Tintina Gold Province Study, Alaska and Yukon Territory, 2002–2007 Understanding the Origin, Emplacement, and Environmental Signature of Mineral Resources

Background Alaska’s mineral resources are as vast as the land itself. The Tintina gold province (TGP) encompasses roughly 150,000 square kilometers and NORTHWEST is bounded on the north by the Kaltag- TERRITORIES Tintina fault and on the south by the

A L A S K A CANADA Farewell-Denali fault. This is an expan- Fault Y U K O N Tintina

UNITED STATES T E R R I T O R Y sive region with limited road or navi- Kaltag - Yukon - Ryan Lode Fort Knox- Tanana Brewery gable river access. It stretches westward deposit Creek FairbanksTrue North deposits Upland deposit in a broad arc from British Columbia, Pogo Scheelite Dome Mountains G O L D deposit deposit Canada, through southeastern and central s Dawson d T I N T I N A n P R O V I N C E a Mayo to southwestern Alaska, United States. l Denali w Kuskokwim Farewell - o Fault The region’s climate is subarctic and L Donlin Creek r deposit e v includes major physiographic delinea- Ri n tions and ecoregions such as the Yukon- Yuko Anchorage Whitehorse Tanana upland, the Yukon River low- Pebble deposit lands, and the Kuskokwim Mountains BRITISH COLUMBIA (Nowacki and others, 2002). Some of the first placer and lode gold discoveries in northern North Amer- Figure 1. Landsat-based general index map of the Tintina gold province in Alaska and ica were in the TGP in 1886. The TGP is Canada showing seven of its major gold deposits plus the Pebble deposit (figure base, Hart once again the focus of a resurgence in and others, 2002). mineral exploration, development, and mining activity. This resurgence stems from new discoveries (the Pogo and The Tintina gold province is an arc-shaped 2,000-kilometer-long metallogenic Donlin Creek deposits) as well as the province that extends from northern British Columbia, through the Yukon Territory, application of modern extraction meth- and across and into southwestern Alaska. In the United States, the province remains ods. New methods have provided access a prime area for gold exploration and includes such large gold deposits as Pogo, to previously known but economically Fort Knox-True North, and Donlin Creek. In recent years, gold exploration and development and mining activity have restrictive resources (such as the Fort accelerated in the area. Plans have been discussed for public and private projects Knox-True North and Scheelite Dome and infrastructures associated with development. deposits). In addition, the TGP hosts A U.S. Geological Survey study undertaken from 2002 to 2007 provides a numerous non-gold-related mineral- context for understanding why and how the mineral resources of the area were deposit types. formed, why this area is so abundantly endowed, and how the environmental sig- With the exception of the recent natures that are characteristic of the area are related to the development of mineral increase in the exploration activity at the resources. Characterization of natural baseline metal concentrations in the area’s porphyry copper-gold Pebble deposit watersheds is necessary to address future land-use issues related to mining and/or near Lake Iliamna in 2001 (fig. 1), by far, infrastructure activities. A thorough understanding of water-rock and element- most exploration dollars spent over the bioavailability processes will help predict the possible environmental impact of past decade for the identification of new development. gold resources in Alaska and the Yukon The five tasks of this study add to the science of defining and understanding Territory have been in the TGP (Hart and an “intrusion-related gold system.” others, 2002).

U.S. Department of the Interior Fact Sheet 2007–3061 U.S. Geological Survey October 2007 160° Arctic Circle 150° 130° 140° Fault Y U K O N intina T T E R R I T O R Y NORTHWEST Kaltag - 1 TERRITORIES Fairbanks 5 3 3 5 4 2 Dawson 5 Fault Denali 2 A L A S K A 60° Farewell - TES Anchorage TA Whitehorse 60° CANADA UNITED S BRITISH COLUMBIA 0 200 400 600 800 KILOMETERS EXPLANATION Tintina gold province 0 200 400 MILES Project task study areas

1 Origin of Tintina gold province

2 Geologic framework of Tintina gold province gold deposits Figure 3. Field geologic observations 3 Biologic and hydrologic setting, biogeochemistry, and water-rock processes and various geophysical investigations aid in understanding the structure and Economic geology and environmental setting of regional volcanic rock-hosted massive-sulfide (VMS) deposits 4 stratigraphy of bedrock and associated 5 Development of geoenvironmental mineral-deposit model for Tintina gold province gold deposits mineralization.

Major geologic fault system

Major mineral deposit

Figure 2. Tintina gold province of Alaska and the Yukon Territory.

Five Tasks of the Study 2. Geologic framework of TGP gold deposits From 2002 to 2007, a U.S. Geo- logical Survey (USGS) study of the TGP The framework geologic studies are key in supporting the ore-genesis focused on the following five integrated research and the regional hydrologic tasks in the fields of geology, geophysics, and geoenvironmental research. Char- hydrology, and geochemistry: acterization of the tectonic setting and metallogeny of the Yukon-Tanana up- Figure 4. Altered rock (such as the 1. Origin of Tintina gold province land involved identifying the dominant reddish color) lead USGS geologists to look Understanding the origin of TGP structural framework in key areas. This for mineral-rich areas. gold deposits will help gain a funda- work helps scientists understand the style and timing of tectonism and its mental scientific understanding of how control on plutonism and emplacement these gold deposits form. In cooperation of ore-forming systems. The frame- with academia and industry, this study work geologic studies include 1:63,360- collected and characterized ore samples scale geologic mapping that is key in from the major gold systems of the TGP, supporting the studies. as well as barren samples of intrusive rocks associated with the ore. Detailed 3. Biologic and hydrologic setting, isotopic and geochemical studies estab- biogeochemistry, and water-rock lish possible sources for the hydrothermal processes fluids and associated molten rock. These The geochemical signature of the results help refine the overall genetic- boreal forest, riparian, and tundra vegeta- exploration model for the epizonal gold tion zones were studied; these are the deposits in the area. This understanding major subarctic ecosystems that make up this region of the TGP. Character- lies at the heart of ore-genesis research ization of the geochemical signature Figure 5. Acidic, metal-rich drainage is and helps us come to a fundamental provides information on the extent of studied to define the geochemical signature scientific understanding of how these rock-water interactions and of element and weathering behavior of undisturbed gold deposits form. bioavailability in different geologic mineral deposits. terranes. This includes examination of tion) of the Bonnifield mining district the geologic substrate (mineralized and volcanic rock-hosted massive-sulfide non-mineralized) reflected in the aque- deposits. This was accomplished ous, stream-sediment, and biogeochemi- by integrating data from industry with cal environments. Study of the extent of additional data from geochemical and element bioavailability examines poten- stable and radiogenic isotopic studies tial uptake by plants and animals. of drill-core and surface-rock samples. Extensive investigations of the natu- 4. Economic geology and environmental ral weathering of VMS deposits were setting of regional volcanic rock-hosted Figure 6. Historical photo of USGS survey made and the geochemical variability of massive-sulfide (VMS) deposits team atop Boulder Mountain near Circle, selected mineralized watersheds with- Alaska, in the Yukon-Tanana upland (photo Research of this type provides infor- in the Bonnifield mining district were by W.C. Mendenhall, 1901). mation for the USGS Mineral Resources characterized through the sampling and Program’s growing database of undevel- analysis of water, stream-sediment, oped mineralized areas. Defined in the and vegetation samples. These data study are the geology (age, whole-rock are applied to the Mineral Resources geochemistry, and tectonic setting) and Program’s database of geoenvironmental metallogeny (age of ore-deposit forma- mineral-deposit models. 145° 144°30’ 144° 64°30’ 64°30’ Goodpaster

River

60 River Pogo

40

47 32 80 Shawnee 64 Zone 48 Peak eek 55 r C 55 38 Tibbs Goodpaster 34 ectonic T 65 32 Cent 45 ral 32 45 36 26 Creek Grizzly Bear 52 Gray Lead 40 34 10 15 36 Blue Lead Mountain 43 10 45 22 70 22 25 32 Brink 20 Black 22

64°15’ 64°15’ 145° EXPLANATION 144°30’ 144° 0 5 10 15 KILOMETERS Quaternary Paleozoic Alluvium Augen gneiss (Devonian) 0 5 10 MILES Colluvium Diorite gneiss Paleocene Mafic and ultramafic gneiss Rhyolite Orthogneiss Gravel Metasedimentary rock Late Cretaceous Fault—Dashed where approximatly located, dotted where Granite, undivided inferred. Arrows indicate relative horizontal movement MAP Mount Harper batholith Thrust fault—Teeth on upper plate LOCATION Black Mountain intrusion 20 Strike and dip of foliation Brink intrusion 22 Trend and plunge of mineral lineation Diorite and tonalite 55 Trend and plunge of minor fold Contact Gold deposits and occurrences

Figure 7. Many of the gold deposits and occurrences coincide with the Black Mountain tectonic zone in the Big Delta B-1 and B-2 quadrangles. The geologic mapping and investigations of the Black Mountain tectonic zone were part of the USGS 2002–2007 study (Day and others, 2007). 5. Development of a geoenvironmental References Cooperating Agencies, mineral-deposit model for TGP gold Organizations, and Industries Day, W.C., O’Neill, J.M., Aleinikoff, deposits J.N., Green, G.N., Saltus, R.W., and We are deeply indebted to the This research will help establish pre- Gough, L.P., 2007, Geologic map of contribution of our collaborators from development geochemical baselines for the Big Delta B-1 quadrangle, east- government agencies as well as from academia and industry. rocks, soils, surface water, and vegetation central Alaska: U.S. Geological Survey Alaska Department of Environmental in selected watersheds. A definition of Scientific Investigations Map 2975, pamphlet 23 p., 1 plate, scale 1:63,360, Conservation the geochemical signature of ore depos- available online at http://pubs.usgs. Alaska Department of Natural its characteristic of the TGP (Brewery gov/sim/2007/2975/. Resources Creek, Fort Knox-True North, Ryan –Division of Geological & Lode, and Donlin Creek deposits) has Hart, C.J.R., McCoy, D.T., Goldfarb, Geophysical Surveys R.J., Smith, Moira, Roberts, Paul, been developed. –Division of Mining, Land & Water Hulstein, Roger, Bakke, A.A., and The epizonal-type deposits require –Division of Forestry Bundtzen, T.K., 2002, Geology, explo- Avalon Energy Corporation environmental considerations, and pre- ration, and discovery in the Tintina Bureau of Land Management development geochemical background gold province, Alaska and Yukon: Calista Corporation and baseline information (especially for Society of Economic Geologists, Doyon, Limited arsenic, mercury, and antimony levels in Special Publication 9, p. 241–274. Fairbanks Gold Mining, Inc. soils and waters) have been established. Nowacki, Gregory, Spencer, Page, Grayd Resource Corporation This information is critical for resource Fleming, Michael, Brock, Terry, and GW Scientific development and land management. Jorgenson, Torre, 2002, Unified eco- National Park Service systems of Alaska, 2001: U.S. Geolog- –Denali National Park & For More Information ical Survey Open-File Report 02–297, Preserve map scale 1:4,000,000. The TGP study addresses specific –Yukon-Charley Rivers USGS and national goals related to National Preserve mineral resources, including ensuring NovaGold Resources Inc. the availability of reliable geologic, Pacific Alaska Resources Company geochemical, geophysical, and mineral Pacific Rim Geological Consulting, Inc. Teck Cominco Limited locality data for the Nation. Since the The University of Western Australia inception of the TGP study in 2002, more TNR Resources Ltd. than 40 reports and numerous presenta- University of Alaska Anchorage tions have been published. Many of these University of Alaska Fairbanks can be accessed through the following University of Colorado at Boulder Web-based links: Figure 8. USGS geologist Alfred H. Brooks U.S. Department of Agriculture USGS Tintina Gold Province Project and canoe near what would become –Natural Resources Conservation Web Site: http://minerals.usgs.gov/east/ the Bonnifield mining district, Alaska, Service August 27, 1898. Current studies in the tintina/index.html U.S. Geological Survey TGP reflect the long-time interest of USGS USGS Mineral Resources Program scientists in this area (photo credited to –Mineral Resources Program Web Site: http://minerals.usgs.gov/ Alfred H. Brooks). Yukon Geological Survey

By Larry P. Gough ([email protected]) and Warren C. Day ([email protected])