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Metallogenesis of Proterozoic Basins and Stratified Rocks project's planned outcomes

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Task 1: Sediment-hosted Cu-Ag deposits of the Belt Basin

This task aims to improve fundamental understanding of the relationship between Proterozoic basin evolution and genesis of sediment-hosted copper deposits, focusing on the Belt basin in Montana and Idaho, and the generation of its copper (+silver) deposits. The task aims to elucidate factors that define the regional scale mineralizing system, for example:

1. the source(s) of driving energy, fluids and ore components
2. the architecture, timing, and focusing mechanisms of fluid pathways
3. chemical and/or physical processes leading to mineral precipitation at the site(s) of deposition

Focus will be on the genesis of sediment-hosted Cu-Ag deposits in the Revett Formation of the Proterozoic Belt Supergroup in northwest Montana and northern Idaho, and will attempt to place fundamental constraints on the origin, migration and precipitation of ore deposit components. That information will be integrated with new data that is emerging on the tectonic and sedimentologic evolution of the basin, resulting in the definition of the following:

• Age of the deposits
• Sources of the brines that developed into the ore fluids
• Sources of the metals in the deposits
• Direction of ore fluid migration
• Evidence of faulting during the episodes of ore migration/deposition
• Nature of the reductant that interacted with the oxidized ore fluid to precipitate the ore minerals

Task 2: Basin fluid sources of sedimentary exhalative deposits in the Belt Basin

Sedimentary exhalative deposits develop in a sedimentary basin by the submarine venting of metal-rich hydrothermal fluids which precipitate to form sedimentary layers rich in sulfide minerals of lead and zinc, and in some cases copper and cobalt.. This task will focus on these types of base- and precious metal deposits in the Prichard Formation and equivalents within the Belt Supergroup of western Montana and Idaho. We will attempt to establish the variations in sources, processes, and timing of fluid migration and ore formation in the context of basin evolution and tectonic processes active at the time. The results should be useful in future exploration in the Belt and in other Proterozoic rocks around the world.

In order to compile these results this task will:

• Capture as much of the data as possible from decades-long industry exploration programs in Prichard-Aldridge equivalent strata:
  • south of the Canadian border near the world-class Sullivan deposit
  • in and around the Blackbird Cu-Co deposit of central Idaho
  • in and around the Sheep Creek Cu-Co deposits in west-central Montana.
• Using the marker horizons identified by Cominco near the Canadian border, develop a program to sample and geochemically compare time-equivalent strata and use that data to understand the areal pattern of extraction and precipitation of various chemical components. Collaborate with Jim Finch to precisely locate and gather samples from the Sundown and other marker horizons within the Prichard Formation. Establish stratigraphic position through measurement of stratigraphic sections and conduct mapping as necessary. Collect samples and prepare them for chemical and isotopic analysis
• Field work in Blackbird and Sheep Creek areas to define nature of deposits in context of the host sedimentary rocks. Compile Noranda data to identify content and prepare report.
• Obtain or collect sulfide samples from Sullivan, Blackbird, Sheep Creek, and other locations, prepare for Re-Os analysis.

Task 3: Proterozoic stratified rocks as sources of mineral deposit components in the western US

Thick sequences of Proterozoic siliciclastic rocks in the western U.S. contain or are subjacent to world-class metal deposits; respective examples are the Coeur d’Alene (Ag-Cu) district in northern Idaho, and the Carlin (Au) Trend in the Great Basin of north-central Nevada. This task will determine selected primary modal and chemical compositions of both sequences of siliciclastic rocks, in conjunction with investigations under Tasks 1 and 2, and compare the impact of diagenesis, catagenesis, metamorphism, and magmatism on those compositions to ascertain the relative importance of provenance and process in the metallogeny of the two sequences.

The ultimate goal of this Task is to distinguish between Proterozoic strata that contain metallic mineral resources from those that contributed components of such resources. Identification of differences in composition and post-depositional processes that affected Proterozoic strata will contribute toward improvement of exploration success and assessment accuracy.

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