The iron oxide-apatite (IOA) deposits near Mineville in the Adirondack Mountains, New York, have been of interest for their rich magnetite ore since the mid-1700s but have attracted renewed attention due to their potential as rare earth element (REE) resources (McKeown and Klemic, 1956; Lupulescu and others, 2016; Taylor and others, 2018). Apatite is the main REE-host and is found in variable concentrations within ore seams of the regional magnetite deposits. Some apatite crystals are unaltered, relatively homogenous, and inclusion-free, whereas other deposits contain heterogenous apatite with zones of abundant secondary mineral inclusions that were formed through metasomatic reactions with the apatite after initial precipitation. The heterogeneous apatite crystals may have inclusion-free bright zones and intermediate zones in back-scattered electron imagery (BSE), and dark BSE zones that contain inclusions of monazite and thorite. Apatite crystals from twenty-seven samples, including twenty-four ore and three rock samples from a total of nineteen different ore deposits, were analyzed by electron microprobe to obtain their major and minor element geochemistry. Additionally, some magmatic apatite crystals from the ore-hosting Lyon Mountain Granite Gneiss were analyzed for comparison with the ore apatite. The electron microprobe data was collected by personnel of the Southwest Region Geology, Geophysics, and Geochemistry Science Center in Denver, Colorado, for the U.S. Geological Survey (USGS) Mineral Resources Program (MRP). A JEOL 8900 Electron Microprobe with five wavelength dispersive analyzers operated at 20keV accelerating voltage, a 50-nA current (measured on the Faraday cup), and an electron beam diameter of 10 micrometers was utilized. All analyzed crystals are considered fluorapatite, with fluorine contents ranging from approximately 3.5 to 6.6%. Some apatite crystals from ore contain greater than 15% total REE, whereas some others contain less than 1%. Commonly, Y, La, Ce, and Nd are the most abundant REE in the apatite crystals. The magmatic apatite crystals are notably purer with low contents of actinides, REE, and other common minor impurities. Analyses that contained total elemental weight percentages between 97% to 103% were accepted; those analyses with poor totals falling outside of this range were rejected. The different zones within heterogeneous apatite crystals contained lower concentrations of REE and other minor element components in the dark BSE zones than in the bright BSE zones, but both zones had nearly parallel REE profiles. The zones of differing BSE brightness are interpreted to be caused by metasomatic alteration. Although the REE profiles were consistent for a given sample, variations in total REE content and overall chemistry were noted between different deposits and even different ore seams within a given deposit.

Iron oxide-apatite (IOA) deposits of the Adirondack Mountains of New York locally contain elevated REE concentrations (e.g. Taylor and others, 2019). Critical to evaluating resource potential is understanding the genesis of the IOA deposits that host the REE-rich minerals. As part of this effort, the U.S. Geological Survey (USGS) is conducting bedrock geologic mapping, geochronology, geochemistry, and geophysics in the region. Published and ongoing research demonstrates the spatial association of IOA deposits with the Lyon Mountain Granite Gneiss (LMG), so understanding the relationship of the LMG to the IOA deposits is important for resource evaluation—however the age and origin of the LMG remain contentious. As a result, the USGS undertook a petrologic and geochronologic study of the LMG and Hawkeye Granite Gneiss to better understand the temporal relationship between ores and the LMG. Electron microprobe (EMP) analyses of the feldspars in the sampled rocks was conducted as part of this research. Twelve samples, including four samples of Hawkeye Granite Gneiss, seven samples of Lyon Mountain Granite Gneiss, and one amphibolite were collected from the Adirondack massif in upstate NY (see Aleinikoff and others, 2021 Figure 1 and Table 1). Feldspar grains from these samples were analyzed by electron microprobe to determine their major and minor element geochemistry. The electron microprobe data was collected by personnel of the Florence Bascom Geoscience Center in Reston, Virginia, for the U.S. Geological Survey (USGS) National Cooperative Geological Mapping Program (NCGMP). A fully automated JEOL 8900 Electron Microprobe with five wavelength dispersive analyzers operated at 15keV accelerating voltage, a 20-nA beam current, and an electron beam diameter of 3-10 micrometers was utilized. The microprobe was operated using Probe for EPMA software (Donovan, 2015). The feldspars of the analyzed samples included plagioclase, k-feldspar, microperthite, and microantiperthite. The latter two are fine-scale exsolution intergrowths of plagioclase and K-feldspar. The grain size of plagioclase was typically coarse (>100 µm) and easily analyzed by electron microprobe methods. However, the microperthite and microantiperthite commonly had exsolution lamellae <10 µm in width. As a result, some EMP analyses overlapped lamellae of different composition and are mixed analyses. All analyses with total elemental weight percentages between 98 and 102% are reported. These data were collected in two analytical sessions on 4/26/2019 and 4/30/2019. The spectrometer configuration including analyzing crystal, X-ray line, and on peak count times were as follows: Spectrometer 1 - TAP crystal, NaKα, 20s, MgKα 30s, Spectrometer 2 - LIFH crystal, FeKα 20s, BaLα 20s, Spectrometer 3 - TAP crystal, SiKα 25s, AlKα 25s, Spectrometer 4 - PETJ crystal, CaKα 25s, TiKα 25s, Spectrometer 5 - PETJ crystal, KKα 20s, SrLα 20s. All background corrections were done by linear interpolation of off-peak backgrounds, and off-peak background count times were half the on peak time for each background position. The matrix correction algorithm of Armstrong/Love Scott phi-rho-z (Armstrong, 1988) was used along with the mass absorption coefficients of Henke (1982) for all analyses. Detection limits (3σ) based on counting statistics were ~0.02 wt% for SiO2, CaO, MgO, Al2O3, K2O, 0.03 wt% for Na2O, 0.04wt% for TiO2, 0.05 wt% for FeO, 0.06 wt% for SrO, and 0.07 wt% for Ba. Machine stability throughout the analyses and between sessions was documented by the analysis of secondary standard FSLC (Lake County, plagioclase) in sets of 7 analyses roughly every 12 hours. For major oxides (>10 wt%) the total range of the average value from each of these sets varies by < ± 3% relative, within QC bounds of ± 3%, and for the minor oxide Na2O varies by 9% relative within the QC bound of ±10%. The published value for FLSC (Huebner and Woodruff, 1985) and the value and uncertainty (1σ) measured during

Iron oxide-apatite (IOA) deposits of the Adirondack Mountains of New York locally contain elevated REE concentrations (e.g. Taylor and others, 2019). Critical to evaluating resource potential is understanding the genesis of the IOA deposits that host the REE-rich minerals. As part of this effort, the U.S. Geological Survey (USGS) is conducting bedrock geologic mapping, geochronology, geochemistry, and geophysics in the region. Published and ongoing research demonstrates the spatial association of IOA deposits with the Lyon Mountain Granite Gneiss (LMG), so understanding the relationship of the LMG to the IOA deposits is important for resource evaluation—however the age and origin of the LMG remain contentious. As a result, the USGS undertook a petrologic and geochronologic study of the LMG and Hawkeye Granite Gneiss to better understand the temporal relationship between ores and the LMG. Electron microprobe (EMP) analyses of the feldspars in the sampled rocks was conducted as part of this research. Twelve samples, including four samples of Hawkeye Granite Gneiss, seven samples of Lyon Mountain Granite Gneiss, and one amphibolite were collected from the Adirondack massif in upstate NY (see Aleinikoff and others, 2021 Figure 1 and Table 1). Feldspar grains from these samples were analyzed by electron microprobe to determine their major and minor element geochemistry. The electron microprobe data was collected by personnel of the Florence Bascom Geoscience Center in Reston, Virginia, for the U.S. Geological Survey (USGS) National Cooperative Geological Mapping Program (NCGMP). A fully automated JEOL 8900 Electron Microprobe with five wavelength dispersive analyzers operated at 15keV accelerating voltage, a 20-nA beam current, and an electron beam diameter of 3-10 micrometers was utilized. The microprobe was operated using Probe for EPMA software (Donovan, 2015). The feldspars of the analyzed samples included plagioclase, k-feldspar, microperthite, and microantiperthite. The latter two are fine-scale exsolution intergrowths of plagioclase and K-feldspar. The grain size of plagioclase was typically coarse (>100 µm) and easily analyzed by electron microprobe methods. However, the microperthite and microantiperthite commonly had exsolution lamellae <10 µm in width. As a result, some EMP analyses overlapped lamellae of different composition and are mixed analyses. All analyses with total elemental weight percentages between 98 and 102% are reported. These data were collected in two analytical sessions on 4/26/2019 and 4/30/2019. The spectrometer configuration including analyzing crystal, X-ray line, and on peak count times were as follows: Spectrometer 1 - TAP crystal, NaKα, 20s, MgKα 30s, Spectrometer 2 - LIFH crystal, FeKα 20s, BaLα 20s, Spectrometer 3 - TAP crystal, SiKα 25s, AlKα 25s, Spectrometer 4 - PETJ crystal, CaKα 25s, TiKα 25s, Spectrometer 5 - PETJ crystal, KKα 20s, SrLα 20s. All background corrections were done by linear interpolation of off-peak backgrounds, and off-peak background count times were half the on peak time for each background position. The matrix correction algorithm of Armstrong/Love Scott phi-rho-z (Armstrong, 1988) was used along with the mass absorption coefficients of Henke (1982) for all analyses. Detection limits (3σ) based on counting statistics were ~0.02 wt% for SiO2, CaO, MgO, Al2O3, K2O, 0.03 wt% for Na2O, 0.04wt% for TiO2, 0.05 wt% for FeO, 0.06 wt% for SrO, and 0.07 wt% for Ba. Machine stability throughout the analyses and between sessions was documented by the analysis of secondary standard FSLC (Lake County, plagioclase) in sets of 7 analyses roughly every 12 hours. For major oxides (>10 wt%) the total range of the average value from each of these sets varies by < ± 3% relative, within QC bounds of ± 3%, and for the minor oxide Na2O varies by 9% relative within the QC bound of ±10%. The published value for FLSC (Huebner and Woodruff, 1985) and the value and uncertainty (1σ) measured during

The exploration for porphyry deposits in some parts of Alaska may require unconventional exploration geochemical methods, depending on type of cover. The Taurus deposit and others in the region are mostly concealed by residual soils that in part include ash and loess, and therefore traditional stream sediment samples typically contain subdued geochemical signatures. Indicator mineral studies include collection of stream sediment samples and analysis using automated SEM mineralogical techniques. The presence of select minerals in the stream sediments may indicate mineralization. In addition, the chemistry of specific minerals may be used to distinguish a hydrothermal origin as opposed to others, and include apatite, rutile, and titanite. The electron probe data in this data release were collected for apatite, rutile, and titanite by personnel of the Geology, Geophysics, and Geochemistry Science Center in Denver, Colorado, for the U.S. Geological Survey (USGS) Mineral Resources Program (MRP). Appreciable differences in chemistry were noted for these minerals in mineralized rock and stream sediment samples draining these rocks compared to sediment samples away from mineralization.

The exploration for porphyry deposits in some parts of Alaska may require unconventional exploration geochemical methods, depending on type of cover. The Taurus deposit and others in the region are mostly concealed by residual soils that in part include ash and loess, and therefore traditional stream sediment samples typically contain subdued geochemical signatures. Indicator mineral studies include collection of stream sediment samples and analysis using automated SEM mineralogical techniques. The presence of select minerals in the stream sediments may indicate mineralization. In addition, the chemistry of specific minerals may be used to distinguish a hydrothermal origin as opposed to others, and include apatite, rutile, and titanite. The electron probe data in this data release were collected for apatite, rutile, and titanite by personnel of the Geology, Geophysics, and Geochemistry Science Center in Denver, Colorado, for the U.S. Geological Survey (USGS) Mineral Resources Program (MRP). Appreciable differences in chemistry were noted for these minerals in mineralized rock and stream sediment samples draining these rocks compared to sediment samples away from mineralization.

This data release presents high-spatial resolution geochemical analyses collected from Mesoproterozoic apatite crystals in igneous rocks from the St. Francois Mountains terrane and coeval ore rocks from the Pea Ridge iron oxide-apatite-rare earth element (IOA-REE) and Boss iron oxide-copper-gold (IOCG) deposits. These deposits are located in the southeast Missouri iron metallogenic province. These data support a journal article entitled, “Apatite trace element geochemistry and cathodoluminescent textures—A comparison between regional magmatism and the Pea Ridge IOA-REE and Boss IOCG deposits, southeastern Missouri iron metallogenic province, USA” by Celestine N. Mercer, Kathryn E. Watts, and Juliane Gross, that is published in Ore Geology Reviews. The goal of these data is to use apatite geochemical data to elucidate the petrogenetic histories of the samples and help evaluate ore deposit models. Our sample suite comprises 25 samples, encompassing 8 regional rhyolite suite rocks, including rhyolite host rocks at Pea Ridge and Boss; 6 regional mafic- to intermediate-composition suite rocks, including one intermediate-composition host rock at Boss; 10 ore samples from the Pea Ridge deposit (amphibole-quartz zone, magnetite zone, hematite zone, and REE-bearing hard breccia pipe), and 1 ore sample from the Boss deposit (magnetite-rich ore zone). Prior to quantitative analysis, apatite was identified by petrographic microscope in thick sections and imaged by backscattered electron (BSE) microscopy to distinguish complex textural domains. Apatite crystals contain primary domains as well as secondary and tertiary altered domains. These data were collected at the U.S. Geological Survey (USGS) Denver Microbeam Laboratory using a FEI Quanta 450 field emission gun scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) detector operating at 15-20 kilovolts (kV) and a beam current of 0.1-0.5 nanoamperes (nA). Major and minor element analyses in apatite were analyzed at the USGS Denver Microbeam Laboratory using a JEOL 8900 electron microprobe (EMP). We report 283 spot analyses that were completed using a 15 kV accelerating potential, 20 nA beam current, and the largest spot size possible (about 3-10 micrometers [µm]) to analyze a particular apatite domain while minimizing elemental migration. Natural and synthetic minerals and glasses were used as standards for all EMP analyses. Average detection limits are typically about 200-300 parts per million (ppm) for P, Si, Na, and Cl; about 100 ppm for Ca, S; and about 900 for F. This analytical setup is adequate for routine analysis of Ca, P, Si, Na, and S in apatite, but provides F and Cl analyses with relatively larger uncertainties. Given these operating conditions, the generally F-rich, Cl-poor character of the apatite, the random crystallographic orientations of the grains analyzed, and the total beam exposure of 120 seconds (for F, Cl, Ca, and P), we expect there was an increase in F X-ray counts of up to about 30-40 percent and a decrease in Cl X-ray counts of up to about 20-30 percent (Goldoff and others, 2012). Our analytical accuracy for measurements of the F-rich Wilberforce apatite standard is within ≤3 percent for Ca, P, and Na, but high by about 33 percent for F, suggesting F (and presumably Cl) is inaccurate. Nonetheless, we report measured values of F and Cl data because even with these large uncertainties they clearly demonstrate the basic compositional variety between samples. Trace element concentrations in apatite were measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a Photon Machines Analyte G2 LA system (193 nanometer [nm], 4 nanosecond [ns] excimer) attached to a PerkinElmer DRC-e ICP-MS, housed at the USGS Denver Laser Ablation ICP-MS Laboratory. We report 37 minor and trace elements from 231 apatite spot analyses. Spot ablation was carried out using a 15 to 25 µm spot size at 10 joules per square

This data release presents high-spatial resolution geochemical analyses collected from Mesoproterozoic apatite crystals in igneous rocks from the St. Francois Mountains terrane and coeval ore rocks from the Pea Ridge iron oxide-apatite-rare earth element (IOA-REE) and Boss iron oxide-copper-gold (IOCG) deposits. These deposits are located in the southeast Missouri iron metallogenic province. These data support a journal article entitled, “Apatite trace element geochemistry and cathodoluminescent textures—A comparison between regional magmatism and the Pea Ridge IOA-REE and Boss IOCG deposits, southeastern Missouri iron metallogenic province, USA” by Celestine N. Mercer, Kathryn E. Watts, and Juliane Gross, that is published in Ore Geology Reviews. The goal of these data is to use apatite geochemical data to elucidate the petrogenetic histories of the samples and help evaluate ore deposit models. Our sample suite comprises 25 samples, encompassing 8 regional rhyolite suite rocks, including rhyolite host rocks at Pea Ridge and Boss; 6 regional mafic- to intermediate-composition suite rocks, including one intermediate-composition host rock at Boss; 10 ore samples from the Pea Ridge deposit (amphibole-quartz zone, magnetite zone, hematite zone, and REE-bearing hard breccia pipe), and 1 ore sample from the Boss deposit (magnetite-rich ore zone). Prior to quantitative analysis, apatite was identified by petrographic microscope in thick sections and imaged by backscattered electron (BSE) microscopy to distinguish complex textural domains. Apatite crystals contain primary domains as well as secondary and tertiary altered domains. These data were collected at the U.S. Geological Survey (USGS) Denver Microbeam Laboratory using a FEI Quanta 450 field emission gun scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS) detector operating at 15-20 kilovolts (kV) and a beam current of 0.1-0.5 nanoamperes (nA). Major and minor element analyses in apatite were analyzed at the USGS Denver Microbeam Laboratory using a JEOL 8900 electron microprobe (EMP). We report 283 spot analyses that were completed using a 15 kV accelerating potential, 20 nA beam current, and the largest spot size possible (about 3-10 micrometers [µm]) to analyze a particular apatite domain while minimizing elemental migration. Natural and synthetic minerals and glasses were used as standards for all EMP analyses. Average detection limits are typically about 200-300 parts per million (ppm) for P, Si, Na, and Cl; about 100 ppm for Ca, S; and about 900 for F. This analytical setup is adequate for routine analysis of Ca, P, Si, Na, and S in apatite, but provides F and Cl analyses with relatively larger uncertainties. Given these operating conditions, the generally F-rich, Cl-poor character of the apatite, the random crystallographic orientations of the grains analyzed, and the total beam exposure of 120 seconds (for F, Cl, Ca, and P), we expect there was an increase in F X-ray counts of up to about 30-40 percent and a decrease in Cl X-ray counts of up to about 20-30 percent (Goldoff and others, 2012). Our analytical accuracy for measurements of the F-rich Wilberforce apatite standard is within ≤3 percent for Ca, P, and Na, but high by about 33 percent for F, suggesting F (and presumably Cl) is inaccurate. Nonetheless, we report measured values of F and Cl data because even with these large uncertainties they clearly demonstrate the basic compositional variety between samples. Trace element concentrations in apatite were measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a Photon Machines Analyte G2 LA system (193 nanometer [nm], 4 nanosecond [ns] excimer) attached to a PerkinElmer DRC-e ICP-MS, housed at the USGS Denver Laser Ablation ICP-MS Laboratory. We report 37 minor and trace elements from 231 apatite spot analyses. Spot ablation was carried out using a 15 to 25 µm spot size at 10 joules per square

This data release provides geochemical results of in situ electron probe microanalyses of hydrothermal muscovite associated with gold-bearing quartz veins from the Klamath Mountains, California. Samples were collected from eight different mines in the summer of 2013 and electron probe microanalyses were carried out May 27, 2014 and November 12, 2019.

This data release provides geochemical results of in situ electron probe microanalyses of hydrothermal muscovite associated with gold-bearing quartz veins from the Klamath Mountains, California. Samples were collected from eight different mines in the summer of 2013 and electron probe microanalyses were carried out May 27, 2014 and November 12, 2019.

The ore from historic iron mines of the eastern Adirondack Highlands, New York, contain abundant quantities of rare earth element (REE)-bearing apatite crystals. These apatite crystals are especially enriched in Y, La, Ce, and Nd. In-ground ore, mine waste piles, and tailings piles that are associated with these mines could contain apatite and other REE-bearing phases at elevated concentrations indicating potential as REE resources. This is the first geochemical database for a regional subset of ore and mine waste products for these mines. Thirty-four ore, twenty-nine mine waste, seven host rock, two pegmatite, and one slag sample were collected from these iron oxide-apatite (IOA) mines in the eastern Adirondack Highlands near Mineville and Ticonderoga, New York. The waste pile samples included 25 samples collected from rubble-sized mine waste piles and four samples from processed tailings piles. Waste pile sampling was accomplished by adapting the sampling strategy outlined by Smith and others (2000, 2006), which included collecting 30 to 50 evenly distributed aliquots (subsamples) from across each waste pile that were composited to form a representative composite sample for the pile. The resulting samples ranged from 12.75 to 32.50 pounds (5.78 to 14.74 kilograms) of material, which were crushed, homogenized, and split prior to geochemical analysis. Major elements were analyzed by wavelength dispersive x-ray fluorescence (WDXRF) and 60-element analyses was completed by inductively coupled plasma-optical emission spectroscopy-mass spectroscopy (ICP-OES-MS). Ore samples were preferably collected in situ from the ore seams, but clasts were collected from waste piles if the ore seam was inaccessible. A wide range in chemical values exists for the ore and waste pile samples. Total REE (lanthanides plus yttrium) varies from 11 to greater than 22,000 parts per million (ppm) for waste piles and 15 to greater than 47,000 ppm for ore samples. All waste pile samples have light REE greater than heavy REE content, with light REE/heavy REE ratio ranging from 1.43 to 35.30, with a median value of 2.14. Ore samples with the highest total REE content have larger negative Eu anomalies, and samples with lower total REE have diminished negative Eu anomalies and more notable negative Ce anomalies. A positive correlation for all samples exists between REE and Th, indicating the potential for radiometric surveys as a tool for vectoring toward higher grade resources. The elevated REE found in some of these waste piles and ore samples is similar to or higher than grades found in some rare earth mines and advanced exploration projects. However, targeted selection of specific mines and waste piles would be required due to the large range in REE values found in the Adirondack IOA deposits. References: Smith, K.S., Ramsey, C.A., and Hageman, P.L., 2000, Sampling strategy for the rapid screening of mine-waste dumps on abandoned mine lands, in ICARD 2000—Proceedings from the Fifth International Conference on Acid Rock Drainage, Denver, Colorado, May 21-24, 2000: Society of Mining, Metallurgy, and Exploration, Inc., p. 1453–1461. Smith, K.S., Hageman, P.L., Ramsey, C.A., Wildeman, T.R., and Ranville, J.F., 2006, Reconnaissance sampling and characterization of mine-waste material, in Proceedings of the US Environmental Protection Agency Hard Rock Mining 2006 Conference, Tucson, Arizona, November 14-16, 2006, p. 1–14.