CAPE TOWN, South Africa—In geology, old is gold.

According to the local mining lore here, senior geologists tend to do their work the old-fashioned way. They avoid radar technology, preferring instead to examine termite and ant mounds; they study vegetation and carry divining rods. They're famous in the often cutthroat industry for their efficiency—also for wearing neckties in the blistering heat.

"I only hire old geologists," says Norman Slater, managing director of Slater Coal, a South African coal company. People such as Kevin Petzer, a 65-year-old Zimbabwean who still roams South Africa, Mozambique and Namibia from his base in the KwaZulu-Natal province in eastern South Africa.

Mr. Petzer, who emphasizes that he also has mastered conventional scientific methods, studies ant heaps, fossilized worm-burrows and flowers. The Becium homblei, a white and purple flower, grows best on copper-rich soils. So that's a good place to look for the metal. Mr. Petzer says fossilized burrows from certain prehistoric slugs "mean there's no coal below, because those creatures existed before coal formations, and the coal would have covered them up if it was there." Gold and other metals close to the surface sometimes can be found thanks to samples dug out by ants, Mr. Petzer says.

"If an ant heap is a meter high over ground, which is to say, about 3 feet, it's probably digging up material from three to four meters below, so you can collect samples from those ant heaps," said Mr. Petzer, who says that is a constant ratio. In addition to scouting for minerals, he also helps mining companies find water, since they need lots of it to run their mines. For that, he favors the forked branch of a peach tree.