Hard Rock Mining Tour: Assay Office Museum

James F. Bailey Assay Office Museum

The assayer was an important man in the mining community. The assay office was the place prospectors would take their ore samples to find out whether or not they had "struck it rich." The determination of the value of ore was so important that the assayer's word could, and often did, make or break a prospector.

In natural form, precious metals are mixed with other minerals to make ore. It is the assayer's job to determine how much of the ore is valuable, and how much can be discarded. At the James F. Bailey Assay Office in Wall Street, this was done through something called a fire test, which required a sampling of the rock a miner brought in to be pulverized, chemicals added, heated, and separated. The miner was then told to return to the office a day or two later when the assayer would tell him what his find was worth.


Owned by the Bailey family from 1909 to 2001, the Assay Office is now a museum owned by the county. It contains many tools and implements used in the assaying process, as well as furniture and artwork owned by the Bailey family.

Visit the Assay Office

Did You Know?

Assayers calculated the value of ore using assay tons, equal to about 29.167 grams. Precious metals are measured in troy ounces, equal to about 31.1 grams. Miners wanted to know how many troy ounces were in one regular ton (2,000 lbs.) of their ore. The ratio of milligrams to assay tons is the same ratio as troy ounces to tons. So, if an assayer finds that there is one milligram of gold in one assay ton of ore, the miner knows that he has one troy ounce of gold for every ton of the same ore!

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