PGE potential of Ultramafic-Mafic Intrusions in Ontario: Vectors to PGE mineralization and where next..

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1 PGE potential of Ultramafic-Mafic Intrusions in Ontario: Vectors to PGE mineralization and where next.. Rebecca Sproule NewGenCo Pty Ltd, Geodiscovery Group, Perth, Western Australia C. Michael Lesher Department of Earth Sciences, Laurentian University, Sudbury, Ontario

2 Project Sponsors Operation Treasure Hunt Project (Ontario Geological Survey ) Christine Vaillancourt & Carole-Anne MacDonald NSERC CAMIRO

3 Introduction Aims were to identify key criteria for PGE prospectivity Petrogenesis and metallogenesis of 109 maficultramafic intrusions in Ontario (Canada) was determined n = 4830 Range includes: Archean to Palaeoproterozoic intrusions Komatiitic, tholeiitic, calc-alkalic, alkalic and sanukitoid magmatic affinities PGE mineralized economic to PGE-subeconomic to non-mineralised Importantly, WE ANALYSED BARREN INTRUSIONS TO UNDERSTAND THE COMPLETE SYSTEM!!

5 Mineralization Types Type I II III IV V Distribution contact/marginal stratabound internal disseminated stratiform reef-style hydrothermallymetamorphically deposited or mobilized tectonically mobilized Examples Coldwell, Kawene, Shakespeare, Tib Lake, Seagull Roaring River Moshkinabi, Centre Hill, Ghost Range, Seagull, Coldwell Lac des Iles Trout Bay

6 Type 1: Contact marginal: Net-textured ore, Alexo Mine, Dundonald Township

7 Type 2: Internal stratibound disseminated: Ccp-Po blebs in gabbro, Entwine Lake (Jason Arnold)

8 Type 3: Reef Type: Layered gabbro, Moshkinabi (Christine Vaillancourt)

9 Type 4: Hydrothermally remobilized Roby Zone varitextured

11 Type 5: Mineralized SUIF, Trout Bay area, Red Lake region (Christine Vaillancourt)

12 Ni-Co arsenide Pyrrhotite 2 cm Type 5: Ni-Co-PPGE arsenide mineralization in recrystallized Amph-Chl-Tc rock, Peterson property, Red Lake region (Christine Vaillancourt)

13 Petrogenesis

14 10 Crustal contamination versus Enriched source Continental crust N-MORB mixed Upper Continental Crust Continental crust E-MORB mixed La mobility? [La/Sm] MN 1 Different Contaminant? Coldwell Complex Quetico July Falls Lac des Iles-MBI Roaring River Moshkinabi Centre Hill Complex Kamiskotia Otto Seagull intrusion MORB E-MORB Nipissing Gabbro McVicar Lake Trout Bay Tib Lake Mulcahy White Lake Ghost Range Mann intrusion Caribou Lake Shakespeare OIB Proterozoic Pelitic Rock [Nb/Th] MN Enriched Mantle Depleted Mantle

15 Σ[REE] MN Crustal contamination versus Enriched source Unenriched source (normal depleted mantle) Decreasing intercumulus liquid Mg# Enriched source LDI-MBI LDI-NUMI LDI_CL Nipissing Gabbro Quetico McVicar Lake July Falls Trout Bay Tib Lake Roaring River Mulcahy Moshkinabi Coldwell Complex White Lake Centre Hill Complex Ghost Range Kamiskotia Mann intrusion Otto Caribou Lake Seagull intrusion Shakespeare Cumulate rock with 20% intercumulus material (depleted mantle source 90 region) 100 Cumulate rock with 20% intercumulus material (depleted mantle source region + 10% crustal contamination)

16 Crustal contamination Crustal log(s/se) Magmatic Nipissing Gabbro McVicar Lake Trout Bay Roaring River Moshkinabi White Lake Ghost Range Mann intrusion Caribou Lake Shakespeare LDI-CL Quetico July Falls Tib Lake Mulcahy Coldwell Complex Centre Hill Complex Kamiskotia Otto Seagull intrusion LDI-MBI LDI-NUMI Note low S/Se ratios of LDI-MBI and Trout Bay Mg# S-loss

17 Continental Crustal Contamination Mantle Source None to Minor Local Uniform Strongly Depleted (refractory) Moshkinabi Mulcahy McVicar Lake Kamiskotia Caribou Lake Strongly Depleted (refractory), then metasomatically enriched Coldwell Coldwell Lac des Iles - MBI Lac des Iles - NUMI Kawene Roaring River July Falls Otto Shakespeare Normal depleted Centre Hill Mann Trout Bay Ghost Range White Lake Mulcahy Normal depleted, then metasomatically enriched Tib Lake Enriched Seagull Seagull

18 Magma Type PGE mineralization is hosted by intrusions derived from a variety of magma types Most magmas form PGE mineralization Tholeiitic intrusions most commonly host PGE mineralization Alkaline intrusions with large abundances of mafic-ultramafic rocks are a less common host of PGE mineralization

19 Source Composition The most significant PGE reserves and resources (e.g., Coldwell Complex, Lac des Iles, Seagull, Shakespeare) are from intrusions from enriched or metasomatized mantle sources (e.g., sub-arc mantle) PGE mineralization is also associated with intrusions from normal depleted mantle (e.g., Moshkinabi and Mann intrusions) Such PGE mineralization is typically of lower tonnage and grade

20 Degree of Partial Melting The degree of prior melt extraction is not important mineralized intrusions are derived from sources that have experienced variable degrees of prior partial melting

21 Magma Diversification Processes Mineralized intrusions are either uncontaminated or only locally contaminated by upper crust Where contaminated, may have aided in triggered sulfide saturation Where uncontaminated, sulfide saturation was likely induced by fractionation crystallization In some cases (e.g., Lac des Iles), PGE may have also been concentrated into latestage volatile-rich phases

22 Magma Diversification Processes Intrusions that are uniformly contaminated rarely host significant tenors/tonnages of PGE mineralization can host significant amounts of Ni-Cu-PGE mineralization e.g., the Shakespeare intrusion

23 Metallogenesis

24 Identification of PGE rich magmas [Pd/Zr] MN Enrichment of Pd related to accumulation of PGE-rich sulfides Nipissing Gabbro Quetico McVicar Lake July Falls Trout Bay Tib Lake Roaring River Mulcahy Moshkinabi Coldwell Complex White Lake Centre Hill Complex Ghost Range Kamiskotia Mann intrusion Otto Caribou Lake Seagull intrusion Shakespeare FC AFC LDI-MBI LDI-CL MBI-NUMI Depletion of Pd related to loss of PGE-enriched sulfides Mg#

25 Trend Elevated Pt, Pd Elevated Pt, Pd, but lowest Mg# rocks are depleted PGE follow FC trend, high PGE rocks have accumulated sulfide, and lowest Mg# rocks are depleted PGE follow FC trend, and lowest Mg# rocks are depleted Depleted in PGE, Ni, and Cu above mineralized zone Depleted in PGE, but not Ni or Cu Uniformly depleted Intrusion Lac des Iles-MBI, Trout Bay, Tib Lake Coldwell/Coldwell, Roaring River, Mann/Mann, Lac des Iles- NUMI Moshkinabi, Centre Hill, Seagull/Seagull, Nipissing Gabbro Kawene, Ghost Range, Kamiskotia, Lac des Iles-CL Shakespeare, Nipissing Gabbro Mulcahy McVicar Lake, Otto Stock, White Lake, July Falls, Caribou Lake

26 Sulfide-Saturation History and Mineralization Type Type I contact-type mineralization is associated with rocks containing elevated to normal abundances of PGEs In most cases, the rocks overlying the mineralized zones are depleted in PGEs Type II internal disseminated mineralization is associated with rocks containing high abundances of PGEs However, other, typically more fractionated, portions of the intrusions can be depleted in PGEs

27 Sulfide-Saturation History and Mineralization Type Type III reef type mineralization is associated with rocks containing normal PGE abundances, but enrichment in samples with accumulated PGE Type IV hydrothermally-deposited or hydrothermally-mobilized mineralization is associated with PGE-enriched magmas (in Ontario)

28 Sulfide-Saturation History and Mineralization Type Some intrusions are depleted in PGE, but not Ni or Cu, suggesting that some PGE-enriched sulfides were lost during ascent and/or emplacement Such intrusions still have potential to host Ni-Cu deposits Some intrusions are uniformly depleted in PGE and have little potential for PGE mineralization

29 Sulfide-Saturation History and Mineralization Type Mineralized intrusions with the most significant PGE mineralization (highest grade and largest tonnage) have high background PGE abundances for their Mg# or MgO content

30 Summary Mineralized intrusions with the most significant PGE mineralization (highest grade and largest tonnage) have the high background PGE abundances for their Mg# or MgO content Intrusions derived from enriched sources should be preferentially explored for PGE mineralization Such rocks have high abundances of MILE (Ti, Zr, MREE-HREE) and very high abundances of all HILE (e.g., Cs, Rb, U, Th, Nb, Ta, LREE) Intrusions derived from normal depleted sources are still good targets for PGE mineralization, but are not as favourable

31 Summary In all cases where significant PGE mineralization is present, a specific process has triggered PGE segregation: crustal contamination, magma mixing, and/or fractionation crystallization Uniformly contaminated intrusions have low PGE potential, but such intrusions may host Ni-Cu mineralization The degree of prior melt extraction is not a significant factor for PGE prospectivity

32 So what s the important message out of this for exploration and future work research work.. In Ontario: The best intrusions have high background PGE abundances The intrusions from the best areas have enriched metasomatised mantle Prospective zones with enriched mantle can be mapped out Where next. Fennoscandia do the same relationships apply?

Lecture 38. Igneous geochemistry. Read White Chapter 7 if you haven t already

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