Bulletin of the Geological Survey of Japan，voL49（6），p．299－308，1998

Notes

P置ev量磯ss舳面es⑪輔塩eE越e魍e磁鵬ovO⑪脚瀞h翼y e⑪腿》er一囎㎜．o且y恥崩e囎眼㎜．de盈｝os量琶，Mo盟go畳餓

Gunchingin DEJIDMAA＊and Kazuki NAITo＊＊

Gunchingin DEJIDMAA and Kazuki NAITo（1998）Previous studies on the Erdenetiin ovoo porphyry copper－molybdenum deposit，Mongolia．B％ll．060ムS雄∂．如魏，vo1．49（6），p．299－308，5figs．

Aめstract：The Erdenetiin ovoo deposit in the Bulgan Aimag of Mongolia is the largest copper producer of the nation．According to the information available，the deposit is of porphyry type and cgntrolled by complicated combination of structure，magmatic and geochemical factors。In the mineralized area widely outcropped are two types pf porhyryies：（1）Selenge Comple of Per－ mian time（270－240Ma）and（2）Triassic Erdenet Complex．The mineralization is related geneti－ cally and spatially to the Erdenet Complex．Sericite alteration of the deposit shows the KAr age between210and190Ma．The ore－bearing porphyries intruded rhythmically into the Selenge Com－ plex．Sulfur isotopic compositions of sulfides exhibit bimodal distribution but satisfactory expla－ nation for this phenomenon has not proposed yet．

ore genesis of Erdenetin ovoo is complex and no 1．亘賊ro撫et童o艶 data o：f high （luality are available at present，this The literatures available on the Erdenetiin ovoo note aims only to show representati∀e view on the deposit for westem researchers are scarce although deposit an（1does not necessarily discuss the detail of the deposit has been famous as largest copper pro－ the mineralization and alteration． ducer in Mongolia（Fig．1）．One of the reason for this The Erdenet area is located in the northem part of is that they apPear in Russian in local publications． central Mongolia（Fig．2）。Many ancient pits were Thus the authors have listed up the information on seen before the open－pit mining，from there native this deposit maihly from Russian text books．The copper and turquoise were exploited possibly by summary of these articles are stated in this note．As smal1－scale miners．The first survey of the Erdenetiin

Fig．10pen－pit of the Erdenet mine．

＊MONRUD Co．，Ltd．，P．0．46，Box－130，Ulaanbaatar－ 210646，Mongolia Keywords： Erdenetiin ovoo deposit，Erdenet Complex， ＊＊Mineral and Fuel Resources Department，GSJ porphyry copper，Selenge Complex，Mongolia

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Fig．2Copper－molybdenum metallogenic belts of Mongolia（Sotnikov6如乙，1984）． Star indicates the location of Erdenetiin ovoo． 1－3：Upper Paleozoic orogenic belts（l l Northem Mongolia volcanic belt，2：Central Mongolia volcanic belt，3：Southem Mongolia volcanic belt），4：Intrusions of adamellite－granodiorite，5：Intrusions of gabbro－ monzonite，6：Erdenet－Tsagaan Subarga ore concentrating zone，7：Copper－molybdenum deposits and oc－ currences．

ovoo field was done byF Ushakov and Agomalyan in ErdenetbeltofNW－SEdirection（Fig．2）．Volchanskaya 1963but they did not publish the result．They pointed 6彪1．（1978）and Volchanskaya（1980）considered that out a possibility of existence of stockwork type cop－ the Erdenet ore－bearing area is situated at the inter－ per deposit，and recommended for farther explora－ section of faults with three different directions：E－ tion．In l977，the exploitation of the Erdenetiin ovoo WtrendingErdenetiinfault，N－StrendingCentral deposit was started by open－pit mining．Recently，the Mongolian fault and N－W trending Khar－Airgiin oxi（iized and leache（i zone has been taken out，and fault． the secondary sulfide enrichment zone is being recov－ The Erdenet area is located in the Orkhon－Selenge ered．After1977，the information of the Er（1enetiin Depression which is a part of the northem Mongolian－ ovoo can be found in many literatures：Sotnikov and Vitim Volcanic BeltwhereUpper Paleozoicto Mesozoic Berzina（1985）and Sotnikov6れz乙（1979），Sotnikovα volcanism are recorded．The basement of the depression ごz乙（1981），Sotnikov6渉磁（1984），Sotnikov and Berzina consists of Precambrian and Cambrian formations （1985），Gere16渉o：乙（1984）and Gere1αα乙（1985），：Koval with Devonian volcano－sedimentary rocks．In the and．Gere1（1986），Gere1（1989），Gavrilovaαα乙，（1984）， southern part of the depression，the Carboniferous Gavrilova6勧よ，（1988），Gavrilova6齢乙，（1989）。Among marine sedimentary rocks and Triassic sedimentary these literatures，Gavrilova6砲1（1984），Gavrilova6彪1 and volcanic rocks are distribute（i．Permian intrusive （1988），and Gavrilovaε砂1（1989），areimportant．Because rocks of the Orkhon－Selenge Depression was named these researches were’done by scientist including the“Selenge Complex”by Mikhalov and Shabalovskii resident geologists，an（1the attention was pai（i on ore （1971）．Insi（ie the complex，three phases are noticed： mineralogy and hydrothermal alteration of the deposit． first phase／gabbro，gabbro－diorite，diorite，monzonite， These studies lea（l to廿le publication of a book“Porphyry rarely monzodioritel secon（1（main）phase／subalkaline Molybdenum－Copper Deposit of Erdenetiin ovoo”，in granite，granO（iiOrite，granOSyenite，Syenite，qUartZ－ 1989． syenitel third phase／two groups of igneous rocks，whi¢h occur separately．In the Er（ienet area third phase of the complex inclu（ies stocks an（1dikes of granodiorite 2。 Regio醜＆1setti蟄g a醜損geo亘ogy porphyry an（i granite porphyry，but in other places， Sotnikovα召乙（1984）considere（i t血at a volcano－Plutonic the rocks are fine granular leucocratic granite，granite－ belt which designates Mongolian－Vitim Volcanic Belt aplite and microgranite（Mikhalov，1971）．Yashima and in northem Mongolia hosts copper mineralization， ＊1“Erdenetiin ovoo”is the name of the porphyry Cu－Mo and the Erdenetiin ovoo＊10re deposit is found at the deposit，while“Erdenet”is the name of the mining intersection of this belt and the Tsagaa塾Subarga一 company。

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blocks，and stated that the boundary between these ＼＼ blocks is the Bukhaingolyn fault．In the westem block， ’気． 弓隔＼1 the basement is deeper than that of eastern block．In the eastem margin of the Erdenet cross structure， ＼＼ 0匁 the mass of alkaline basalt，trachybasalt，trachyan－ ＼＼ぽ1＞／く一 desite of the Upper Permian to Early Triassic age is ’＼＼＼｛！’ト lying with disconformity on the Permian rocks being intruded by gabbro－syenite an（1granosyenite－granite associations．In westem side and in the southem part of the cross structure，the Permian rocks is covered with the sandy conglomerate of the mid（11e to Upper Triassic age（Abzoga suite）and the trachya．ndesite 二獣，ノ mass with rhyolite and trachyrhyolite of the Upper Triassic to Early Jurassic age． The mineralized zone of the Erdenet area is found 、㎞ 3 ス＼ ，一 in the“Erdenet cross structure7’that is located in the 心 く麺鳳 northeastem part of the westem block of the Orkhon－ 團・臼2Eヨ3 ＼楓 Selenge Depression．The area is widely occupied by ’曳、 Permian volcanic rocks（Hanyi Series）and fels爺c ＼ intrusions．The Upper Triassic to Lower Jurassic Fig。3 Scheme of structure of the Erdenet ore bearing formation is also seen in the block an（i this formation zone（after Sotnikov6渉σ孟1984） consists of trachyandesite，trachybasalt－porphyry and 1：granodiorite porphyry，plagio－granite porphyry of ore trachyan（iesite・basalt with high sodium content bearing complex，2：zones of ore－metasomatitic forma－ （Kepejinskas and Luchitskii，1974）．The stratigraphy of tions，3：faults。 volcanogenic andsedimentary rocks，andpetrochemistry were reported by Kepejinskas and Luchitskii（1973）； Kepejinskas and Luchitskii（1974）l Mossakovskii and Matrenitskii（1978），Yashima and Matrenitskii（1979）， Tomortogeo（1972）l Mossakovskii（1975）l Mossakovskii Matrenitskii（1977）and Matrenitskii（1981）clarified and Tomortogeo（1976）l Saltykovskii and Orolmaa the following three independent associations in the （1977）and Gavrilova召地よ（1984）．The Hanyi series in Selenge Complex：1／Gabbro syenite（P22）12／Syenite， the westem block is characterized by a combination granosyenite，granite（P2－T1）13／Monzogabbro－diorite， of pyroclastic rocks and bimodal calc－alkaline lava． syenite，granite porphyry（Er（ienet type：P2－T1）． The volcanic rocks of the Hanyi Series with lower Gavrilova6齢乙（1984）summarized results of these Al203content，subalkaline an（i alkaline composition studies and established following sequences of con－ are commonly developed in the westem block． stituent rocks of the Orkhon－Selenge Depression： The mineralized zone of the Erdenet area with20－25 1）Granite－granosyenite，T3－J1 km length is located in the center of a narrow dome 2）Trachyandesite（Mogod suite），T3－J1 stmcture，which consists ofgranodioriteandmor切ogranite 3）Molasse（Abzoga suite），T2－T3 of main second phase of the Selenge Complex．Around 4）Granite．granosyenite，P2－T1，256－226Ma（KAr） the dome structure，the Permian volcanic rocks and 5）Gabbro－syenite，P22，268－242Ma（K－Ar） the basement of the Orkhon－Selenge Depression are 6）Basalt－trachybasalt（suite of basic effusion），P2 distributed．In the northern part of the mineralized 7）Sedimentary volcanogenic rocks（tuffaceous suite）， zone，Precambrian metamorphic rocks are also Pl2－P21 distributed．Dikes and the porphyritic plutons intrude 8）Alkaline granosyenite and granite，234Ma（K－Ar） into the center of the mineralized zone．Mi㎞alov（1971）， 9）Rhyolite－trachyThyolite（suite o：f aci（五c ef血sions），P1 Khasin切α1．（1977），Pavlenkoα召1．（1974）considere（i 10）Trachybasalt－trachyandesite（suite of basic and these porphyritic intrusions as members of the Selenge intermediate effusions），Pl Complex．Yashina and Matrenitskii（1978）described 11）Interval for sedimentation that so－called Selenge Complex includes two groups： 12）Gray color molasse，C1－C2 Upper Permian rocks and Lower Triassic rocks．The 13）San（1y siltstone，marine，C1 former is the general type of syenite－granosyenite－ granite，an（1血e latter inclu（ies porphyritic intrusions of monzogabbro－diorite－syenite－graniteporphyly．Sotnikov 3．Geo亙ogyo£職i聾era亘亘ze岨are＆ αζz乙（1984）stated仕しat Erdenet－type po耳）hyritic intrusiQns 3．IGeo且ogy are younger than Selenge Complex and have different Mossakovskii and Tomortogeo（1976）divided the origin from the Selenge Complex．Based on such studies， Orkhon－Selenge Depression into westem and．eastem these intrusions are separate（i from the Selenge

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Complex and are now called as“Erdenet Complex” gigantic breccia body（Gavrilova6渉σ乙，1989）due to （Sotnikov6厩乙，1985）．According to Gavrilova6勧よ， explosive processes and complicated tectonics of the （1989）the chemical composition of the complex belongs zone（Fig・4）・In the brecciated body，fragments of to hi3h alumina，potassium－sodium，calc－alkaline se－ granodiorite・porphyry are cemented with dacite of ries．The Na20content is as high as4．02－5．9wt．％in several phases．An explosive pipe，possible neck of all stages．Low Rb（40－68ppm）and high Sr（800－1100 the volcanism，is seen in the complex．Granodiorite ppm）and Ba（1000－1100ppm）are also typical feature fragments in this pipe are cemented by plagioclase－ of this complex．Based on the information stated porphyry， （iacite and their autochthonous breccia． above，the intrusive rocks within the Er（1enet cross The southeastem stock has pear－1ike shape。The stock structure area could be divided into four groups： ，has60to700contact against the wall illustrating the 1）Lower Paleozoic complex in the Precambrian upper part of dome－lik：e shape，and vertical contact basement in deeper part and the contacts fall toward center of 2）Upper Pe面an Selenge gabbro－granosyer丘te－grar近te stock in the950－1000m depth．The northwestem stock complex has horseshoe－1ike shape in surface with complicated 3）Erdenet Porphyry Complex steep boun（1aries．In deeper portion，the stock consists 4）UpPer Triassic to Early Jurassic leucogranite of two steep fallen bodies that are connected in upper Recent Mongolian geological kingdom tend to accept horizonsofflat－1yingpartwith300－400mthickness． the distinction between Upper Permian Selenge Com－ The northem contact of the stock with complicated Plex and UpPer Triassic to Early Jurassic Erdenet shape fall steeply and vertically into southward． Complex． The structure of hydrothermal system of the deposit The sequence of all porphyritic phase is as follows： can be outlined based on the （1istribution o：f SiO2 1）diorite porphyry and microdiorite anomaly．The distribution can be traced down to 2）granodiorite porphyry（main part），Plagio－granite 1600m，which implies that the hydrothermal system porphyry had at least about1．6km extension．Such situation is 3）fine grained，middle grained granodiorite in as－ also suggested by the distribution of Na，K an（i Rb sociation with breccia anomalies． 4）fine granular aplite with increase of alkaline Quartz metasomatite and quartz breccia are Being different from these description，Professor widely distributed in the southeastem part of the Gerers group at Mongolian Technical University southwestem stock．The quartz－sericite metasomα一 have an unique idea on the genesis of Erdenetiin tite has a two－layer structure．The lower layer（900－ ovoo．Gere1α認，（1984），Kova1αα乙，（1985），Koval 1100mabovesealeve1）correspondstoarootzoneof and Gerel（1986），and Gerel（1990）thought that the hydrothermal system．It consists of separated pillar－ Erdenet type intrusions were formed as a series of 1ike an（1steep fractured bodies．The upper layer magma with trachyte and trachyandesite and consid－ （1100－1600mabovesealeve1）surroundsallstocks ered that the Early Mesozoic trachyte and trachyan－ and satellites intrusions．The thickness of the upper desite to be genetically related to the mineralization． layer are650－700m inthe southwestem part，500－550m In the following paragraphs we use Selenge an（i in the center and300－400m in northwestem part． Erdenet classification to describe the mineralization Gavrilova6オg乙（1989）considered that the lower at Erdenet．Based on this concept，it can be stated layer of the deposit corresponds to a zone o：f vertica1／ that most part of the Cu－Mo deposits occur within steep－angle channel where ore bearing hydrothermal the Er（ienet Complex． solution was focused．The upper layer of the deposit behaved as a chamber where the mineralizing fluid 3．2 Str賦ct聰re o釜t最e m亘遡er＆亙de亙｝os亙t precipitated minerals．The contour of elemental con－ The deposit is located in the intersection of faults centration in the lower horizon suggests verticaI of NE－SW，NW－SE，N－S and E－W trends．South－ chamel of migration of elements，but horizontal shape westem and northeastem side of the Erdenetiin ovoo of the contour line is common in the upper horizons． area have steep boundaries into which magma as－ An important structural factor of the deposit is fault cen（ied．The mineralized zone inclu（1es a cupola of of N－S，：NW－SE，E－W and NE－SW directions．The granodiorite of the Selenge Complex and stocks and intersection of these faults determine（1the high level of dikes of the Erdenet Complex．The Er（1enet Complex fracturing－ability and of permeability．All these faults rocks are distributed as dome－1ike bodies an（i sate1－ are o1（1er and have been active during the formation lites in the cupola mentioned above．The porphyries of the deposit，and after formation of the deposit of third phase have mostly E－W direction and steep some of them played an important role．Sotnikovα ：falling，and the porphyries of fourth and fifth phase α乙（1984）noted thatfaults ofNW－SE，NE－SWandN－ have NE－SWdirection． S directions give the structural control of the miner－ The Er（ienet Complex is roughly divi（ied into alize（l zone and the deposits（Fig．3）．The faults of southeastem and northwestem stocks，and contains NW－SE direction controlled the mineralization，the

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KAr age（Sotnikov6齢乙，1985）． 4，．2 M宜neral a，ssociat宜o盟 Khasin 6渉 6zよ （1977） consi（iered that all primary Ore minerals，ore mineral association and miner－ minerals were formed within a stage between the alization stages are describe（i by Yakovlev and injectlon of grano（1iorite porphyry stock an（i injection Tamsran（1977），Khasin6オ磁（1977），Gavrilovaα認 of dacite porphyry（1ike but（1id not report relationship （1984，1989）and Sotnikov and Berzina（1989）．First between the porphyries and mineralization／alteration． description of minerals has given by Yakovlev and Yakovlev and Tamsran（1977）proposed that the Tamsran（1977）．By Khasin6渉認（1977），the mineral－ mineralization only took place in the third phase ofthe ogy of the deposit was shown as follows： Selenge Complex．Sotnikov and Berzina（1989）obser▽e（1・ 1）Major minerals of primary ore are pyrite，chal－ that hydrothermal alteration an（i porphyritic intrusions copyrite，chalcosine，covellite，bornite，sphalerite，ga－ have close spatial relationship，and considered that血ey Iena，magnetite，clay－ore，molybdenite，quartz，feldspar， are products of same magma－hydrothermal system． and sericite．Accessories are gypsum and fluorite． They also stated that the hydrothermal system at 2）Predominant minerals of secondary enrichment Erdenetiin ovoo was（1eveloped in the final period of zone are chalcosine，covellite，chalcopyrite，bornite， development of the porphyritic system or after the molybdenite，pyrite，clay－ore，turquoise，and chryso－ solidification of the porphyries，but did not point colla． which phase of intrusion was important for the 3〉Major minerals in oxidized and Ieached zone are mineralization．Gavrilova召砲よ（1989）examined each malachite，chessylite，chrysocolla，brochantite，native phase o：f the intrusions and propose（i an i（lea on the coPPer，and powellite． relationship between magmatism an（i hydrothermal Khasin6厩乙（1977）is different from Yakovlev an（1 activity．They consi（1ered the first phase porphyry Tamsran（1977）on the following points： most important： 1）The chalcocite，covellite and bomite have two 1）The first（main）stage of hydrothermal alteration origin as hypogene（in primary ore）and as supergene of rocks developed after the intrusion of the first （insecondarysulfidezone）． phase porphyry． 2）The turquoise is formed in secon（1ary’sulfide en－ 2）Second stage of hy（irothermal alteration occurre（1 richment zone。 after the second phase porphyry intru（ied with mo－ Gavrilovaα認（1989）clarified following mineral 1ybdemm mineralization．The hydrothermal solution associations＝magnetite，pyrite－quartz，molybdenite－ in this stage caused brecciation of rocks alld in－ quartz，chalcopyrite－pyrite－quartz，metacrystals of pyrite， creased the number of quartz network pyrrhotite（cubanite）一chalcopyrite（drop－1ike），chalcocite－ 3）Porphyries of the thir（i phase seems to have bornite，galena－sphalerite－tennantite（polymetallic）an（1 caused copper and molybdenum mineralization．The zeolite－gypsum－carbonate associations．Magnetite copper content is around900－1900ppm and molybde－ association is developed widely at marginal portion num10－40ppm． of the deposit．The magnetite association is distributed 4）Porphyries of the fourth phase such as leucopor－ in the southwestem，westem and northwestem parts phyry，rhyodacite－dacite－an（1esite－dacite－tonalite por－ of the deposit．Pyrite－quartz association occurs in phyry accompany small amount of pyrite－chalcopyrite two places＝one in the periphery with chlorite and network． the other in the center of the deposit forming special 5）Porphyries of the fifth（fina1）phase carry small pyrite pillar：in the place，where is decreased the amount of pyrite－quartz，molybder丘te－quartz，chalcopyrite－ scale of quartz－sericite metasomatite．Pyrite is pyrite－quartz networks． formed an insets of different size and a network with Sotnikov and Berzina（1989）studied three phases of different thickness．Pyrite of the central part of the porphyries and concluded that the first an（i second deposit is different from that of the periphery part phases are associated with mineralizations as follows： which is large size and occurrence is inclusions of 1）Potassium feldspathization，with／without biotite． chalcopyrite，molybdenite and others．Molybdenite－ 2）Quartz－sericite alteration with pyrite． quartz association distributes in all horizons of primary 3）Quartz－pyrite－molybdenite association with and secondary ores．But scales of the minerals are chalcopyrite． different．The association is presented molybdenite－ 4）Quartz－pyrite－chalcopyrite association with quartz network and rare inset of molybdenite．In molyb（1enite． molybdenite－quartz network is marked a presence of 5）Galena－sphalerite association． pyrite an（i chalcopyrite． Chalcopyrite－pyrite一（luartz 6）Quartz－pyrite association． association is（ieveloped in all horizons of the deposit． 7）Quartz（chalcedony）一carbonate association． The ratio of pyrite and chalcopyrite in this associa－ Gavrilova6渉砿（1984）and Gavrilovaα認（1989） tion is change（i vertically in the cross section，for ex－ clarified five stages of mineralization which accom－ ample pyrite is dominant in the upPer part，and cha1－ panied by five phases of porphyritic intrusions． copyrite is dominant in the lower part．ChalcOpyrite is replaced by chalcocite and covellite in the above

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horizons of secon（iary sulfi（ie enrichment zone，and Molybdenum has an opposite tendency to the monomineral chalcopyrite occurs in size of O。n mm distribution for Cu．Molybdenum content in marginal in the Iower part of the deposit，rarely with network area of ore body is O．02％，but O．012％in the central of O．5－1cm thickness．Gavrilovaα認（1989）noted part． that chalcopyrite of the association is replaced by hypogene chalcocite and bomite in the lower part of 4．3恥δro翫erma丑a旦terat豊o麺 the（leposit．Pyrrhotite－chalcopyrite（droP－like）asso－ Regionally the alteration shows a zonal distribu－ ciation occurs in massive pyrite of pyrite－quartz and tion．The quartz－sericite zone is（1eveloped in the center chalcopyrite－quartz associations by droP－like form． of the stockwork being changed outward into sericite－ Sometimes cubanite is observed in this association． chlorite and then carbonate－epi（10te－chlorite zone．In Hypogene chalcocite－bomite association was described the upPer part of the zone argilization is notice（i． by Gavrilovaα認（1984）．Gavrilovaαα乙（1989）noted． Sometimes potassium feld．spathization with or with－ that the abun（iance of sulfur and coPPer in hydro廿lermal out hydrothermal biotite and tourmaline is observe（i． solution lead to form of hypogene bornite．They also The quartz－sericite zone changes the degree of a1－ marked that this association occurs in secondary teration place to place with quartz－sericite ratio to sulfide enrichment zone or in deeper levels．This host rock from10％to more than70％．An altered association distributes mainly in southeastem part of rock with the quartz－sericite composition＞70％is the deposit．This association consists of bomite， calle（i secon（iary quartzite at the mining office．In chalcocite，chalcopyrite，pyrite，sphalerite，tennantite， the eastern part o：f the deposit the porphyritic stock galena，molybdenite and mtile，and hematite occurs and alteration zones are cut by a large fault of N－S in the upPer horizons，and magnetite occurs in the direction． lower horizons．Monomineral bomite and chalcocite－ bomite veinlets distribute widely．Metacrystals of 4．4SecO恥daryzO鷺e pyrite is observed in cubic form including micro－ The vertical zonal structure is traced clearly as inclusions of quartz，rutile，magnetite，pyrrhotite and follows：oxi（1ized and leached ore zone，secondary others． sulfide enrichment zone，primary ore zone．In the Polymetallic association occurs byF separated zones southeastern part，hypogene chalcocite－bornite asso－ of the deposit．This association consists of galena， ciation in upPer part changes into chalcopyrite－pyrite－ sphalerite and temantite，and forms network．Pyrite－ quartz association in deeper part． quartz，molybdenite－quartz，chalcopyrite－pyrite－quartz The thickness of oxidized and leached zone changes associations are cut by this network。Zeolite－gypsum－ fromlOmto90mandofsecondarysulfideenrich－ carbonate non－ore association occurs by network， mentzonefrom60minthesideto300minthecen－ crossing all hypogene associations and all rocks in ter of the ore bo（1y．The content of Cu changes from ore bearing stockwork．Zeolite is presented by O．8％ to 7．6％ in secondary su1：fide zone of central clinoptilolite and laumontite．Gypsum is developed in part of the（leposit an（l is decreased into margin of the upPer horizons of the deposit，and anhydrite de－ the deposit．The content of Mo is changed from velops in the lower horizons．Carbonates distribute O．001％to O．76％in secondary sulfide zone．The pri－ widely and are presented mainly by calcite．Bomite－ mary ore zone is discovered in150－500m depth from chalcocite－covellite supergene association distributes surface and is marked in1000m（1epth by dri11hole． in secondary sulfide enrichment zone．Primary cha1－ The secondary sulfide enrichment zone includes copyrite，temantite，sphalerite and other minerals 85％of ore．The size of the ore body is2800m by300－ are replaced by chalcocite，covellite an（i bornite． 1300minthesurfaceandis1000mby600minthe Distribution of some minerals show the vertical prlma「y ore zone・ zonal structure．Content o：f pyrite，sphaleritel galena， temantite and especially clay－ore decrease toward 5．亙sot曜cs舳d互es deeper part．Clay－ore is foun（i only in the upPer part of the deposit．Changes of trace elements content in Sulfur isotopic composition of ore was studied by ore－minerals show the vertical zonal structure．For Tugarinov6齢よ（1974）．They determined the ratio of example，Se and Co contents in pyrite increase into sulfur isotopic composition（Fig．5）。The♂4S value of deeper part of the deposit，but Ni content decreases． the sulfides ranges from－3．3to十2．7％o with an Se content in chalcopyrite increase into（1eePer Pa「t average value of十〇．4％o Molybdenite is weakly ofthedeposit．Anhydriteisdistributedfrom400mto enriched inが4S（十1to十L5％o）compared to sulfides l200m．Calcite increases in deeper part．Copper content of copper and pyrite．The values show no（iifference in primary ore changes from O．4－0．5％in the center in vertical section．Suchhomogeneous sulfur composition ofstockworkdownto500mdepthfromthepresent is a result of homogenization of sulfur before the surface，and between 500－1000m depth，0．2－0．3％． mineralization．The value ofが4S for thesulfates ranges Molybdenum content is O．025％in primary ore． from十9．1to十12。5％o The study evidenced two stages

一305一 Bz6116訪z6ゾ云h6（弛olog乞6αl Sz67z7ののワψごzn，『Vlol．49，ハ汚o．6，ヱ998

⑭鋤⑭ □師te 図Chalcopydte 圏Bomite 回M・iy図enite

⑭趣 皿Gypsum

働 ⑱

4 一2 0 2 4 6 8 10 12 δS34％o

Fig．5Sulfur isotope composition of sulfides and sulfates of copper－molybdenum deposits of Erdenetiin ovoo． （Tugarinov8彪乙，1974）．

of hydrothermal ore formation．In the secon（1stage， hydrothermal activity l3）change in morphology of ore formation is characterized by increasing in magmatic rocks from stock－1ike to dike with con－ oxidation potential of solution．The precipitation of comitant decrease of the scale in magmatism and in molybdenite was relate（1to the first stage，but ore－metasomatic process l4）change in shape of ore－ chalcopyrite precipitated during the first and second bodies from network－stockwork to veinlet or string． stage．The additional study・of sulfur isotope was The mineralization is relate（i genetically and spa－ done by Voinkov6オα1．（1977）．Theδ34S values of tially to stocks of porphyritic intrusions，Erdenet pyrite and chalcopyrite show bimodal distribution Complex．The ore－bearing porphyries intruded rhyth－ with peaks at－2％o（in network）and at O％o（in mically into the Selenge Complex．Many authors are disseminated type），and bomite with peaks at－2％o thinking that each phase of porphyry is associate（i and O％o．Based on such result，they interpreted the with mineralization but some authors are assuming schematic process of ore formation in the Erdenetiin single pulse mineralization． ovoo deposit as follows：（1）after intensive fracture of The mineralized zone in the Erdenet Complex holds host rocks，the hydrothermal solution was precipitated a two－1ayer stmcture．The lower layer is steep・angle root small amount of ore in network and disseminated－ of magma－hydrothermal system and includes separated type with sulfur isotope composition of similar to pillar－1ike ore zones．The upper layer surrom（1s mostly meteoritic compositionl（2）new fractures which were all portion of the deposit an（i has sickle－1ike shape relate（1to the intrusion of dikes were（ieveloped and with a flat portion．Gavrilova6砲乙（1989）considered ore minerals were precipitated，and in this stage the that the upPer layer o：f ore body corresponds to a hydrothermal solution was more oxidized．Perhaps chamber，where ore bearing solution and flui（1 second fracturing was more intensive and loca1，so the deposited． sulfides with decreasedが4S were distributed locally only in the lower part of the（ieposit．The precipitation AckRowleδgement：Professor O．Gerel of Mongolian of larger size and disseminated chalcopyrite may be Technical University kindlyF allowed G．D．to use her related with the second stage． e－mail system to communicate with the editorial board of this special issue。

6．Co髄d服面賦g rem＆rks Re歪ere趙ces According to the information available，the Er－ denetiin ovoo deposit is controlled by complicated Gavrilova，S．P．，Didenko，M．1．，Orolmaa，D． combination of structure，magmatic and geochemical （1988）The role of study of space picture and factors．Gavrilova6麺よ（1989）we11described features morphology of surface for discovery of central of the Erdenetiin ovoo deposit as follows：1）inter－ stmcture inregion ofpalaeo－volcanism：Complex mittent rhythmical injection of magmatic source and study of rare metal ore area，Publication of fluid－hydrothermal activity and associated ore miner－ IMGRE＊2，Moscow，8－28（in Russian）．

alization l2）close relationship between magmatic ＊21MGRE is the acronym of the Institute of Mineralogy， rocks，hydrotherma1－metasomatic products and ore Geochemistry and Crystalgeochemistry of Rare Ele－ minerals in all phases or stages of the magma一 ments of Russia（E4宛o〆sηo渉（3）．

一306一 P柳加s吻伽so％E名ご6吻伽汐oゆh鍔C％一ハ4046郷πの⑳伽磁α副

Gavrilova，S．P．，Maximyk，1．E。，Oro㎞aa，D．（1984） Mikhalov，E．V．（1971）Intrusive complexes of Features of magmatism and composition of northeastem Mongolia．動Magmatism and ore of coppermolybdenum deposit Erdenetiin Metallogeny of Mongolian People7s陣Republic， ovoo．動Endoger丘c Ore FormaHonsofMongolia， Nedra，Moscow，60－77（in Russian）． Nauka，Moscow，101－105（in Russian）． Mikhalov，E．V．，Shabalovskii，A．E．（1971）Ore Gavrilova，S．P．，Maximyk，1．E．，Orolmaa，D．（1989） controlling significance of cross an（1diagonal The molybdenum－copper porphyritic（1eposit faults in eastem and central Mongolia．動 Erdenetiin ovoo，Mongolian People’s Republic， Magmatism and Metallogeny of Mongolian Publication of IMGRE＊2，Moscow，40p．（in Peopleフs Republic，Nedra，Moscow，142－147 Russian）． （inRussian）． Gerel，0．（1990） Petrology，geochemistry and Mossakovskii，A．A。（1975）Orogenic structures mineralization of subalkaline Mesozoic an（i volcanism o：f Paleozoic of Eurasia and its magmatism in Mongolia．D．Sc．Dissertation， position in process of the motion of continental Irkutsk，30p．（in Russian）． earth crust，Nauka，Moscow，318p．（in Russian）． Gere1，0．，Kova1，P．V．and Tseden，Ts．（1984） Mossakovskii，A．A．，Tomortogeo，0．（1972）The Geochemistry of Late Paleozoic porphyritic scheme ofstratigraphyofPe㎞anandMesozoic intmsive of Erdenet area．Abstracts of the volcano－sedimentary formations of Orkhon－ Conference，Geochemistry and Geochemical Selenge depression，Mongolian Peopleフs Re－ Exploration Method of Ore Deposits，37－38 public，ム～61）07まs6ゾゑh6乙㎜～ノ10とz46履ソ（ゾSo勿7zo8＆ （in Russian）． 206，no．5． Kepejinskas，V．V．，Luchitskii，1．V．（1973）The Mossakovskii，A．A．，Tomortogeo，0．（1976）Upper Permian volcanic association of central Paleozoic of Mongolia，Nauka，Moscow，p127． Mongolia．加Associations of Volcanic Rocks Movsesyan，S．A．，Isaenko，M．P．（1974）Complex in Mongolian Peopleフs Republic and Its copper－molybdenum deposits．：Nedra，Moscow Composition and Stratigraphycal Position， （in Russian）． Nauka，Moscow，71－93（in Russian）． Pavlenko，A．S．，Filippov，L．V．，Orlova，L．P．（1974） Kepejinskas，V。V．，Luchitskii，1。V．（1974）Continental Granitoid Formations of Central Asian Fold Volcanic Associations of Central Mongolia， Belt，Nauka，Moscow，223p．（in Russian）． Nauka，Moscow，72p。（in Russian）． Saltykovskii，A．K．，Orolmaa，D．（1977） Upper Khasin，R．A．，Marinov，N．A．，Khurts，Ch．，Yakimov， Paleozoic to early Mesozoic volcanism of L。1．（1977）Copper－molybdenum deposits Er－ northem Mongolia and westem Zabaikalya， denetiin ovoo in northem Mongolia．G6010劇 Nauka，Moscow，202p．（in Russian）． げ0名召Z）砂os傭，no．6，3－15（inRussian）． Sotnikov，V．1．，Berzina，A．P．（1985）On the place Kova1，P．V．，Gere1，0．，Smimov，V．N。，Tseden，Ts． of ore porphyries in the scheme for orogenic （1985）The porphyritic association of Er（1enet magmatism of copper－molybdenum ore knots area（petrography and chemical composition）． of Mongolia．G6010劇伽ゴG吻勿s総no．5，3－ 動Questions of Geology and Metallogeny of 10（in Russian with English abstract）． Eastem Mongolia，The Kherlen Geological Sotnikov，V．1．，Berzina，A。P。（1989）Prolonged Expedition Issue，Ulaanbaatar，59－112 （in discrete oriente（1development of ore－magmatic Russian）． systems in coPPer－molybdenum formation。 Koval，P。V．，Gere1，0．（1986）Volcanic association G6010gyα％4（360ゆ勿s乞oS no．1，41－45（in Russian of areas of porphyritic copPer mineralization with English abstract）． of Mongo1－Okhotsk zone．動Geochemistry of Sotnikov，V．L，Berzina，A．P。，Bold，D．（1984） Volcanic Rocks of Different Geo－Dynamical Regularity of distributionofcopper－molybdenum Situations， Nauka， Novosibirsk， 69－93 （in mineralization of Mongolia．動Endogenic Ore Russian）． Formations of Mongolia，Nauka，89－101（in Matrenitskii，A．T．（1977）Anewdata aboutvolcano－ Russian）． Plutonic association of Orkhon－Selenge de－ Sotnikov，V．1．，Berzina，A．P．，Skorokhodov，V．N． pression of Mongolia．動FundamentalProblems （1981）Metallogeny ofcopper andmolybdenum of Geology of Mongolia，Nauka，Moscow，101－ of Mongolian People’s Republic．肋Questions 104（in Russian）． of Magmatism and Metallogeny of Mongolian Matrenitskii，A．T．（1981）Characteristics of Up． People’s Republic，Nauka，Novosibirsk，9－18 per Paleozoic orogenic magmatism and its （in Russian）． ore－bea血g（for example of Orkhon－Selenge Sotnikov，V．1．，Berzina，A．P．，Jamsran，M．（1985） depression of MPR）．動Petrology and Mi丘一 Copper Ore Formations of Mongolian People’s eralization of Magmatic Formation Indicator， Republic，Nauka，Novosibirsk，225p．（in Russian）． Nauka，Moscow，353－373（in Russian）． Sotnikov，V．1．，Tamsran，M．，Berzina，A．P．（1979）

一307一 Bz6116あ銘（ゾ云h6G60Jo9乞αzl Sz67∂¢y（ゾノ4汐α％，Vb乙49，．〈砂．61ヱ998

Aboutendogeniccopperfoma哲onsofMongolia Yakovlev，B．A．，Tamsran，M．（1977）Erdenetiin 動Geological Construction an（1Regularity of ore knot：Geology of Mongolian People’s Distribution of Territory of MPR，Ulaanbaatar Republic，v．3，Usefu10re－Mineralization，Ned：ra， ，（local publication），32－33． Moscow，167－175（in Russian）． Tugarinov，A．1．，Voinkov，D．M．，Grinenko，L N．， Yashina，R．M．，Matrenitskii，A．T．（1978）Petro－ Pavlenko，A。S．，（1974）Isotopic composition chemistry of volcanic an（i intrusive rocks of and sources of molybdenum－copper minerali－ the Orkhon－Selenge depression（Mongolia）。 zation of Mongolia．G606h伽砿no．2，171－178 P706664勿z8s6ゾ孟h6乙忍SR／166z46％z夕（ZプSoづ6％66s， （in Russian with English abstract）． no．10，26－42（in Russian）． Voinkov，D．M．，Grinenko，L．N．，Garamjav，D．， Yashina，R．M．，Matrenitskii，A．T。（1979）Upper Tamsran，M．（1977）About sequence of ore Paleozoic magmatism of northem Mongolia formation in porphyritic coPPer deposit Er－ and its metallogenic features二Geology and denetiin ovoo in Mongolia．P706664初8sげ孟h6 Magmatism of Mongolia，Nauka，Moscow， 乙GSネ～∬忽h E4z6αzあoηα1乃zsガ劾彪，G80109ソαノz4 96－113（inRussian）． 助）loπzガo％，no．1，77－80（in Russian）． Yashina，R．M。，Pavlov，V．A．，Arakalyants，M．M． Volchanskaya，1．K．（1980）The regularity of dis－ （1977）Absolute age and structural story of tribution of endogenic mineralization of the Paleozoic granitoid and alkaline rocks Mongolia on faults of morphostructure analysis in the northern Mongolia．P706664初8sゲ伽 G6010窪y（ゾ0㎎Z）のos蜘no．4，86－96（in Russian）． USSRz46α46郷夕げS6勿π66s，（｝601090翻IS6吻s， Volchanskaya，1．K，Baskina，V．八，Favorskaya，M． no．6，20－33（inRussian）． A．（1978）Mendional oreconcentratedstmctures of central and eastem Mongolia．Rのo窩のh6 Received January14，1998 USSノ～∠46α48柳げS6魏66畠240，no．3，666－668 Accepted Apri116，1998 （inRussian）．

モンゴル国エルデネティンオヴォ鉱床に関する研究の総括

G．Dejidmaa・内藤一樹

要 旨

モンゴル国最大のポーフィリー型銅鉱床であるエルデネティンオヴォ （通称エルデネット鉱山）につ いて既存のロシア語文献を調査した．鉱床はエルデネットクロスストラクチャーに構造規制されている． 鉱化帯には二畳紀のセレンゲ複合岩体とそれに貫入する三畳紀のエルデネット複合岩体が広く分布する． 銅鉱化作用は後者に密接に伴っており，変質帯のセリサイトは210から190Maの値を示す．したがっ て鉱化作用の主体はエルデネット複合岩体に起因すると考えられる．硫化物の硫黄同位体比は双峰性分 布を示すが十分な研究は行われていない．

一308一