Matthew McConaughey stretches out of his chair, stretches his arm out for a handshake and stretches back down in one long, languid movement.

I’m wracking my brain to think of another human being that might team his smart, long-length, camel-coloured jacket with a defiantly scruffy beard. Nope. Just him.

Somehow, that stylistic contradiction is emblematic of the McConaughey paradox.

That charming Texas-born drawl and languorous body language is at odds with an actor who is driven and deliberate, who lost more than 20kg for his Oscar-winning turn in Dallas Buyers Club, only to deliver an acceptance speech that could pass for a killer mantra at an expensive self-help seminar: “So you see every day, every week, every month, and every year of my life, my hero’s always 10 years away,” he explained.

“I’m never going to be my hero. I’m not going to attain that. I know I’m not. And that’s just fine with me, because that keeps me with somebody to keep on chasing.”

And now he's rocking a bald cap and a 20kg weight gain as Kenny Wells, the incorrigible rascal at the centre of Gold. It's not his best look.

“To come down in weight is a militant monastic thing,” says the 47-year-old. “You lose weight at 2.5 pounds a week. Click. Click. Click. To go up is less precise. I mean things start stretching in odd places. You eat everything. Cheeseburgers. Cereal. Thai food. Beer.

“But after the first 20 days, all of a sudden you wake up one day and everything has settled. Gravity is pulling your haunch down. This is real weight. Putting it on wasn’t as scientific as losing weight. But it was a whole lot more fun.”

Bronzed and shirtless

McConaughey spent much of his career running around looking bronzed and shirtless in romantic comedies. He participates in triathlons. He once sailed down the Amazon river and trekked to Mali as a promotional gimmick for the 2005 movie Sahara. Feeling like a tub of lard can’t have been that easy, surely?

“But I didn’t feel like crap. And I thought I was going to. I thought I was going to get to a certain point where I would be like this . . .” He flops his head back and wheezes dramatically.

“But I didn’t. Know what I learned? The only thing that makes you feel like crap is the thought of quitting. Even if you’re indulging. So when I would wake up on a Monday morning after a big heavy weekend, I’d look in the mirror and think: ‘Hey, you’re doing your job; you’re getting there.’ I wasn’t thinking: ‘Oh, Jeez, look at yourself, we got to do something.’

“Of course, I did this for six months, not six years. If it was six years, you’re talking about not making it past 55.”

Kenny Wells is based on David Walsh, the founder of Bre-X Minerals, a small, unsuccessful Canadian mining company.

In the early 1990s, the fortunes of Bre-X changed when Walsh and a geologist named Michael de Guzman (Michael Acosta in the film, as played by Edgar Ramirez) decided to purchase land in Indonesia that they believed was gold-rich.

They soon reported a tremendous find and the company’s worth rocketed into billions. That was not the end of the story.

To help shape the character, McConaughey also drew on memories of his father, a pipe-selling entrepreneur in the oil business, who died of a heart attack 24 years ago.

“He’s an original guy,” grins McConaughey. “He’s not trying to be anybody else. He has no attitude. He’s just a consumer of life. A guy with the willpower and the balls to literally wake up after a dream and get a one-way ticket to Indonesia. If I can find characters like this it’s a real coup for me.

“You can argue with his morals or say he’s sleazy. But he’s just trying to survive. He’s hustling his way toward getting what he wants. He’s a by-hook-or-by-crook guy.”

He doesn’t stay in character, he says, although “my wife tells me it’s a little bit like living with a different man every time”.

In this spirit, his onscreen exuberance in Gold made for popular overspill at home, where McConaughey's wife, the former Brazilian model and television performer Camila Alves, and children – sons Levi (8), Livingston (4), and daughter Vida (7) – enjoyed a new familial anarchy.

‘Captain Fun’

“My nickname at home was Captain Fun,” says McConaughey. “I became a yes man. Anything that was fun I was all for it. A bowling alley at 10pm on a school night? Let’s do it. Pizza for breakfast? Great idea. Milkshakes with the pizza? Even better. I still consider myself a fun guy. But we had to get back to a little more discipline after six months of yes.”

The adventure didn’t stop there, not when the shooting locations included Thailand and Indonesia.

“It was living adventure. Being flooded out and having to stay in the jungle for weeks at a time. Taking midnight walkabouts with my son with headlamps on. Riding elephants. Getting in cobra pits. We have a snake wrangler, but you don’t know if your next step is on a cobra. There are snakes everywhere.

“In real life I’m, let’s get out there, let’s learn some survival techniques. And I had to go against that instinct a bit. Because Kenny Wells almost died. He didn’t know if he was going to be cannibalised when he got out there.”

Meeting McConaughey, you quickly realise that he always talks about the characters he has played as if they were old friends.

Even Rust Cohle, his crushingly nihilistic sleuth on True Detective (typical philosophical nugget: "Maybe the honourable thing for our species to do is deny our programming, stop reproducing, walk hand in hand into extinction"), raises a fond smile of remembrance.

“I had a great time living with Rust Cohle when I was Rust Cohle,” insists the actor.

“I could stay relaxed because he was a guy who was sort of on an island. He was not a guy who was looking to make new friends. In some ways trauma is what is easy about him because you can drop down as low as you can go.

“You ask yourself: What’s the truth about my guy? That’s not a question you can ask yourself in a romantic comedy. Because often the truth is I’d get way more pissed off than my character does if she did that to me. But that would make for a shit romantic comedy. So you have to stay buoyant, stay on the cloud.”

The McConaissance

McConaughey may have lucked into acting after the casting agent for Richard Linklater’s Dazed And Confused ran into him in an Austin bar, but his subsequent career and the McConaissance – a body of work that includes Killer Joe, Mud, Dallas Buyers Club, The Wolf of Wall Street, Interstellar and True Dectective – resulted from careful calibrations. Was there a particular moment when he decided he had enough of the standard rom-com dash to get the girl?

“It crept up on me for a bit, but I do remember a couple of specific moments. I remember getting another romantic comedy – which I enjoyed doing by the way – and thinking: oh this is a good one, I could do this tomorrow. And then thinking: oops. I’ve done a movie like this. Quite a few movies like this. I could do this tomorrow.

“But maybe I’d like to find something and think: I don’t know how I’m going to do this one.

“I had my agent to back me. I checked with my money man to make sure I could pay the rent for a while. I talked it over with my wife because I can get a little wobbly when I’m not working and I didn’t know how long it was going to be dry. And she said: ‘Let’s hold out until you get something that really turns you on.’ ”

He shakes his head: “And then I wasn’t offered anything for over a year and a half.”

I wonder if he can remember the first time he heard the phrase the McConaissance? Was he surprised when it entered common parlance?

“I think it was at Sundance. An interviewer used the term and I said ‘What?’”

He smiles: “And I guess it did stick somewhat.”

- Gold is out now on general release.