the portovelo mining district relation of mineralisation to porphyry and epithermal environments
TRANSCRIPT
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The Portovelo mining district: relation of mineralisation to
porphyry and epithermal environments
Richard Spencer, July Montenegro, Alina Gaibor, Patricio Perez,
Glenda Mantilla, Franklin Viera, Camille Spencer & Jorge Barreno
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History
Mercadillo: 1549SADCO: 1905-1950 3.6Moz Au
12Moz AgCIMA 1950-1965 0.38Moz AuBIRA & others: To present 1MozTOTAL 5Moz Au
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VeinsVein Width (m) Grade Tonnage Produced
Portovelo Mine
Abundancia 1.75 15.2 1,573,360
769,706
Jorupe 1.42 10.44 929,810 312,138
Portovelo 1.98 18.8 385,926 232,880
Cantabria 1.56 11.6 397,099 148,077
Tamayo 1.07 11.4 364,396 133,084
Soroche 1.53 13.1 212,264 89,598
Agua Dulce 1.36 17.4 148,993 83,451
Guillermo 1.62 24.0 97,216 75,115
Tablon 1.16 10.2 222,348 72,706
Nudo West 2.14 11.8 168,645 64,232
Tres Reyes 1.09 13.4 134,230 57,637
Veinteseis 1.70 24.9 61,304 49,062
Fortuna 1.33 13.8 79,510 35,238
Barbasco 1.50 11.83 88,547 33,689
Portovelo W 1.54 8.0 77,187 19,925
Quebrada 0.77 28.7 8827 8,145
Matalanga 0.73 19.9 11,792 7,546
Second phase production, Portovelo Mine 2,192,232
R-Nivel Mine
Cristina 0.91 18.2 422,093 246,768
Jane Sur 1.55 7.5 252,193 60,862
Jane Norte 1.36 4.9 71,914 11,387
Sub-total R-Nivel 319,018
Total second phase mining 2,511,250
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Format
1. Tectonic setting
2. Alteration• Zoning• Tilting
3. Mineralisation
4. Future exploration• Hard rock• Footwall of thrusts• Ore shoot orientation
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Format
1. Tectonic setting
2. Alteration• Zoning• Tilting
3. Mineralisation
4. Future exploration• Hard rock• Footwall of thrusts• Ore shoot orientation
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Portovelo: location
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Portovelo: structural setting – Oligocene extension
Oligocenegrowth sequences
Lopolithic intrusivesat onset of Miocene inversion?
Piñas normal fault
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Whole rock data:intrusives
Alkali index:AI = (Na2O + K2O) (SiO2-43) x 0.17
0,00
0,50
1,00
1,50
2,00
2,50
3,00
0 5 10 15 20
Al2O3
Tholeiitic
Calc-alkaline
Al2O3
AI
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0
1
2
3
4
5
6
0 10 20 30 40 50 60 70
SiO2
K2
O+
Na
O
Whole rock data:intrusives
Basaltic andesite
Andesite-diorite
SiO2
K2O
+N
aO Gabbro-basalt
“Melanocratic diorite”
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Oligocene
Saraguro Group
Piñas fault
Jubones F
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Miocene inversion of Piñas basin
Piñas fault
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Late Oligocene – Miocene inversion
Jubones F
Piñas F
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Portovelo: location
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Portovelo vein system & intrusives
Intrusives:• RL sigmoids• Change in stress field? - dextral - compressional• “Tholeiitic” composition
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Format
1. Tectonic setting
2. Alteration• Zoning• Tilting
3. Mineralisation
4. Future exploration• Hard rock• Footwall of thrusts• Ore shoot orientation
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District-scalealterationzoning
Coo
ling
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WESTWARD TILT
Cooling
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Curipamba, vein: Sadco data, Au gradeContact of illite – illite-smectite inclined to SQuartz content increases with depth
90% calcite 50% calcite50% quartz
• 40% calcite• 60% quartz• Illite
SOUTHWARD TILT
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Portovelo vein system & intrusives
Post-mineraltilt to the SW
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Format
1. Tectonic setting
2. Alteration• Zoning• Tilting
3. Mineralisation
4. Future exploration• Hard rock• Footwall of thrusts• Ore shoot orientation
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Base metal distribution
Coo
ling
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Au distribution
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Long section of the Sesmo vein Au & base metal distribution
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Abundancia vein (Sadco data)
Grade Thickness
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Tamayo vein: host-rock control
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Intermediate sulphidation epithermal
• High base metal content• High NaCl in fluid inclusions (<18 wt %)• Near-neutral pH hydrothermal fluids
• Carbonate-bearing veins• Minor adularia• Fluorite• Au over large vertical interval (800m)
• Association with porphyry• Association with tholeiitic – calc-alkaline
transitional rocks (basaltic andesite)
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1. Tectonic setting
2. Alteration• Zoning• Tilting
3. Mineralisation
4. Future exploration• Hard rock• Footwall of
thrusts• Ore shoots• New veins
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Systematics of ore shoots: Abundancia vein
Brittle host rock
En echelon ore shoots hanging under thrusts
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Extensions to vein system
New veins
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West 1 Vein
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West 2 Vein
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Conclusions
• Continuum from porphyry to epithermal environments
• Intermediate sulphidation epithermal
• Controls on mineralisation:• Brittle host rock• Proximity to footwall of thrusts• Highest gold content in:
• illite-stable part of alteration system
• In sphalerite-dominated part of system
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Exploration
• Focus on SW part of vein system
• Exploring existing veins: Go South beneath illite-smectite zone
• Exploring for new veins:Go west – extension to left-stepping en echelon system
• Controls on mineralisation – detail• Thrusts• Hard rock• Alteration
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Explorationfocus
Area for explorationfocus
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Chemical zoning in Viscaya vein