Tintina Metallogenic Province Integrated Studies on Geologic Framework, Mineral Resources, and Environmental Signatures

Project summary:

Geographically the project region has been called the "Tintina gold belt" (referred to henceforth as the Tintina gold province (TGP)), a 200-km-wide, 1,200-km-long arc, bounded by the Tintina-Kaltag fault systems on the north and the Denali-Fairwell fault systems on the south. This region extends from northern British Columbia west to southwest Alaska (Goldfarb and others, 2000; Smith, 2000). The area is sub-arctic in climate and includes major ecoregions such as Interior Highlands (Yukon-Tanana Upland), Interior Lowlands, and Coastal Plains (Gallant and others, 1995).

Within the past four years the TGP region of Alaska has experienced accelerated gold exploration, development, and mining activity (Fort Knox and True North mines in the west near Fairbanks and the Pogo mine in the east). In addition, the State and industry have discussed plans for the construction of a gas pipeline, railroad corridor, and associated infrastructure that would impact the eastern segment of the belt. Also within TGP is Fort Greeley, where, in the summer of '02, construction of the U.S. Missile Defense System began. In the southwestern extent of TGP, the BLM, Native Corporations (Bering Sea, Calista, and Doyon), and industry are gearing up their exploration and characterization of the Aniak Mining District. The State (Division of Geological and Geophysical Surveys, DGGS) has recently focused much of its resources and activities in the eastern part of the belt, creating detailed quadranglespecific geological and geophysical maps in anticipation of both mineral resource development and expanded environmental impact. Also, the Alaska Division of Mining and Water Management and the BLM have actively supported USGS water-quality studies related to historical and current mining activities. We continue to receive requests from the Alaska State Departments of Environmental Conservation and of Health and Social Services for regional geochemical background/baseline data. Opportunities abound for integrated studies on predominantly public lands that benefit land management and regulatory agencies, industry, an Alaska Native interests.

A major emphasis of this watershed-based project will be the integration of regional hydrologic, geologic, geochemical, and geophysical studies. This activity would have as its core the expertise and activities related to the construction of regional framework-based products (e.g., structural geologic studies of mineralized and unmineralized terrane; metallogeny of plutonic rocks; hydrologic pathways; understanding of both VMS and gold-depositing hydrothermal systems; etc.) which will assist the more site-specific process-oriented studies (e.g., water-rock geochemical processes; uptake, transport, and bioavailability of metals; fluid sources responsible for ore-body genesis). Both the regional framework and site-specific approaches will progress together and will complement each other by being co-located and by having integrated objectives.

USGS Scientists Bronwen Wang and Larry Gough examine soil moisture lysimeters

Project Objectives:

The Tintina gold province is an arcuate, 1,200-km-long metallogenic province extending from northern British Columbia into southwestern Alaska. The province includes such large gold deposits as Pogo, Fort Knox, True North, Donlin Creek, and Shotgun and remains a prime area for gold exploration. This Project will address several critical issues related to origin, controls on emplacement, and the environmental consequences related to development of mineral resources.

The project objectives include:

Define the geochemical characteristics of the ore fluids and granitoids associated with the major intrusion-related gold systems of the Tintina gold province. Results will attempt to better fingerprint and discriminate between mid- Cretaceous fluids of a regional metamorphic, contact metamorphic, and magmatic exsolution origin.
Characterize the tectonic setting and metallogeny of the Yukon-Tanana Upland by identifying the dominant structural domains and determining how the structural fabric elements vary across the region and how they correlate with time. Evaluate the relationship between regional hydrologic systems and major geologic structural elements.
Characterize the tectonic setting, petrogenesis, and metallogeny of the Bonnifield VMS deposits and epizonal gold deposits of the Yukon-Tanana Upland in order to compare these deposit types with other, previously studied deposits in the eastern Alaska Range and Yukon Territory. Establish pre-development geochemical baselines for rocks, soils, surface water, and vegetation in selected watersheds in the Bonnifield Mining District (and adjacent Trident Glacier belt), the Fairbanks Mining District, and the Yukon-Tanana Upland.
Define environmental geochemical signatures for natural, undisturbed VMS and low-sulfide (epizonal) gold vein deposits in sub-arctic climatic setting as additions to the Mineral Resources Program’s growing database of geoenvironmental models.
Characterize drainage from both developed and undeveloped mineralized areas. Focus on areas downstream from mercury-, antimony-, and arsenic-rich gold deposits. Using these data assess the degree of metal loading in local streams due to both the natural weathering of deposits and past mining activity. Pathways of metal dispersion within the secondary environment will be comprehensively evaluated.
Characterize the geochemical signature imparted to the aqueous, stream sediment, and biogeochemical environments from the geologic (mineralized and non-mineralized) substrate in order to provide information on the extent of rockwater interactions and element bioavailability in different geologic terranes.

The ultimate success of this project relies on the integration of five tasks, each with communal and as well as individual strategies and approaches. The integrated geologic/hydrologic/geochemical approach is made possible by the diversity of expertise represented by the project personnel, and represents an unconventional, but certainly robust way of studying metallogenesis, natural rock-water processes, and element bioavailability.

Task 1 - Origin of gold deposits: geochemistry of intrusion-related gold systems of the Tintina gold province:

In cooperation with other workers in academia and industry, plans to select a suite of ore samples that will be collected from the major gold systems of the Tintina gold province (TGP). In addition, unaltered samples of intrusive rocks that are spatially associated with the granites will be collected. Detailed isotopic and geochemical studies will attempt to establish possible source(s) for the hydrothermal fluids and coeval melts, and results will be used to refine the overall genetic/exploration model for the new epizonal gold deposits that characterize the area.

Task 2 - Geologic Framework: Regional tectonic setting of the Yukon-Tanana terrane and its control on fluid flow and watershed hydrology:

Will conduct detailed geologic and geochemical framework studies that will support the new field studies (in the Tasks 1, 2, 3, and 5) as well as help define the tectonic controls on plutonism, mineralization, and groundwater flow. These goals can only be successfully addressed by working as a team with the other Project members inasmuch as no one person or Task has the expertise to solve these larger issues. Because field-based research is so expensive and time consuming, the needs of the entire Project must converge on specific target areas. These will be selected in part using the regional database compilation, which will highlight geochemical terranes anomalous in both economic and geoenvironmentally important elements.

Task 3 - Biologic and hydrologic setting, biogeochemistry and water-rock processes:

Seeks to define rock-water, soil development, and trace element mobility and element bioavailability processes that may be closely linked to geologic landscape controls. This strategy is being conducted within the boreal forest--the major sub-arctic ecosystem that makes up this region. Both mineralized and non-mineralized terranes will be examined and the success of this task will be measured by how well we advance our overall understanding of the relation between bedrock geochemistry and structure and the transport and bioavailability of elements and ions. This task focuses on defining the chemical evolution of ground and surface waters and of vegetation and supporting soils. Sources and residence times of waters will be evaluated in the context of geologic units and structures as they control local and regional hydrology.

Task 4 - Economic geology and environmental setting of regional VMS deposit types, northern Alaska Range:

Seeks to characterize the natural geochemical variability of selected watersheds within the Bonnifield Mining District and adjacent Trident Glacier belt through systematic water and stream sediment sampling. It seeks to define bedrock geology (age, whole rock geochemistry, and tectonic setting of meta-igneous protoliths), metal content of gossans, and metallogeny of the Bonnifield VMS. This will be accomplished by integrating data from industry with additional data from geochemical and stable and radiogenic isotopic studies of drill core along with a smaller number of surface rock samples. The task will conduct synthetic meteoric water leach tests of gossans and associated altered bedrock to determine natural releases of metals into the aquatic environment.

Task 5 - Geoenvironmental model for epizonal Hg-Sb-As-Au systems of the Tintina gold province:

Seeks to define the geochemical character of the epizonal ore deposits of the Tintina gold province (e.g. Brewery Creek, True North, Donlin Creek) as these deposits are likely to be of important environment concern. Establishment of pre-mining background and baseline information, especially for As, Hg, and Sb levels in soils and waters, is critical information for land managers and regulators involved with the resource development. Also, the potential impact in the sub-arctic environment on local soils, vegetation, and waters from mining these ores will be evaluated.

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U.S. Department of the Interior, U.S. Geological Survey, Reston, VA, USA
URL http://minerals.usgs.gov/west/projects/tint.shtml
Contact: Western Minerals Team
Last modification: Tuesday, 17-Aug-2004 13:59:04 EDT
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