Influence of magmatic arc geothermal systems on porphyry ...

<strong>Influence</strong> <strong>of</strong> <strong>magmatic</strong> <strong>arc</strong><strong>geothermal</strong> <strong>systems</strong> onporphyry-epithermal Au-Cu-Agexploration modelswww.corbettgeology.com

Geothermal environments

Magnatic <strong>arc</strong> hydrothermal <strong>systems</strong>

Magmatic <strong>arc</strong> porphyry to epithermal

Southern Negros Geothermal Field

Time in porphyry Cu-Au evolution

Porphyry emplacement,prograde alterationBiotiteSt Tomas, PhilippinesK feldspar floodingZhongdian, ChinaMagnetiteRidgeway, Australia

Porphyry style Aand M veinsM veins Copper HillA veins, Ridgeway

Propylitic alterationchloriteepidoteactinolite

Time in porphyry Cu-Au evolution

Barren shouldersto porphyry Cu-AuLookout Rocks, New ZealandEkwai Debom, Frieda River, PNG

Southern Negros

Geothermal Analogy

Early <strong>magmatic</strong> volatiles – RocksNegros Is., PhillipinesVuda, FijiPeak Hill, AustraliaBulahdelah, Australia

Pyrite-rich AAA, Quimsacocha, Ecuador

Time in porphyry Cu-Au evolution

B veinsChatree,ThailandCopper Hill,Australia

C veinsGrasberg, IndonesiaCopper HillRidgeway

B veins cut M veinsNamosi FijiLindero ArgentinaRio Grande Argentina

Retrograde alteration

aerom

Time in porphyry Cu-Au evolution

Collapse <strong>of</strong> Acid waters

Collapsingadvanced argillicalteration

Time in porphyry Cu-Au evolution

Magmatic <strong>arc</strong> porphyry to epithermal

D veins in porphyry-high sulphidationLa Coipa, ChilePoposa, Argentina

Formation <strong>of</strong> high sulphidation

MOSTHOT ACIDHigh sulphidationzoned acid alterationVughy orresidual silicaAluniteLESSERHOT ACIDPyrophyllite-diasporeDickite-kaolinite

High sulphidation at different levels

High sulphidation epithermal Au

MineralizationMt Kasi, FijiMaragorik, PNGEl Indio, ChileYanacocha, Peru

GangueNena, PNGLama, ArgentinaTambo, ChileNansatsu Deposits, Japan

Wafi fluid evolution

Wafi –low sulphidation Au

Steam heatedalteration

Hypogene oxidation in high sulphidationPierina, Peruepithermal <strong>systems</strong>Veladero, Argentina

Magmatic <strong>arc</strong> porphyry to epithermal

Styles <strong>of</strong> <strong>magmatic</strong> <strong>arc</strong> Cu-Au

Low sulphidation Quartz-Sulphide Au + CuBilimoia Papua New GuineaLake Cowal, Australia

Round Mountain, Nevada

Transition to porphyry Cu-AuSheeted veins - Maricunga Belt, ChileD veinSheeted veins - Cadia,Australia

Sediment HostedReplacement GoldGoldstrike pit

Polymetallic Au-AgCarbonate-base metal Au

Bicarbonate waters

Carbonate-base metal Au –Leach and Corbett, 1993, 1994, 1995; Corbett and Leach, 1998KelianPorgera

Andean Polymetallic Au-AgCaylloma, PeruArcata, Peru1000 oz/t Ag

FresnilloPolymetallic Ag-Au MexicoPalmarejo

Two epithermal Au-Ag end members

Geothermalenvironments

Porgera Zone VII

Low sulphidation EpithermalChalcedony-Ginguro Au-Ag veinsFormerly describedas adularia-sericiteor quartz-adulariaveins

Banded chalcedony-ginguro Au-Ag veins-ElPeñonon..CracowBanded quartz vein -Golden CrossQuartz pseudomorphing platycarbonateAdulariaVera NancyHishikari

Visible AuAsacha, KamchatkaGinguro bandsMidas, NevadaVera Nancy, AustHishikari, Japan

Acid sulphate capsChanpamge Pool, New ZealandArcata, Peru

Au deposition bymixing <strong>of</strong> ore fluidswith low pH waters223 g/t Au &17,642 g/t Ag

Andean Lithocaps

Lookout Rocks, New ZealandRising <strong>magmatic</strong>volatiles –barren shouldersBulahdelah

Collapsingcondensate watersMineral Hill

Collapsing advanced argillic alteration

High sulphidation epithermal AuNena, Papua New Guinea

Steam heatedalterationQuimsacocha, Ecuador

Acid Sulphatealteration zones186 g/t Au, 3720 g/t AgGuadalupe, Palmarejo Mexico

Styles <strong>of</strong> acid alteration♦ Rising <strong>magmatic</strong> volatiles (barren shoulders)♦ Collapsing condensate waters (phyllic alteration)♦ Strongly acidic collapsing condensate waters(advanced argillic alteration)♦ High sulphidation epithermal (zoned advanced argillicto argillic alteration)♦ Steam heated above high sulphidation epithermal♦ Acid sulphate above low sulphidation epithermal

Styles <strong>of</strong> acid alteration

Conclusion♦ Magmatic <strong>arc</strong> <strong>geothermal</strong> <strong>systems</strong> are analogousto porphyry Cu-Au, high sulphidation andintrusion-related low sulphidation ores♦ Geothermal and petrological studies have aided inand understanding <strong>of</strong> the:– Evolution <strong>of</strong> ore <strong>systems</strong> and setting <strong>of</strong> mineraliation– Distinguish between varying styles advanced argillicargillicalteration with different relationships tomineralisation– Conceptual geological models as an aid to thecategorisation <strong>of</strong> ore <strong>systems</strong> and exploration– Zoned alteration and its relationship to mineralisationusing the pH vs temp figure

Terry’s pH vs temperature figure

Some alteration zonation patterns♦ 1. Low sulphidation acidsulphate cap♦ 2. High sulphidation steamheated cap♦ 3. High sulphidation highlevel structurally controlled♦ 4. High sulphidation deeplevel permeabilitycontrolled♦ 5. Rising early <strong>magmatic</strong>volatiles (barren shoulder)♦ 6 Low sulphidation argillicvein halos♦ 7. Porphyry related argillic♦ 8. Porphyry related phyllic♦ 9. Evolving potassicpropylitic

Magmatic <strong>arc</strong> porphyry to epithermal

Styles <strong>of</strong> <strong>magmatic</strong> <strong>arc</strong> Cu-Au

Lithocaps