MINERAL INVESTIGATION of the Iditarod-George MPanning Block, Central Kuskokwim River Area, Alaska 1983 By Mark P. Meyor Alaska Field Operation Center, Anchorage, Alaska rnj~~~½f for0 bw*"a of nLmW '2 U II I/ ;1x' /I I _- I f U~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I Pr~per"by lowu of Mmfr'-iE _IiI I' peare teSmofM Iy I t4 o#" MINERAL INVESTIGATION OF THE IDITAROD-GEORGE PLANNING BLOCK, CENTRAL KUSKOKWIM RIVER AREA, ALASKA by Mark P. Meyer Alaska Field Operations Center, Anchorage, Alaska ****~~A*.~~AAA*************************************. UNITED STATES DEPARTMENT OF THE INTERIOR William Clark, Secretary - BUREAU OF MINES Robert B. Horton, Director CONTENTS Page Abstract..................................................................................... 1 Introduction. ..................................oo.......... 2 Land status and study area.. .. .......__ ...... 2 Physiography and access............ .. .o................. .. 5 Acknowledgments..... ... o...... -o-o-... ..... ....... 7 Previous investigations................................. ........... 7 Mining history................................................. 9 Claim and mineral- distribution...... .... .. ...... 12 Present invest-igations. ........................... 16 Lithology................................................-... 18 Ku skok wim G ro or..o o o u. 21 Iditarod Basalt.. 21 Albite rhyol ite. .. ..... oo....... ... o 22 Biotite basalt... ....o...... -... .... o...... ............ 22 Quartz diaae ... .... o-o-o.... 23 Quartz monzonite.. .... .. 23 Getmuna Rhyolite Group..... ........ 23 Holukuk Baslt.. o.... 24 Gravel deposits....... ............................... 24 Glacial deposits... ..................... 24 Flood-plain deeposits..... ............... .. .o ... ... 25 Structural geology........ ....... ...... o ...... ........... 25 Folds..........oo.o.- .... .o ...o ....... .-.-..............-. 25 Faults...................... o............... ..... 25 i CONTENTS - Continued Page Mineral resources .............................................. 26 Locatable mineral resources ....... ......... .... .... ... 27 Lode deposits .............................................. 27 Mercury-antimony .........................................* ** * 27 Gold-silver ...... ........................................ 28 Antimony............................................................................... 29 Molybdenum............................................................................. 29 Copper-lead-zinc ..................................................30 Gemstone .................. ...... ..................................... 30 Placer-deposits ............ - 30 Gold-silver ....................................... ..... 31 Mercury................................................................................ 32 Tungsten............................................................................... 32 Leasable-mineral resources............................ ........ 32 Coal deposits........................................................................ 33 Oil and gas ................................................ .....33 Geothermal energy ........................................... ........33 Salable mineral resources ................................................34 Mineralized areas................................................................ 34 Multi-element mineralized areas ..................... ....... .. 35 Single element mineralized areas ............................. 37 Conclusions.................................................................................. 38 CONTENTS - Continued Page Bi bl iography................................................................................... 40 Appendix A. - Sample results ...........****************........ 58 120 Appendix B. 7 Mineral property summaries ....................... ILLUSTRATIONS 1. Location of the Iditarod-George study area. ..........eeeee 3 2. Location map of the Iditarod-George Planning Block ......... 4 3. Mining districts :of the Iditarod-George study area ............. 6 4. Generalized geology -map--of--the Idi-tarod-George-=study area.-. -in pocket--s-. 5. Mines, prospects-, and occurrence- map-of=-the I-di-tarod-George- study-area ................ ................ ................. in pocket--- 6. Sample location map of the Iditarod-George study area ...... in pocket 7. Mineralized area map of the Iditarod-George study area ..... in pocket TABLES 1. Production data from the Iditarod-George study area ........ 10 2. Mines,-prospects, and occurrences in the Iditarod-George study area........... ........................ ....... 13 3. Mean and standard deviation of 1983 samples, Iditarod-George study area ....... ... ................. 19 4. Lithology of the Iditarod-George study area ................ 20 MINERAL INVESTIGATION OF THE IDITAROD-GEORGE PLANNING BLOCK, CENTRAL KUSKOKWIM RIVER AREA, ALASKA By Mark P. Meyer-./ ABSTRACT In 1983 two Bureau of Mines geologists made a literature search supplemented by a 10-day field reconnaissance for the Bureau of Land Management to delineate mineralized areas in the Iditarod-George Planning Block, southwestern Alaska. Deposits described in the literature include: 1) lode mercury-antimony; 2) lode gold-silver; 3) lode antimony; 4) lode molybdenum; 5) lode copper-lead-zinc; 6) lode gemstone; -7) placer gold- silver; 8) placer tungsten; 9) placer mercury; 10) coal; 11) oil and gas; 12) sand and gravel and a 13) geothermally active area. Identified during the literature search were 7 lode mines, 15 placer mines, 10 lode prospects, 9 lode occurrences, 10 placer prospects, 12 placer-occurrences, 2 coal - prospects-, 1-gemstone occurrence,- and 1 sand and- gravel pit. Stream sediment and rock samples .were taken to supplement data from the literature as an aid in verifying the presence of minerals and de- lineating the regionally mineralized areas. Fourteen mineralized zones contain anomalous concentrations of multiple elements; twelve areas have single elements; two areas contain coal deposits; two areas have been reported to have potential for oil and gas; one area is geothermally active; and all of the stream valleys contain sand and gravel. Metals of possible economic interest found in the 1983 samples from the study area include antimony, chromium, cobalt, copper, gold, lead, manganese, 1/ Project geologist, Alaska Field Operations Center, Anchorage, Alaska 1 mercury, molybdenum, nickel, tin, titanium, and tungsten. Placer deposits include gold, mercury, and tungsten. Deposit grades and reserves were not estimated. INTRODUCTION The Federal Land Policy and Management Act (43 U.S.C. 1701) and the Alaska National Interest Lands Conservation Act (16 U.S.C. 3148) mandated that the Bureau of Land Management (BLM) identify the leasable, locatable, and salable minerals on public lands and to use that information in the - development of land use plans-and the subsequent-zuse- disposition-, or occupancy-for multiple-use purposes.-- -To fulfill this mandate, the BLM made an interagency agreement with the Bureau of Mines (Bureau) to conduct a 4-month study of the Iditarod-George Planning Block, in the central Kuskokwim River area, Alaska (figures 1 and 2). The Bureau's work consisted primarily of literature-research supplemented by limited field investigation that included stream sediment and rock sampling. This report summarizes the pertinent -general-geology as--described-in the literature, shows the locations of mining claims and known mineral occurrences, and outlines the areas considered to be mineralized. LAND STATUS AND STUDY AREA The Iditarod-George Planning Block consists of BLM-administered public lands surrounded by other federal, state, and private lands. Some private lands occur in the planning block. The planning block totals approximately 3.5 million acres and extends from Black Mountain on the east to the Yukon River on the west; and from Henderson Mountain on the south to a 2 \ v ~~~~~tudy a re a EIGUIM 1. - Locaticn of the Iditarod-George study area. 3 Y~ ~ ~ *;A ~ ~ ~ ~ J N ~~~~~~LEGEND BOMI study area boundary / Idltarod-GeorgO planning block 0 1 2 *4 "Ites 12Scal 24 a' Kilometers FIGIME 2. - Locaticn Isap of thle Iditaocr-Cecrge P1arning Blocek point approximately 25 mi north of the town of Flat (figure 2). Included in the study area are the Aniak and Iditarod Mining Districts (figure 3). The planning block is made up of a large central block with an erratic outline and numerous small, widely-scattered detached areas. The study area is made up of a larger rectangular area which encom- passed all of the planning block (figure 2). The portion of the study area which are not- admirristere-d by BLM was also investigated because geologic trends with similar types of mineralization may extend into the planning block. PHYSIOGRAPHY AND ACCESS The study area, which is in the Kuskokwim Mountains Physiographic Province (Wahrhaftig, 1965), is characterized by-rolling hills and- - isolated peaks. The Kuskokwim Mountains are dissected by streams and rivers, including the gorge of the Kuskokwim River and the broad open valleys of the Iditarod and George Rivers.-- The hi-gher elevations.were glaciated during the last glacial advance. Elevations range from 50 ft above sea level along the Kuskokwim and Yukon Rivers to over 3,750 ft in the Horn Mountains. Westward, the rolling hills grade into the broad flood plain of the Yukon River. Vegetation in the area includes extensive stands of spruce, willow, and alder in the floodplains; stands of spruce, alder,