GEOFF BENNETT: Mankind has mined the Earth's surface for thousands of years, searching for the metals and minerals that have made it possible to build our cities, arm our militaries and develop new technologies.

Now there's a furious race to find even more metal that will enable the world's energy transition away from fossil fuels.

And that furious race leads mining operators to hunt for deposits in increasingly remote locations, none more so than the floor of the distant Bismarck Sea in Papua New Guinea, where one company this summer started to dig at what may become the world's first operational deep-sea mining site.

Videographer Edward Kiernan and special correspondent Willem Marx traveled there to witness firsthand this extraordinary new industry, difficult and complex, but also dangerous and controversial.

WILLEM MARX: On the island of New Ireland, getting out to sea can sometimes prove a struggle.

A new jetty's construction, the completion of nearby buildings remain projects for the future.

But beneath these waves, there's a new kind of treasure rush for copper and gold that may one day soon help to fund them.

This quiet pebbly beach on a remote Pacific archipelago may not look like much, but just over the horizon, a group of sailors and engineers are engaged in a series of scientific tests.

And the wealthy investors behind them hope that one day this lonely beach might become a gateway to a multibillion-dollar industry.

A smoke-belching catamaran approaches, our ride across the Bismarck Sea, named for a long-ago chancellor in Germany, which once colonized this region.

Two hot, rolling hours later, in the distance, our destination appears, the MV Coco.

Prow to stern, it measures 270 feet, a triumph of maritime technology, now 14,000 miles from home.

Several stories' high, strong thrusters keep this ship entirely stationery for days at a time 20 miles offshore, and on top of its target site, a mile beneath the surface.

Owned by a Danish firm, OCT Offshore, it's been leased and refitted by a company called Magellan, with more than a decade of deep-sea expertise.

Yet journalists have never before been allowed on board to document this kind of work deep-sea mining.

Inside a darkened room, over 12-hour shifts, a pilot and co-pilot steer a remotely operated vehicle, or ROV, far below their cockpit seats.

JOHN MATHESON, ROV Supervisor, Magellan: You just need to come back to a safer heading.

WILLEM MARX: They're supervised by John Matheson.

We're talking about an ROV that's around a mile deep right now?

JOHN MATHESON: Yes.

WILLEM MARX: I see 1,500 meters there.

JOHN MATHESON: The pressure that's under, the weight of the water, can be massive.

So... WILLEM MARX: And so what's its job?

JOHN MATHESON: It's basically the eyes, isn't it?

That's all we are, and supplying the power.

WILLEM MARX: An umbilical cord and a separate cable connect the surface vessel to both the ROV and a 12-ton grabbing mechanism far below.

The ROV transmits power to the grab and guides its movements as it punches and claws through the seafloor's surface, then scoops up the resulting rocks.

It deposits most of these spoils in a nearby stockpile, but twice a day hauls some up to the ship far above.

With help from the crew, high up on the bridge and an operator perched above the vast rear deck, where the enormous winch and perpetual motion is central to this ship's mission.

Underwater mapping experts monitor what's already been excavated and where, while also planning the next day's digging.

These waters hardly seem to challenge the team from Magellan, since it sometimes operates at four times these depths.

The relatively calm surface here allow this massive mining experiment to continue, almost uninterrupted, 24/7, for more than two months.

How difficult is this kind of work compared to other stuff you have done in the past?

JOHN MATHESON: Operationally, it's as easy as we could probably get.

But it takes a lot of strain on the ROV, I would say.

WILLEM MARX: Overseeing this operation is James Holt, one of two so-called offshore managers aboard the Coco.

JAMES HOLT, Offshore Manager, Magellan: With the trial mining permit, we have been given permission to remove 180 tons for sampling process, so you can get a better picture of what's actually down there, what the deposit looks like, how it's placed around.

And, then hopefully, we will move forward into the full-on mining permit, where we will be able to develop the whole site.

WILLEM MARX: This is a frontier industry, and the team on board the Coco are essentially trying out this technique, hoping it will be financially rewarding and environmentally friendly enough to justify a far larger effort that would be the first of its kind on Earth.

As the grab's jaws unlock, out tumbles tons of rock, much of it visibly rich in copper.

This latest haul is photographed, then broken up with a power drill for easier packing and processing.

Seen in slow motion, this time-consuming process forms part of this feasibility study to determine the most efficient approach to mining such deep-sea sites.

But the concentration of copper found here will also help decide if such a high-cost operation could be high reward too.

Each grab of this material they bring up from the ocean floor weighs several tons, and with the current price of copper and the concentration of the metal they're finding in this ore, you're looking at several thousand dollars right here.

You multiply that dozens of times and dozens of grabs each day and you're suddenly talking about real money.

Seeking to confirm the copper concentration is Paul Lahari, one of two onboard geologists from Papua New Guinea.

He pulls out several samples of the rocks to test inside his makeshift laboratory just yards away.

He used a device called an XRF that can offer a rough estimate of the metal concentration or grade inside each chunk he's selected.

Grab 350, that means you have done 350 of these already this trip?

PAUL LAHARI, Geologist: That's correct, yes.

So, yes.

So, basically, it's not the number of grabs that come on board.

What happens is, you also get -- you count the number of grabs from excavating site to stockpile.

WILLEM MARX: What are you expecting to find in this rock, and what do you hope to find in this rock?

PAUL LAHARI: Well, I'm hoping to find if I can get good grades of copper.

And if the XRF can detect the gold as well, I think that would be pretty good.

WILLEM MARX: The gold?

PAUL LAHARI: Yes, gold and copper.

So... WILLEM MARX: Every one of the 180 tons brought on board will eventually be tested back onshore in Australia to get the most accurate data.

Another local scientist on board is focused not on the potential wealth this venture might create, but the potential harm it may cause.

Each time the grabbing device heads to the surface with fresh material from the seabed floor, Nicole Frani collects data on how this impacts the nearby ocean.

She does this in part with a couple dozen tubes lowered hundreds of feet down on yet another winch, designed to sample water at a dozen different depths below the vessel.

NICOLE FRANI, Environmental Scientist: It triggers according to the pressures.

And once it comes back up, it brings up water samples of each depth, 12 depths, goes back down, on deck.

I switch it off, put the caps on.

Then I collect the water quality meter from each of the sample bottles.

WILLEM MARX: Her major focus is monitoring the cloud of silt that's disturbed from the seabed known as the plume.

NICOLE FRANI: We need to know how widely its spreading out and how it can affect the sea life below.

If there's so much plume going around, or if it settles, it may harm the sea life, and the biodiversity underneath.

WILLEM MARX: And this kind of data collection is key to the work of this entire crew.

JAMES HOLT: The major part of our job here is accurate log keeping of where the samples are coming from, what depth the samples are coming from, how much energy was used to actually produce that sample.

And that, together with the environmental data, when we pull up the two environmental moorings that we have put in place, which are monitoring what's going on here all the time, then we will be able to present a decent case for why we should be allowed to start commercial mining here.

WILLEM MARX: That case must be made to Papua New Guinea's government and local communities.

Navigating those two challenges that we will examine in our next reports could make this complex engineering effort on board seem relatively straightforward.

For the "PBS News Hour," I'm Willem Marx in the Bismarck Sea.