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Geology and Mineral Resources of the White Mountains National

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Geology and Mineral Resources of the White Mountains National DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Geology and Mineral Resources of the White Mountains National Recreation Area, East-central Alaska Edited by 1 O Florence R. Weber , Richard B. McCammon , C. Dean Rinehart , Thomas D. Light , and Karen L. Wheeler Open-File Report 88-284 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the USGS. luSGS Fairbanks, AK; 2USGS Reston, VA; 3USGS Menlo Park, CA; 4USGS Anchorage, AK TABLE OF CONTENTS Abstract ................................................... 1 I. Introduction ............................................... 2 II. Geologic Framework ......................................... 4 III. Geophysical Studies ........................................ 59 IV. Geochemistry ............................................... 77 Appendices IV-A. Histograms and frequency distributions of rock sample data Appendix IV-B. Histograms and frequency distributions of heavy-mineral-concentrate sample data Appendix IV-C. Histograms and frequency distributions of stream-sediment sample data V. Mineral Resource Assessment ................................ 95 Appendix V-A. MARK3 program ............................. 121 LIST OF PLATES (plates in pocket) II-A. Geologic map of WMNRA II-B. Geologic cross section, WMNRA III-A. Aeromagnetic map of the WMNRA III-B. Gravity map of the WMNRA IV-A. Map showing distribution of Ag, As, and Au in heavy-mineral- concentrate samples, WMNRA IV-B. Map showing distribution of Cd, Pb, and Zn in heavy-mineral- concentrate samples, WMNRA IV-C. Map showing distribution of Cu, Fe, Mo, Sb and W in heavy-mineral- concentrate samples, WMNRA IV-D. Map showing distribution of B, Be, Bi, Nb, and Th in heavy-mineral- concentrate samples, WMNRA IV-E. Map showing distribution of Ag, Ba, Cd, Pb, and Zn in heavy-mineral- concentrate samples, WMNRA IV-F. Map showing distribution of As, Cu, Mo, Sb, and Sn in heavy-mineral- concentrate samples, WMNRA IV-G. Map showing distribution of B, Be, Bi, La, Nb in heavy-mineral- concentrate samples, WMNRA IV-H. Map showing distribution of Ag, As, and Au in rock samples, WMNRA IV-I. Map showing distribution of Ba, Cd, Pb, and Zn in rock samples, WMNRA IV-J. Map showing distribution of Cu, Mo, Sb, and Sn in rock samples, WMNRA IV-K. Map showing distribution of B, Be, Bi, La, Nb, and Th in rock samples, WMNRA IV-L. Geochemical contour map showing distribution of Ag, As, and Au in WMNRA IV-M. Geochemical contour map showing distribution of Ba, Cd, Cu, Pb, and Zn in WMNRA IV-N. Geochemical contour map showing distribution of As, Cu, Fe, Mo, Sb, Sn, and W in WMNRA IV-0. Geochemical contour map showing distribution of B, Be, Bi, La, Nb and Th in WMNRA IV-P. Map showing distribution of sample sites in the WMNRA IV-Q. Drainage Basin map showing distribution of geochemical anomalies in WMNRA IV-R. Map showing distribution at ore-related minerals in the non-magnetic fraction of heavy-mineral-concentrate samples V. Map showing areas favorable for mineral resource occurrences, WMNRA ii LIST OF FIGURES 1-1. Index map showing location of WMNRA ........................ 3 II-l. Map showing location of geologic stations .................. 11 II-2. Mode and norm plots of rocks from the Cache Mountain and Victoria Mountain plutons ................................ 20 III-l. Magnetometer profile, constant elevation ................... 64 HI-2. Magnetometer profile, detailed, complex model .............. 65 III-3. Magnetometer profile, complex model ........................ 66 III-4. Map showing station numbers and location of resistivity section A-A' ............................................. 74 IV-1. Geochemically anomalous areas in the WMNRA ................. 90 111 LIST OF TABLES II-l. Chemical analyses and norms representing the granite of Cache Mountain and quartz syenite/quartz rnonzonite of Victoria Mountain ........................................ 19 II-2. K-Ar Data .................................................. 21 II-3. Chemical analyses and norms of selected samples from the Roy Creek prospect ................................... 35 II-4. Fossil collection localities in the WMNRA................... 51 III-l. Explanations for aerornagnetic and gravity maps ............. 61 IV-1. Limits of determination for the spectrographic analysis of rocks stream sediments, and moss-trap sediments ....... 78 IV-2. Univariate statistics for rock samples for WMNRA ........... 79 IV-3. Univariate statistics for heavy-mineral concentrate for samples, WMNRA ........................................... 80 IV-4. Univariate statistics for stream-sediment for samples, WMNRA ........................................... 81 IV-5. Univariate statistics for coarse moss-trap sediment samples, WMNRA ........................................... 82 IV-6. Univariate statistics for fine moss-trap sediment samples, WMNRA ........................................... 83 IV-7. Threshold values and elements selected from geochemical data ......................................... 85 IV-8. List of geochemical plates showing the elements plotted and the sample media ............................. 87 V-l. List of significant mineralized rock, stream sediment, and pan concentrate samples in the WMNRA ................. 96 V-2. Rare earth, uranium, and thorium analyses of selected samples from the Roy Creek prospect ...................... 101 V-3. U-Th-REE minerals identified in the Roy Creek prospect ..... 102 V-4. Tonnage and grade statistics for known thorium veins districts in the United States ........................... 104 V-5. Chemical analyses of the Tolovana Limestone ................ 107 V-6 Estimation of Endowment of high-calcium limestone for the Tolovana Limestone ................................... 108 V-7. Probability of existence and expected number of undiscovered deposits within the WMNRA ................... 115 V-8. Estimates of undiscovered endowment for metals and nonmetals in the WMNRA ................................... 116 IV ABSTRACT This assessment of the potential for undiscovered mineral resources for part of the White Mountains National Recreation Area (WMNRA), Alaska, has been prepared for the U.S. Bureau of Land Management in time to meet the 1988 deadline for land-use decisions for this area. Geologic, geochemical, and geophysical data have been compiled at both 1:63,360 and 1:250,000 scales, and all available published information on mineral deposits and occurrences has been used in assessing the potential mineral resources of the area. The White Mountains National Recreation Area is a part of the Yukon-Tanana Upland, primarily a terrane of quartzitic, pelitic, and calcic metasedimentary rocks with some metamorphosed mafic and felsic igneous rocks that have been intruded by Mesozoic and Cenozoic granitic rocks and minor amounts of intermediate and mafic rocks. The disruptive structures in the area are major thrust faults and strike-slip fault splays of the Tintina fault zone. We have made subjective probablistic estimates for the existence and the number of undiscovered deposits within the part of the WMNRA that we evaluated. For most of the deposit types, the probability that one or more undiscovered deposits exists is low, based on the lack of evidence of mineralization in the rocks exposed at the surface. However, placer gold has been recovered from Nome Creek and its tributaries within the WMNRA since the turn of the century, and the cumulative production to date is estimated to be 29,000 oz. Based on the currently available data, we estimate that there is a probability of 0.5 for the occurrence of placer gold and polymetallic vein deposits, a probability of 0.1 for Sn-greisen, Th/REE veins, lode Au, and sedimentary exhalative Pb-Zn deposits. There is also a probability of 0.05 for a tungsten-skarn deposit. In addition, given the existence of one deposit, we estimate a 0.5 probability of 2 and a 0.10 probability for 3 or more placer gold deposits, and a 0.10 probability for 2 or more lode gold or polymetallic vein deposits. We have also estimated the mean undiscovered mineral resource endowment in the study area for Au, Ag, Pb, Sn, Th, W, Zn, rare-earth oxides, and high-calcium limestone. At the present time, we do not expect significant undiscovered resources of chromium, asbestos, nickel, or diamonds. The recent report of the occurrence of platinum in gold samples in the nearby Tolovana mining district makes platinum worthy of further consideration as a potential metallic resource. I. INTRODUCTION This report has been prepared in response to a congressional mandate that directs the U.S. Geological Survey with the assistance of the State of Alaska Geological Survey to prepare a mineral resource assessment for the White Mountains National Recreation Area (WMNRA) in time for the Bureau of Land Management to meet the 1988 deadline for land-use decisions for this area. In order to accomplish this objective, an accelerated program of field mapping, geochemical and geophysical surveying, and mineral resource investigations were undertaken during 1986 and 1987. The results of our investigations are presented in this report. The following information is provided: (1) detailed geologic maps at 1:63,360 scale showing bedrock and surficial geology, with accompanying text describing the major rock units, structure, and stratigraphy (2) gravimetic and aeromagnetic maps at 1:63,360 scale,
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