UNCLASSIFIED Geology - Mineralogy This document consists of 26 pages/ plus 1 figure. Series A GEOLOGICAL SURVEY RECONNAISSANCE FOR RADIOACTIVE DEPOSITS IN THE DARBY MOUNTAINS DISTRICT, SEWARD PENINSULA, ALASKA* By Walter S. West March 1953 Trace Elements Investigations Report 53 This preliminary report is dis­ tributed without editorial and technical review for conformity with official standards and no­ menclature, it is not for pub- lic inspection or quotation. 'This report concerns work done on behalf of the Division of Raw Materials of the U» S* Atomic Energy Commission USGS - T£l Report 53 GEOLOGY - MINERALOGY Distribution (Series A) No. of copies American Cyanamid Company, Winchester ............... 1 Argonne National Laboratory ...«.....«......*.«.«. 1 Atomic Energy Commission/ Washington ................ 2 Battelle Memorial Institute/ Columbus ................. 1 Carbide and Carbon Chemicals Company, Y-12 Area ......... 1 Division of Raw Materials/ Grants .................. 1 Division of Raw Materials, Denver................... 1 Division of Raw Materials, Hot Springs ................ 1 Division of Raw Materials, New Y>rk ................ 6 Division of Raw j Materials, Salt Lake City ............... 1 Division of Raw Materials, Richfield .................. 1 Division of Raw Materials, Butte . ................... 1 Division of Raw Materials, Washington ................ 3 Dow Chemical Company, Pittsburg ................... 1 Exploration Division, Grand Junction Operations Office ....... 1 Grand Junction Operations Office .................. 1 Technical Information Service, Oak Ridge ............... 6 Tennessee Valley Authority, Wilson Dam ............... 1 Terr. Dept. Mines, Juneau (P. H. HoldsworHi) ............ 1 Terr. Dept. Mines, Ketchikan (A. E. Glover) ............. 1 Terr. Dept. Mines/ College (L. L. Pattoh). .............. 1 Terr. Dept. Mines, Nome (D. Jones) ................ o 1 U. S. Geological Survey; Mineral Deposits Branch, Washington ................. 1 Geochemistry and Petrology Branch, Washington .,......*.. 1 Geophysics Branch, Washington .................... 1 Alaskan Geology Branch, Washington ................. 8 Fuels Branch, Washington .*.*..*...............» 1 G. O. Gates, San Francisco ..................... 2 L. H. Saarela, Anchorage ................. ...... 1 C. L. Sains bury, Juneau ..*........«..*.*....... 1 R. M. Chapman, Fairbanks ...................... 1 V. E. McKeivey, Washington ..................... 1 L. R. Page, Denver .......................... 1 R* P. Fischer, Grand Junction ..,.....«........*.. 1 A. E. Weissenborn, Spokane ..................... 1 TEPCO, Washington .......................... 5 (Including master) "oT~__ CONTENTS Page Abstract «a»«. •..,,.*..••• ••*•»•.***a*«**«» 5 Introduction •>«»*<>.»„*<>*. *....,••».«....»•««.. 5 Geology «•. •••o.. »•..*.•• ...«•.•*•,•«•*»•.•. 7 Undivided metamorphic rocks . a »*.,...» . » , * . » » • 7 Paleozoic rocks *„.». ,«„*«»*»-. * , ,*•••,., 8 Greenstone and greenstone schist ..•«...«*•*.«•«.. 8 Undivided igneous complex .»•*.,....»..«.»..«» 8 Granite ...,,4.. ,.....*•*».**,.«.•*«»« 9 Ungalik conglomerate *..-..•..«... «*•.*. ».*.„«» 9 Basalt d.»aa«.4>»^.tt»a*«»***«ae»«aaa«o<)« 9 Unconsoiidqted deposits » . 0 0 . „ 0 . 0 . „ , . 0 „ . » 0 a . 10 Hot springs 4«« 0 » 0 a d « .«..••».»..•»,*.... 10 Veins e . eo » 0 *«*. *.•*.....«•••••»*•«•. 10 Mineral deposits ,„*„»„««, «.*...*«. ^**^*«« '.« 11 r. Radioactivity investigations .«....«..»..4'«* .*«•••••• 12 f Kachauik Creek-Cheenik Creek area .*»*....*....*. 13 McKinley Creek-Brydn Creek arete A . ..»»*.••.•«*.* 14 Portage Creek-Cape Darby area ,.. ...«..*..,« a . 15 Norton lay coastal area between Cape Darby and the Kwihiuk River to*,*.....*..*..*.,,.*.. 18 Kwinluk River . „ . ....... * ..,»»...».,..«»* 19 Tubutulik River area «............<.»..*...... 21 Summary and conclusions . ..•».*»•••«•.. * •**. 24 Literature cited *„»„*. o». «.....•«»•.. .«..*««««« 26 Unpublished reports •«»•«*«. .»«•»•«. .*.4«.»o**«.«. 26 ILLUSTRATION Figure 1. Geologic map of the Darby Mountains district, Seward Peninsula, Alaska *.»,.. 4 ,*..«. » « . 4 • « • in envelope TABLES Page Tdble 1. Mineralogy of selected radioactive heavy-mineral fractions of concentrates from the Portage Creek-Cape Darby area » « . 17 2 0 Mineralogy of heavy-mineral fractions (greater than 3.3 specific gravity) of concentrates from the Tubutulik River area .«'.«.•..«.*,*•«••..«•«...;»» 23 RECONNAISSANCE FOR RADIOACTIVE DEPOSITS IN THE DARIY MOUNTAINS DISTRICT, SEWARD PENINSULA, ALASKA By Walter S. West ABSTRACT Radioactivity in the Darby Mountains district of the Seward Peninsula, Alaska, appears to be directly related to the occurrence of granite. Concentrates from placers derived from areas containing granite -are more radioactive than concentrates from placers not derived from the granite and, generally, contain from 0.01 to 0.05 percent equivalent uranium. The radioactivity of these concentrates is largely due to radioactive elements in common accessory-minerals in granite/ such as sphene, allanite, and zircon, and locally, monazite^ Locally, in the Clear Creek-Vulcan Creek area, the headwaters of the Kwteluk Riverj and on Golovin Bay near McKinley Creek, concentrates from placers derived from granitic terrain contain as much as 0 0 1 percent equivalent uranium* Th& higher radioactivity of the concentrates from the Clear Creek area and on Golovin Bay is due chiefly to an unidentified uranium- titanium niobate, whereas the higher radioactivity at the headwaters of the Kwiniuk River is due to thorianite. INTRODUCTION The Darby Mountains district is situated in the southeastern part of the Seward Peninsula, Alaska (fig« 1)« The Darby Mountains have a general north-south trend and extend from Cape Darby on the south to the southeastern portion of the Bendeleben Mountains on the north, a distance of approximately 75 miles* The area is bounded on the west by Golovin Sound, Goiovin Bay, and the Fish River and in general on the east by Norton Bay and the Tubutulik River, although the upper half of the latter river dissects the eastern flank of the mountains The area is accessible from Nome, approximately 70 miles to the west, by air to two small airstrips, one located at Goloyin on the western side of the Darby Peninsula and the other at White Mountain on ihe Fish River and the Moses Point Civil Aeronautics Authority airfield near the mouth of the Kwiniuk River, 46 miles northeast of Golovin. There are no good harbors along the entire coast« Transportation of supplies within the area must be accomplished by tractor or in part by small boats, as there are no roads. The Darby Mountains are a relatively bw range with the highest peaks seldom rising to over 3,000 feet above sea level. In tfie heart of the range giactation has produced cirques and steep-sided, U-shaped valleys. Some streams have cut deep valleys, Wave action along the southern coast of the Darby Peninsula has produced a rugged coast with high cliffs and a beach so dightly developed that it is impossible to walk along the shore in many places* The greater part of the Darby Mountains district is made up of well rounded tundra** or vegetation-covered hills and mountains. Rock pinnacles, talus, and rock fragments occur on and near the tops of many mountains, but bedrock outcrops are surprisingly scarce. Previous investigations (Gault, Black, Lyons, 1946; Killeen and White, 1950; and West and Matzko, 1952) in the Buckland-Kiwalik district to the northeast of the Darby Mountains revealed the presence of uranothorianite and several other less radioactive minerals wfeteffy distributed, but toeally concentrated, In areas under­ lain by febit igneous rocks. The purpose of the 1948 reconnaissance in the Darby Mountains was to determine whether similar radioactive minerals also occur in the felslc igneous rocks of this district* and, if present, attempt to discover any sites of high concentration rfnd the bedrock source of such minerals * The reconnaissance was conducted during the summer of 1948 by a field party consisting of W« S» West, geologist, and A. E» Nessett, J 0 J e Otoyuk, and U Mo tkleaslk, camp assistants. Time permitted only the investigation of the southern and eastern parts of the district * The route followed is indicated by the location of camps, numbered In chronologic order starting at Golovln, on figure 1* GEOLOGY The only work of the Geological Survey in the Darby Mountains district prior to this investigation was done by two parties, those of Mendenhall (1$01), who In 1900 mqpped both topographically and geologically fthfc1 Koyuk River valley and parts of the Darby Mountains on an exploration-reconnaissance scale; and of Smith and Eakin (1911), who in 1909 mapped the area between Nulato and Council on a similar scale« The geologic features of the Darby Mountains district are described briefly be low» Undivided metamorphic rocks The oldest rocks In the district occur mainly along the western flanks of the Darby Mountains and are the folded and sheared metamorphic rocks of pre-Silurian and possibly pre-Cambrian age (fig* 1). These rocks consist of quartzose, calcareous/ 8 biotitic, chloritic, feldspothic, and graphitic schist and thin limestones. The schist has been cut by greenstone/ granite, diorite, and other igneous rocks which have had a share in the met amor ph ism and obliteration of the original characters of the schist * Paleozoic rocks Paleozoic rocks of Carboniferous, Devonian, and Silurian age are best re­ presented along the eastern flank of the Darby Mountains