Pebble, Alaska: Teaching Economic Geology and Its Broader Context Through a Case Study of a Controversial Mining Project

ELIZABETH HOLLEY ( is an assistant professor of mining engineering at Colorado School of Mines, Golden, CO.

Economic geology is a fundamentally interdisciplinary field. The study of ore deposits involves not only the characterization of ore and its processes of formation, but also related fields such as geochemistry, hydrology, and environmental geology. In addition, economic geologists engage with engineers and other technical professionals, as well as communities, because ore deposits are mined in increasingly complex technical, environmental, and social contexts. This article presents a case study-based teaching unit used to deliver content in economic geology, environmental geochemistry, hydrology, engineering geology, and public policy to third- and fourth-year undergraduates in geology and mining engineering at Colorado School of Mines. The unit uses the Pebble mineral deposit in Alaska as the focal point to engage students with data that help scientists, engineers, and policy-makers decide whether and how an ore deposit should be mined. Pebble is one of the world's largest porphyry gold-copper-molybdenum deposits, located in a seismically active area in the headwaters of a subsistence and commercial salmon fishery (Holley and Mitcham, 2016). In five hands-on and small-group activities, students learn about the characteristics of the ore deposit and its geological setting, and then they apply this information in order to come to their own conclusions about whether or not the deposit should be mined.

The Pebble Case study is a recent modification that is part of a broader curricular effort to involve more active learning and clearer ties to applications, particularly for engineering students (Holley, 2017). We typically cover so many geological concepts and ore deposit styles in the semester that students begin to tune out unless presented with memorable and engaging context. I began using the Pebble case study in my courses in 2014 and find it resonates with students particularly because it is controversial. As the teaching unit develops, students become more personally invested in the exercises because they want to inform their own opinions about the potential implications of mining the Pebble deposit. They enjoy applying their newly acquired geological knowledge about Pebble in the capstone stakeholder engagement exercise because it gives them a chance to see the issue from multiple perspectives. In recent years this has been the most memorable class session of the semester, as students throw themselves into an assigned role that they may not personally agree with and then negotiate from that perspective whether and how the Pebble project should be moved forward. This year a student commented, "It was great to learn how the geology that we learned in class intersected with the other disciplines, which is actually what we will see in our future real-world careers."

The activities are detailed in the following pages, and supplementary content is provided for classroom use.

1. Introduction to the Pebble Case Study and the economic geology of porphyry ore deposits: lecture and hands-on rock lab

Students are introduced to porphyry ore deposits in the context of the Pebble Case Study (see supplemental material, Holley, 2017; More information can be found on the company's website (, which includes links to the NI 43-101 Technical Report on the project, including information on the geology, maps, and discussion of the proposed mine plan (Wardrop, 2011). For the economic geology of porphyry ore deposits, Sillitoe (2010) is a useful resource, and the geology of the Pebble deposit has been described by Lang et al. (2013).

For a simpler introduction, the investment company Sprott Global Resources has a YouTube series of lectures on ore deposits, including the third in the series "Porphyries, Skarns, and IOCGs," which covers the geology of porphyry deposits at an introductory level geared towards investors ( The Society of Economic Geologists has recently introduced a traveling course titled "Economic Geology 101" which covers a variety of fundamentals and ore deposit styles including porphyry deposits ( Training_Curriculum/SEG/_Events/SEG_Education_ and_Training_Curriculum.aspx?hkey=a0009232-6689-4a89-8bd5-18776e8becfa).

In our porphyry deposit lab exercise, students identify characteristics in samples from classic ore deposits around the world and then place the samples within a schematic cartoon of a porphyry ore system. For institutions without access to rock samples, this exercise might be adapted to use digital images of samples or collections from a museum.

2. Hydrologic context: reading and small-group written assignment

Students work together to answer questions about the hydrology of the Pebble deposit area after reading a short document (see on the environmental baseline study conducted at the site (Pebble Limited Partnership, 2012). The questions focus on the surface water and groundwater conditions at Pebble, how the area's geology governs the exchange between surface and groundwater, and the critical nature of environmental baseline studies.

3. Tailings and seismicity: group reading activity

This group reading activity allows the class to hear a diversity of perspectives on the science behind the Pebble project without an onerous homework load. Papers, to be derived from four readings, are assigned (see the list on page 7), and one quarter of the class reads each paper for homework.

During class, teams who read the same paper meet to come to consensus on the following questions:

- From what perspective (and by what type of authors) is your article written?
- Is it biased?
- What are the five main points your classmates should know?
- What are the implications for the Pebble Project?

Finally, the teams are reorganized into groups of four—each member read a different paper, so the whole assignment is represented. Each member shares the answers agreed upon by their first groups from the first part of the session. The deliverable is a short group write-up of the answers to the above questions for each paper, and the content is tested on the final exam.

4. Environmental geochemistry: spreadsheet lab using real data

Here students use real environmental baseline data from the Pebble project to calculate the potential for acid mine drainage (see supplemental material, Holley, 2017; The acid-generating potential varies depending on which data points students select, which leads to a discussion on sampling bias and the value of large data sets.

5. Stakeholder engagement: small group role-play

In the capstone exercise for the unit, students participate in a stakeholder engagement exercise generally modeled after the "Pebble Dialogue" process initiated by the mining company Anglo American when that company was considering developing the mine. (See the Online Extras section to access the Stakeholder Exercise.) Prior to this exercise the students read an article about this process (Holley and Mitcham, 2016). This is a two-part small group activity similar to #3 above. The students number off into teams, each of which represents a different group of stakeholders: board members of the mining company, engineers contracted to design the tailings facility, environmental scientists at the USEPA, and members of an Alaskan native corporation in the area. Each team reviews the reading, identifies environmental concerns and how the mine plan should address them, and establishes a position on the project. Then the groups reform to comprise one member from each stakeholder category, in order to negotiate the next steps and who should cover the cost. The deliverable from this exercise is the discussion itself, but a final paper on this topic could be added as a summative assessment.

ONLINE EXTRA: Supplemental Information


Davies, M.P., Lighthall, P.C., Rice, S., and Martin, T.E., 2002, Design of tailings dams and impoundments, keynote address, Tailings and Mine Waste Practices Conference, Society of Mining, Metallurgy and Mineral Exploration, Phoenix, 2002, 18 p.

Holley, E.A., 2017, Engaging engineering students in geoscience through case studies and active learning, Journal of Geoscience Education, v. 65, p. 240-249.

Holley, E.A., and Mitcham, C., 2016, The Pebble Mine dialogue: A case study in public engagement and the social license to operate, Resources Policy, v. 47, p. 18-27.

Kayen, R., Thompson, E., Minasian, D., Moss, R.E.S., Collins, B.D., Sitar, N., Dreger, D., and Carver, G., 2004, Geotechnical reconnaissance of the 2002 Denali Fault, Alaska, Earthquake, Earthquake Spectra, v. 20, p. 639-667.

Lang, J.R., Gregory, M.J., Rebagliati, C.M., Payne, J.G., Oliver, J.L., and Roberts, K., 2013, Geology and magmatichydrothermal evolution of the giant Pebble porphyry copper-gold-molybdenum deposit, southwest Alaska, Economic Geology, v. 108, p. 437-462.

Pebble Limited Partnership, 2012, The Pebble Environment: A scientific overview of environmental and social data in southwest Alaska, 53 p., available at (accessed March 31, 2019)

Petticrew, E.L., Albers, S.J., Baldwin, S.A., Carmack, E.C., Dery, S.J., Gantner, N., Graves, K.E., Laval, B., Morrison, J., Owens, P.N., Selbie, D.T., and Vagle, S., 2015, The impact of a catastrophic mine tailings impoundment spill into one of North America's largest fjord lakes: Quesnel Lake, British Columbia, Canada, Geophysical Research Letters, v. 42, p. 3347-3355.

Sillitoe, R.H., 2010, Porphyry copper systems, Economic Geology, v. 105, p. 3-41.

Wardrop, 2011, Preliminary assessment of the Pebble Project, Southwest Alaska, for Northern Dynasty Minerals Ltd, NI 43-101 Technical Report, Vancouver, British Columbia.