Regional Geology, Sioux Lookout Orogenic Belt - Geology Ontario

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Introduction The Sioux Lookout orogenic belt (Figure 1) is a relatively small segment of the vast network of Late Archean (2.7 Ga) supracrustal rocks and associated intrusions that comprise the “western Wabigoon region” of the Wabigoon subprovince (Blackburn et al. 1991). The following preliminary reports of results from recent reconnaissance--scale bedrock mapping of the Sioux Lookout orogenic belt (an approximately 1000 km 2 study area; Devaney and Borowik 1994; Devaney et al. 1995a,b; Devaney and Babin 1996, Devaney 1997, 1998, 1999a), this report summarizes the descriptive and interpretative aspects of the various supracrustal units which constitute most of the Sioux Lookout orogenic belt (Figures 1, 2, and map in pocket), with an emphasis on the metasedimentary and fragmental metavolcanic units. This knowledge has been integrated with other geological data selected from previous studies in order to place the mineral occurrences of the Sioux Lookout orogenic belt in an improved tectono--stratigraphic context and thus aid mineral exploration. ACCESS The Sioux Lookout area is easily reached by road (Highway 72; Figure 1) and airplane. A network of subsidiary roads and highways and the larger lakes (Minnitaki, Little Vermilion, “Big” Vermilion, Abram, Pelican) provide excellent access throughout the area. ACKNOWLEDGMENTS Senior assistants A. Borowik, D. King and D. Babin mapped a significant part of the study area. Junior assistants M.McKenzie, M.Mitchell, B. MacFarlane, P. Smoter, M. Smethurst, D. Leng, J. Brownbill and W. Chisel provided fine field assistance, including some independent mapping by McKenzie, Smoter and Smethurst. D. Janes and G. Seim (Sioux Lookout Resident Geologist’s Office) and the Ministry of Natural Resources provided much valuable support for the field operations. L.D. Ayres, P.C. Thurston, D.W. Davis and D.G.F. Long offered useful geological advice during their field visits. R.O. Page’s gift of unpublished volcanological data, including a map of the Northeast Bay of Minnitaki Lake area, is greatly appreciated. Earlier versions of this manuscript were edited by P.C. Thurston, D.G.F. Long, and G.M. Stott. PREVIOUS WORK The distribution and apparent thickness (width of units perpendicular to strike) of the various lithological units in the Sioux Lookout orogenic belt study area (Figure 1) is shown in detail on the maps of Johnston (1969, 1972) and Devaney et al. (1995b; map in pocket). Figure 2 is a cross--section summarizing the general geology of the Sioux Lookout orogenic belt, and illustrates how previous studies contrast with this study. Mapping of the Sioux Lookout orogenic belt appears to have followed a 20 year cycle, with the main periods of study in the 1930s, 1950s, 1970s and 1990s. Following the earliest geological exploration of the Sioux Lookout area, which include reports of gold mineralization dating back to 1898 (Johnston 1972), Hurst (1933) produced the first modern geological map of the Sioux Lookout orogenic belt and Horwood (1938) reported on mineralized areas east of Sioux Lookout (Zarn Lake area). Pettijohn (1934, 1935, 1936, 1937, 1939) studied selected parts of the Sioux Lookout orogenic belt and was one of the first geologists to perform specialized sedimentological research on Archean metasediments, and his attempts at larger--scale stratigraphic correlation (Pettijohn 1937) are part of the foundation of similar contemporary efforts (Blackburn et al. 1985, 1991). New observations and interpretations of Pettijohn’s “Patara Formation” (Figure 3) are an important part of the present study. 1
Page 1: Ontario Geological Survey Open File
Page 5: e Queen’s Printer for Ontario, 20
Page 11: Large--Scale Structures ...........
Page 15: 25. Stage 5 sedimentation and tecto
Page 19: A large volume of basaltic strata (
Page 23 and 24: A large number of assessment file r
Page 25 and 26: The term “Neepawa Group” is mis
Page 27 and 28: Northern Volcanic belt from central
Page 29 and 30: amount of interbedded BIF units in
Page 31 and 32: limited by poor quality exposures,
Page 33 and 34: with small intermediate--felsic vol
Page 35 and 36: Interpretation The conglomeratic as
Page 37 and 38: separated by faulting into the two
Page 39 and 40: Miles Lake At the west end of Miles
Page 41 and 42: (plagioclase--phyric clasts are ver
Page 43 and 44: Part of this outcrop (about 1 m of
Page 45 and 46: Pillows are locally abundant and fo
Page 47 and 48: geochemical data (see “Geochemist
Page 49 and 50: CENTRAL VOLCANIC BELT: PICKEREL ARM
Page 51 and 52: BIF units, sub--exhalite alteration
Page 53 and 54: One outcrop contains important exam
Page 55 and 56: Most of the apparent paleocurrents
Page 57 and 58: change) from eastern pyroclastic fa
Page 59 and 60: Quartz veins with low to flat dips
Page 61 and 62: Observations made during the presen
Page 63 and 64: REE characteristics of the Patara F
Page 65 and 66: 6a--c and Figures 12a,c) are common
Page 67 and 68: STAGES 0, 1 The hypothesis that the
Page 69 and 70: subduction zone was likely to have
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structures, see: Christie--Blick an
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Laramide--type uplift, south--verge
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and contrast sharply with structura
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southeast--striking schistosity alo
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thrusting may be difficult or impos
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Lookout orogenic belt. This would c
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1988) interpreted the basal unit of
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In contrast, the ca. 2719-2713 Ma a
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interpretations of an appropriately
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The predominantly basaltic Stages 1
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Devaney 1997, 1999a) and other part
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strata (flat to 30 o dip southeast)
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misleading because it normally sugg
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Blackburn, C.E., Hinz, P., Storey,
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Devaney, J.R. 1997. Stratigraphy an
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Groves, D.I. and Foster, R.P. 1991.
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Larbi, Y., Stevenson, R., Breaks, F
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Pearce, J.A. and Peate, D.W. 1995.
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Steidtmann, J.R. and Schmitt, J.G.
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89 Figure 1a. Location and general
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91 Figure 2. Sioux Lookout orogenic
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Figure 4. Stratovolcanic transgress
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Figure 5b. Geochemical sample locat
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Figure 7. Plots of selected high fi
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Figure 8. Continued 99
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Figure 9. Continued 101
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Figure 11. Chondrite--normalized ra
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Figure 11. Continued. m) Northeast
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Figure 12. Continued. g) dioritic r
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Figure 13. Rb versus Y+Nb discrimin
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Figure 14. Continued. 111
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Figure 16. Th/Nb versus Nb/Y discri
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Figure 18. Adakite classification d
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Figure 20. Extended trace element p
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Figure 22a. Cross--sectional cartoo
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Figure 23. Semi--schematic map of t
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Figure 25. Stage 5 sedimentation an
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Figure 27. Cartoon scenario for dra
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Figure 29. Sinistral--sense positiv
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Figure 31. Stage 6 sedimentation an
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Figure 33. The proposed lineament p
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Table 1. Major and selected trace e
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Table 1. Continued Sample 94JRD--00
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Table 1. Continued. Sample 94JRD--0
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Table 1. Continued. Sample 94JRD--0
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Table 1. Continued. Sample 94JRD--B
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Table 1. Continued. Sample 95JRD--B
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Table 2. Classification of unaltere
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Table 3. Average major oxide compos
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Table 7. Summary of discrimination
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ISSN 0826--9580 ISBN 0--7778--9540-
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Regional Geology, Sioux Lookout Orogenic Belt - Geology Ontario

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