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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 ([email protected]% Cu 3.8g/t Ag; 0.03g/t Au)
Mantoverde ([email protected]% Cu 0.11g/t Au)
La Candelaria ([email protected]% 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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