For Robert J. "Bob" Mackenzie, the school year means teaching classes in astronomy, physics and geology at Wasatch Academy.

Summer vacation can mean working on the solar house he and his wife, Doni, are building in Mt. Pleasant or staking out a mining claim somewhere in the Old West with Chris Johnson, his partner, who is also a teaching geologist.Two of the claims they've developed have been leased to a mining company. "They help to supplement a teacher's salary," Mackenzie said.

He grew up in the Chicago area, read Mark Twain's "Roughing It," heard tales of Virginia City and the Comstock Lode from his grandfather and thus came to make his career choice - geology.

That choice took him to Wheaton College in Illinois for a degree in geology and then, with a fellowship in hand, to the University of Wyoming for a master's in geophysics.

That degree led Mackenzie to jobs with two mining companies based in Salt Lake City. He traveled throughout the West in search of industrial metals and precious minerals.

Four years later he formed his own company, Front Range Minerals, and continued his exploratory work through a half-dozen states.

"It was an ever-beckoning but rootless way of life," Mackenzie said. He opted to put down roots. That meant marriage, a home, children and a less-wandering job. He met Doni, a Brigham Young University coed - "my very best claim."

Mackenzie taught for two years at Utah Valley Community College before making the move to Wasatch Academy.

"I very much enjoy teaching," Mackenzie said, although he could make several times his teaching salary as an exploratory geologist.

On one of his exploratory expeditions into western Nevada, Mackenzie located an early claim patent to the abandoned El Dorado silver mine on Prospect Mountain and bought the claim.

Not, he explains, because he thinks the claim - in the 1870s one of the richest in the Eureka District - will ever be worked again. It was abandoned because pumps failed to keep underground water from flooding the lower reaches of the mine. Those areas are still inaccessible.

"The legend still persists," Mackenzie said, "that there's a rich undeveloped silver vein a half-mile beneath the earth's surface at the El Dorado."

But he doesn't expect to find if there's truth to the legend. He bought the claim, Mackenzie said, as his small contribution to the abiding story of the Old West.

But the El Dorado may produce returns of a different kind. Mackenzie has incorporated El Dorado Mines Ltd. and has published a 12-page breezily written but also scholarly history of the El Dorado and Star of the West silver mines. And he is offering vertical-square-foot shares in El Dorado for sale at a nominal price.

"That's how shares were often sold in the old days," Mackenzie explained. An El Dorado purchaser receives an embossed certificate.

What will become of the money from the sale of shares? "We have a lot of people come to the food bank at Wasatch Academy for help," he said.

"Doni and I want to do our share. We're giving the money to poor people to help them build solar greenhouses to grow food and save on their energy bills."