Not Just Gold
Lesson by Rachel Hughes
Edited By Stephanie Nardei

Time: 2 - 3 class periods
Prep Time: Photocopying of maps, data sheets and articles (20 minutes)
Materials: Map of region
Data sheet
Abridged article.


Previously students explored the hydrothermal mechanism that gives rise to gold and other ore deposits. In this lesson, students are presented a conundrum. In an area where gold is found in stream sediments and where there is a gold mine, there are also significant levels of arsenic in the water. These streams are part of the watershed that acts as a source of drinking water for the local population.

  • Is the industrial mining operation to blame for the arsenic or could there be other reasons why it’s there?
Using data from a real study, students devise an explanation for the arsenic in the drinking water and state whether the mining company is at fault for the high levels of arsenic in the drinking water. The situation is not a black and white case.

Students will:
  1. Articulate a possible relationship between arsenic and gold deposits in a written statement using data to substantiate the relationship they describe.
  2. Use real data to determine the source of the arsenic in the drinking water.
National Science Education Standards
Content Area D: Earth and Space Science
Geochemical Cycles
The earth is a system containing essentially a fixed amount of each stable chemical atom or element. Each element can exist in several different chemical reservoirs. Each element on earth moves among reservoirs in the solid earth, oceans, atmosphere, and organisms as part of geochemical cycles.

Teacher Background
Arsenic, like gold, is deposited and concentrated in the bedrock by hydrothermal activity. As an area of bedrock, including the magma and meteoric water that is part of the rock, is super heated by a magma body, minerals move out of the rock into solution. As the water moves up and away from the heat source, the conditions change and the minerals that had become part of the solution now move out of solution. Due to different chemistries, the various minerals precipitate out of solution in differing conditions. However some routinely precipitate out of solution at around the same time, for example, arsenic and gold. When the mineral precipitates out of solution it leaves an ore deposit. These ores are often deposited along the cracks in the rock that resulted from the immense heat and pressure that the original magma body exerted on the rock.

Related and Resource Websites

PULSE Resources on Arsenic http://pulse.pharmacy.arizona.edu/resources/arsenic/teachers.htm
EPA Drinking Water in Schools http://www.epa.gov/safewater/schools/index.html

Mineral Deposits
Britannica Online: Mineral Deposits http://www.britannica.com/eb/article-82178

National Academies Press on Mineral Resources http://orsted.nap.edu/openbook.php?record_id=9035&page=5

How do Hot Springs Work? http://pulse.pharmacy.arizona.edu/resources/images/hotsprings.jpg
Hot Springs & Geothermal Areas http://pulse.pharmacy.arizona.edu/resources/hotsprings.pdf
PDF File of the Hot Springs document



1. Students should be familiar with the health effects of arsenic poisoning from earlier classes. Start class by presenting the following scenario to the class.

Monica Diaz lives with her family in rural Arizona. She has lived there for about 15 years. Recently she visited her doctor’s office with complaints about a skin affliction on her hands and feet. She has hyperpigmentation (dark spots) and keratoses over her hands and feet. The doctor asks her about when these symptoms started appearing. Monica isn’t able to identify when the keratoses exactly started, perhaps a couple of months ago, but the black spots began appearing more recently. The doctor takes some blood work and asks her about her occupational environment and her water supply. Where does she get her water from? What type of environment does she live in, what does she have contact with, and what does she do?What do they think is wrong with the patient? They should use the background they’ve gained from previous classes to justify their reasoning. Why might the doctor be asking the questions about environment and water source? What other information would the doctor need to ask or find out?

2. Review the scenario with students and point out the evidence for arsenic poisoning.

3. Ask students how much arsenic can be in the water and yet still be safe to drink. Students will have been exposed to this in earlier lessons.

4. Review what the health risks of arsenic in drinking water are.

5. Review the national (EPA) and worldwide (WHO) standards for arsenic levels in drinking water.

6. Present the following scenario to students: Health issues of local people in this Chilean area. In the Elqui watershed there is an increased prevalence of bladder and skin cancers, even among adolescents. Many of the people have skin keratoses, and hyperpigmentation.

7. Students should recognize the similarities between the scenario that they reviewed at the beginning of class and this scenario. Explain that public health officials have pinpointed arsenic as the probable cause of the ailments. However, where is the arsenic coming from? While the data from water close to the mine indicates that there are significant amounts of arsenic in this water source, there is data from other areas within the watershed with high levels of arsenic. Is the mine responsible for the high levels of arsenic in the water?

8. Present raw data given in Figure 1 and the map #1. Explain to students that drawing upon the past lessons will help them determine where the arsenic is coming from. Direct students to place the raw data on map #1 which shows the geology.

9. Students are given the map data. Students postulate what they think is happening.

10. Students are presented with additional information such as increased erosion due to the weather phenomenon known as El Nino, and increased amounts of arsenic in the water as a result of mining processes. Students read the abridged version of the actual article provided and respond to questions.

11. Using the data and research paper, students write a paper as if reporting back to the community leaders and health officials. Included should be a description of the problem and the suspected origin of the problem. Can it be attributed to the mines or are other factors responsible? Students make a recommendation in their papers for action to be taken for reducing risks. Students should also include some of the maps and data points they correlated to within their reports.

Finish report.

Embedded Assessment

Students’ prior knowledge of health impacts of arsenic can be assessed in their spoken responses to the first scenario. If students are able to analyze data and draw conclusions, this can be assessed in their articulation of a possible relationship between arsenic and gold deposits in a written statement. If students are able to use real data to determine the source of the arsenic in the drinking water and present that in a written format, this can be assessed in the written report.

PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

1996-2007, The University of Arizona
Last update: November 10, 2009
  Page Content: Rachel Hughes
Web Master: Travis Biazo