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

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fraction (A1a) also overlaps concordia, but has a distinctly higher 207 Pb/ 206 Pb age at 2695.1±3.3 Ma, and is interpreted as reflecting a mixture of an inherited component (e.g., 2703 Ma or older Tisdale assemblage) and magmatic growth within the porphyry at 2684 Ma. A 2684 Ma age for D2 deformation is consistent with the general observation by Bateman et al. (2004) that folds of this generation occurred after deposition of Porcupine assemblage (
03PJM-131 Quartz-feldspar porphyry, Pamour Mine area, Whitney Township (NAD83, Zone 17 UTM 489978E, 5373473N; #19 on Figure 2 and Table 1) As described by MacDonald and Piercey (2003) and MacDonald, Piercey and Hamilton (2005), the recently identified Pamour body southwest of Pamour Mine is a weakly foliated, moderately fresh, quartz- and feldspar-bearing porphyry carrying minor biotite alteration (disseminated fine flakes or 5– 20 mm clusters), and little pyrite. Phenocrysts within the porphyry average 1 to 2 mm, but reach up to 5 mm in maximum dimension. This unit sharply intrudes strongly altered (talc-carbonate) ultramafic volcanic rocks of the Hersey Lake formation in the lower Tisdale assemblage. The Pamour porphyry appears to truncate an earlier structural foliation developed in the host rocks, and is itself characterized internally by only a weak fabric, which may have originated by magmatic flow (MacDonald and Piercey 2003; MacDonald, Piercey and Hamilton 2004; 2005; Bateman et al. 2004, 2005, this study). The significance of this is discussed below. A representative sample of the porphyry was collected for dating from the 340.8 to 392 m interval of Porcupine Joint Venture drill hole 18986. Quartz-feldspar porphyry sample 03PJM-131 yielded a relatively diverse population of poor-quality zircons, comprising small, generally square bipyramids, pale to medium brown in colour, and often cracked, frosted or turbid, with some of the larger grains being slightly rounded (resorbed xenocrysts?). The best-quality (clearest, inclusion- and crack-free) grains were given strong air-abrasion before final selection and analysis, but the results are scattered: three fractions lie on or near concordia between 2680 and 2703 Ma (2 of these fractions have large errors, due in part to elevated common Pb; Table A1; Figure 5E). These data likely reflect varying degrees of zircon inheritance from the Tisdale assemblage or underlying units within porphyry magmatic grains. Two darker brown single grains are both highly discordant (A1b, A1c: Figure 5E). However, the datum for a single brown square bipyramid (fraction A1f) is only slightly discordant (0.5%) and at present provides the best estimate for the age of the sample, at 2677.5±2.0 Ma ( 207 Pb/ 206 Pb age). This interpretation is based on the assumption that analysis A1f itself does not contain inheritance; further, because of its minor discordance, the 2677.5 Ma age could be regarded as a minimum time of emplacement. Preliminary U/Pb results have been obtained for minor, euhedral pale yellow titanite from this sample. Two initial single-grain fractions are variably discordant, but suggest an upper intercept age of ~2673±11 Ma. Although imprecise, the titanite age is consistent with simple cooling through ca. 600°C following igneous crystallization, as defined by the best zircon age estimate near 2677.5 Ma. In summary, the best approximation of the age of emplacement of the Pamour porphyry is provisionally estimated at 2677.5±2.0 Ma, though this conclusion is based upon a slightly discordant single analysis. A more robust assessment of the true age of the body is hampered by inheritance and Pbloss effects. Although younger than most other porphyry intrusions in the Timmins area (ca. 2687– 2692 Ma), the ca. 2678 Ma age is entirely consistent with the observation that the Pamour intrusion carries less of a structural fabric than its counterparts and host rocks and may therefore independently provide a minimum age for D2 deformation. This interpretation is supported independently by the age of the Hoyle Pond porphyry (2684.4±1.9 Ma: see 03ED-096A above), which may be synchronous with D2 structures. An interesting additional observation is that the ca. 2678 Ma Pamour porphyry age correlates with a distinct population of youngest detrital zircons found within Dome formation sediments of the lowermost Timiskaming Group (2679 Ma: Ayer et al. 2003; Corfu, Jackson and Sutcliffe 1991). 119
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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
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Albitite dikes are crosscut by gold
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Worming Geophysical Data Treatment
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In Timmins, the first generation of
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Figure 20. Geological sketch map of
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from Halfmoon Lake, only 2 km to th
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The Blake River Group is divided in
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Figure 22. Geological map of Munro
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Mine stratigraphic succession, have
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Figure 24. Geological map of Currie
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Table 5. Simplified classification
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mesocumulate). The Stoughton-Roquem
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Shaw Dome Area GEOLOGICAL SETTING T
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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 118 and 119: The Timmins and Kirkland Lake-Larde
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 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
Page 168 and 169: Table A2. continued 204 U Th Pb* Pb
Page 170 and 171: Table A2. continued 204 U Th Pb* Pb
Page 172: Metric Conversion Table Conversion
Page 175 and 176: Chart A. Magnetic and Gravity Three
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