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Bulletin of the Geological Survey of Japan,vo1.35(11),p.565-582,1984 553.43:553.21(83)
M我囎危o Ty恥e Co璽》夢er I》e幽os脆s童醜
一縄R㊧V童ew
c踊le
Takeo SATO*
SATo,Takeo(1984) Manto type copper deposits in Chile-a review。
1αPαn,vo1.35(11),P.565-582.
B房〃. GεoZ. 5μ7V.
A眺纏c琶3Many manto type copper su1且de(1eposits occur in the Coastal Range of Chile
being hoste(1by Jurassic to Early Tertiary volcanic-dominant formations.The host rocks
are most commonly amygdaroidal Iava Hows an(1volcaniclastics of various compositions。
Limestones and calcareous shales are also mineralized.Major ore minerals are cha1-
copyrite,bomite an(1chalcocite in association with pyrite,hematite and/or magnetite。
Wallrock alteration is generally very weak or none.
By examining published data on geology,geochemistry and mineralogy of the
host rocks and ore(ieposits,it is suggested that dehydration processes due to a(lvance(l
burial metamorphism might be responsible for the formation of the Chilean manto type
copper deposits.Accumulation of thick eugeosynclinal piles containing abundant copper.
rich volcanics in the westem part of the Andean geosyncline during the Jurassic an(i
Cretaceous times may explain why the Chilean Coastal Range is rich in this unique
type of coPPer (ieposits.
旦。 亙聡電登o磁眼c亘量⑪聡
Manto type stratifom copPer sumde de-
posits are widely distributed,in the Coastal
Range of north-central Ch丑e (F五9.1 and
Table1)。They have several unique charac-
tehstics in comparison with other types of
stratiform coPPer depositsl(1)they are
hosted by marine and continental volcanics
of Jurassic to Eocene in age and,1ess com-
monly,by limestones and shales interbedded
with the volcanicsl(2)amygdules of lavas
and matric“s of volcanic brecc五as and vo1-
canic sandstones are the most favourable
sites of mineralizationl(3) chalcopyrite,
bornite and chalcocite are the major coPPer
su1丘des coexisting with pyrite,hematite and/
or magnetite三(4) wallrock alteration is
generally very weak or none,being undis-
tinguishable from regional diagenetic alter-ation.
*Mineral Deposits Department,Geological Survey of Japan,Higashi1.1-3,Yatabe,Tsukuba,Iba- raki,305 Japan
The purpose of this article is to review
recent knowledge on this unique type of
coPPer deposits from literatures and the
present authofs own observationsl during his
stay in Chile in November-December,1981.
2. G錨e戯Geo夏⑪蟹一A醗且e査Rev量ew o鉦
曲eTec鯉量c躍亟M我9鐡伽Evo恥⑳鑓o髄he A麟e蹴Ge⑪sy麗髄聡e
The Jurassic to Eocene volcanics hosting
the manto type copPer deposits are the prod-
ucts of the Andean orogenic cycle,which is
interpreted to have been contro皿ed by the
subduction of an oceanic(Paci且c)crust un(ler
the South American continent(RuTLAND,1971; CoIRA α αZ., 1982). CoIRA α αZ.
(1982)divided the Andean orogenic cycleinto two principal stages,∫.6.,the Jurassic-
Early Cretaceous stage and the Late Creta-
CeOUS-ReCent Stage.
The Jurassic-Early Cretaceous stage 五s
characte血ed by the accumulation of a thick
pile of volcanic-dominant sequences in the
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Zone o f UPPer Cre-
o曾qceous (コnd Eocenevolcαnic-dominqntS. equences
Zone of Lower Cre_tdCeOUS VOICqniC-
dominqnt$equences
Zone of Jurqssicvoicqnic-dominαnt
sequences
⑭ Mqjor mqnto type deposits
Buenq EsperGnzq
SusonG
Mqntos Blqncos
Puntq dei Cobre
Jq rdl n
Amolqnqs
Arqueros
Tqlcunq
Esperqnzα
El Squce
Los Mqqui串
Guαyαc6n
EI Soldqdo
Cerro Negro Po r t q l es
AnimGS
El SqlQdo
LoAguirre 6
70。WFig.1 Map of north-central Chile showing distributions of Jurassic to Eocene volcan!g-
dominant sequences and major manto type copper deposits(greatly simpli血ed from Mapa
Geo16gico de Chile(1:1,000,000),1982/1983,Servicio Nacional de Geologia y Minerfa)。
copper
切ミ簿欝.
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ハ4傭oTypεCOPρε7DεPOS’‘S(T.5α10)
Coastal R.ange of north-central Chile (Fig.
1)。 The volcano-sedimentaries,overlying
marine sediments of early Liassic age,are
several thousand meters thick and have great
lateral extensions. They grade into foss翌fer-
ous marine sed㎞ents toward east,and RUIZ
αα乙 (1965) 血ferred an eugeosync1血al en-
vironment for the volcanic-dominant se-
quences and a miogeosynclinal environment
for the ma血e sediments.According to amodem interpretation based on plate tectonics
by CoIRAααZ。(1982),the former is attrib-
uted to a magmatic arc and the latter to an
ensialic back arc basin.
The products of the Jurassic magmatic arc
are typically exposed in the Antofagasta-
Tocopilla region,where they host several
manto type deposits(see Fig。1).They are
called the:La Negra formation and consist
mainly of lavas of andesite,10w-silica andes-
ite,high-K andesite and oliv血e basalt with
occasiona1血tercalations of volcanic breccias,
tuffs an(i sandstones (LosERT,1973;1974).
PALAcIos(1978)(iist血guished tholeiitic,calc-
alka1血e and alkal血e suites,but could not
note any temporal nor spatial zonation among
them。The initial strontium isotopic ratios of
the Jurassic plutonic rocks,which are sup-
posed to be comagmatic with the contem-
poraneous volcanics (LosERT,1973),are as
low as O.70344suggesting a primitive source
for the Jurassic magmas(SHIBATAαα1.,1984).
In the Early Cretaceous,the site of mag-
matism shifted eastward and the sedimentary
basin was narrowed.CoIRA窃αZ.(1982)suggested eastward m萱gration of the magmatic
arc an(i shr血kage of the back arc basin at
this stage.
The Early Cretaceous sequences are com-
posed mainly of intermediate and felsic vo1-
canics intercalated with ma血e sediments;
ignimbrite and continental sed㎞ents occur
locally。They are hosting many manto type
deposits especially in the north Santiago area,
which will be described.in detail in a follow-
ing chapter.
The site of magmatism shifted farther east
in Late Cretaceous to the westem footh皿s
of the Cord皿era Occidenta1,and the sedi-
mentary environment of the Andean geo-
syncline became totally continenta1。CoIRAααZ.(1982) inferred that the previous arc-
back arc basin pair was replaced,by a single
eastwar(i migrating magmatic arc at the end
of Early Cretaceous probably as a result of
the且nal open㎞g of the Atlantic and the
active westward movement of the SouthAmerican Plate。This can be interpreted as
the change of plate subduction regime from
Mariana type to Chilean type as de且ned by
UYEDA and KANAMoRI(1979). The volcanism of Late Cretaceous and
Early Tertiary is characterized by extrusion
of felsic lavas and ign㎞brites,but basalt and
andesite were also produced.These volcanics
host some manto type deposits inclu(ling the
weHknown Mantos Blancos deposit,whichoccurs in Late Cretaceous,dacitic lavas.
The initial strontium isotopic ratios of
the plutonic and volcanic rocks of this time
span increase with time from O.7022-0.7035
in Late Cretaceous to O.7043-0.7057 血
Early Tertiary(McNuTTαα1.,1975).This
t㎞e-dependent increase in initial ratio is
recognized to cont血ue量n younger rocks,an(i
McN’uTTααZ.(1975)supposed that the
magmas were generated by partial melting血rst in the subducted oceanic crust and then
in the hangingwall mantle peridotite.
In summary,tectonic reg三me of the Andean
geosyncline changed greatly at the en(l of
Early Cretaceous,and at the same time the
depositional environment changed in general
from marine to continenta1。The chemistryof volcanics and the site of magma generation
also appear to have changed with time.It
is noteworthy that the manto type copper
deposits occur in the rocks of whole time
span from Jurassic to Early Tertiary and in
various Iithologies regardless of rock chemis-
try,sedimentary facies or regional tectonics.
一567一
_、幽
B麗〃εだn o1孟hθσθ0108’6αZ Sμ7v6y o∫1αραnフVoZ.35,ハ1α 11
Table l Some Major Manto Type
No.
12
3
45
678
9
10
11
12
13
14
15
16
17
18
Name of Deposit orDistrict((1eposit type)
Buena Esperanza,(II)
Susana(II)
Mantos Blancos(m)
Punta del Cobre (1)
Jardin (III)
Amolanas(m)Arqueros(Ill?)
Talcuna(1)
Socorro
Vasquez Chilena Coca-Cola
Andacollo
Po(ierosa and Bienvenido
TamborEsperanza (1?)
EI Sauce (1?)
Los Maquis(II)
Guayacan(1)
EI So1(1a(10 (III)
CerroNegro(1)
Portales(1?)
Animas(1)
EI Sala(io (III)
Lo Aguirre(III)
Location(1at.S/10n.W)
22。11’/70。14/
22。40ノノ70。15ノ
23。26ノ/70。04〆
27。30〆/70。15/
27。43ノ/70。12ノ
28。02ノ/70。03/
29。45ノ/70。56’
29。53ノ/70。53ノ
30。04〆/70。37ノ
32。27ノ/71。04/
32。28ノ/71。04!
32。32771。05ノ
32。38〆/71。06’
32。34ノ/70。51/
32。38ノ/70。52ノ
32。40’/70。54/
32。45//70。58/
33。27ノ/70。56’
Formation(age)
La Negra(J)
La Negra(」)
Augusta Victoria(LK)
Cha,fiarcillo (EK)
Hornitos (E)
Homitos(E)
Arqueros(EK)
Quebrada Marquesa(EK)
Pucalume(LK)
Lo Prado
Lo Prado
Lo Prado
(EK)
(EK)
(EK)
Lo Prado (EK)
Las Chilca.s (LK)
La,s Chilcas (LK)
Cerro Morado(LK)
Veta Negra,(EK)
Veta Negra(EK)
HostRock
Amyg。andesite andbasalt
Amyg,andesite3nd basalt
Dacite
“Albitophyre’y and breccia
Rhyolite and ignimbrite
Rhyolite
Limestone
Lapilli tuff an(1sandstone
Conglomerate and sandstone
Limestone
Limestone and shale
Andesite and calcareous shale
Limestone,tuff br.and andesite
Volcanic breccia、
Carbonaceous and calcareous shale
Andesitic breccia
Rhyolite and welded tu躍
An(1esite
Abbreviations for age.J Jurassic,EK Early Cretaceous,LK Late Cretaceous,E Eocene。
3. Genejfal C量亘aし亙漉c宜e酸s重重cs我】燈dl C且ξ亘ss量最回
C面0賦O置伽C鯉e蹴M懸琶o Type Copper }eposi宣s
More than且fty manto type copper de-
posits are known in Chile(ε.9.,RuIzααZ.,
1965). Of these,18 deposits or(listricts are
relatively well described and listed in Table1.
Traditionally they have been classi血ed mainly
on the basis of host rock lithology (CARTERラ
19611RuIzαα1.,1965). In this paper,the
deposits w皿be subdivided on the basis of
the shape of deposits because the morphologi-
cal class重cation appears to be more con-
venient to sort the characteristics of the manto
type copper deposits that show various modes
of occuπence.
Type亘含s1継曲側樋勧閾 躍幽e聖o曲 This type is characterized by occurrence
of many smal orebodies in a particular
stratigraphic horセon. Orebodies are tabular
in form and are connected each other by a
weakly mineralized zone。In many cases the
mineralized horizon is a Iithologic boundary
一568一
ハ4傭oTypθCOPP87Z)6ρos’ごs(T。Sαごo)
Copper Deposits in Chile.
Sulfide Assemblage
cc,bn,cp,dg,cv,py
cc,cp,py,cv,bn
cc,bn,cp,py,cv,gn
cp,pycc,bn,dg,cv,cp,py,
sp,gn
bn,cc,cp
cc,cv,bn,cp,py,gn
bn,cp,cc,gn
cp,cc
cp,py
cp,py
cp,py,bn
cc,dg,bn,cp
bn,cp,cc,py
cp,bn,cc,cv,py
bn,cp,cv
bn,dg,cc,cv,py
Reserve(R)IProduction(P) (in1,000tons)
2,500(P)
8,000 (R)
43,000 (P unti11981)22,500 (R)
3,500(Pfor1800-1978)
2,800 (R)
3,800(R.)
240(R)
215(R)
36(R)
140(R)
16(R)
810(R)
50(R)
650(R)
28,100(R)
1,600 (P unti11963)
180 (P for1978-1980)
11,100 (R)
Grade
3%Cu1.7%Cu,30-409/tAg
1.51-1.90%Cu
L6%Cu,21g/tAg
6%Cu
2.0%Cu
1.2%Cu,10g/tAg
1.50%℃u,509/tAg
1.50%Cu2.32%℃u,41g/tAg
1.5-1。7%Cu,15g/tAg
2.5%Cu
1.2-L5%Cu,15g/tAg
1.13%Cu,53g/tAg
4.75%Cu
1.8-2.2%Cu
1.5-2.096Cu
1.8%Cu
1.9%Cu
2.8%Cu
1.3-1.8%Cu
2.14%Cu
Source
:Ruizθω1.(1971)
Esp宣noza (1981b),
Palacios and Definis(1981)
Anonymons(1981)
Camus(1980)Zentilli(1974)
Zentilli(1974)
Kamono an(1Bori6(1982)
Kamono and Bori6(1982)
Kamono and Bori6(1982)
JICA(1980)
JICA(1980)
Ruizθ1α1.(1971),
JICA(1980)
Ruizαα1,(1965),1.1.M.Ch(1980)
Ruiz61α1. (1965,1971)
Ruizθ∫α1。 (1971)
JICA(1980)
JICA(1980)
1.1.M.Ch. (1980)
Abbreviations for minerals. bn:
py:
bornite,cc:chalocite,cp
pyrite,sp:sphalerite・
chalcopyrite,cv covelline,(lg:digenite,gn galena,
such as a boundary between volcanics an(1
sed㎞ents. Typical and well-described ex-
amples of this type are the Talcuna district
near La Serena(KAMoNoεしnd BoRI6,1982)
and the Punta del Cobre(iistrict near Copiapo
(CAMus, 1980)。
In the Talcuna district,mineralization took
place in a2to12meters thick lapilli tuff/
tuffaceous sandstone horizon sandwitched by
a血underlying andesitic tuf[breccia/lava unit
and an overly血.g sandstone/s凱重stone unit(Fig・
2).Uppermost amygd』aloidal parts of the
underlying andesitic lavas are also mineral-
ized.The m1neralization continues at least
5㎞along this hor並on. Of this m血era1並ed
bed only restricted parts are of economic
grade and minable.NW-SE trending vertical
faults,which themselves are mineralized to
economic grade,apPear to have controled
thehighgradeparts(seeFig・2)・Thereisno distinct wallrock:alteration observed,but
the host volcano-se(iimentaries are regiona11y
altered into calcite-chlorite-analcime-hematite
assemblage w五th epidote and prehnite de一
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ハ4傭oTyp8COPPθ7P8pos甜s(T.5伽)
veloped in stratigraphically lower levels。It
is noteworthy that bedded Mn-Fe oxidemineralization occurs in the tuffaceous sand-
stone/s丑tstone hortzon overlying the coPPer
horizon.It is more widespread than the
copper mineralization and becomes thicker
toward southwest,where the copper bed.dis-
apPears (Fig.2)。 Genetic relationship be-
tween the two m3neralizations are not wel
understood.
In電he Punta del Cobre district,many ore-
bodies,occur in an andesitic breccia horizon
between underlying massive andesite andoverly血g shale. Here aga加.the site of eco-
nomic concentration of coPPer apPears to be
controlled by faults.Wallrock alteration is
not clearly distinguished from regional alter一
ation except for increase in amount of chlorite
and sericite toward orebo(1ies especially near
the mineralized faults.
Other deposits with sim丑ar features include
Guayacan(R.uIzααZ。,19713CARTER.,1961),
Cerro Negro(RuIzααZ.,1971)and Animas
(JICA,1980).Though information is not
sumcient,many of the smal deposits Iisted
in RuIz訂α1。(1965)and JICA(1980)maybe include(i五n this type.
Type鯉3S甑ke認勧曲買翻e脚s量重s In this type many tabular orebodies occur
in lithologically favourable parts of host
rocksラsuch as amygdaloidal How tops of lavas
an(1 calcareous sed㎞ents altemating withshale or siltstone.
A well-described example of this type is
\4 ¥ ‘
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GGbbro
Ai†ered GqbbrQ(cq『ci†e一$erlci†e)
Al十ered Gqbbro(epido+e-chlori†e-cqlcl+e-serici+e)
BrecclQ Plpe(minerqlized)
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Orebodies
:Fig.3W-E cross section of the Buena Esperanza deposit(PALAcIos and DEFINIs,1981).
一571一
B麗ZZ訂’n oプ1h6σ60108∫cαZ5「μ7v召y o/1αPαn,70Z.35,1〉o.11
the Buena Esperanza deposits near Tocopilla
(LosERT,1973,19741PALAcIos and DEFINls,
1981),It is composed of at least28parallel
orebodies occurring血the Jurassic La Negra
formation(Fig.3)。Ore grade mineralization}
is confined to amygdaloid.al且ow tops of an-
desitic lavas and volcaniclastic lenses,occur-
ring as amygdule-f皿ings,thin veinlets and
disseminations.Weak mineralization extendsto massive basal parts of the lava fしows and
to the gabbroic intrusive and the breccia
pipeラwhich appear to have controlled the
site of mineralization(Fig。3)。Wallrock
alteration is not conspicuous, but deta丑ed
stu(iies by LosERT(1973)an(1PALAcIos and
DEFIMs(1981)indicate that the alteration
mineral assemblage in and near the ore-
bodies is albite-calcite-sericite-chlorite-hema-
tite,which is d迅!erent from that of regional
alteration in disapPearance of zeolites,prehn-
ite,pumpellyite and/or epidote.The Susana
deposit situated about50km south of Buena
Esperanza has similar features(EsPINozA,
1981b).
The Los Maquis deposit near Cabildo
(CARTER,1961)is a good example of stacked
tabular deposits in calcareous sediments.It
occurs in a limestone member of the Early
Cretaceous Lo Prado formation and consists
of several tabula,r orebodies each O.5 to 3
meters thick.Orebodies are separated each
other by barren s丑tstone beds。 The Los
Maquis deposit is unique in that abundant
grossular gamet occurs as a gangue mineral
SUggeSting a COntaCt metaSOmatiC natUre Of
the mineralization(CARTERラ1961).
Type皿3Pse翻os謝舗蓋疑o㎜団e聖osi重s
This type is characterize(i by irregular
pseudostratiform orebodies generally obliquely
cutt血g the stratification of host rocks. Ore
minerals occur as五ne dissemination and
veinlets.Host rocks are various but most
commonly acid lava Hows and ign㎞brites。
AtypicalexampleofthistypeistheMantos Blancos deposit near Antofagasta(Fig.4)。 Here irregular blanket-1ike ore-
bodies,each100to200meters thick,occurin the Augusta Victoria continental volcanic
formation of Late Cretaceous in age.A1-
though the volcanic sequence in the Mantos
Blancos district contains lava flows and fiow,
breccias of andesite and dacite, only the
dacitic units are mineralized (ANoNIMous,
1981)。Other examples of type III include
E
ELVIRAPIT △ ム
rr.ノ~蹄.}、で、.級iムヘムムムムムムム
○
i婁コ.・・r、
400m
W .MARl NA PIT △ ∠』 A △ OUINTA PI下
蕊簸/・鋤瓢,購驚綴薫 鰭無二鱗窪ll:響・とコ1、 7、ノー・ハ’丸!, r
ヨコ 禦:’.∫賜ヲーゴ』艇』ヲ1※1鴛コr「「≦「 コ,.ゴ1∵』:r’』』・:耳・・※〕』』:・r∵』
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、=
』・1・臼1M・’ 前ン 完 ・1鵯・1㌧一
膨 O×l DE G、3-L7%Sol.Cu)
纒 CHALCOCITE (1,8-2.5% lns.Cu)
匿ヨ雛盟RI臨尼YRITE「]HEMATITE(SPECULARITE)
lG・RELIMITS
DEE P
凶MAFICDIKES[銅INTRuSIVEANDESITE
MARi N A
「ZIR・CKC・NTACTS
慶ヨFAuLT14五]uPPERuNlT:ANDESITEFL・WANDFL・WBRECCIA
E三IMIDDLEuNIT:DACITEFL・WANDFL・WBRECCIA
E],L・WERuNIT;QUARTZ-EYEDACITE
Fig.4E』W cross section of the westem part of the Mantos Blancos deposit(after
ANONIMous,1981).
一572一
ハ4磁oTypεCOPP87Z)ερos’ごs(T。5αオo♪
Jardin and Amolanas(in Eocene rhyolitic
flows and ignimbrites),EI Soldado(in Early
Cretaceous volcano-sed㎞entaries 血clu(1ing
ign㎞brites),EI Salado (血Early Cretaceous
dacitic fiows and welded,tu廷s) and.:Lo
Aguirre(in Early Cretaceous andesites and
dacitic fbws).
Another important feature of this type is
the presence of we11-developed alteration
halos.For example,the Mantos Blancos ore-
bodies are surroun(1ed by extensive albiti-
zation and s皿icification(ANoMMous,1981),
the El Soldado by albitization (TERRAzAs,
1977),and the EI Sala(10by siHcification and
sericitization (HuETE,1969). This is con-
trastive to other types,whose alteration is
generally very weak:.Ore mineralogy of type
IH deposits is,however,similar to that of
other types. It shoul(l be also noted that the
deposits of type III tend to have much larger
scales in terms of ore reserve and/or pro-
duction than the deposits of other types
(Table1).
4・跳亘曲面棚o置漁蜘丁脚eCo脚e翼 璽》e鯉o曲睡勲No曲s蹴翻悪o A買e我一A盟 Ex購聖貝e⑪憂曲e量罵Re・
蜘囎置Ge伽蜘s£臨鍔
In an area between Cabildo an(i T皿t聾,
about50to lOO km north-northwest of San-
tiago,there is a cluster of many manto type
coPPer deposits(Figs。5a and b).Exami-nation of this area may provide basic infor-
mation for mderstanding regional geologicsetting of this type of(leposits.The following
descriptions are based mainly on THoMAs(1958),Rulz α αZ. (1965),LEvl (1969,
1970)and JICA(1980). Ge⑪且o霧y
The area is geologically composed of vo1-
canic-dominant sequences of more than20km in accumulated thickness and ranging
in age from Jurassic to Early Tertiary as wel
as many granitoid stocks and batholiths in-
truded in them(Fig.5and Table2)。It pro-
vi(ies a typical geologic traverse of the CoastaI
Range of the Andean orogenic belt,which
corresponds to the “eugeosyncline,,of RuIz
訂αZ.(1965)and the“magmatic ar♂ofCOIRAαα」.(1982).
The Jurassic-Elarly Tertiary sequences are
composed mainly of intermediate and felsic
lavas,flow breccias,ignimbrites and pyro-
clastics with intercalations of limestone lenses
and clastic sediments.The Jurassic to Lower
Cretaceous units are characterized by relative
abundance of ignimbrites,and the“Middle”
and UpPer Cretaceous units by andesitic lavas
and flow breccias with subordinate felsic
Iavas and ignimbrites(Table2)。The de-
positional environment was partly mar盤1e
(predominantly shallow water)and partlyten℃strial dur血g Jurassic an(i Early Creta-
ceous, and exclusively terrestrial during
“Middle”Cretaceous to Early Tertiary.
There are three major unconfomities in
this thick volcano-sed㎞entary p丑e。They are
the Pataguaunconformitybetween the Middle
Jurassic Me16n fomation and the LowerCretaceousl Lo Prado fonnation,the Peral皿o
unconfomity between the“Middle”Creta-ceous Cerro Morado fomation and the Upper
Cretaceous Las Chilcas formation,and the
Lo Valle unconfomity between the :LasChilcas formation and the Lo Valle formation
of Late Cretaceous and/or Early Tertiary血
age(see Table2).
The plutonic rocks in the area are pene-
contemporaneous with the intruded sequences。
They are mostly tonalite and granodiorite in
composition and belong to I-type magnetite
series・ For detaHs of the plutonic rocks,the
rea(ier should refer to亙sHIHARAαα1.(1984).
Me訟mo買幽員s㎜/Re露o囎且A艮琶e置鋤纒
The roc:ks of the area as well as pre-Neo-
gene sequences of the Andean geosyncline in
general have been regionally altered血to zeo-
1ite to greenschist facies(LEvI,1970).The
metamorphic grade increases stratigraphicaly
downward and the isograds are essentially
parallel with bedding without any apparent re-
Iation to granitoi(i 血trusives3 the orig血al
textures of the rocks are wel preserved with-
out any intemal deformation(:LEvI,1969,1970).
一573一
B那ZZε枷oμh6σθoZo9∫cαZ3薩7vεyo〃αPαn,yoZ.35,1〉o.11
Although the above-mentioned features血dicate that the regional alteration of this
area corresponds to burial metamorphism as
described in New Zealand.(CooMBs,1960),
detaile(l stu(iies by ]LEvl (1969, 1970) re-
vealed out that the metamorphism of the
area has some unique characteristicsl that is,
though metamorphic grade generally increases
with stratigraphic depth,abrupt discontinui-
ties in metamorphic grade are observe(l
at malor unconfomities.Since there are
three unconfomities in the Jurassic to:Lower
71。15, 71。OO, 「
32。30,
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[QUATERNARYロコTERTIARY
匡LASCHlLCASF・RMATI・N
匡亟CERR・M・RAD・F・RMATl・N
羅VETANEGRAF・RMATl・N
懸L・PRAD・F・RMAT!・N8,
融鼎☆・・C
CRETACEOUS
巨コTRIASSIC
回PALE・Z・IC図CEN瀦A塁亀鵬聖R鴨糊ORITEe椀〕
匪璽C・ASTBA砿纏摺ALITE,ADAMEUTEetc〕
麟 ㊤ MANTO TYPE COPPER DEPOSITS
lO Ei SGuce
I I Los Mqquls
33。001 12け
33015,
GuqyqCGn
13 EI Soldαdo
14=Cerro Negro
15・ PQr†Qles
16 Anirnqs
17曹 El SolQdO
一』5kmFig.5a Simplified geologic map and distribution of manto type copper deposits of the north
Santiago area(after THoMAs,1958;CARTER an(1ALIsTE,19621」亙CA,1980)。
一574一
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去ム ム ム ヘ ム 〉 〉 〉 〉 〉
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Fig.5b Cross sections along A-A’to E-E,1ines in Fig.5a).
ミ§む
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向
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B配ZZε伽oμh6GεoZo9εcαZS㍑7vεyo∫1αP偽γoZ.35,1〉o.11
Table2 Stratigraphic relations and lithologies of Jurassic to Early Tertiary formations of the
Coastal Range of Central Chile(modi且ed from LEvI,1970).
STRATIGRAPHIC AGE THICK一目THILOGY AND DEPOSIT【ONAL ENVIRONMENT
UMT NESS
の⊃ >
o」L』匡 >rOく α:く LI Andesitic pyroclastic rocks,mostly ignimbrites,and lavas,
LO VALLEFORMATION
くト _LI l一 匡α二 α=
o O]600m partly brecciated;mmoracid pyroclastic rocks,mostly [gnl-
mbrites;lacustrine,fluviati『e and mud flow deposits,partly
\1- oし」
z
Iahars.
トく く一 乙0 幽乙乙ε σ1VOOIVFOR〃17γ
LAS
CHILCASFORMATlON
の⊃o国oくト]
2600 to
Mostly 刊uviatile and mud flow(in part lahar) deposits;
subordinate brackish-water sediments、 Andesitic lavas
partiy brecciated, and subordinate andesitic pyroclastic =
PERAUしLO匡o 7000m rocks l scarce acid ignimbrites.
STRATA ]トく一 ρだR,4乙ノL乙O U〈〆00〈〆FOR〃17》!
一皿一’♂’一〃NOVICIADO の
MEMBER ⊃o
= 山 Brecciated andesitic lavas and clastic rocks,mostly mudZO一
CERRO oく
fIows (probably lahars);subordinate acid [avas.
トく
MORADO ト]
Σ匡
FORMATlON 匡o
oL
=ω
5500
( OCOA 」o
to Andesitic iavas,partly brecciated;scarce acid ignimbrites
にσ国Z
MEMBER o一Σ=
7500m and continental ciastic rocks,mostly mud 刊ows (probablyIahars)∂ndlacustrinedeposits.
く」■]> PUREHUE
MEMBER
o↑>」匡く国
Andesiticiavas,partIybrecciated,andcontinentalclastlcrocks,mostIy lacustrine and deltaic deposits;subordinateacid ignimbrites and mud flows (probably [ahars)
ZOFくΣ
LO PRADOFORMATION S.S.
ω⊃o]
700 to
l500m
Acid pyroclastic rocks,mostly ignimbrites and brecclated
lavas;marIne near-shore clastic rocks and limestones;conセinentalfluvidtileand/ordeltaicsedimentslsubordinatgandesitic Iavas
匡O」 PACHACAMA
Qくト O to Acld ignimbrites and lavas,and continental clastic rocks;
oFORMATlON 国
匡o
1000m subordinate andesitlc lavas.
Oく匡 > Marine clastic rocks,partly turbidites,and subordinate(ユ PATAGUA 」
匡 2000m marlnechertsandlimestQnesl subordinateacidignimbri一
oFORMATION く
国 tes and andesitiC lavas.
」 PA払G崩 捌00解OR〃’7γ
ZOFく
FORQUETA〇一ωωく
Continental clastic rocks,mostly mud fIows (probabIy
lahars)and fluviati[e sedimentsl andesitic lavas,most【yΣ MEMBER 匡 brecciated,and acid ignimbrites.匡O」
⊃「
2100 to
Z、o NOGALES
]Jo
5500mAcid ignimbrites,and marine near-shore ciastic rocks
」]Σ
MEMBERo’
一Σ
and [imestones.
AJIAL
O o←u」あ 」 の
750 Acid ignimbrites,very subordinate andesitic brecciated
FORMATlON>一〇 く一 〇 α=
巽……ヨ
]
to
l300mlavas,and marine hear-shore clastic rocks and Iimestones.
QUEBRADA o 一>・(ノ》
」 の300 Marine clastic rocks and limestones;minor acid
DEL POBREFORMATlON
匡くく に国 ⊃
「
to
Iゴ50mignimbrites and scarce andesit1c lavas.
PRE-JURASSIC BASEMENT
ハ4αnオo TyρεCoρρε7D8pos髭s(T,S伽o♪
Tertiary formations in this area(see Table2),
four metamorphic series are recognセed in
them;∫.ε.,one below the Patagua unconformi-
ty,one between the Patagua and the Pera1皿o
unconformities,one between the Pera1虹10and
the Lo Valle unconformities,and the last
above the Lo Valle unconfomity。Amongthese the丘rst two range from prehnite-pump-
eUyite facies at the top to greenschist facis3t
the bottoml the third series in the Upper Cre-
taceous formations ranges from zeolite facies
to prehnite-pumpellyite facies in most places
with local occurrences of greenschist facies
at the bottoml and the last series in the
Upper Cretaceous and/or Lower Tertiaryformation is of zeolite facies throughout.
LEvl (1969) also noted that,血 a s血91e
lava flow unit,the non-amygdaloidal base is
relatively unaltered,whereas the amygdaloidal
top is strongly altere(1. This suggests that
deuteric action has played an important role
in the burial metamorphism in this area,
which is supported by considerable changes
in chemical composition du血g metamor-
phism(LEvI,19741CHAvEz an(1NIsTERENKo,
1974) an(l presence of ve血ets conta血ing
calcite,zeolites, epidote, etc.in the altered
rocks (LEvI,1970).
⑪置e恥卿s亘重s
The north Santiago area is one of the
richest area of the manto type coPPer de-
posits.JICA (1980)1isted up about30deposits in the area(Fig.5),of which major
eight are shown血Table L
Stratigraphic horizons of the host rocks
range from the Lo Prado to the LasChilcas formationsl no deposits are known
in the Jurassic formation or the Upper Cre-
taceous and/or Lower Tertiary:Lo Valle
formation(see:Fig5).The deposits occurin various host roc:ks such as lavas,ignim-
brites,flow breccias,volcaniclastics,calcare-
ous shales and limestones。Their shapes and
modes of occurrence are also various㎞.clud_
・ing aU the three types mentioned earlier.
There is no apparent regional control on
the site of mineralization.Although smal1
量ntrusive bodies, faults and/or stratigraphic
horizons apPear to have locaHy controlled
mineralization in some places(CARTER,19611
HuETE,19691TERR.AzAs,19771JICA,1980),regional distribution of the deposits in this
area are not related to any particu1&r strati-
graphic horizons,depositional environment of
host rocks or plutonic bodies.
5。亘》量s鐸ss量翻s
Ge鵬es量s
An exhalative sedimentary orig㎞seems to
be favoured by some Ch且ean geologists for.
the manto type coPPer deposits(ε.9。,Rulz
8∫αZ.ラ1971∋CAMus,1980;EsPINozA,1981a)。
However these authors have failed to present,
nor has the present author could observe
in the fie1(i,any deHnite proof for the syn-
genetic orig血 of 血e deposits。 For instance
synsedimentary and other features character-
istic to volcanic-hosted or sed㎞ent-hos、ted
massive sulfide deposits,for which syngenetic
origins are almost unanimously accepted,are
completely lacking in the manto type de-
posits.The following discussions will there-
fore be made under a working hypothesisthat the Chilean manto type copper depos玉ts
are of epigenetic orig豊n.
In consideration of the mineralizing pro-
cesses of the manto type deposits,the fo1-
10wing characteristics of the deposits are
㎞portant:
1) The mineralization occurs in varioushorizons in Jurassic to Eocene volcano-sedi-
mentary sequences of marine and continental
origins.
2) The mineralization took:place most fa-
vourably in porous rocks such as amyg(1aloi-
dal lavas and volcanic breccias or in chemi-
cally weakl rocks such as calcareous beds.
3) The site of mineralization is localy con-
trolled in many cases by faults and in some
other cases by intrusive bodies.
4) Except for type III,there is no(listinct
wallrock&1teration near the orebodies,but
the host volcano-sedimentary pile is exten-
sively altered by diagenetic or burial meta-
morphic processes.
一577一
β尻IZ8だn oノ孟hθσεolo9∫cαZ S配7vθy o∫1αραn,70Z.35,1〉o.11
5) The ore mineralogy is characterized by
assemblages of low sulfur to metals ratios。
6) Calcite is the only common ganguemineraL
Many of these features suggest that the
mineralization is(ie且nitely of hy(1rothermal
origin,but the lack of distinct wallrock alter-
ation might indicate that the responsible Huids
did not posses very different chemistriesl nor
temperatures from those of comate or meta-
morphic waters that must have been in equi-
1ibrium with the regionally altered host rocks.
NlsTERENK:oααZ。(1973)reported且11ing
temperature of Huid inclusions from some
manto type deposits.In the Buena Esperanza
deposit,且ling temperatures of inclusions in
calcite from the ores range from650to195。C,which are almost the same with those
in authigenic calcite and quartz from andes-
ite stratigraphically far below the mineralized
horizon。This suggests that the mineralizing
Huid had similar temperatures to comate or
metamorphic waters。It is also suggestedfrom these temperature data that the gabbroic
intrusive at Buena Esperanza(see Fig.3)did
not act as a source of the mineralizing Huid
nor heat.
In contrast,五11ing temperatures of inclu-
sions in amygdule-f皿ing quartz from the El
Salado deposit belonging to type III are very
high ranging from273。to430。C,and halitecrystals were observed in the inclusions sug-
gest血g high salinities of the inclusion fluids
(NlsTER.ENKoεωZ.,1973).At El Salado,a
granitic intrusive is intruded underneath the
ore deposit. It is conceivable that the 血_
trusive provided heat or possibly the miner-
alizing 且uid itself responsible for the for-
mation of the EI Salado deposit.The same
may apply to other type III deposits which
are spatially in close association with gran-
itoid intrusives and surrounded by wel-
developed alteration halos.
As to the source of mineralizing Huids,
information is too scarce to draw any con-
clusion・However it apPears very suggestive
in considering the fluid source that the host
rocks underwent advanced burial metamor一
phism,and that the alteration and gangue
mineralogy is essentially the same with that
of the metamo甲hosed host rocks except for
some type III deposits・
As cited earlier,LEvI (1969, 1970)
demonstrated that the burial metamoq⊇hism
in the north Santiago area took place re-
peatedly.The manto type copper deposits in
this area are confine(i to the sequences that
underwent prehnite-pumpellyite to greenschist
facies metamorphisml none is present in the
Lo Valle formation that has suffered only
zeolite facies metamorphism。
It is suggested here that metamorphic
water produced by dehydration processes of
prehnite-pumpellyite and higher facies meta-
morphism is one of the most plausible candi-
dates for the mineralizing fiuid responsible
for the Chilean manto type copper deposits。
S囎ce⑪昼c⑪齢e置 If it is correct that the mineralizing Huid is
of metamorphic origin,the source of copPer
is most likely the host volcano-sed㎞entary
rock:s.Trace element geochemistry of the
Chilean volcanics have been studied by
CHAvEz and NIsTERENKo(1974),ZENTILLI(1974),CAMPANo an(1GuERRA(1975)andPALAclos (1978). S血ce aU the Jurassic an(1
Cretaceous,volcanics have been more or less
altered』,the samples analyzed by these authors
include“little altere(i”rocks.
CHAvEz and NlsTERENKo(1974)analyzed
Cretaceous andesites from some localities of
the Coastal Range and foun(1that their coP-
per contents vary considerably from place to
to place。It is noteworthy in their data that
the andesites of the Arqueros formation,
which underlies the Talcuna district,contain
anomalously high copper averaging256ppm.
ZENTILH(1974)studied geochemistry of
Jurassic to ,Quaternary volcanics along a
latitudinal section between26and29degrees
south.Although some elements such as Yexhibit systematic variations along the sec-
tion,coPPer shows no regular pattem.By
comparing the Chilean volcanics with the辻
equivalents in the Circum-Pac坦c belt,he
found that coPPer is slightly higher in the
一578一
ハ4αnオo TyρεCoρρ87Dεpos∫1s(T。5碗o)
Chilean rocks but when only andesites are
compared Chilean andesites are lower in
copper.However,although he did not note,
his analytical data seem to indicate that the
coPPer contents of the Chilean andesites vary
with age.For example,the Jurassic andes-
ites contain90to375ppm Cu whne theNeogene andesites contain10to32ppm Cu。 Geochemistry of the Jurassic volcanics was
studied血deta最by CAMPANo and GuER.RA(1975) and PALAclos (1978). PALAclos(1978) (iivi(ied the Jurassic basalts and an-
desites of the La Negra formation in northem
Chile into tholeiitic,calc-alkaline an(i alka1血e
suite,and reported the廿average copPer con-
tents as66ppm(SiO2ニ55。4%),113ppm(SiO2=・57.8%)and72ppm(SiO2=55.6%),
respectively.Ee also compared the Jurassic
calc-alkaline suite with the Ceneozoic qua,rtz-
1atiandesites from the Central Andes andfound that the former is much higher in cop-
per than the latter(44ppm),again suggest-
ing an apParent (iecrease of coPPer content
with age。
Geochemistry of the altered or meta-
morphosed volcanics as compared with that
of ‘‘fresh” equivalents has been studied
by LosERT (1973, 1974), CHAvEz an(i
NIsTERENKo(1974)and LEvl(1974).A且of these authors have noticed that copper was
highly mobile during regioml alteration or
burial metamorphism.They are in generalagreement with that copper as well as sulfur
is depleted to a considerable degree in the
altered rocks especially in epi(iotized rocks.
JoLLY(1974),in his study of the Michi-
gan native coPPer district,showed that copPer
was leached from epidotized or more highly
metamorphosed rocks in the zone of de-
hydration,percolated upward to lower tem-
perature levels,and was precipitated 血 the
zone of hydration where pumpellyite,preh-
nite laumontite and chlorite are the principal
hydration minerals.This model can be rea-
sonably aPPlied to behaviour of coPPer in
the metamorphosed rocks of the Andeangeosyncline, an(i also to the genesis of the
Chilean manto type copper deposits.
The ava皿able analytical data in the litera-
tures cited above seem to suggest that some
major districts of the manto type coPPer
deposits are un(ierlain regionaly by thick
volcanic sequences that are primar虹y rich in
copper。The Antofagasta-Tocop皿a district in
the Jurassic volcanics and the Talcuna dis-
trict underla㎞by the anomalously copper-
rich Arqueros formation are such examples.
Combining the above discussions together,
the Chilean manto type copper deposits may
be concluded to be burial metamorphic or
diagenetic-hydrothermal in origin.Some type
III deposits may have been affected by local
high-temperature convection cells caused by
granitoid intrusives,which might have also
provided mineralizing fしuids and coPPer at
least partian.y.
Other coPPer deposits of s㎞i【ar orig血
are those of the Michigan native copper
district,U.S.A.,which are associated with
the subaerial Keweenawan basalts.Accord一血g to JoLLY (1974), copPer sulfi(ies a.re
rare in the Keweenawan rocks,because sulfur
is oxidized to SO2gas in subaerial environ-
ment an(l escapes into the atmosphere be-
fore solidification. In contrast,the Jurassic
to Cretaceous volcanics of the Andean geo-
syncline contains a signi且cant proportion of
subaqueous volcanics which were erupted
under shallow marine or continental lacus-
trine environments.CHAvEz an(l NlsTERENKo
(1974)estimate that68to83%of the cop-
per in the“fresh”Cretaceous andesites from
Chile is present as sulfides probably in the
form of magmatic su1丘de globules。It is likely
that these magmatic su1且des are the dominant
source of both copper and sulfur in the manto
type deposits。This may explain the lowsulfur/metal ratio of the manto type deposits,
because sulfur/metal ratios of magmatic su1-
fide globules are generally low(CzAMANsKE
andMooRE,19771SKINNER and:PEcK,1969).
In conclusion,advance of burial metamor-
phism to prehnite-pumpellyite or higher
facies 血 coPPer-rich, subaqueous volcanics
is suggested to be the necessary factor for
the formation of the manto type copper de一
一579一
』
鷹皿F一司
BμZZα’n o∫オh6σε0108∫cαZ3μ7vεy o/1αραn,ヨVoZ.35,ハ70.11
posits.Accumulation of thick eugeosync1五nal
P虹es contain血g abundant coPPer-rich vol-
canics in the Andean geosyncline during the
Jurassic to Cretaceous times and repeated
burial metamorphism having taken place in
them may explain why the Ch丑ean Coastal
Range forms a unique卑etallogenic province
characterized by this peculiar type of coPPer
deposits。
Aek皿ow畳e調geme醜s31wish to acknowledgethe excellent field guide and warm hospitality
provided by Dr.Carlos ULRIKsEN G.andML Hisashi:KAMoNo duringmy stay in Ch五e.
Special thanks are due to Dr.Femando
HENRIQuEz,who intruduced me to publi-cations and university reports written in Span-
ish,and Mrs.Minoru SuMITA and Hisashi
KAMoNoラwho generously allowed me to have
access to their unpublishe(i data.
Re置eπe亘且ees
ANoNIMous(1981)Mantos Blancos.ル伽∫n8ハ4αg.,
vo1。147,P.458-471.
CAMPANo,P.and GuERRA,N.(1975) Distribuci6n
de Cr,Ni,Co,Cu,Zn y Pb en Rocas Igneas
y Sedimentares del Norte de Chile.Thεsls
sめアn漉θ41o LαUn∫vε7s∫磁44ε1〉oπ8,61P.
CAMus,F。(1980) Posible modelo gen6tico para
los yacimientos de cobre del distrito minero
Punta del Cobre. Rεv∫s∫α G60Z.Ch∫」ε,no.
11,p.51-76.
CARTER,W,D,(1961)Yacimientos de cobre tipo
manto.1nsム1nvεsオ.GεoZ.Ch∫1ε,Bol顔n,
no,10,30P.
an(1ALlsTE,N.(1962) Cua(1rangulo
Me16n。 1nsオ.1nvεs∫.G801.,unpub.rep.
CHAvEz,L an(i NIsTERENKo,G.(1974) Algunos
aspectos de la geoqufmica de las andesitas
de Chile.In KLoHN,E.ed.,Colo9μio soゐ76
F6n67nεnOS48!伽7α016nyMε薦溺07万S解0
εnRo6αS70ZO4n’σαsyln!7泥S’VαS,PεP.
GεoZ。,Un∫v。4εCh’Z6,PめZ.,no.41,p.97-
127.
CoIRA,B。,DAvIDsoN,J.ラMPoDozIs,C.and RAMos,
V。(1982) Tectonic and magmatic evolu-
tion of the An(les of Nortem Argentina and
Chile。 Eαπh So∫.R8v.,vo1.18,P.303-332.
CooMBs,D.S.(1960) :Lower grade mineral facies
in New Zealand. 211h ln1θ7nα∫. G召oZ.
Con87.,ハ70748n,part 13ラp.339_351.
CzAMANsKE,G.K.and MooRE,」.G.(1977)Com- position an(i phase chemistry of sulfide
globules in basalt from Mi(i-Atlantic rift
valley near37。N lat.GθoZ.Soo.!4nz。Bμ〃.ラ
vo1.88,P.587-599。
EspINozA,S。(1981a) Volcanismo y metalog6nesis,
una introducci6n al tema.In!誕惚s4θ1ε7.
CoZo卿030わ7ε7010αn∫sn¢oyM磁lo96nθ一
s∫s。 Dep.Geociencias,Univ。del Norte,
p.16-27.
(1981b) Esbozo metalog6nico(1el dis-
trito Carolina de Michlla,II Regi6n,Chile、
InZo1α34θ1ε7.Colo卿osoゐ78アolcαn一
∫sηzo y ハ4ε観096nθsis,Dep.Geocienciasシ
Univ.del Norteンp.71-81.
HuETE,C.(1969) Geologfa del Distrito Minero
de Catemu y de la Mina EI Salado.Dεp.
σεoc∫6nc∫α,Un∫v.4召Ch∫1召,43p.
1。1.M.Ch。(1980) Lα ハ4∫nθ76α 8n Chilε. Inst.Ing.
Minas Ch且e,131p.
IsHIHARA,S.,ULRnζsEN,C.E.,SATo,K.,TERAsHIMA,
S.,SATo,T.and ENDo,Y.(1984) Plutonic
rocks of North-Central Chile. Bz6〃.σε01.
Sμ7v.∫opαn,vo1。35,p.503-536.
JICA(1980) R6ρoπo∫P701εo13祝7v6y onハ4∫nθmZ
Rεso〃768s ∫n 1h8 弼V6s1 Sαn!如go !歪78α. Ja-
pan Intem.Cooper&tion Agency,47p.(in
Japanese)。
JoLLY,W.T.(1974)Behavior of Cu,Zn,and Ni
during prehnite-pumpellyite rank metamor-
phism of the Keweenawan basalts,northem
Michigan.E60n。σ601.,vo1.69,p,1118-
1125.
KAMoNo,H.and BoRI6,R.(1982) 1nvεn艀∫o PoZか
n1α41∫oos y Es魏4’0 σ60」68∫co D∫S!7∫10
ハ4∫nε70 TαZc麗nα. CORFO-AM亙 82/14,
145p.
LEvl,B.(1969) Burial metamorphism of a Cre-
taceous volcanic sequence west from San-
tiago, Chile. Con∫7. ハ4’nε7α1. Pθかol.ラ vo1.
24,p.30-49.
(1970) Burial metamorphic episodes in
the Andean geosyncline,Central Chile.
σεol.Rz4n4schα配, vo1.59, P.994-1013.
(1974) Variaci6n de algunos elementos
en trazas (iurante la alteraci6n regional de
coladas andesiticas del Cretacico Medio en
Chile. In KLo正【N,E.ed., CoZo(1躍o soわ76
Fθn6〃3θnOS48!伽7α0∫61ηMε孟㈱07戸S襯0
6n Rooαs IVolo4n∫cαs y lnか麗slvαs, Dep.
Geo1.,Univ。de Chile,PubL,no.41,p.129_
137.
一580一
ハ4傭oTypεCO迎θ7Dθpos’孟s(T。3αオo)
LosERT,」.(1973) Genesis of Copper Minerali-
zations an(1Associated Alterations in the
Jurassic Volcanic Rocks of the Buena Es-
peranza Mining Area.D8p.GεoZ。,Un∫v。
4ε Ch’」ε,Pub1.,no.40,64P.
(1974) Alteration and associated cop-
per mineralization in the Jurassic volcanic
rocks of the Buena Esperanz&mining area
(Antofagasta province,northem Chile).In
KLoHN,E.ed.,CoZo(~躍o so67εFεn6η2εnos
48!位87α0∫6nyハ4伽7no7ガS7noεnRoOαS 70Zc4n加s y ln枷3∫vαs,Dep。Geo1.,Univ.
de Chile,Pub1.,no。41,P。51-85.
McNuTT,:R。H:.,CRocKETラ」.H.,CLARK,A.H。,
CAELLEs,J.C.,FARRAR,E.,HAYNEs,S.J.
and ZENTI皿,M.(1975)Initia187Sr/86Sr ratios of plutonic an(1volcanic rocks of the
central Andes between latitudes26。and 29。 south. Eαπh PJαnε1. So∫. Lεπ., vol.
27,p.305-313。NIsTERENKo,G.V.,LosERT,」.,CHAvEz,:L,and
NAuMov,V.B.(1973) Temperatums y presiones de formaci6n algunos yacimientos
cupriferos de Chile. R8vな厩 σ80Z。 Ch∫1θ,
no.1ラP。74-84.PALAclos,C.(1978) The Jurassic Paleovolcanism
in Northern Chile. D∫ssθπαだon s泥わη¢〃1ε4
ガo EZ》67hα74-1ζα71s-Un∫vε7s1δ∫ z麗 丁撹7∫ng6n,
99P. and DEFINls,A.(1981) Petrologfa del
yacimientos Buena Esperanza,II Regi6n,
norte en Chile. In.4ααs4ε1ε7.CoZo(1μ’o
soわ76 70Zoαn’s配o y ハ4ααZo96n8s∫s,Dep.
Geociencias,Univ.del Norte,p.48_67.
RuIz,C.F.,AGuIRRE,L.CoRvALAN,」.,KLoHN,C.,
KLoHN,E.and LEvl,B。(1965) G80Zo9毎
y y’αo∫n¢∫ε1π03 ハ48‘αZ6∫ε70s 4θ Ch∫Z8. Inst,
Inv.Geo1.Chile,305P.Rulz,C.F.,AGu凪RE,A.,EGERT,E.,EspINozA,W。,
:PEEBLEs,F.,QuEzADA,R。and sER踏No, M. (1971) Strata-boun(1 coPPer sulphide
deposits of Chile. 300.ハ4∫n∫ng σεo乙 1α一
Pαn,Spεo.1s5μθ,no.3,P.252-260。
RuTLAND,R.W.R.(1971)Andean orogeny and sea
floor spreading. 1〉α∫z678, vo1.233, P。252-
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ratios of late Paleozoic granitic rocks from
northemChile.飾〃.GεoJ.5『κ7v.1叩αn,
voL35,P。537-545.SKINNER,B.J.and PEcK,D.L.(1969) An im-
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G80Z.ハ40no97.,no.4,P.310-322.
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ZEN皿H,M.(1974) Geological Evolution and
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349P.
チリ国のマント型銅鉱床
佐藤壮郎
要 旨
チリの海岸山脈地域には,ジュラ紀から第三紀前期の火山岩に富む地層を母岩とする多くのマント型
銅鉱床を産する.鉱床はアミグデュールに富む溶岩あるいは火山角礫岩を母岩とすることが最も普通で
あるが,石灰岩を母岩とすることもある.主要な鉱石鉱物は,黄銅鉱,斑銅鉱及び輝銅鉱であり,黄鉄
鉱,赤鉄鉱,磁鉄鉱を伴う.母岩の変質は一般に非常に微弱である.
文献等により鉱床及び母岩の産状,地球化学的特性,鉱物組成などを検討した結果,埋没変成作用の
進行により放出された変成水により鉱床が形成されたことが示唆される.初成的に銅に富む火山岩を多
一581一
一」
β配1Zα’n o/1h8σεolo8’【:αZ Sμ7v8y o11σPαn,レ「oZ.35,2〉o.11
量に含む地層が,アンデス地向斜に厚く堆積したことが,チリの海岸山脈地域がマント型銅鉱床で特徴
づけられる特異な鉱床生成区を形成している理由であろう.
(受付:1984年9月12日1受理:1984年10月1日)
一582一