Assayer
From Memory Alpha, the free Star Trek reference
An assayer is an individual who examines metallic ores and minerals in order to determine the content, amount and value of the metal.
After traveling back to 1893 San Francisco Earth, Lieutenant Commander Data visited a gentleman named Ches Whitley who worked at the county assayer's office. During his visit, Data claimed to be a geological engineer who was interested in locating information about mining operations during the 1850s. (TNG: "Time's Arrow, Part II")
