Evaluating the role of deep Earth processes in mineral deposit formation, North Cascades, Washington.

Author(s)

Colton Bell

Faculty Mentor(s)

Christopher Mattinson (Geological Sciences)

Abstract

The demand for new technologies and clean energy sources has brought an increase in demand for mineral resources to supply the elements needed. Sulfide minerals are the source of many economically significant elements, such as copper, and are thought to be concentrated by a combination of deep and shallow processes. However, the role of processes deep in Earth’s crust is not well known compared to shallower processes. The Chelan Migmatite Complex is located in the North Cascades near Chelan, Washington and has a multistage history spanning both deep and shallow processes. Preliminary results for a sample recording the deep stages of the geologic history shows an early stage with abundant pyrite (FeS2) containing minor inclusions of chalcopyrite (CuFeS2), with a later stage associated with the replacement of sulfide minerals by magnetite (Fe3O4). These observations suggest that the concentration of copper occurs at the earliest stages of the geologic history, which occurred approximately 30 km deep in the crust. The next stages of my research will further characterize mineral abundances and compositions, as well as compare the relations of samples recording varying depths across the multistage history.

Keywords: Cascades, Sulfides, Mineral Resources

Presentation

8 thoughts on “Evaluating the role of deep Earth processes in mineral deposit formation, North Cascades, Washington.”

  1. I’ve been on many field trips to the Chelan migmatite complex, and it’s very interesting to hear about this economic geology application. What is the abundance of the units containing the economically significant minerals. Would this geological formation ever be economically viable?

    1. Hi Lisa! For the outcrop I was studying, the quartz diorite gneiss unit is the predominant unit containing the economically significant minerals, specifically the pyrite and chalcopyrite. However, the sulfides do occur in the magma mixing and coarse banded gneiss units as well, but future work will determine which sulfides are present in those units and whether they are a result of magmatic or hydrothermal processes. As of now, I would say this formation would not be economically viable due to the initial minor abundance of the economically significant minerals that has been observed.
      Thanks for tuning in and your questions!

  2. Colton and Chris,
    I think your poster on “deep Earth processes” is really well written and presented.
    Congratulations to you both!
    Jim Gartrell

  3. Super cool! Well done presentation! How long do you think It took before the first replacement event of pyrite to chalcopyrite started to take place? Then how long before Chalcopyrite started becoming Iron oxide? Is it typical for these kinds of deep earth processes rocks to have these multi-stage replacement events appear band-like wrapping around the perimeter of the pyrite?

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