Bulletin of the Geological Survey of Japan，voL51（1），p．17－28，2000

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Shunso IsHIHARA＊，Masahiro YAHATA＊＊，Yukitoshi URAsHIMA＊＊＊ and Yasushi WATANABE＊

Shunso IsHIHARA，Masahiro YAHATA，Yukitoshi URAsHIMA and Yasushi WATANABE（2000） Late Cenozoic ore deposits and their sulfur isotopic ratios ofthe northeastem Hokkaido，Japan． B％ll． G601．Sz6プ∂．ノのごzη，vo1。51 （1），P．17－28，4figs．，3tables．

Abst聡ct：Sulfur isotopic ratio（δ34S）was determined on sulfide minerals and ores from base metal deposits（23samples），gold－silver deposits（29samples）and mercury deposits（9samples），and a large number of negativeδ34S values were discovered．Together with the previously reported data， the base metal deposits have two groups ofδ』34S values：一12．9to－9．8and－2．7to十6．2permi1．The first group is considered genetically related to ilmenite－series granitoids，which have－6．3permil on an averageδ34S value of the rock sulfur．The secon（i group is essentially forme（i with magnetite－ series volcanic and subvolcanic activities（Motokura－Jotoku），but locally contaminated with sedimentary sulfur from the wall rocks（Kitami）． Gold－silver（ieposits have a wi（ie range of－9．O to十9．O pemilδ34S．The values are especially low （一9．0～一〇．7％o）in those of the Omu－Sanm graben and the northemmost part of the Monbetsu一 ：Kamishihoro graben，where important ore deposits of：Konomai，Hokuryu，Numano－ue and Sanru are distributed．These negativeδ34S values may indicate the existence of reduce（i－series volcanic rocksintheseregions．Aregiona1N－Svariationintheδ34Svaluesofthegold－silverdepositsseen in the northeastern Hokkai（io is considered to reflect essentially the regiona1（iifference in the ilmenite／magnetite－series volcanic activities． Mercury deposits have the most negative values（一14．2to十〇．4％o）among the three commodity groups，and could also be related to ilmenite－series volcanism．

northeastem Hokkaido and compile all the available isotopic（iata of the ore sulfur．Analyzed samples were 1．亙臨ro伽ct置o醜 hand－picked by using a（1ental drilling machine，or Late Cenozoic volcanism of the back－arc basins of whole rock in most of gold－quartz veins，which con－ the Japanese Islands is known associated with fruitful tain little and very fine grained sulfides in genera1． mineralization of mainly Kuroko an（i base－n｝etal vein The isotope analyses were performed by conventional types that have positive δ34S values of ore sulfur SO2methods at the Central Laboratory of the Mit－ around4．5permi1（lshihara an（1Sasaki，19781Sasaki subishi Material Corporation，Omiya，Japan and and Ishihara，1980）．Ore deposits of the Kitami prov－ Chinese Aca（1emy of Geological Sciences，Beijing． ince of the back－arc side of the Kuril Arc，however， The analytical errors are said as±0．2permi1． are different from those of other provinces showing The Kitami province is underlain by Cretaceous－ often negative values on the ore δ34S values，in Paleogene se（iimentary rocks of the Hidaka Super－ contrast to the positive values of Southwest Hok－ group in the west and Iate Jurassic－Paleogene sedi－ kaido（lshihara and Matsueda，1997）．The difference mentary and igneous metamorphic rocks of the To－ is considered to reflect reduced and oxidized mag－ koro Belt in the east．They have been faulted to horst maticactivities（lshiharaαα1．，1996）． and graben blocks．Tertiary granitoi（1s（lshihara砿 In this paper，we report a（iditional analyses of the α1。，1998）intmded into the horst，while Late Cenozoic δ34S values of ores from the Kitami province of the volcanism and sedimentation occurred in grabens， which strike north－south and northeast－southwest． Related ore deposits occur in an（i around the grabens ＊Geological Survey of Japan，1－1－3Higashi，Tsukuba， 305－8567，Japan ＊＊Geological Survey of Hokkaido，North19，West12， Keywords：Late Cenozoic，Kitami province，volcanogenic， Kita－ku，SapPoro，060－0819，Japan base metal deposit，gold－silver deposit，mercury deposit， ＊＊＊2－2－2，Nishi－lshiki，Kagoshima，890－0002，Japan δ』34S value，ilmenite series，magnetite series

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づノ嚢脚 1 Hgdeposits Au－Agdeposits Cu－Pb－Zn deposits

メEMゾ 團 Miooene feisio voloaniGs ／、21 、181禽 あ・・． 團 Tertiarygranitoids Motoku「aプ1讃 一 ￥1〆鱗濡鑓u隻ゴ Graben and oauldron 1／無驚〆〆ノ N・y・・1口s糠醗① 口Monbetsu l os メ 麟、． 1 メ 蒔1嵩f…、事l l璽ノ融庵鰭 メ

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42。 143。 144。

Fig．1 Basement division，depressed zone and locality of the studied ore deposits in the northeastem Hokkaido．The numbers correspond to those in Tables1，2and3．EM，Esashi－Motokura grabenl OS，Omu－Sanru graben，MK，Monbetsu－ Kamishihoro graben．

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（Fig．1），which are here named，from north to south， Jotoku veins，10cated at1．5km northeast of the as Esashi－Motokura graben，Omu－Samru graben and Motokura deposit，are similar in mamer of the vein Monbetsu－Kamishihoro graben （Yahata，1997）． system to that of the Motokura deposit．The vein Quaternary volcanoes are present in the southern part constituents are．also similar except for the lack of along the volcanic front of the Kuri1－arc volcanic sulfate minerals．The ore－forming sulfi（ies of the chain． Motokura deposits giveδ34S values of十2．8to十LO Metal mining was most active in1950s in the north－ permi1，whereas those of Jotoku veins yie1（i十6．2 eastem Hokkaido（Urashima，1961）．The ore deposits and 十3．8permi1． of the：Kitami province are mostly hosted in the late Cenozoic volcanic and sedimentary rocks and rarely 2．2臨ねm量δe夢osits in the basement．The late Cenozoic volcanic rocks The ore deposit was discoverd before1934，and was have whole－rock ages ranging from15．1Ma to pres－ mined most actively in the1950’s decade．The totaI ent，and the related ore deposits have K－Ar adularia production was590，000tons of crude ores containing and whole－rock alteration ages of14．4－0．33Ma metals of Ag22．2tons，Cu4，720tons，Pb8，850tons，Zn （Watanabe19961Yahata6地1．，1996），which have 14，750tons and iron sulfides53，690tons（Yamada6オ been classified into three metallogenic epochs of the α1．，1980）． middle Miocene，upper Miocene－Pliocene，and The Kitami（ieposit is located in the basement at the Pliocene－Quatemary （lshihara， 1998）． The ore westem rim of north－south trending Miocene volcano （1eposits can be（iivided into three groups of the as－ －sedimentary，Monbetsu－Kamishihoro graben（Fig．1， sociated ore metals：base meta1，precious metal and Yahata6渉α1．，1988）．The basement was intm（1ed by mercury（Fig．1），and are describe（1from north to numerous east－westerly dikes of intermediate compo－ south in the following paragraphs．The obtainedδ34S sition（mostly SiO264．4－70．5％），which are subdivi（1ed values from the ore deposits are listed in Tables l to into earlier quartz－phenocryst－free grano（1iorite por－ 3． phyry（14．4－14．2Ma）and later quartz－phenocryst－ bearing granodiorite porphyry （13．2－11．1 Ma， Watanabeαα1．，1999）． 2．B我seMetal：De脚s置ts The veins strike in east－west and dip steeply south． Base metal deposits are rare in the：Kitami province The major ore minerals are pyrite，chalcopyrite， among which three ore deposits of Kitami，Motokura sphalerite，galena and pyrrhotite， and the gangue and Jotoku are economically important．They occur in minerals are quartz，chlorite，sericite and calcite． the Esashi－Motokura depression zone and in the Presence of pyrrhotite and sphalerite star（Yamada， westem rim of the Monbetsu一：Kamishihoro graben， 1963）indicate that this deposit formed at lower oxy－ and are all vein types and rich in lead and zinc，rather gen fugacity and at higher temperature than the than copper，which is unusual in the base metal Motokura vein deposit． mineralization of the back－arc zones（lshihara and Sulfur isotopic ratios of mineral separates and Sasaki，1995）．Kuroko type is recorded at two loca1－ composite samples of the Kitami deposit vary from ities：Fumi and Nemuro（Hasegawa6砂1．，1983）． －4．2to－0．2permi1，much smaller thanδ34S values of Motokura and Jotoku veins．However，the Motokura 2．1Motok腿聡a翻Jotok腿αe脚s量ts and Jotoku deposits are volcanogenic，while the The Motokura deposit was discovered in1936and Kitami deposits are plutonogenic and their negative mined during1950－1960’s decades．Total production is δ34S values may have been effected locally by wa11－ ！50，000tons containing Au30kg，Ag14．4tons，Cu rock sedimentary sulfur，similar to the ore sulfur of 1，500tons，Pb18，600tons，Zn12，900tons，pyrite24，600 the Chichibu mine area（lshihara6渉α1．，1987）． tons（Yama（1a6渉α1．，1980）．Thus the ore（1eposit is Toward the due south of Kitami mine，several base rich in Iead． metal prospects are known to occur around the west－ The Motokura d．eposit is und．erlain by Miocene emrim of the Monbetsu－Kamishihoro graben．All are andesitic and rhyolitic rocks which intercalate some hosted in Miocene volcanic rocks andgave two differ－ conglomerate and sandstone．According to Bamba et entvalues as十1．2permi1δ34S ontheWNW－trending al．（1958），the ore deposits are hoste（玉in propylitized base metal veins at Yahagi－Tatsumi，and十4．5permil andesites and are composed ofE－W and N500Estrik－ δ34S on the pyritized volcanic rocks at Koki． ing vein systems．The major ore minerals are pyrite， chalcopyrite，sphalerite and galena．Gangue minerals 2．3臨rokot蹄eores，恥湘a賊：Ne鑓ro are mostly quartz，and some sericite and others includ－ Two Kuroko－type（ieposits are known to occur in ing barite and gypsum，which are present in druse of the whole eastem Hokkaido．One at Fumi in the the ore veins．K－Ar age of adularia－bearing silicified Kitami province is massive orebody occurring in rock is12．3±0．6Ma（Yahata6厩1．，1996）and altered argillized brecciate（i tuff close to rhyolitic dike rhyolite is12．2±0．2Ma（lshihara，1998）． （Yamada，1963）．The volcanic rocks are later

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Cu－Pb－Zn depbsits 6 （n＝26） Granitoid related

80 畏 Au－Ag deposits 罵 口 （n＝43） 65 6 ｝o ね

iii8 客 0 Hgdeposits 6 （n＝13）

0 一15 一10 一5 0 十5 十10 δ34S（％o）

Fig．2 Histograms ofδ34S values of the sulfide ores and minerals from the northeastem Hokkaido． identified as terrestrial ash flow deposits（Yahataα from－9．8to－12，9permi1（Table1，nos．10and l1）． α1．，1988）．The footwall has been silicified．These Pyrite filling joint of Aibetsu－dam ilmenite－series features are not of typical Kuroko deposits，but simi－ biotite granite（lshihara6厩1．，1998）has similarδ34S 1ar to atypical one of Kamikita deposit in nothern value of－9．8permi1．δ34S values of rock sulfur of late H：onshu（Lee切召1．，1974）．Sphalerite－rich composite Cenozoic granitoids are averaged as－6．3permi1（n＝ sample of this Fumi deposit giveδ34S values of十4．6 3，Sasaki an（11shihara，1979），and ore sulfur is about permi1，which is very similar to the average Kuroko 3permil lower than rock sulfur（Sasaki6地1．，1984）． value of十4．5permi1（Sasaki and Ishihara，1980） Thus，the Nakaetsu and Aibetsu－dam sulfides are The other example of Nemuro（ieposit is typical one consi（1ered originated in the ilmenite－series granitic being composed of Kuroko an（i Oko（yellow ore） activities． bodies occurring in rhyolitic tuffs overlain by mu（1－ stone．Gypsum ore bodies are also present（Kinoshita， 3。Go亙d我髄〔丑s盟ver de1Dosits 1939）．Composite sample of lead－zone ores gives十3．8 permi1，which is also close to theδ34S value of typical Gold－silver（1eposits are economically most impor－ Kuroko ores（Sasaki an（11shihara，1980）． tant in the Kitami Province。They are essentially vein Histogram of all the analyses are shown in Figure2． type and numerous in number（MITI，1990a），but The volcanics－related ores range from－4．2to十6．2 large ones，the pro（1uction more than100kg Au meta1， permi1，which are quite different fromδ34S values of are the following ten mines（JMIA，19681MITI，1990 the granitoid－related ores，mentioned below。 b）：

2。40reαe脚s置tsre亘就edtogr蹴itoids Mines Au Ag Ag／Au Ore deposits related to ilmenite－series granitoids Konomai 73．181 tons 1243 tons 17．0 are very rare in central Hokkai（10，but the Nakaetsu Hokuryu 2．924 11，268 3．85 Cu－As deposit may be the one genetically comected Kitano－o 2．916 2．503 0．86 with Tertiary granitic activity，because it occurs fi11－ Numano－ue 1．405 94．149 67．0 ing fractures of sedimentary rocks of Hidaka Super－ Sanru 1．340 8．127 6．07 group at due－south of N－S trending ilmenite－series Ikutawara 0．505 3．938 7．80 granitic pluton and the alteration age is30Ma，which Tokoro 0．092 2．321 25．2 is much older than Miocene－Pliocene volcanic activ－ Muka 0．186 0．814 4．38 ities． Saroma 0．162 0．766 4．73 The ore deposit is also unusual as volcanogenic Ryuo 0．100 0．855 8．55 （1eposit，being rich in As and In（Tsushima切召1．， 1999）．The constituent sulfides，including pyrite，ar－ These Au－Ag deposits，mostly of the lowsulfidation senopyrite，and chalcopyrite，range in the δ34S value type，are hoste（i in the late Cenozoic volcano－se（iimen一

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Table l Sulfur isotopic ratios of base metal deposits，NE｝Iokkaido．

No．and Locality δ34S（％。） Analyze（1minerals Sample no．（analyst）

1Motokura，Heian B mainbody ＋1．0 Cp，cp－qz vein Ishihara＆Sasaki（1994） （1itto ＋1．8 Sp，cp－sp－gn－py breccia veip UR－LGK7A（MB） ditto ＋2．2 Gn， ditto UR－LGK7B（MB） ditto，Heianvein，driftW ＋2．3 Sp，brown sp－amethyst qz 94MTO1（MB） ditto，HeianChudanE ＋2．8 Sp，sp in clay zone 94MTO7（MB） 2Jotoku，1st adit117m ＋3．8 Py，py－qz vein UR－LG12A（MB） ditto ＋6．2 Gn，gn－qz veinlet UR－LG12B（MB） 3 Kitami，一50mL －4．2 Composite，py－cp－po Ishihara＆Sasaki（1994） dittto，mine dump －0．2 Py，alteredhomfels 94070212（MB） ditto，mine（1ump －0．6 py，py－ch1－ser rock 94070213（MB） ditto，N240vein，W20B －0．7 Py，gn－sp－py vein UR－NGF2A（MB） ditto，N240vein，W20B －1．4 Sp， ditto UR－NGF2B（MB） ditto，N240vein，2nd adit －2．1 Sp＞＞cp，py，1atest－stage sp 94KTO3（MB） ditto，N240vein，＋20mL，W20 －2．7 Sp，sp－py drusy qz vein in 94KTO2A（MB） ch1－py host rock N5500rebody，center 一1．7 Po－sp＞py－cp bande（玉ore 94KT164（MB） 4 3kmNE ofMaruseppu －0．3 Py，py－bearing gd poη1）hyry 95KTM11（MB） 5 Koki，mine waste ＋4．0，4．5 Py，py・diss．altered tu丘 96072706A（CAGS） 6 Yahagi－Tatsumi 十1．2 Sp，sp－cp－py－qz vein in pyroclastics GSH（MB） 7 Fumi（”Kuroko”），minedump 十4．6 Sp＞＞py－cp－gn disseminated 96072705 in andesitic pyroclastics （MB） 8 Nemuro（Kuroko） ＋3．8 Composite，gn－sp－py ore Nemuro－18（CAGS） 9 Kokko －0．4 Py＞as－sp－cp－quartz vein Tokah－KKB in silici五ed andesite （MB） 10Aibetsu dam 一9．8 Py，py五11ing joint of granite 95092701（MB） ll Nakaetsu，outcroP －9．8 Py，py－as－cpore 97NKO3（CAGS） ditto －10．1 As，ditto 97NKO1（CAGS） （1itto －12．9 Cp， 97NKO2（CAGS） ditto －10．8 Cp，cp＞＞gn－spore 97NKGSH－MT（CAGS）

Abbreviations：as－arsenopyhte，cp－chalcopyhte，gn－galena，py－pyhte，po－pyπhotite，qz－qua丘z，sp－sphalehte，ch1－chlonte， ser－sericite，comp－composite，gd－granodiorite． Analysts：MB，Mitsubishi Central Lab．l CAGS，ChineseAcademy ofGeological Sciences。

tary rocks，which occur in several depression zones The ore deposit is vein type having more than10 controlled by basement stmctures and regional fault－ veins．Their average widths vary from10m（e．g．， ing（cf．，Fig．4）．Absence of the high sulfi（1ation type is Kuchan－nai No．5）to l m．Single vein extends up to consi（1ered due to reduced type of volcanism prevai1－ 2．5km（Kuchan－nai No．8）．The vertical extent is500 ing in the Kitami province（lshihara and Matsueda， m（Kuchan－naiNo，5）to90m，whichisFujishima 1997）。 vein swarms（Kondohαα1．，19671JMIA，1968）． The main ore minerals are native Au，native Ag， 3．1：Ko齢m瓠d鐙osit argentite，pyragyrite，pyrite andmarcasite．Wallrock Konomai deposit was discovered in1915．The pro－ alteration mineralogy is characteristically quartz－ser－ duction was initiated in1917・（Sumitomo Mining Co．， icite－adularia and calcite－pyrite in the andesite，an（i 1981）．The mine area is underlain by Cretaceous quartz－sericite－adularia－kaolinite－montmorillonite in sedimentary rocks of the Hidaka Supergroup and the rhyolitic host rocks． overlying Miocene sedimentary and volcanic rocks． Sulfur isotopic ratios of the Konomai veinεvary The ore deposit occurs in the westem part of the from－7．2to－2．3permi1δ34S，which cou1（1be consid・ Monbetsu－Kamishihoro graben and is hosted by an・ ered a small variation for the widespreading of the ore desite and rhyolite． deposits．

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Table2 Sulfur isotope ratios of ores from Au－Ag deposits，NE Hokkaido．

Mine δ34S（％。） Analyzed minerals Sample no．（analyst）

12 Utanoboh，outcrop 一〇．9 Ag sulfides，Ginguro－qz vein UTA－2A（MB） ditto，7MAHH1面11－core －1．5 Py，pyritizedpumice in rhyolitictuff UTA－138．6（MB） ditto，ditto －2．0 Py，detdtal pyrite in sandstone UTA－178．2（MB） Kami－Omu，outcroP13 －3．5 Ag sulfi（1es Ishihara＆Sasaki（1994） Omu，outcrOP14 －9．0 Ag sulfide，in milky qz mass 950M－4（MB） Hoku㎎u，waste15 －7．1 Py，py－Au－qz vein Ishihara＆Sasaki（1994） ditto －7．3 Py，py－Au一（1z veinlets in brecciated vein HKR－2（MB） 16 Saml －7．0 Pyrargirite Shikazono（1987） ditto，waste －0．7 Py，py in dmsy Au－qz vein Ishihara＆Sasaki（1994） ditto，ditto －0．9 Py，py in banded Au－qz vein ditto ditto，ditto －4．5 Py，massiveore 95092705（MB） 17 0towa，waste ofupper adit ＊一3．1 Py，py－Au－qz vein OTY9（MB） （1itto，that oflower adit －3．9 Py，py disseminatedinbrecciamatrix OTY3（CAGS） Koudo，outcroP18 －1．3 Py，occurring in silici丘ed rock Ishihara＆Sasaki（1994） Numano－ue，waste19 －1．6 Py，Ag sulfi（1es，Au－qz vein NMY8（MB） Konomai20 －2．3 Py，sp，cp，gn Shikazono（1987） ditto －7．2 Py，py－qzvein Ishihara＆Sasaki （1994） ditto，Sanoko－Tsudo －5．7 Massive cp＞as partofveins intuffbreccia UR－PFG7（MB） ditto，ditto －6．1 SP＞Py＞cP Part of veins in tuff breccia UR－PFG8（MB） ditto，5th adit outcrop －5．2 Py，py－Au－qz vein 96102203（CAGS） ditto，ditto －6．5 Py，fine py in Au－qz vein 96102204（CAGS） ditto，ditto －7．1 Py，py in dnlsy Au－qz vein 96102205（CAGS） ditto，South －4．1 Py，py－mcqzvein KY95（CAGS） 21 Ryuo －5．8 Cp，py，sp，pol Shikazono（1987） ditto 十1．9 Ag sulfi（1es，Au－qz vein RY8（MB） 22 Kitano－o ＋0．3 Py，in silici五ed tuff Ishihara＆Sasaki（1994） ditto ＊十〇．6 Py？，silicasinter KTY5（MB） ditto，north 十〇．4 Py，py disseminated in rhyolite 2MAHB5，199．2m（CAGS） Taihoku23 十2．4 Py～，py－Au－qz vein THK2（MB） Tokoro24 十6．6 ？，Au－qz network in breccia T：KY7（MB） Rubeshibe25 ＊十1。4 ～，Au－qz vein RB1（MB） Muka26 十3．4 ＊ PyP，py－silicified rock MKY6（MB） ditto －0．6 Ag sulfides，Ginguro（1z vein GSJH－6（MB） 27 ：Kok：ka 十2．2 PyP，Au－qz vein GSJH－5（MB） 28 Jindai 一1．6 ＊ Ag sulfidesP，Au－qz vein in tuffbreccia JD8（MB） Onneyu29 ＊十6．5 Py，py－Au－qz vein ONE3（MB） ditto －1．6 Py，py disseminated silici丘ed dacite ONE7（CAGS） Harutomi30 －2．0 Ag sulfi（1es？in Au－qz vein Ishihara＆Sasaki（1994） 31 Akaban－nosawa，float 十4．3 ＊ Py，py－Au－qz vein AKB1（MB） 32 Metou 十9．4 ＊ Py，py－Au一（lz network MTO1（MB） Seta，4MAHB6，182m33 十〇．3 Py，py in Au－qz vein Ishihara＆Sasaki（1994） ditto，ditto，182．5m 十〇．9 Py，ditto ditto 34Tokachi－Mitsumata 十〇．9 Py，in altered rock TM6（CAGS）

＊Withlarge error（±0．5～1．0％o）due to small amounts ofsu1飼es contained．Abbreviations： ms－marcasite， pG1－polybasite。Forthe other abbreviations ofminerals andthe analysts，see Table1．

3．20儘erorede脚s童ts lava flow or lava at the top but changing to dike at the Other gold－silver deposits are mostly hosted in bottom of the veins（e．g．，Hokuryu and Sanru，JMIA， rhyolites and tuffaceous sediments．The rhyolites are 1968）．The rhyolites are considered genetically relate（i

一22一 C6noβoJo o名64砂05露s召多z4δ34S z76zlz昭㊤ ∬o海hσづ40 （途hJh召名とz6オごzl．）

to the gold－silver mineralizations． Sulfur isotopic Sorachi－Ezo and Tokoro Belts（Hasegawaα召1．， ratios of these ore deposits vary generally from－9．O 1983）． to 十9．4permi1δ』34S （Table2，Fig．2）．They are The largest Itomuka deposit was discovered in1936 generally low in the north and high in the south． and the total production was Hg2897tons（JMIA， At Seta deposits，δL34S values of pyrites from gold－ 1968）．It occurs in Miocene sedimentary and andesitic quartz veins were reported to be O．3and O．9permi1 to rhyolitic rocks，which uncomformably overlie the （lshihara and Sasaki，1995）．Recent detailed stu（1y basement rocks at just south of the mine．The in（iicates that pyrites from go1（1－quartz veins have mineralization was considered genetically related to δ34S values of－1．3～十〇．1permi1，while those of the rhyolitic dikes（JMIA，1968）． silicifie（1host rocks have a wider range of－3．2～十2．6 Both native Hg and cinnabar fill fractures of shear－ pemil（Yahata and Matsueda，1999）．Their averageis ed zones，whichstrike N60。E～E－W dipping N．Aver－ －0．2permil（n＝18），which is similar to our average age width varies from7to l meter，and maximum value of十〇．6permi1（n＝2）． length is140meters along the strike （e。9．，4th vein） Some large differences are observed on the ores and240meters along the dip（e．g．，7th vein）．The host from the same locality（Konomai，Omeyu and Ryuo）． rocks have been pervasively altered to calcite，chlor－ Veins at Konomai are distribute（1in a very wi（1e area， ite an（1quartzl the assemblage sericite－montmonri1－ but Omeyu and Ryuo veins are small in scale。We 10nite occurs typically in cinnabar orebody， but need further analyses on systematically collected sam－ kaolinite occurs with native Hg－cinnabar orebodies． ples from the latter two（1eposits． Accessory sulfides are pyrite and marcasite． Cimabar an（1pyrite of the Itomuka deposits have constant values of－4．7～一3．5permilδ34S（Table3）． 4．Merc腿ry de聾os童ts Ryusho（1en mine，which was discovered in1943，then The beginning of mercury mining goes back to7th called Hokuchin mine and later changed to Ryu－ century in Japan for cinnabar used as vermilion to shoden，is Iocated much to the north of the Itomuka ancient architecture and also medicine．About40tons mine（Fig．1）．The ore deposit is stratabound－dis－ were spent to casting of the big Buddha of the Todai seminated type occurring in Miocene tuffaceous sand－ －ji temple，Nara，in747－749AD（Yajima，1951，1958）． stones（Kujirai and Kono，1971）．The mineralizations The cinnabar was mined in the southem Nara－Mie are composed of an early stage of quartz－pyrite（一 region，where the old capital Nara was located．This cinnabar）and the Iater stage of chlorite－pyrite（mar－ mining district became the secon（i largest in the1930s casite）一calcite－cinnabar（JMIA，1968）． after（1iscovery of two large and many small mercury Sulfur isotopic ratios vary from－1．4to－0．6permi1 deposits in the northeastern Hokkaido． δ34S，which are heavier than those of the Itomuka Mercury deposits tend to occur in the basement deposits，but are similar to nearby Uttsu deposit of terranes with a little Late Cenozoic volcanic rocks（e． －1．7to－0．8permi1δ34S，which occurs in the basement g．，Itomuka an（i Ryushoden）．Small ones occur very Sedimentary rOCkS． widely not only・in the Hidaka Belt but also in the δ34S values of other mines are lowest at Kitabaya一

Table3 Sulfur isotopic ratios of ores from mercury deposits，NE Hokkaido．

Locality δ34S（％。） An且1yzed samples Sample no．（analyst） 35 Uttsu 一1．7 Cn，cn（一py）一bea血gqu旗多vein 94GSJHO1（MB） ditto，2nd edit －0．8 Cn，cn staining altered shale UR－DGYO1（MB） 36 Ryusho（ien －0．6 Cn，cn（iisseminated in argillized rock Ishihara＆Sasaki（1994） ditto －1．4 Py，py disseminated in altered rock ditto Hokuchin －1．2 Cn，cn－bearing altered rock，open pit UR－DGR（MB） 371tomuka，7th edit －3．5 Cn，euhed■al x1，負11ing丘acture of altered rock UR－JJHO7（MB） （iitto －4．6 Cn，cn－Hg in altered rock Ishihara＆Sasaki（1994） （1itto －4．7 Cn，cn－py disseminated silicified tuff ditto ditto，East －4．6 Py，pyritized altered lava ITM23（MB） ditto，ditto －3．7 ditto ITM24（MB） 38 Kitabayashi －14。3 Cn，cn（1isseminated sandstone 94GSJHO2（MB） 39 0keto， －4．2 Py，argillized rhyolite 94070208（MB） 40Hidaka 十〇．4 Cn，cn disseminated in altered limestone 94GSJHO4（MB）

Abbreviations： cn－cinnabar，Hg－Native merculy，py－pyrite，x1－clysta1．Forthe other abbreviations andthe analysts， see Table1．

一23一 βz61」6痂z（ゾ云h606010gづαzl Sz67∂のげノψ伽z，V7∂1．51，〈ろo．1，2000

shi where cimabar ores occur in the basement sand・ sulfurs in the Japanese Islan（is （Sasaki and Ishihara， stone，an（l highest at Hidaka （ieposit occurring in 198011shihara6厩1．，1988）．The same may be true in limestone of the basement． the late Cenozoic volcanic fields． TheMotokura Pb－Znveins oftheEsashi－Motokura graben are hosted in propylite and related volcanic 5。Sulf皿lsoto函V翻a伽聖inT蓋me＆翻S腿ce rocks to the mineralization is stricktly unknown The initial proposal of southward migration of （JMIA，1968）。Recomaissance study indicates that Miocenevolcanism（Watanabe andYamaguchi，1988） volcanic rocks of the Motokura－Jotoku mineralized in the Kitami Province was confirmed by additional area along the Tokushibetsu River have magnetic data including those of the mineralized materials（see susceptibilityof4．5tolO．5x10－3Slunitforandesites Fig．50f Ishihara，1998）．That is，ore deposits from and4．5to6．O x10－3SI unit for rhyolitic rocks，which Utanobori gold mine southward to the：Kitami base－ indicate they belong to magnetite series． metal mine give middle Miocene ages，and Ryuo Rhyolites of the Utanoboriyama volcanic complex southward，they show late Miocene and Pliocene ages． have magnetic susceptibility of5。0～6．5x10『3SI unit。 Figure3is the N20。W－S20。E profile ofδ34S values Glassy rhyolitic dome located to the WSW of the of the studie（10re deposits．The values are（1ifferent WSW－ENE trending Au－Ag veins of the Utanobori within the middle Miocene group．For example，δ34S mine，which could be related genetically to the miner・ values of the Jotoku－Motokura Pb－Zn deposits are alization has magnetic susceptibility of4．0～4．5x10－3 higher than those of the Kitami Pb－Zn deposits，and SI unit．belonging to magnetite series．Thus，the rela－ δ34S values of Utanobori Au－Ag deposits are higher tionship between magnetite－series volcanic rocks and than those of the Konomai Au－Ag deposits． positiveδ34S values is also seen in the Easashi－Moto－ Genetical relationshipbetweenthe oxidizedmagnet－ kura graben． ite－se「ies granitoids and positiveδ34S values，and the The difference between the Jotoku deposit（average reduced ilmenite－series granitoids and negativeδ34S of5。0％o）and Motokura deposit（average of2。0％o） values are well established on both rock an（i ore can be explained by the presence an（i absence of

North（N200W） South

O Metou δ34S （％。）

Tokoro O 90nneyu

［ Jotoku 十5 醗Fumi 1 0Akabannosawa ㈱Kokl l Muka Taihoku E O 1 ○ Kokka Ryuo Q Motokura Yahagi ll 「 ㈱9 Rubeshibe l Kitam’ I l Seta3 麟コ 0 1盆 Kitanoo 16 0 Utt、u露亀K・d・・。 § Utanobori 1Φ 1のコ 1 O NumanQue Jindai 田arutomi 』 邸 1Σ 1 『 1 Sanru ・牝・wa3 KamトOmuO G）Oketo

一5 ltomuka Konomai 6 H・kuryuqb 6

Omu O

一10 0 Albetsu Nakaetsu

GraAitoid re［ated

ぐ一一一一385kmr一一〉

Fig．3 North－south plots ofδ34S values of the sulfide ores and minerals from the northeastem Hokkaido。

一24一 C6％ozoJ6076伽os露sαη4δ34S∂α1郷，πoh勧40（勧伽昭6齢」．）

ミlf繕滅

〈＞ Hgdeposits 輪 Au－Agdeposits 騰 Gu－Pb－Zn deposits

話、曜湾 区］Faults 国Depressi・nz・neandgraben 1雛執 團Cauldr・nandcaldera 團Basementr・Gks

漁

Fig．4 Regional distribution of averagedδ34S values of individual ore deposits from the northeastem H：okkaido．

sulfate minerals．δ34S values of th6Utanobori Au－Ag Hg deposits of the northern part vary －5，5 to －1．1 deposit are lower than the base metal deposits．This pemil in their average，while those of the southern fact is widely seen on the Japanese Neogene ore part range from－1．6to十6．6permil in their average． deposits an（1can be explaine（i by more oxi（1ize（1 Some of the volcanic rocks in the northem part show nature of the Au－Ag－bearing ore fluid than the base low magnetic susceptibility as1．8～9．2x10－3SI unit metal ore solution （Shikazono，1987）． （seeappendixVoflshihara6オα1，，1995）．Genetically Au－Ag deposits at Hokuryu，Sanru and Omu occur related volcanic rocks for the：Konomai deposits are in the Omu－Sanru graben to the south（Fig．4）．They considered andesite and rhyolite （JMIA，1968）． have averageδ34S values from－9．O to－3．3permil，thus Although a detailed stu（ly is necessary on the opaque depleted in34S。They are hosted in rhyolites which are minerals，we consider that the andesite and rhyolite considere（1genetically related to the mineralization could belong to ilmenite series or intermediate series （JMIA，1968）．The rhyolite could belong to ilmenite for theδ34S values． series，though we need to study the Fe－Ti oxide Among base metal deposits an（i prospects at the minerals． westem rim of the Monbetsu－Kamishihoro graben， In the Monbetsu－Kamishihoro graben，Au－Ag and whose averageδL34S values vary from－1．7to4．3

一25一 Bz61」6渉初（ゾ云h6G60Jogσαzl S％7z7の（ゾ血1）ごz7z，『レbl．5ヱ，ハ石o．1，2000 permi1，the Kitami ores may have received some S解∂．如催，9，99－108． sulfur from the intruded pelitic wall－rocks and the Hasegawa，K．，Tarashima，K．and Kurosawa，K． original magnetite－series value may have been （1983）Metallic mineral resources of Hok－ conv♀rted to the observed negative value，because of kaidO．lnG60109ッ伽4〃魏名召1ノ～6SO％κ6Sげ proximity of the ores to the sediments and higher ∬oh々σσ40，Vo1．III，62p．，Geol．Surv．Hok－ temperature of their formation（cf．Ishiharaαα1．， kaidQ． 1987），as compared with Au－Ag deposits．Base metal Ishihara，S．（1998）・Mineralization ages of the prospects at Koki and Yahagi－Tatsumi have positive Kitami metallogenic province，northeastem δ34S values（Table1）． Hokkaido．B％ll．G801．S％γ”．ノ⑳観，49，469－ Mercury deposits have a wide range ofδ34S values， 476． though the values are biased to negative side，The ore Ishihara，S．and Matsueda，H．（1997）・Genesis of deposits occur inMiocenevolcanicrockswithshallow two contrasting metallogenic provinces in the basement or within the basement rocks．It is not clear back－arc basins of Hokkai（io，Japan．Pzo6． that the mineralization could be telethermal type of 30孟h1％彪ηz．G60乙 Coη8ア，9，P．3－13． ilmenite－series volcanism or occurred with meteoric Ishihara，S．and Sasaki，A．（1978）Sulfur of water circulation with none－igneous heat extracting Kurokodeposits－Adeep－seatedoriginP Hg from the basement rocks． 乃伽初8G60Jo盟，28，361－367． Ishihara，S．and Sasaki，A．（1994）Sulfur isotopic characteristics of late Cenozoic ore（ieposits 6．Co醜c亙1阻sio聡s at the arc junction of Hokkaido，Japan．Th6 Sulfur isotopic ratios of the ores from late Cenozoic 鳶1伽4・4π，3，122－130。 age in the northeastem Hokkaido have been Ishihara，S．，Terashima，S．and Tsukimura，K． examined and a large number of negativeδ34S values （1987）Spatial distribution of magnetic sus－ have been discovered．The observedδ34S values are ceptibility and ore elements，and cause of divided in two distinct groups：granitoid－related ore local reduction on magnetite－series deposits such as the Nakaetsu having－12．9 to －9．8 granitoids and related ore deposits at Chi－ pemil，which is reasonable because the granitoids chibu，central Japan．ノぼ勿z勿zg O60♂o劇，37，15－ have－6．3permil rock sulfur on the average（Sasaki 28． and Ishihara，1979），and volcanogenic ore dePosits， Ishihara，S．，Yahata，M．and Urashima，Y．（1996） which are most important economica11y in the north－ Time and space variation ofδ』34S of ore eastem Hokkaido．The latter group can be divided sulfur of NE Hokkaido （abst．）．∠46s！％1． into Au－Ag，Cu－Pb－Zn and Hg ore deposits．The base ／bz％．乃グ磐。G600h6％z．Soo．∫曜）α％（Sapporo），4 metal deposits vary from－4．2to十6．2permi1δ34S． D13． Negative values of the Kitami ore deposit may have Ishihara，S．，Sasaki，A．and Terashima，S．（1988） been formed by interaction of the original ore fluid Sulfur in granitoids and its role for minera1－ with the wall－rock sedimentary sulfur．Thus，the ization．．Pグoo．7渉hQ襯4．MGOO助窺．（1986）， essential value for the base metal mineralization is 573－581．，E．Schweizerbart7sche Verlagsbuch－ considered to be a positive value． han（11ung． Ores of Au－Ag deposits have a wid．e range of－9．O Ishihara，S．，Tanaka，R．，Nakagawa，M．andGoto， to十9．O permi1．Theδ34S values vary within the major Y．（1995）Magnetic susceptibility of late middle Miocene depositsl they are most depleted in34S Cenozoic volcanic rocks of east－central Hok－ in those of the Sanm－Omu graben and the northem kaido an（1the Kuril Islan（1s．1～6soz6名66 G601． part of the Monbetsu－Kamishihoro graben．The nega－ 助66．途s％6，no．18，217－228． tive values are thought of the related volcanic rocks Ishihara，S。，Matsuhisa，Y．，Tanaka，R．，Ihara，H．， of ilmenite and／or intermediate series and the positive Nagasaka，A．Koike，T。and Shibata，K． values of magnetite－series volcanic rocks．Thus，the （1998）The timing and geneses of ilmenite－ major gold－silver deposits of Konomai，Hokuryu， SerieS and magnetite－SerieS granitiC mag－ Numano－ue and Sanru were related to the reduced－ matism in the north－central Hokkaido， series volcanism，while only small ones were formed Japan．Bz611．G801．Sz67zノ．ノ碑）磁z，49，605－620、 with an oxidized－series volcanism in the northeastem JMIA（Japan Mining Industry Association，1968） Hokkaido． Oz6Z）砂os漉げノψ翻．941p． Kinoshita，K．（1939）Kuroko deposits of Hok－ kaido．ノbz67。ノくyz6shz6ノレf脅zわzg∠Lsso6．10，no．10， Re£ere遡ces 1－17． Bamba，T．，Igarashi，T．and Kikuchi，T．（1958） Kondoh，K．，Sukeda，K．and Hashimoto，K．（1967） CoPPer－1eεしd－zinc sulphide ore deposits of the Geology and ore deposits in the area of the Imai－Motokura mine，Hokkaido．伽ll。G601． Kohnomai mine（1）On the relation of geolog一

一26一 C6％020づo o名6461）os露s6z％4 δ34S zノごzh昭s，伽をた6zづ40 （途hづh6z名とz6渉α1．）

ical structure and mineralization．〃伽初9 Urashima，Y．（1961）Metallogenetic provinces of G6010劇，17，72－80． northeastern Hokkai（io， Japan．ノ6％7． E6z6． Kujirai，S．and Kono，J．（1971）Recent progress on S（ガ．，∬oゐhσ乞40 U勿乞zノ．，11，Ser．4，95－118． mercury exploration at the Ryusho（1en mine， Watanabe，Y．（1996）Genesisofvein－hostingfrac－ Hokkaido．乃伽初gG6010劇，21，19－28． tures in the Kitami region，Hokkaido，Japan． Lee，M．S．，Miyajima，T．andMizumoto，H．（1974） 1～6so嬬6G60109夕，46，151－166． Geology of the Kamikita mine，Aomori Pre－ Watanabe，Y．and Yamaguchi，S．（1988）K－Ar fecture，with special reference to genesis of ages of Miocene volcanic rocks and tectonics fragmantal ores．班初初9060乙助60．鳶s％6，no． in the Nayoro－Asahikawa region，northem 6，53－66． Hokkaido．Eα7孟h Soづ6no6，42，91－99． MITI（Ministry of Intemational Trade＆Indus－ Watanabe，Y．，Dolgor，B．and Ishihara，S．（1999） try，1990a）R勿oπげz69加αlg60109魏l Porphyry－relate（1base－metal mineralization s魏吻ゴ▽o励劾h勧40．β∠4繊．265p．，MMAJ． at the Kitami（1eposit in northeast Hokkaido， MITI（Ministry of Intemational Trade＆Indus－ Japan．E60多z．G601．（in press）． try， 1990b） ノ～の07渉 （ゾ z8gJo多z6zl 960109歪6σ1 Yahata，M．（1997）Neogene Monbetsu－Kamishi－ 吻むNo7云h伽肋認40，β∠47即．List of meta1－ horo graben in the・northeast Hokkaido， 1ic deposits．390P．，MMAJ． Japan．ノ～の抗 （｝（30乙 Sz67∂．1乃ゐhα乞40，68，43－56． Sasaki，A．and Ishihara，S．（1979）Sulfur isotopic Yahata，M．and Matsueda，H．（1999）Plio－Pleis－ composition of the magnetite－series an（1i1－ tocene hydrothermal activity related to gold menite－series granitoids in Japan．Co％加6． mineralization in the Seta area，northeastem 〃伽名召1．P6渉701．68，107－115． Hokkai（io，Japan．R6soz6z66（｝6010窪y，49，131－ Sasaki，A．and Ishihara，S．（1980）Sulfur isotopic 145． characteristics of granitoi（is an（i related Yahata，M．，Kubota，Y．，Kurosawa，K．and mineral deposits in Japan．Pzoo．5孟h（2襯4． Yamamoto，K．（1996）Mineralization ages of 五4GOZ）⑦郷．（ヱ978）E．Schweizerbart’sche some epithermal deposits in the northeastem Verlagsbuchhandlung，Stuttgart，325－335． Hokkaido，Japan．∠4η％襯1〃忽．So6．R6so％π6 Sasaki，A．，Ulriksen，C．E．，Sato，K．and Ishihara， G6010野，Abstracts，35． S． （1984） Sulfur isotope reconnaissance of Yahata，M．，Tajika，J．，Kurosawa，K．and Matsu－ porphyry coPPer and manto－type deposits in nami，T．（1988）助乙伽伽η云翻げオh6960－ Chile and the Phillippines．Bz61乙 G601．Sz67z7． log短1彫勿げ如αη，Scale1：50，000，“Maruse－ 鋤伽，35，615－622． ppu Hokubu”．GeoL Surv．Hokkai（10，110p． Shikazono，N．（1987）Isotopic composition and Yajima，S．（1951）Mercury deposits of Hokkaido． origin of sulfide sulfur of Neogene Au－Ag 伽h肋づ40 Sh乞sh歪孟sz6一ッoho，no．17，1－72，GeoL and base metal vein－type deposits in Japan． Soc．Hokkai（io． ノioz67．Eα6．SoJ．，U勿乞∂．710々yo，Sec．II，21，239－ Yajima，S．（1958）Mercury deposits of Japan． 255． ．P砿1．S％z癩Co彫窺．y∂1．，379－393． Sumitomo Mining Co．（1981）Exploration history Yamada，K．（1963）Copper－1ead－zinc deposits of of Kieslager deposits of the Besshi an（i ：Kitami mine，Kitami district，northeastem Sazare，and Au－bearing quartz vein deposits Japan．βz611．G601．Sz67z7．ノ砿）召多z，14，751－774． at KOnOmai．〃’吻醐召11～6SO躍66S助10剛づ0％ Yama（1a，K．，Su（io，S．，Sato，T．，Fujii，N．，Sawa， げ加観，v。1，219－294，Soc．Mining Geolts． T．，Hattori，H．，Sato，H．，Aikawa，T．（1980） Japan． Mine summary report．Vo1．I North－east Tsushima，N．，Matsueda，H．and Ishihara，S． Japan．ム～諺）ゑ （3601．Sz67zノ．翅）ごz7z，310P． （1999） Polymetallic mineralization at the Nakaetsu coPPer deposits，central Hokkai（10， Received August19，1999 Japan．ノ～6soz6z66 G6010霧ソ，49，89－97． Accepted November8，1999

一27一 βz61」6あ％の「云h606010gづαzl Sz67z2βy（ゾノ¢クζz％，Vb乙5ヱ，．〈砂．1，2000

北海道北東部における新生代後期の鉱床と硫黄同位体比

石原舜三・八幡正弘・浦島幸世・渡辺 寧

要 旨

標記地域のベースメタル鉱床（23試料），金銀鉱床（29試料），水銀鉱床（9試料）から得られた鉱石 および硫化鉱物のδ34S値を求めた。これらの結果を報告すると共に，既存データと合わせて全域の総括を 行った。べ一スメタル鉱床のδ34S値は一12．9から一9．8パーミルのグループ，および一2．7から＋6．2パーミ ルのグループに2大別される。前者は北海道中軸帯のチタン鉄鉱系花歯岩類が平均して一6．3パーミルの 岩石δ34S値を持つことから考察して，この花崩岩類に由来する鉱液から生成した可能性が高い。後者は磁 鉄鉱系の火山岩ないし浅成貫入岩相に関連して生成した鉱床であるが，北見鉱床では壁岩の堆積岩から 硫黄を同化した可能性が考えられる。 金銀鉱床は一9．0パーミルから＋9．0パーミルに至る幅広い値を持ち，δ34S値は雄武一珊瑠グラーベン帯， 紋別一上士幌グラーベン帯北部の鉱床で特に低い（一9．0～一〇．7％。）。ここには鴻之舞・北隆・沼の上・珊 瑠などの主要鉱床が分布している。鉱床硫黄と関係火成岩の硫黄同位体比の経験則から推察して，この 地方の主要金銀鉱床はチタン鉄鉱系火山岩類に関係して生成したものと考えられる。水銀鉱床は3鉱種 の中で最も小さいδ34S値を示し，これもチタン鉄鉱系火山岩類に関連して生じた可能性がある。

一28一