Mr. Steyer sold his ownership stake in Farallon in late 2012, but he has not cut ties with it entirely. He remains a passive investor, his aides said, though they declined to describe the size of his investment. Employees at Farallon screen out any fossil-fuel-related holdings from his portfolio, and he no longer earns a share of the profits from the fund, the aides said.

Farallon is still invested in carbon-generating industries, and the aides declined to say whether Mr. Steyer had asked it to sell those holdings, a request that would presumably hold significant sway given his role as a founder.

The Australian mine, known as Maules Creek, illustrates the complexities of Mr. Steyer’s efforts to distance himself. Farallon was a major investor in a 2009 deal aimed at developing the mine, lending an Australian entrepreneur hundreds of millions of dollars to buy out the previous owner, according to people involved in the transaction. Eventually, the entrepreneur took the mine public, turning Farallon’s investment into a large profit. An executive involved in the original deal estimated that Farallon earned tens of millions of dollars.

Farallon remains an investor in Maules Creek to this day. Mining at the site, expected to start in 2015, will last up to 30 years, yield as much as 13 million tons of coal a year and generate about 30 million tons of carbon dioxide a year, according to Ian Lowe, the former head of the School of Science at Griffith University in Queensland, Australia. (The company that owns the mine, Whitehaven Coal, disputes the carbon dioxide projection.)

Given Mr. Steyer’s reputation as an active environmentalist, Australian opponents of the mine were startled to learn of his firm’s role as an early investor.

“It’s gobsmacking,” Philip Spark, president of the Northern Inland Council for the Environment, a nonprofit trying to stop construction of the mine, said in a telephone interview. “It’s amazing that such a person could have been involved in this project.”

Mark Carnegie, an investment banker in Australia who was involved in the Maules Creek deal, said he could sense even then that Mr. Steyer was struggling to reconcile his motivations as a profit-seeking investor with his growing anxieties about the environment.