When Rio Tinto Plc (RIO) and Glencore Plc (GLCNF) sit down to talk merger, they're not just negotiating what goes into the deal. They're negotiating what stays out. And right now, the elephant in the room is coal—specifically, what happens to Glencore's coal operations if this thing actually goes through.

This isn't your typical mining merger story about getting bigger and more powerful. It's about subtraction. And for ETF investors, that subtraction could be the most interesting part.

The Coal Problem Nobody Wants

Glencore's coal franchise might only account for about 8% of the combined entity's EBITDA, but it's become a major headache for institutional investors who care about ESG metrics. The solution being floated? Carve it out entirely.

There are a couple ways this could work. The first is a straight spinoff into a separately listed company, much like what BHP Group Ltd (BHP) did a decade ago when it created South32 Ltd (SOUHY). The second option is a pre-merger spin-out, or potentially even a narrower deal where Rio just goes after Glencore's copper assets and leaves the rest behind.

Either way, the goal is the same: get coal off the balance sheet before ESG-focused investors start asking uncomfortable questions.

Building a Copper Colossus

If Rio and Glencore do merge—minus the coal—they'd immediately become a copper superpower. We're talking about control of roughly 7% of global copper production, which would make the combined entity the dominant player in the space overnight.

That matters a lot for copper-focused funds. ETFs like the Global X Copper Miners ETF (COPX) and broader materials plays like the iShares MSCI Global Metals & Mining Producers ETF (PICK) would almost certainly see their sector weightings shift. And with copper prices trading above $13,000 per ton and the IEA projecting demand growth of up to 50% by 2040, these funds are increasingly viewed as bets on electrification, data centers, and grid buildouts—not just commodity cycles.

What Happens to the ETFs?

A coal spinoff introduces some fascinating dynamics across the ETF landscape. For one, pure-play coal funds like the Range Global Coal Index ETF (COAL) could suddenly gain exposure to a newly listed, cash-generative coal company. That might appeal to yield-focused investors who aren't worried about ESG screens.

Meanwhile, diversified mining ETFs would see their coal exposure drop, which could improve their ESG credentials practically overnight. Take the SPDR S&P Metals & Mining ETF (XME), which uses an equal-weighted approach and holds a mix of diversified miners, steelmakers, and specialty metals companies. Right now, it has indirect coal exposure through diversified producers. But if coal gets carved out, the fund's fossil fuel sensitivity drops while its exposure to cyclical metals tied to construction, power grids, and data centers rises. Over time, that repositions XME as more of an energy transition play than a traditional resource fund.

The ESG Angle Gets Real

Here's where things get interesting for ESG investors. A lot of climate-aligned and ESG-screened materials funds currently underweight diversified miners specifically because of fossil fuel exposure. If coal is structurally removed from the Rio-Glencore entity, those funds might reconsider their allocations. That could unlock fresh inflows into ESG-focused global equity ETFs that have struggled to reconcile energy transition demand with the messy realities of mining.

The "cleaner miner" label actually matters now, especially as institutional capital looks for ways to support electrification without compromising on sustainability commitments.

The Rebalancing Wild Card

Of course, any spinoff or partial asset deal comes with its own complications. Index providers like MSCI, FTSE, and S&P would need to rebalance their benchmarks, which could create short-term volatility for passive ETFs tracking those indices. That's not necessarily a bad thing—it's just something ETF holders need to be aware of.

What's clear is that when coal gets its own listing and copper takes center stage, this isn't a passive side story for ETF investors. It's a structural shift they'll need to rebalance around, whether they like it or not. The energy transition is forcing mining companies to choose what they want to be—and ETFs are going to reflect those choices whether they're ready or not.