To Top of Mongolian Geoscientist
To Geological Investigation Center
No. 22, October 1, 2003
Fluid inclusion and stable isotope studies of Au-bearing epithermal
quartz veins in South Korea and eastern Mongolia.(Text)
Se-Jung Chi, Soo-Young Kim, Jung-Kwon Park, J. Badamgaravand and N.
Tungalag --- 3
Permian paleogeography of the South Kitakami Block (Northeast Japan)
in Eastern Asia based on the ammonoid fauna(Text)
H. HASEGAWA, M. EHIRO and A. MISAKI --- 6
Palynocomplex of the Lower Cretaceous sediments of the Eastern Mongolia(Text)
N. ICHINNOROV --- 12
Petrology and Rb-Sr geochronology of lamprophyre dike, Tsagaan Tsahir
Uul area, Bayanhongor, Mongolia(Text)
S. Jargalan and H. Fujimaki --- 17
Structural Characteristics of gravitational tilting structures caused
by force of constant gravity: examples from Southwest Japan(Text)
K. Kashiwagi and S. Yokoyama --- 22
Spatial delineation of the various components in soil around mineralized
spots distributed in Mongolian quadrangle L-49-12.(Text)
Kim, Soo-Young, Chi, Se-Jung, J. Badangarav and N. Tungalag ---
23
Petrology and Mineral chemistry of Shavariin Tsaram and Mandalgovi
basalts, Mongolia(Text)
Y. Majigsuren, A. Kitakaze and S. Jargalan --- 25
Petrological characteristics of the Hantaishir ophiolite complex,
Altai region, Mongolia(Text)
I. Matsumoto and O. Tomurtogoo --- 27
Geological and Geochemical Features of Kuroko-type Volcanogenic Massive
Sulfide Ore Deposits in Japan (Text)
T. Mizuta and D. Ishiyama --- 29
Standardized legend of plutonic rocks for the 1:200,000 quadrangle
geological map series in Japan.(Text)
Y. Nishioka --- 41
Comparison between the Honam Shear Zone and the Funatsu Shear Zone
-A study on geological correlation between the Korean Peninsula
and the Hida Belt of southwest Japan (Text)
Yutaka TAKAHASHI, Weon-Seo KEE and Bok Chul KIM --- 42
Geochemistry of the rocks of Bayanhongor Ophiolie in Central Mongolia:
implication for its origin (Text)
D. Tomurhuu and O. Tomurtogoo --- 46
Forming process of the Hida Marginal Belt, SW Japan: as a Mesozoic
tectonic zone (Text)
K. TSUKADA --- 48
Mongolian Geoscientist, no. 22, October 1, 2003, p.3-5
Fluid inclusion and stable isotope studies of Au-bearing epithermal quartz veins in South Korea and eastern Mongolia
Se-Jung Chi(1), Soo-Young Kim(1), Jung-Kwon Park(1), J. Badamgarav(2)
and N. Tungalag(2)
(1) KIGAM, Daejeon, Korea
(2) IGMR, Ulaanbaatar, Mongolia
Most Au-bearing quartz vein deposits in South Korea are associated
with Jurassic and Cretaceous granites. Cretaceous granites have been
shown to be higher level intrusions (<2-3 km) than Jurassic granites
(>5 km) (Tsusue et al., 1981; Watanabe, 1981). Three main types of gold
deposits have been documented which display a consistent relationship among
depth, water-to-rock ratio (degree of meteoric water involvement) and Au/Ag
ratio (Shelton, 1986; So et al., 1987a, b, ; So and Shelton, 1987a, b;
Shelton et al., 1988; 1988a, b; 1989a, b): Mesothermal Au-rich gold deposits,
Korean-type Au-Ag deposits and Epithermal Ag-rich deposits.
Mesothermal Au-rich deposits are associated with Jurassic vulcanism
and are characterized by high Au-Ag ratios (5:1-8:1). Minor amounts of
ore minerals occurs as disseminates of mainly pyrite, pyrrhotite and chalcopyrite
and native gold. Fluid inclusion data indicate that gold deposition occurred
at temperatures of 300° to 370℃ in response to unmixing of CO2-rich fluids
at depths of >4.5 km. Korean-type Au-Ag deposits are associated with Late
Jurassic-Early Cretaceous granites and are characterized by Au/Ag ratios
of 1:3-2:1 and a general paucity of sulfide minerals. Gold deposition occurred
at temperatures near 270℃ in response to boiling and cooling at depths
near one km. Epithermal Ag-rich deposits are associated with Late Cretaceous-Tertiary
granites and are characterized by lower Au/Ag ratios (1:10-1:200) and more
abundant and complex sulfide mineralization. Gold-silver deposition occurred
at temperatures of <240℃ in response to boiling and cooling at depths
of <1.0km (So and Shelton, 1987b; So et al., 1987a).
Oxygen isotope data for Korean Au deposits display various degree
of δ18O enrichment relative to meteoric water, produced by exchange hot
igneous or metamorphic rocks, by classic 18O shift. δ18O values
of individual mines are related to their Au/Ag ratio and reflect
their depth of formation. Mesothermal Au-rich deposits display the largest
δ18O shfit indicating the highest degree of water-rock interaction
(lowest water/rock ratios) as shown in Fig.1. Korean-type Au-Ag deposits
display δ18O shfit intermediate to those of epithermal and mesothermal
deposits. Epithermal Ag-rich deposits display the smallest δ18O
shfit indicating a lesser degree of water-rock isotope interaction.
The isotopic compositions of hydrothermal fluids from the Ulaan
Togoi and Chulu Tolgoi in eastern Mongolia indicate that meteoric water
was dominant fluid component.(Fig.1). Fluid inclusion data indicate that
mineralization occurred at temperatures of <260℃ from less saline fluids.
Mongolian Geoscientist, no. 22, October 1, 2003, p.6-11
Permian paleogeography of the South Kitakami Block (Northeast Japan) in Eastern Asia based on the ammonoid fauna
Hitoshi HASEGAWA, Masayuki EHIRO and Akihiro MISAKI (Tohoku Univ.)
During Permian to Triassic time, the eastern part of the Tethys Sea was dotted with some large continental blocks: North China, South China (Yangtze and Cathaysia) and Indochina blocks. There are also many small continental blocks having pre-Cambrian basements, such as the Bureya and Khanka in northeast China-Russian Far East (Fig.1). The Japanese Islands along the eastern margin of the Asian continent is mostly composed of latest Paleozoic to Mesozoic accretionary complexes, but also include the old (Caledonian) microcontinental blocks, such as the South Kitakami and Kurosegawa blocks (South Kitakami Microcontinent; Ehiro and Kanisawa, 1999). The amalgamation processes of these small continental blocks are important to elucidate the tectonic history of East Asia.
Where was the South Kitakami Block located during Permian Time?
The South Kitakami Block is considered to be located near the
continental blocks, such as North China, South China and Indochina. Because
Permian flora of the South Kitakami Block belongs to the Cathaysia Floral
Province (Asama, 1985) and differs from that of Australia, which belongs
to the Gondwanan province. However, with regard to the precise location
of the South Kitakami Block in the Cathaysian Province during Permian,
following two different opinions have been presented (Fig.2).
1) Located near the South China
The bases of this opinion are as follows; Permian bivalve fauna (Fang
and Yin, 1995; Nakazawa, 1991), ammonoid fauna (Ehiro, 1997), coral fauna
(Minato and Kato, 1965), Middle to Late Permian fusulinoidean fauna (Ozawa,
1987), and the biotic composition of the Middle Permian reef limestone
(Kawamura and Machiyama, 1995).
2) Located along the northern margin of the North China
The bases are; Middle Permian brachiopod fauna (Tazawa, 1991; Shi et
al, 1995), the Middle Carboniferous to Early Permian fusulinoidean fauna
(Ishii, 1991).
Permian Ammonoid Paleobiogeography in the Eastern Tethys
Provinciality of ammonoid fauna had been present throughout
the whole of Permian time. Therefore, ammonoid fossils are suitable for
estimating the paleogeography during the Permian. Ehiro (1997) recognized
four Permian ammonoid provinces; The Boreal Province [BP], the Equatorial
American Province [EAP], the Equatorial Tethyan Province [ETP], and the
Peri-Gondowanan Province [PGP]
The characteristic ammonoid genera of each province and epoch are as
follows.
*Early Permian
Among the Early Permian ammonoids, Juresanites，Paragastrioceras，and
Uraloceras characterize the BP and PGP, whereas genera belonging to the
Perrinitidae, except for Subperrinites reported from the Yukon Territory,
Canada, are restricted to the EAP and ETP.
Unfortunately, only two genera of ammonoid have been reported
from the South Kitakami Block, and no ammonoid mentioned above has yet
been found there.
*Middle Permian
In the early Middle Permian (Roadian), Sverdrupites and Daubichites
characterized the BP. There were, however, no genera endemic to the BP
and PGP during the rest of Middle Permian (Wordian to Capitanian). On the
contrary, the EAP and ETP had distinctive faunas during the Middle Permian.
All the genera belonging to the subfamily Kufengoceratinae were restricted
in the EAP and ETP, and have so far been reported from Texas, Coahuila
and South China. Such ceratitid genera as Paraceltites, Cibolites, Nielsenoceras
and Doulingoceras occur from Texas, Coahuila, Tunisia and South China.
Timorites was also restricted to the EAP and ETP, occurring in such localities
as Texas, Coahuila, Dzhulfa, Abadeh, Timor and South China, except for
one locality in the Central Himalayas. Demarezites has been known from
southwestern North America and Timor.
In the South Kitakami block, 13 genera of ammonoids have been
reported from the Middle Permian. They include such characteristic genera
of the ETP as Paraceltites, Cibolites and Timorites. Cibolites was also
collected from the Kurosegawa district of Southwest Japan.
*Late Permian
Among the Late Permian ammonoids, most of xenodiscoidean, except
for Xenodiscus and Paratirolites, and all otoceratoideans are restricted
to the EAP and ETP, appearing in such localitities as Coahuila, Dzhulfa,
Abadeh and South China. Pseudogastrioceras has also been reported from
many localitities in ETP, such as Dzhulfa, Abadeh, Southeast Asia and South
China. There were no genera endemic to the BP and PGP during the Late Permian
as in the Middle Permian.
The Late Permian strata in the South Kitakami block yield 11
genera of ammonoids including Timorites, Pseudogastrioceras and some araxoceratids.
The Upper Permian of Sikhote-Alin also yields an araxoceratid and xenodiscids
such as Xenodiscus. Therefore, the South Kitakami and Khanka blocks are
considered to have belonged to the ETP during the Late Permian as well
as the Middle Permian.
Discovery of Perrinites and Demarezites from South Kitakami block
and its paleogeographic significance
As stated above, unlike in the Middle and Late Permian strata,
ammonoid fossils are very rare in the Lower Permian of the South Kitakami
Block and only two cosmopolitan genera of ammonoid have hitherto been reported.
And no Roadian ammonoid having a certain age data has been reported.
Recently, however, we discovered Demarezites from the Hosoo
Formation (Misaki and Ehiro, in prep.) and Perrinites in association with
Prostacheoceras from the Sotokawame Formation (Yosida et al, 1992) in South
Kitakami Block. Demarezites is assigned to be Roadian and, as discusssed
above, one of the typical equatorial ammonoids. Perrinitid ammonoids characterize
the ETP, such as South China, Thailand and Timor. But they also occur in
the strata belonging to the EAP, such as southwestern North America and
Central America. According to Leonova (2002), genus Perrinites ranges from
Kungurian to Roadian and is known only from southwestern North America
and Central America. Therefore, it is concluded that the South Kitakami-Kurosegawa
block had located in the equatorial province near the South China or equatorial
America during the Permian.
Permian paleogeography of the Inner Mongolia in Eastern Asia
In eastern Asia, Uraloceras has been reported from the western
Inner Mongolia and northwestern Gansu in North China, and Paragastrioceras
from the western Inner Mongolia. Therefore, it is considered that the Tarim
block and probably the northwestern margin of North China block were in
the BP in Early Permian time.
In Middle Permian time (Roadian-Wordian), only cosmopolitan genera
of ammonoid have been reported from the western Inner Mongolia. There were
no genera endemic to the ETP and EAP during Middle to Late Permian. Therefore,
it is considered that Inner Mongolia still belonged in the BP in Middle
to Late Permian.
References
Asama K, Asano T, Sato E and Yamada Y (1985) Jour Geol Soc, Japan,
91; 425-426.
Ehiro M (1997) Jin Y. and Dineley, D., eds., Proc 30th Int. Geol. Congr.,
v.12, 18-28.
Ehiro M (1998) Jin Y. et. al., eds., Palaeoworld, No.9; 113-122.
Ehiro M and Kanisawa S (1999) In; Metcalfe I (ed), Gondwana dispersion
and Asian accretion; 283-295, AA Balkema, Rotterdam.
Ehiro M (2001) Earth Science (Chikyu Kagaku)., v.55, 71-81.
Fang Z and Yin D (1995) Acta Palaeont Sinica, 34; 301-315.
Ishii K (1991) In ; Ishii K, Liu X, Ichikawa K and Huang B (eds), Pre-Jurassic
geology of Inner Mongolia, China. Report of China-Japan Cooperative Research
Group, 1987-1989; 189-199, Matsuya Insatsu, Osaka.
Kawamura T and Machiyama H (1995) Sediment Geol, 99; 135-150.
Leonova, T.B., 2002, Paleont. Jour., v.36, S1-S114
Nakazawa K (1991) In; Kotaka T, Dickins JM, McKenzie KG, Mori K, Ogasawara
K and
Stanley GD Jr (eds), Shallow Tethys 3; 3-20, Saito Ho-on Kai, Sendai.
Ozawa T (1987) In ; Taira A and Tashiro M (eds), Historical biogeography
and plate tectonic evolution of Japan and Eastern Asia ; 45-63, Terra Sci
Publ Comp, Tokyo.
Shi GR, Archbold NW and Zhan L (1995) Palaeogeogr Palaeoclimatol Palaeoecol,
114; 241-271.
Tazawa J (1991) In; Ishii K, Liu X, Ichikawa K and Huang B (eds), Pre-Jurassic
geology of Inner Mongolia, China. Report of China-Japan Cooperative Research
Group, 1987-1989; 213-230, Matsuya Insatsu, Osaka.
Yoshida K, Machiyama H, Kato M and Kawamura M (1992) Earth Science
(Chikyu Kagaku)., v. 46, 97-104.
Mongolian Geoscientist, no.22, October 1, 2003, p.12-16
Palynocomplex of the Lower Cretaceous sediments of the Eastern Mongolia
Niiden ICHINNOROV
Paleontological Center, Academy of Sciences
Ulaanbaatar-51, P.O. Box 260, Mongolia
Samples from Lower Cretaceous sediments at localityes Bayan-Erkhet, Shine-khudag, Khukhteeg, Tevshiin-Govi, Khuren Dukh, Shivee-Ovoo and Aduunchuluu were analyzed for palynomorphs. Three palynological assemblages, assemblage I, II and III, were identified. They show Lower Cretaceous Hauterivian-Barremian, Aptian-Albian and Albian in age.
Assemblage I
Assemblage I was identified from Shinekhudag Formation from
the Shine-khudag locality. The assemblage abounds in gymnosperm pollen
in which Coniferales predominates (69-72%). Bisaccate conifer pollen of
the genus Pinuspollenites ( P. similis, P. elongatus), Piceapollenites
(P. exiloides), Abiespollenites ( A. orientalis, A. editus), Keteleria
(K. mesozoica) are always present. Less frequent is monosaccate conifer
pollen Sciadopityspollenites sp., Cycadopites sp., Variavesiculites delicatus,
Classopollis sp., Chasmatosporites sp., and Inaperturapollenites dettmanii.
Spores are not numerous (1-3%) and are represented mostly by Cicatricosisporites
australiensis, Baculatisporites sp., and Cyathidites australis.
The age of Assemblage I is Hauterivian-Barremian. The assemblage
contains species Abiespollenites orientalis, Abiespollenites editus,
Phyllocladidites bibulbus, that are always found in Lower Cretacous sediments.
No forms of the genera Foraminisporites, Pilosisporites, Laevigatosporites
that were observed are peculiar to Aptian and Albian.
Assemblage II
Assemblage II was identified from Tevshiin-Govi Formation from
the Shivee-Ovoo locality. The assemblage abounds in gymnosperm pollens
within which, as in the previous assemblage, Coniferales predominates (25-77%).
An important difference from the previous assemblage is amount of spores
becomes greater (5-60%). Among the gymnosperm pollen, most abundant
are the bisaccate pollen grains of Pinuspollenites ( P. insignis, P.minimus,
P.similis), Podocarpidites (P. luteus, P. decorus), Cedripidites
(Cedripidites admirabilis) are always present. Again, as in Assemblage
I, less frequently is monosaccate conifer pollen Araucariacidites australis,
Retimonosulcites sp., Cycadopites sp., and Classopollis classoides.
Spores are represented mostly by Cicatricosisporites exiloides, C. australiensis,
Lygodiumsporites subsimplex, Maculatisporites asper, Pilosisporites notensis,
Rousesporites reticulatus, Foraminisporites asymmetricus, F. wonthaggiensis,
Cooksonites variabilis and Aequitriradites spinulosus.
The age of Assemblage II is Aptian-Albian. The assemblage contains
species Foraminisporites asymmetricus, F. wonthaggiensis, Cooksonites variabilis,
Rousesporites reticulatus that are always found in Aptian-Albian sediments.
This assemblage is characterized by absence of Angeosperm pollen.
Assemblage III
This assemblage characterized by wide distribution. Assemblage
III was distinguished from Bayan-Erkhet Formation from the Bayan-Erkhet
locality, Khukhteeg Formation from the Khukh-Teeg locality, Zuunbayan Formation
from the Khuren Dukh locality, Tevshiin-Govi Formation from the Tevshiin-Govi,
Shivee-Ovoo and Aduunchuluu localityes. The assemblage of these localityes
is characterized by abundance of gymnosperm pollens (50-98%) except the
Shivee-Ovoo locality. In spores and pollen diagram of Shivee-Ovoo, the
amount of spores becomes greater (30-47%), mainly through an increase in
specimens of the spores Rousesporites reticulatus, Klukisporites scaberis,
Kuylisporites lunaris, Cicatricosisporites minutaestriatus, Stenozonotriletes
divulgatus, Foraminisporites wonthaggiensis, Coptospora sp., Pilosisporites
trichopapillosus, P. notensis.
The gymnosperm pollen of this assemblage is represented mostly
by which, as in the previous two assemblages, Coniferales predominates
(29-78%). An important difference from the previous assemblages is the
appearance of some new species spores Stenozonotriletes divulgatus, Todisporites
grandis, Lophotriletes spurius and among the Angeosperm pollen are occur
Striatopollis sarstedtensis, Proxoapertites operculatus, Tricolpites sp.,
Clavatipollenites rotundiformis, C. hughesii, Palmites sp., Retitricolpites
sp., Fraxinopollenites constrictus and Asteropollis asteroides.
Assemblage III is determined to be Albian. Some of the species
Stenozonotriletes divulgatus, Lophotriletes spurius, Retitricolpites sp.,
Fraxinopollenites constrictus just listed were described or mentioned in
the Albian-Senomanian Formations.
Correlation
According to the above palynological data, the Lower Cretaceous palynoassemblages
of the Eastern Mongolia are most similar to Lower Cretaceous palynoassemblages
of the Transbaikalia (Kotova, 1964, 1968, 1970) and North-Eastern China
(Shang, 1991,1994,1997).
Mongolian Geoscientist, no. 22, October 1, 2003, p.17-21
Petrology and Rb-Sr geochronology of lamprophyre dike, Tsagaan Tsahir Uul area, Bayanhongor, Mongolia
S. Jargalan and H.Fujimaki
Tsagaan Tsahir Uul area is located in the southwestern part of
Mongolia: 700 km SW from Ulaanbaatar. Geology of the district is known
well for gold mineralization, and it is comprised in the southeastern part
of the Bayanhongor metallogenic belt.
The Tsagaan Tsahir Uul area is composed of Proterozoic metamorphic
rock, Baidrag batholith and Ulaan tolgoi diorite stock. The granitic batholith
is intruded by several lamprophyre dikes, quartz porphyry dikes, and cut
by a number of quartz veins. At the northeast part of the Tsagaan Tsahir
Uul area dikes of lamprophyre and quartz porphyry are intersects each other.
It is clearly seen in the field that the quartz porphyry dike is cut by
the lamprophyre dike.
The lamprophyre dike is massive and homogenous and it is from
1 m to 3m in width and approximately 4 km in length. At the northeastern
end the dike branches, and its width increases up to 10 m. The lamprophyre
is dark in color fine grained and contains many xenoliths of host granite.
Xenoliths of the granite, are strongly affected by potassium sparization
and has reddish color. At the contact with lamprophyre dike the host granite
is altered to the same extent. The lamprophyre dike intersects with longitudinal
striking quartz-porphyry dike at its northeastern end. In the field it
is clear that the quartz porphyry is cut by lamprophyre.
Lamprophyre is dark in color and fine grained. It is composed
of olivine, amphibole and clinopyroxenes as phenocrysts. Plagioclase, potassium
feldspar, biotite and amphibole occur as the groundmass. The rock is fairly
altered producing talc, chlorite and calcite. Under microscope it has fine
grained holocrystalline texture. Olivine occurs as phenocryst in the fine
grained groundmass and forms euhedral grains ranging from 1 mm to 2 mm
in size. Most of olivine is altered and changed to talc. Composition of
olivine ranges from Fo92.9 to Fo84.6 without any clear compositional variation
between core and rim.
Amphibole occurs both as phenocryst and as groundmass. Amphibole
phenocrysts are subhedral to euhedral grains and some of them are as long
as 4 mm. In groundmass it is euhedral and up to 0.5mm in length. Amphiboles
are characterized by a wide variation of all major element compositions.
Their Mg value [100Mg/(Mg+Fe+Mn)] ranges from 70 to 57. Amphiboles in lamprophyre
are high in titanium content ranging from 3.02 to 6.23 wt%, indicating
they include kaersutite in composition. Clinopyroxenes occur mostly in
groundmass and rarely as phenocryst. It is euhedral and reaches to 0.5
mm in size. Mineral chemistry of pyroxenes shows that they are typical
augite in composition. The cation ratios Ca:Mg:Fe range from 38.8:47.6:13.6
to 46.6:36.6:16.8. Pyroxenes are slightly rich in titan. Biotites are rare
and these are small books and their sizes reach up to 0.3mm. Compositional
variations of biotite are wide: the range of Mg value is from 72 to 49;
and Al2O3, TiO2 contents are from 15.8 to 13.8 and from 8.62 to 2.56 wt%,
respectively. Biotites have high Ti contents they are phlogopite-eastonite
in chemical composition.
Plagioclases and potassium feldspars are subhedral to euhedral
grains small in size up to 0.3 mm in length and have albite twinning. The
compositional range of plagioclase is An45Ab49Or6 - An12Ab74Or14. They
are andesine and oligoclase in composition. Potassium feldspars show two
different compositions; one is from Or60.9 to Or74.4, showing composition
of sanidine. Another one ranges from Or86.5 to Or95.2, showing orthoclase
composition.
Compositional variation of SiO2 of lamprophyre dike ranges from
45.62 to 55.77 wt% (Fig-1). In the Harker diagram major oxides of lamprophyre
have good correlation with SiO2, showing a single smooth trend. TiO2, FeOt,
MgO, CaO, MnO decrease, and Al2O3 and K2O increase with increasing SiO2
content. Potassium content of lamprophyre is notable high and its K2O/Na2O
ratio varies from 1.14 to 0.4. Mg value of lamprophyre ranges from 45.2
to 35.9. Lamprophyre is characterized by enriched contents of such incompatible
elements as K, Rb, and Ba, and also by elevated abundances of compatible
elements like Mg (9.11-4.33 wt%), Cr (368-158 ppm), and Ni (174-56 ppm).
On MORB normalized diagrams, enrichment of K, Rb and Ba can be noticed
relative to Sr, and two troughs exist at the Nb and Ti (Fig-2).
Chondrite normalized REE patterns for lamprophyre shows gradual
depletion from La to Lu with no or weakly negative Eu anomaly. It is highly
enriched in LREE (Fig. 3).
The lamprophyre dike is rather homogenous and the rock samples
are similar in composition, and large variation of the Rb/Sr ratio could
not be expected.
The calculation of Rb-Sr isochron was a similar method after
York (1969) and the decay constant for 87Rb used λ=0.42X10-11/y (Steiger
and Jager). Analytical errors were 0.2% for 87Rb/86Sr ratio and 0.0015%
for 87Sr/86Sr ratio. This isochron yields an age of 248.61±18.5 Ma, with
a 87Sr/86Sr initial ratio of 0.706096 (Fig. 4).
Mineralogical and chemical composition of the lamprophyre dike
from Tsagaan Tsahir Uul area is similar to those of published calc-alkaline
lamprophyres. Determined age show much difference with previous age reported.
After detailed checking the previous study we would like to note that the
reported age of 351.75±236.69 Ma for lamprophyre dike (MMAJ&JICA),
is unsatisfied because Rb-Sr isochron was calculated using only 3 samples
and analytical error for that is as high as ±236.69.
We report new age of 248.61±18.5 Ma (Late Permian) with 87Sr/86Sr
initial ratio is 0.706096 for lamprophyre dike.
Mongolian Geoscientist, no. 22, October 1, 2003, p. 22
Structural Characteristics of gravitational tilting structures caused by force of constant gravity: examples from Southwest Japan
Kenji Kashiwagi(1) and Shunji Yokoyama(2)
(1) Institute of Geoscience, GSJ, AIST, Tsukuba, 305-8567, Japan
(2) Kochi Univ., Kochi, 780-8520, Japan
It is presently a well-known fact that hard rocks characterized
by steeply-dipping planar structures bend downward on a slope surface due
to a constant force of gravity, and result in the formation of the gravitational
tilting structures. We show some noted characteristics of the gravitational
tilting structure on the base of our current studies in southwestern Japan.
The gravitational tilting structure has been formed in
various lithofacies such as slate, pelitic schist, alternation of sandstone
and mudstone, bedded chert, jointed granitic porphyry, and so on. The structure
is characterized by two open fracture sets; type A and type B. The fracture
of type A is transformed from the planar planes such as slaty cleavage,
bedding, joint, and so on. This fracture is parallel to the planar planes.
The fracture of type B is a tension fracture perpendicular to the type
A fracture, and its fracture surface is generally jagged and rough. These
fractures have never been filled with mineral vein, but sometimes with
soil and vegetation. Some small-scale fractures formed between the type
A fractures indicate sense of dip slop along planar planes. These morphologic
features of fractures are important to analyze the formative process of
the gravitational tilting structure, and will be discussed.
Mongolian Geoscientist, no. 22, October 1, 2003, p.23-24
Spatial delineation of the various components in soil around mineralized spots distributed in Mongolian quadrangle L-49-12
*Kim,Soo-Young, *Chi,Se-Jung, **J.Badangarav and N.Tungalag
* Korea Institute of geoscience and Mineral Resources
** Institute of Geology and Mineral resources of Mongolia
The studied area is located in 70 km west of Choibalsan
city in Eastern Mongolia and pertinent to the Mongolian Quadrangles L-49-12
block. In terms of tectonic provincial classification, the studied
areas belong to the marginal terrane of passive continent of Dereen Davaa.
This terrane is classified into 1) gneiss, amphibolite, and marble of lower
proterozoic period, 2)middle to upper Riphean meta-sandstone, slate, conglomerate,
3) shallow sea sedimentary rocks of Silurian period and 4) flysch sedimentary
rocks, volcanic-plutonic rocks and fossil bearing limestone of Devonian
period.
The surveyed area is a part of east Mongolia and Mongolia
- Preargun volcanic belts which were formed by upper Mesozoic continental
rift and geodynamic igneous activities. The geology of this area consists
of upper Jurassic to lower Cretaceous volcanic sediments/effusive rocks
and upper Paleozoic to lower Mesozoic acid to intermediate intrusive rocks.
Above mentioned strata generally lie on the Permian plutonic rocks with
their boundary contacted unconformitively or in fault. According to the
aerial photo, 7 epochs of volcanic activities are observed in subject areas.
The target areas for the geological and geochemical exploration
in the current surveys were chosen by engaging the interpretation of various
geological data collected in Mongolia. The selected areas were confirmed
of the mineralization by grid sampling of the soil and rocks chips around
outcrops. Geochemical atlas of the survey areas were elaborated on Ulaan
Tolgoi, Chuloot Tolgoi, Somber Ovoo(1, 2, 3, 4), ArUrt ,HorHoit, three
mountain areas, 74-5 and 75-1 occurrences(fig.1). Soil geochemical survey
covered 10 Km2 around No. 60 occurrence in L-49-19 quadrangle and was applied
to the open fractured system in the survey areas.
According to the statistical processes such as univariate
and multivariate analyses and graphic distribution of each element, average
contents of most elements range in the background of the volcanic sediments
of the surveyed areas. The distribution patterns of analyzed elements reflect
the lithologic and geologic characteristics in the most area but Bulgan
area(chuloot tolgoi), somber ovoo(1, 2, 3, 4), Distribution of the
poly-metallic elements in Bulgan area shows NE direction along to the quartz
lode developed in volcanic rock assemblages, areas of which might
be anomalous for Au and As, Bi, Sb as a possible pathfinder of mineralization.
Mongolian Geoscientist, no. 22, October 1, 2003, p.25-26
Petrology and Mineral chemistry of Shavariin Tsaram and Mandalgovi basalts, Mongolia
Y. Majigsuren, A. Kitakaze and S. Jargalan
Basaltic rock samples from Sahavrin Tsaram and Mandalgovi
area have been studied by EPM Analyses for mineral chemistry and by XRF
analyses for major and trace elements at the Tohoku University.
Main rock forming minerals such as feldspar, pyroxene,
olivine, garnet, mica spinel were analyzed.
Olivine occurs as xenolith and in groundmass. Chemical
composition of olivine varies from Fo68.5 to Fo99.6. Fo number of xenolithic
olivine tend to higher than olivine in groundmass. Olivines in Shavar Tsaram
basalt (Fo69-Fo99.6) show higher Fo content comparing to Mandalgovi basalt
(Fo69.5-Fo90.7).
Pyroxenes are mostly in groundmass in Shavar Tsaram basalt,
and in phenocryst and groundmass in Mandalgovi basalt. Pyroxenes
are mostly diopside, and some of them are enstatite in composition (Fig-1).
No compositional difference observed between pyroxene
in Shavar Tsaram basalt and Mandalgovi basalt.
Plagioclases are in phenocryst and groundmass. Ab number
of plagioclases varies from Ab1.7 to Ab99.1 (Fig-2). An number of plagioclases
in Mandalgovi basalt is higher than Shavar Tsaram basalt. Or number of
feldspar Or50-Or72. Or number of feldspars in Shavar Tsaram basalt is higher
than Mandalgovi basalt. There are some high albite plagioclases in both
types of basalt.
Geochemistry of basaltic rock shows that they are high
potassium calc alkaline and composition. SiO2 content varies from 48.8
to 50.7 wt%, while it ranges from 44.2 to 45.8 wt% in Mandalgovi basalt.
Shavar Tsaram basalt is picritic basalt in composition,
while Mandalgovi basalt is basaltic andesite.
On MORB normalized trace element spider diagram show basaltic
rocks of two areas show similar characteristics. Rocks are enriched in
LILE and almost similar to similar with MORB value in HFSE.
Mongolian Geoscientist, no. 22, October 1, 2003, p.27-28
Petrological characteristics of the Hantaishir ophiolite complex, Altai region, Mongolia
Ichiro Matsumoto* and Onongin Tomurtogoo**
* Department of Earth Sciences, Faculty of Education, Shimane University,
Matsue,
Shimane 690-8504, Japan
** Mongolian Technical University, Ulaanbaatar 211137, Mongolia
The petrological characteristics of the Hantaishir ophiolite
complex, Altai region, Mongolia, have been examined. The Hantaishir ophiolite
complex contains two large ultramafic massifs (the Taishir and Naran massifs),
sheeted dike complex and serpentine m?lange zone including blocks of chromitite
and peridotites (e.g. Zonenshain and Kuzmin, 1978; Bat-Erden et al., 1996;
Matsumoto et al., 1998). The ultramafic massifs consist mainly of harzburgite
and dunite with a small amount of podiform chromitite. Cr/(Cr+Al) atomic
ratios of chromian spinels from the peridotites and sheeted dikes are high
(>0.7), as well as from chromitite (>0.8). Fo contents of olivine in the
peridotites have a relatively narrow range (91.8-93.0). ) Most of the sheeted
dikes are of boninite-type HMA. The sheeted dikes also have high Cr# spinels
ranging from 0.80 to 0.82, characteristic of spinels in boninites.
Both the mantle and the crustal members of the Hantaishir
ophiolite complex have island arc-characteristics. The high Cr# of chromian
spinels in the podiform chromitites may indicate a genetic link with boninites.
Coexistence of podiform chromitite and boninite suggests that the Hantaishir
ophiolite complex has formed in an intra-oceanic subduction zone from a
depleted mantle source (Matsumoto and Tomurtogoo, 2003).
This work was performed as part of the JICA (Japan
International Cooperation Agency)-IGMR (Institute of Geology and Mineral
Resources of Mongolia) project, and its result is combined with additional
new data. We are greatly indebted to JICA- IGMR for the opportunity to
participate in this project.
References
Bat-Erden, G., Bat-Ereedui, Y., Tomurtogoo, O., Gibsher, A.S. and Sovetov,
Y. C.
(1996) Lake’s island arc terrane. Geo
Bagts Co. Ltd., Ulaanbaatar, 10p.
Matsumoto I. and Tomurtogoo, O. (2003) Petrological characteristics
of the Hantaishir
ophiolite complex, Altai region, Mongolia
: Coexistence of podiform chromitite
and boninite. Gondwana Res, v.6, pp.
161-169.
Matsumoto I., Tomurtogoo, O., Nakajima T., Takahashi Y., Takahashi
T. and Sato Y.
(1998) Hantaishir ophiolite complex
and chromitite, Altai region, Mongolia.
J. Geol. Soc. Japan, v. 104, pp. VII-VIII.
Zonenshain, L. P. and Kuzmin, M. I. (1978) The Khan-Taishir ophiolite
complex of
Western Mongolia, its petrology, origin
and comparison with other ophiolitic
complexes. Contrib. Mineral. Petrol.,
v. 67, pp. 95-105.
Mongolian Geoscientist, no. 22, October 1, 2003, p.29-40
Geological and Geochemical Features of Kuroko-type Volcanogenic Massive Sulfide Ore Deposits in Japan
Toshio Mizuta and Daizo Ishiyama
Institute of Earth Sciences and Technology, Akita University
1-1 Tegata-gakuen, Akita, JAPAN, 010-8502
Abstract: Volcanic-associated massive sulfide deposits (VMSD)
are mostly stratiform accumulations of sulfide minerals that precipitate
from hydrothermal fluids on the sea-floor. Among the VMSDs, the Kuroko
deposits in Japan are closely associated with submarine felsic volcanism,
and are famous for their polymetallic compositions. The volcanic and sedimentary
rocks have been strongly, hydrothermally altered to so-called “Green-tuff”
of Middle Miocene age. The stratiform orebodies are mostly underlain by
stock-work siliceous orebodies.
General features of Kuroko deposits are geologically and geochemically
explained. The features of two representative Kuroko deposits are mentioned.
First deposit is the Motoyama Kuroko deposit as a lager-scale deposit,
and the second is the Nurukawa deposit as Au-rich smaller-sized deposits.
Geological and geochemical characteristics of the deposits reveal that
the Kuroko deposits have formed syngenetically by hydrothermal activity
associated with submarine felsic rocks.
Introduction
VMSDs are mostly stratiform accumulations of sulfide minerals
that precipitate from hydrothermal fluids at or below the sea-floor in
a wide range of ancient and mode geological settings. Precise descriptive
researches on sea-floor sulfides and vent fluids have provided modern analogs
for the land-based VMSDs. From the recent data, VMSDs on land could be
divided into three genetic types of ore deposits such as Cyprus-type, Besshi-type
and Kuroko-type ore deposits. The third type of Kuroko deposits is strata-bound,
polymetallic (Cu-Pb-Zn) sulfide-sulfate ore deposits with minor Au and
Ag. These deposits with ores in black color are call as Kuroko deposit
(“Kuro” means black and “ko” is ore in Japanese). The Kuroko deposits
are widely located within a narrow “Green-tuff” belt ranging from Northeast
to Southwest Japan (Fig. 1).
Many geological, mineralogical and geochemical studies have
been carried out for the Kuroko deposits (e.g., Ishihara ed., 1983, Ohmoto,
H. and Skinner, B. J. eds., 1983). Kuroko ore formation is associated with
the Japan Sea related formations. The Kuroko ores are considered to have
formed on the seafloor at depths of ca. 2000 to 3000 m from the foraminafera
assemblages in the Kuroko-related strata in the Hokuroku district (e.g.,
Matoba, 1983).
The formation of the entire Japan Sea is considered to have
occurred during 32 to 10Ma (Tamaki et al., 1992). It is also well established
through paleomagnetic studies that the counter-clockwise rotation of NE
Japan had taken place during ca. 21 and 18Ma (Hoshi and Takahashi, 1999).
The inferred formation ages for the Kuroko ores from the Hokuroku district
range form 16 to 13Ma (e.g., Kaneoka, 1983; Tanimura et al., 1983). The
Japan sea opening age of 18Ma is obviously older than the ages inferred
for the Kuroko deposits in the Hokuroku district, Akita Prefecture Northeast
Japan. The previous estimations for the Kuroko ores range from 16Ma to
11Ma (e.g., Kaneoka, 1983; Tani-mura et al., 1983; Horikoshi, 1990). The
assessment based on geological evidence and fossil ages indicates 15.5-15.2
Ma for the Hokuroku Kuroko formation (Horikoshi, 1990). Moreover, Terakado
(2001) reported Re-Os isochron age of 14.3Ma for the Kuroko deposits of
the Hokuroku district.
General Features of Kuroko deposits
The Kuroko deposits are also closely associated with extensive
submarine felsic vol-canism. Both the volcanic and sedimentary rocks have
been strongly hydrothermally altered to so-called "Green Tuff". The stratiform
orebodies are occasionally underlain by stockwork orebodies of pyrite and
chalcopyrite. These geologic features suggest that the Kuroko deposits
have formed syngenetically by hydrothermal activity associated with submarine
felsic volcanism (Sato, 1974).
The Kuroko deposits, massive sulfide deposits mainly consisting
of Kuroko (in narrow sense black ore), Oko (yellow ore) and Keiko (siliceous
ore), are typically developed in the Middle Miocene formations of the Hokuroku
district (Sato, 1974, Fig. 2). The Kuroko deposits are stratiform or lenticular
orebodies, being concordant with surrounding sediments. The most deposits
are accompanying stringer or disseminated orebodies of Keiko beneath the
massive orebodies.
The Kuroko ores are intimate mixture of dark iron-rich sphalerite,
galena, barite and minor quantities of chalcopyrite, pyrite and tetrahedrite.
They usually have a compact and massive texture, but fine laminations,
false bedding, and graded bedding reflect their sedimentary origin. The
Oko ores (Yellow ore) are characterized by the yellow color resulting from
the presence of chalcopyrite interstitial to the dominant pyrite. With
respect to typical Kuroko deposits, the Kuroko ores lie on the upper half
of the strati-form ore body and the Oko ores are dominant in the lower
half (Sato, 1974).
The footwall alteration zone consists of various kinds of clay
minerals (muscovite, chlorite, nacrite, dickite, montmorillonite, illite/mont-morillonite
mixed-layer minerals with rare kao-linite). These clay-sulfide distributions
indicate that the Kuroko-type mineralization and hydro-thermal alteration
proceeded simultaneously, or at least the time interval between both events
was short enough to maintain similar geothermal gradients in the submarine
hydrothermal system.
Examples of lager scale Kuroko deposits
The Motoyama Kuroko deposits: The Motoyama deposit is first
discovered Kuroko deposits in Japan. It is one of the main Kuroko -type
deposits of the Kosaka mining district locating in the eastern part of
the Hokuroku basin. The Uchinotai and the Uwamuki Kuroko deposits are also
distributing just south of the Motoyama open-pit.
Geology of the Kosaka area consists of Paleozoic basement rocks
and Neogene rocks which are divided into following five Middle Miocene
formations. Kuroko deposits in this area were formed the upper most horizon
of the Uwamuki Formation. 'White rhyolite' (altered rhyolitic lava-dome)
and Motoyama volcanic breccia typically crop out at the western wall of
the Motoyama open pit and constitute the footwall of the Motoyama Kuroko
deposits. The Motoyama volcanic breccia is assumed to have resulted from
phreatic explosion of white rhyolite in the relatively shallow sea.
The altered rocks were suffered at least two stage of hydrothermal
alteration. The White Rhyolite and the Motoyama volcanic breccia (footwall
rocks) were experienced the early stage hydrothermal alteration of Kuroko
mineralization. The younger stage alteration extends from the Akamori tuff
(hanging-walls) up to the Harukizawa tuff. There are four distinct alteration
zones were found in the Motoyama area. The alteration mineral assemblages
in rocks from weakly to stronger alteration zones are compiled as follows:
Zone I: Quartz - mordenite (with relict plagioclase)
Zone II: Quartz -montmorillonite - chlorite> sericite (with relict
plagioclase)
Zone III: Quartz-chlorite>sericite (with relict plagioclase)
Zone V: Quartz - sericite
Zone IV is distributed only in the white rhyolite and Motoyama
volcanic breccia. Predominance of association of quartz-sericite-chlorite
as the alteration association could be pointed out the close relationship
to the Kuroko mineralization. Zone I, II, and III are mainly distributed
in hanging-wall rocks and peripheral zones of footwall rocks.
Barite is mainly observed in black ore fragments in the Uwamuki
tuff and in siliceous orebodies in the Motoyama volcanic breccia just below
the Kuroko massive orebodies. And barite crystals are also found in marginal
low-grade siliceous orebodies in the Baramori area and in the proximity
of the White Rhyolite. Mineral assemblages of some Kuroko fragments in
the Kuroko bearing horizon are mainly composed of sphalerite, galena, chalcopyrite,
and barite. Crystal sizes of barite in highly mineralized siliceous ores
just below the Kuroko massive orebodies are much larger than those in the
samples of Kuroko massive ore fragments and in the samples of low-grade
siliceous ores far apart from the Kuroko massive orebodies
Homogenization temperatures of inclusion in quartz for
veinlets quartz in the white rhyolite range from 280°C to 361°C, veinlets
quartz in the Motoyama volcanic breccia range from 214°C to 334°C, and
in the siliceous ore range from 200°C to 358°C (Karangan, 1994). Filling
tempera-tures of inclusions in barite are 240°C to 280°C for siliceous
ores just below the Kuroko massive orebodies with salinities of 0.8-3.1
wt%. Inclusions of barite from the White Rhyolite range from 205°C to
255°C (with salinities of 0.7-2.7 wt% NaCl equivalent), barite in the
Motoyama volcanic breccia of the Baramori area range from 190°C to 230°C
(with salinities of 0.2-3.1 wt% NaCl equivalent), and in the barite-bearing
black ore fragments range from 180°C to 230°C with salinities of 2.3-4.0
wt% NaCl equivalent. With exception of Kuroko fragments, filling temperatures
and salinities of barite are higher for high-grade siliceous ores just
below the Kuroko massive orebodies and are getting lower values with the
distance from the center of Kuroko ore mineralization. Stable isotopic
compositions of oxygen and hydrogen for quartz in siliceous ores, and altered
acidic rocks in some upper horizon are complied as follows.δ18O of quartz
in siliceous ores and of acidic rocks in upper Akamori Formation.
Example of smaller size Au-bearing Kuroko deposits
The Nurukawa Kuroko deposits: The deposit is located in the northeast
margin of the Hokuroku district, northeastern Japan, an area in which many
Kuroko deposits are distributed (Fig. 4). The average Au content of typical
Kuroko deposits in the Hokuroku district is 1.3 g/ton (Tanimura et al.
1983). The average Au content of the Nurukawa deposit is 6.8 g/ton (Yamada
et al. 1988) that is much higher than typical Kuroko deposits. In this
paper, we describe and compare the mode of occurrence of ores and the geochemical
characteristics of Au and Pb-Zn mineralization of the Nurukawa deposit.
The Nurukawa Kuroko deposit was also formed in Middle Miocene.
The Nurukawa deposit consists of five orebodies, Nos. 1 to 5. The largest
No. 5 orebody is composed of an Au-bearing stockwork siliceous orebody.
The Au-bearing orebody, and a massive base-metal orebody are in ascending
order. The Au-bearing stockwork siliceous orebody is funnel-shaped, and
the Au-bearing bedded siliceous orebody is dish-shaped, and the massive
base-metal orebody is thinly lenticu-lar in shape (Fig. 3; Yamada et al.
1988).
Mode of Occurrence of Ores: The ores of No. 5 orebody are divided into
four types: Au-bearing ore. Au-bearing stockwork and bedded orebodies consist
of Au-bearing and Pb-Zn-bearing siliceous ores. Massive base-metal orebodies
consist of compact and brec-ciated siliceous ore, Pb-Zn-bearing siliceous
ore, massive black ore and brecciated black black ores. Au-bearing siliceous
ores are cut by a stockwork of Pb-Zn-bearing siliceous ores. Au-bearing
siliceous ores consist of major amounts of pyrite, chalcopyrite and quartz,
and lesser amounts of electrum, sphalerite, galena, hematite and kaolinite
and sericite. Pb-Zn-bearing siliceous ores include major amounts of quartz,
sphalerite and galena, and small amounts of chalcopyrite, pyrite and sericite.
The main constituent minerals of compact and brecciated black ores are
sphalerite, galena, pyrite, chalcopyrite and barite, with lesser amounts
of tetrahedrite, pearceite, pyrargyrite and sericite and rarely electrum
and bornite.
The clay-bearing layer shows a banded texture, thus texture
suggests that the clay minerals were precipitated directly from a hydrothermal
solution. Based on the fact that the mineral assemblage of kaolinite and
sericite is in altered rocks of Au-bearing siliceous ores and clay layers
in brecciated black ores, there is a possibility that the pH of hydrothermal
solution forming Au-bearing siliceous ores and black ores is more acidic
than the pH of hydrothermal solution forming typical Kuroko deposits.
Homogenization temperatures and salinities of fluid inclusions
in quartz of Au-bearing siliceous ores and in sphalerite and barite of
brecciated black ores were found to be 253 to 286°C and 3.3 to 5.3 wt%
NaCl eq. for quartz, 210 to 252°C and 2.7 to 4.1wt% NaCl eq. for sphalerite,
and 145 to 262°C and 1.5 to 2.7 wt%, NaCl eq. for barite, respectively
(Fig. 4). Homogenization temperatures and salinities of fluid inclusions
in the Au-bearing siliceous ores are higher than those of fluid inclusions
in the brecciated black ores. The salinity of fluid inclusions in the brecciated
black ores is similar to the salinity of seawater.
The oxygen isotopic ratios of quartz in Au-bearing siliceous
ores and Pb-Zn-bearing siliceous ores range from +9.2 to +10.2 and +9.0
to +10.0‰, respectively. The oxygen isotopic ratio of quartz crystals
in druse of brecciated black ores is +10.5‰ (Yamada et al. 1988). There
is no significant difference among these oxygen isotopic ratios.
The oxygen isotopic ratios of fluid responsible for the formation
of Au-bearing siliceous and black ores were estimated on the basis of oxygen
isotopic ratios of quartz, and the formation temperatures and fractionation
factor of quartz-water (Matsuhisa et al., 1979). The ranges of the calculated
oxygen isotopic ratios of hydrothermal solution responsible for Au-bearing
siliceous ores and brecciated black ores are +0.4 to +2.8‰ and -0.5 to
+1.7‰, respectively.
Hydrogen isotopic ratios of kaolinite of Au-rich siliceous
ores range from -62 to -53‰. The hydrogen isotopic ratios of kaolinite
are about 30 per mil lower than those of kaolinite that is associated with
typical Kuroko deposits in Japan (Fig. 5). The hydrogen isotopic ratios
are also different from those of kaolinite equilibrated with meteoric water
from vein-type deposits and modern geothermal area in Japan. Hydrogen isotopic
ratios for hydrothermal solution responsible for Au-bearing siliceous ores
were also calculated using the hydrogen isotopic ratios of kaolinite, the
formation temperatures, and the fractionation factor of kaolinite-water
by Sheppard and Gilg (1996). The calculated hydrogen isotopic ratios range
from -47 to -33‰. The hydrogen isotopic ratios of hydrothermal solution
directly extracted from fluid inclusions in quartz for Au-bearing siliceous
ores range from -55 to ?45 ‰.
Genetic model of the Nurukawa deposit: Con-sidering the higher salinity
of fluid inclusions of Au-bearing siliceous ores (Fig. 4) and the relationships
of hydrogen and oxygen isotopic ratios of hydrothermal solution (Fig. 6),
it is thought that the Au-bearing siliceous ores at No. 5 orebody of the
Nurukawa deposit were formed by hydrothermal solution containing fluid
of magmatic origin. The fluid responsible for the formation of black ores,
on the other hand, is dominantly of seawater origin. Based on the geological
relationships around the Nurukawa deposit (Fig. 2), there is a possibility
that the generation of fluid of magmatic origin was caused by the emplacement
of dacitic crypto-lava-domes under the Nurukawa deposit.
When the Au-bearing siliceous ores were formed, the contribution
of fluid of magmatic origin to hydrothermal solution of seawater origin
would have been large. In the case of the formation of black ores, the
hydrothermal solution is thought to be mainly a solution of seawater origin,
and the fluid of magmatic origin would have occasionally mixed with the
hydrothermal solution. The style of circulation of hydrothermal solution
changes from the hydrothermal system associated with great contribution
of magmatic water to the sea-water dominant hydrothermal system according
to the decline in activity of dacitic magmatism.
Concluding remarks
Assuming the equilibrium of quartz (and/or plagioclase
in the acidic rocks) and hydrothermal solution in a closed system, the
solution responsible for Kuroko minerali-zation and barite crystallization
should be derived from circulating seawater-acidic vol-canic rock system.
These observed data reveals that siliceous orebodies just below the Kuroko
massive ores are located in the central portion of Kuroko mineralization
and the tem-perature decease of hydrothermal fluids were not so large with
small degree of seawater mixing. The Kuroko deposits surely formed under
conditions similar to some present-day hydrothermal fields and the associated
metalliferous sediments.
REFERENCES
Horikoshi, E. (1990) Opening of the Sea of Japan and Kuroko deposit
formation. Mineral. Deposita 25, 140-145.
Horikoshi, E., ed. (1983) Island Arcs, Marginal Seas, and Kuroko deposits
(Mining Geol., Special Issue, No. 11. The Society of Mining Geologists
of Japan.
Hoshi, H. and Takahashi, M. (1999) Miocene counter-clockwise rotation
of Northeast Japan: a review and new model. Bull. Geol. Survey Japan 50,
3-16.
Ishihara, S. (ed.), (1974) Geology of Kuroko deposits. Mining Geol.
Special Issue, No. 6., The Society of Mining Geologists of Japan.
Kaneoka, I. (1983) On the radiometric ages of volcanic rocks from the
northeastern part of the Honshu Island, Japan. Island Arcs, Marginal Seas,
and Kuroko deposits, Mining Geol. Special Issue, No. 11, 69-78.
Kano, K. and Yoshida, F. (1984) Radiometric ages of the Neogene in
central eastern Shimane prefecture, Japan, and their implications in stratigraphic
correlation. Bull. Geol. Surv. Japan 35, 159-170.
Karangan, N. (1994MS) Alteration and fluid inclusion studies of the
Motoyama Kuroko deposit, Kosaka, Akita Prefecture, Japan. Master
thesis, Mining College, Akita University.
Marumo, K., Nagasawa, K. & Y. Kuroda 1980. Mineralogy and hydrogen
isotope geochemistry of clay minerals in the Ohnuma geothermal area, northeastern
Japan. Earth Planet. Sci. Let. 47: 255-262.
Matoba, Y. (1983) A discussion on the estimation of the sea depth in
the Hokuroku district during the time of the Kuroko deposition. Island
Arcs, Marginal Seas, and Kuroko deposits, Mining Geol. Special Issue, No.
11, 69-78.
Matsubaya, O. & K. Marumo 1986. Hydrogen isotopic evidence for
conservation of water in clay minerals. Fifth International Symposium on
Water-Rock Interaction Extended Abstract: 382-385.
Matsuhisa, Y., Goldsmith, J. R. & R. N. Clayton 1979. Oxygen isotopic
fractionation in the system quartz-albite-anorthite-water. Geochim. et
Cosmochim. Acta 43: 1131-1140.
Ohmoto, H. and Skinner, B. J. (eds.), (1983) The Kuroko and Related
Volcanogenic Massive Sulfide Deposits (Econ. Geol. Monograph 5, Economic
Geology Publishing Company, New Haven.
Otofuji, Y. (1996) Large tectonic movement of the Japan arc in late
Cenozoic time inferred from paleomagnetism: review and synthesis.
The Island Arc 5, 229-249.
Sato, T. (1974) Distribution and setting of the Kuroko deposits. Mining
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Tamaki, K., Suyehiro, K., Allan, J., Ingle, J. C. and Pisciotto, K.
A. (1992) Tectonic synthesis and implications of Japan Sea ODP drilling.
Proc. ODP Int. Rep. 127, 1333-1348.
Tanimura, S., Date, J., Takahashi, T. & H. Ohmoto 1983. Geologic
setting of the Kuroko deposits, Japan. Part II. Stratigraphy and structure
of the Hokuroku district. Econ. Geol. Monograph 5: 24-38.
Taylor, H. P. Jr. 1979. Oxygen and hydrogen isotope relationships in
hydrothermal mineral deposits. In H. L. Barnes (ed), Geochemistry of Hydrothermal
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Terakado, Y. (2001) Re-Os dating of the Kuroko deposits from the Hokuroku
district, Akita Prefecture, Northeast Japan. J. Geol. Soc. Japan 107, 345-349.
Yamada, R. (1988) Geology of the Au-Ag-Rich Kuroko Deposit at Nurukawa,
Aomori Prefecture. Society of Mining Geologists of Japan, Guidebook (Kuroko
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Mongolian Geoscientist, no. 22, October 1, 2003, p.41
Standardized legend of plutonic rocks for the 1:200,000 quadrangle geological map series in Japan
Yoshiharu Nishioka
Geological Survey of Japan/AIST, Tsukuba, Ibaraki 305-8567, Japan
I made the tentative plan of the unified legend (the plutonic
rocks) for 1:200,000 geological maps in Japan. The unified legend
were made from "Geological map of Japan 1 : 1,000,000 3rd edition" (Geological
Survey of Japan, 1992). I was picked up point that I should improve, through
the work that applies the legend item of the published 1:200,000 quadrangle
geological maps to the legend item of 1:1,000,000 geological map.
Also, collecting the data that is published age with the Rb-Sr whole rock
isochron datinge, I re-examined age classification. As a result,
as for lithology, the granitic rocks and the granodioritic rocks were subdivided
newly. Regarding the age, such a change that each Miocene (N2), Early
Cretaceous (K1), Late Cretaceous (K2) is divided to 2 ages and the plutonic
rocks of the Triassic period be newly established was put.
The example of the legend items of the published 1:200,000 quadrangle
geological maps which item correspond to each unified legend item.
Also, the result that did the correspondence of the legend items about
the 16 sheet maps around highly populated areas, was shown. From now on
and it needs to make the one that piles up examination and be able to use
across Japan.
Mongolian Geoscientist, no. 22, October 1, 2003, p.42-45
Comparison between the Honam Shear Zone and the Funatsu
Shear Zone
-A study on geological correlation between the Korean
Peninsula and the Hida Belt of southwest Japan
Yutaka TAKAHASHI (1), Weon-Seo KEE (2) and Bok Chul KIM (2)
(1) Geological Survey of Japan, (2) Korea Institute of Geoscience and
Mineral Resources
The Japanese Islands are regarded to have been located on the eastern margin of the Asian Continent, next to the Korean Peninsula, before the opening of Japan Sea. Therefore, correlative study between the Korean Peninsula and the Japanese Islands is important for understanding the tectonics of East Asia.
Geology of the Honam Shear Zone
The Ogcheon Belt is a medium P/T type metamorphic belt of middle
to late Paleozoic (Cluzel et al., 1991). It elongates northeast to southwest
in the Korean Peninsula, on the northwestern side of which is occupied
by the Precambrian Gyeonggi Massif, and on the southeastern side by the
Precambrian Yeongnam Massif.
The Honam Shear Zone (Yanai et al., 1985) is composed of several
dextral shear zones situated in and around the Ogcheon Belt. The authors
surveyed mainly on granitic mylonites in the Jeonju Shear Zone, the Yongkwang
Shear Zone and the Sunchang Shear Zone. These mylonites exhibit dextral
shear
sense and intruded by the Jurassic Daebo Granite. The timing of mylonitization
is regarded to be Triassic to Jurassic (Cluzel et al., 1991). Recent study
revealed that mylonitization of the Namwon Granite (slightly mylonitized
Jurassic Daebo Granite) had taken place early Middle Jurassic (180-160
Ma), because CHIME ages of the Namwon Granite are around 180 Ma (Cho et
al., 1999). Hwang et al.(2000) also suggested that the maximum age of ductile
shearing in the Jeonju Shear Zone is 165.8±2.0Ma, based on the U-Pb SHRIMP
zircon age of mylonitized granite.
Geology of the Funatsu Shear Zone
The Hida Belt is composed mainly of the low P/T type Hida Metamorphic
Rocks and the Funatsu Granites. The metamorphic ages of the Hida Metamorphic
Rocks are considered to be around 320 Ma, 240 Ma and 180 Ma (Sohma and
Kunugiza, 1993). The Unazuki Belt is a medium P/T type metamorphic belt
of Late Permian, situated along the southeastern margin of the Hida Belt,
and was correlated to the Ogcheon Belt (Hiroi et al., 1981). The Funatsu
Granites are Jurassic granitic rocks intruding into the Hida and Unazuki
metamorphic rocks and covered with the Tetori Group of Middle Jurassic
to Early Cretaceous. The Funatsu Granites are classified into Shimonomoto
Type (earlier and basic, mainly tonalite and granodiorite) and the Funatsu
Type (later and acidic, mainly alkali feldspar porphyritic coarse-grained
granite), whose radiometric ages are around 180 Ma (Shibata and Nozawa,
1984).
The Funatsu Shear Zone (Komatsu et al., 1993) is a mylonite
zone located in the Hida Belt, whose original rocks are mainly granites.
To the west of Kamioka Town, ultramylonite appears in granitic mylonite
zone and the massive Funatsu Granite intrudes into the granitic mylonites
cutting the mylonitic foliation (Kano, 2000). At upper stream of the Hayatsukigawa
River, Ohkumayama Granodiorite (Shimonomoto type of the Funatsu Granites,
183 Ma) intrudes into the granitic mylonite (Harayama et al., 2000). The
age of mylonitization of the Funatsu Shear Zone is regarded to be Triassic
(240-215 Ma). Because the mylonitization should be prior to the intrusion
of the Funatsu Granites and K-Ar age of hornblende in basic mylonite is
215 Ma (Shibata and Nozawa, 1978) and U-Pb ages of zircon and sphen in
granitic mylonite are around 240 Ma (Ishizaka and Yamaguchi, 1969). In
upper reaches of the Joganjigawa River, the Iwaidani Mylonite Zone (Harayama
et al., 1991) appears, whose original rocks are Shimonomoto Type of the
Funatsu Granites. This means at least, two times of mylonitization had
taken place in the Hida Belt. The second mylonitization post-dates intrusion
of the Funatsu Granites and possibly correlative to the mylonitization
of the Namwon Granite (180-160 Ma) in the Ogcheon Belt.
Correlation between the Hida Belt and the Korean Peninsula
Various ideas are published on the correlation between the Hida
Belt and the Korean Peninsula (Hiroi, 1981; Sohma and Kunugiza, 1993; Komatsu
et al., 1993; Cluzel et al., 1991 etc.). Hiroi (1981) correlated the Unazuki
Belt to the Ogcheon Belt and the Hida Belt to the Gyoenggi Massif. However,
as mentioned above, main metamorphism of the Hida Belt had taken place
in Paleozoic time. Therefore the Hida Belt cannot be correlated to the
Precambrian Gyeonggi Massif. Komatsu et al. (1993) regarded the Funatsu
Shear Zone as a northeastern extension of the Honam Shear Zone based on
their same shear sense and timing of mylonitization. Sohma and Kunugiza
(1993) regarded the Ogcheon Belt and the Unazuki Belt as a collision zone
between Sino-Korea and Yangtze Cratons. On the other hand, Cruzel (1991)
regarded the Yeongnam Massif and Oki-Hida Belt as a single geologic unit,
which moved southward along the Honam Shear Zone, based on paleobiogeographic
evidences. As described in Komatsu (1993), the sense and timing of mylonitization
in the Honam Shear Zone and the Funatsu Shear Zone are the same (dextral,
Triassic to Jurassic). And the position of the Ogcheon Belt and the Hida
Belt, before opening of the Japan Sea, is regarded to be geographically
continuous. Therefore, the Funatsu Shear Zone and the Honam Shear Zone
is regarded as a Triassic (?) to Jurassic dextral shear zone along the
eastern margin of the Asian Continent.
References
Cho, K., Takagi, H. and Suzuki, K. (1999) CHIME monazite age of granitic
rocks in the Sunchang shear zone, Korea: timing of dextral ductile shear.
Geosciences Journal. 3, 1-15.
Cluzel, D., Lee, B. J. and Cadet, J. P. (1991) Indosinian dextral ductile
fault system and synkinematic plutonism in the southwest of the Ogcheon
belt. Indosinan dextral ductile fault system and synkinematic plutonism
in the southwest of the Ogcheon belt (South Korea). Tectonophysics, no.
194, 131-151.
Harayama, S., Takeuchi, M., Nakano, S., Satoh, T. and Takizawa, F.
(1991) Geology of the Yarigatake District. With Geological Sheet Map at
1: 50,000, Geol. Surv. Japan, 173 p. (in Japanese with English abstract).
Harayama, S., Takahashi, Y., Nakano, S. and Kariya, Y. (2000) Geology
of the Tateyama District. With Geological Sheet Map at 1:50,000, Geol.
Surv. Japan, 218 p. (in Japanese with English abstract).
Hiroi, Y. (1981) Subdivision of the Hida metamorphic complex, central
Japan, and its bearing on the geology of the Far East in pre-Sea of Japan.
Tectonophysics, no. 76, 317-333.
Hwang, J. H., Choi, P. ?y., Kim, B. ?C., Kee, W. ?S. and Song, K. ?Y.
(2000) Geological report of the Muan Sheet(1:25,000). Korea Institute of
Geoscience and Mineral Resources, 58p.
Ishizaka, K. and Yamaguchi, M. (1969) U-Th-Pb ages of sphen and zircon
from the Hida metamorphic terrain, Japan. Earth Planet. Sci. Let., 6, 179-185.
Kano, T. (2000) Geology of the Hida Granites and granitic magmatism
in East Asia -Regionally metamorphosed granitoids-. Earth monthly, sp.publ.,
no. 30, Frontier for the study of granites -toward the new stage for granitoids
geneses-, 171-176.
Komatsu, M., Nagase, M., Naito, K., Kanno, T., Ujihara, M. and Toyoshima,
T. (1993) Structure and tectonics of the Hida Massif, central Japan. Mem.
Geol. Soc. Japan, no. 42, 39-62.
Shibata, K. and Nozawa, T. (1978) K-Ar ages of Hornblendes from the
Hida Metamorphic Belt. Jour. Min. Petrol. Econ. Geol., 73, 137-141.
Shibata, K. and Nozawa, T. (1984) Isotopic ages of the Funatsu Granitic
Rocks. Jour. Min. Petrol. Econ. Geol., 79, 289-298.
Sohma, T. and Kunugiza, K. (1993) The formation of the Hida nappe and
the tectonics of Mesozoic sediments: The tectonic evolution of the Hida
region, Central Japan. Mem. Geol. Soc. Japan, no. 42, 1-20.
Yanai,, S., Park, B. S. and Otoh, S. (1985) The Honam Shear zone (South
Korea): deformation and tectonic implication in the Far East. Sci. Rep.
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Mongolian Geoscientist, no. 22, October 1, 2003, p.46-47
Geochemistry of the rocks of Bayanhongor Ophiolie in Central Mongolia: implication for its origin
D. Tomurhuu and O. Tomurtogoo
Institute of Geology & Mineral Resources, MAS
P.O.Box118, Ulaanbaatar 210351,Mongolia
E-mail: inst_geology@arvis.ac.mn
The Bayanhongor Ophiolite in Central Mongolia is a one of largest
Ophiolite complex in Central Asian Orogenic belt (CAOB). The igneous rocks
of this complex consist both mantle and crustal suites and include metamorphic
peridotite, cumulate series rocks, sheeted dike complex and pillow basalts.
The associated sedimentary rocks are represented by both siliceous and
carbonate rocks filling the interpillow space or sometimes occur as lenses
or thin broken layer in volcanic sequences.
The detailed investigation of the geochemistry of the volcanic
suites of the Bayanhongor Ophiolite resulted in the following features
have been underlined. spider
In mantle normalized trace element spiderdiagrams, the majority
of the rocks reveal positive Nb and negative Pb anomalies which are the
main features of the oceanic magmatic rocks, but the patterns mainly fit
the OIBs (oceanic island basalts) and E-MORBs ( E-type Midoceanic ridge
basalts). However there are the exceptions of few samples of both sheeted
dikes and pillow lavas showing no anomaly or opposite anomaly of Pb. These
features of the rocks have been ascribed to the either contamination with
the host rocks or to the fractional crystallization. Two distinct group
can be identified using chondrite normalized REE patterns for samples from
Bayanhongor Ophiolite. These are a LREE enriched group with La/Yb
ratios ranging from 4.94 to 7.11 and a flat REE to slightly enriched LREE
group with La/Yb ratios of 1.4-2.4. Another immobile elements as Zr , Y,
Ti give quite consistent result suggesting that the rocks could be formed
in tectonic environment that involve not only component of the mid oceanic
spreading center, but some plume component as well.
The lack of field evidence for abnormally thick oceanic crust
and well developed sheeted dike complex suggests that if a plume was involved
then it was small and probably impinged on or near the to the mid-oceanic
spreading center.
The best interpretation of these results in term of tectonic
environment would be one similar to that in the present day Law basin,
where plume is impinging on or near to the mid-oceanic spreading center.
The lack of the rocks with N-MORB characteristics can be explained that
a section of oceanic crust with raised topography and low density would
be preferentially obducted on arrival the subduction zone.
Mongolian Geoscientist, no. 22, October 1, 2003, p.48
Forming process of the Hida Marginal Belt, SW Japan: as a Mesozoic tectonic zone
Kazuhiro TSUKADA (1)
(1) The Nagoya University Museum, Nagoya 464-8601, Japan
The Hida marginal belt (HMB), which consists of various kinds
of fault-bound blocks, is located between the continental massif of the
Hida belt and the Mesozoic accretionary complex of the Mino belt in central
Japan. Detailed field investigation reveals that the HMB had grown through
the two different movements, i.e. dextral and sinistral movements. The
dextral ductile shear zones run in the southern marginal part of the Hida
belt and the northern part of the HMB, whereas the sinistral cataclastic
shear zones occur in the southern part of the HMB and the northern marginal
part of the Mino belt.
The dextral ductile shear zones occur in the Jurassic Granite,
and are cut by the granite dated around 100 Ma. These facts indicate that
the dextral ductile shearing lasted after Jurassic time, and had finished
by Early Cretaceous time at least. A sinistral cataclastic shear zone occurs
in the Lower Cretaceous beds of the HMB. The sinistral shear zones in the
HMB are unconformably covered by undeformed lowermost Cretaceous volcanic
rocks. Hence, it is obvious that the sinistral shearing lasted after early
Cretaceous time, and had finished by latest Cretaceous time.
Geologic map and field evidence seem to suggest that the Jurassic
dextral movement formed basic structure of the HMB, i.e. formation of the
‘proto-HMB.’ It is considered that the Hida belt have been a proper of
the China block before the opening of Sea of Japan (e.g. Soma and Kunugiza,
1993). A compilation of paleomagnetic data in Asia (Enkin et al, 1992)
suggests that the China block shifted northward in Late Triassic to Jurassic
times. The dextral shearing might be attributed to the dragging force from
the northward drifting China Block (Otoh et al., 1999). Following the dextral
movement, the sinistral movement restructured the ‘proto-HMB’ to complete
the present feature of the HMB. The Cretaceous sinistral movement might
result in the sinistral collision between the proto-HMB and the Mino belt.