Rare-Earth Element (REE) Potential in the Ray Mountains Area, Central Alaska A.L. Tuzzolino 1* , R.J. Newberry 1 , and L.K. Freeman 2 1 Department of Geology and Geophysics, University of Alaska Fairbanks, 2 Alaska Division of Geological & Geophysical Surveys, Fairbanks, AK, * [email protected] Alaska Miners Association 2013 Annual Convention Anchorage, Alaska 6-10 November 2013 Project Overview Panned Concetrates Background • The Ruby Batholith, located within the Ray Mountains and Hodzana Uplands, is a Cretaceous monzogranitic unit that contains numerous plutons. This study will focus on ten of these plutons. • This area has been investigated for the past few decades. There are several reports of anomalous Sn, W, Nb, Ta and rare-earth elements (REEs) (Barkey and Foley, 1986; Barker 1992). • The rare-earth-bearing minerals, allanite, monazite and xenotime, have been identified in heavy mineral panned concentrates as well as the Ruby Batholith granites. Purpose • Assess the REE potential within the Ray Mountains area as part of Alaska’s Strategic and Critical Minerals (SCM) Assessment Program. • Locate sources of elevated REEs. • Characterize the mineralogy of the plutons. Methods • Extensive, helicopter-supported geologic mapping and sampling, including whole-rock, gravels, stream sediments, and heavy mineral panned concentrates. • Modal analyses via chemical stains, petrography, geochronology, major-oxide and trace element analyses, slab XRF analyses, electron probe microanalysis (EPMA) wavelength dispersive spectroscopy (WDS) routines and elemental mapping, initial Sr isotopic ratios. Rare-Earth Elements Study Area Initial Sr Isotopic Ratios Radiometric Dating 95 100 105 110 115 120 Pluton Radiometric Age (Ma) Zircon U/Pb Hbl K/Ar biotite K/Ar and Ar/Ar Rb/Sr Melazitna Ray Mntns W Sithylemenkat Hot Springs Kanuti Hodzana Fractionation Trends References Future Work Conclusions No Name Creek Pluton Acknowledgements Y 39 La 57 Ce 58 Pr 59 Nd 60 Pm 61 Sm 62 Eu 63 Gd 64 Tb 65 Dy 66 Ho 67 Er 68 Tm 69 Yb 70 Lu 71 Light Rare-Earth Elements (LREEs) Heavy Rare-Earth Elements + Y (HREYs) Silicate Phosphate Allanite (Ce,Ca,Y,La) 2 (Al,Fe 2+ ,Fe 3+ ) 3 (SiO 4 ) 3 (OH) Monazite (Ce,La,Nd,Th)(P,Si)O 4 Xenotime (Y,HREE)PO 4 Mineralogy • There are hundreds of REE minerals you’ve never heard of! • The common REE minerals in the Ruby Batholith: • Allanite and monazite have crystal lattice structures that favor the larger LREEs, while xenotime is dominated by the smaller HREYs. 150°W 150°W 150°W 150°W 152°W 152°W 66°N Ray Mountains East Sithlyemenkat Ray River Fort Hamlin Hills No Name Creek Hot Springs Kanuti Bonanza 150°W 150°W 150°W 150°W 152°W 152°W 66°N 25 km Dalton Highway Trans-Alaska Pipeline TANANA BEAVER BETTLES LIVENGOOD MELOZITNA Tanana Alatna Rampart Fairbanks Bettles Stevens Village 20 Kilometers Yukon River Tertiary Tb Td Kgr Ruby Batholith Ruby Terrane PzZsr MzZmr Pzcr Pzpr Quaternary QTgl QTgr Qua Tozitna/Angayuchum Terrane JDv MzPzum • The field area is located 125 miles NW of Fairbanks. Ray Mountains West Coal Creek 150°0'0"W 150°30'0"W 151°0'0"W 66°0'0"N 0 5 10 15 20 2.5 Kilometers HREY/LREE 1.02 - 1.89 0.56 - 1.01 0.33 - 0.55 0.13 - 0.32 0.00 - 0.12 Fort Hamlin Hills 150°W 150°W 150°W 152°W 152°W 66°N 25 km TREY (ppm) 0 - 500 501 - 1000 1001 - 2000 2001 - 5000 5001 - 52921 0 5 10 15 20 25 30 35 40 45 0 10 20 30 40 50 60 70 80 90 100 Bonanza Coal Creek Fort Hamlin Hills Hot Springs Kanuti Ray Mountains Ray River Sithylemenkat QTZ KSP PL • The total rare-earth element (TREY) map to the right shows elevated concentrations (ppm) in the southern portion of the field area. • The HREY/LREE map above shows only the southern plutons. The red squares indicate the highest relative HREY concentrations. These anomalous values were collected from Ray River and No Name Creek, draining plutons of the same names, respetively. Additionally, note that Fort Hamlin Hills appear to be draining material with low Sithylemenkat Ray River No Name Creek Modal Composition Mineralogy • Though there is a great deal of variation in trace elements, the major oxide compositions of the Ruby Batholith specimens plot uniformly as monzogranites. Petrography & Elemental Mapping Petrography & Elemental Mapping 12RN344A Th 100um 100um 100um Zr Fe BSE 100um 100um 100um 100um Zr BSE • REE Trends: REEs are more abundant in the southern half of the field area, and HREYs particularly are abundanct in the southeast. • The No Name Creek pluton is unlike any of the other nine: Elevated HREYs and the associated minerals, along with minimal fractionation. 0.707 0.706 0.716 0.706 0.714 0.710 0.707 0.709 0.711 0.717 0.716 0.716 0.718 0.724 0.719 150°0'0"W 66°0'0"N 0 20 10 km • Left: A photomicrograph of a single allanite crystal within sample 12RN344A from the Sithylemenkat pluton. Note the orange-brown zoning and elongate structure. • Right: Elemental maps using EPMA WDS on the same allanite crystal. Note that the scales differ for each element. Elevated Th corresponds with the middle, light-hued zone shown in transmitted light. An enrichment of Ce is evident in the lighter portions as well. Th Ce Y 100um 100um • Inset: The top-left crystal is zircon, the bottom-right is xenotime. Both crystals are tetragonal, so (as long as xenotime is being crystallized) it’s common the find the HREY-beaing mineral in close association with zircon. • Right: Elemental maps using EPMA WDS aid in identification (even of crystals we can’t see!): The top and bottom grains are monazite, while the largest middle crystal is xenotime--with an inclsuion of monazite. Also in the middle of the cluster, as well as at the bottom, are zircons. Ce Y 100um 100um 100um 100um 12RN319A LREE Mineralogy • Top Left: From the No Name Creek pluton, a photomicrograph of a biotite crystal with inclusions of (in order of likely abundance) zircon, monazite, and xenotime. The three grains clustered on the right are the same as those in the elemental map. 100um Zircon Xenotime 150°0'0"W 66°0'0"N Monazite Allanite 0 30 15 km • The map to the left shows locations of samples with known allanite or monazite. • Allanite is the typical REE mineral in the north, while monazite is more common in the south. • Why the segregation? • Allanite is formed in high-Ca systems with a relatively high fO 2 . It is also found with apatite and hornblende. • Monazite requires phosphorous, and is associated with xenotime. Copyright:© 2013 National Geographic Society, i-cubed 3 km • The Melozitna pluton is south of the study area. Meanwhile, the Hodzana pluton is north of the study area. It is included to dispute a potential N-S trend. • The Hot Springs and Kanuti plutons are younger than the others. Though the sample locations were not adjacent to the known Tertiary volcanics, it is plausible that the ages were affected due to reheating. Arth, J.G., Zmuda, C.C., Foley, N.K., and Criss, R.E., 1989, Isotopic and trace element variations in the Ruby Batholith, Alaska, and the nature of the deep crust beneath the Ruby and Angayucham Terranes: Journal of Geophysical Research, v. 94, no. B11, p. 15,941-15,955. Bachmann, E.N., Blessington, M.J., Freeman, L.K., Newberry, R.J., Tuzzolino, A.L., Wright, T.C., and Wylie, William, 2013, Geochemical major-oxide, minor-oxide, trace-element, and rare-earth-element data from rocks and streams sediments collected in 2012 in the Ray Mountains area, Beaver, Bettles, Livengood, and Tanana quadrangles, Alaska: Alaska Division of Geological & Geophysical Surveys Raw Data File 2013-5, 4 p. http://www.dggs.alaska.gov/pubs/id/25386 Barker, J.C., 1992, Investigation of tin-rare earth element placers in the Ray River watershed: USBM OFR 34-91, 63 p., 1 sheet, scale 1:63,360. http://dggs.alaska.gov/pubs/id/21385 Barker, J.C., and Foley, J.Y., 1986, Tin reconnaissance of the Kanuti and Hodzana rivers uplands, central Alaska: U.S. Bureau of Mines IC9104, 27 p. http://dggs.alaska.gov/pubs/id/21287 Freeman, L.K., Newberry, R.J., Bachmann, E.N., Blessington, M.J., Tuzzolino, A.L., and Werdon, M.B., 2012, Geologic Resource Assessment of Strategic and Critical Minerals, Ray Mountains Area, Central Alaska [abs.]: Alaska Miners Association Annual Convention, Nov. 5-11, 2012, p. 16-18. http://akminers.accountsupport.com/abstracts2012.pdf Miller, T.P., 1989, Contrasting Plutonic Rock Suites of the Yukon-Koyukuk Basin and the Ruby Geanticline, Alaska: Journal of Geophysical Research, v. 94, no. B11, p. 15,969-15,987. Patton, W.W., Jr., Stern, T.W., Arth, J.G., and Carlson, Christine, 1987, New U/Pb ages from granite and granite gneiss in the Ruby Geanticline and southern Brooks Range, Alaska: Journal of Geology, v. 95, no. 1, p. 118-126. Ucore Rare Metals, Inc., 2012, Ucore confirms widespread rare earth mineralization in central Alaska: Press Release January 16, 2012, Halifax, Nova Scotia. http://ucore.com/ucore-confirms-widespread-rare-earth-mineralization-in-central-alaska • In the summer of 2013, additional field mapping and sample collection (red dots on map) were performed in the No Name Creek area, about ten miles north of the Yukon Bridge. • The samples will undergo major-oxide and trace element analyses and geochronolgic (Ar-Ar and U-Pn), petrographic and microprobe studies. The Ray Mountains rare-earth element mineral assessment project is a component of the Strategic and Critical Minerals (SCM) assessment under the Alaska Airborne Geophysical/Geological Mineral Inventory (AGGMI) program funded by the Alaska State Legislature. This student research is being conducted under the Joint Support for Graduate Student Research Internship Program through a Memorandum of Agreement between the Alaska Division of Geological & Geophysical Surveys (ADGGS) and the University of Alaska Fairbanks (UAF) Department of Geology and Geophysics. This poster has been reviewed by Karri Sicard ([email protected]). • Thorough petrographic investigations characterizing mineralogy and alteration. • Construction of an EPMA WDS routine to analyze for monazite and its zoning. • Ar-Ar and U-Pb dating on samples from No Name Creek, Ray River, Hot Springs and Kanuti plutons. • Initial Sr isotopic compositions for the Bonanza, Coal Creek, Fort Hamlin Hills, Ray Mountains and Ray River plutons. • Geochemical analyses and petrographic studies of the 2013 No Name Creek samples • Compilation of an REE resource assessment report by the summer of 2014. • The initial Sr isotopic ratios (SIR) are calculated from an age of 110 Ma. • SIR data taken from Arth et al. (1989) • The SIR is the ratio: of 87 Sr / 86 Sr. • Minerals in different geologic settings have variable ratios. • The initial SIR vary greatly in the Ruby Batholith because the starting material for each pluton appears to be different. Even within plutons, there appears to be a lack of homogeneity. • SIR in the Ruby Batholith increase to the south. 100 200 300 400 500 600 700 800 900 1000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 wt % TiO2 ppm Rb RayMtnE RayMtnW Melozi Ray R Sith FHH NNC CoalCk HS Bonan Kanuti 0 1 2 3 4 5 6 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 wt % TiO2 Ce/Y NNC HS Kanuti RayMtnE Ray R Sith Bonan CoalCk FtHH LEFT: The plutons are divided into two categories when plotted back to an original Rb value. The northern plutons (Kanuti, Hot Springs, Bonanza) yeild initial Rb values of 180 ± 20. The remaining plutons plot an original Rb value of 300 ± 30. Yet within that range, Coal Creek and FHH behave as the northern plutons do, with Rb only incerasing slightly with fractionation. RIGHT: All plutons* express an increase in HREY/LREE (with Y & Ce acting as proxies for such) with fracctionation, just at differing rates. * Notice that No Name Creek has no apparent change in the ratio with fractionation and that all rocks have low Ce/Y ratios to start.