ClassificationofPorphyry-RelatedDeposits_Seedorf

Classification of Porphyry-Related

Deposits

Eric SeedorffDirector, Lowell Program in Economic Geology

Department of Geosciences

University of Arizona

Main points, I.

Porphyry deposits grouped into five classes based on the economically dominant metal in the deposits Gold, copper, molybdenum, tungsten, tin

Five classes are further subdivided Total of 13 subclasses

For ease of recognition, names of subclasses are combinations ofigneous rock compositions and major and by-product metals

Nonetheless, for both practical and theoretical reasons, deposits not classified strictly on the basis of either Igneous rock analyses, or

Metal ratios

Lower level groupings Related to structural style of alteration-mineralization

Provisions also made for other dimensions of variability

Main points, II. Correlation of igneous compositions with types of major and by-product metals Reflects first-order control of magmatic composition on source and transport of metals

Importance of magmatic processes also is reflected by Correlation of magmatic compositions with metal suites observed in distal, low-temperature veins

Rough correlation of magmatic compositions with metals observed in high-sulfidation epithermal deposits--more mafic igneous compositions with Cu-Au and more silicic compositions with Ag-rich advanced argillic alteration

Exploration consequences Metal suites observed in distal, low-temperature veins and in high-sulfidation epithermal deposits can be used to target specific subclasses of porphyry systems

Historical methods of classification

Principal metals Cu-Mo, Cu-Au-Mo, Cu-Au, Mo, etc.

Morphology of orebodies (function of tectonic setting and depth of emplacement) Plutonic, volcanic, classic

Tectonic setting Continental arc, island arc, etc.

Many others

Panguna, PNG (Clark, 1990, Plate 1)

Considerations Quantitative data

Have the appearance of objectivity, but

May not be best approach to classification

Average (mean) grades and metal ratios are a function of Depth of erosion and composition of host rock

Supergene processes cause certain elements to be Preferentially enriched or depleted, so

Metal contents of weathered or partially weathered deposits are skewed according to their position in the weathering profile

Production data are strongly affected by Differences in recovery between principal and by-product metals

Short-term economic variations

Petrologic classifications Can be highly distorted by alterationespecially classification systems that involve alkalis

Classification hierarchy

Deposit type (1)Porphyry deposits

Classes (5)Based on the principal contained metals

Subclasses (13)Based loosely on

Compositions of intrusive rocks

Major and by-product metals

Other distinctive features

For smaller classes, only one subclass recognized

Lower levels

Classes

Based on the principal contained metals

ClassesPorphyry gold

Porphyry copper

Porphyry molybdenum

Porphyry tungsten

Porphyry tin

Subclasses: Definition and naming Classification based on

Compositions of intrusive rocks Major and by-product metals Other distinctive features

The compositional ranges overlap between subclasses Igneous compositions need not be precise

Deposits not classified on the basis of strict use of either Igneous rock analyses, or Metal ratios

Names of subclasses--for ease of recognition--are combinations of

Intrusive rock compositions, and Major and by-product metals

Subclasses Porphyry gold (1)

Dioritic porphyry Au

Porphyry copper (4) Tonalitic-granodioritic porphyry Cu-(Au-Mo)

Quartz monzodioritic-granitic porphyry Cu-(Mo)

Monzonitic porphyry Cu-(Mo-Au) deposits

Syenitic porphyry Cu-(Au)

Porphyry molybdenum (6) Monzonitic porphyry Mo-(Au)

Syenitic porphyry Mo

Quartz monzonitic-granitic porphyry Mo-Cu

Granitic porphyry Mo

Trondhjemitic Mo

Rhyolitic porphyry Mo

Porphyry tungsten (1) Rhyolitic porphyry W-Mo

Porphyry tin (1) Rhyodacitic porphyry Sn

Further divisions Based on structural styles (Einaudi, 1982)

Disseminated Lode Breccia

Accommodating other dimensions of variability Dominant wall rocks

Ultramafic to intermediate igneous rocks Carbonate wall rocks Quartzose

Evolutionary style (Seedorff and Einaudi, 2004a) Continuum from perfectly unidirectional to perfectly cyclical tocomposite

Sulfidation state (Einaudi et al., 2003) Temperatures of ore deposition (Seedorff and Einaudi, 2004b) Distal expressions and links to other deposit types, e.g.,

Epithermal deposits (Seedorff et al., 2005)

Porphyry gold

Dioritic porphyry AuCerro Casale, Aldebarn dist., Chile

Lobo, Chile

Marte, Chile

Morosayhuas, Per

Palmetto, Nevada

Pancho, Refugio dist., Chile

Verde, Refugio dist., Chile

Zule, CaliforniaCerro Casale to Cerro Catedral, Aldebarn dist., Chile (Vila and Sillitoe, 1991, Fig. 7)

Marte deposit, Maricunga dist., Chile (Vila et al., 1991, Fig. 2)

Distinctive characteristics of dioritic porphyry Au deposits Presence of banded quartz veinlets with vapor-rich inclusions

Magnetite-rich

Commonly containA veinlets and biotitic alteration

Pyritic D veins and pyrite-albite-clay alteration

Quartz-alunite ledges

Banded quartz veinlets cutting A veinlets(Muntean and Einaudi, 2001, Fig. 5A)

Dioritic porphyry Au deposits

Distal expressions and links to other deposit types

Distal, low-temperature veins associated with advanced argillic alteration contain Anomalous base metals

Anomalous Hg, Sb, As, Ba

Porphyry gold deposits and gold mass balance issues

Largest porphyry gold depositsContain less gold than many porphyry copper deposits

Certain porphyry molybdenum depositswhich are known for being Au-poorcontain comparable amounts of total contained gold

Au/Ag, Cu/Mo ratios for porphyry gold deposits

Data are sparseTwo deposits plotted

Au/Ag ratiosFairly high

Cu/Mo ratios At the low end of the range exhibited by porphyry copper deposits (surprising)

Cu/Mo/Au ratios for porphyry gold deposits

Porphyry gold deposits occur in lower right part of triangle, transitional with tonalitic-granodioritic porphyry Cu-(Au-Mo)

Relationship to other classes Forms a continuum with the porphyry copper class In particular the tonalitic-granodioritic porphyry Cu-(Au-Mo) subclass

Linked through their gradational igneous compositions

Cerro Casale deposit, Maricunga belt, ChileCan be regarded as the dioritic porphyry Au deposit closest to being transitional into the porphyry copper class

Perol and Chailhuagn, Minas Conga district, PerCan be regarded as tonalitic-granodioritic porphyry Cu-(Au-Mo) deposits closest to being transitional into the porphyry gold class (note: also have banded quartz veinlets)

Porphyry copper

Two subalkaline subclassesTonalitic-granodioritic porphyry Cu-(Au-Mo)

Most common subclass in island arcs (but also occur in continental arcs)

Quartz monzodioritic-granitic porphyry Cu-(Mo) Most common subclass in continental arcs

Two alkaline subclasses Monzonitic porphyry Cu-(Mo-Au)

Extensional settings and back arc settings?

Syenitic porphyry Cu-(Au) Extensional settings and back arc settings?

Tonalitic-granodioritic porphyry Cu-(Au-Mo) Antapaccay, Tintaya dist., Per Aqtoghai (Aktogai) dist.,

Kazakhstan Atlas, Philippines Batu Hijau, Indonesia Bell, Babine Lake dist., British

Columbia Buffalo Valley, Nevada Casino, Yukon Territory Copper Canyon, Nevada Dexing, China Dizon, Philippines Dos Pobres, Safford dist., Arizona El Arco, Baja California, Mxico Erdenet, Mongolia Exploradora, Chile

Bell and Granisle deposits, Babine Lake dist., British Columbia (Dirom et al., 1995, Plate)

Casino deposit, Yukon Territory (Bower et al., 1995, Fig. 2)

Tonalitic-granodioritic porphyry Cu-(Au-Mo) Far Southeast, Mankayan dist.,

Philippines Fish Lake, British Columbia Gaby, Chile Granisle, Babine Lake dist., British

Columbia Guinaoang (Tirad), Mankayan dist.,

Philippines Island Copper, British Columbia Kal'makyr, Almalyk dist., Uzbekistan Koloula, Solomon Islands La Esperanza, Chile La Fortuna, Chile Lumbay, Philippines Malpica, Sinaloa, Mxico Mazama, Washington Oyu Tolgoi, Mongolia?

Oyu Tolgoi, Mongolia (photo by Eric Seedorff)

Fish Lake, British Columbia (Caira et al., 1995, Fig. 2)

Tonalitic-granodioritic porphyry Cu-(Au-Mo) Panguna, Papua New Guinea Peavine-Wedekind, Nevada Park Premier-Park Konold, Utah Pebble Copper, Alaska Qonyrat (Kounrad), Kazakhstan Salavat, Ural belt, Russia Santa Cruz, Philippines Santo Toms II, Philippines Sar Cheshmeh, Iran Schaft Creek, British Columbia Sipalay (Cansibit), Philippines Tameapa, Sinaloa, Mxico Tampakan, Philippines Tanam, Puerto Rico Tintaya, Per Washougal, Washington Yandera, Papua New Guinea

Pebble Copper, Alaska (Bouley et al., 1995, Fig. 2)

Tonalitic-granodioritic porphyry Cu-(Au-Mo) Distal expressions and links to other deposit types

High-sulfidation epithermal Au-Cu deposits with advanced argillic alteration being the distal expressions of an underlying porphyry system Lepanto, Mankayan dist., Philippines Nena, Frieda River dist., Papua New Guinea Wafi, Papua New Guinea Certain occurrences in the Yanacocha district, Per

High-sulfidation epithermal Au-Cu deposits with advanced argillic alteration with more speculative links to an underlying porphyry system Alto Chicama, Per Chelopech, Bulgaria Chinkuashih, Taiwan El Indio-Tambo, Chile Goldfield, Nevada Mulatos, Sonora, Mxico Pascua-Lama, Chile-Argentina Peak Hill, New South Wales Pierina, Per Summitville, Colorado Temora (Gidginbung), New South Wales

Carlin-like, distal disseminated Au-Ag deposits Bau, Sarawak, Malaysia El Hueso and Jernimo, Potrerillos dist., Chile Ratatotok, North Sulawesi, Indonesia

Au/Ag, Cu/Mo ratios of tonalitic-granodioritic porphyry Cu-(Au-Mo) deposits

Au/Ag ratios Fairly high--typically >0.3

Somewhat greater than the values for average silicic, intermediate, and mafic rocks

Cu/Mo ratios Vary by more than two orders of magnitude

Subclass may deserve further subdivision

Cu/Mo/Au ratios for tonalitic-granodioritic porphyry Cu-(Au-Mo) deposits

Tonalitic-granodioritic porphyry Cu-(Au-Mo) deposits occur in center-right part of triangle, with large overlap with monzonitic Cu-(Mo-Au) deposits

Variation within tonalitic-granodioritic porphyry Cu-(Au-Mo) More mafic and/or Mo-poor

examples Koloula, Solomon Islands

Salavat, Ural belt, Russia

Panguna, Bougainville, Papua New Guinea

Perol and Chailhuagn, Minas Conga district, Per?

Less mafic and/or more Mo-rich examples Island Copper, British

Columbia, Canada

Sipalay (Cansibit), Philippines

Panguna (Clark, 1990 , Plate 1)

Island Copper (Perell et al., 1995, Fig. 1)

Variation within tonalitic-granodioritic porphyry Cu-(Au-Mo)

More mafic and/or Mo-poor examples

Less mafic and/or more Mo-rich examples

Tonalitic-granodioritic porphyry Cu-(Au-Mo)

deposits occur in center-right part of triangle, with

large overlap with monzonitic Cu-(Mo-Au)

deposits


Antamina, Per

Cananea, Sonora

Christmas, Arizona

Chuquicamata, Chile

El Salvador, Chile

La Escondida, Chile

Antamina, Per (OConnor, 2000, Foto 1)

Cerro Indio Muerto, El Salvador, Chile (Gustafson and Hunt, 1975,

Fig. 1)

Quartz monzodioritic-granitic porphyry Cu-(Mo) Huckleberry, British Columbia

Lornex-Valley, Highland Valley dist., British Columbia

Morenci, Arizona

Huckleberry, British Columbia (Jackson and Illerbrun, 1995, Fig. 2)

Lornex and Valley deposits, Highland Valley dist., British Columbia (Schroeter, ed.,

1995, Plate)

Quartz monzodioritic-granitic porphyry Cu-(Mo) Pima-Mission, Pima dist., Arizona

Resolution (Magma Porphyry), Superior dist., Arizona

Pima deposit, Pima district, Arizona (Titley and Hicks, eds., 1966,

Plate)

Resolution (Magma Porphyry), Superior dist., Arizona (photo

by Eric Seedorff)

Quartz monzodioritic-granitic porphyry Cu-(Mo) San Manuel-Kalamazoo, Arizona

Santa Rita, New Mexico

Sierrita-Esperanza, Pima dist., Arizona

Yerington dist., Nevada

San Manuel-Kalamazoo, Arizona, during operation (photo by Eric Seedorff)

Yerington mine, Nevada (photo by Eric Seedorff)


Distal expressions and links to other deposit types Distal, low-temperature veins contain

Cu, As, Ag and variable amounts of Sb and Au, primarily in sulfosalts (especially tennantite)

High-sulfidation Ag deposits with advanced argillic alteration with more speculative links to an underlying porphyry system Cerro de Pasco, Per

Huanzala, Per

Julcani, Per

Magma vein and mantos, Superior dist., Arizona

Quiruvilca, Per

Carlin-like, distal disseminated Au-Ag deposits Pursima Concepcin, Yauricocha dist., Per

Au/Ag, Cu/Mo ratios of quartz monzodioritic-granitic porphyry Cu-(Mo) deposits

Au/Ag ratios Low: more than an order of magnitude less than the values for average silicic, intermediate, and mafic rocks

Much lower than their more mafic counterparts

Cu/Mo ratios Similar to values for average silicic to intermediate rocks

Cu/Mo/Au ratios for quartz monzodioritic-granitic porphyry Cu-(Mo) deposits

Quartz monzodioritic-granitic porphyry Cu-(Mo) deposits occur in upper left part of triangle, with some overlap with other subclasses

Variation within quartz monzodioritic-granitic porphyry Cu-(Mo) deposits

More Au-rich examplesEl Salvador, Chile

Potrerillos, Chile

More Au-poor and Mo-rich examplesChuquicamata, Chile

Sierrita-Esperanza, Pima dist., Arizona

Cerro Indio Muerto, El Salvador, Chile (Gustafson and Hunt, 1975, Fig. 1)

Geologic map of the Chuquicamata open pit (Ossandn et al., 2001)

Monzonitic porphyry Cu-(Mo-Au) Afton-Ajax, British Columbia

Bingham, Utah

Bisbee, Arizona

Sacramento pit, Bisbee district, Arizona (photo by Peter Kresan)

Ajax, British Columbia

(Ross et al., 1995, Fig. 1)

Afton pit, British

Columbia (photo by Eric

Seedorff)

Monzonitic porphyry Cu-(Mo-Au) Cadia, New South Wales

Copper Mountain-Ingerbelle, British Columbia

Dinkidi, Philippines

Copper Mountain dist., British Columbia (Stanley et al., 1995, Plate 1)

Ingerbelle pit, British Columbia (photo by Eric

Seedorff)

Monzonitic porphyry Cu-(Mo-Au)

Endeavour deposits, Goonumbla dist., New South Wales

Kharmagtai, Mongolia

Monywa, Myanmar

Mount Milligan, British Columbia

Mount Milligan, British Columbia (Sketchley et al.,

1995, Fig. 2)

Northparkes operations, Goonumbla dist., NSW (Lickfold et al., 2003, Fig.2A)


Ok Tedi, Papua New Guinea

Peschanka, Russia

Rialto, New Mexico

Robinson (Ely), Nevada

Skouries, Greece

Yulong, Tibet, China

Looking west across the Robinson district, near

Ely, Nevada, 1993

Ok Tedi deposit prior to mining,

Mt. Fubilan, Papua New Guinea

(Gustafson and Titley, eds., 1978,

Plate)


Transitional or possible examplesBajo de la Alumbrera, Argentina

Grasberg, Indonesia

First few benches of the open pit at Bajo de la Alumbrera, Argentina, 1998 (photo by Eric Seedorff)

Grasberg pit, Indonesia (Mealey, 1996)

Distinctive features of monzonitic porphyry Cu-(Mo-Au) deposits

Subequal importance of Au and Mo

Quartz phenocrysts generally absent

Bingham pit, 1979 (photo by Eric Seedorff)

Monzonitic porphyry Cu-(Mo-Au) deposits Distal expressions and links to other deposit types

High-sulfidation Cu-Au deposits with advanced argillic alteration being the distal expressions of an underlying porphyry system North Ore Shoot, Bingham dist., Utah

Carlin-like, distal disseminated Au-Ag deposits Barneys Canyon and Melco deposits, Bingham dist., Utah

Star Pointer, Kranovich, and JD Hill deposits, Robinson dist., Nevada

Intermediate- and low-sulfidation Pb-Zn-Ag-(Cu-Au) vein, carbonate replacement, and skarn deposits Lark deposit, Bingham dist., Utah

Aultman, Puritan, and Pilot Knob deposits, Robinson dist., Nevada

High-sulfidation Cu-Au deposits with advanced argillic alteration with more speculative links to an underlying porphyry system Ladolam, Lihir, Papua New Guinea

Pao, Philippines

Au/Ag, Cu/Mo ratios of monzonitic porphyry Cu-(Mo-Au) deposits

Au/Ag ratios Similar Au/Ag ratios to the subalkaline, tonalitic-granodioritic porphyry Cu-(Au-Mo) deposits

Cu/Mo ratios Similar Cu/Mo ratios to the subalkaline, tonalitic-granodioritic porphyry Cu-(Au-Mo) deposits

Except that monzonitic deposits may exhibit a more restricted range

Cu/Mo/Au ratios for monzonitic porphyry Cu-(Mo-Au) deposits

Monzonitic porphyry Cu-(Mo-Au) deposits occur in center-right part of triangle, with overlap with other subclasses

Syenitic porphyry Cu-(Au)

Galore Creek, British Columbia

Lorraine, British Columbia

Mount Polley (Cariboo-Bell), British Columbia

Rayfield River, British Columbia Galore Creek, British Columbia, Canada

(Sutherland Brown, ed., 1976, Plate)

Distinctive features of syenitic porphyry Cu-(Au) deposits

Igneous rocks Generally silica-undersaturated

Alteration minerals Common biotite, K-feldspar, anhydrite Locally abundant garnet, diopside, actinolite Sericite uncommon

Quartz veins rare to absent Sulfide-oxide assemblages

Mostly involve bornite, chalcopyrite, magnetite Poor in pyrite

Metals Mo-poor Au- and Ag-rich

Au/Ag, Cu/Mo ratios of syenitic porphyry Cu-(Au) deposits

Au/Ag ratios Intermediate Au/Ag ratios

Cu/Mo ratiosSome of the highest Cu/Mo ratios of all porphyry deposits

Cu/Mo/Au ratios for syenitic porphyry Cu-(Au) deposits

Data are sparse, but syenitic porphyry Cu-(Au) deposits appear to occur along right edge of triangle in middle of Cu and Au vertices, with monzonitic Cu-(Mo-Au) deposits

Porphyry molybdenum

Monzonitic porphyry Mo-(Au)




Trondhjemitic porphyry Mo


Monzonitic porphyry Mo-(Au)

Central City, Colorado

Golden Sunlight, Montana

Jamestown, Colorado

Three Rivers, New Mexico


Big Ben, Montana

Bordvika-Vragla, Norway

Cave Peak, Texas

Flammefjeld, Kangerlussuaq complex,Greenland

Malmbjerg, Werner Bjerge complex, Greenland

Marinkas Kwela, Namibia

Nordli, NorwayAlkaline porphyry Mo deposits, East Greenland (Brooks et al., 2004, cover of Economic Geology)

Quartz monzonitic-granitic porphyry Mo-Cu Prime examples

Buckingham, Nevada

Cannivan Gulch, Montana

Cumobabi, Sonora

East Qonyrat (East Kounrad), Kazakhstan

Hall (Nevada Moly), Nevada

Kadzaran, Armenia

Montezuma, Colorado

New Boston-Blue Ribbon, Nevada

Opodepe (El Crestn), Sonora

Opodepe (El Crestn), Sonora


Transitional or possible examples (other workers classify some of these as porphyry Cu deposits)

Berg, British Columbia

Catheart Mountain, Maine

Mineral Park, Arizona

Mount Tolman, Washington

Jinduicheng, China

Distinctive characteristics of quartz monzonitic-granitic porphyry Mo-Cu deposits Subequal Mo and Cu Porphyries tend to have

Fairly large phenocrysts of plagioclase, K-feldspar, and biotite Distinctive large quartz eyes

USTs common Secondary biotite and K-feldspar both common Mo commonly occurs in

Early quartz veins with K-feldspar envelopes Quartz veins containing molybdenite, chalcopyrite, and pyrite

Bornite uncommon Pyritic veins with greisen muscovite common Ca-rich gangue minerals

Prime examples may have fluorite Transitional varieties tend to have anhydrite

Quartz monzonitic-granitic porphyry Mo-Cu Distal expressions and links to other deposit typesDistal, low-temperature veins contain

Cu, As, and Au and variable amounts of Sn, W, Bi, and Sb, primarily in sulfosalts (especially tetrahedrite)

High-sulfidation Ag deposits with advanced argillic alteration being the distal expressions of an underlying porphyry system Equity Silver (Sam Goosly), British Columbia

Flathead mine, Hog Heaven dist., Montana

Washington Hill, Nevada

Granitic porphyry Mo Prime examples

Burroughs Bay, Alaska

Compaccha, Per Endako, British Columbia

Kitsault, Alice Arm dist., British Columbia

Quartz Hill, Alaska Roundy Creek, British Columbia

Thompson Creek, Idaho

White Cloud, Idaho

Endako mine, British Columbia, Canada (Sutherland Brown, ed.,

1976, Plate 6)

Endako and Denak East pits (Bysouth and Wong, 1995,

Fig. 2)


Transitional or possible examplesAdanac (Ruby Creek), British Columbia

Boss Mountain, British Columbia

Red Mountain, YT

Yorke-Hardy (Glacier Gulch), British Columbia

Yorke-Hardy (Glacier Gulch), British Columbia (Bright and Jonson, 1976, Fig. 2)

Distinctive features of granitic porphyry Mo deposits

Igneous compositionsSilicic but not highly evolved in terms of trace elements

Sulfide-oxide assemblagesPyrite is common

MetalsMo-rich

Relatively Cu-poor

Lacks enrichment in exotic elements

Trondhjemitic porphyry Mo

Bald Hill, New Zealand

Kirki, Greece

Mink Lake, Ontario

Trout Lake, British Columbia

Setting Net Lake, Ontario


Bear Mountain, Alaska

Climax, Colorado

Fachinal, Chile

Molybdenite-rich boulder, Climax, Colorado (photo by Eric Seedorff)

Open pit at Climax, Colorado (photo by Eric Seedorff)


Henderson-Urad, Colorado

Mount Hope, Nevada

Mount Emmons-Redwell Basin, Colorado

Pine Grove, Utah

Questa, New Mexico

Silver Creek (Rico), Colorado

Two views of Henderson-Urad, Red Mountain, Colorado (photos by Eric Seedorff)

Distinctive features of rhyolitic porphyry Mo deposits Igneous compositions

High-silica rhyolite Highly evolved in terms of trace elements, e.g., enriched in F, Rb, Nb

and strongly depleted in Sr, Zr

Sulfide-oxide assemblages Assemblages do not contain both molybdenite and pyrite Molybdenite and wolframite generally do not occur in same

assemblages Copper minerals are absent

Metals Mo-rich, with anomalous W W occurs as wolframite, deposited with topaz sericite and with pyrite Very Cu-poor Cu anomalies occur in Pb-Zn halo, as chalcopyrite blebs in sphalerite Enriched in a suite of exotic elements such as Nb, Ta, U, Th

Ca-rich gangue minerals Generally dominated by fluorite



Distal, low-temperature veins contain Zn-Pb-Ag, anomalous in Bi and Sn but poor in Cu and Au, primarily in base metal sulfides (i.e., sulfosalts are rare)

Porphyry tungsten Rhyolitic porphyry W-Mo

Mount Pleasant, New Brunswick True Hill, New Brunswick

Sulfide-oxide assemblages Molybdenite and wolframite commonly occur together in the same assemblage

Pyrite is present but not abundant Pyrrhotite locally abundant, with occurrences of loellingite Numerous Sn, As, and Bi minerals present Represent substantially lower oxidation and sulfidation states than any porphyry molybdenum deposit

Metals Subequal W and Mo Major association of Sn-Bi-As W occurs as wolframite and molybdenite

Rhyolitic porphyry W-Mo


Distal, low-temperature veins contain Zn-Pb-Cu-As-Bi-Sn-W in veins with complex mineralogy

Porphyry tin

Rhyodacitic porphyry Sn

Cerro Rico (Potos), Bolivia

Chorolque, Bolivia

Llallagua, Bolivia

Majuba Hill, Nevada

Oruro, Bolivia

Distinctive features of rhyodacitic porphyry Sn deposits

Igneous compositionsRhyodacitic, peraluminous compositions

Sulfide-oxide assemblagesPyrite is abundantPyrrhotite commonly is present

MetalsBi and As present, with abundant Ag

Other characteristicsAbundant tourmalineTourmaline apparently proxies for K-feldspar in highest-temperature assemblages

Breccias common to ubiquitous

Rhyodacitic porphyry Sn


Distal, low-temperature veins contain Sn-Ag lodes with associated Bi, Sb, Cu, Pb, and Zn in veins with complex mineralogy

Bi-W-Sn lode deposits with advanced argillic alteration with speculative link to an underlying porphyry system Tasna, Bolivia

Review: Classification hierarchy

Deposit type (1)Porphyry deposits

Classes (5)Based on the principal contained metals

Subclasses (13)Based loosely on

Compositions of intrusive rocks

Major and by-product metals

Other distinctive features

For smaller classes, only one subclass recognized

Lower levels

Structural styles: End members

Disseminated Replacement

Carbonate hosted

Igneous hosted

Lode

Mineralization occurs in lodes

Breccia

Mineralization occurs in breccias

Disseminated style

DisseminatedMineralization occurs in veinletsExamples near end members

Batu Hijau, Indonesia Dexing, China Sar Cheshmeh, Iran Yerington, Nevada San Manuel-Kalamazoo, Arizona Ray, Arizona Mount Milligan, British Columbia Peschanka, Russia Berg, British Columbia Mineral Park, Arizona Endako, British Columbia Henderson, Colorado

Lode style Lode

Mineralization Occurs in through-going Cu-rich lodes with minerals that are characteristic of high- and very high-sulfidation states, and/or

Is hosted by rocks that exhibit advanced argillic alteration andintense sericitic alteration with silicification

Examples near end member or with important lode component Butte, Montana (Main Stage) Rosario, Collahuasi, district, Chile Yauricocha, Per Bisbee, Arizona Turnley Ridge, Montana Monywa, Myanmar Cerro Rico (Potos), Bolivia

Breccia style Breccia

Mineralization occurs in breccias

Examples near end member or with important breccia componentRo Blanco-Los Bronces, ChileKharmagtai, MongoliaMount Polley (Cariboo-Bell), British ColumbiaCumobabi, Sonora, MxicoCave Peak, TexasMount Pleasant, New BrunswickLlallagua, Bolivia

Conclusions about structural styles

Structural styles cut across deposit types

Many deposits are hybrids of two or three end members

Classification: Further divisions Accommodating other dimensions of variability

Dominant wall rocks Ultramafic to intermediate igneous rocks Carbonate wall rocks Quartzose

Evolutionary style (Seedorff and Einaudi, 2004a) Continuum from perfectly unidirectional to perfectly cyclical to composite

Sulfidation state (Einaudi et al., 2003)Temperatures of ore deposition (Seedorff and Einaudi, 2004b)

Distal expressions and links to other deposit types, e.g., Epithermal deposits

Summary of classification

Porphyry deposits grouped into five classes based on the economically dominant metal in the deposits Gold, copper, molybdenum, tungsten, tin

Five classes are further subdivided Total of 13 subclasses

For ease of recognition, names of subclasses are combinations ofigneous rock compositions and major and by-product metals

Nonetheless, for both practical and theoretical reasons, deposits not classified strictly on the basis of either Igneous rock analyses, or

Metal ratios

Lower level groupings Related to structural style of alteration-mineralization

Provisions also made for other dimensions of variability

Genetic implications and exploration consequences Correlation of igneous compositions with types of major and by-product metals Reflects first-order control of magmatic composition on source and transport of metals

Importance of magmatic processes also is reflected by Correlation of magmatic compositions with metal suites observed in distal, low-temperature veins

Rough correlation of magmatic compositions with metals observed in high-sulfidation epithermal deposits--more mafic igneous compositions with Cu-Au and more silicic compositions with Ag-rich advanced argillic alteration

Exploration consequences Metal suites observed in distal, low-temperature veins and in high-sulfidation epithermal deposits can be used to target specific subclasses of porphyry systems

ClassificationofPorphyry-RelatedDeposits_Seedorf

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