Overview of Results from the Greenstone ... - Geology Ontario

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The Timmins and Kirkland Lake–Larder Lake gold and intrusion subprojects utilized detailed mapping and structural studies, lithogeochemistry and geochronology to provide an improved understanding of the relationships between and the ages of the various assemblages, and the timing of intrusions, structural, alteration and epigenetic gold mineralization episodes. The results of these studies documented the existence of multiple gold mineralizing events at both Timmins and Kirkland Lake. In the Timmins area, the main structural and gold mineralization events included ▪ D1 uplift and excision of upper Tisdale stratigraphy with formation of an angular unconformity predating deposition of Porcupine assemblage at 2690 Ma. ▪ An early, lower grade gold mineralizing event predates the Timiskaming unconformity and may be synchronous with D2, which produced thrusting and folding and early south-over-north dip-slip movement on the Porcupine–Destor deformation zone (PDDZ) between 2685 and 2676 Ma. ▪ The later main stage of gold mineralization is associated with D3, a protracted event which coincided with the opening of the Timiskaming basin but also overprints the Timiskaming sediments. The D3 folding and faulting are coeval with up to 13 km of left-lateral strike-slip movement on the PDDZ. The main stage of gold mineralization provided most of the ore at the Hollinger-McIntyre, Dome and Hoyle Pond mines. Rhenium-osmium analyses of molybdenite associated with gold mineralization at the McIntyre Mine provided an age of 2672±7 Ma and, at the Dome Mine, 2670±10 Ma. ▪ D4, produced by transpressional strain, included folding and faulting that preserved Timiskaming assemblages in synclines along the PDDZ and is associated with a late stage gold mineralization event along the Pamour Mine trend. In the Kirkland Lake–Larder Lake area, the main structural and gold mineralization events, all post- Timiskaming, include ▪ D2, corresponding to the reverse-dextral (south-over-north) movement along the Larder Lake– Cadillac deformation zone (possibly correlated to the D3 event in Timmins). Gold mineralization hosted by the Larder Lake–Cadillac and Upper Canada deformation zones (e.g., Anoki, McBean and Upper Canada deposits) formed synchronously with D2. ▪ D3, related to the east-west shortening. ▪ D4, corresponding to the northwest-southeast shortening. Gold mineralization of the Narrows Break (about 2.5 km north of the Larder Lake–Cadillac deformation zone, and 350 m north of the Kirkland Lake Main Break) is synchronous with D4. ▪ The Kirkland Lake gold deposits consist of gold and telluride-bearing, sulphide-poor quartz veins associated with the brittle to brittle-ductile Kirkland Lake fault (Main Break) and its subsidiary splays. The association of veins with brittle faults suggest relatively shallow crustal levels of mineralization. Distinct metal signature and mineralization style suggest that Kirkland Lake deposit probably represents a stand-alone hydrothermal system that is unrelated to gold deposits along the Larder Lake–Cadillac deformation zone and its splays. A deep magmatic fluid source (sharing analogies with the alkalic magmatic mineralization systems, as defined by Jensen and Barton 2000) appears most probable for the Kirkland Lake mineralization. Gold-bearing veins could have formed early in the D4 event, synchronously with south-over-north reverse-dextral to reverse movement along the Main Break. Alternatively, mineralization could have pre-dated D4. 92
A new metamorphic framework has provided additional constraints on the setting of gold deposits and a new tool for gold exploration. ▪ The metamorphic pattern in the study area is the result of superposition of regional metamorphism on narrow higher grade contact metamorphic aureoles that formed at different times immediately adjacent to granitic intrusions, indicating that most of the granitoids are older than the regional metamorphic event. ▪ Pre-Timiskaming phases of deformation were less penetrative and occurred at shallower depths in the crust and at lower temperatures than post-Timiskaming deformation. ▪ Post-Timiskaming deformation, when peak regional metamorphic conditions prevailed, was most conducive to formation of large syn-metamorphic (orogenic) gold deposits. There is a striking spatial relationship of the boundary between the lower and upper greenschist metamorphic zones and a significant number of gold mines. Newly identified high priority targets are defined by the coincidence of metamorphic anomalies with major structural features, specific rock compositions, and moderate to intense deformation. ▪ The pre-regional metamorphic ages inferred for most of the intrusive plutonic rocks in between the Porcupine–Destor and Larder Lake–Cadillac deformation zones suggests targeting for granite- and porphyry-related gold deposits in this area. Regional structural patterns are now better understood, in part based upon improved knowledge of the distribution of the stratigraphy and intrusions in conjunction with detailed and regional-scale geophysical surveys including magnetic, gravity and reflection seismic surveys. Major external intrusive units, such as Round Lake and Kenogamissi batholiths, include predominantly synvolcanic phases that occupy anticlinal culminations in common with the situation in Quebec (Daigneault, Mueller and Chown 2004), whereas the late syntectonic intrusions had a relatively minor localized structural effect on the surrounding supracrustal rocks. Regional deformation zones are the loci of major faults, which have been reactivated repeatedly and have exerted control on the distribution of early volcanic (“Keewatin”) and late sedimentary assemblages. All assemblages were constructed in an autochthonous fashion and have been locally juxtaposed along regional structures during major ductile deformation events that involved predominantly north-south transpressional shortening. Our geophysical interpretations and conclusions and preliminary interpretations from the Discover Abitibi seismic reflection surveys (Reed, Snyder and Salisbury 2005) ▪ demonstrate the sense of dip on major structures and lithological units with inversions of magnetic and gravity data; ▪ demonstrate the sense of dip on major lithological units and major strike-slip faults using reflection seismic data; ▪ demonstrate a southerly dip for the Porcupine–Destor fault in the Matheson to Nighthawk Lake segment, with a change to steep northerly dip in the Timmins camp; ▪ verify that the Shaw structure is domal and may be cored by a granitic body; ▪ indicate higher impedance units (Tisdale assemblage volcanic rocks?) occur in anticlinal structures (D2?) beneath the Porcupine assemblage sedimentary rocks north of Timmins. This report represents the first comprehensive multidisciplinary synthesis at greenstone belt scale since the widespread acceptance of autochthonous models for greenstone belt evolution (Ayer, Amelin et al. 2002; Thurston 2002). As such, it considerably advances understanding of Abitibi greenstone belt architecture and metallogeny with specific emphasis on copper-zinc, nickel-copper-PGE and gold mineralization and with numerous insights and recommendations that are directly applicable to exploration for these commodities. 93
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ISBN 0-7794-8652-8 THESE TERMS GOVE
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ONTARIO GEOLOGICAL SURVEY Open File
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Contents Abstract .................
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Appendix 1. Thermal Ionization Mass
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Miscellaneous Release—Data 155 Di
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The Timmins area and Kirkland Lake-
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Overview of Results from the Greens
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3. The geophysical subproject funct
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The following Preliminary Maps have
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Samples with zircons analyzed by SH
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Figure 4. U/Pb concordia plots of T
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Figure 6. U/Pb concordia plot of TI
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Targeting of several of these overg
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Figure 10. U/Pb SHRIMP results from
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In northwest Cleaver Township, a fe
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SHRIMP U/Pb dating was carried out
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Stratigraphic Framework In this sec
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PACAUD ASSEMBLAGE The 2750 to 2735
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The iron formation and chert brecci
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(thickness) of banded iron-poor iro
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clast conglomerates at the top of t
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BLAKE RIVER ASSEMBLAGE Lower Part T
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The Krist formation consists of cal
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Timmins Area In the Timmins area, t
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Kirkland Lake-Larder Lake Area Hyde
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Intrusion Framework The plutonic ro
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The youngest dated synvolcanic mafi
Page 68 and 69: Albitite dikes are crosscut by gold
Page 70 and 71: Worming Geophysical Data Treatment
Page 72 and 73: In Timmins, the first generation of
Page 74 and 75: Figure 20. Geological sketch map of
Page 76 and 77: from Halfmoon Lake, only 2 km to th
Page 78 and 79: The Blake River Group is divided in
Page 80 and 81: Figure 22. Geological map of Munro
Page 82 and 83: Mine stratigraphic succession, have
Page 84 and 85: Figure 24. Geological map of Currie
Page 86 and 87: Table 5. Simplified classification
Page 88 and 89: mesocumulate). The Stoughton-Roquem
Page 90 and 91: Shaw Dome Area GEOLOGICAL SETTING T
Page 92 and 93: 66 Figure 26. A generalized map of
Page 94 and 95: 1999) in their REE patterns and oth
Page 96 and 97: plumbing system geometrically stabl
Page 98 and 99: GOLD MINERALIZATION Production comm
Page 100 and 101: The Narrows Break mineralized zone,
Page 102 and 103: Table 7. Diagnostic mineral assembl
Page 104 and 105: anomaly and the Dome Mine (Figures
Page 106 and 107: Recommendations • Further testing
Page 108 and 109: of the inversion product. (Recent a
Page 110 and 111: the evidence for pre-Pacaud strata
Page 112 and 113: plutonism suggests the onset of reg
Page 114 and 115: Watkinson and Comba 1989; Gibson an
Page 116 and 117: The Kirkland Lake giant gold deposi
Page 120 and 121: References Ames, D.E., Bleeker, W.,
Page 122 and 123: Bleeker, W., Parrish, R.R. and Sage
Page 124 and 125: Galley, A.G., Pilote, P. and Davis,
Page 126 and 127: Heather, K.B., Percival, J.A., Mose
Page 128 and 129: Lesher, C.M., 1989. Komatiite-assoc
Page 130 and 131: Péloquin, A.S., Verpaelst, P., and
Page 132 and 133: Stern, R.A. 1997. The GSC sensitive
Page 134 and 135: 108 This page left blank intentiona
Page 136 and 137: THERMAL IONIZATION MASS SPECTROMETR
Page 138 and 139: 04BHA-0462 Granophyre, Kamiskotia G
Page 140 and 141: contrastingly have been dated near
Page 142 and 143: The revised age of 2672.8±1.1 Ma f
Page 144 and 145: fraction (A1a) also overlaps concor
Page 146 and 147: 04JAA-0010 Albitite dike cutting Ti
Page 148 and 149: Therefore, on geochronological grou
Page 150 and 151: Three individual grains were analyz
Page 152 and 153: 03VOI-0422-1 Trachytic lava, Timisk
Page 154 and 155: 03SJP-115-1 Monzonite, Clifford sto
Page 156 and 157: the original Corfu (1993) age, only
Page 158 and 159: Table A1. U/Pb isotopic data for zi
Page 160 and 161: 206 Sample Analysis Description Wei
Page 162 and 163: Appendix 2 Sensitive High-Resolutio
Page 164 and 165: Table A2. Ion microprobe (SHRIMP II
Page 166 and 167: Table A2. continued Struct. U Th Pb
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Table A2. continued 204 U Th Pb* Pb
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Table A2. continued 204 U Th Pb* Pb
Page 172:
Metric Conversion Table Conversion
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Chart A. Magnetic and Gravity Three
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