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Activity1: Introduction. (about 15 minutes)
Introduce the need for assaying by referring to the ore processing activity "How did the miners know which rocks had silver in them so after all that processing they would make money?" Students discuss in their group ways they might have known. (Seeing the silver containing minerals, mining a little bit first) Actually, because the miners were looking for gold, the mines opened as gold mines. Initially the silver ore was not recognized and was discarded as "blue mud."
Activity 2: Collection of clay suspension in water. Wear safety goggles when doing lab exercises. (about one hour including writing observations and procedure)
This is a model for one step of the method used for finding out the amount of precious metal in a sample. The suspended clay (representing the precious metal throughout the rock) is collected by alum. Follow the method in the Lab Activity with Fire Assaying.
Activity 3: Read about the actual Fire Assay method (about one half hour)
The Fire Assay article describes the method of fire assaying that was used in Virginia City in the late 1800s and is still used today. Read the article and discuss how the method works. List the steps and compare the lab activity to the reading to find similarities and differences.
Activity 4: Summarize (about one half hour)
Summarize the steps of the fire assay method. Consider errors that could be introduced at each step and suggest ways either to reduce the errors or to know if the errors actually occurred.
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