Johannesburg, South Africa ? The ship was laden with tons of copper ingots, elephant tusks, gold coins – and cannons to fend off pirates.

But it had nothing to protect it from the fierce weather off a particularly bleak stretch of inhospitable African coast, and it sank 500 years ago.

Now it has been found, stumbled upon by De Beers geologists prospecting for diamonds off Namibia.

“If you’re mining on the coast, sooner or later you’ll find a wreck,” archaeologist Dieter Noli said in an interview Thursday.

Namdeb Diamond Corp., a joint venture of the government of Namibia and De Beers, first reported the April 1 find in a statement Wednesday, and planned a news conference in the Namibian capital next week.

The company had cleared and drained a stretch of seabed, building an earthen wall to keep the water out so geologists could work. Noli said one of the geologists saw a few ingots, but had no idea what they were. Then the team found what looked like cannon barrels.

The geologists stopped the brutal earth-moving work of searching for diamonds and sent photos to Noli, who had done research in the Namibian desert since the mid-1980s and has advised De Beers since 1996 on the archaeological impact of its operations in Namibia.

The find “was what I’d been waiting for, for 20 years,” Noli said. “Understandably, I was pretty excited. I still am.”

Noli’s original specialty was the desert, but because of Namdeb’s offshore explorations, he had been preparing for the possibility of a wreck, even learning to dive.

After the discovery, he brought in Bruno Werz, an expert in the field, to help research the wreck. Noli has studied maritime artifacts with Werz, who was one of his instructors at the University of Cape Town.

Judging from the notables depicted on the hoard of Spanish and Portuguese coins, and the type of cannons and navigational equipment, the ship went down in the late 1400s or early 1500s, around the time Vasco de Gama and Columbus were plying the waters of the New World.

“Based on the goods they were carrying, it’s almost certain that it dates from that time,” said John Broadwater, chief archaeologist at the U.S. National Oceanic and Atmospheric Administration.

“This find is very exciting because very few vessels from that period have been discovered,” he said, adding that many early ships were thought to have wrecked in that area.

It was, Noli said, “a period when Africa was just being opened up, when the whole world was being opened up.”

He compared the remnants – ingots, ivory, coins, coffin-sized timber fragments – to evidence at a crime scene.

“The surf would have pounded that wreck to smithereens,” he said. “It’s not like ‘Pirates of the Caribbean,’ with a ship more or less intact.”

He and Werz are trying to fit the pieces into a story. They divide their time between inventorying the find in Namibia and doing research in museums and libraries in Cape Town, South Africa, from where Noli spoke by phone Thursday.

Eventually, they will go to Portugal or Spain to search for records of a vessel with similar cargo that went missing.

“You don’t turn a skipper loose with a cargo of that value and have no record of it,” Noli said.