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Singkat saja pengguna: Southwest Pacific rim sistem emas-tembaga:. Struktur, alterasi dan mineralisasi, G Corbett &

T Leach, 5/97 Edn

Greg Corbett Layanan Geological 29 Carr Street North Sydney NSW 2060 Australia Ph (61 2 99!9 "060 #a$ (61 2 99!% %&"%

')ail

SOUTHWEST PACIFIC RIMGOLD-TEMBAGA

Struktur, Perubahan,

SYSTEMS!"an M#nera$#%a%#

SHORT COURSE MA&UAL

DRAFT pada tanggal 24 Mei 1997

GJ Corbett dan TM Leach*erry Leach *erry Leach dan Co P+ ,o$ 1!0 Coro)andel Selandia ,aru Ph (6% - &66 -6%2 ')ail leach.ihug/co)/n


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pendek saja pengguna: Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett

& T Leach, 5/97 Ednmanual.

RI&G'ASA&

ini mengla!i"ia!ian dan menggambaran ga#a #ang berbeda dari da#a $aci"ic rim !i!tem

ema!%tembaga& dan anali!i! pro!e! bi'ih pembent( hidrotermal) *n+e!tiga!i dari !i!tem inidalam hal !tr(t(r& per(bahan& dan ga#a minerali!a!i memberian in"orma!i #ang dapat

membant( menent(an arah aliran "l(ida dalam berembang !i!tem hidrotermal)

,tr(t(r (tama meloali!a!i !i!tem hidrotermal magmati dalam pengat(ran b(!(r magmati

dan menciptaan ling(ngan dilational bi'ih ho!ting dalam !tr(t(r ana & (m(mn#a pada !(d(t

tinggi (nt( !tr(t(r pengendali) -erbeda ga#a on+ergen!i mempengar(hi ga#a !tr(t(r (tama

dan ling(ngan bi'ih pembent() -re!i ter'adi di !ebagian be!ar depo!ito ema!%tembaga dan

dapat diategorian !ebagai pand(an (nt( memahami ling(ngan bi'ih pembent( !ebagai

orela!i #ang l(a! #ang 'ela! antara bre!i dan minerali!a!i ga#a)

,(h( dan p. cairan dianggap #ang paling penting dari ban#a "ator #ang mengontrol 'eni!

altera!i hidrotermal) Mineral hidrotermal dila!i"ia!ian dalam d(a "ator ini memb(atinterpreta!i bermana data per(bahan) /em(nginan meani!me tran!porta!i logam dan

tran!porta!i& memberian eranga (nt( memahami di!trib(!i logam dalam !i!tem #ang

berh(b(ngan dengan intr(!i)

,i!tem $or"iri tembaga%ema! mengembangan !eitar intr(!i #ang terloali!a!i dalam b(!(r

+olcanopl(tonic oleh are!i daerah 0arc paralel ata( pemindahan 0b(!(r normal !tr(t(r)

$endinginan intr(!i emplaced di tinggi ha!il tingat era di ehilangan pana! ond(ti" dan

pembent(an aal (mp(lan altera!i diategorian) *ni dii(ti oleh lar(tan padat dari cairan

magma dan pembent(an !tocor (nt( !i!tem (rat (ar!a #ang didomina!i !heeted&

(m(mn#a !epan'ang tepi dan di !eitar arapa! dari intr(!i) Minerali!a!i beri(tn#a ter'adi

dalam !(at( ling(ngan #ang ond(!i" (nt( pengendapan logam& dan it( dita"!iran baha

ondi!i ini diciptaan !ebagai ha!il dari pendinginan& ter(tama oleh encer perairan meroet)

Minerali!a!i tembaga por"iri beron!entra!i di 3ona terbe!ar paleo%permeabilita!& (m(mn#a di

!epan'ang e!alahan diendalian margin dari intr(!i ho!t dan re"ract(red (rat !tocor #ang

!(dah ada) Di(!(lan minerali!a!i #ang ter(tama ha!il dari pencamp(ran air meteori dengan

cairan magmati bantalan logam%& m(ngin bera!al dari !(mber magma be!ar di edalaman)

Depo!ito "or!iterite men(n'(an prograd !er(pa dan per(bahan retrograde dan minerali!a!i

dalam menanggapi emplacement dari intr(!i e dalam bat( ap(r)

Tinggi !(l"ida!i !i!tem ema!%tembaga terbent( dari pana!& a!am& cairan magmati #ang

dit(r(nan dan memperpan'ang dari por"iri e re3im epitermal) -ent( per(bahan tinggi

!(l"ida!i !ebagai bah( dan topi (nt( intr(!i por"iri& di mana 3ona!i di per(bahan mencerminan

pendinginan progre!i" dan pen(r(nan beri(tn#a dalam p. cairan dalam menanggapi di!o!ia!i

bertahap ga! magmati reati") ,(h( pembent(an tinggi !i!tem ini& pro!imal intr(!i !(mber&

di!imp(lan (nt( menghambat pembent(an minerali!a!i tembaga%ema! #ang ter'adi di

dingin& ling(ngan #ang lebih di!tal) ,i!tem ini dila!i"ia!ian men(r(t domina!i bai ontrol

!tr(t(ral ata( litologi (nt( aliran "l(ida !ebagai anggota ontin(m) ,em(a !i!tem minerali!a!i

men(n'(an arateri!ti 3ona!i altera!i #ang diha!ilan dari pendinginan progre!i" dan

netrali!a!i cairan magmati #ang didomina!i hot a!am oleh rea!i dengan bat(an ho!t dan air


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tanah) aria!i dalam ga#a minerali!a!i& and(ngan logam dan per(bahan mineralogi&

tergant(ng pada !(h( dan ompo!i!i cairan) D(a tahap altera!i dan minerali!a!i model

di(!(lan #ang men(n'(an baha cairan (ap #ang didomina!i aal mengembangan

diategorian& (m(mn#a pra per(bahan minerali!a!i& #ang o+erprinted dan bia!an#a

terbre!ian !elama in"l(5e! cairan #ang a#a cairan minerali!a!i) ,i!tem high !(l"ida!i adalah

tembaga a#a di edalaman dan ema! #ang a#a di tingat era #ang lebih tinggi)

-erbagai ga#a !i!tem ema! !(l"ida!i rendah mendomina!i di pengat(ran !(bd(!i miring& di

mana cairan magmati bermigra!i dari bat(an !(mber intr(!i e dalam ling(ngan #ang

mengand(ng air meteori #ang berbeda ompo!i!i dan !(h() Logam ela! dari ema! dan

em(nginan tembaga%bantalan di edalaman& melal(i ema! dengan logam da!ar di tingat

menengah& (nt( mengand(ng ema!%pera di tertinggi era tingatpengg(na6)


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pendek saja Southwest Pacific rim sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett & T Leach,

5/97 Edn.

(art3 !(l"ida ema! 8 tembaga !i!tem membent( pro!imal bat(an !(mber magmati&

ter(tama dengan pencamp(ran cairan magmati dengan mendalam beredar dingin dan encer

perairan meroet) /arbonat%da!ar !i!tem logam ema! terbent( pada tingat #ang lebih tinggi&

ter(tama oleh rea!i cairan magmati #ang didomina!i dengan p. rendah& C

2

%rich perairan) /(ar!a

!i!tem ema!%pera epitermal terbent( di tingat era tertinggi dan menampilan h(b(ngan

#ang paling di!tal e !(mber magmati) :ilai ema! -onan3a mengembangan !i!tem ini

dengan pencamp(ran lebih encer& mendidih& cairan magmati #ang dit(r(nan dengan

mengo!ida!i air tanah) /elompo ini #ang terahir dari depo!ito adalah tran!i!i e ad(laria%

!eri!it epithermal !i!tem ema!%pera +ena la!i) Tele!coping dapat menceta di berbagai ga#a

!(l"ida!i rendah minerali!a!i ema! pada !at( !ama lain ata( pada intr(!i !(mber por"iri)

Depo!ito ema! !edimen ho!t pengganti #ang di !ini tergolong geneti #ang terait dengan

!(l"ida!i rendah !i!tem (ar!a%!(l"ida& nam(n berembang pada bat(an arbonat reati")

Ad(laria%!eri!it epithermal depo!it ema!%pera terbent( pada pengat(ran era tinggi dengan

tida adan#a !(mber intr(!i 'ela! (nt( minerali!a!i ) ,i!tem ini berbeda dengan peningatan

edalaman dari6 (m(mn#a tand(! !(r"icial !inter ; depo!ito air pana!& (nt( !tocor (rat

+ena ; bre!i& dan "i!(ra) -at(an da!ar rap(h "rat(r bai dan !angat meaili ho!t ompeten

(nt( "i!!(re +ena dalam pengat(ran !tr(t(ral dilational) Reening model mendidih !elama

pengendapan dari perairan meteori dari mineral gang(e arateri!ti #ang terdiri banded

(ar!a& ad(laria dan p!e(domorphing (ar!a plat# arbonat) :am(n& berharga dan logam

da!ar #ang mendalilan har(! magmatic% bera!al dan teron!entra!i di band%a#a !(l"ida tipi!&

bia!an#a dengan mineral !(h( tanah liat rendah) Minerali!a!i arena it( dita"!iran telah

di!impan ter(tama oleh pencamp(ran (pelling& (m(mn#a mendidih& cairan minerali!a!idengan dingin& pengo!ida!i air tanah)

Model bi'ih ditent(an di!ini berg(na dalam !em(a tahap e!plora!i mineral& dari penga(an

ga#a depo!ito & (nt( penggambaran 'al(r aliran "l(ida !ebagai !arana menargetan bi'ih ela!

tinggi& ata( bat( !(mber por"iri)


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pendek saja Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett & T

Leach , 5/97 Edn.

ISI (! karakter#%t#k E)a%-Te)ba*a h#"r+ter)a$ S#%te) ((

i $endah(l(an 11 ii /on!ept(al model e!plora!i 11 iii /la!i"ia!i 12 i+ arateri!ti Fl(id 1=

2) $ana! -(mi Ling(ngan (nt( $aci"ic Rim i pengat(ran !i!temhidrotermal%pana! b(mi ati" 1> ii ,ilicic ben(a dan g(n(ng berapi !i!tem b(!(r hidrotermal 1>

iii /arateri!ti Filipina terait intr(!i !i!tem hidrotermal ati" 17 a 3ona!i Fi!io%imia dalam

!i!tem pana! b(mi Filipina 17 b -er(rangn#a Tahapan !i!tem pana! b(mi ati" 1? c Analogi

dengan !i!tem bi'ih pembent( 19 d Ga#a Filipina !i!tem hidrotermal ati" 2@ e


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saja pendek pengguna: rim sistem emas-tembaga Southwest Pacific: struktur, alterasi dan mineralisasi, G Corbett &

T Leach , 5/97 Edn.

c "le5(re! 47 d .anging dinding membagi 47 e re t(na! 47 +ii ,tr(t(r dalam r(ang dan

at( 4? +iii ,hear indiator ra!a 49 i5 $or"iri dan terait intr(!i pola "rat(r >@ a Meani!me

(nt( "rat(r pembang(nan >@ b $or"iri terait !i!tem "rat(r >1 1) tingat Tinggi pengat(ran >1

2) Deeper pengat(ran tingat >2 5 bre!i >4 a $endah(l(an >4 b /la!i"ia!i >> 1) i!tilah

de!ripti" >> 2) hal geneti > c $rimer non%hidrotermal bre!i > d bre!i hidrotermal re

terait >7 1) Magmati hidrotermal bre!i >7 2) phreatomagmatic bre!i @ =) bre!i "reati = 4)

dilational bre!i > >) Magmati hidrotermal bre!i in'e!i > ) hidrotermal bre!i r(nt(hn#a

7) $emb(baran bre!i 7 5i /e!imp(lan 7

4) ontrol pada hidrotermal per(bahan dan Minerali!a!i ? i $endah(l(an ? ii ,(h( dan p.

ontrol pada per(bahan mineralogi 9 a elompo ,ilica 7@ b al(nit elompo 7@ c /aolin

elompo 71 d elompo *llit 71 e elompo Chlorite 71 " Calc%!iliat elompo 72 g

elompo mineral lainn#a 72 i+ 3ona $er(bahan terait dengan !i!tem bi'ih 7= + /ontrol pada

depo!i!i "a!e gang(e 74 a ,ilica 74

b arbonat 7> c ,(l"at 7> +i /ontrol pada depo!i!i logam 7 a ema! 7 b tembaga 7? c

Memimpin dan !eng 77 d $era 7? e ema! ehal(!an 7?

>) ema!%tembaga ,i!tem di $or"iri Ling(ngan ?@ i $or"iri tembaga%ema! ?@ a ,tr(t(r ?@ 1)

Menetapan ?@ 2 ) pola Frat(r ; +ena ?@ b model aal dari altera!i dan minerali!a!i 3ona!i ?1

c model e'adian o+erprinting pol#pha!al di barat da#a !i!tem por"iri $aci"ic ?2


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pendek saja pengguna: Southwest Pacific rim sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett &

T Leach, 5/97 Edn.

1) Tahap *6 $erpindahan pana! dan per(bahan diategorian ?= 2) Tahap **6 =) Tahap ***6 pendinginan tahap ahir dan depo!i!i logam ?? 4) Tahap *6 $o!t%

mineral "ili& argili dan ma'( argili menceta 91 d Ringa!an 92 ii depo!ito "or!iterite 9= a

$endah(l(an 9= b $ro!e! pembent(an "or!iterite 94 1) prograd i!ochemical 94 2) prograd

meta!omatic 9> =) Retrograde 9 c "or!iterite bi'ih depo!ito 9 iii -re!i%ho!t ema! depo!ito

9? i+ $or"iri%terait ba!a depo!ito ema!%tembaga 9?

) Tinggi !(l"ida!i gold%Copper ,i!tem 1@@ i /arateri!ti 1@@ a /la!i"ia!i 1@@ b analog Acti+e

1@1 c D(a tahap altera!i dan minerali!a!i Model 1@2 1) acara a#a olatile%1@2 2) LiB(id a#a

acara 1@= d Minerali!a!i 1@= ii !i!tem tinggi !(l"ida!i dibent( !ebagai bah( (nt( intr(!i

por"iri 1@4 a /arateri!ti 1@4 b Contoh 1@> iii litologi diendalian !(l"ida!i tinggi !i!tem

ema!%tembaga 1@? a /arateri!ti 1@? b Contoh 1@? i+ ,ecara !tr(t(ral diendalian

!(l"ida!i tinggi !i!tem ema!%tembaga 112 a /arateri!ti 112 b Contoh 11= + Compo!ite

!tr(t(ral ; litologi diendalian !(l"ida!i tinggi !i!tem ema!%tembaga 11?

a /arateri!ti 11? b Contoh 11? +i .#brid tinggi%rendah !i!tem ema! !(l"ida!i 121 a

/arateri!ti 121 b Contoh 122 +ii Tinggi !(l"ida!i !i!tem ema! e5halati+e 124 a /arateri!ti

124 b analog Acti+e 124 c Contoh 12>

7) $or"iri%terait Lo !(l"ida!i ema! !i!tem 12 i /la!i"ia!i 12 a $endah(l(an 12 b r(tan

peri!tia 12 c 'eni! !(l"ida!i rendah !i!tem #ang berh(b(ngan dengan por"iri ema! 127 ii

(art3%!(l"ida ema! 8 !i!tem tembaga 12? a $endah(l(an 12? b menetapan ,tr(t(ral 129

c $er(bahan dan minerali!a!i 1=@ d Contoh 1=1 iii !i!tem ema! Carbonate%logam da!ar 141

a $endah(l(an 141


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Singkat saja pengguna: Southwest Pacific rim sistem emas-tembaga:. Struktur, alterasi dan mineralisasi, G Corbett &

T Leach, 5/97 Edn

b De"ini!i 141 c Di!trib(!i 141 d menetapan Geological 142 e ,tr(t(r 14= " altera!i dan

minerali!a!i 144 g 3ona!i dalam ga#a +ena dan minerali!a!i 14> h model aliran "l(ida 14 i

Contoh 14 ' /e!imp(lan 12 i+ !i!tem epitermal (ar!a ema!%pera 1= a $endah(l(an 1=

b /arateri!ti 1= c ,tr(t(r pengat(ran 14 d Contoh 1>

1) terait dengan minerali!a!i terait intr(!i 2) $eripheral (nt( intr(!i terait minerali!a!i 1? =)

terait dengan ad(laria%!eri!it epithermal !i!tem ema!%pera 17@ e /e!imp(lan 17> +

,edimen%ho!t pengganti depo!ito ema! 17 a Char acteri!tic! 17 b Contoh 177

?) ad(laria%,eri!it epitermal ema!%pera ,i!tem 1?@ i /la!i"ia!i 1?@ ii Contoh 1?1 iii Tetoni

menetapan 1?1 i+ ,tr(t(r 1?2 + /arateri!ti Cairan dan (bahan hidrotermal 1?= +i)

Minerali!a!i 1?4 +ii) Jeni! depo!ito ema!%pera epitermal 1?> a ,inter dan hidrotermal 0air

pana! depo!ito bre!i 1?> 1) /arateri!ti 1?> 2) Contoh 1? b +ena !tocor (ar!a

depo!ito ema!%pera 1?? 1) /arateri!ti 1?? 2) Contoh 1?? c Fi!!(re +ena ata( arang 1?9 1)

/arateri!ti 1?9 2) Contoh 1?9 9) /e!imp(lan 194 i $endah(l(an 194 ii model e!plora!i

ema!%tembaga di genera!i pro#e 194 model e!plora!i iii Gold%tembaga di pengintaian

pro!pe!i 19> i+ model e!plora!i ema!%tembaga dalam pro#e pembang(nan 19> + model

Fle!ibel 19 capan Terima /a!ih 19? Re"eren!i di(tip 19? Lampiran *) Da"tar ,ingatan 2=>

DAFTAR GAMBAR

1)1) $aci"ic rim minerali!a!i ema!%tembaga model 1)2) Da#a $a!i"i pele ema!%tembaga

e'adian 1)=) (ran +! ela! beberapa da#a $aci"ic rim tembaga%ema! e'adian 1)4)

$en(r(nan cairan !(l"ida!i tinggi dan rendah


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Singkat saja pengguna: Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett

& T Leach, 5/97 Edn

2)1)),i!tem pana! b(mi ati" dan depo!it bi'ih hidrotermal 2)2) Model on!ept(al (nt( !i!tem

eretaan pana! b(mi embali%arc !iliat 2)=) Model on!ept(al % b(!(r +(lani !i!tem

hidrotermal 2)4) /on!ept(al Model % hidrologi dari tingat dangal dalam !i!tem pana! b(mi 2&>)

Filipina % bidang pana! b(mi& pengat(ran tetoni& tambang tembaga%ema! dan pro!pe 2))

Lapangan pana! b(mi Tongonan % !tr(t(ral pengat(ran 2&7) Alto $(nca % model hidrologi 2&?)

Lapangan pana! b(mi -iliran % termal "it(r 2&9) ,i!tem pana! b(mi -iliran % on!ept(al cro!!

!ection 2)1@) Lapangan pana! b(mi Tongonan % on!ept(al cro!! !ection 2)11) -idang pana!

b(mi !elatan :egro! % pengat(ran 2)12) :egro! !elatan lapangan pana! b(mi % on!ept(al

cro!! !ection 2)1=) Lapangan pana! b(mi -acon%Manito % on!ept(al cro!! !ection 2)14)

Lapangan pana! b(mi -acon%Manito % on!ept(al cro!! !ection 2)1>) ,i!tem pana! b(mi di

olcanic arc%Cordillera pengat(ran 2)1) ,i!tem pana! b(mi Amacan % cro!! !ection 2)17)

Lapangan pana! b(mi Dalan % cro!! !ection 2)1?) Ac(pan % geologi pengat(ran 2)19) -ag(io

Di!trict& Filipina % ontrol !tr(t(ral dan per(bahan

=)1) $aci"ic Rim piring bata! =&2) /on+ergen!i dan "rat(r !i!tem !ebagai orthogonal terhadapmiring =)=) Da#a $aci"ic pele pengat(ran tembaga%ema! por"iri =)4) ,tr(t(r Tran!"er dan

!i!tem por"iri di $ap(a :e G(inea =&>) ,tr(t(r Con'(gate mentran!"er& magmati!me dan

per(bahan on+ergen!i =)) ,i!tem "rat(r dilational di pengat(ran orthogonal on+ergen!i =&7)

,tr(t(r #ang terbent( dalam h(b(ngan dengan gempa b(mi di *ran =)?) ,tr(t(r di

pengat(ran miring on+ergen!i =&9) ,i!tem "rat(r pada pengat(ran miring on+ergen!i =)1@)

-or peng('ian etegangan (rat minerali!a!i =)11) Central Ta!man lipat belt& tim(r A(!tralia =)12)

Mt M(ro& /alimantan& *ndone!ia =)1=) ena dilational =)14) $en#(l(han dan minerali!a!i ga#a

pada tingat era berbeda =)1>) G#mpie p(ll%terpi!ah ba!om dan ladang ema! =)1) Frat(r ;

+ena dan intr(!i por"iri =)17) Ling(ngan pembent(an bre!i =)1?) -re!i magmati%

hidrotermal % !(b +olani bre!i pipa =)19) -re!i magmati%hidrotermal % pipa t(rmalin bre!i&

Chili =)2@) -re!i phreatomagmatic =)21) -re!i "reati =)22) -re!i magmati%hidrotermal %

in'e!i bre!i

4)1) $er(bahan mineralogi (m(m dalam !i!tem hidrotermal 4)2) /ontrol (nt( (ar!a elar(tan

4)=) /ontrol (nt( al!it elar(tan 4)4) /ontrol (nt( barit dan anhidrit elar(tan 4)>) /elar(tan

A(& C( dan En relati" terhadap !(h( dan p. 4&) /ontrol elar(tan ema! 4&7) /ontrol !eng&

timah dan tembaga elar(tan 4)?) )1) ,illitoe dan Gappe Model tembaga por"iri >)2) Model tembaga por"iri tahap * dan **


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saja Pendek pengguna: Southwest Pacific pelek sistem emas-tembaga:. Struktur, alterasi dan mineralisasi, G Corbett

& T Leach, 5/97 Edn

>)=) $or"iri Model tembaga tahap ***a dan ***b >)4) r(tan paragenetic altera!i dan minerali!a!i

tembaga%ema! di !i!tem por"iri >)>) $or"iri per(bahan mineralogi >)) Di!trib(!i !pa!ial dan

temporal mineral tembaga%ema! >&7) ) /(da%*+aal % perm(aan per(bahan )) /(da%*+aal % penampang

per(bahan )7) Looo(t Roc! % rencana per(bahan )?) Looo(t Roc! % penampang

per(bahan )9) (da& Fi'i % !tr(t(r dan per(bahan )1@) (da& Fi'i % linta! on!ept(al bagian

)11) ila#ah a"i%-(lolo % !tr(t(ral pengat(ran )12) a"i& $ap(a :e G(inea % rencana

per(bahan )1=) a"i& $ap(a :(gini % bagian #ang pan'ang dari per(bahan )14) Ra""erte# ini

tembaga%ema! penampang on!ept(al& a"i )1>) Depo!ito :an!at!(& Jepang &1) Miah %

per(bahan )17) Miah % model on!ept(al )1?) Frieda%:ena % pengat(ran )19) Frieda%:ena %

per(bahan dan !tr(t(r )2@) :ena % per(bahan )21) :ena % cro!! !ection 47@@: )22) :ena %

cro!! !ection >2@@n )2=) :ena % per(bahan bagian pan'ang )24) Lepanto ; F,< % !tr(t(ralpengat(ran &2>) Lepanto ; F,< % geologi dan minerali!a!i )2) Mt /a!i& Fi'i % C,AMT ; ,tr(t(r

)27) Mt /a!i& Fi'i % !tr(t(r dan minerali!a!i model (nt( daerah pit terb(a )2?) $ea .ill %

!tr(t(r )29) $ea .ill % paragenetic (r(t &=@) $ea .ill % cro!! !ection )=1) Maragori %

pengat(ran )=2) Maragori % per(bahan )==) Maragori cro!! !ection )=4) -aone%-ineba!e&

,angihe Apaah& *ndone!ia &=>) An'ing liar % pengat(ran )=) ild Dog % geologi )=7) An'ing

liar % on!ept(al cro!! !ection )=?) Ma!(pa Ria % geologi

7)1) ,i!tem !(l"ida!i rendah ema!%tembaga % temporal dan !pa!ial 3ona!i 7)2) ,(l"ida!i rendah

!i!tem ema!%tembaga % la!i"ia!i dan model aliran "l(ida 7)=) ,i!tem ema!%tembaga !(l"ida!i

rendah % per(bahan 7)4) Depo!it ema! Ladolam % geologi 7)>) Depo!it ema! Ladolam % model

on!ept(al 7)) /id!ton % pengat(ran 7)7) /id!ton % geologi 7)?) /id!ton % paragenetic (r(tan7&9) /id!ton % di!trib(!i gang(e dan bi'ih "a!e 7)1@) -ilimoia % ,tr(t(r


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Kursus singkat pengguna: Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G

Corbett & T Leach, 5/97 Edn

7)11))-ilimoia % paragenetic (r(t 7)12) -ilimoia % model on!ept(al 7)1=) Araompa % paragenetic

(r(t 7)14) Araompa % inl(!i Data cairan 7)1>) ,i!tem ema! logam arbonat%ba!e % paragenetic

(r(t 7)1) ,i!tem ema! logam arbonat%ba!e % Data cairan inl(!i 7)17) ,i!tem ema! logam

da!ar arbonat % 3ona!i 7)1?) /elian % pengat(ran 7)19) /elian % geologi 7)2@) /elian % aliran

"l(ida +etor 7)21) /elian % arbonat gari! !pe!ie! 2>@ < 7)22) $orgera % pengat(ran 7)2=)

$orgera % ,tr(t(r 7)24) $orgera % ar(ari !tr(t(r 7&2>) $orgera % cro!! !ection 7)2) $orgera

% paragenetic (r(t 7)27) $orgera % di!trib(!i !pe!ie! arbonat 7)2?) -(lolo graben 7)29) Morobe

gold"ield% di!trib(!i +ertial !i!tem 7&=@) a( diatreme%maar omple! 7)=1) /erimenge %

ompo!it cro!! !ection 7)=2) oodlar *!land % !tr(t(r regional 7)==) -(!ai& oodlar *!land %

loa!i rencana penampang 7)=4) -(!ai % minerali!a!i cro!! !ection 7)=>) -(!ai % per(bahan

penampang 7)=) -(!ai % paragenetic (r(t 7)=7) Maniape % ,tr(t(r 7)=?) Maniape % cro!!

!ection 7)=9) Maniape % paragenetic (r(t 7)4@) Mt /are % arbonat%logam da!ar penampang

7)41)


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pengguna pendek saja: Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett

& T Leach, 5/97 Edn

?&7))aihi 0Martha .ill % !tr(t(r ?&?) .i!hiari % geologi ?&9) .i!hiari& Jepang % per(bahan

penampang

DAFTAR TABEL1)1) /arateri!ti $aci"ic pele minerali!a!i ema!%tembaga 1&2) $erbedaan antara !i!tem

rendah dan tinggi !(l"ida!i 2)1) Geoimia "l(ida dari beberapa !i!tem pana! b(mi Filipina dan

,elandia -ar( #ang dipilih =)1) /arateri!ti bre!i pipa 7)1) $erbandingan antara epitermal

(ar!a ema!%pera dan ad(laria%!eri!it epithermal depo!it ema!%pera


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pendek saja pengguna: Southwest Pacific rim sistem emas-tembaga:. Struktur, alterasi dan mineralisasi, G Corbett &

T Leach, 5/97 Edn

( 'ARA'TERISTI' e)a% TEMBAGA HIDROTERMAL SISTEM

# Pen"ahu$uan

ini adalah pand(an #ang dig(naan (nt( (r!(! !ingat dari nama #ang !ama di!a'ian pada/M ; ,


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integra!i ini dapat mengarah pada pengembangan model e!plora!i on!ept(al) ,tr(t(r (tama

meloali!a!i gangg(an dan !tr(t(r minor memberian per!iapan tanah) ,t(di tentang petrologi

mel(i!an ga#a altera!i dan minerali!a!i& arateri!ti cairan dan meani!me depo!i!i bi'ih)

,inte!i! !tr(t(r dan petrologi dapat menent(an 'al(r aliran "l(ida dalam !i!tem bi'ih

hidrotermal) mencari bi'ih mendorong e5plorationi!t! (nt( men'adi #ang pertama (nt(

mengembangan ata( meman"aatan e!plora!i on!ept(al


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Ga)bar/ 1/1

### '$a%#.#ka%#

,eb(ah la!i"ia!i !ederhana dig(naan (nt( membedaan dan menge+al(a!i ga#a #ang

berbeda dari da#a $aci"ic rim ema!%tembaga minerali!a!i 0Gambar) 1)1& Tabel 1) n!(r

la!i"ia!i ini adalah6 tingat era #ang mencerminan edeatan dengan !(mber magmati)

Tingat !(l"ida!i dila!i"ia!ian !ebagai !(l"ida!i tinggi ata( rendah mengac( pada

arateri!ti imia dari cairan minerali!a!i 0baah!ebagai6)

-erbagai tingat era pembent(an memberian da!ar (tama (nt( perbedaan ga#a #ang

berbeda ,i!tem $or"iri%ho!t di dalam ata( #g terleta di baah (nt( gangg(an di edalaman

bia!an#a lebih be!ar dari 1 m) Co5 dan ,inger 019?? memberian edalaman rata%rata =& m

(nt( depo!ito tembaga por"iri%mol#bden(m pl(toni& ter(tama dari $a!i"i tim(r& dan

edalaman rata%rata !eitar 1 m (nt( ema!%tembaga porph#rie! ha! lingaran $a!i"i barat

da#a) ,illitoe 0199=a meneanan tingat +ertial 01 m eH 2 m dan bent( !ilinder dari

depo!ito #ang terahir) Depo!ito ter!eb(t mengand(ng and(ngan logam terbe!ar dari ga#a

#ang berbeda dari da#a $aci"ic pele !i!tem ema! tembaga& tetapi nilai (m(mn#a lebih rendah

daripada ga#a lain dari minerali!a!i 0Gambar) 1)=& dan ini mer(paan target e!plora!i (tama

(nt( tona!e ma!!al& ela! rendah )

minerali!a!ipor"iri i!tilah dig(naan dalam man(al ini (nt( menggambaran tingat tinggi

menggangg( bat( bia!a& tetapi tida !elal( dengan te!t(r por"iriti& dan tida har(! bing(ng

dengan t(b(h tembaga%ema! por"iri dalam arti !empitpengg(na6)


5/97 Ednpengguna:.


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pendek saja Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett & T Leach,

5/97 ednpengguna:.


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5/97 ednpengguna:.


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pendek saja Southwest Pacific pelek sistem emas-tembaga: Struktur, alterasi dan mineralisasi, G Corbett & T Leach,

5/97 Edn.

depo!ito Me!othermal di'ela!an oleh Lindgren 01922 !ebagai Idibent( ))) pada !(h(

menengah dan teananI dan dalam la!i"ia!i ini terma!( orang%orang #ang diembangan

pada !(h( #ang lebih tinggi daripada depo!ito epitermal& #ait(H =@@oC 0.a#ba et al) 19?>)

Morri!on 019?? '(ga mengg(naan i!tilah me!othermal Lindgen (nt( +ena di!tri Charter!

Toer!& A(!tralia tim(r& !ementara .enle# dan -erger 0199= menga(i e!(litan melan'(tan

dengan epithermal i!tilah (nt( berbagai depo!ito #ang lebih dalam !eperti /elian& *ndone!ia

0-agian 7 )iii)') Da#a $aci"ic pele depo!ito me!othermal di'ela!an di!ini !ebagai (ar!a%

!(l"ida ema! 8 tembaga 0terma!( Charter! Toer! ata( arbonat%logam da!ar ema!

0terma!( /elian& (nt( menghindari ebing(ngan dengan pengg(naan me!othermal 'anga

dengan ,late -elt dan depo!it Mother Lode 0.odg!on& 199=& dimana depo!ito (ar!a%!(l"ida

m(ngin terait 0Morri!on& 19??) /(ar!a%!(l"ida ema! 8 tembaga dan arbonat%da!ar depo!ito

ema! logam dapat membent( !(mber da#a #ang c((p be!ar dan nilai ema! !edang

0Gambar) 1)=)

Depo!ito epitermal terbent( pada edalaman dangal dan !(h( (rang dari =@@oC 0.a#ba etal) 19?> dan menca(p berbagai depo!ito !(l"ida!i rendah dan tinggi) -eberapa& !(l"ida!i

ter(tama rendah& tampilan ditinggian i!i pera dan lain%lain ditandai dengan nilai logam

bonan3a melebihi =@ g ; t A( 0Gambar) 1)=) :ilai logam #ang lebih tinggi !et('( (nt(

penambangan baah tanah depo!ito& #ang bia!an#a membent( pemb(l(h darah "i!(ra&

ter(tama dalam pengat(ran !en!iti" ling(ngan 0mi!aln#a& .i!hiari& Jepang!ebagai6)

Ga#a #ang berbeda dari da#a $aci"ic rim !i!tem ema!%tembaga arena it( dila!i"ia!ian

$or"iri%terait hich incl(de!6

porph#r# copper%gold !arn copper%gold breccia gold%copper porph#r# 0and alaline

gold

.igh !(l"idation gold%copper) Altho(gh commonl# de!cribed a! epithermal in the geological

literat(re& high !(l"idation !#!tem! e5tend to the me!othermal and porph#r# regime!& and +ar#

"rom6

barren porph#r# !ho(lder!& !tr(ct(rall# controlled gold%copper& lithologicall# controlled

gold%copper& compo!ite !tr(ct(rall#%lithologicall# controlled gold%copper& h#brid !#!tem!

high%lo !(l"idation gold& e5halati+e gold)

Lo !(l"idation !#!tem! are gro(ped a!6

porph#r#%related depo!it! demon!trate the clo!e!t relation!hip to a magmatic !o(rce and "orm

a contin((m to progre!!i+el# !hallo cr(!tal le+el! and aa# "rom the intr(!ion !o(rce a!6

B(art3%!(l"ide gold 8 copper& carbonate%ba!e metal gold& epithermal B(art3 gold%!il+er&

!ediment%ho!ted replacement gold& ad(laria%!ericite epithermal gold%!il+er !#!tem! are

!(bdi+ided ith increa!ing depth a!6 !inter and h#drothermal breccia gold%!il+er 0hot !pring

depo!it! in ,illitoe& 199=b& !tocor B(art3 +ein gold%!il+er& "i!!(re +ein gold%!il+er&

Man# o" the!e term! are de"ined belo& and the characteri!tic! o" di""erent depo!it t#pe! and

!ome e5ample! are !(mmari!ed in Table 1)1)


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Short course manual: Southwest Pacific rim gold-copper systems: Structure, alteration and mineralization, G Corbett

& T Leach, 5/97 Edn.

#/ F$u#" Chara0ter#%t#0%

The ph#!ico%chemical characteri!tic! o" the h#drothermal "l(id! control the6

t#pe and B(antit# o" metal! tran!ported& proce!!e! hich prod(ce minerali3ation& locationo" the minerali3ation& herea! the characteri!tic! o" the ho!t roc control the mechani!m! o"

"l(id "lo 0.edenB(i!t& 19?7) A concept(al model "or the tran!portation o" "l(id! "rom a

dega!!ing magma to porph#r#& high !(l"idation and lo !(l"idation !#!tem! i! ill(!trated in

Fig(re 1)4 and the characteri!tic! o" high and lo !(l"idation !#!tem! compared in Table 1)2)

Co(ntr# roc! become more competent 0brittle a! a re!(lt o" contact metamorphi!m d(ring the

initial emplacement o" high le+el porph#r# intr(!ion!) Fract(ring i! initiated at the cooled margin!

o" the intr(!ion and e5tend! into the ho!t co(ntr# roc!) Cooling o" the porph#r# intr(!ion and

the parent melt i! accompanied b# the progre!!i+e e5!ol(tion o" di!!ol+ed !alt!& magmatic

+olatile! 0mainl# .

2

& ,

2

& C

2

& .

2

,& .F and .Cl& and

metal!& and their tran!"er into the "ract(red carapace 0.enle# and Mc:abb& 197?) Di!per!ion

and mi5ing o" the!e magmatic "l(id! ith circ(lating meteoric%dominated "l(id!& re!(lt! in the

3oned alteration and minerali3ation hich characteri3e! porph#r# copper depo!it! 0.enle# and

Mc:abb& 197?K eg& Gra!berg and -at( .i'a( in *ndone!iaK Tedi and $ang(na in $ap(a :e

G(inea) ,arn! "orm here minerali3ing porph#r# intr(!ion! are emplaced into calcareo(! ho!t

roc! 0eg&


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,& .Cl& .F and brine! are

channelled "rom the !o(rce intr(!ion (p deep !eated "ract(re;"a(lt 3one! and ri!e rapidl# ith

minimal roc reaction or mi5ing ith circ(lating meteoric "l(id!) The progre!!i+e

di!proportionation o" magmatic ,

2

into .

2

,

and .

2

,

4

ithin the +apo(r pl(me& occ(r! at temperat(re! belo appro5imatel# 4@@oC& and a!

the temperat(re decrea!e!& increa!ing amo(nt! o" .

2

,

4

and .

2

, are prod(ced 0R#e et al)& 1992) .

2

,

4

and .Cl

are in"erred to !tart to di!!ociate at temperat(re! o" aro(nd =@@oC 0.edenB(i!t and

Loen!tern& 1994& and progre!!i+el# "orm hot acidic "l(id! a! a re!(lt o" the tran!ition "rom ,

2

to .

2

,

4

) ithin dilational !tr(ct(re!

and;or permeable lithologie!& the!e hot acidic "l(id! mi5 ith circ(lating meteoric ater! and

react ith co(ntr# roc to "orm gold%copper depo!it! 0R#e& 199=) *nitiall# .edenB(i!t 019?7

termed the!e !#!tem! high !(l"idation a! !(l"(r i! in a high o5idation !tate o" 84& beca(!e o"

the dominance o" magmatic ,

2

) .oe+er&


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more recentl# 0.edenB(i!t et al)& 1994K hite and .edenB(i!t& 199>& the term high !(l"idation

ha! been (!ed to indicate the pre!ence o" the relati+el# high !(l"idation !tate !(l"ide mineral!

!(ch a! enargite& l(3onite and tennantite in the!e !#!tem!) The ab(ndance o" !(l"(r cannot be

(!ed !olel# a! a criteria to di!ting(i!h beteen lo and high !(l"idation !#!tem!) Altho(gh !(l"(r

!pecie! are commonl# ab(ndant in mo!t !o(the!t $aci"ic high !(l"idation !#!tem!& !ome lo

!(l"idation !#!tem! are !(l"(r%rich 0eg& Ladolam& $ap(a :e G(inea)


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*n lo !(l"idation !#!tem!& magmatic "l(id! hich contain di!!ol+ed reacti+e ga!e!& are red(ced

b# roc reaction and dil(tion b# circ(lating meteoric ater! 0,immon!& 199>) Thi! red(ction

re!(lt! in a "l(id dominated b# di!!ol+ed !alt! 0mainl# :aCl and b# .

2

, a! the main !(l"(r !pecie!& and i! interpreted 0Giggenbach&

1992 to occ(r at the root! o" lo !(l"idation !#!tem!& here circ(lating meteoric ater! acB(ire

magmatic +olatile! and probabl# metal!) *n thi! ca!e the !(l"(r i! pre!ent at an o5idation !tate o"

%2 0dominated b# .

2

, and a!

there"ore termed b# .edenB(i!t 019?7 a! lo !(l"idation) More recentl# 0eg& hite and

.edenB(i!t& 199>& the term lo !(l"idation ha! been (!ed to indicate the depo!ition o" lo

!(l"idation !(l"ide mineral! 0!(ch a! !phalerite& galena& chalcop#rite& "rom the!e red(ced& near%ne(tral p. "l(id!) nder the!e red(ced condition!& !(l"ide! are the onl# !econdar# !(l"(r%

bearing mineral!& ith p#rrhotite dominant abo+e =@@oC& and p#rite at loer temperat(re!

0Giggenbach& 19?7) Lo !(l"idation gold and gold%!il+er depo!it! incl(de6 Lihir and $orgera&

$ap(a :e G(ineaK /elian& *ndone!iaK /id!ton& ea!tern A(!traliaK Golden Cro!! and aihi&

:e EealandK .i!hiari& Japan)

*t i! interpreted herein& that there i! an e+ol(tion "rom porph#r# to lo !(l"idation%!t#le "l(id!

thro(gh progre!!i+e mi5ing o" the magmatic%deri+ed "l(id ith circ(lating "l(id! and ater%roc

reaction) The mi5ing o" lo !(l"idation& minerali3ed "l(id! ith circ(lating "l(id! o" di""erent

ph#!ico%chemical characteri!tic! prod(ce! depo!it! hich are 3oned +erticall# and hori3ontall#

ith relation to the !o(rce intr(!ion& "rom pro5imal high temperat(re to cooler di!tal !etting! a!6

B(art3%!(l"ide gold 8 copper& to carbonate%ba!e metal gold& and epithermal B(art3 gold%!il+er)

Ad(laria%!ericite epithermal gold%!il+er !#!tem! are "ormed mainl# "rom circ(lating boiling

meteoric ater! and are characteri3ed b# the pre!ence o" banded B(art3& ad(laria and B(art3

p!e(domorphing plat# carbonate) .oe+er& a !igni"icant proportion o" the gold minerali3ation in

the!e !#!tem! i! interpreted herein to ha+e depo!ited a! a re!(lt o" the B(enching o" circ(lating

"l(id!& hich ha+e incorporated the metal! "rom deep magmatic !o(rce!)


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*able 12


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1 GEOTHERMAL E&2IRO&ME&T FOR SOUTHWEST PACIFIC GOLD-COPPER

# Sett#n*% +. A0t#/e H3"r+ther)a$-Ge+ther)a$ S3%te)%

Geothermal !#!tem! !t(died o+er the pa!t to decade! pro+ide an increa!ed (nder!tanding o"the proce!!e! hich tae place d(ring the "ormation o" h#drothermal ore depo!it!) Geothermal

!#!tem! are enco(ntered in a ide range o" geological !etting! and each one ma# be

analogo(! to a di!tinct !t#le o" ore%"orming !#!tem) The!e can be cla!!i"ied in term! o" their

cr(!tal !etting and probable heat !o(rce 0eg& .enle#& 19?>aK Fig) 2)1)

Magmatic%!o(rced oceanic geothermal !#!tem! occ(r in a!!ociation ith6 oceanic cr(!t along

mid%ocean ridge!& ocean i!land +olcanoe! "ormed in relation to hot !pot!& bac%arc ba!in!& and

+olcanic arc! along inter%oceanic !(bd(ction 3one! 0de Ronde& 199>) ) Acti+e h#drothermal !#!tem! hich ha+e a magmatic heat !o(rce ma# be a!!ociated ith

cr(!tal ri"ting ithin a continental cr(!t& either in bac%arc ri"t 3one! 0eg& Ta(po olcanic Eone&

:e Eealand& or in continental ri"t 3one! 0eg&


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i! con!idered to be deepl# b(ried 0H>% m batholith! 0.edenB(i!t& 19?& o" in"erred

granite;granodiorite compo!ition& hich "ormed "rom melted continental cr(!t 0.enle#& 19?>bK

Fig) 2)2) ater recharge i! deri+ed "rom meteoric gro(nd ater! and the intr(!ion !(pplie!

heat& chloride& !ome ga!e!& and po!!ibl# other element!) The re!(ltant "l(id i! commonl#

termed chloride re!er+oir or chloride h#drothermal "l(id! in geothermal !cience!) -oiling occ(r!

at !hallo le+el! in re!pon!e to red(ced pre!!(re and "orm! near%!(r"ace to pha!e 3one!)The (pelling


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chloride h#drothermal "l(id& or chloride re!er+oir& generall# reache! the !(r"ace a! boiling

!pring!& hich depo!it !ilica !inter! either abo+e the main (p"lo 3one a!!ociated ith

h#drothermal er(ption crater! 0eg& Champagne $ool& aiotap(& and haai $ool& -roadland! in

:e EealandK .edenB(i!t& 199@6 Table 2)1& or in o(t"lo 3one! 0eg& raeiorao& :e

EealandK ,heppard and L#on& 19?4K ,immon! et al)& 1992) Minor 3one! o" acid !(l"ate "l(id!

re!(lt "rom the o5idation o" .

2

, in !(r"ace gro(nd ater! 0eg& Rotoaa& :e EealandK

/r(pp and ,eard& 19?76 aimang(& :e EealandK ,immon! et al)& 1992) C

2

%rich ater! "orm at !hallo le+el!

here the ga! i! ab!orbed into cool h#drothermal "l(id! or gro(nd ater& and the recharge o"

the!e ater! to depth! o" (p to 12@@ m ha! been recorded at the margin! o" the -roadland!geothermal "ield& :e Eealand 0.edenB(i!t& 199@)

Acti+e h#drothermal !#!tem! a!!ociated ith +olcanic arc terrain! di!pla# a n(mber o"

characteri!tic! hich are !igni"icantl# di""erent "rom tho!e in continental !ilicic en+ironment!

0.enle# and K Fig!) 2)2& 2)=) *n the!e !#!tem! meteoric recharge i!

t#picall# heated b# m(ltiple !hallo 02%= m porph#r# intr(!ion!& hich contrib(te !igni"icant

amo(nt! o" magmatic ga!e!& !ol(te!& and metal! to the circ(lating h#drothermal !#!tem 0.enle#

and Mc:abb& 197?) The (pelling ne(tral chloride "l(id! do not reach the !(r"ace abo+e the

(p"lo 3one! 0-ogie and Lale!!& 19?7) Thi! ma# be d(e to6 !ealing ca(!ed b# !ilici"ication

and carbonate;!(l"ate depo!ition at the inter"ace beteen !(r"icial and chloride "l(id! 0!ee

belo& the pre!ence o" good hori3ontal permeabilit#& or in!(""icient pre!!(re in the chloride

re!er+oir) .ori3ontal permeabilit# can be pro+ided b# either regional or !(b!idiar# !tr(ct(re!& or

poro(! p#rocla!tic (nit!) The topograph# in +olcanic terrain! abo+e the (p"lo 3one! i! t#picall#

!teep& and there"ore the pre!!(re 0ga! 8 hot h#dro!tatic i! in!(""icient to o+ercome thi! high

h#dro!tatic head) Rather& the chloride re!er+oir "l(id! "lo laterall# "or (p to >%1@ m to loer

ele+ation!& commonl# near !ea le+el 0-ogie et al)& 19?7K !ee Camb(cal ,pring chemi!tr#& Table

2)1) *n !ome ca!e! drilling ha! not enco(ntered circ(lating chloride h#drothermal ater! (ntil

(p to >@@%1@@@ m belo !(r"ace)

Fl(id chemi!tr# o" the deep circ(lating h#drothermal "l(id i! al!o !igni"icantl# di""erent beteen

!ilicic continental 0:e Eealand and magmatic arc 0$hilippine! geothermal !#!tem! 0Re#e!&

199>K Table 2)1) $hilippine geothermal !#!tem! locall# contain (p to >@ percent magmatic

component& herea! :e Eealand geothermal !#!tem! commonl# contain =%4 percent

magmatic component 0Re#e! et al)& 199=) The "l(id! in :e Eealand !#!tem! are dil(te 0

1@@@%2@@@ ppm Cl& herea! the $hilippine !#!tem! are almo!t an order o" magnit(de more

!aline 0(p to H 1@&@@@%1>&@@@ ppm Cl) *n addition& the $hilippine !#!tem! generall# e5hibit a

!igni"icantl# higher di!!ol+ed ga! content) The apparent !alinit# 0act(al !alinit# 8 di!!ol+ed

ga!e! o" $hilippine acti+e h#drothermal !#!tem! range! "rom 2% t percent :aCl& herea! the

apparent !alinit# o" :e Eealand !#!tem! i! generall# 1 t percent :aCl 0.edenB(i!t and


31/515

.enle#& 19?>b) The!e apparent !alinitie! o" $hilippine geothermal !#!tem! are comparable to

!alinitie! hich are deri+ed "rom "l(id incl(!ion anal#!e! on +ein! in porph#r#%related gold

depo!it! 0,ection 7) n the other hand& the apparent !alinit# o" "l(id! in :e Eealand

geothermal !#!tem! appro5imate! the dil(te "l(id compo!ition deri+ed "rom "l(id incl(!ion data

on banded B(art3%ad(laria +ein! hich ho!t epithermal gold%!il+er depo!it! 0.edenB(i!t and

.enle#& 19?>b)

The "olloing !ection in+e!tigate! the $hilippine acti+e porph#r# !#!tem! in more detail a! a

g(ide to the (nder!tanding& e5ploration& and de+elopment o" intr(!ion%related gold%copper ore

!#!tem!)

### Chara0ter#%t#0% +. A0t#/e Ph#$##ne Intru%#+n-Re$ate" H3"r+ther)a$ %3%te)%

a Ph3%#0+-0he)#0a$ 4+nat#+n% +. Ph#$##ne *e+ther)a$ %3%te)%

The "olloing "o(r di!tinct ph#!ical and chemical 3one! ha+e been identi"ied 0Mitchell and

Leach& 1991 in acti+e $hilippine h#drothermal !#!tem! 0Fig) 2)=6


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1) A Cond(cti+e 3one i! enco(ntered at depth in man# !#!tem!& t#picall# ithin impermeable

intr(!ion! or ba!ement !ediment!) .eat tran!"er i! predominantl# b# cond(ction d(e to lac o"

"ract(ring) here high%le+el intr(!ion! ha+e been emplaced into +olcanic roc!& impermeable

contact metamorphic mineral a!!emblage! compri!e biotite%magnetite and clinop#ro5ene 8

amphibole 8 biotite) Local !arn mineral a!!emblage! are enco(ntered at contact! beteen

intr(!ion! and calcareo(! !ediment! 0eg& Alto $ea& Le#teK Fig) 2)76 $alinpinon& ,o(thern

:egro!K Fig!) 2)11& 2)12)

2) A Con+ecti+e 3one "orm! ithin the (pelling pl(me o" all $hilippine geothermal !#!tem!&

ithin permeable deep%!eated "a(lt 3one! and !hatter 3one! at the intr(!ion contact!) The

re!er+oir "l(id i! commonl# !lightl# le!! than ne(tral p. 0>%& at 2>@oC d(e to !igni"icant

di!!ol+ed ga! content!& and i! !at(rated ith re!pect to B(art3 0.enle# et al)& 19?4) The

alteration e5hibit! a 3onation "rom6 pota!!ic 0predominantl# biotite ith minor !econdar#

"eld!par alteration at depth& to +ario(! prop#litic alteration 3one! dominated b# actinolite&

epidote& or chlorite%3eolite! at progre!!i+el# !halloer le+el!)

=) A To%$ha!e 3one i! enco(ntered at !hallo le+el! and in o(t"lo 3one! here the +apo(r

pre!!(re e5ceed! the con"ining pre!!(re& and re!(lt! in e5!ol(tion o" ater +apo(r and other

ga!e! 0mainl# C

2

& and le!!er

amo(nt! o" .

2

, "rom the h#drothermal "l(id) Thi! ga! e5!ol(tion 0or boiling can be initiated at

depth! o" 2 m or more in !ome !#!tem! 0-ogie and Lale!!& 19?7) Ab!orption o" the!e ga!e!at !halloer le+el!& into cool h#drothermal ater! or gro(nd ater!& re!(lt! in the "ormation o"

moderatel# lo p.& C

2

%rich ater!)

4) A $hreatic 3one 03one o" !at(ration compri!e! a n(mber o" gro(nd ater aB(i"er! hich are

perched abo+e the chloride h#drothermal !#!tem 0Fig) 2)=) C

2

ga!e!& hich e5!ol+ed "rom the to pha!e 3one at

depth& are ab!orbed into the!e gro(nd ater! to prod(ce C2

%rich ater!) The dega!!ing o" C

2

at the !(r"ace

prod(ce! ne(tral bicarbonate ater! hich commonl# depo!it tra+ertine depo!it! 0eg& Amacan

geothermal "ield& MindanaoK $:C%a)


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The o5idation o" .

2

, ga!e!& hich are al!o deri+ed "rom the to pha!e 3one at depth& can onl#

occ(r in the ado!e 3one 0ie the 3one o" aeration abo+e the phreatic 3one here ab(ndant "ree

o5#gen i! a+ailable) The o5idation o" .

2

, (pon contact ith the atmo!phere prod(ce! nati+e !(l"(r in h#drothermal

!ol"atara! b# a !erie! o" reaction! !(mmari!ed a! .

2

, 81;2

2

%%H ,o 8 .

2

0,choen et al)& 197=) The o5idation o" .2

, ithin

aerated gro(nd ater! prod(ce! cool !(l"(ric acid& or acid !(l"ate ater!& thro(gh a

complicated !erie! o" reaction! hich can be !(mmari!ed a! .

2

, 8 2

2

%%H .

2

,

4

0,choen et al)& 197=K !ee *li'an ,pring

chemi!tr#& Table 2)1) Leaching o" ho!t roc! at the !ite o" "ormation o" the acid !(l"ate ater!

prod(ce! poro(! !ilica alteration hich con!i!t! o" amorpho(! !ilica& cri!tobalite and;or

trid#mite) $rogre!!i+e ne(trali3ation in re!pon!e to all roc reaction and;or mi5ing ith gro(nd

ater "orm! 3one! o" !ilica%al(nite& !ilica%aolinite and !ilica%!mectite alteration 0,choen et al)&

197=) G#p!(m i! commonl# enco(ntered ith carbonate! near !(r"ace in mi5ed

bicarbonate;C

2

%rich and acid !(l"ate ater! 0Leach et al)& 19?K !ee Mala(na# !pring

anal#!e!& Table 2)1)

Cool acid !(l"ate ater! are al!o "ormed in a !(r"icial !(pergene en+ironment!& here the# are

related to the o5idation o" !(l"ide!& and rai!ed abo+e the ater table b# tectonic (pli"t or

e5po!ed b# ero!ion 0R#e et al)& 1992)


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,team%heated acid !(l"ate ater! "ormed in the +ado!e 3one and in !(pergene en+ironment!&

are di!tinctl# di""erent "rom hot !(l"(ric acid in high !(l"idation !#!tem! 0,ection ) *n the!e

magmatic en+ironment!& ,

2

and

.Cl ga!e!& hich are e5!ol+ed "rom the cr#!talli!ing melt& di!proportionate and di!!ociate at

!halloer 0ie cooler le+el! to "orm hot acidic "l(id! 0R#e& 199=K .edenB(i!t and Loen!tern&

1994) here the!e magmatic "l(id! reach the !(r"ace directl# magmatic !ol"atara! ma#

de+elop) Geothermal drilling in the $hilippine! attempt! to a+oid inter!ection o" the!e hot

corro!i+e "l(id!& altho(gh a! de!cribed belo& e5ploration o" (lcan&


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-iliran *!land& ha! enco(ntered magmatic%deri+ed acidic "l(id! at aro(nd 1 m "rom the !(r"ace)

Recent drilling at Alto $ea 0Re#e! et al)& 199= and Mt) $inat(bo 0R(a#a et al)& 1992

inter!ected 3one! hich ere dominated b# magmatic acid "l(id!)

b Wan#n* %ta*e% +. the a0t#/e Ph#$##ne %3%te)%

A! intr(!ion! cool and h#drothermal !#!tem! ane& the decrea!e in temperat(re and re!er+oir

pre!!(re re!(lt! in dra don o" !(r"icial ater! deep into the h#drothermal !#!tem) Cool& lo

p. C

2

%rich and acid !(l"ate

ater! ha+e been enco(ntered at depth! (p to 2@@@ m in !ome $hilippine geothermal "ield!

0Re#e!& 199@b) Don%hole pre!!(re;temperat(re 0Leach et al)& 19?& geochemical 0Lale!! et

al)& 19?=& and !table i!otope anal#!e! 0Robin!on et al)& 19?7 o" the!e ater! ha+e con"irmed

that the# are deri+ed "rom perched aB(i"er! in the phreatic and +ado!e 3one!)

Mi5ing o" cool& de!cending& lo p. !(l"ate and;or C

2

%rich !(r"icial "l(id! ith hot !ilica%!at(rated deep

h#drothermal "l(id! 0Fig) 2)4 re!(lt! in depo!ition o" carbonate! and !(l"ate! 0in re!pon!e to

increa!ing temperat(re! and !ilici"ication 0in re!pon!e to coolingK Leach et al)& 19?) A! the

h#drothermal !#!tem! are in+ariabl# located in tectonicall# acti+e area!& ma'or "ract(re;"a(lt

!#!tem! ma# be contin(all# reopened& permitting de!cent o" !(r"icial "l(id! to progre!!i+el#

deeper le+el!) The o+erall e""ect o" thi! i! to !eal mo!t permeable "eat(re! and "orm

impermeable cap! in the (pper le+el! o" the!e h#drothermal !#!tem! 0-ogie and Lale!!&

19?7)

Acid !(l"ate ater! ha+e been enco(ntered at !igni"icant depth! channelled don permeable

!tr(ct(re! 0eg& (p to 1>@@ m belo the !(r"ace in the -acon Manito geothermal "ieldK Re#e!&

199@a) The ater! maintain& to !ome e5tent& their acidit# to the!e depth! d(e to i!olation "rom

the deep ne(tral chloride "l(id!& po!!ibl# b# bro(ght abo(t b# all roc alteration and mineral

depo!ition ithin the !tr(ct(re!) The +ertical 3onation ithin the!e !tr(ct(re!& "rom !hallo to

deeper le+el! o"6 g#p!(m to anh#drite& and o" al(nite %%H al(nite 8 aolinite %%H dicite %%H

p#roph#llite 8 dia!pore in the!e !tr(ct(re! 0Leach et al)& 19?K Re#e!& 199@a& i! indicati+e o"

progre!!i+e heating and ne(trali3ation o" de!cending acid !(l"ate ater!)


38/515

2

%rich

ater! into the chloride re!er+oir)

The near%ne(tral chloride h#drothermal "l(id i! depleted in magne!i(m 0generall# 1 ppmK Table

2)1 and iron 0@)=%@)4 ppmK $RL -rone& per!) comm(n)K G(nnla(g!!on and Arnor!!on& 19?2

relati+e to calci(m 0H1@@%2@@ ppm "or $hilippine !#!tem!K Table 2)1) Altho(gh data on the

mangane!e le+el! in geothermal !#!tem! are generall# not a+ailable& the a(thor! in"er the!e to

al!o be lo& comparable to iron and mangane!e) n the other hand magne!i(m 0and probabl#

iron and mangane!e i! enriched in the lo p. C

2

%rich and acid

!(l"ate ater! 0Mala(na# !pring!& Table 2)1& and in !ome "eeder 3one! in ell! 0eg& don hole

!ample! at 14@@ m in C:%1& -acon Manito& and at ?>@ m in -R%& -roadland!) The pre!ence o"

Fe%& Mg% and Mn%carbonate! to deep le+el! in acti+e geothermal !#!tem! i! there"ore related to

the inc(r!ion o" C

2

%rich

!(r"icial ater!) A! calci(m i! common in both !(r"icial and deep "l(id!& calcite can be depo!ited

"rom both t#pe! o" "l(id! 0,immon! and Chri!ten!en& 1994)

*t i! interpreted herein that the de!cending acid !(l"ate and C

2

%rich ater! are locall# entrained in

"ract(re! hich contain (pelling chloride "l(id!) The mi5ing o" the!e "l(id! o" !(b!tantiall#

di""erent "l(id ph#!ico%chemi!tr# re!(lt! in the depo!ition o" !(l"ate!& carbonate! and B(art3 to

"orm mineral depo!it!& in a


39/515


40/515

Altho(gh drilling o" acti+e h#drothermal !#!tem! in the $hilippine! ha! not enco(ntered

economic porph#r# copper%gold ore& grade! o" @)1%@)2 percent copper ere recorded 0Mitchell

and Leach& 1991 "rom core hich contain! chalcop#rite%chlorite +einlet! hich c(t pota!!ic

alteration at $alinpinon) *n the Tongonan geothermal "ield& common chalcop#rite i! locall#

ab(ndant at depth aro(nd the contact! o" high le+el intr(!ion!) n the other hand& !phalerite

and galena are le!! ab(ndant and are re!tricted to the margin! and at !halloer cr(!tal le+el!0Are+alo& 19?)

Depo!it! o" !phalerite& galena& chalcop#rite and nati+e gold occ(r a! !cale! ithin $alinpinon

ell!& and are intergron ith anh#drite and barite gang(e mineral! 0AG Re#e!& per!)

comm(n)) The!e !cale! occ(r here there i! an in"lo o" !hallo acid !(l"ate ater!& and are

herein interpreted to re!(lt "rom entrainment and mi5ing o" the!e lo p. ater! ith deep !aline

chlorite "l(id! d(ring di!charge)


41/515

#G/ 2/!

,cale! depo!ited "rom deep chloride re!er+oir "l(id! in bac%pre!!(re plate! in !(r"ace pipeor

"rom the Tongonan geothermal "ield ha+e graded (p to ten! o" percent o" copper 0mainl# a!

tennantite& percent! o" lead and 3inc& tho(!and! o" ppm !il+er& and h(ndred! o" ppm gold 0R)

.arper and T) LeachK (np(bl) $:C%


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(p to H=@@%=>@oC) The!e in+e!tigation! ha+e permitted the in!pection o" potential ore%"orming

!#!tem! d(ring +ario(! !tage! o" de+elopment) Detailed petrological or 0eg& Re#e!& 19?>&

199@a& 199@bK Leach and -ogie& 19?2& Leach et al)& 19?=& 19? ha! been carried o(t on the!e

!#!tem!) Thi! ha! alloed 3onation! in alteration and minerali3ation ith "l(id chemi!tr# to be

compared to pre!!(re%temperat(re mea!(rement! at depth! "rom hich !ample! ere

reco+ered) The "ormation condition! o" the +ario(! mineral pha!e! ha+e there"ore been

empiricall# determined 0eg& Leach et al)& 19?K Re#e!& 199@b)

" St3$e% +. Ph#$##ne a0t#/e h3"r+ther)a$ %3%te)%

The $hilippine! i! a t#pical magmatic arc !etting "or porph#r#%related h#drothermal !#!tem!

0Fig) 2)>) :eogene magmatic arc! parallel the $hilippine trench to the !o(thea!t and the Manila

trench to the northe!t& and minor arc! are a!!ociated ith the :egro! and Cotabato trenche!

in the !o(the!t o" the $hilippine! 0Mitchell and Leach& 1991K Fig) 2)>) Circ(lating ne(tral

chloride h#drothermal !#!tem! in the $hilippine! ha+e not been enco(ntered in a!!ociation ith

large !trato+olcanoe! 0-ogie and Lale!!& 19? !(ch a! Mt) Ma#on and Mt) $inat(bo 0R(a#a

et al)& 1992) olcanic depo!it! deri+ed "rom the!e !trato+olcanoe! are t#picall# (ni"orm in

compo!ition thro(gh time 0eg& ba!altic ande!ite at Mt) Ma#on& indicati+e o" a deep 04%> m&

large& predominantl# (ndi""erentiated magma chamber)

Acti+e h#drothermal !#!tem! in the $hilippine! are& hoe+er& enco(ntered in the "olloing to

main geological;tectonic !etting! 0Re#e!& 199@bK Mitchell and Leach& 19916

1) Large h#drothermal !#!tem! are ho!ted in thic +olcanic or +olcanicla!tic !eB(ence!) The!e

!#!tem! occ(r ithin compo!ite +olcanic terrain! either parallel to !(bd(ction 3one! 0eg& Alto

$ea& $alinpinon& -acon Manito& and are probabl# deri+ed "rom di""erentiating magma

chamber! at !hallo cr(!tal le+el!K or occ(r ithin "a+o(rable !tr(ct(re!& !(ch a! dilational 'og!

and !pla#! related to ma'or "a(lt! 0eg& Tongonan& -iliran) The!e large con+ecti+e !#!tem! "orm

e5ten!i+e alteration haloe! hich are herein interpreted to be !imilar to porph#r#% copper;!arn

!#!tem!)

2) .#drothermal !#!tem!& ith re!tricted "l(id "lo path!& are ho!ted in dilational !tr(ct(ral

!etting! ithin competent and relati+el# impermeable ba!ement meta!ediment! and older

intr(!ion!& in Cordillera region! o"


43/515

e5hibit !(r"ace thermal mani"e!tation! that the# become target! "or geothermal energ#

e5ploration) All acti+e porph#r# !#!tem! drilled in the $hilippine! are interpreted herein to ha+e

alread# (ndergone the tran!"er o" heat into the ho!t co(ntr# roc 0!ee belo "or Alto $ea

hich ha! re!(lted in the "ormation o" horn"el! at the intr(!ion%+olcanic roc;!ediment contact!

0eg& Tongonan& $alinpion& Alto $ea& -acon%Manito& and 3oned !arn! in calcareo(! ho!t roc!

0eg& $alinpinon& Alto $ea)


44/515



2) Magmatic +olatile pl(me n -iliran *!land 0(lcan region and at Alto $ea& pl(me! o"

magmatic +olatile! are c(rrentl# being emplaced into pre%e5i!ting 3oned !arn and contact

h#drothermal alteration a!!emblage! 0Re#e! et al)& 199=K Lale!! and Gon3ale3& 19?2) Don

hole mea!(rement! indicate that the!e magmatic +apo(r! are po!!ibl# deri+ed "rom a +er# hot

0H=@@%4@@oC "l(id hich i! interpreted b# the a(thor! to ha+e e5!ol+ed d(ring earl#

cr#!talli3ation o" a high le+el melt 0belo& and ha! locall# +ented directl# to the !(r"ace a!

magmatic !ol"atara! 0eg& (lcan& -iliran *!))

=) Con+ecti+e h#drothermal alteration Relea!e o" heat and "l(id! "rom the high le+el intr(!ion!

e!tabli!he! deep circ(lating meteoric h#drothermal !#!tem! into hich magmatic "l(id! are

entrained 0.enle# and ) The

Tongonan geothermal !#!tem i! interpreted herein to c(rrentl# occ(r at thi! !tage o"

de+elopment) The high "l(id temperat(re! 0H=2@oCK Re#e!& 199@b and !alinitie! 0H1>&@@@ ppmCl%K Table 2)1 !(gge!t that a !igni"icant inp(t o" magmatic brine "rom the cooling melt ha! been

entrained into the con+ecting h#drothermal !#!tem) Altho(gh onl# minor ba!e metal

minerali3ation ha! been depo!ited "rom thi! hot& moderatel# !aline !#!tem 0Leach and eigel&

19?4K Are+alo& 19?& !igni"icant lead%3inc minerali3ation ha! been prod(ced b# "la!hing "l(id!

"rom depth! o" H2)> m to near ambient condition! ithin !(r"ace pipeor 0Mitchell and Leach&

1991) *t ha! there"ore been interpreted 0Are+alo& 19? that the circ(lating chloride brine at

Tongonan i! !(b!tantiall# (nder!at(rated ith re!pect to ba!e and precio(! metal!) .oe+er&

the depo!ition o" !igni"icant ba!e and precio(! metal minerali3ation can be ind(ced (nder

e5treme arti"icial condition! a! o(tlined abo+e)

4) Dra don o" !(r"icial ater! Cooling o" the intr(!i+e heat !o(rce i! herein interpreted toind(ce a pre!!(re dra don o" cool dil(te meteoric ater! and !hallo& moderatel# lo p.

acid !(l"ate and C

2

%rich ater! to con!iderable depth! ithin the

chloride re!er+oir 0eg& $alinpinon& -acon Manito) Thi! dra don o" !hallo%deri+ed ater! i!

interpreted 0eg& Re#e!& 199@b to re!(lt in the "ormation o" a 3oned ph#llic and later argillic

o+erprint! on pre%e5i!ting h#drothermal alteration) The dra don o" the!e "l(id! can re!(lt in

mineral depo!ition and !(b!eB(ent progre!!i+e !ealing o" permeable channel! at !hallo

le+el!& and the de+elopment o" an impermeable cap on the !#!tem 0Lale!! et al)& 19?=)

Altho(gh !#!tem! !(ch a! $alinpinon are dil(te relati+e to Tongonan 0Table 2)1 and interpretedherein to ha+e been drilled at a late !tage in it! e+ol(tion& the mo!t !igni"icant copper

minerali3ation inter!ected to date in a $hilippine geothermal !#!tem i! "rom $alinpinon)

#/ E5a)$e% +. A0t#/e Intru%#+n-Re$ate" H3"r+ther)a$ S3%te)% #n the Ph#$##ne%

a Lar*e "#%%e)#nate" %3%te)% #n er)eab$e h+%t r+0k% #n 0+)+%#te /+$0an#0 terra#n%

1) No(ng ,#!tem! Dominated b# Magmatic apo(r!


45/515

i Alto $ea Geothermal ,#!tem 0!(mmari!ed "rom Re#e! et al)& 199=

The Alto $ea geothermal !#!tem& in northern Le#te& i! ho!ted in a +olcanic arc hich e5tend!

along the ea!tern margin o" the $hilippine "a(lt 0Fig!) 2)>& 2)) Drilling ithin the Alto $ea

geothermal !#!tem inter!ected a !patiall# re!tricted magmatic +apo(r pl(me !o(rced "rom a

dega!!ing high le+el intr(!ion at depth 0Fig) 2)7)


46/515




47/515



Thi! +apo(r pl(me penetrate! into a ea& circ(lating& moderatel# !aline 07>@@ ppm Cl%

h#drothermal !#!tem& and at depth ha! ca(!ed a locali3ed ad+anced argillic alteration

a!!emblage to o+erprint on 3oned pota!!ic%prop#litic alteration)

The acti+e h#drothermal !#!tem at Alto $ea 0Fig) 2)7 i! ho!ted in $liocene to Recent ande!ite%

dacite +olcanic! and !(b+olcanic B(art3 diorite die!& hich pa!! don into a thic !eB(ence

0H2@@@ m o" Late Miocene to $lei!tocene& locall# calcareo(!& marine !edimentar# breccia!&

!ilt!tone!& m(d!tone! and h#alocla!tite! 0-inahaan Formation) -a!ement roc! compri!e

Cretaceo(! har3b(rgite and p#ro5enite)

Compo!ite +olcanic centre!& dome! and collap!e caldera! are de+eloped ithin dilational :

trending !egment! 0Alto and Cental "a(lt! o" the $hilippine "a(lt !#!tem) Additional permeabilit#

ithin the +olcanic% !edimentar# !eB(ence i! al!o pro+ided b# !(b!idiar# @ percent magmatic component& and i! deri+ed "rom a +er#

hot 0H4@@oC& !aline 0H17&@@@ ppm Cl% "l(id) *t i! interpreted herein that the !o(rce o" thi! "l(id

and the B(art3 diorite die! i! a dega!!ing recent intr(!ion at depth) Alteration at depth 017@@%

1?@@ m belo !(r"ace ithin thi! magmatic +apo(r%rich chimne# i! locali3ed along "ract(re!

and con!i!t! o" B(art3%p#roph#llite%al(nite 8 dia!pore%anh#drite and minor apatite& 3(n#ite and

topa3)

The +apo(r chimne# i! dominated b# C

2

a! the main ga! pha!e) Re#e! et al) 0199= interpreted that

the lac o" Cl%,

4

in the magmatic ater! 0de!pite the local occ(rrence o" magmatic%deri+ed ad+anced

argillic alteration indicate! that either the con+er!ion o" acidic o5idi3ing magmatic to ne(tral p."l(id! i! no complete& or it i! limited to region! o" the geothermal "ield hich ha+e not #et been

drilled) Recent drilling ha! in "act inter!ected permeable "ract(re 3one! hich prod(ce hot

acidic& magmatic%deri+ed acidic "l(id! 0AG Re#e! per!) comm(n)& 199>)

ii -iliran 0data "rom6 Mitchell and Leach& 1991K Lale!! and Gon3ale3& 19?2

The (lcan thermal area i! aligned "or =%4 m along a :< trending !(t(re 3one 0(lcan "a(lt

hich tran!ect! the i!land o" -iliran& north o" Le#te a! a po!!ible arc normal !tr(ct(re "ormed


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perpendic(lar to the $hilippine trench 0Fig) 2)?) The pre!ence o" !(per%heated !team& ,

2

ga!e! and .Cl conden!ate! in the (lcan

thermal area ha! been interpreted 0Lale!! and Gon3ale3& 19?2 to indicate that the (lcan

"a(lt i! directl# +enting hot magmatic +olatile! to the !(r"ace) The -iliran !#!tem i! there"ore

herein in"erred to repre!ent an acti+e analog(e o" high !(l"idation !#!tem!)

The geothermal !#!tem at -iliran i! ho!ted in ba!ement metamorphic! hich are o+erlain b#

=@@ m o" calcareo(! !ediment! and then b# a 1)>%2 m thic !eB(ence o" ande!itic +olcanic and

+olcanicla!tic roc! 0Fig) 2)9) There are no recent +olcanic! at the !(r"ace hich might

repre!ent the e5tr(!i+e roc eB(i+alent! o" an intr(!i+e !o(rce "or the heat and magmatic "l(id!

ithin the c(rrentl# acti+e h#drothermal !#!tem)


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Drilling peripheral to the (lcan "a(lt enco(ntered ne(tral "l(id! ith a !igni"icant "l(orine content

0(p to => ppm& compared to 1%= ppm "rom other $hilippine !#!tem!K Mitchell and Leach& 1991&

hich !(gge!t! that there i! a !igni"icant inp(t o" magmatic "l(id!) Drill hole -:%= inter!ected a

permeable 3one at aro(nd 1@@@ m& interpreted herein to be a !pla# o"" the (lcan "a(lt& and thi!

prod(ced +er# hot 0=1@%=2@oC& acidic 0p. = "l(id! 0Table 2)1)

Don hole temperat(re!& e!timated "rom alteration mineralog#& are loer than act(al mea!(red

temperat(re! in -iliran ell! 0Lale!! and Gon3ale3& 19?2& impl#ing that the h#drothermal

!#!tem i! !till heating (p) Drilling at -iliran "ailed to enco(nter an e5ten!i+e h#drothermal

!#!tem "or geothermal e5ploitation& po!!ibl# beca(!e o" the #o(th"(l nat(re o" the !#!tem)

The -iliran geothermal !#!tem ill(!trate! !trong !tr(ct(ral control "or the +enting o" magmatic

+olatile! "rom a dega!!ing magma at depth) The in"erred #o(th"(l nat(re o" the high !(l"idation

!#!tem at -iliran& implie! that the e5!ol(tion o" +olatile! "rom a dega!!ing magma& and the

"ormation o" hot acidic "l(id!& co(ld occ(r at an earl# !tage in the e+ol(tion o" a h#drothermal

!#!tem)

2) Circ(lating .#drothermal ,#!tem!

i Tongonan 0data "rom6 Leach et al)& 19?=K Are+alo& 19?K Re#e!& 199@bK Mitchell and Leach&

1991

The Tongonan geothermal "ield i! !it(ated in a 12 m long graben "ormed ithin a dilational 'og

in the $hilippine "a(lt& on the i!land o" Le#te 0Fig) 2)) Thi! 'og ha! been acti+e at lea!t !ince

the Miocene& and controlled the emplacement o" a n(mber o" intr(!ion! ranging "rom6 a large

B(art3 diorite to granodiorite 01@%11 Ma) pl(ton beteen the ea!t and central $hilippine "a(lt!&

diorite porph#rie! 0= Ma) along the margin! o" the older pl(ton& and recent "el!ic porph#rie! and

a!!ociated high le+el dacite pl(g! and die! emplaced along dilational !pla#! c(tting the dioritepl(ton 0Fig!) 2)& 2)1@) The heat !o(rce "or the c(rrentl# acti+e !#!tem i! interpreted to be a

deep melt hich ha! "ed the "el!ic die!) The !(ite o" intr(!ion! ere emplaced into a thic

!eB(ence o" Miocene to $liocene +olcanic!& and there are no +olcanic! that co(ld repre!ent

e5tr(!i+e eB(i+alent! o" the recent dacitic intr(!ion!) Ten m to the !o(thea!t& the +olcanic

centre! o" Mt) Janagdan and Alto $ea are aligned parallel to the trend o" !(bd(ction along the

$hilippine trench)

The high !alinit# o" the circ(lating h#drothermal "l(id! 0(p to 1&@@@ ppm ClK ell 4@7& Table 2)1

!(gge!t! that there i! a !igni"icant inp(t o" magmatic%deri+ed "l(id!) Condition! interpreted "rom

the alteration mineralog# in the ,ambaloran and Mahiao region! 0Fig) 2)1@ are generall#

comparable to tho!e deri+ed "rom don hole temperat(re and chemical anal#!e! 0Leach et al)&19?K Re#e!& 199@b) Thi! agreement beteen data "rom the alteration a!!emblage! and "l(id

condition! in thi! part o" the "ield !(gge!t! that there i! eB(ilibri(m beteen the "l(id! and all

roc& and i! herein interpreted to !(gge!t that the c(rrent !#!tem i! at lea!t !table& i" not a5ing)

n the other hand& argillic to ad+anced argillic alteration& ca(!ed b# de!cending cool lo p.

"l(id! 0eg& ell 4@2& Table 2)1& o+erprint! earlier pota!!ic and inner prop#litic a!!emblage!

a!!ociated ith diorite intr(!ion! along the branche! o" the $hilippine "a(lt) The ne(tral chloride

"l(id! migrate laterall# 0o(t"lo along the central $hilippine "a(lt& and +ent to the !(r"ace a!


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ne(tral chloride !pring! at loer ele+ation! in the -ao alle#& >% m to the !o(the!t)

The Tongonan geothermal "ield i! an e5ample o" a !#!tem in hich there i! !trong !tr(ct(ral

control to the !etting o" intr(!ion emplacement and a!!ociated o+erprinting porph#r#%!t#le

h#drothermal !#!tem!) The large dilational "a(lt 'og hich ho!t! the geothermal !#!tem ha!

been reacti+ated !e+eral time! and alloed the emplacement o" di""erent generation! o"

intr(!ion!) Thi! !trong !tr(ct(ral control o" m(ltiple porph#r#%!t#le h#drothermal !#!tem! at

Tongonan i! analogo(! to the tectonic control de!cribed herein "or the emplacement o"

intr(!ion! a!!ociated ith man# circ(m $aci"ic porph#r# copper depo!it! 0eg& Nandera& $ap(a

:e G(ineaK


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Title# et al)& 197?)

=) Collap!ing .#drothermal ,#!tem!

i ,o(thern :egro! Geothermal Field 0data "rom6 ,ea!tre!!& 19?2K Leach and -ogie& 19?2KEaide& 19?4K Re#e!& 199@bK Mitchell and Leach& 1991

To geothermal !#!tem! occ(r ithin the C(erno! de :egro! +olcanic centre) The!e are the

northern $alinpinon and the !o(thern -a!la#%Da(in "ield! 0Fig) 2)11) The +olcanic centre

compri!e! tin pea!& dacite dome!& and para!itic cone! to the !o(th and ea!t& and a

p#rocla!tic platea( to the north) The mo!t recent p#rocla!tic "lo! 014&@@@ #ear! -$ are dacitic

and ere er(pted "rom a +ent 2 m north o" the !(mmit crater!)

The $alinpinon geothermal !#!tem i! ho!ted in a 1)> m thic !eB(ence o" Miocene%Recent

+olcanic! hich o+erlie % m north o" the $alinpinon

geothermal !#!tem& a! ell a! in a belt e5tending north along the i!land o" :egro! and into

Ma!bate *!land 0Mitchell and Leach& 1991)

$h#llic alteration 0illite;m(!co+ite%B(art3%p#rite 8 anh#drite 8 carbonate occ(r! at !hallo le+el!

ithin a to%pha!e 3one dominated b# mi5ed C


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2

%rich and acid !(l"ate ater!& and at depth o+erprinting

earlier pota!!ic and prop#litic alteration 0Leach and -ogie& 19?2K Re#e!& 199@b) *t i! !pec(lated

b# the a(thor! that the deep ph#llic o+erprint ha! been ca(!ed b# the dra don o" !hallo

ater!)


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"ormed earl# in the e+ol(tion o" the $alinpinon !#!tem& and are !trongl# !tr(ct(rall# controlled b#

"a(lt! hich "acilitated the emplacement o" the m(ltiple porph#r# intr(!ion!) At pre!ent& the

$alinpinon acti+e porph#r# !#!tem i! at an earl# !tage o" collap!e& !(ch that cool acid !(l"ate&

C

2

%rich and meteoric ater! are

de!cending in re!pon!e to pre!!(re dra don) Thi! dra don ha! created a ph#llic alteration

o+erprint on the e5i!ting 3oned prop#litic%pota!!ic alteration) The relati+el# dil(te 07&@@@ ppm

Cl nat(re o" the!e "l(id! !(gge!t! that there i! onl# a minor magmatic inp(t at thi! !tage o"

e+ol(tion o" the h#drothermal !#!tem)

The geological !etting o" $alinpinon ha! man# !imilaritie! to the $ang(na porph#r# copper

depo!it& -o(gan+ille& $ap(a :e G(inea 0-aldin et al)& 197?& here m(ltiple minerali3ing

porph#r# intr(!ion! ere emplaced at the margin o" a large B(art3 diorite pl(ton) Thegeochemi!tr# and don hole temperat(re;pre!!(re data "rom the -a!la#%Da(in geothermal

"ield& m to the !o(th& i! interpreted 0.arper and Are+alo& 19?2 to indicate that thi! !#!tem

probabl# relate! to a !eparate !erie! o" intr(!ion! at depth& hich are co%genetic ith the

C(erno! de :egro! +olcanic!)

ii -acon%Manito Geothermal Field& ,o(thern L(3on 0data "rom6 Lale!! et al)& 19?=K Re#e!&

19?>K Mitchell and Leach& 1991

The -acon%Manito geothermal "ield occ(r! in the -icol +olcanic arc in !o(thern L(3on& mida#

beteen the acti+e large !trato+olcanoe! o" Ma#on and -(l(!an 0Fig) 2)>) The -acon%Manito

h#drothermal !#!tem i! ho!ted in a comple5 compo!ite +olcanic terrain o" dome!& pl(g!& and

collap!ed caldera! ranging in compo!ition "rom dacite to ba!altic ande!ite) p to 2?@@ m o"+olcanic roc! compri!ing mainl# ande!ite!& b(t ranging "rom dacite to ba!alt& o+erlie a

!(cce!!ion o" Miocene to @@ m 0Lale!! et al)&

19?=K eg& Table 2)1& 14@@ m don hole !ample& C:%1& ca(!ed progre!!i+e o+erprinting


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alteration e+ent! 0Fig) 2)14) The de!cent o" cool& lo p. "l(id! into hotter en+ironment! ha!

re!(lted in ide!pread depo!ition o" carbonate!& !(l"ate!& and !ilica ca(!ing the (pper 1@@@ m

to become impermeable 0Leach et al)& 19?) The!e "l(id! ha+e "ormed e5ten!i+e ph#llic and

local argillic alteration hich o+erprint pota!!ic alteration ithin& and pro5imal to& the Caa#an

intr(!ion!) *t i! !pec(lated herein that the dra don o" acid !(l"ate and C

2

%rich ater! a!

ca(!ed b# the aning o" the heat !o(rce "or the h#drothermal !#!tem in the Caa#an region)

The m(ltiple high le+el intr(!ion!& and o+erprinted pota!!ic%prop#litic& ph#llic and argillic

alteration a!!emblage! at Caa#an& are !imilar to "eat(re! recorded in the


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Miocene age and locall# containing o(tcropping porph#r# copper depo!it!& and Me!o3oic

metamorphic ba!ement comple5e! 0Mitchell and Leach& 1991)

Recentl# emplaced !hallo le+el pl(g! and !toc!& commonl# along contact! o" pre%e5i!tingintr(!ion!& are herein interpreted to repre!ent the heat !o(rce! "or h#drothermal !#!tem!)

Dacite dome!& diatreme breccia! and a!!ociated p#rocla!tic roc! "orm e5tr(!i+e pha!e! o"

the!e pl(g! and !toc!) Meteoric recharge originate! at ele+ation! higher than the acti+e

h#drothermal !#!tem) The re!triction o" +ertical permeabilit# to !tr(ct(re!& and dome and

diatreme contact!& ca(!e! the chloride "l(id! to approach the !(r"ace ithin con"ined (p"lo

"eat(re!& thereb# "acilitating the mi5ing o" the (pelling "l(id! ith !(r"icial C

2

%rich and acid !(l"ate "l(id!) Di!tal

o(t"lo! "ollo dilational !tr(ct(re! and "orm dil(te ne(tral chloride !pring! at loer ele+ation!)

The!e acti+e h#drothermal !#!tem! a!!ociated ith +olcanic arc! in cordillera !etting! areanalogo(! to porph#r#%related B(art3%!(l"ide gold 8 copper& carbonate%ba!e metal gold& and

epithermal B(art3 gold%!il+er depo!it! de!cribed herein 0,ection 7)

i Amacan Geothermal Field 0data "rom6 -arnett et al)& 19?>K $:C%aK Mitchell and

Leach& 1991

The Amacan geothermal "ield in :orth Da+ao& ea!t Mindanao 0Fig) 2)> i! ho!ted in Me!o3oic

metamorphic and


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2

%rich !(r"icial ater!& or a !igni"icant inp(t o"

magmatic +olatile! into the circ(lating h#drothermal !#!tem)

ii Dalan Geothermal Field 0data "rom6 $:C%


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The Ac(pan gold mine& 1> m !o(thea!t o" -ag(io 0Fig!) 2)>& 2)19 e5ploited gold minerali3ation

ho!ted in :< trending !tr(ct(re! hich c(t the 1 Ma -alatoc diatreme and a!!ociated dacite

pl(g 0Fig) 2)1?) The diatreme and pl(g 0an endogeno(! dome ere emplaced into a !erie! o"

older Miocene to $liocene intr(!ion! and ande!ite +olcanic roc!) .ot ater !eepage! ere

common thro(gho(t the (pper le+el! o" the Ac(pan gold mine& and !team and boiling ater

di!charge! at deeper le+el!) Geothermal drilling enco(ntered onl# minor permeabilit# ithin the

diatreme at aro(nd 1@@@%12@@ m depth)

A compari!on o" don hole condition! 0$:C%b and "l(id incl(!ion data 0,ain! et

al)& 1979K Cooe and -loom& 199@ !(gge!t! that the ater and !team enco(ntered in the mine

are mani"e!tation! o" the d#ing pha!e o" a once e5ten!i+e h#drothermal !#!tem hich depo!ited

the gold minerali3ation 0Cooe and -loom& 199@) The !t#le! o" alteration and minerali3ation at

the Ac(pan mine are de!cribed in more detail in ,ection 7)iii on carbonate%ba!e metal gold

depo!it!)

/ C+n0$u%#+n%

1) T#pe! o" Acti+e $orph#r# ,#!tem!

Acti+e geothermal !#!tem! in the $hilippine! pro+ide in!ight! into the proce!! o" "ormation o"

porph#r# copper and porph#r#%related gold depo!it!) Drilling to depth! o" o+er =)> m& o+er

more than 2@%=@ !B( m& enable! the de+elopment o" comprehen!i+e alteration& minerali3ation&

and "l(id "lo model! "or the!e acti+e porph#r# !#!tem!)

*ntr(!ion%related acti+e h#drothermal !#!tem! in the $hilippine! are o" to main t#pe! 0Re#e!

199@b& either6 i large di""(!e !#!tem! ad'acent to& or "laned b#& compo!ite ande!itic +olcanic

comple5e! 0eg& Tongonan& $alinpinon& -acon%Manito& or ii !maller !#!tem! a!!ociated ith

dacite or !ilicic ande!ite pl(g! or dome! ho!ted in cordillera !etting! 0eg& Amacan& Dalan& Ac(pan)

The large geothermal !#!tem! at Tongonan& $alinpinon& and -acon%Manito& are a!!ociated ith

permeabilit# pro+ided b# either regional !tr(ct(re!& or compo!ite +olcanic en+ironment!)

,hallo 02%= m m(ltiple intr(!ion! and;or parent melt! at depth repre!ent the heat !o(rce!

and po!!ibl# pro+ide a !igni"icant component o" magmatic "l(id! "or the circ(lating h#drothermal

!#!tem) *n !(ch !etting!& intr(!ion! are emplaced into !eB(ence! o" relati+el# permeable

"ract(red +olcanic roc!) Thi! ide!pread lateral permeabilit# ca(!e! "l(id! to permeate a

!igni"icant roc +ol(me& thereb# prod(cing large area! o" alteration and minerali3ation 3onation!

hich are comparable to man# porph#r# copper%gold !#!tem!)

*" intr(!ion! are emplaced into ba!ement !edimentar#& metamorphic or intr(!i+e roc! hichocc(r ithin the cordillera region! o" the $hilippine!& h#drothermal "l(id "lo ill be re!tricted to

permeable !tr(ct(re! and intr(!ion contact!) .ere& +olcani!m i! limited to dome!&

diatreme;maar +olcano comple5e!& and a!!ociated p#rocla!tic material) The con"inement o"

"l(id! to narro permeable 3one! permit! the chloride h#drothermal "l(id! to reach +er# !hallo

cr(!tal le+el!& here the# are able to interact ith gro(nd ater& C

2


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%rich and acid

!(l"ate ater!) Thi! t#pe o" acti+e h#drothermal !#!tem i! po!t(lated to be analogo(! to the lo

!(l"idation intr(!ion%related gold depo!it! enco(ntered thro(gho(t the !o(the!t $aci"ic rim

0,ection 7)

2)


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,(b!eB(ent cooling o" the intr(!ion! ha! been accompanied b# e5!ol(tion o" "l(id! and the

"ormation o" magmatic +apo(r pl(me! 0eg& Alto $ea and -iliran) Fl(id "lo ma# be controlled

b# the !ame dilational !tr(ct(re! hich "acilitated the emplacement o" the intr(!ion) The!e

+apo(r! can +ent to the !(r"ace a! magmatic !ol"atara! 0eg& (lcan) The progre!!i+e

di!proportionation o" magmatic ,

2

& and the di!!ociation

o" .Cl and .

2

,

4

are in"erred to "orm acidic "l(id! hich locall# prod(ce an ad+anced argillic

o+erprint on the earlier high temperat(re contact alteration 0eg& Alto $ea)

Con+ecti+e h#drothermal !#!tem! de+elop hen the heat pro+ided b# an intr(!ion at depth& and

po!!ibl# al!o b# +enting magmatic "l(id!& re!(lt! in the "ormation o" circ(lating meteoric%

dominated h#drothermal !#!tem! at higher cr(!tal le+el!)


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6 STRUCTURE OF MAGMATIC ORE SYSTEMS

# Intr+"u0t#+n

.#drothermal !#!tem! de+elop "rom the interpla# o" "l(id! and !tr(ct(re!& a! ell a! man# other +ariable! !(ch a! hot roc t#pe& temperat(re& geochemi!tr# etc) Fl(id! "acilitate !tr(ct(ral

d#namic! and the !tr(ct(re! di!trib(te "l(id! into the !(rro(nding roc!) -rittle "ract(ring ithin

competent ho!t roc! in the (pper portion o" the cr(!t pro+ide! permeabilit# "or the "ormation o"

magmatic%arc gold%copper alteration and minerali3ation) er# large B(antitie! o" "l(id ma# be

reB(ired to tran!port economic B(antitie! o" gold) At !ol(bilitie! o" 1@ ppb 0Fig) 4)& 1@ %7 litre!

o" "l(id 0or abo(t the eB(i+alent o" an ol#mpic !imming pool o(ld be reB(ired to tran!port

abo(t = o(nce! o" gold 0-ron& 19?)

Ma'or regional cr(!tal !tr(ct(re! act a! cond(it! "or ri!ing porph#r# intr(!ion! hich are the heat

!o(rce! "or h#drothermal !#!tem!) Fl(id! e5!ol+e "rom porph#r# intr(!ion!& mi5 ith gro(nd

ater! and depo!it mineral! in peripheral !etting! and "ill "ract(re! a! +ein!& or the open !paceithin breccia!) Mo+ement on the ma'or controlling !tr(ct(re! commonl# create! ore%ho!ting

dilational en+ironment! in high angle !(b!idiar# !tr(ct(re!& partic(larl# in !etting! o" obliB(e

con+ergence) Drilling grid orientation! !ho(ld tae the!e ang(lar relation!hip! beteen the

!tr(ct(ral grain o" a di!trict and !(b!idiar# minerali3ed !tr(ct(re! into con!ideration)

,t#le! o" minerali3ation and "ract(re pattern! in o(tcrop !cale ma# be go+erned b# tectonic

!etting at continental !cale)


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direction o" dip and mo+ement& and dip! (nder the magmatic i!land arc 0eg& -anda& Mariana

arc!K Fig!) 1)2& =)1) D(ring !(bd(ction& continental roc! and o""!hore !ediment! ma# become

metamorpho!ed and de"ormed and de+elop into a mo(ntaino(! accretionar# pri!m 0eg& the

.ighland! o" $ap(a :e G(inea) $artial melting o" !(bd(cted continental and oceanic material

at depth ill gi+e ri!e to magmatic i!land arc! hich con!tit(te +olcanic and +olcanicla!tic roc!

at !(r"ace and pa!! donard to intr(!ion pha!e!) $orph#r# intr(!ion! are emplaced at depth!o" 1%2 m& hile di""erentiated "el!ic and +olatile%rich intr(!ion! ma# ri!e to


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higher cr(!tal le+el!& and large batholithic bodie! occ(r at greate!t depth!) nder ideal

condition! "l(id! ma#

#G/ "/1

e+ol+e "rom the porph#r# en+ironment to "orm lo and high !(l"idation gold%copper

minerali3ation o(t!ide the porph#r# en+ironment) The cla!!i"ication o" ,illitoe 01992 ha! been

modi"ied to categori3e "o(r tectonic !etting! "or !o(the!t $aci"ic rim ore%related magmati!m a!6

a rthogonal con+ergence

*n orthogonal con+ergence to plate! collide at angle! o" ro(ghl# 9@o to each other in a manner

!imilar to the !cenario de!cribed abo+e)


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o" the $aci"ic plate "acilitated the "ormation o" the no di!membered i!land arc! e5tending "rom

the i!land! o" Man(! to :e *reland& :e -ritain& and -o(gan+ille in $ap(a :e G(inea& and

G(adalcanal the ,olomon *!land!& b(t cea!ed ith the 'amming o" !(bd(ction b# the tong

Ja+a $latea( 0Fig) 1)2K Da+ie!& 1994 and re"erence! therein) hile Miocene porph#r#

minerali3ation at :e -ritain 0Title#& 197? and Man(! *!land 0Ma!on and McDonald& 197?

de+eloped (nder condition! o" orthogonal con+ergence& #o(nger !#!tem! are de!cribed belo)

Anal#!e! o" +ein and "ract(re pattern! "ormed in a!!ociation ith porph#rie! emplaced in

orthogonal arc! !(gge!t that man# intr(!ion! "ormed d(ring e5ten!ion regime!) Tectonic

rela5ation ithin an o+erall contractional en+ironment pro+ide! one po!!ible mechani!m "or

locali3ed e5ten!ion in both time and place) :on%planar and high angle !tr(ct(re! in orthogonal

arc! ma# al!o "acilitate locali3ed e5ten!ion) Rela5ation ma# tae the "orm o" a re+er!al o"

orthogonal con+ergence& or change to obliB(e con+ergence) Molten +olatile%rich magma hich

ha! been con!trained at depth d(ring orthogonal con+ergence& ma# be ind(ced to ri!e rapidl# to

"orm porph#r# intr(!ion! (nder the!e changed condition!) Mineral depo!ition occ(r! at highercr(!tal le+el! (nder cooler condition!) ,etting! o" orthogonal con+ergence are cond(ci+e to the

"ormation o" porph#r# copper% gold depo!it! in hich mo!t minerali3ation occ(r! clo!e to& or

ithin& the intr(!ion)

b bliB(e con+ergence

*n !etting! o" obliB(e con+ergence 0Fig!) =)1& =)2& the plate! !lide pa!t each other) Ma'or

tran!c(rrent "a(lt !#!tem! accommodate m(ch o" the di!placement 0eg& $hilippine "a(lt&

$hilippine!& Fig!) 2)1& 2)>K ,(matran "a(lt !#!tem& *ndone!ia& Fig) 1)2K Alpine "a(lt& :e

Eealand& Fig) 7)47K (een Charlotte "a(lt& e!tern CanadaK ,an Andrea! "a(lt& e!tern ,A)

,o(the!t $aci"ic arc! characteri3ed b# !etting! o" obliB(e con+ergence incl(de6 the $liocene

to Recent in :orthern L(3on and Mindanao in the $hilippine!& and the c(rrent e!tern portion o"

the -anda arc in *ndone!iaK $lio%$lei!tocene Taian 0,illitoe& 1992 and the rdo+ician%,il(rian

o" the Lachlan "old belt 0belo) Anal#!e! o" "ract(re !#!tem! !(gge!t that minerali3ation

de+elop! in man# orthogonal magmatic arc! d(ring locali3ed cha

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