ホタテガイ適正養殖可能数量(TASC) 制度システムづくり事業TASC 数量については、平成12~14年度に実施したホタテガイ適正収容量調査3)と、平成20
Tkeg聡繍o量岨ser量es量nBay蹴臨艦9⑪職re窺,ce醜聡且照o … · Bulletin of仕しe...
Transcript of Tkeg聡繍o量岨ser量es量nBay蹴臨艦9⑪職re窺,ce醜聡且照o … · Bulletin of仕しe...
Bulletin of仕しe Geological Survey of Japan,voL49(1),p.25-32,1998
Tkeg聡繍o量岨ser量es量nBay蹴臨艦9⑪職re窺,ce醜聡且照o㎜go量訟
Yuhei TAKAHAsHI*,Sambuu OYuNGEREL*,Kazuki NAITo**,
and Baljinnyamiin DELGERTsoGT***
Yuhei TAKAHAsHI,Samb皿OYuNGERAL,Kazuki NAITo,and BaljimyFamiin DELGERTsoGT(1998)The
granitoid series in Bayankhongor area,central Mongolia.動ll。G601.S%7∂.J吻観,vo1.48(1),p.25-
32,7figs.
Abst臓ct:The granitoid series in Bayankhongor area,central Mongolia,has been investigated
using magnetic susceptibility and chemical data.In Riphean,the ilmenite-series granitoids were
domin&nt.In early Paleozoic,the ilmenite-series granitoids were dominant,but the magnetite・
series granitoi(1s were also distributed in southwestem part of the study area.In late Paleozoic,
the magnetite-series granitoids were predominant.The boundary between magnetite-an(1ilmenite・
series granitoids shifted northeastward in early Paleozoic to late Paleozoic.Shifting of the
boundary between the two series may be genetically related to the(1evelopment of the Khangay
Zone,which consists of middle to late Paleozoic strata。Mesozoic granitoids are ilmenite-series
granitoids.
In late Paleozoic,Cu and Au deposits are distributed within the magnetite-series granitoi(1s
area.SnandWdepositsoccuraroundtheboundarybetweenthetwoseriesandintheilmenite・series dominant area.These distribution pattems indicate that the redox potential decreases from
southwest to northeast in late Paleozoic granitoids of the study area.
1.亙薦ro撫ct置o醜
The greatest contribution to the grahite petrology
during the last quarter of century is consi(1ered to be
the proposition of the granitoid series and genetic
types.In the granitoid series classification,the grani-
tOidS are diVided intO magnetite-and ilmenite-SerieS
(lshihara,1977).The magnetite-series granitoidsαre
characterized by the presence of magnetite and high
Fe3+/Fe2+whole-rock ratio and crystallize under the
oxidizing con(iition.The ilmenite-series granitoi(1s
are characterize(1by the lack of magnetite an(i low
Fe3+/Fe2+whole-rock ratio an(i solidify under the re-
ducing environment.Practically,the granitoid series
is often investigated using mo(1al ratio of opaque
minerals property(lshihara,1977)and magnetic sus-
ceptibility(lshihara,1979).On the other hand,Chap-
pe11and White(1974)recognized two(iifferent gran-
ite types l I-type and S-type.The I-type granitoids
are characterize(1by the occurrence of Ca-bearing
mafic minerals and low Al203/(Na20十K20十CaO)ra-
tio and the S-type granitoids by the presence o:f alu一
*IGMR Project,Bureau of Geological Survey,Ulaan-
baatar-210613,Central P.0.Box-1047,Mongolia
**Mineral and Fuel Resources Department,GSJ
***MCS Intemational Co.Ltd,Ulaanbaatar-13,Central P.0.Box-989,Mongolia
minous minerals and high A1203/(Na20十K20十CaO)
ratio.The I-type granitoids are contribute(1by igne-
ous rocks in the process of their magmatic genesis
an(1the S-type granitoids by pelitic sedimentary
rocks.In ad(iition,A-type(alkaline and anorogenic)
granitoids and M-type(upPer mantle origin)grani-
toi(1s haVe also been proposed as derivatives of the I-
type granitoids(Loiselle and Wones,1974;White,
1979).The granitoid series and I-S-A-M types have
been employed as tools for mineral exploration,be-
cause they are closely associated with particular
metal deposits(lshihara,19811Blevin and Chappe11,
19951Sillitoe,1996).
We are currently engaged in the metallogenic map
project of the Bayankhongor area,central Mongolia,
as a part of the technical transfer program of the Ja-
pan Intemational Cooperation Agency(JICA).The
Proterozoic to Mesozoic granitoids and many metal
deposits occur in this area,but petrological consi(i-
eration base(1upon the above mentioned schemes
have not yet been performed.
For the granitoids in the Bayankhongor area,we
now elaborate petrological characteristics and
magnetic susceptibility,in particular.And we discuss
the spatial variations of the granitoid series and in-
fer the relationships between granitoid series and ore
KeyWOrdS:granitOid,magnetite-SerieS,ore deposits,Bayankhongor,Mongolia
ilmenite-series,
一25一
Bz6116渉勿zρ∫云h6G60JogJαzl Sz67zノのノ(ゾノψα%,Vbl.49,〈乙o.ヱ,ヱ998
G臓醜脆o董ds血臨e恥ay蹴臨01塑g翻鑓餓
980000E
47『20’N、’二5’・
β㌦ 陶ヤ ヤ ロ
ニ、! 、!、 K上a岨gay Zone ^^6{=
’・ノ… 蔓 ^^^^ 曳s懸二魁K㌦. J肛ga亘㎝、象’ミ!、’、ノ、’・・ 回Dzag9^=^
’2
蓋‘簿砺。..裁琴’ goo looo
庵葱 吻 ,莚,葬.論.慕嵐
ミ!こ’ミ’k屠 ≡韻ayan㎞。ng。r 鋤§£’罷’
S ’ . 0 9
0
歴ヨMes・罐、畿購、。、
田U且aanbaatar 45・圃Late惚驚、離藤h鉦、、g.1。.m,1,ん
U:Ulaagchin comp且ex,Su:Samn uul Gomplex, Th:Tsoch huduc granodiorite,Tk:Tsogt Khayrkhan complex,Tn:Tsogt Khayrkhan一
110
100km
12♂E
亀u隣 曝 く> Su
u竪
T
’ 詠誼y註6ef Tg oへ’、’!、’、 ’、ノK㌧!、 ’・菖hl ’・’・二・
臨・・も
norしh diorito,D:Daltyn-am complox,S:Shar
burd diorite
薩翻E肛互yP撮e・z・icgr㎝it・ids
Og:110rdovician”granite,Tg:Togtochi-shi
complex,Tm:Telmcn complcx,B:Baidrag
complex
睡翻Vend圭an-C㎜bri㎝gabbr・ids
羅Riphe㎝gr㎜it・ids
回Pr・ter・z・icg㈱t・ids
45020’N
1G20001E
Fig.1 Geologic map.
and Tungalag(1997).
Simplified and based upon By・amba(1985),State Geological Fund(1995)
deposits in the area.
2.Geo夏ogicse姫聾9
The Bayankhongor area has been geologicallystudied by many geologists(6.8:.,Koptevaα磁,19841
:Kepezhinskas an(i Zhirakovsky,19871Teraokla6雄乙,
1996).Recently,Tungalag(1997)geotectonically di-
vided the district into Baidrag,Bayankhongor,Dzag
and Khangay Zones from south to north.Simplified
geologic map is shown in Fig.1.
The Baidrag Zone consists of Archean high-gra(1e
metamorphic rocks ranging from amphibolite togranulite facies and Proterozoic metamorphic rocks
of greenschist facies.The Bayankhongor Zone is lat-
est Proterozoic to Cambrian geologic mit.It consists
of psamitic,pelitic and basic schists with calcareous
and quartzose rocks.In addition,the ophiolitic rocks
such as ultramafic rocks,gabbro,sheeted dike and
pillow lava are also expose(1.These rocks sometimes
occur as allochthonous structure.The Dzag Zone
consists mainly of Cambrian to Ordovician san(1stone
associated with conglomerate and mudstone.TheKhangay Zone consists of Devonian to Carboniferous
turbidite sediments.Many granitic bodies intrude
these zones.These granitic bodies have been named
after local geogエaphical names in the geologic map
sheets L200,000 (Zabotkin,19881 Davaa,19891
Bayarsaihan,19901Tomurchodor,19901)as shownin the legend in Fig.1.
3。Geo且ogy,懸gne伽suscep伽ilitya翻c翫emistry of the gr&瀬to亘ds
3.1恥esc蜘tionofgeology我賊magnet旦csusce夢・
t漏蹴y
Lower Prote窟ozoic gr蹴ite:Exposures of these
rocks are confined in comparatively small area east
of the Baidrag River.The U-Pb zircon radiometric
ages from these rocks range from1825to2646Ma(Kepezhinskas and Zhirakovsky,1987).Medium-to
coarse-grained granite is exposed at20km north-
west of Bombogor and medium-grained leucocratic
granite at10km northwest of Bombogor.Thesegranites intrude the gneiss of the Baidrag Zone with
conformable contact.These granitic rocks arestrongly deformed.Magnetic susceptibility of these
rock:s is less than l x10-3SIU(SI unit).
R恥ぬea麗gra鷺ite:Riphean granite is restricted in
distribution・15km southwest and40km east of フ
Bombogor and the area10to50km south of Nariyn
Tee1.This granite is distributed in the metamorphic
rocks of the Baidrag Zone.The Pb-Pb age data
range from 1000to1222Ma(Zabotkin,19881Tomurchodor,1990).Most of the rock types are
medium-to coarse-grained Ieucocratic granite,but
rarely fine-grained.Some of them are deformed and
foliated.In ad(iition,dioritic facies is locally exposed.
Magnetic susceptibility of the Riphean granite is
mostly less than l x lO-3SIU and partly2to7x10-3
SIU。 Early Pa亙eozo且c granito五dls:The early Paleozoic
granitoids are Cambrian to Ordovician batholithic
bodies and“Ordovician”small granitic bodies.The
batholithic bo(1ies are named Baidrag complex,Te1-
men cQmplex and Togtochi-shi complex in the usual
geologic map sheets(θ.g.,Zabotkin,19881Davaa,1989).
The Baidrag complex(B in Fig.1)is widely ex-
pose(1in central to eastern part of the stu(1y area.
This complex intrudes the metamorphic rocks of the
Baidrag Zone.Ages of the complex are Cambrian to
一26一
G名傭渉0σ4S6吻劇40%gol宛ピ7肱且珊S皿6地1.ノ
Ordovician(Andreas,19701Zabotkin,19881Taka-hashi and Delgertsogt,1997).It mainly consists of
partly porphyritic medium-to coarse-grained biotite
granite.In eaStem area,mediUm-grained leUCO-
granite is dominant.Magnetic susceptibility of the
rocks is less than l x10-3SIU in most of the area,
but is7x10-3SIU in foliated facies at18km south-
west of Bayankhongor City.Dioritic body is exposed
at10-15km south of Bombogor as mafic facies of
the Baidra墓complex.Magnetic susceptibility of the
dioritic body is in the range of O.3-2.9x10-3SIU.
The Telmen complex(Tm)is exposed at60to70km WSW of Dzag.This complex intrudes the meta-
morphic rocks of the Baidrag Zone.The main rock
type of the complex is heterogeneous foliated coarse.
grained biotite tonalite.It sometimes includes fine-
grained melanocratic gneissose rocks and shows
migmatitic apPearance due to the obscure margins of
the inclusions.Its magnetic susceptibility is up to18
x lO-3SIU.
The Togtochi-shi complex(Tg)is mainly distrib-
uted near Nariyn Teel in eastem part of the stu(1y
area.It is also locally cropped out at about25km
south of Dzag in northem part.The complex mainly
consists of weakly foliated fine-to medium-grained
biotite granite.This granite sometimes contains gar-
net.Magnetic susceptibility of this complex is less
than l x10-3SIU.
The“Ordovician”granites(Og)are small granitic
bodies(mostly a few hmdred meter across)cropped
out in the Bayakhongor and Dzag Zones.Most of
them are medium-to coarse-grained granite and a1-
tered,that is,boitite is totally chloritized.These bod-
ies discordantly intrude the sedimentary rocks of the
Bayankhongor and Dzag Zones.Though no ra(iio-
metric age of these bodies is known,they are ge-
010gically considered to be Ordovician or possibly
even Silurian.Magnetic susceptibility of these rocks
is less than l x10-3SIU.
肱tePa且eozo旦cgr蹴童te・曲riteco獅亘ex:lnlate
Paleozoic,some dioritic or diorite-granite complexes
intruded into the Baidrag and Bayankhongor Zones.
They have been name(1Shar burd diorite,Daltyn-am
complex,Tsogt Khayrkhan-north diorite,TsogtKhayrkhan complex,Tsoch hu(iuc granodiorite,Sa-
ran uul complex,and Ulaagchin complex(Zabotkin,
19881Tomurchudor,19901Takahashi6オ磁,1997).They are generally stock-like intrusive bodies and a
few km across.They generally show high magnetic
susceptibility.
The Shar burd diorite(S in Fig.1)crops out at
about40km west of Bayankhongor.It intrudes the
Baidrag complex.The Shar burd diorite was dated
341Ma by:K-Ar method(Borzakovskii and Su-prunov,1990)and250Ma by Rb-Sr whole rock
method(JICA and MMAJ,1997).The rock ismedium-grained monzodiorite(Takahashi6臨よ,1997).
Magnetic susceptibility of this rock is16to26x10-3
SIU.
The Daltyn-am complex(D)crops out at about70
km northwest of Bayankhongor.It intrudes discor-
dantly into the basic schist of the Bayankhongor
Zone.It consists mainly of diorite an(i granite.Dio-
rite often includes gabbroic rocks.Medium-grained
granite intrudes medium-grained diorite to quartz
diorite with leucocratic medium-grained granite mar-
gin(a few centimeters width).Magnetic susceptibi1-
ity of this complex is2to9x10『3SIU in granitic fa-
cies and4to14x10-3SIU in dioritic facies.
The Tsogt Khayrkhan-north diorite(Tn)is distrib-
uted as a small intmsive bo(iy in the Bayankhongor
Zone,about30km northwest of Bombogor.This dio-
rite is tentatively called Tsogt Khaykham-north dio-
rite(Takahashi6紹乙,1997).Magnetic susceptibility
of the(iiorite is12to19x10-3SIU.
The Tsogt Khayrkhan complex(Tk)crops out at
15km west of Bombogor and intrudes metamorphicrocks of the Bai(1rag Zone.Izokh8渉α乙(1990)have in-
vestigated this complex in detail and named it Baid-
rag massif.However,name“Baidrag”has been used
in other geological units such as Baidrag Zone and
Baidrag complex.Takahashiα磁(1997)rename(1the Baidrag massif to Tsogt:Khayrkhan complex to
for avoiding any confusion.The complex has been
dated312Ma by KAr method(lzokh6抱乙,1990).This complex consists of gabbro and diorite.Mag-
netic susceptibility of the complex is8to!7x10-3
SIU in dioritic facies and17to33x10-3SfU in gab-
broic facies.
The Tsoch hu(1uc granodiorite(Th)crops out at
about50km south of Nariyn TeeL This bounds to
the Ulaagchin complex and is covered by younger
sediments.It consists of medium-grained granodio-
rite.Its magnetic susceptibility is20to23x10-3SIU.
The Saran uul complex(Su)is located about50
km south of Bayankhongor.It consists of tonalite,
granite porphyry and andesite.Magnetic susceptibi1-
ity of tonalite is4to10x10-3SIU.
The Ulaagchin complex(U)is distributed in vari-
ous places in southern part of the study area.It in-
trudes the metamorphic rocks in Baydrag Zone with
discordant bomdary.For example,it intrudes gneiss
With leucocratic margin and cuts the structure of the
gneiss at about60km south of Nariyn TeeL This
complex shows granitic and dioritic facies.Magnetic
susceptibility of the UIaagchin complex is high l10
to34x10-3SIU in dioritic facies and l3to16x10-3
SIU in granitic facies.
:Kha聡g&y comμex:The batholithic granitic bod-
ies,which are mostly distributed in the Khangay
Zone,have・been called Khangay complex or Khan-
gay granites(6.g.,Davaa,1988).In the study area,
this complex(K in Fig.1)crops out around Nariyn
Tee1,Galuut and northwestem district.This complex
一27一
Bz61」α勿z(ゾ云h6G60109歪αzl Sz67z7のノ(ゾノ砂召7z,Vbl.49,ハ沼o.1,ヱ998
discordantly intrudes strata o:f the Khangay and
Dzag Zones.The radiometric ages of the complex
are256Ma by K-Ar biotite method(Heraskov,1966)
and200-250Ma by Rb-Sr method(Tomorchudor,1990).The Khangay complex consists mainly of
coarse-grained granite and partly of medium-to
coarse-grained diorite.Generally,these rocks are
equigranular and massive,but locally foliated(6.g.,
in Nariyn Tee1).Magnetic susceptibility of the com-
plex is mostly less than l x10-3SIU,but Iocally
more than lO x10-3SIU in northem area.
S甑ar腿s go且com夢藍ex:The batholithic redd,ish
granitic bodies,which are mostly distributed in the
Baidrag Zone,have been hitherto called Shar us gol
complex(e.g.,Davaa,1989).The Shar us gol complex
(Sh in Fig.1)crops out wi(iely in the study area.This
complex mostly intrudes discordantly into metamor-
phic rocks of the Baidrag Zone.This complex in-
trudes Permian volcanic rocks,too.Radiometric age
of the complex is216Ma by K-Ar method(Zabotkin,
1988).The complex consists mainly of coarse-grained
granite and partly of fine-graine(1granite.It has been
observed that the fine-grained granite intru(ies the
coarse-grained facies at10km south of Nariyn TeeL
In central part of the stu(ly area,the(iioritic rocks
crop out as marginal facies of the complex.The
coarse-grained granite has a characteristic of re(idish
colore(i Kfeldspar an(i sometimes shows porphyritic
texture.Magnetic su5ceptibility of the complex is
generally high l10to24x10-3SIU.
獺esozo亘c gr蹴量t磁s:The Mesozoic granitic body
in the study area is called Egiin davaa complex
(Bayarsaihan,1990).It crops out at about20to40
km east of Jargalant.Radiometric ages are124to
175Ma by Rb-Sr method and101Ma by K-Armethod(Bayarsaihan,1990).It consists of weakly fo-
1iated equigranular fine-to medium-grained granite.
Its magnetic susceptibility is less than l x10-3SIU.
of granitoi(is is.around2.7g/cm3.Therefore,the
value of the bomdary between magnetite-andilmenite-seriesgranitoidsisκslu二4x3.14x2.7xlOO
x10-6=3.3x10-3.Because the Kappameter shows X.
X(x10-3SIU),the magnetite-s∈ries granitoids are
defined in the case of value over3.3and the ilmenite-
series in the case of value less than3.3.
R量油e撒g聡説o量ds:Magnetic susceptibility ofRiphean granitoids is mostly less than l x10-3SIU.
Some of them show magnetic susceptibility arQund5
x10『3SIU。It has been observed that the ilmenite-
series granitoids are dominant in Riphean.
E&即P我且eozo亘c gr躍itoi岨s:Magnetic susceptibi1-
ity of the early Paleozoic granitoids is shown in Fig.
2.Most of the granitoids show low magnetic suscep一
M隷9轍量e鰯c麟輔麗yo置G膿瞭翻s睡臨蜘翻e㈱量c
侮
臼刀
ミ) ○ ○
◆ノ
、
◆
喧
◆
℃
、
D
8黛
◆
口o q
○○ く)
麟>10(x10-3SIU)
翻3-10
⑳1-3
0く1
0
3.2 Gra聾量to亘d series 艮巌sedl胆夢o簸 mag璽e瓠e s魍s陶
c錨t掘翫y The magnetite-and ilmenite-series rocks can be
distinguished by means of their(1ifferent magnetic
susceptibilities.The magnetite-series rocks show
high values(more than100x10-6emu/g,Ishihara,
1977)while the ilmenite-series rocks$how low values
(1ess than lOO x10-6emu/g).Magnetic susceptibility
was previously measured in powdered samples,andCGS units(emu/g)was used(6.g.,Ishihara,1977).Re-
cently,the magnetic susceptibility can be easily
measure(1in field with Kappameter and SI unit is
adopted.Ueno(1987)worked out conversions be-
tween SI and.CGS units for rock magnetism.The re-
1ationship between the volume magnetic susceptibil-
ityκsl in SI units and the specific magnetic suscepti-
bilityκcGs in CGS units is given by the formulaκsl=4
叩κcGs,whereρis the(1ensity of rocks.The densisty
Fig.2Magnetic susceptibility of the granitoids in early
Paleozoic.
M歌9翻直cs曝麟量醐量ty⑪霞Gr蹴翻岨s量醜L鍾eぬ畳e翻o量c
晶観/鞭 9
、
圏、
欝
濠、瀬 ◎
0 100km
讐、、
α灘 ◆◆
野 o
◎ o
騰>10(x10-3S田)
麟3-10
麟1-3
0<1
跨噂誉1&’◎◎..、疇
Fig.3Magnetic susceptibility of the granitoids in late
Paleozoic.
一28一
OZ伽渉0躍S67蜘ハ40%go伽ピ7泌且崩S皿αα1.ノ
tibility and,in other words,belong to the ilmenite-
series.However,in northwestem(Telmen complex)an(1southem side(a part of Togtokh-shil complex),
magnetite-series granitoids are (1istributed.The
bomdary between magnetite-and ilmenite-series
granitoids mns from about60km west Of Dzag to
about90km southwest of Bayankhongor.Thisboundary is at20to80km distance from northemmargin of the Baidrag Zone.
Late Pa亙eozoic gr蹴量to量虚s:。Magnetic susceptibi1-
ity in the late Paleozoic granitoids is shown in Fig.3.
The magnetite-series granitoids are dominant instock-1ike granitediorite complex and the batholithic
Shar us gol complex,and the ilmenite-series grani-
toids are dominant mostly in the Khangay complex.
The ilmerdte-series granitoids are also distributed in
the momtains100km southwest of Bayankhongor.The boundary between the magnetite-an(1ilmenite-
series granitoids runs from about40km south of
Nariyn Teel to about30km west of Dzag.Thisbomdary matches with southem margin of the Bay-
ankhongor Zone in eastern part,northem margin of
the Dzag Zone in central part and southem margin
of the Bayankhongor Zone in northwestem part ofthe stu(iy area.
Mesozo且c g聡睡o誠s:Mesozoic granitoids are dis-
tributed only in east of Jargalant.They show low
magnetic susceptibility and,therefore,are ilmenite-
SerieS granitOi(iS.
3。3C地em亘stry o亙t恥e Pa且eozo且c gra賊亘to量〔丑s
As mentioned above,the spatial variation in the
Paleozoic granitoid series is recognized.Such kin(i o:f
variation should also be examined for chemical fea-
tures.Fortunately,many chemical data have been
publishe(i in the explanation texts of the geological
map sheets (6.g.,Zabotkin,1988; Davaa,19891
Bayarsaihan,19901Tomurchodor,1990).We ar-ranged these data and our unpublishe(1data to under-
stand petrochemical characteristics of the granitoids
in the stu(iy area.
A亘腿爺聾賦m sa撫ratio取量醜αex(AS亘):The granitic
rocks cou1(1be(1erived from two contrasting types of
source rocks:igneous and sedi血entary(the I-and S-
types),which were firstlyギecognized in southeastem
Australia by Chappell and White(1974).The I.S
scheme is not petrographic,but a genetic classifica-
tion.Thus,features of each granite type are not in
themselves diagnostic.Nevertheless,we tried to
compare our data with the rocks in southeastemAustralia.
Figure4shows relationship between ASI and total
Fe as FeO in the granitoids in the Bayankhongor
area.In this figure,areas of I-an(l S-type granitoi(is
of Lachan Fold Belt in southeastem Australia are
also drawn.The granitoids in the Bayankhongor
area are not always distinctive in I-S scheme,be一
2.5
EarlyPaleOZO童C2.0
S-type
1.5⇔
一の<
⇔⇔ ⇔
1.0《》㊥
⑱1-type
0.5
0.0
0 1 2 3 4 5 6 7 8 9TotalFeasFeO(wt.%)
2.5
⇔
L鍾ePaleozoic2.0
S-type
Hの<
15 ⇔
⑱⑱ ⇔⑱㊥⇔ ⑱
1-type
1.0 ⑲ ⇔⑱
鞠ぬ 磯⇔
⑱ ⇔ 愈⑱
0.5
0.0
0 1 2 3 4 5 6 7 8 9Tota1FeasFeO(wt,%)
Fig.4 Relationship between Aluminum Saturation In-dex(ASI)and total Fe as FeO of the granitoids Regions
of I-and S-types are cited from Blevin an(l Chappel1(1995).
盟騰騨齪y⑪臨£G膿醜⑪趣瞼▽瞼9聖e203撫Oo棚⑪。5(E翻盈y馳且㊧㈱童c)
臼刀
◎ △
○
、
軌
℃
農
、
9
翻
灘 q
O口
口
q B
0
q
0 100㎞
℃
醗90-100%
羅60-90%
轟40.60%
麟10-40%
0 0-10%
でド
も 毯。 〔〉
Fig.5 Frequency of the granitoids having Fe203/FeO ra-
tio higher than O.5(Early Paleozoic)。
cause most of them are felsic.However,high FeO
rocks in late Paleozoic granitoids show I-type char-
acteristiCS..
Fe203/量eO rat量o l The magnetite-and ilmenite-
series of Ishihara(1977)are also recognized by chem-
istry.That is,the granitoid series can be defined
base(i upon Fe203/FeO ratio in ad(iition to presence
一29一
Bz〆1ε琵%(ゾ≠h6G60109乞αzl Sz4∂61y(ゾノ砂(z%,1乙ol.49,ハゐo.1,ヱ998
翫e鱗e齪y o童魎e G聡臨量踊d.s臨輔臨9
Fe2103挽Oover⑪。5(:L麗琶£閥e㈱量c)
臼〃
も
『緊
汐
麟懸
麟
轟
蝋
灘
購
、
∂灘
欝△
麟
q
㈱
o
Q
℃
0
灘90-100%
翻60・90%
轟40-60%
㈱1040%
00-10%
100km
灘
q羅 、 騰
《
噛 9。も o
曳
Fig.6 Frequency of the granitoids having Fe203/FeO ra-
tio higher than O.5(Late Paleozoic).
or absence of magnetite and magnetic susceptibility
(Takahashi,1985).In genera1,the rocks with Fe203/
FeO ratio higher than O.5belong to magnetite-series、
and the rocks with the ratio less than O.5belong to
ilmenite-series.
The frequency of the rocks having Fe203/FeO ra-
tio more than O.5 in sub-area,divi(ie(1 suitably for
each granitic body,is shown on the map(Figs.5and
6).The frequency higher than60%indicates that the
magnetite-series granitoids are dominant,while the
frequency lower than40%shows that the ilmenite-
series granitoids are dominant.The granitoids with
the frequency40to60%are trasitiona1.The distribu-
tions of magnetite-and ilmenite-series granitoids
based upon chemistry are generally conformable
with those based upon magnetic susceptibility,though the boundaries of the two series do not match
perfectly.
4.D量S磯ssion
4。1S腿tia且varia窟ion睡thegranitoMser五es
As mentioned above,the granitoid series has
changed in each period.This is summarized as fol.
10ws.In Riphean,the ilmenite-series granitoids were
dominant。In early Paleozoic,ilmenite-series grani-
toids were dominant,but magnetite-series granitoids
appeared in southwestem part of the study area.In
late Paleozoic,the magnetite-series granitoids were
dominant in the study area and the ilmenite-series
granitoids were distributed only in northeastem part.
As a result,the boundary between the magnetite-
and ilmenite-series granitoids shifted northeastward
in Paleozoic.The Mesozoic granitoids in the area
were ilmenite-series.
In these variations,the northeastward shifting of
the boundary between two series in Paleozoic is in一
teresting from the view point of tectonic develop-
tnent of the area.Paleozoic strata show northeast-
ward younging,that is,from Dzag Zone in early to
middle Paleozoic to Khangay Zone in middle to late
Paleozoic.This younging polarity indicates that sub-
duction occurred during Paleozoic in north of the
study area,and Iocation o:f subduction shifted north-
eastward with the formation of the Dzag and Khan-
gay Zones.Accor(1ing to Unrug(1996),the Siberia
and North China cratons were separate(1in Paleo-
zoic,and the subduction under continent might have
begun an(1continue(1around the stu(1y area.This
910bal tectonic setting also supPorts our inference.In
short,it is concluded that spatial variation in grani-
toid series in Paleozoic can be explained with deve1-
opment of the Khangay Zone.
The above mentioned results are conformable with
the stu(iies in Japan. In Cretaceous to Paleogene
granitoids in southwestem Japan,the ilmenite-series
granitoids are dominant in oceanic si(ie and the
magnetite-series in the inner continental side (lshi-
hara, 1981). Horikoshi (1976) suggested that the
magnetite-series granitoids are roots of volcanic belt
under tensional stress :field.In the stu(iy area,the
ilmenite-series granitoids are dominant in north.
This fact indicates younging northward oceanic side
as shown in the strata.In a(1dition,the magnetite-
series granitoid(Shar us gol complex)intrudes Per-
mian volcanic rocks,which means volcanic belt.
4。2Re旦atio醜s蚤恥蝕etweengr撒itoidseries蹴通met&亘deposits i醜丑&te P乱leozoic
Now,the granitoid series in the area will be dis-
cussed from the view point of mineral resources.In-
formation on the mineral resources in the study area
can be gathered from“Mineral Resources Map of
Re輔o鵬踊帥e琶we錨腿e翻姐e聖o曲躍鵡gr躍翻鵬ser量es量期L鍾eP曲o踊c
Sn
0
臼“研 W
ぜ幾蕪翫
.璽爵・・
100km
・Cu
も
o
WhSn・Au
v 鴬
o
Fig.7 Relationship between the selected metal deposits
and dle granitoid series in late Paleozoic,
一30一
G窺癬0づ4S6吻&ハ40n801宛ピ7盈且舶S皿6如1.ノ
Bayankhongor Zone”prepare(1by Borzakovskii an(1
Suprunov(1990).In this map,the mineral resources
are(1ivided into three levels l i.e.,deposit,ore show-
ing,an(i mineralized point in decreasing order of size.
We selected the mineral resources from deposit and
ore showing related to late Paleozoic igneous activ-
ity.MineralsofCu,Sn,WandAuhavebeenusedfor our discussion.Even though Mo is also important,
the metal occurs only as mineralized points in the
study area.
Figure7shows the relationship between ore depos-
its and granitoid-series in late Paleozoic.The Cu and
Au deposits are distributed within the magnetite-
seriesgranitoidsarea.Ontheotherhand,SnandWdeposits occur around the boundary between the
magnetite-and ilmenite-series granitoids or in the
ilmenite-series dominant area.These zonal arrange-
ments of the mineral resources an(1granitoid series
may be interprete(1with re(10x state of the granitic
magma. Sillitoe(1996)summarised the control of selected
metal deposits by the degree of fractionation an(1re-
dox state of genetically related granitic rocks.In Fig.
20f Si11itoe(1996),the Cu-Au,Au,Cu-Mo and Mo
metal deposits have been r31ated to the magnetite-
series granitoids and the W,Sn and Sn-W to the
ilmenite-series granitoids.The W-Mo deposit is Io-
cated in the boundary of the two series.Judging
from these relationships,we infer that the redox po-
tential decreases from southwest to northeast in late
Paleozoic granitoids of the stu(ly area.
5.S醜mmary
The granitoid series in Bayankhongor area,cen-
tral Mongolia,were investigated using magnetic sus-
ceptibility and chemical data.In Riphean,ilmenite-
series granitoids were(10minant.In early Paleozoic,
ilmenite-series granitoids were (iominant, but
magnetite-series granitoids apPeared in southwestem
part of the study area.In late Paleozoic,magnetite-
series granitoi(1s were predominant.The boundary
between magnetite-and ilmenite-series granitoids
shifted northeastward during Paleozoic.Mesozoic
granitoids were ilmenite-series granitoids.
These variations are interesting from the view
point of tectonic developments in the area.Among
these,Paleozoic granitoi(is in the stu(iy area may be
products associated with subduction.The shifting of
bomdary between magnetite-and ilmenite-seriesgranitoids is conformable wi車h the development of
the Khangay Zone in middle to late Paleozoic.
In late Paleozoic granitoids,Cu and Au deposits
are distributed within the magnetite-series granitoids
area.SnandWdepositsoccuraromdtheboundarybetween the magnetite-and ilmenite-series granitoids
or in the ilmenite-series(10minant area.These(1istri一
butions indicate that the redox potential decreases
from southwest to northeast in late Paleozoic grani-
toi(1s o:f the stu(1y area.
Ac㎞ow旦egeme薦s:We are much indebted to Chi-
kao Kurimoto(Geological Survey of Japan)and Yoi-
chi Sato(Dowa Engineering Co.)for useful informa-
tion on geology an(1mineral resources of the study
area.We would like to thank Shiro Itoh(Chief advi-
sor of IGMR project)and Tetsuich Takagi(Geologi-
cal Survey of Japan)for their helpful suggestions on
improvements of this manuscript.
Re£ere聾ees
Andreas,D.(1970)Geological sheet map(L-47-
55E,56,67E,68),1:100,000.Open file re-
port in Geological Funds of Mongolia no.
1895.(in Russian)
Bayarsaihan,Ts.(1990)Geological sheet map (L-47-X),1:200,000.Open file report in Geo-
10gical Funds of Mongolia no.4421.(in Mon-
golian)
Blevin,P.L.and Chappe11,B.W.(1995)Chem-
istry,origin,and evolution of mineralize(i
granites in the Lachlan Fold Belt,Australia=
the metallogeny of I-an(1S-type granites.
E60ηo吻6G60109,90,1604-1619.
Borzakovskii,Yu.A.and Suprunov,E.A.(1990)
Geological and mineralogical resources map
in westem Mongolia in1:500,000scale with
explanation notes.Open file report in Geo-
10gical Funds of Mongolia no.4496.(in Mon-
golian)
Byarゆa,G。(1985)Tectonic formation map of
Mongolia,1=2,500,000.Institute of Geology
and Mineral Resources.(in Mongolian)
Chappe11,B.W.and White,A.J.R(1974)Two contrasting granite types.」Rαo舜セ06010窪y,8,
173-174.
Davaa,0.(1989)Geological sheet map(L-47- IX),1:200,000.Open file report in Geologi-
cal Fmds of Mongolia no.4313.(in Mongo-
1ian)
Heraskov,N.N.(1966)Geological sheet map (IV,Bayankhongor),L1,000,000.Open file
report in Geological Funds of Mongolia no.
1752.(in Russian)
Horikoshi,E. (1976) Tectonics of granitic
magma and the related mineral deposits.
躍力zカzg G6010g Special Issure,no.7,1-14.(in
Jpanese with English abstract)
Ishihara,S.(1977)The magnetite.series and ilmenite-series granitic rocks.ノ匠勿z勿z8’G601-
09夕,27,293-305.
Ishihara,S.(1979)Kappameter KT-3and its apPlication for some volcanic rocks in Ja一
一31一
Bz6116ガηのヂ云h6G60Jo9づαzl Sz67z7みρノノ4クごz%,Vb乙49,.〈汚o.ヱ,ヱ998
Pan.Zヲz61乙G60109づ6召l Sz67∂¢y(ゾノ砿)召%,3〔),513-
519.
Ishihara,S.(1981) The granitoids series and
mineralization.E60%o痂606010盟,75th An- niv.Vo1.,458-484.
Izokh,A.E.,Polyakov,G.V.,Krivenko,A.P.,
Bognibov,V.1.and・Bayarbileg(1990) The
gabbro fomations of Westem Mongolia. Nauka,269p.(in Russian)
JICA and MMAJ(1997)Report on the mineral
exploration in the Tsagaan Tsakhir Uul area,Mongolia(phase I).223p.
Kepezhinskas,K.P.and Zhirakovsky,V.Zu。 (1987)Mineralogical criteria for structure
and metamorphic evolution of the earthンs
crust of the Bayankhongorskaja zone.∫06- oJo砂6zづG60φh澹ぢαz,8,63-70.(in Russian)
Kopteva,V.,Kuzumin,M.1.,Tomurtogoo,0. (1984) Structure of the upper part of Bay-
ankhongor ophiolite zone,Mongolia.G60孟60 孟07zあs,18,481-490.(in Russian)
Loiselle,M.C.and Wones,D.R.(1979)Charac-
terization an(i origin of anorogenic granites.
G60乙So6..∠しηεπ6α且6s動α6≠ω歪云h Pアog窺窺,11,
468.
Sillitoe,R.H.(1996)Granites and metal depos-
its.助ゑso伽,19,126-133.
State Geological Fund(1995)Geological map of
Mongolia,1:3,200,000.
Takahashi,M.(1985)A proposal and develop- ment of granitoids series conc6pt.ハ4醐.G60乙
Soo. ノ砿)ごz%, no.25, 225-244. (in Japanese
with English abstract)
Takahashi,Y.and Delgertsogt,B.(1997) New
K-Ar age for the Baydrag complex.〃』oη一
gol乞α%Gεoso勿多zあs渉,no.3,35.
Takahashi,Y.,Oyungere1,S.,and Delgertsogt,B.
(1997)Petrography of some dioritic bodies
in the Bayankhongor area,central Mongolia
with special reference to relationship be-
tween twinning lawS and geolOgical Setting.
〃o銘gol伽060s6伽渉客s渉,no.5,6-17.
Teraoka,Y.,Suzuki,M.,Tmgalag,F.,Ichimo-
rov,N.and Sakamaki,Y.(1996)Tectonic framework of the Bayankhongor area,west
Mongolia.伽1乙G60109磁l S鍛矧6ゾ乖卯%, 47,447-455.
Tomurchodor,Ch.(1990)Geological sheet map
(L-47-XVI and XVII),1:200,000.Open file
report in Geological Funds of Mongolia no.
4357and4415.(in Mongolian)
Tungalag,F.(1997) Stratigraphy and structural
geology of Precambrian and Paleozoic strata in Bayankhongor area. κongol伽%
G60s6勧耐,no.3,4-11.
Ueno,H.(1987) Conversions between SI and
CGS mits for rock magnetism.カ%7%16ゾん一
加Jogy,ハ伽徽logy伽4E60%o解露G6010gy,82, 441-444.(in Japanese with English abstract)
Unrug,R.(1996)The assembly of Gond- wanalan(1.動ゑso463,19,11-20.
White,A.」.R.(1979)Source of granite mag-
mas。G60乙Soαz4耀飢∠46s厩吻孟h P70g,11,
539.
Zabotkin,L.B.(1988)Geological sheet map(L-
47-XXIII and XXIV),1:200,000.Open file
report in Geological Fun(1s of Mongolia
no.4276.(inRussian)
Received November17,1997
Accepted December15,1997
モンゴル中央部,バヤンホンゴル地域における花嵩岩系列
高橋裕平・Sambuu Oyungerel・内藤一樹・Balji撒yamiln pelgertsogt
要 旨
モンゴル中央部バヤンホンゴル地域における花闘岩系列を帯磁率と化学組成から調べた.リフェアン
にはチタン鉄鉱系花商岩類が卓越する.古生代前期にはチタン鉄鉱系花南岩類が卓越するが,わずかに
調査地域南西部に磁鉄鉱系花商岩類が分布する.古生代後期には磁鉄鉱系花闘岩類が卓越する.磁鉄鉱
系とチタン鉄鉱系花商岩類の境界は古生代前期から後期にかけて北東に移動した.この移動は古生代中
後期のハンガイ帯の発達と関係づけられる.中生代花闘岩類はチタン鉄鉱系である.
古生代後期には銅及び金鉱床が磁鉄鉱系花闘岩類地域に分布する.錫及びタングステン鉱床は磁鉄鉱
系とチタン鉄鉱系花闘岩類の境界付近かチタン鉄鉱系花商岩類地域に分布する.これらから調査地域の
古生代後期花闘岩類は南西から北東へ還元的になることが示唆される.
一32一