(Bloomberg Opinion) — A combination of hefty dividends and contracting output is turning the world’s second-largest miner into the poster child for a $1.5 trillion industry’s growth quandary.Rio Tinto Group announced a record $3.7 billion final dividend Wednesday, adding to $11.9 billion of cash returns already paid in 2019. Yet it produced less iron ore, copper and aluminum, leaving market prices to lift underlying earnings by 18%. Rio’s Pilbara operations stumbled early in the year. Its Mongolian copper mine, a key source of future production and the basis of a greener portfolio, is now not only sorely overdue and over-budget, but also tangled in international tax arbitration. The $86 billion mining giant isn’t alone. High dividend yields and pedestrian output have begun to define resources heavyweights that used to be known for the exact opposite. Diversified groups relied on their varied sources of cash to expand, but large-scale opportunities are scarcer than ever, and portfolios look far less diverse too, once coal and other less appealing assets have been carved off. At Rio, iron ore now accounts for three-quarters of its underlying Ebitda.For investors, it hasn’t been all bad news. Since Chief Executive Officer Jean-Sebastien Jacques took the helm in 2016, Rio’s total return including reinvested dividends adds up to an impressive 112%, outpacing most rivals.Yet much of that is due to generous payouts. For a company that digs stuff up for a living, this may not be sustainable — especially for one that aims to build a portfolio better aligned with a carbon-light global economy. It may also be an indication of just how hard it is to change. Rio paid shareholders in 2019 more than double its capital expenditure budget for the same year.One priority has been copper. Under Jacques, head of that unit until he became CEO, Rio has said it wants to add more of the red metal as its existing mines age, and will look at other green ingredients, those for rechargeable batteries and the like. Yet a unit set up to consider just such deals hasn’t sealed a single one despite considering more than 200 opportunities, and the company has suffered blow after blow in Mongolia. Its Oyu Tolgoi mine in the South Gobi accounts for only a fraction of Rio’s value today, but could dictate the company’s fortunes. So far, it’s mostly an unhelpful headache. The mine, which Rio holds through Canada-listed Turquoise Hill Resources Ltd., is one of the largest copper deposits around, and could produce an annual 550,000 metric tons of copper, almost as much as Rio produced last year, plus 450,000 ounces of gold. In the parlance of big miners, it moves the needle.Unfortunately, it also encapsulates everything that makes such projects so challenging: tough geography, messy local politics and complex geology. The cost of the largest, underground, portion has swelled to as much as $7.2 billion, and could rise again when a final estimate is published later in 2020. First production may now be be 30 months later than predicted. Fears of a cash call have dragged down Turquoise Hill shares.In the latest development, Rio announced last week it would begin arbitration proceedings to solve a tax dispute. Few arbitration deals yield significant victories — ask Barrick Gold Corp. and Antofagasta Plc, which won a $5.8 billion ruling against Pakistan last year — and they tend to irk host governments, so it’s a worrying sign. The risk is that Oyu Tolgoi becomes Rio Tinto’s own version of Freeport-McMoRan Inc.’s Indonesian pride and joy, Grasberg – wonderful in theory, nearly impossible in practice.Rio won’t drop Mongolia, and not just because of Jacques’ own attachment to the project. A copper option, however long-dated, is valuable, even if the company doesn’t yet jump in to buy out Turquoise Hill minority shareholders.But what then? Rio has manageable debt and ample cash — $9.2 billion in free cash flow in 2019, the highest level in almost a decade — and deals look cheaper as shares in copper-heavy Freeport and First Quantum Minerals Ltd. have roughly halved since 2018. Perhaps, though, not cheap enough to warrant wrestling with Freeport’s U.S. liabilities or First Quantum’s Zambian operations.Rio isn’t shrinking quite yet. It has exploration projects, and iron-ore production already did better in the second half, albeit still short of the company’s ultimate target. Yet with Oyu Tolgoi mired in arbitration and geological complexities, and the economy swiftly shifting, it might be time for Rio to consider just how creative it can get.To contact the author of this story: Clara Ferreira Marques at [email protected] contact the editor responsible for this story: Matthew Brooker at [email protected] column does not necessarily reflect the opinion of Bloomberg LP and its owners.Clara Ferreira Marques is a Bloomberg Opinion columnist covering commodities and environmental, social and governance issues. Previously, she was an associate editor for Reuters Breakingviews, and editor and correspondent for Reuters in Singapore, India, the U.K., Italy and Russia.For more articles like this, please visit us at bloomberg.com/opinionSubscribe now to stay ahead with the most trusted business news source.©2020 Bloomberg L.P.