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The Mesozoic IOCG Deposits in the Central Andes

A Refined IOCG Ore-forming Model in the

Palaeozoic Continental Margin

Huayong Chen

Guangzhou Institute of Geochemistry Chinese Academy of Sciences

PACRIM 2015, Hong Kong

Distribution of IOCG Deposits

Modified from Corriveau, 2007

Cloncurry

Olympic Dam

Norbotten

Central Andes Carajás

Kangdian

Global Resources of IOCG Deposits Deposit Tonnage

(Mt) Cu (%)

Au (g/t)

Ag (g/t)

Other metals (%)

Olympic Dam, Australia

3810 1.0 0.5 3.6 U (0.04) REE

Salobo, Brazil 789 0.96 0.52 55

Cristalino, Brazil 500 1.0 0.3

Aitik, Sweden 606 0.38 0.21

Candelaria, Chile 470 0.95 0.22 3.1

Mantoverde, Chile 400 0.52 0.11

Mina Justa, Peru 347 0.71 0.03 3.83

Ernest Henry, Australia

167 1.1 0.54 Co (0.05)

Timing of IOCG

Deposits

Corriveau, 2009

Late Archean Carajas District, Brazil

Early-mid Proterozoic Olympic Dam, Cloncurry District, Australia; Aitik, Sweden Kangdian district, China

Mesozoic Central Andes

IOCG Model: Ore-forming fluids

Williams et al., 2005; Williams, 2009

IOCG Ore-forming fluids Debate in the Central Andes

IO + CG

Magmatic-hydrothermal (Pollard, 2001, 2006; Marschik and Fontboté, 2001; Sillitoe, 2003; Rieger et al., 2010)

Similar to Porphyry, Skarn systems

Non-magmatic hydrothermal (Ullrich and Clark, 1999; Benavides et al., 2007; Chen

et al., 2011; Marschik and Kendrick, 2014)

IOCG’s in the Andes

Mina Justa (347Mt@0.71% Cu 3.8g/t Ag; 0.03g/t Au)

Mantoverde (400Mt@0.52% Cu 0.11g/t Au)

La Candelaria (470Mt@0.95% Cu 0.22g/t Au)

To constrain a ore deposit model

Candelaria, Chile

1. Ore Deposit Geology

2. Paragenesis of alteration and mineralization

3. Nature of ore-forming fluids

Ore Deposit Model

Regional Geology of South-Central Peru

Chen et al., 2010

Deposit Geology – Mina Justa

Deposit Geology – Mina Justa

Chen et al., 2010

Location of the Chilean IOCGs

Ages of host rocks in the Mantoverde district: Sierra Dieciocho pluton 120-125 Ma La Negra Formation: Middle to Upper Jurassic

Deposit Geology of

Mantoverde

Benavides et al., 2007

Benavides et al., 2007

Cu orebody

magnetite

Deposit Geology – La Candelaria

After Marschik and Fontboté, 2001

La Candelaria Cross section

Modified from Marschik and Fontboté, 2001; Arevalo et al., 2006

Summary of Geology

1. located in the margin of the Mesozoic volcanic basin

2. controlled by faults (most are normal or detachement)

3. genetic relationships to intrusions not clear in many cases

Coast near Mantoverde Chile

To constrain a ore deposit model

Candelaria, Chile

1. Ore Deposit Geology

2. Paragenesis of alteration and mineralization

3. Nature of ore-forming fluids

Ore Deposit Model

Alteration and Mineralization Paragenesis– Mina Justa

Alteration and Mineralization Paragenesis– Mina Justa

Alteration and Mineralization Paragenesis– Mina Justa

540- 600 oC

80-220 oC (mode at 140 oC)

154-156 Ma 142 Ma

109 Ma

101-104 Ma

95-99 Ma

Alteration and Mineralization – Mantoverde

128 Ma (U-Pb)

117-121 Ma (K-Ar)

Benavides et al., 2007

Alteration and Mineralization – La Candelaria

(Ullrich and Clark, 1999)

115 Ma

112 Ma

Act Cpy Mus

Mt

Summary of Paragenesis

Candelaria, Chile

1. magnetite stage commonly prior to the Cu stage, could be about 5-10 my. in some cases

2. magnetite stage could form under much higher temperatures than Cu stage

3. Calcite and hematite are common in Cu stage

To constrain a ore deposit model

Candelaria, Chile

1. Ore Deposit Geology

2. Paragenesis of alteration and mineralization

3. Nature of ore-forming fluids

Ore Deposit Model

Low-temperature fluids of the Cu mineralization stage, Mina Justa

• Low-T, Ca-dominant medium to high salinity (basin brine ?) • Low-T, Na-K dominant low salinity (meteoric water ?)

Laser Ablation-Time Of Flight-ICPMS analysis of individual inclusions

Basinal Brines for Cu (-Ag) mineralization at Mina Justa

Sulfur Isotope data

O-H isotopes of ore-forming fluids at Mina Justa

Magmatic fluids

Basinal Brines

System evolved under retrograde conditions. The incursion of fluids with isotopically heavy sulphur and light oxygen is evident from the intermediate to the late stages.

Magnetite Orthoclase Biotite Tourmaline Titanite Quartz Muscovite Chlorite Anhydrite Scapolite Rutile Epidote Hematite Pyrite Chalcopyrite Gold Siderite Calcite

STAGE I STAGE II ORE STAGE III STAGE IV K and Fe Chlorite-Muscov. Specular Hematite- Late calcite Metasomatism Quartz Chalcopyrite veins

500 to 550˚C δ34Sfluid~0‰ δ18Ofluid~+9‰

300 to 350˚C δ34Sfluid~+10 to +15‰ δ18Ofluid~+6 to +10‰

200 to 250˚C δ34Sfluid~ +25‰ δ18Ofluid~ +5‰

Basinal Brines for Cu (-Au) mineralization at Mantoverde

Basinal Brines for Cu (-Au) mineralization at Mantoverde (seawater ?)

δ18Ofluid

δDflu

id

Fluid mixing in ore stage

Compositional range for Fluid in equilibrium with Mt (500˚C)

Basinal Brines for Cu (-Au) mineralization at Mantoverde

From Alex Fitzpatrick (2008)

External fluids for Cu (-Au) mineralization at La Candelaria

Fluid inclusion A wide range of temperatures (200-450oC)

Ullrich and Clark (1997)

External fluids for Cu (-Au) mineralization at La Candelaria

From Ullrich and Clark (1999) Ullrich et al., 2001

δ34 S

δ18O

External fluids for Cu (-Au) mineralization at La Candelaria

Marschik and Kendrick, 2014

Summary of ore-forming fluids

1. magnetite stage fluids has higher temperatures and clear magmatic-hydrothermal features

2. Cu stage fluids show lower temperatures and signals of external fluids (e.g., seawater or basin brines)

To constrain a ore deposit model

Candelaria, Chile

1. Ore Deposit Geology

2. Paragenesis of alteration and mineralization

3. Nature of ore-forming fluids

Ore Deposit Model

Ore Genetic Model – Mina Justa

Chen et al., 2010

Ore Genetic Model – Mina Justa

Chen et al., 2010

Mantoverde: Ore Genetic Model

Mantoverde

ca. 130 Ma Benavides, 2006

Mantoverde: Ore Genetic Model

Benavides, 2006

Mantoverde

ca. 117 Ma

Ore Genetic Model – La Candelaria

Magmatic fluids

external fluids

IV

V

From Ullrich and Clark, 1999 Ullrich et al., 2001

Ore Genetic Model – Andean IOCG

Large Andean IOCG deposits and potentially related deposits, e.g., Manto-type Cu, CIB iron, small IOCG veins and porphyry Cu (Au-Mo)

S, Cu ?

Andean IOCG – not lonely

1

4 5

Kangdian

Eastern Tianshan

IOCG deposits in Eastern Tianshan

345-320 Ma intra-arc or back-arc basin 320-300 Ma inversion of basin

Important ore deposits formed during basin inversion, including Fe, Cu-Fe and some Ag-Cu deposits

Similar features to Andean IOCG deposits

1. Cu stage postdated magnetite and pyrite

2. magnetite stage has much higher temperatures (580oC) than Cu stage (170oC)

3.Cu stage ore-forming fluids are Ca-Mg dominated

Peak at 170 oC

Candelaria, Chile

Central Andean IOCG Deposit

Model

Can be applied to

Other districts on the Paleozoic continental

margins

We need more work… Eastern Tianshan

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