The Palmer Hill ore body consists of massive magnetite, with quartz, apatite, microcline, albite, fluorite, and zircon. Disseminated magnetite is

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1 DR Data Repository Item DR-1 Ore deposit descriptions Palmer Hill The Palmer Hill ore body consists of massive magnetite, with quartz, apatite, microcline, albite, fluorite, and zircon. Disseminated magnetite is common throughout the host granites in the Palmer Hill mine area, but is generally lacking in depleted zones up to 100 meters wide adjacent to the ore body (Hagner and Collins, 1967). The ore was approximately 3 meters thick at Palmer Hill over a distance of ~600m narrows to 1 meter (Postel, 1952). The ore body lies in the axis of a northeast plunging syncline with brecciated and mylonitized zones in the hanging wall and footwall. The ore body and fold are bounded on the southeast by a northeast trending fault. The host rock in the vicinity of the ore is dominated by microcline granite gneiss. Microcline is partially corroded or crosscut by albite and hematite partially replaces magnetite in the host granite. Arnold Hill The ore bodies at Arnold Hill are a mixture or magnetite, hematite, martite (pseudomorphic hematite after magnetite) and minor apatite and zircon. Calcite, jasper, and amphibole/chlorite breccia are common at the margins of the ore adjacent to the host rock. Three main ore bodies were mined here two of which were magnetite and one martite. The thickness of all 3 ore bodies ranges from 1 to 7 meters. The ore bodies plunge to the northeast and may occupy the east limb of a syncline (Postel, 1952). The host rock at Arnold Hill is dominated by albitic gneiss. Albite has replaced the perthitic feldspar granite.

2 Skiff Mountain The ore consists of two main bodies approximately 40 meters apart and is concordant with the gneissic foliation. The lower ore has been mined out and is inaccessible. The upper ore consists of a half-meter thick body of massive magnetite, apatite, and quartz. The host rock immediately above and below the ore consists of quartz-albite gneiss and is depleted in disseminated magnetite for 0.5 meters above the ore. Thirty to 40 meters above the ore body, the host rock returns to perthitic granite (McLelland et al., 2002). Old Bed Ore samples from the Old Bed mine consist of magnetite, apatite, clinopyroxene, and quartz. Early workers describe the Old Bed ore as part of a larger ore body that pinches and swells and is thickest in the hinge of an overturned antiform that is dissected by faulting (Kemp, 1908; Gallager, 1937). The ore is up to 15m thick. This series ore bodies is greater than 800 meters long and in some regions of the fold hinge is 60 meters thick. Perthitic granite is common in the hanging wall of the Old Bed ore.

3 Data Repository Item DR-2 Analytical Techniques Zircon separation was done using standard crushing, heavy liquids, and magnetic methods, following removal of magnetite using a hand magnet on the crushed ore. Zircon crystals were hand picked from the non-magnetic fraction (the remaining magnetite, hematite, and martite, were removed during this stage) and mounted in epoxy resin and polished to reveal the crystal interiors. The mounts were gold coated and imaged with a Hitachi S-4300 scanning electron microscope (SEM) using cathodoluminescence (CL) to identify internal structures and zoning. Back-scattered electron (BSE) imaging was used to identify fractures and inclusions within the grains and to identify analytical spot locations precisely after the analyses were done. Uranium-Th-Pb and Pb-Pb zircon analyses for the 4 samples in this study were done using the Cameca IMS 1270 ion-microprobe at the Swedish Museum of Natural History following the methods first described by Whitehouse et al. (1999) and later modified in Whitehouse and Kamber (2005). The calibration of U/Pb ratios is based on the 1065 Ma zircon standard with U and Pb concentrations of 80 and 15 ppm, respectively (Weiedenbeck et al., 1995). For our sample in which high U concentrations precluded accurate U/Pb calculations only 207 Pb/ 206 Pb ages were calculated. Data reduction is done using Excel macros developed at the Swedish Museum of Natural History in Stockholm. Applicable to all material, age determinations and errors were calculated using Isoplot version 3.34 (Ludwig, 2003). U-Pb data are plotted as 2 error ellipses.

4 All age errors quoted in the text are 2 unless specifically stated otherwise. Common Pb corrections were applied to all ion probe data. An average composition for modern day terrestrial common Pb is assumed (Stacey and Kramers, 1975). References Cited Gallagher, D., 1937, Origin of the magnetite deposits at Lyon Mountain, N. Y: New York State Museum Bulletin, p. 85. Hagner, A.F., and Collins, L.G., 1967, Magnetite ore formed during regional metamorphism, Ausable magnetite district, New York: Economic Geology, v. 62, p Kemp, J. F., The Mineville-Port Henry mine group: in Newland, David H., Geology of the Adirondack magnetite iron ores, New York State Museum Bulletin 119, p Ludwig, K.R., 2003, User's Manual for Isoplot 3.00, A geochronological toolkit for Microsoft Excel: Berkley Geochronology Center Special Publication No. 4 Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, p. 207.

5 McLelland, J., Morrison, J., Selleck, B., Cunningham, B., Olson, C., and Schmidt, K., 2002, Hydrothermal alteration of late- to post-tectonic Lyon Mountain granitic gneiss, Adirondack Mountains, New York; origin of quartz-sillimanite segregations, quartz-albite lithologies, and associated Kiruna-type low-ti Feoxide deposits: Journal of Metamorphic Geology, v. 20, p Postel, A.W., 1952, Geology of the Clinton County magnetite district: United States Geological Survey Professional Paper, v. 237, p. 88. Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, p Whitehouse, M.J., Kamber, B.S., and Moorbath, S., 1999, Age significance of U- Th-Pb zircon data from early Archaean rocks of west Greenland--a reassessment based on combined ion-microprobe and imaging studies: Chemical Geology, v. 160, p Whitehouse, M.J., and Kamber, B.S., 2005, Assigning Dates to Thin Gneissic Veins in High-Grade Metamorphic Terranes: A Cautionary Tale from Akilia, Southwest Greenland: J. Petrology, v. 46, p

6 Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., Quadt, A.V., Roddick, J.C., and Spiegel, W., 1995, Three natural zircon standards for U- Th-Pb, Lu-Hf, trace element and REE analyses: Geostandards and Geoanalytical Research, v. 19, p

7 Data Repository Table DR1 Ion microprobe U-Th-Pb results for the Lyon Mountain Granite and associated iron ores (used for Figure 3 in Valley et al.l). Sample U(ppm) Th (ppm) Pb (ppm) Th/U f206 * 238U/206Pb sigma% 207Pb/206Pb sigma% 207Pb/206Pb Ma error 206Pb/238U Ma error Palmer Hill granite (99-4b) 1B {0.01} A B** {0.21} B {0.03} C {0.04} B {0.01} A {0.03} B {0.08} C B D Arnold Hill granite (99-5a) 1A {0.01} B A {0.00} A {0.00} B A {0.07} B C {0.09} A {0.00} B {0.01} A B A {0.01} B B A {0.01} C A Palmer Hill magnetite ore (99-4a) 1A B A A B a b c a a b a a

8 Arnold Hill magnetite ore (ah-6b) 1a b a a b b c b Skiff Mountain magnetite ore (00-01) 2A B {0.04} A {0.07} B {0.17} C {0.06} A Old Bed Ore (obo)

9 Notes: All errors are 1 sigma *Percent of Pb206 that is common Pb, brackets indicate 204 was too small to measure **Analyses with crossed out data are inherited zircon cores or points that have experienced excessive Pb loss and have been eliminated from concordia plots for clarity

10 Data Repository Figure DR-4 Complimentary CL and BSE images of representative zircon samples from the Palmer Hill ore (99-4a). CL BSE Figure DR1 100 um 100 um CL BSE 100 um 100 um CL BSE 100 um 100 um CL BSE 100 um 100 um

McClelland & Oldow, p. 1

McClelland & Oldow, p. 1 U-Pb Analytical Methods Zircons were separated from each of the seven 1 to 4 kg samples samples (see Fig. 1 for locations) by standard crushing and gravimetric techniques, picked