocks occur. rock consisted of calcite, clay minerals and small Those include Jian Group in Liaoning Province amounts of quartz and feldspar. (CHEN et al., 1990), Mashan Group in Heilong- Fig. 4 (C) shows REE patterns of calc-silicate jiang Province (JIANG, 1990), Jining Group in In- rocks. Their low FREE is due to the high content ner Mongolia Province (WANG, 1989), Kongling of calcite, because as well known sedimentary cal- Group in Hubei Province (Lu and JIANG, 1988) cites are poor in REEs. The shape of REE patterns and Shuidigou Group in Henan Province (CHENet is similar to that of alumina-rich rocks. This al., 1990). The Jingshan Group in Shandong means that clay minerals are the major control of Province is the sixth known occurrence of rare earth elements in calc-silicate rocks. khondalite seires in China. 44(1), 1994 Occurrence and geochemistry of khondalite series in the Shandong peninsula, China 47

rocks in its upper part (JI et al., submitted). Figs. 5 (A) and (B) show the REE patterns of intermediate and felsic volcanic rocks in Jiaodong greenstone belt. They are similar to the patterns of alumina-rich rocks and quartzo-feldspathic rocks as given in Figs. 4 (A) and (B), respectively. Thus the greenstone belt probably was the source of detrital materials for the khondalite series, that is, intermediate volcanics in the Jiaodong Group could be the source of alumina-rich rocks of the Jingshan Group, and felsic volcanics are of quartzo-feldspathic rocks. 4. 3 Depositional environment Although intense metamorphism and deforma- tion have destroyed original texture and structure of rocks, depositional environment of protolith of khondalite series could be estimated as follows. In the lower part of H1 and upper part of H3 Sub- groups, thick and undisturbed accumulation of alumina-rich sediments suggests that the deposi- Fig. 5 Chondrite-normalized REE patterns for the tional environment may have been under quiet Jiaodong greenstone belt (Ji et al., submitted) water on a stable shelf in early Proterozoic. This (A) for intermediate volcanic rocks (SiO2 = 54 - 64 %) region could be correlated to a present-day conti- (B) for felsic volcanic rocks (SiO2 > 70 %) nental shelf zone, probably an Atlantic-type margin (BARBEYet al., 1982). BARBEY et al. (1982) 4. 2 Provenance of detrital materials also considered such thick aluminous sediments to As shown in Fig. 1, the Jingshan Group is dis- be marine turbiditedeposits (flysch). The bulky tributed mainly around the south of Jiaodong metapelitic rocks imply the existence of warm Archean greenstone belt. On the basis of this and humidclimatic conditions (MOORE, 1990). space relation, the greenstone belt is a possible Wide and thick carbonate rocks in the upper source area of the detrital materials for the parts of H1 and H2 Subgroupssuggest a shallow khondalite rocks. water sedimentary environment. Dolomitic As stated before, the REE patterns for alumina- marble may have been formed by dolomitization rich rocks given in Fig. 4 (A) are similar to those of limestone(BONNATI, 1966). The changein the for post-Archean sedimentary rocks given by Mg/Caratio in a singlebed reflectsa selectivedo- TAYLORet al. (1986; Fig. 4-a). Those sediments lomitizationand also possibly changeof sea wa- were interpreted by them to have been derived ter salinity (USDOWSKI,1967). The quartzite- from K-rich granitic plutons. MCLENNAN et al. marble associationperhaps represents early Prot- (1980) found that Archean sedimentary rocks in erozoic strand line (DISSANAYAKEand MUNA- greenstone belts generally have different REE pat- SINGHE,1984), and such blanket-type sedimen- terns from those of sedimentary rocks of post- tary beds could be deposited in stable shelf area Archean age. This difference was related to the in- (PETTIJOHN,1963). The large thicknessof magne- trusion of K-rich granites produced by intracrustal site ore bodies reflectsthat the depositionalenvi- melting near the end of Archean (MCLENNANet ronmentprobably belonged to bay or lagoon. The al., 1980). In the Shandong Peninsula, however, paleoclimate is estimated to have been hot if such Archean K-rich granitic plutons have not evaporationwas the case for magnesitization. been so far observed. BARBEYet al. (1982)indicated that the original The greenstone belt in the Shandong Peninsula materialsfor calc-silicaterocks werederived from contains a large amount of calc-alkalic volcanic a nearby shallow-watercarbonate platform. As 48 H. JI, H. SHIMAZAKI,S. HU and Y. ZHAO RESOURCE GEOLOGY:

the iron ore layers are restricted in the calc-silicate References rocks, the depositional environment for the iron

ores should also be under shallow sea water. BARBEY, P., CAPADEVILLA, R. and HAMEURT, J. (1982): Major and transition trace element abundance in the khondalite Phosphorus ores generally distribute along the suit of the granulite belt of Lapland (Fennoscandia), evi- continental shelf environment of 200 to 2,000 m dence for an early Proterozoic flysch belt. Precambrian water depth (MULLINS and FASCH, 1985), and Res., 16, 273•`290. probably are the products of fauna activities. BONNATI, E. (1966): Deep sea authigenic calcite and dolomite. It is of interest to note that the depositional en- Science, 154, 643•`645. vironment was also under stable shallow water for CHACKO, T., RAVINDRA KUMAR, G. R. and NEWTON, R. C. the original rocks of graphite gneisses at the lower (1987): Metamorphic P-T conditions of Kerala (South In- part of H3 Subgroup, where simple microbial or- dia) khondalite belt, a granulite facies supracrustal terrain.

ganisms (special algae) could have thrived, and Jour. Geol., 95, 343•`358. the paleoclimate should have been warm and CHEN, Y. J., Hu, S. X. and JI, H. Z. (1990): The khondalite and damp for the growth of flora. A large quantity of gold deposits in North China Platform. Gold Geol. 23, microbial remains was buried, and turned to 17-22 (in Chinese). COORAY, P. G. (1962): Charnockites and their association graphite deposits through diagenetic and metamorphic processes. Thus the graphite deposits in gneisses in the Precambrian of Ceylon. Quart. Jour. Geol. Soc. London, 118, 239•`266. khondalite series are obviously the products of DISSANAYAKE, C. B. and MUNASINGHE, T. (1984): Reconstruc- first large-scale activity of organisms on the earth. tion of the Precambrian sedimentary basin in the granulite Some previous researchers held that the deposits belt of Sri Lanka. Chem. Geol., 47, 221•`247. are of inorganic origin, and that graphite was GRAY, C. M. (1977): The geochemistry of central Australia formed as a metamorphic product of carbonates. granulites in relation to the chemical and isotopic effects A biogenic origin for graphite of the Nansu mine of granulite facies metamorphism. Contrib. Mineral. was proposed by LAN (1981) through his carbon Petrol., 65, 79•`89. isotope studies. The average carbon isotope value GROMET, L. P., DYMEK, R. F., HASKIN, L. A. and KOROTEV, R. is -22.2 •¬ (PDB) for graphites , and that is -0.7•¬ L. (1984): The "North American Shale Composite": Its for calcites from marbles. These isotopic data sup- compilation, major and trace element characteristics. Geochim. Cosmochim. Acta, 48, 2469•`2482. port the idea that graphite was indeed formed from HEIER, K. S. (1973): Geochemistry of granulite facies rocks organic materials, and the original rocks of graph- and problems of their origin. Phil. Trans. Roy. Soc. Lon- ite gneisses probably are black siltstone or sand- don, A273, 429•`442. stone in Proterozoic era. HORMANN, P. K., RAITH, M., RAASE, P., ACKERMAND, D. and As a brief summary of above considerations, the SEIFERT, F. (1980): The granulite complex of Finnish

deposional environment of the original rocks of Lappland: Petrology and metamorphic conditions in the

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中華人民共和国山東半島に分布するコンダライトシリーズの産状と地球化学

季海章・島崎英彦・胡受奚・趙乙英

要旨:中華人民共和国山東半島に分布するジンシャン要および希土類元素の分析データは,原岩を構成した砕 (荊山)グループは,高度の変成を受けた下部原生代の変成屑物は堆積時に近くにあっだ始生代のジアドン(交東)グ岩であり,典型的なコンダライトシリーズの岩石である. リーンストーンベルトから供給されたことを示している. このグループ中には石墨・マグネサイト・燐・鉄の鉱床岩石組合せから,原岩の堆積時の環境は安定大陸の縁辺の産出がしられており,この点でも典型的なコンダライ部に存在した浅海が考えられる.アルミナに富む厚い砕トシリーズの岩石であるといえる.変成度は角閃岩相か屑岩の堆積や,大量の生物起源の石墨およびマグネサイらグラニュライト相に達する. ト鉱床の存在は,堆積時の古気候が温暖で湿潤であったジンシャングループの岩石の原岩は富アルミナ岩・石ことを示している. 英長石質岩・珪灰岩・炭酸塩岩の4種に分類できる.主