Layer, P.W. Solie, D.N. 200811 tabular digital data Raw Data File RDF 2008-5 Fairbanks, Alaska - USA State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys 14 p. http://www.dggs.dnr.state.ak.us/pubs/pubs?reqtype=citation&ID=17861 40Ar/39Ar data from seven plutonic samples and one metamorphic sample collected during mineral assessment studies in 1991 show that various rock units in the Selawik Hills plutonic complex were emplaced in the order syenite/monzonite (nonfoliated, 106.6 ± 0.8 Ma; foliated, 101.7 ± 0.7 Ma; both on hornblende), followed by nepheline syenite (103.7 ± 0.8 Ma on hornblende) and then quartz monzonite (100.4 ± 3.7 Ma on biotite). 40Ar/39Ar data from Granite Mountain hornblendes yielded ages slightly older, but overlapping, those from Selawik Hills. In this suite, the silica-undersaturated phase appears to be younger (105.7 ±0.8 Ma) than the silica-saturated phase(s) (106.8 ± 0.8 Ma and 107.1 ± 0.8 Ma). In 1991, the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted helicopter-supported field work in west-central Alaska as part a state-wide project to review selected areas of federal land that were eligible at the time for selection by Alaska to become state land. DGGS's role in the project was to evaluate mineral resource potential in the eligible units of land by acquiring data to outline permissive mineral terranes and to define mineral deposit types that could occur in each land selection unit (DGGS Staff, 1992). The data in this report resulted from investigations in the Selawik Hills and Granite Mountain areas as part of the land selection project. Geochemical and major oxide data (Solie and others, 1993a) and electron microprobe data (Solie and others, 1993b) were previously published.A brief discussion of our 40Ar/39Ar results from the Selawik Hills was presented at a Geological Society of America meeting (Solie and Layer, 1993). The purpose of this DGGS Raw Data File (RDF) is to present all our 40Ar/39Ar results from the Selawik Hills and Granite Mountain and make them available for use. Attribute information for the followingtables (entities) is included in this metadata file under the "Entity_and_Attribution_Information" section: >Locations_Results_AnalyticalData coordinates of sample locations, 40Ar/39Ar age summary, analytical data (Tables 1, 2, 3) 1991 observed Complete None planned -161.5744 -159.8142 66.17045 65.40369 None 40Ar/39Ar Age Dates Analytical Results Ar-Ar Geochronology Granite Hornblende Igneous Rocks Plutonic Rocks None Granite Mountain Candle Quadrangle Selawik Quadrangle None Cretaceous Albian Early Cretaceous Mesozoic This report and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below). Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. User specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys GIS Data Manager/Cartographer mailing and physical

3354 College Road

Fairbanks AK 99709-3707 (907) 451-5029 (907) 451-5020 (907) 451-5050 dggspubs@alaska.gov You may view our web site at http://www.dggs.dnr.state.ak.us for the latest information on available data.Please e-mail your questions and data requests when possible since our web site and e-mail address will remain current even if our phone number and mailing address change. This research was supported by State funding to the Alaska Division of Geological & Geophysical Surveys. Additional Acknowledgments: members of the 1991 DGGS field teams: Thomas K. Bundtzen, Rainer J. Newberry, Greg M. Laird, Ellen E. Harris, Milt A. Wiltse, Jeffrey T. Kline, Thomas E. Smith, Shirley A. Liss and Karen H. Clautice.Review of draft manuscript by D.J. Szumigala. All field locations were visually determined by the geologists in the field and recorded on a 1:63,360 topographic map. Coordinates were digitized visually from the field maps. DGGS submitted eight rock samples to the UAF Geochronology Laboratory for 40Ar/39Ar dating; three were collected from Granite Mountain in the Candle B-5 quadrangle and four were collected from the Selawik Hills in the Selawik quadrangle.Major oxide and selected trace element analyses for some of the samples are included in Solie and others (1993a). Separates for 40Ar/39Ar dating were prepared to >99.5 percent purity (visual inspection) using standard heavy liquid and magnetic separation techniques followed by hand-picking under a binocular microscope.Thin section examination of the samples prior to crushing indicated that the chosen minerals were free from alteration and sufficiently coarse-grained for mechanical separation.For all minerals, grains in the size range of 250 - 500 microns were used.For each sample, ~50-80 mg of biotite or 250-350 mg of hornblende or ‘whole rock’ (phenocryst-free groundmass) was packaged in an aluminum foil tube and irradiated in position 5C at the McMaster University nuclear reactor, in Hamilton, Ontario.Approximately 20 samples were irradiated at a time.Six packages containing ~20 mg of the standard mineral mmhb-1 (Samson and Alexander, 1987) with an age of 513.9 Ma (Lanphere and others, 1990) were also irradiated with the samples to determine the irradiation parameter (J) and the flux gradient in the reactor.Samples and standards were analyzed 45 to 90 days after irradiation. The irradiated samples were step-heated on-line in a Modifications Ltd. low-blank furnace.Temperature control was better than 5 degrees and a maximum temperature in excess of 1600o C was achievable to ensure complete sample fusion.The extracted argon was purified in a two-stage process using a liquid nitrogen cold finger and two SAES Zr-Al getters.Prior to measurement of the Ar, the gas was collected on an activated charcoal finger.The purified Ar gas was measured using a Nuclide 6-60-SGA 15 cm mass spectrometer.The sensitivity of the spectrometer is 6.5 x 10-15 mol/mV and system noise is generally around 0.02 mV.System blanks are generally better than 1 X 10-14 mol for 40Ar.Argon isotopic measurements for both samples and standards were corrected for the system blanks, for decay of37Ar and 39Ar, and for reactor-induced isotopic interferences.Ages were calculated using the equations and corrections from McDougall and Harrison (1999) and the constants from Steiger and Jaeger (1977).Age, Ca/K and Cl/K spectra plots are shown in figure 3, andanalytical age data are shown in Tables 2 and 3.All errors on analyses are reported at the 1-sigma level. For each mass spectrometer analysis, five Ar isotope abundances are measured.36Ar is used to determine the amount of atmospheric or initial Ar in the sample, 37Ar provides an estimation of the Ca content in the mineral, 38Ar provides an estimation of the Cl content, 39Ar reflects the K content and 40Ar is a mixture of initial and radiogenic Ar.The age of the sample is proportional to the ratio of the amount of radiogenic 40Ar to the amount of 39Ar produced by neutron bombardment from 40K.All samples were dated by the 40Ar/39Ar step-heating method.In this method, a sample is heated to progressively higher temperatures in a double-vacuum resistance-heated furnace, and the argon isotopes are measured and age determined for each step (fraction).The integrated age is the age given by the total gas measured in all fractions and is equivalent to a potassium-argon (K-Ar) age. The fractions are commonly plotted on an age spectrum plot for analysis.A spectrum provides a plateau age if three or more consecutive gas fractions represent at least 50% of the total gas release and are within two standard deviations of each other (Mean Square Weighted Deviation less than ~2.5).If the fractions do not meet the criteria for a plateau due to intrafraction scatter in ages, then a weighted mean age of ‘plateau-like’ fractions, with each fraction weighted by the volume of 39Ar released, is calculated. No topologic relationships are present in the data. This dataset includes all of the samples submitted for 40Ar/39Ar age date analyses from the Selawik and Candle quadrangle which were collected by DGGS during the summer of 1991.Hand samples and thin sections are no longer available for the samples dated. The brief sample descriptions in text are compiled from field notes and some preliminary petrographic notes from 1991. Sample locations were determined visually by geologist in the field, using a brunton compass and altimeter and topographic map. Locations were then digitized visually from the field maps using ArcGIS v9.2. 100 The sample locations were found in the field using a compass and altimeter. Considering the errors inherent in the USGS topographic maps, locating oneself in the field,and the methods of digitizing stations, samples are located to an accuracy of between 10 and 100 meters. Lanphere, M.A. Dalrymple, G.B. Fleck, R.J. Pringle, M.S. 1990 journal article EOS Transactions of the American Geophysical Union v. 71 (abstract), P. 1658 paper 1990 publication date Lanphere and others, 1990 Describes intercalibration standards McDougall, Ian Harrison, T.M. 1999 2 book chapter Oxford Oxford University Press 269 pp paper 1999 publication date McDougall and others, 1999 Source reference for equations and corrections used in age calculation. Samson, S.D. Alexander, E.C. 1987 journal article Chemical Geology v. 66 p.27-34 paper 1987 publication date Samson and Alexander, 1987 Interlaboratory calibration data for age determination Steiger, R.H. Jager, E 1977 journal article Earth and Planetary Science Letters v.36 p. 359-363 paper 1977 publication date Steiger and Jager, 1977 discussion of use of decay constants in age determination Solie, D.N. Harris, E.E. Bundtzen, T.K. Wiltse, M.A. Newberry, R.J. Kline, J.T. Smith, T.E. 199303 document Public Data File PDF 93-16a Fairbanks AK Alaska Division of Geological & Geophysical Surveys 54 p. paper 1993 observed Solie and others, 1993a geochemical and major oxide data from study area Solie, D.N. Severin, K.P. Lear, K.G. 199305 document Public Data File PDF 93-16b Fairbanks AK Alaska Division of Geological & Geophysical Surveys 11 p. paper 1993 observed Solie and others, 1993b electron microprobe data from rocks in study area Solie, D.N. Layer, P.W. 1993 document Geological Society of America Abstracts with Programs v.25, no.5 abstract, p.149. paper 1993 observed Solie and Layer, 1993 preliminary presentation of age results Fieldwork - Alaska Division of Geological & Geophysical Surveys (DGGS) conducted helicopter-supported field work in west-central Alaska as part a state-wide project to review selected areas of federal land that were eligible at the time for selection by Alaska to become state land.Rock samples were collected in the Selawik Hills and Granite Mountain areas during summer 1991. Members of the field crew were Diana N. Solie, Thomas K. Bundtzen, Rainer J. Newberry, Greg M. Laird, Ellen E. Harris, Milt A. Wiltse, Jeffrey T. Kline, Thomas E. Smith, Shirley A. Liss and Karen H. Clautice.Geochemical and major oxide data from samples collected during the Selawik Hills project were published (Solie and others, 1993a). Selected electron microprobe data from rocks collected from Selawik Hills and Granite Mountain were published in Solie and others, 1993b. A brief discussion of the 40Ar/39Ar age results was given in an abstract by Solie and Layer (1993). Solie and others, 1993a Solie and others, 1993b Solie and Layer, 1993 199107 Labwork - Separates for 40Ar/39Ar dating were prepared to >99.5 percent purity (visual inspection) using standard heavy liquid and magnetic separation techniques followed by hand-picking under a binocular microscope.Thin section examination of the samples prior to crushing indicated that the chosen minerals were free from alteration and sufficiently coarse-grained for mechanical separation.For all minerals, grains in the size range of 250 - 500 microns were used.For each sample, ~50-80 mg of biotite or 250-350 mg of hornblende or ‘whole rock’ (phenocryst-free groundmass) was packaged in an aluminum foil tube and irradiated in position 5C at the McMaster University nuclear reactor, in Hamilton, Ontario.Approximately 20 samples were irradiated at a time.Six packages containing ~20 mg of the standard mineral mmhb-1 (Samson and Alexander, 1987) with an age of 513.9 Ma (Lanphere and others, 1990) were also irradiated with the samples to determine the irradiation parameter (J) and the flux gradient in the reactor.Samples and standards were analyzed 45 to 90 days after irradiation. The irradiated samples were step-heated on-line in a Modifications Ltd. low-blank furnace.Temperature control was better than 5 degrees and a maximum temperature in excess of 1600o C was achievable to ensure complete sample fusion.The extracted argon was purified in a two-stage process using a liquid nitrogen cold finger and two SAES Zr-Al getters.Prior to measurement of the Ar, the gas was collected on an activated charcoal finger.The purified Ar gas was measured using a Nuclide 6-60-SGA 15 cm mass spectrometer.The sensitivity of the spectrometer is 6.5 x 10-15 mol/mV and system noise is generally around 0.02 mV.System blanks are generally better than 1 X 10-14 mol for 40Ar.Argon isotopic measurements for both samples and standards were corrected for the system blanks, for decay of37Ar and 39Ar, and for reactor-induced isotopic interferences.Ages were calculated using the equations and corrections from McDougall and Harrison (1999) and the constants from Steiger and Jaeger (1977). All errors on analyses are reported at the 1-sigma level. For each mass spectrometer analysis, five Ar isotope abundances are measured.36Ar is used to determine the amount of atmospheric or initial Ar in the sample, 37Ar provides an estimation of the Ca content in the mineral, 38Ar provides an estimation of the Cl content, 39Ar reflects the K content and 40Ar is a mixture of initial and radiogenic Ar.The age of the sample is proportional to the ratio of the amount of radiogenic 40Ar to the amount of 39Ar produced by neutron bombardment from 40K. Samson and Alexander, 1987 Lanphere and others, 1990 McDougall and Harrison, 1999 Steiger and Jaeger, 1977 1991 Point Universal Transverse Mercator 4 9.9996 -153.000 0 500000 0 coordinate pair 1 1 meters Locations_Results_AnalyticalData North American Datum of 1927 Clarke 1866 6378206.4 294.978698 Locations_Results_AnalyticalData Table1_coordinates.csv Coordinates for 40Ar/39Ar samples Alaska Division of Geological & Geophysical Surveys SampleNo Items in the Sample Number field Alaska Division of Geological & Geophysical Surveys Sample numbers are unique identifiers derived from the last two digits of the year the sample was collected, initials of the geologist's name who collected it, and the consecutively numbered station location. If more than one sample was collected from the station location, each is assigned a letter (a, b, c, etc) designator as well. Easting UTM easting coordinate, Zone 4, NAD 27 Alaska Division of Geological & Geophysical Surveys 394311 463220 m Northing UTM northing coordinate, Zone 4, NAD 27 Alaska Division of Geological & Geophysical Surveys 7255163 7339612 m Latitude Latitude coordinate, NAD 27 Alaska Division of Geological & Geophysical Surveys 65.40369 66.17045 decimal degree Longitude Longitude coordinate, NAD27 Alaska Division of Geological & Geophysical Surveys 159.81421 161.57441 decimal degree Locations_Results_AnalyticalData Table2_agesummary.csv Summary table for 40Ar/39Ar data Alaska Division of Geological & Geohysical Surveys Min. Material used for age date Alaska Division of Geological & Geophysical Surveys Material used for dating. Includes Bio (biotite) or Hbd (hornblende). Integrated Age (Ma) Integrated age in million years, Alaska Division of Geological & Geophysical Surveys 98.8+-0.7 107.4+-0.8 Ma Plateau Age Summarizes the Plateau (P) Age or the Weighted Mean (W) Age in Million years for each sample Alaska Division of Geological & Geophysical Surveys 100.4+-3.7 107.1+-0.8 Ma Plateau Information Summarizes number of fractions, percent 39Ar released and MSWD for each sample Alaska Division of Geological & Geophysical Surveys # of fractions, % 39Ar released, MSWD for each sample SampleName Items in the Sample Name field Alaska Division of Geological & Geophysical Surveys Sample numbers are unique identifiers derived from the last two digits of the year the sample was collected, initials of the geologist's name who collected it, and the consecutively numbered station location. If more than one sample was collected from the station location, each is assigned a letter (a, b, c, etc) designator as well. Rock type name of rock type of sample Alaska Division of Geological & Geophysical Surveys rock type, either a type of plutonic rock or a generalized metamorphic rock Mass mass of sample that was dated, in grams Alaska Division of Geological & Geophysical Surveys 0.0605 0.3588 grams # number of fractions in the step heat Alaska Division of Geological & Geophysical Surveys 9 12 each K2O Weight % K2O as estimated from 39Ar release Alaska Division of Geological & Geophysical Surveys 0.72 7.15 weight % CaO weight % CaO estimated from 37Ar release Alaska Division of Geological & Geophysical Surveys 0.64 15.37 weight % Isochron age Isochron age and intial 40Ar/36Ar, both calculated from regression of isotopic compositions of individual step-heated fractions. Initial is the intercept of regression line. Alaska Division of Geological & Geophysical Surveys 101.6+-0.8 107.1+-0.8 Ma Locations_Results_AnalyticalData Table3_analytical data.csv For each sample, the 40Ar/39Ar analytical data associated with each temperature recorded is presented. Alaska Division of Geological & Geophysical Surveys Temp Temperature in Degrees C of step for which data were recorded Alaska Division of Geological & Geophysical Surveys 400 1600 Degrees C Cum. 39Ar Cumulative 39Argon Alaska Division of Geological & Geophysical Surveys 0.0000 1.0000 40Ar/39Ar measured Measured 40Ar/39Ar ratio at each heating step, corrected for blank and 39Ar decay Alaska Division of Geological & Geophysical Surveys 0.0001 634.0000 +/- Defines the size of the error bars for each ratio measurement to one standard deviation Alaska Division of Geological & Geophysical Surveys 0.0000 509.0000 37Ar/39Ar measured The ratio of 37Ar to 39Ar measured at each temperature interval for each sample corrected for blank and 37Ar and 39Ar decay Alaska Division of Geological & Geophysical Surveys 0.00000 23.00000 36Ar/39Ar Ratio of amounts of 36Ar to 39Ar measured at each temperature interval for each sample corrected for blank and 39Ar decay Alaska Division of Geological & Geophysical Surveys 0.0000 3.2000 % Atm. 40Ar Percent of 40Ar which is atmospheric in composition Alaska Division of Geological & Geophysical Surveys 0.0 150.0 Ca/K ratio of Calcium to Potassium as determined from 37Ar/39Ar Alaska Division of Geological & Geophysical Surveys 0.0000 43.0000 Cl/K ration of Chloring to Potassium as determined from 38Ar/39Ar Alaska Division of Geological & Geophysical Surveys 0.00000 0.15000 40Ar*/39ArK ratio of radiogenic 40Ar to 39Ar derived from potassium Alaska Division of Geological & Geophysical Surveys 0.0000 12.0000 Age (Ma) calculated age for each temperature step for each sample Alaska Division of Geological & Geophysical Surveys 0.0 185.0 Ma +-(Ma) Defines the size of the error bars for each measurement to one standard deviation Alaska Division of Geological & Geophysical Surveys 0.2 3167.0 Ma State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys Natural Resource Technician mailing and physical

3354 College Road

Fairbanks AK 99709-3707 USA 907-451-5020 None available. 907-451-5050 dggspubs@alaska.gov 8 am to 4:30 pm, Monday through Friday, except State holidays Please view our Web site (http://www.dggs.dnr.state.ak.us) for the latest information on available data. Please contact us using the e-mail address provided above when possible. Raw-Data File The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester or anyone else exceed the fee paid for the electronic service or product. Current publication is available on paper. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. Printed publication can be purchased (contact information below) plus shipping if mailed. Two weeks unless special arrangements are made and an express fee is paid. PDF 1.6 No compression applied http://www.dggs.dnr.state.ak.us/pubs/pubs.jsp Digital files on CD-ROM are available (contact information below). Scanned images of these products may be viewed online or downloaded for free from the DGGS Web site. Order by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. 20081031 State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys Metadata Manager mailing and physical address

3354 College Road

Fairbanks AK 99709-3707 USA 907-451-5039 907-451-5050 dggspubs@alaska.gov 8 am to 4:30 pm, Monday through Friday, except State holidays. Please contact us through the e-mail address above whenever possible. FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998 none If the user has modified the data in any way they are obligated to describe the types of modifications they have performed in the supporting metadata file. User specifically agrees not to imply that changes they made were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys.