The Rio Tinto Ltd (ASX: RIO) share price is in the green today.

Shares in the S&P/ASX 200 Index (ASX: XJO) mining giant closed yesterday trading for $119.46. In morning trade on Tuesday, shares are changing hands for $119.77 apiece, up 0.3%.

For some context, the ASX 200 is up 0.4% at this same time.

This follows on major lithium project development news.

Here's what's happening.

Rio Tinto share price gains on expanding lithium footprint

The Rio Tinto share price is pushing higher after the miner announced that it has signed binding joint venture agreements with Codelco.

The agreement will see the joint venture partners develop and operate a high-grade lithium project in the Salar de Maricunga, located in Chile.

Rio Tinto will fund studies and development costs to acquire a 49.99% interest in the project through which Codelco holds its licenses and mining concessions in the Salar de Maricunga.

According to the release, Salar de Maricunga is a large lithium-containing resource base with the potential for long-life and low-cost production. And the Rio Tinto share price could enjoy some longer-term support, with the project's brine reported to have one of the highest average grades of lithium content in the world.

Management said the JV agreement is the next step in strengthening Rio Tinto and Chile's roles as leading suppliers of materials for the global energy transition.

As part of the agreement, Rio Tinto will invest up to US$900 million (AU$1.4 billion).

That consists of US$350 million of initial funding into the JV company for additional studies and resource analysis to progress the project through to a final investment decision.

Rio will also invest US$500 million into the company once a decision is made to proceed with the project, towards construction costs.

And if the joint venture achieves its aim of delivering first lithium by the end of 2030, Rio Tinto will put another US$50 million into the company.

Additional capital requirements will be funded by both Rio Tinto and Codelco in line with their share of ownership of the joint venture.

What did management say?

Commenting on the AU$1.4 billion agreement that could be helping to lift the Rio Tinto share price today, CEO Jakob Stausholm said, "Developing this significant lithium resource will deliver further value-adding growth in our portfolio of critical minerals essential for the energy transition."

Stausholm noted, "Codelco is a strategic partner for Rio Tinto in Chile, with this agreement building on our copper joint ventures."

Codelco chairman Maximo Pacheco added:

This project continues our lithium diversification strategy, which is essential for the energy transition, with a world-class partner in Rio Tinto that represents the most attractive option for Codelco and the country.

Management expects the transaction to close by the end of the first quarter of 2026.

Rio Tinto share price snapshot

With today's intraday small boost factored in, the Rio Tinto share price is up 1.2% in 2025.