g eol 5320 a dvanced i gneous and m etamorphic p etrology modeling the petrology and pge reef...
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GEOL 5320 GEOL 5320 ADVANCED IGNEOUS AND ADVANCED IGNEOUS AND METAMORPHIC PETROLOGYMETAMORPHIC PETROLOGY
Modeling the Petrology Modeling the Petrology
and PGE Reef Mineralization and PGE Reef Mineralization
of the Sonju Lake Intrusionof the Sonju Lake Intrusion
December 7, 2009
Sonju LakeIntrusion
The The Sonju Sonju Lake Lake IntrusionIntrusion
From MGS Map M-71 (Miller et al., 1989)
Leucogranite
Quartz ferromonzonite
Apatitic olivine ferromonzodiorite
Apatite olivine ferrodiorite
Ol-bearing oxide gabbro
Ol-bearing gabbro
Troctolite-augite troctolite
DuniteMelatroctolite
PCFOAg
PCFOAh
PCFoi
PC(O)fi
POcfi
OOP
Modal Rock NamesCumulus Code
Cumulus Mineral Mode
Modal Variations
Modal Variation and Cumulus TextureModal Variation and Cumulus Texture
Cryptic VariationCryptic Variation
1 km>20 km
>10 km
Sheet-like Geometry of the Sonju Lake IntrusionSheet-like Geometry of the Sonju Lake Intrusion
Estimation of Bulk Composition Becomes a 1-dimensional problem
SiO2 47.6TiO2 2.28Al2O3 14.0FeOt 14.7MnO 0.21MgO 8.3CaO 9.4Na2O 2.47K2O 0.55P2O5 0.30Volatiles 0.20Total 100.0mg# 50.2
Sc 34V 192Cr 111Co 75Ni 185Rb 20Sr 233Ba 171Y 20Zr 114Nb 17Hf 3.1La 14.7Ce 33.4Sm 4.1Eu 1.6Tb 0.8Yb 2.1 Lu .32
Bulk Intrusion CompositionBulk Intrusion Composition= Parent Magma= Parent Magma
= moderately evolved olivine tholeiitic basalt= moderately evolved olivine tholeiitic basalt
From Miller and Chandler (1998)and Miller and Ripley (1997)
Liquid Line of DescentLiquid Line of Descent
Calculated by summing composition of rock column above a specific horizon
Fractional Crystallization ModellingFractional Crystallization ModellingCHAOS 2 (NIELSEN, 1990)CHAOS 2 (NIELSEN, 1990)
Model Parameters : fO2 = -2 log QFM; trapped liquid = 20%
0 100 200 300 400 500 600
Cu (ppm)
Discovery of Stratiform Discovery of Stratiform PGE MineralizationPGE Mineralization
Skaergaard Intrusion
Feb. 1999
PGEPGEReefReef
Outcrop SamplingOutcrop Sampling
From Miller (1999)
SLI ChemostratigraphySLI Chemostratigraphy
Evolution of Evolution of Sulfide in theSulfide in theSonju LakeSonju LakeIntrusionIntrusion
Exploration Exploration Drilling by Drilling by Franconia Franconia MineralsMinerals
July 2002
1 cm
Core Logging and SamplingCore Logging and Sampling
Sampling RegimeSampling RegimePhase 1 – 1’ sample every 10’Phase 1- continuous 1’ across PMZ423 Total Whole Rock Analyses
Plagioclase
65-73%
Detailed Geochemical Profiling of the PMZDetailed Geochemical Profiling of the PMZ
SL02-1
Cu-Pd RatiosCu-Pd Ratios
Precious Metals Zone (PMZ)
Meters above Cu-Au break SL02-1
Pd (ppb)
Cu
/Pd
after Barnes et al. (1993)
PMZ MetallogenesisPMZ Metallogenesis
• What was the PGE mineralizing agent?Cu-Fe Sulfide - close physical association of PGM and “cumulus” chalcopyrite
• Why the paucity of sulfide in the PMZ?Sulfide dissolution by deuteric and low-T hydrothermal fluids – dissolution and
replacement textures in sulfide associated with silicate alteration;
secondary pyrite above PMZ
• Are the stratigraphic variations in grade primary?Yes for Pd & Pt, not for Cu and Au – Pd and Pt concentrations correlate to
subtle silicate layering; textural evidence of unreactive PGM; experimental evidence of Au and Cu mobility in oxidizing fluids
PGE Mineralizing Agent?PGE Mineralizing Agent?
Cu-Fe Sulfide? Fe-Ti Oxide???
Data from SL02-1 PMZ 0 to 105m below Cu-Au Break
Meters above Cu-Au break
Precious Metals Zone (PMZ)
““Cumulus” Sulfide in the PMZCumulus” Sulfide in the PMZ
SL02-1
SL02-2 SL02-3
100 um
Bn
Cp
Cp
Paucity of Sulfide in PMZ?Paucity of Sulfide in PMZ?
UralitizedUralitizedAugiteAugite
PGMPGM
Chl-ActChl-ActUraliteUralite
Mobility of SulfideMobility of Sulfide
Desulfurization and Oxidation of Cu SulfideDesulfurization and Oxidation of Cu Sulfide
Are Metal Offsets Primary?Are Metal Offsets Primary?
Kinetic ModelPreservation of variable degrees of disequilibriumduring sulfide liquation
Controls on Equilibrium•Sulf/Sil distribution coefficient
•Diffusivity of metals in silicate melt
•Nucleation density of sulfide droplet
•Size/Growth rates of sulfide droplets
•Settling rate of sulfide (strain rate of silicate melt)
Relationship of PGE to Modal Variations in the PMZPlagioclase Augite Fe-Ti Oxide
From Andersen et al. (1998)
Correlation of Leucocratic Gabbro to Skaergaard Platinova ReefsCorrelation of Leucocratic Gabbro to Skaergaard Platinova Reefs
Restite PGM / Resorbed Sulfide
Chlorite- Actinolite
Cp
Augite
Augite
Pd-Sb
50 um
Plagioclase
Pd-Sb
CpActinolite
Augite
Augite
50 um
Cp
Pt-Pd-As
50 um
Correlation by Secondary Pd PeaksCorrelation by Secondary Pd Peaks
Mineralization ModelMineralization Model ““Downer” StageDowner” Stage
Upgrading sulfide in intercumulus magma
Initial sulfidesaturation
PGE scavenging of magma columncomplete
Dsulf/sil~104-108
Rapid Diffusion
Dsulf/sil~102
Slow Diffusion
Mineralization ModelMineralization Model ““Upper” StageUpper” Stage
ClassicOffsetOffsetSkaergaard-typeSkaergaard-type
Met
ers
abo
ve s
ulf
ide
incr
ease
Met
ers
abo
ve s
ulf
ide
incr
ease
Comparing the SLI to other PGE reefsComparing the SLI to other PGE reefs
IF ONLY.....IF ONLY.....
PGEreefs
PELE – MELTS-based Modeling Programdeveloped by Alan Boudreau
MH - magnetite-hematite4 Fe3O4 + O2 = 6 Fe2O3
NiNiO nickel-nickel oxide2 Ni + O2 = 2 NiO
FMQ fayalite-magnetite-qtz3 Fe2SiO4 +O2 = 2 Fe3O4 + 3 SiO2
WM wustite -magnetite3 Fe1-xO + O2 ~ Fe3O4
IW iron - wustite2(1-x) Fe + O2 = 2 Fe1-xO
QIF quartz-iron-fayalite2 Fe + SiO2 + O2 = Fe2SiO4
Common fO2 range for magmatic conditions
arc
non-arc
Oxygen Buffers