U-Pb SHRIMP and Sm-Nd Isotopic Results from the La Ronge Horseshoe Project

U-Pb SHRIMP and Sm-Nd Isotopic Results from the La Ronge Horseshoe Project: Evidence for a New Archean Inlier and a 1.84 Ga Arc Complex Related to Subduction under the Flin Flon–Glennie Complex

Ralf O. Maxeiner 1, Nicole M. Rayner 2, and Rob A. Creaser 3

Maxeiner, R.O., Rayner, N.M., and Creaser, R.A. (2014): U-Pb SHRIMP and Sm-Nd isotopic results from the La Ronge Horseshoe Project: evidence for a new Archean inlier and a 1.84 Ga arc complex related to subduction under the Flin Flon– Glennie complex; in Summary of Investigations 2014, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2014-4.2, Paper A-8, 16p.

Abstract Analytical results in support of the La Ronge Horseshoe project, a 1:20 000-scale bedrock mapping project northwest of La Ronge, are reported here together with preliminary conclusions. An area of granitic gneisses, suspected to represent a hitherto unrecognized Archean inlier in the southeastern Rottenstone Domain, yielded a calculated Sm-Nd model age of 3.29 Ga and an ƐNd(t) of -9.8 (t=1900 Ma), consistent with the field interpretations. This new area of isotopically evolved rocks is located about 30 km to the southeast of the Archean Black Bear Island Lake inlier. A feldspathic quartzite from a sedimentary succession (Sturdy Island assemblage) mantling the latter yielded 207Pb/206Pb ages between 2547 Ma and 1778 Ma, with the vast majority falling between 1940 and 1810 Ma. Replicate analyses on the youngest zircon constrain the maximum age of deposition to 1851 ±11 Ma. The Sturdy Island assemblage is cut by an undated phase of the Wathaman Batholith, which elsewhere yields ages of 1865 to 1850 Ma. Consequently, the age of deposition, taking the crosscutting relationship into account, must be around 1850 Ma. The Sm-Nd model age for the feldspathic quartzite is 2.65 Ga, with an ƐNd(t) of -4.4 (t=1900 Ma), which is consistent with the detrital zircon population of the sample.

In the western Glennie Domain, a homogeneous granodiorite (Nemeiben Lake intrusive suite) containing xenoliths of foliated granodiorite gneiss, yielded a crystallization age of 1853 ±3 Ma. A suite of megacrystic, hornblende- bearing monzonitic to granitic rocks (Rachkewich Lake pluton) cuts the Nemeiben Lake intrusive suite. A monzonite from this crosscutting suite yielded a U-Pb crystallization age of 1844 ±5 Ma, with the interpreted age of inherited zircon grains between 1879 and 1877 Ma. The calculated Sm-Nd model age (TDM) is 2.43 Ga and the ƐNd(t) value for the rock is -1.6 (t=1900 Ma), suggesting that the magma from which the rock crystallized has had some interaction with older crust.

Based on these new data, in conjunction with the field evidence, a first-order structural break is proposed separating Archean inliers and sedimentary sequences of the southern Rottenstone Domain from volcanoplutonic rocks of the Flin Flon–Glennie complex, of which the 1853 Ma Nemeiben Lake intrusive suite is a part. The crosscutting 1844 Ma Rachkewich Lake pluton represents a continental arc complex, built on the edge of the Flin Flon–Glennie complex, prior to its collision with Archean components such as the Sask craton.

Keywords: geochronology, continental arc, Black Bear Island Lake inlier, Glennie Domain, Rottenstone Domain, Reindeer Zone, Trans-Hudson Orogen, Paleoproterozoic, Archean, SHRIMP.

1. Introduction The La Ronge Horseshoe project (Maxeiner and MacLachlan, 2010; Maxeiner, 2011; Maxeiner and Fischbuch, 2012; Maxeiner et al., 2013a) was devised to map a poorly understood segment of the Reindeer Zone (Figure 1) of central Saskatchewan. Large parts of this area have not been mapped since the early 1950s and mid-1960s, and as a result, interpretations and subdivisions of protoliths lacked detail and supporting analytical work. Small components of the Horseshoe area were mapped at 1:20 000 scale in the mid-1980s to early 1990s (Slimmon, 1986; Lewry, 1986; Chiarenzelli et al., 1987; Thomas, 1993; Maxeiner and Sibbald, 1995). The results of this work enhanced understanding and analytical characterization of the depositional environments of the supracrustal rocks, emplacement history of the plutons, and lithotectonic history of this part of the Trans-Hudson Orogen.

1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 200 - 2101 Scarth Street, Regina, SK S4P 2H9. 2 Natural Resources Canada, Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8. 3 University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3.

Saskatchewan Geological Survey 1 Summary of Investigations 2014, Volume 2

Figure 1 – Location map and detailed geological map of the Little Crooked – Black Bear Island lakes area (modified after Maxeiner and Fischbuch, 2012), showing location of samples described in text. Index map abbreviations: FFD – Flin Flon Domain, GD – Glennie Domain, KD – Kisseynew Domain, LRD – La Ronge Domain, NIH – Nistowiak, Iskwatikan and Hunter Bay tectonic windows, PW – Pelican tectonic window, RD – Rottenstone Domain, WB – Wathaman Batholith.

Saskatchewan Geological Survey 2 Summary of Investigations 2014, Volume 2 Since 2010, 1:20 000-scale mapping in select areas has helped to delineate a number of distinct lithotectonic assemblages and to define the boundaries of Archean inliers and their contact relationships with bounding Orosirian4 (2.05 to 1.80 Ga) supracrustal belts and crosscutting plutons. By using analytical methods, including whole-rock geochemistry, as well as U-Pb and Sm-Nd isotopic results (Maxeiner et al., 2010, 2012, 2013b; Maxeiner and Kamber, 2011; Maxeiner and Rayner, 2011), these different lithotectonic components have been further constrained. This paper summarizes the most recent analytical results from the La Ronge Horseshoe project. Based on the new U-Pb zircon and Sm-Nd isotopic data, a number of exciting preliminary conclusions can be drawn. The data provide supporting evidence for the existence of 1) an area of isotopically evolved (?Archean) rocks along the east side of the Birch Rapids straight belt, 2) a circa 1.84 Ga arc complex at the western extent of the Flin Flon–Glennie Complex, and 3) an Orosirian-aged feldspathic quartzite-psammite succession mantling the Archean Black Bear Island Lake inlier.

2. Local Geology of the Black Bear Island Lake Area The area was first mapped by Morris (1963, 1965) and had since been visited by a number of other workers (Lewry and Slimmon, 1985; Bethune, 2006; Bickford et al., 2001; Rayner et al., 2005). Maxeiner and Fischbuch (2012) mapped Little Crooked Lake and Black Bear Island Lake at 1:20 000 scale. Their work provided more detail of the extent and lithological makeup of the Archean Black Bear Island Lake inlier, located at the northwestern end of the map area. The Archean rocks are separated from the surrounding Sturdy Island assemblage by a high strain zone. The Sturdy Island assemblage is dominated by psammitic rocks, with less extensive units of feldspathic quartzite and mafic volcanic rock. It is intruded by megacrystic quartz monzonites, which appear similar to and are physically connected to the main part of the circa 1.86 Ga Wathaman Batholith. To the southeast, anatectic melt sheets separate the Sturdy Island assemblage from an aluminous succession of pelitic to psammopelitic rocks that have been strongly deformed and transposed within the Birch Rapids straight belt. This succession was named the Birch Rapids assemblage (Maxeiner and Fischbuch, 2012) and has been affected by partial melting, giving rise to abundant anatectic melt sheets.

To the southeast of the Birch Rapids assemblage is an area, at least 20 km2 in size, of intensely deformed granitic gneisses and augen granite, which were speculated to represent another Archean inlier (ibid.). These are separated by another high strain zone (Rachkewich Lake shear zone) from a several-kilometre-wide zone of megacrystic and hornblende-bearing monzonite, quartz monzonite, and monzodiorite (Rachkewich Lake pluton). These latter rocks have a striking visual resemblance to those of the Wathaman Batholith to the northwest, but have no physical continuity with them and are separated from them by the Rachkewich Lake shear zone (an extension of the Howard Lake mylonite zone located some 20 km further to the southwest; Coté, 1994). The Rachkewich Lake pluton is therefore now considered to be part of an intrusive complex that is not related to the Wathaman Batholith.

The southern component of the remainder of the 2012 map area is dominated by tonalitic to granodioritic rocks (Nemeiben Lake intrusive suite) intruding a mafic volcanoplutonic succession (Freestone Lake assemblage) and bounding sedimentary succession (Crew Lake assemblage).

The structural history was summarized by Maxeiner and Fischbuch (2012), who suggested that the deformational history of the Birch Rapids straight belt and the area to the northwest (i.e., the Rottenstone Domain) could not be easily reconciled with that to the southeast (i.e., the Glennie Domain).

3. Analytical Techniques Building the provincial U-Pb and Sm-Nd databases will help characterize and fingerprint the various lithotectonic sedimentary and volcanic assemblages in the Reindeer Zone, as well as shed light on the presence and character of older structural inliers. A total of five samples were collected for analysis during this study (Table 1). Three samples (RM1201-7001, 7003, and -7005) were submitted for U-Pb zircon dating (Table 2) utilizing the Sensitive High- Resolution Ion MicroProbe (SHRIMP). One of these (RM1201-7005), along with two undated samples (RM1201- 010 and -012), was also submitted for Sm-Nd isotopic analysis (Table 3) to better constrain the provenance of sedimentary rock sequences and to help refine the paleoplate tectonic amalgamation history. U-Pb geochronology was carried out using the SHRIMP at the Geological Survey of Canada in Ottawa. SHRIMP analytical procedures followed those described by Stern (1997), with standards and U-Pb calibration methods following Stern and Amelin (2003). U-Pb results are presented in Table 2, with analytical details given in the footnotes. The Sm-Nd analytical work (Table 3) was carried out at the University of Alberta and analytical methods are identical to those described in Rayner et al. (2009) for analyses carried out on rocks of the Pelican Narrows area.

4 The following subdivisions of Paleoproterozoic time have been adopted from Gradstein et al. (2004): Siderian (2.50 to 2.30 Ga), Rhyacian (2.30 to 2.05 Ga), Orosirian (2.05 to 1.80 Ga), and Statherian (1.80 to 1.60 Ga).

Saskatchewan Geological Survey 3 Summary of Investigations 2014, Volume 2 Table 1 – List of samples, with UTM coordinates. Zone 13 (NAD 83) Sample # Data Lab # Station # Lithology Suite Location UTM_E UTM_N

RM1201-010 Sm-Nd n.a. RM12-08-011 Megacrystic monzonite Rachkewich Lake pluton North Rachkewich Lake 475516 6155057

RM1201-012 Sm-Nd n.a. RM12-10-006 Granitic gneiss Birch Rapids inlier West of Rachkewich Lake 473734 6156586

RM1201-7001 U-Pb z11025 RM12-14-008 Megacrystic monzonite Rachkewich Lake pluton North Rachkewich Lake 475127 6155036

RM1201-7003 U-Pb z11024 RM12-18-007 Homogeneous granodiorite Nemeiben Lake intrusive suite Central Little Crooked Lake 477147 6151667

RM1201-7005 U-Pb; Sm-Nd z11028 RM12-33-022 Feldspathic quartzite/psammite Sturdy Island assemblage East Sturdy Island, Black Bear Island Lake 467594 6163684

Table 2 – SHRIMP U-Pb data. Little Crooked Lake homogeneous granodiorite; RM1201-7003 (GSC lab number z11024, SHRIMP mount IP713) Apparent Ages (Ma) 204 206 204 208 207 206 207 206 206 207 207 Spot name U Th Th Yb Hf Pb Pb* f(206) Pb* Pb* Pb* Corr Pb* Pb Pb Pb Pb Disc. (ppm) (ppm) U (ppm) (ppm) 206Pb % ± (ppm) % 206Pb* % ± 235U % ± 238U % ± Coeff 206Pb* % ± 238U 238U (±) 206Pb 206Pb (±) (%)

11024-37.1 393 78 0.206 104 9633 9.0E-5 25 112 0.155 0.062 4.3 5.12 1.58 0.3319 1.46 0.925 0.1120 0.6 1848 23 1831 11 -1.0 11024-28.1 415 67 0.167 136 11253 5.3E-5 23 115 0.092 0.051 4.8 4.99 1.57 0.3224 1.47 0.933 0.1123 0.6 1801 23 1837 10 2.2 11024-7.1 521 93 0.185 138 12013 4.9E-5 40 146 0.085 0.053 3.8 5.05 1.52 0.3260 1.44 0.945 0.1124 0.5 1819 23 1838 9 1.2 11024-10.1 383 100 0.269 61 8680 3.7E-5 25 109 0.063 0.077 3.5 5.15 1.53 0.3322 1.45 0.946 0.1124 0.5 1849 23 1839 9 -0.6 11024-3.1 767 161 0.217 143 12117 2.0E-5 34 220 0.034 0.063 2.8 5.17 1.47 0.3334 1.43 0.971 0.1125 0.4 1855 23 1841 6 -0.9 11024-39.1 1263 480 0.393 214 11300 2.9E-4 13 362 0.500 0.120 2.0 5.18 1.64 0.3334 1.53 0.934 0.1127 0.6 1855 25 1843 11 -0.8 11024-35.1 961 195 0.209 163 12951 1.8E-5 26 272 0.031 0.063 3.1 5.12 1.48 0.3289 1.43 0.966 0.1129 0.4 1833 23 1846 7 0.8 11024-17.1 1913 445 0.240 234 14035 2.9E-4 10 557 0.498 0.067 2.1 5.28 1.50 0.3389 1.42 0.952 0.1129 0.5 1881 23 1847 8 -2.1 11024-38.1 378 79 0.216 150 12569 5.1E-5 37 107 0.088 0.067 4.9 5.11 1.64 0.3284 1.50 0.912 0.1130 0.7 1831 24 1848 12 1.1 11024-20.1 1095 266 0.250 182 12134 2.0E-5 34 313 0.034 0.071 2.8 5.18 1.52 0.3323 1.48 0.970 0.1130 0.4 1849 24 1849 7 0.0 11024-18.1 1032 258 0.258 161 12369 2.0E-5 32 285 0.035 0.077 2.6 5.01 1.47 0.3216 1.42 0.969 0.1130 0.4 1798 22 1849 7 3.2 11024-15.1 1273 308 0.250 236 12634 1.5E-5 21 377 0.027 0.079 2.0 5.38 1.44 0.3450 1.41 0.981 0.1130 0.3 1911 23 1849 5 -3.9 11024-36.1 1180 290 0.254 199 12636 5.6E-5 22 339 0.096 0.075 2.2 5.21 1.45 0.3340 1.42 0.974 0.1131 0.3 1858 23 1851 6 -0.5 11024-25.1 864 176 0.210 192 12444 5.1E-5 18 249 0.088 0.062 2.8 5.22 1.47 0.3348 1.42 0.969 0.1132 0.4 1862 23 1851 7 -0.7 11024-8.1 995 216 0.225 264 11339 1.8E-5 23 288 0.030 0.065 2.6 5.27 1.46 0.3374 1.42 0.973 0.1132 0.3 1874 23 1851 6 -1.4 11024-33.1 1016 282 0.287 215 10674 2.4E-5 22 290 0.041 0.091 2.4 5.19 1.48 0.3325 1.43 0.969 0.1133 0.4 1851 23 1853 7 0.1 11024-19.1 1313 377 0.297 179 13685 3.9E-5 20 345 0.068 0.087 3.0 4.77 1.51 0.3056 1.44 0.955 0.1133 0.4 1719 22 1853 8 8.2 11024-42.1 1099 246 0.231 245 11904 2.2E-5 23 324 0.039 0.070 2.8 5.37 1.49 0.3436 1.45 0.969 0.1133 0.4 1904 24 1853 7 -3.2 11024-43.1 860 218 0.262 184 10916 1.9E-5 37 248 0.033 0.071 2.7 5.24 1.47 0.3351 1.42 0.970 0.1133 0.4 1863 23 1854 7 -0.6 11024-32.1 1429 817 0.591 461 9105 1.6E-4 14 422 0.276 0.172 1.4 5.38 1.48 0.3441 1.43 0.963 0.1135 0.4 1906 24 1856 7 -3.1 11024-12.1 1157 307 0.274 212 11312 2.1E-5 24 332 0.036 0.083 1.9 5.24 1.44 0.3346 1.41 0.981 0.1135 0.3 1860 23 1856 5 -0.2 11024-41.1 734 180 0.254 202 10039 -2.2E-5 71 209 -0.037 0.077 2.8 5.20 1.49 0.3319 1.43 0.959 0.1136 0.4 1848 23 1859 8 0.7 11024-1.1 845 256 0.313 234 9629 5.2E-5 27 239 0.090 0.094 1.9 5.17 1.46 0.3297 1.42 0.973 0.1138 0.3 1837 23 1861 6 1.5 11024-11.1 720 126 0.181 235 11978 2.8E-5 26 200 0.049 0.053 3.7 5.07 1.50 0.3230 1.44 0.958 0.1139 0.4 1805 23 1863 8 3.6 11024-40.1 1059 231 0.225 170 12937 2.2E-5 26 307 0.039 0.066 3.1 5.30 1.72 0.3371 1.68 0.973 0.1140 0.4 1873 27 1864 7 -0.5 11024-27.1 616 132 0.222 197 11059 7.6E-5 53 173 0.131 0.054 4.4 5.15 1.65 0.3274 1.49 0.905 0.1141 0.7 1826 24 1865 13 2.4 11024-21.1 670 238 0.368 252 8023 --- 100 188 0.000 0.111 2.6 5.15 1.58 0.3271 1.52 0.963 0.1141 0.4 1824 24 1866 8 2.6 11024-23.1 525 89 0.174 130 12281 ---- 891 153 -0.001 0.055 3.8 5.39 1.59 0.3400 1.52 0.960 0.1149 0.4 1886 25 1879 8 -0.5

Saskatchewan Geological Survey 4 Summary of Investigations 2014, Volume 2 Table 2, cont’d

Rachkewich Lake megacrystic monzonite; RM1201-7001 (GSC lab number z11025, SHRIMP mount IP702) Apparent Ages (Ma) 204 206 204 208* 207* 206* 207* 206 206 207 207 Spot name U Th Th Yb Hf Pb Pb* f(206) Pb Pb Pb Corr Pb Pb Pb Pb Pb Disc. (ppm) (ppm) U (ppm) (ppm) 206Pb % ± (ppm) % 206*Pb % ± 235U % ± 238U % ± Coeff 206*Pb % ± 238U 238U (±) 206Pb 206Pb (±) (%)

11025-16.2 154 52 0.350 156 8448 5.9E-4 10 43 1.015 0.100 2.0 4.96 1.32 0.3249 1.05 0.796 0.1107 0.8 1814 17 1812 15 -0.1 11025-5.1 114 39 0.350 139 8808 1.4E-4 43 32 0.242 0.098 2.9 5.05 1.41 0.3301 1.08 0.764 0.1110 0.9 1839 17 1816 17 -1.5 11025-6.1 77 26 0.342 141 8241 3.0E-6 128 23 0.005 0.111 3.5 5.22 1.32 0.3395 1.16 0.875 0.1114 0.6 1884 19 1823 12 -3.9 11025-18.1 288 149 0.534 441 8699 6.9E-5 32 81 0.119 0.157 1.5 5.03 1.13 0.3267 1.04 0.925 0.1117 0.4 1822 17 1827 8 0.3 11025-16.1 123 31 0.263 133 9236 1.8E-4 24 33 0.305 0.078 3.2 4.85 1.31 0.3146 1.09 0.832 0.1118 0.7 1763 17 1829 13 4.1 11025-43.1 266 112 0.437 281 9966 5.2E-5 20 68 0.091 0.126 5.4 4.62 1.50 0.2996 1.32 0.881 0.1119 0.7 1689 20 1830 13 8.7 11025-22.1 239 89 0.387 205 9270 4.0E-6 348 68 0.007 0.111 2.0 5.13 1.20 0.3326 1.13 0.941 0.1119 0.4 1851 18 1831 7 -1.3 11025-5.2 142 42 0.309 139 10084 1.4E-4 32 40 0.244 0.090 3.1 5.09 1.35 0.3293 1.11 0.826 0.1121 0.8 1835 18 1833 14 -0.1 11025-41.1 139 55 0.405 220 8588 6.6E-5 57 39 0.115 0.118 2.7 5.09 1.27 0.3292 1.07 0.846 0.1122 0.7 1835 17 1836 12 0.1 11025-42.1 112 40 0.371 190 9231 8.1E-6 252 33 0.014 0.106 3.1 5.28 2.53 0.3410 2.46 0.971 0.1122 0.6 1892 40 1836 11 -3.5 11025-15.1 158 55 0.360 167 8962 5.0E-5 17 45 0.087 0.099 2.5 5.14 1.47 0.3318 1.30 0.883 0.1123 0.7 1847 21 1838 12 -0.6 11025-20.1 86 29 0.347 125 8719 1.5E-4 14 24 0.252 0.105 3.4 5.08 1.28 0.3276 1.10 0.857 0.1124 0.7 1827 17 1838 12 0.7 11025-40.1 298 106 0.367 231 10574 2.0E-4 15 82 0.341 0.109 1.9 5.00 1.15 0.3224 1.04 0.901 0.1125 0.5 1801 16 1840 9 2.4 11025-8.1 128 43 0.351 194 8336 7.2E-5 21 36 0.126 0.105 2.8 5.03 1.19 0.3239 1.07 0.894 0.1125 0.5 1809 17 1840 10 1.9 11025-37.1 201 70 0.362 191 9562 8.3E-5 17 56 0.144 0.100 5.4 5.06 1.42 0.3259 1.34 0.944 0.1125 0.5 1819 21 1841 9 1.4 11025-36.1 118 43 0.376 166 9178 7.4E-6 284 33 0.013 0.111 3.1 5.13 1.58 0.3296 1.46 0.923 0.1128 0.6 1836 23 1845 11 0.5 11025-44.1 73 27 0.380 157 8290 2.3E-4 46 21 0.397 0.119 3.4 5.09 1.83 0.3270 1.13 0.617 0.1128 1.4 1824 18 1845 26 1.3 11025-7.1 191 60 0.323 164 10139 6.9E-5 29 53 0.119 0.093 2.5 5.02 1.15 0.3229 1.05 0.909 0.1128 0.5 1804 16 1846 9 2.6 11025-1.2 153 70 0.475 267 8933 --- 1383 44 0.001 0.139 2.5 5.17 1.25 0.3324 1.14 0.913 0.1129 0.5 1850 18 1846 9 -0.2 11025-19.1 106 38 0.367 165 8292 4.8E-5 28 30 0.083 0.108 3.0 5.10 1.22 0.3274 1.08 0.885 0.1129 0.6 1826 17 1846 10 1.3 11025-39.1 275 99 0.370 217 9960 8.5E-5 37 78 0.148 0.110 2.0 5.13 1.16 0.3288 1.04 0.892 0.1132 0.5 1833 17 1851 9 1.1 11025-6.2 93 36 0.397 181 7959 7.4E-5 20 26 0.129 0.116 2.6 5.16 1.19 0.3306 1.07 0.898 0.1132 0.5 1841 17 1851 9 0.6 11025-4.1 238 80 0.347 194 10082 7.2E-5 44 66 0.125 0.103 2.1 5.07 1.17 0.3244 1.04 0.890 0.1133 0.5 1811 16 1852 10 2.5 11025-9.1 156 80 0.532 308 8016 --- 87 44 0.000 0.158 3.2 5.15 1.14 0.3284 1.05 0.923 0.1137 0.4 1831 17 1860 8 1.8 11025-13.1 147 50 0.348 152 9472 -4.7E-6 123 42 -0.008 0.104 2.6 5.24 1.25 0.3335 1.16 0.931 0.1140 0.5 1855 19 1864 8 0.5 11025-38.1 195 98 0.517 339 8357 5.5E-5 19 55 0.095 0.153 2.0 5.18 1.14 0.3294 1.05 0.921 0.1140 0.4 1835 17 1865 8 1.8 11025-1.1 137 49 0.367 166 8441 ---- 88 39 -0.001 0.117 2.3 5.22 1.14 0.3299 1.05 0.926 0.1148 0.4 1838 17 1877 8 2.4 11025-11.1 71 27 0.389 121 8237 5.3E-5 66 20 0.092 0.117 3.5 5.13 1.36 0.3239 1.12 0.822 0.1149 0.8 1809 18 1879 14 4.3 11025-3.1 194 56 0.301 159 10174 --- 5930 54 0.001 0.094 2.6 5.11 1.20 0.3225 1.05 0.875 0.1149 0.6 1802 17 1879 10 4.7

Sturdy Island assemblage feldspathic quartzite; RM1201-7005 (GSC Lab number z11028, SHRIMP mount IP702) Apparent Ages (Ma) 204 206 204 208* 207* 206* 207* 206 206 207 207 Spot name U Th Th Yb Hf Pb Pb* f(206) Pb Pb Pb Corr Pb Pb Pb Pb Pb Disc. (ppm) (ppm) U (ppm) (ppm) 206Pb % ± (ppm) % 206*Pb % ± 235U % ± 238U % ± Coeff 206*Pb % ± 238U 238U (±) 206Pb 206Pb (±) (%)

11028-13.1 18 7 0.424 60 6350 8.4E-4 14 5 1.455 0.130 5.3 4.88 2.35 0.3254 1.33 0.567 0.1087 1.9 1816 21 1778 35 -2.5 11028-9.1 28 18 0.670 101 8000 4.2E-4 34 8 0.735 0.209 3.5 5.10 2.35 0.3341 1.23 0.526 0.1107 2.0 1858 20 1811 36 -3.0 11028-78.1 20 13 0.680 81 7286 1.3E-3 19 6 2.193 0.167 4.6 5.20 3.70 0.3390 1.78 0.482 0.1112 3.2 1882 29 1820 59 -3.9 11028-21.1 36 26 0.733 123 8014 4.8E-4 22 10 0.837 0.210 3.1 5.15 1.96 0.3347 1.18 0.602 0.1116 1.6 1861 19 1826 28 -2.2 11028-30.1 148 95 0.660 203 9734 3.6E-4 26 41 0.626 0.197 1.7 4.99 1.64 0.3236 1.06 0.650 0.1118 1.2 1807 17 1829 23 1.4 11028-31.1 135 75 0.572 196 9787 1.9E-4 25 38 0.337 0.166 2.1 5.15 1.36 0.3320 1.13 0.829 0.1126 0.8 1848 18 1841 14 -0.4 11028-60.1 558 237 0.438 322 11444 1.5E-5 55 160 0.026 0.127 1.1 5.18 1.04 0.3340 1.01 0.975 0.1126 0.2 1858 16 1841 4 -1.0

Saskatchewan Geological Survey 5 Summary of Investigations 2014, Volume 2 Table 2, cont’d Apparent Ages (Ma) 204 206 204 208 207 206 207 206 206 207 207 Spot name U Th Th Yb Hf Pb Pb* f(206) Pb* Pb* Pb* Corr Pb* Pb Pb Pb Pb Disc. (ppm) (ppm) U (ppm) (ppm) 206Pb % ± (ppm) % 206Pb* % ± 235U % ± 238U % ± Coeff 206Pb* % ± 238U 238U (±) 206Pb 206Pb (±) (%)

11028-10.1 163 156 0.989 326 9124 2.7E-4 13 46 0.467 0.293 1.3 5.16 1.25 0.3322 1.11 0.887 0.1126 0.6 1849 18 1841 11 -0.5 11028-48.1 158 143 0.931 318 9366 1.6E-4 18 45 0.283 0.273 1.4 5.12 1.18 0.3300 1.05 0.887 0.1126 0.5 1838 17 1842 10 0.2 11028-16.1 132 73 0.572 152 10415 7.2E-5 52 39 0.124 0.161 1.9 5.30 1.23 0.3413 1.06 0.866 0.1126 0.6 1893 17 1842 11 -3.2 11028-53.1 18 10 0.579 92 7164 9.8E-4 26 5 1.703 0.164 4.8 5.26 3.63 0.3383 1.41 0.389 0.1128 3.3 1878 23 1844 61 -2.1 11028-30.2 123 81 0.678 188 10216 1.8E-4 25 35 0.304 0.203 2.0 5.16 1.30 0.3313 1.07 0.826 0.1129 0.7 1845 17 1846 13 0.1 11028-11.1 217 167 0.793 270 10227 5.9E-5 25 62 0.103 0.235 1.2 5.18 1.09 0.3328 1.03 0.941 0.1130 0.4 1852 17 1847 7 -0.3 11028-30.4 195 109 0.579 184 10875 1.6E-4 18 55 0.280 0.168 1.7 5.12 1.21 0.3287 1.09 0.902 0.1130 0.5 1832 17 1848 9 1.0 11028-46.1 72 35 0.502 127 10150 2.9E-4 23 20 0.510 0.144 2.7 5.19 1.49 0.3324 1.10 0.739 0.1131 1.0 1850 18 1851 18 0.0 11028-36.1 207 139 0.697 153 6934 1.3E-4 21 60 0.221 0.210 1.5 5.25 1.25 0.3355 1.04 0.835 0.1134 0.7 1865 17 1855 12 -0.7 11028-15.1 326 204 0.644 348 10111 1.5E-4 18 92 0.254 0.202 1.1 5.15 1.21 0.3296 1.14 0.940 0.1134 0.4 1836 18 1855 7 1.1 11028-68.1 142 133 0.969 316 9179 -1.4E-6 75 41 -0.002 0.293 1.4 5.21 1.13 0.3328 1.05 0.929 0.1135 0.4 1852 17 1857 8 0.3 11028-12.1 44 32 0.749 137 8183 1.5E-4 20 12 0.253 0.222 2.8 5.21 1.44 0.3325 1.20 0.833 0.1137 0.8 1850 19 1859 14 0.5 11028-14.1 219 209 0.985 401 9042 2.1E-5 83 58 0.036 0.298 1.3 4.80 1.64 0.3061 1.58 0.964 0.1137 0.4 1721 24 1859 8 8.4 11028-30.3 161 93 0.599 177 10929 6.1E-5 22 43 0.105 0.177 2.1 4.93 1.17 0.3143 1.06 0.901 0.1138 0.5 1762 16 1861 9 6.1 11028-82.1 232 123 0.546 239 11233 5.1E-5 39 67 0.088 0.166 1.4 5.27 1.20 0.3347 1.14 0.945 0.1141 0.4 1861 18 1866 7 0.3 11028-86.1 71 30 0.434 156 8656 5.7E-4 16 21 0.994 0.127 2.7 5.31 1.65 0.3374 1.10 0.666 0.1142 1.2 1874 18 1867 22 -0.4 11028-67.1 699 594 0.878 360 8625 2.6E-5 31 201 0.045 0.262 0.7 5.29 1.04 0.3355 1.01 0.979 0.1143 0.2 1865 16 1869 4 0.3 11028-24.1 155 98 0.653 284 9057 1.2E-4 26 44 0.203 0.187 3.0 5.27 1.17 0.3344 1.04 0.892 0.1144 0.5 1860 17 1870 10 0.6 11028-18.1 167 145 0.900 209 10431 9.2E-5 33 48 0.159 0.267 1.3 5.26 1.21 0.3333 1.09 0.903 0.1144 0.5 1854 18 1871 9 1.0 11028-84.1 228 150 0.679 320 11331 6.1E-4 18 65 1.059 0.218 1.2 5.27 1.66 0.3332 1.06 0.637 0.1146 1.3 1854 17 1874 23 1.3 11028-77.1 72 41 0.592 146 10515 7.8E-4 32 21 1.351 0.165 2.5 5.36 3.88 0.3393 1.18 0.305 0.1147 3.7 1883 19 1874 67 -0.5 11028-22.1 132 79 0.621 156 11343 4.4E-4 11 38 0.763 0.183 1.8 5.35 1.29 0.3380 1.05 0.820 0.1147 0.7 1877 17 1875 13 -0.1 11028-2.1 349 293 0.868 340 10987 4.0E-5 23 101 0.070 0.259 0.9 5.35 1.11 0.3377 1.08 0.970 0.1150 0.3 1875 18 1880 5 0.3 11028-70.1 647 704 1.125 591 9469 1.2E-5 26 190 0.021 0.335 0.6 5.41 1.03 0.3412 1.02 0.981 0.1150 0.2 1892 17 1880 4 -0.7 11028-79.1 249 167 0.694 164 10437 6.2E-6 249 71 0.011 0.207 1.4 5.29 1.10 0.3332 1.03 0.937 0.1151 0.4 1854 17 1881 7 1.7 11028-80.1 170 116 0.707 162 10132 1.0E-5 94 49 0.018 0.201 1.7 5.32 1.13 0.3331 1.05 0.928 0.1158 0.4 1854 17 1892 8 2.3 11028-28.1 88 71 0.832 238 8297 4.3E-5 99 25 0.074 0.248 1.9 5.28 1.29 0.3304 1.08 0.833 0.1158 0.7 1840 17 1893 13 3.2 11028-1.1 48 30 0.641 166 8362 1.4E-4 85 14 0.244 0.189 2.9 5.36 1.93 0.3354 1.14 0.592 0.1159 1.6 1865 18 1895 28 1.8 11028-35.1 63 45 0.737 145 9693 4.8E-5 77 18 0.083 0.224 4.1 5.44 1.62 0.3398 1.12 0.689 0.1161 1.2 1886 18 1897 21 0.7 11028-43.1 66 29 0.460 110 9620 1.6E-4 32 20 0.281 0.133 3.0 5.54 1.40 0.3460 1.11 0.790 0.1161 0.9 1915 18 1897 15 -1.1 11028-62.1 130 75 0.596 158 10539 1.3E-4 34 37 0.231 0.178 1.9 5.39 1.26 0.3364 1.06 0.840 0.1162 0.7 1870 17 1898 12 1.8 11028-47.1 246 144 0.603 219 12111 8.5E-5 21 73 0.147 0.180 1.3 5.56 1.09 0.3465 1.03 0.940 0.1165 0.4 1918 17 1903 7 -0.9 11028-71.1 166 123 0.770 182 10210 9.6E-6 65 48 0.017 0.222 1.5 5.41 1.11 0.3364 1.04 0.937 0.1166 0.4 1869 17 1904 7 2.1 11028-64.1 299 333 1.151 393 8098 1.0E-4 21 89 0.174 0.343 0.9 5.56 1.10 0.3451 1.03 0.941 0.1168 0.4 1911 17 1908 7 -0.2 11028-8.1 342 127 0.384 403 11420 1.6E-5 26 100 0.027 0.115 1.4 5.49 1.09 0.3411 1.02 0.937 0.1168 0.4 1892 17 1908 7 1.0 11028-32.1 80 47 0.607 179 9489 1.5E-4 64 24 0.257 0.178 2.4 5.57 1.82 0.3456 1.36 0.743 0.1169 1.2 1914 22 1909 22 -0.3 11028-38.1 204 143 0.722 799 7535 5.6E-5 70 60 0.098 0.217 1.4 5.50 1.23 0.3412 1.09 0.886 0.1170 0.6 1893 18 1911 10 1.1 11028-55.1 254 237 0.961 578 9624 7.3E-5 30 74 0.126 0.286 1.1 5.48 1.16 0.3393 1.09 0.939 0.1170 0.4 1883 18 1912 7 1.7 11028-85.1 217 105 0.502 189 12229 9.7E-5 22 64 0.167 0.143 1.6 5.55 1.12 0.3435 1.04 0.932 0.1172 0.4 1904 17 1914 7 0.6 11028-40.1 218 151 0.712 295 11423 3.4E-5 64 65 0.058 0.210 1.4 5.59 1.12 0.3459 1.04 0.927 0.1172 0.4 1915 17 1914 8 -0.1 11028-83.1 215 111 0.534 244 11359 4.8E-5 17 63 0.083 0.158 2.6 5.53 1.10 0.3414 1.04 0.944 0.1175 0.4 1893 17 1918 6 1.5 11028-51.1 123 71 0.592 203 9280 3.0E-5 36 36 0.052 0.174 2.0 5.51 1.15 0.3400 1.06 0.919 0.1176 0.5 1887 17 1920 8 2.0

Saskatchewan Geological Survey 6 Summary of Investigations 2014, Volume 2 Table 2, cont’d Apparent Ages (Ma) 204 206 204 208 207 206 207 206 206 207 207 Spot name U Th Th Yb Hf Pb Pb* f(206) Pb* Pb* Pb* Corr Pb* Pb Pb Pb Pb Disc. (ppm) (ppm) U (ppm) (ppm) 206Pb % ± (ppm) % 206Pb* % ± 235U % ± 238U % ± Coeff 206Pb* % ± 238U 238U (±) 206Pb 206Pb (±) (%)

11028-59.1 31 23 0.743 164 7949 4.6E-4 15 9 0.791 0.244 3.3 5.47 1.72 0.3371 1.22 0.711 0.1176 1.2 1873 20 1921 22 2.9 11028-25.1 64 65 1.040 174 8879 3.6E-5 76 19 0.062 0.321 1.9 5.63 1.39 0.3465 1.23 0.880 0.1177 0.7 1918 20 1922 12 0.3 11028-72.1 135 125 0.961 412 9462 3.7E-5 139 40 0.064 0.289 1.5 5.65 1.37 0.3469 1.17 0.851 0.1181 0.7 1920 19 1927 13 0.4 11028-39.1 128 107 0.870 395 8003 6.0E-5 21 38 0.103 0.262 1.6 5.63 1.24 0.3448 1.15 0.926 0.1183 0.5 1910 19 1931 8 1.3 11028-42.1 54 53 1.021 188 11358 -1.3E-5 783 16 -0.022 0.308 2.3 5.63 1.81 0.3432 1.27 0.700 0.1189 1.3 1902 21 1940 23 2.2 11028-49.1 25 18 0.741 99 8442 5.0E-5 149 7 0.087 0.232 3.8 5.80 1.78 0.3419 1.26 0.709 0.1231 1.3 1896 21 2002 22 6.1 11028-19.1 291 219 0.776 142 11850 1.3E-6 96 105 0.002 0.230 1.6 8.52 1.05 0.4196 1.02 0.975 0.1473 0.2 2259 19 2314 4 2.8 11028-63.1 567 569 1.038 460 11285 2.3E-4 7 220 0.396 0.311 0.6 9.58 1.09 0.4525 1.07 0.980 0.1535 0.2 2406 21 2386 4 -1.0 11028-45.1 159 220 1.423 271 12481 8.5E-5 22 61 0.148 0.412 1.0 9.59 1.10 0.4476 1.04 0.950 0.1553 0.3 2384 21 2406 6 1.0 11028-27.1 98 68 0.723 256 8602 7.1E-5 29 40 0.123 0.210 1.6 11.03 1.14 0.4799 1.07 0.938 0.1667 0.4 2527 22 2525 7 -0.1 11028-75.1 220 134 0.627 299 8347 3.8E-5 16 91 0.066 0.179 1.3 11.07 1.08 0.4800 1.05 0.971 0.1673 0.3 2527 22 2530 4 0.2 11028-26.1 190 118 0.643 268 8030 7.3E-5 30 78 0.126 0.183 1.4 11.11 1.13 0.4770 1.09 0.958 0.1690 0.3 2514 23 2547 5 1.6

Notes (see Stern, 1997):

Spot name follows the convention x-y.z; where x = sample number, y = grain number and z = spot number. Multiple analyses in an individual spot are labelled as x-y.z.z

Uncertainties reported at 1σ and are calculated by using SQUID 2.22.08.04.30, rev. 30 Apr 2008 f(206)204 refers to mole % of total 206Pb that is due to common Pb, calculated using the 204Pb method; common Pb composition used is the surface blank ( 204Pb/206Pb: 0.05770; 207Pb/206Pb: 0.89500; 208Pb/206Pb: 2.13840)

* refers to radiogenic Pb (corrected for common Pb)

Disc.: Discordance given as difference between measured 206Pb*/238U ratio and the expected 206Pb*/238U ratio at t=207Pb*/206Pb*: age, in percent.

Calibration standard 6266; U = 910 ppm; Age = 559 Ma; 206Pb/238U = 0.09059

Analytical details for SHRIMP mount IP713 (sample RM1201-7003): 13µm spot, 2nA primary intensity, 6 scans Error in 206Pb/238U calibration 1.39% (included)

Mass fractionation correction of 0.3% applied to 207Pb/206Pb results based on measurement of secondary standard z1242 (accepted 207Pb/206Pb ratio = 0.18292)

Analytical details for SHRIMP mount IP702 (samples RM1201-7001 and -7005): 25µm spot, 6nA primary intensity, 6 scans Error in 206Pb/238U calibration 1.00% (included)

No mass fractionation correction was applied to 207Pb/206Pb results based on measurement of secondary standard z1242 (accepted 207Pb/206Pb ratio = 0.18292)

Table 3 – Sm-Nd isotopic data for selected samples from the Black Bear Island Lake area.

Sm Nd uncert. CHUR Sample 147 144 143 144 143 144 (ppm) (ppm) Sm/ Nd Nd/ Nd0 ± 2σ εNd0 TDM Ga TMa εNdT Nd/ NdT @ TMa RM1201-7005 2.9583 16.8855 0.1059 0.511279 0.000008 -26.5 2.65 1900 -4.4 0.509954 0.510179 RM1201-010 9.5300 56.2587 0.1024 0.511379 0.000009 -24.6 2.43 1900 -1.6 0.510099 0.510179 RM1201-012 4.9008 23.6015 0.1256 0.511248 0.000011 -27.1 3.29 1900 -9.8 0.509678 0.510179

Notes: TDM is the depleted mantle model age calculated using the linear model of Goldstein et al. (1984).

TMa is the age at which the value for epsilon Nd (εNdT) is calculated. CHUR = Chondritic Uniform Reservoir.

Saskatchewan Geological Survey 7 Summary of Investigations 2014, Volume 2 4. Results a) Birch Rapids Granitic Gneiss, Southern Rottenstone Domain (Sample RM1201-012) A sample of granitic gneiss (RM1201-012) was collected from a proposed structural inlier (Maxeiner and Fischbuch, 2012) to test the field hypothesis that it represents older, possibly Archean, crust. In the field, an augen syenogranite (Figure 2A) occupying an area about 1.8 km in width and >10 km in length, was identified northwest of Rachkewich Lake and along strike at Birch Rapids on the Churchill River (Figure 1). These exposures bear a strong resemblance to those of the Archean Black Bear Island Lake inlier, located about 20 km to the west. Both areas are characterized by intensely deformed granitic gneisses and augen gneisses. The Birch Rapids gneiss is separated from the Black Bear Island Lake inlier by two strongly mylonitized sedimentary successions, transposed anatectic melt sheets, and intrusive sheets of the Wathaman Batholith. No U-Pb zircon data were acquired for this granitic gneiss, though Sm-Nd isotopic analysis yielded an ƐNd(t) value of -9.8 (t=1900 Ma) and a depleted mantle model age (TDM, Goldstein et al., 1984) of 3.3 Ga (Table 3). This provides evidence that these rocks represent a previously unrecognized piece of evolved crust in the Reindeer Zone, although it is possible that the evolved character has been imposed by inheritance. Further isotopic work and U-Pb geochronology are needed to clarify this. b) Little Crooked Lake Granodiorite, Nemeiben Lake Intrusive Suite, Western Glennie Domain (Sample RM1201-7003) Extending over an area approximately 40 km in diameter, the Nemeiben Lake intrusive suite (NLIS) is one of the most widespread suites of felsic intrusive rocks of the La Ronge Horseshoe project area (Figure 1; Maxeiner and MacLachlan, 2010; Maxeiner, 2011; Maxeiner and Fischbuch, 2012). The suite is dominated by granodiorite, tonalite and minor granite, and is generally characterized by homogeneous, medium- to coarse-grained intrusive rocks that range in structural appearance from massive to gneissic. The dominant mafic mineral phase is biotite (5 to 15%) with minor amounts of magnetite and hornblende. These tonalite to granodiorite intrusions are part of a widespread suite prominent throughout the western Glennie Domain, for which there are currently no age constraints. They could correlate with compositionally similar rocks exposed throughout the Rottenstone Domain and dated between 1833 and 1822 Ma (MacLachlan, 2005; Clarke et al., 2005) or, alternatively, they could correlate with rocks of the <1860 Ma successor arc suite (e.g., Syme et al., 1998). A previous attempt to date a tonalite from this intrusive suite (Maxeiner et al., 2012) failed due to high Hf concentrations in the zircon.

Field relationships indicate that the NLIS postdates the mafic volcanic rocks of the Freestone Lake assemblage, as well as the sedimentary rocks of the Crew Lake assemblage. At the sample location, a homogeneous granodiorite contains decimetre-scale xenoliths of fine-grained intermediate rocks of uncertain origin (Figure 2B) and amphibolite, tentatively interpreted as being of volcanic origin. Zircon recovered from this sample are prismatic, pale brown with oscillatory zoning visible in plane light as well as in back-scattered electron (BSE) images. No core/rim structures are evident. Twenty-eight analyses from 28 separate zircon grains gave individual 207Pb/206Pb ages ranging from 1831 to 1879 Ma (Table 2) with a mean of 1853 ±3 Ma (MSWD=1.5), which is interpreted as the crystallization age of the granodiorite (Figure 3A).

A northeast-trending mylonite zone overprints the granodiorite just west of the sample site. Consequently, the granodiorite becomes progressively more deformed westward and takes on a gneissic appearance, locally containing transposed screens of amphibolite. A few hundred metres to the north and in several other locations around Little Crooked Lake, older gneissic granodiorite xenoliths (Figure 2C) are contained within the dated NLIS granodiorite. On outcrop scale, plutons of the intrusive suite are cut by granitic pegmatite, and at map scale the suite is intruded by the Rachkewich Lake monzonite suite (sample RM1201-7001) and by 1838 ±6 Ma monzodiorite intrusions (Maxeiner et al., 2012) in the Nemeiben Lake area.

Since the granodiorite contains older, deformed, gneissic granodiorite inclusions and amphibolite inclusions, its crystallization age provides a minimum age for D1 deformation at Little Crooked Lake. Since the pluton itself has been overprinted by a northeast-trending mylonite zone, it also provides a maximum age for this deformational event.

c) Rachkewich Lake Monzonite, Western Glennie Domain (RM1201-7001/RM1201-010) Units of megacrystic monzonite, quartz monzonite and monzogranite underlying the area between Little Crooked Lake and Rachkewich Lake (Figure 1), together form the bulk of the Rachkewich Lake pluton.This pluton is separated from the Birch Rapids granitic gneisses by a mylonite zone (Rachkewich Lake shear zone) and intrudes the Nemeiben Lake intrusive suite (sample RM1201-7003). Its rocks are commonly characterized by a seriate texture with K-feldspar phenocrysts up to 5 cm long and a matrix containing abundant hornblende (Figure 2D).

Saskatchewan Geological Survey 8 Summary of Investigations 2014, Volume 2 Strongly variable quartz content on most outcrops gives rise to gradational variations from monzonitic to granitic compositions and, accordingly, boundaries between map units of the pluton are also gradational.

Sample RM1201-7001 is a homogeneous, weakly deformed megacrystic monzonite containing abundant hornblende and biotite (Figure 2E). Generally, the monzonite is moderately to strongly foliated, and locally mylonitic, particularly near the intrusion’s contact with isotopically evolved Birch Rapids granitic gneiss to the northwest. Xenoliths of granodiorite gneiss, similar to the ones within the Little Crooked Lake granodiorite (sample RM1201- 7003), also occur in the granitic phases of the Rachkewich Lake pluton. Many outcrops reveal late, crosscutting granite pegmatite and mafic dykes, as well as rare fine-grained felsic dykes.

Figure 2 – Outcrop photographs of: A) granitic gneiss collected in suspected structural inlier; sample location of RM1201- 012; B) homogeneous granodiorite of the Nemeiben Lake intrusive suite containing fine-grained intermediate xenolith; sample location for RM1201-7003; C) granodiorite of the Nemeiben Lake intrusive suite with foliated and folded granodiorite gneiss xenolith; from outcrop 300 m along strike to the north of sample location RM1201-7003; D) typical homogeneous megacrystic monzonite of the Rachkewich Lake pluton with small fine-grained mafic xenolith; station RM12-08-009; E) monzonite of the Rachkewich Lake pluton (location of sample RM1201-7001); F) tightly folded (F2) layering in feldspathic quartzite of the Sturdy Island assemblage (location of sample RM1201-7005).

Saskatchewan Geological Survey 9 Summary of Investigations 2014, Volume 2

Figure 3 – Concordia plots for: A) homogeneous granodiorite of the Nemeiben Lake intrusive suite (sample RM1201-7003; GSC lab number z11024); and B) Rachkewich Lake monzonite (sample RM1201-7001, GSC lab number z11025). Error ellipses are plotted at the 2σ uncertainty interval. See text for discussion.

The heavy mineral separates derived from the monzonite sample contained abundant, large prismatic zircon grains of generally good quality. Fractures and inclusions are few, and little to no alteration is apparent in BSE images. Oscillatory zoning is evident in most grains and no core/rim relationships were observed. Twenty-nine analyses on 25 zircon grains yielded 207Pb/206Pb ages between 1812 Ma and 1879 Ma (Table 2; Figure 3B). The three youngest results (grains #5, 6, 16) as well as a replicate analysis on grain #1 were not reproducible. Excluding these younger analyses, the weighted mean 207Pb/206Pb age of the combined dataset is 1848 ±7 Ma (n=25, 4 rejects, MSWD=2.6). Although the morphology and chemical characteristics of the zircon population is quite uniform (U=70 to 300 ppm, Th/U=0.3 to 0.5), the non-reproducibility of some results and the excess scatter suggests a combination of cryptic Pb-loss and inheritance are present in the sample. Excluding the three oldest grains (1879 to 1877 Ma) as xenocrysts, in addition to the younger replicates, the mean of the remainder of the population is 1844 ±5 Ma (MSWD=1.5, n=22), which is interpreted as the crystallization age of the monzonite. These data fit well with the observation that the Rachkewich Lake pluton intrudes a suite of older granodioritic rocks (sample RM1201-7001; 1853 ±3 Ma) and contains xenoliths of granodiorite gneisses (not dated). Volcanic and plutonic rocks between 1880 and 1870 Ma are known in the La Ronge and Rottenstone domains to the north

Saskatchewan Geological Survey 10 Summary of Investigations 2014, Volume 2 (e.g., Bickford et al., 1986; Corrigan et al., 2001), so the presence of xenocrysts of this age in younger intrusive rocks is not surprising.

Sm-Nd data (Table 2) from a separate sample of megacrystic monzonite from the Rachkewich Lake pluton, collected ~300 m away on the eastern shore of Rachkewich Lake (RM1201-010; Figure 1), yielded an ƐNd(t) of -1.6 (t=1900 Ma) and a TDM age of 2.43 Ga. This suggests that the magma from which the rock crystallized has had some interaction with older crust, although no Archean inherited zircon grains were encountered in the U-Pb dataset.

d) Feldspathic Quartzite, Sturdy Island Assemblage, Southern Rottenstone Domain (Sample RM1201-7005) The Archean Black Bear Island Lake inlier is mantled by the Sturdy Island assemblage and is separated from it by the Hagerty Island shear zone (Figure 1). The assemblage is dominated by a succession of migmatitic psammite- psammopelite (unit SPs) and feldspathic quartzite-migmatitic psammite (unit SQz), as well as minor intermediate to mafic volcaniclastic rock (unit SMv), ferruginous psammite-feldspathic quartzite (units SPsf), and iron-rich pelite (unit SIf). The relative stratigraphic position of the individual units is not known (Maxeiner and Fischbuch, 2012).

Rocks of the Sturdy Island assemblage are similar to some of the basal units of the Wollaston Supergroup (Yeo and Delaney, 2007), such as the Souter Lake Group or parts of the Daly Group. Along strike to the northeast, the Sturdy Island assemblage is also similar to the Hickson Lake assemblage of the Rottenstone Domain (MacLachlan, 2005), which was described as consisting of well-bedded psammopelite, quartzite, calc-silicate rocks, and amphibolite. The Hickson Lake assemblage was also equated with the lower Wollaston Supergroup, based on prominent 2.4 and 2.5 Ga detrital zircon age peaks (ibid.).

The rationale for collecting a sample of this newly recognized assemblage of the western Reindeer Zone was to investigate the possibility that it represents a passive margin succession deposited on the Archean Black Bear Island Lake inlier. Although separated from it by a high strain zone, a detrital zircon ‘barcode’ for the Sturdy Island assemblage would also allow comparison to the sedimentary rocks of the Crew Lake assemblage and other assemblages of the Rottenstone Domain described farther to the north (MacLachlan, 2005).

The Sturdy Island assemblage as a whole is intruded on map scale by megacrystic units of monzonite and quartz monzonite that have physical continuity with units forming part of the Wathaman Batholith. Much later intrusions of anatectic leucogranite are present on outcrop scale and as kilometre-long intrusive sheets (Figure 1).

The sample for U-Pb SHRIMP dating was collected on the east side of Sturdy Island (Figure 1), within unit SPs near its contact with unit SQz, both of which are intricately interlayered on map and outcrop scale. Unit SPs, as described by Maxeiner and Fischbuch (2012), is characterized by metre-scale compositional sedimentary layering between fine-grained psammite and fine- to medium-grained psammopelite. Centimetre- to decimetre-scale layers (Figure 2F) of feldspathic quartzite (origin of the sample) and diopside-bearing calcic psammite are also present. Pink granitic leucosome is prevalent throughout the unit and particularly well developed in the more psammopelitic layers. The sample is primarily composed of quartz (40 to 70%) and K-feldspar (5 to 20%) with lesser amounts of plagioclase (5 to 10%), biotite, and garnet.

An abundant population of large, well-faceted, prismatic zircon was recovered from the sampled feldspathic quartzite layer. The zircon grains vary in quality from clear, colourless, inclusion- and fracture-free, to moderately turbid grains with numerous inclusions, fractures, and alteration. The characteristics in plane light are consistent with the BSE images. As expected from a detrital sample, the zoning patterns vary significantly between grains. Notably, there is no consistent growth of zircon rims across the detrital population, which would be indicative of in situ metamorphic growth.

Sixty-one analyses on 58 zircon grains were carried out and yielded detrital zircon 207Pb/206Pb ages from 2547 Ma to 1778 Ma (Table 2), with the vast majority (53 analyses on 50 grains) falling between 1810 and 1940 Ma (Figure 4A). The dominant modes are centered at 1860 Ma and 1900 Ma (Figure 4B). The maximum age of deposition is constrained by four replicate analyses on an oscillatory zoned zircon grain (#30) with a mean 207Pb/206Pb age of 1851 ±11 Ma (MSWD=0.77; Figure 4A). Although there are some individual analyses with younger ages, these are from zircon grains with very low uranium content and their associated error makes them indistinguishable from the 1850 Ma grouping.

Saskatchewan Geological Survey 11 Summary of Investigations 2014, Volume 2

Figure 4 – Concordia diagram (A) and combined probability density diagram/histogram (B) for feldspathic quartzite RM1201-7005 of the Sturdy Island assemblage. Vertical axis on right-hand side of probability density diagram represents number of zircon grains. Error ellipses plotted at 2σ uncertainty interval. Light grey probability density diagram includes all data including replicates; histogram and light grey probability density curve has been filtered for concordance at 95% level. See text for discussion.

Sm-Nd data (Table 2) for the same sample gave an ƐNd(t) of -4.4 (t=1900 Ma) and a TDM of 2.65 Ga. This suggests that when the sediment was deposited, it received contributions from isotopically evolved sources. The presence of Neoarchean detritus in the same sample is consistent with the evolved ƐNd(t) and TDM values. Although no age constraints from the intrusive Wathaman-like pluton are available, the Sturdy Island assemblage is thought to have been deposited at ca. 1850 Ma based on the maximum depositional age of the feldspathic quartzite (1851 ±11 Ma), the 1865 to 1850 Ma age constraints on the Wathaman Batholith (e.g., Meyer et al., 1992), along with the analytical errors and inferred burial time.

5. Discussion and Preliminary Conclusions These new isotopic constraints, in conjunction with delineation of the supracrustal assemblages and crosscutting intrusive suites, have a number of potentially important implications for the amalgamation history of the southwestern Reindeer Zone. There are contrasting models (e.g., Meyer et al., 1992; Maxeiner et al., 2005; Corrigan et al., 2009; Maxeiner and Rayner, 2011) for the timing of collision between the Flin Flon–Glennie complex (Ashton et al., 1999) and the arc complexes of the La Ronge Domain and older evolved crust of the Sask and Hearne cratons. Obduction of the Lawrence Point suprasubduction zone ophiolite of the La Ronge Domain onto the sedimentary successions of the northern Kisseynew basin was proposed to have occurred between circa 1860 Ma and 1840 Ma in an oceanic realm (Maxeiner et al., 2005). This precludes, as proposed by other workers (Bickford et al., 1990; Meyer et al., 1992; Corrigan et al., 2009), accretion of the La Ronge arc to the Hearne craton margin prior to the emplacement of the Wathaman Batholith.

Saskatchewan Geological Survey 12 Summary of Investigations 2014, Volume 2 The discovery of a new slice of isotopically evolved crust in the southwestern Reindeer Zone, at the eastern extent of a major regional ductile mylonitic belt (Birch Rapids straight belt) raises questions about the affinity of the evolved crust. The exact age of both southern Rottenstone structural inliers and whether they are part of the Hearne craton or represent a separate crustal slice has yet to be determined. Maxeiner and Fischbuch (2012) suggested that it is unlikely that they are part of the Sask craton, based on interpretations of Lithoprobe seismic Line 9, located tens of kilometres to the southwest. Lithoprobe Line 9 (Hajnal et al., 2005) shows a stack of strong west-dipping seismic reflectors, approximately 30 km thick, thereby precluding correlation of the Rottenstone Domain inliers with those of the central Glennie Domain.

The supracrustal rocks mantling the Black Bear Island Lake inlier (Sturdy Island assemblage) and separated from it by a high strain zone cannot be a Rhyacian-aged (2.30 to 2.05 Ga) succession. Instead, they are interpreted to have been deposited close to the age of the youngest detrital zircon (<1851 ±11 Ma), at the younger end of emplacement of the crosscutting plutons of the 1865 to 1850 Ma Wathaman Batholith. The majority of detrital zircon within the succession appears to be derived from a 1.9 Ga source, with lesser Neoarchean-Siderian input. This is consistent with derivation from a mixture of Proterozoic arc complexes and Archean sources and is also consistent with ƐNd values determined for this sample (-4.4; Table 3). The most plausible source of Proterozoic detritus appears to be the Flin Flon–Glennie complex, within which volcanoplutonic rocks varying in age from 1.91 to 1.86 Ga are abundant, although a 1.92 to 1.91 Ga plutonic complex has also been recognized along the eastern margin of the Hearne craton (Maxeiner and Rayner, 2011) and 1.94 to 1.90 Ga is an important age range of thermotectonism in the southeastern Rae craton (e.g., Ashton et al., 2009). The Siderian to Neoarchean detritus is split equally between 2.4 to 2.3 and 2.53 Ga ages, both of which are more typical of the Sask craton than the Hearne craton, although that too could have been derived from the Rae craton. Therefore, it appears more consistent with the data to assume a Flin Flon–Glennie complex / Sask craton source, although the data do not preclude derivation from the Hearne and Rae cratons.

A suite of tonalitic to granodioritic rocks (locally named the Nemeiben Lake intrusive suite) underlying much of the southwestern and indeed the entire Reindeer Zone has yielded a crystallization age of 1853 ±3 Ma. This is a very common age for granodioritic rocks in the region, and these intrusive rocks are most commonly referred to as successor arc plutons (Syme et al., 1998). Field evidence suggests that the Nemeiben Lake intrusive suite postdated another suite of older granodiorite gneisses, which we believe are likely 1880 to 1870 Ma arc plutonic rocks. The fact that these xenoliths have been deformed prior to their incorporation into the Nemeiben Lake intrusive suite lends credence to the model of circa 1870 to 1860 Ma arc accretion (Lucas et al., 1996; Ashton et al., 1999).

The newly recognized Rachkewich Lake pluton (Maxeiner and Fischbuch, 2012) has remarkable geochemical, lithological, and textural similarity to the ca. 1860 to 1850 Ma Wathaman Batholith, but is physically separated from it by the Birch Rapids straight belt and isotopically evolved granitic gneisses (Figure 1). At 1844 ±5 Ma, the pluton is considerably younger than the Wathaman Batholith and compares well in age and lithology with a suite of intermediate to felsic plutonic to subvolcanic intrusions occurring in other parts of the Horseshoe project area (e.g., Maxeiner et al., 2012, 2013b) and throughout the southern Reindeer Zone (e.g., Syme et al., 1998). The pluton appears to intervene between the Birch Rapids granitic gneisses and the NLIS, but because the Rachkewich Lake shear zone separates it from the granitic gneisses, it remains unclear if the pluton ‘stitches’ the two elements or if it is located solely to the southeast of the shear zone.

If the Rachkewich Lake pluton only intruded rocks on the southeast side of the Rachkewich Lake shear zone, the fault may represent a fundamental first-order structural break (?suture), although reactivated during later deformational events. Along this shear zone, rocks of the isotopically evolved Birch Rapids granitic gneisses and the Black Bear Island Lake inlier (?Hearne craton), together with bounding sedimentary basins, have been juxtaposed with those of the Flin Flon–Glennie complex and Sask craton. The Rachkewich Lake pluton, occurring only on the southeast side of the fault, could be part of a more extensive 1.84 Ga arc that formed as a result of subduction under an emerging microcontinent, formed by the collision of the Flin Flon–Glennie complex with the Sask craton (Ashton et al., 1999). The shear zone would represent a potential suture, although much of the deformation along it is much younger due to reactivation. The fact that the Rachkewich Lake pluton has an evolved nature (ƐNd value of -1.56) provides supporting evidence that it was derived from partial melting and interaction with lithosphere that included the Flin Flon–Glennie complex and Sask craton.

It is possible that the Rachkewich Lake pluton represents a component of a larger arc complex that formed as a result of this collision between the Hearne craton and Flin Flon–Glennie complex. An age determination of the Birch Rapids granitic gneiss and further whole-rock geochemical work on the Rachkewich Lake pluton and other 1845 to 1835 Ma intermediate to felsic plutons and subvolcanic intrusions could help to test this hypothesis and put constraints on the early closure history of this part of the Trans-Hudson Orogen.

6. Acknowledgements We would like to thank Ryan Morelli and Ken Ashton for reviewing the manuscript.

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