J-S Jacques became chief executive of Rio Tinto in 2016. Since then, he has led the successful implementation of our value-over-volume strategy. From 2016 through the first half of 2019, we declared a record $30 billion in cash to our shareholders while reducing net debt by $14 billion. We have also significantly strengthened our portfolio, realising $12 billion in sales proceeds, pre-tax. In 2018, we became the only major player in our industry to have a portfolio free of fossil fuel production.
We also continued to innovate and invest in high-quality growth and exploration, including copper-gold mineralisation at the Winu project in Western Australia, announced in 2019, and the Gudai-Darri (Koodaideri) iron ore project in Western Australia, set to be our most technologically advanced mine. Growth projects at Oyu Tolgoi, in Mongolia, and Resolution Copper, in the United States, also continue to progress.
In 2019, we furthered our focus on sustainability with the launch of an education partnership designed to promote interest in STEM education in Australia, and a partnership with China Baowu Steel Group and Tsinghua University, to research, design and implement new ways to reduce carbon emissions and improve environmental performance across the steel value chain.
J-S has been a member of International Council on Mining and Metals (ICMM) since July 2016, joined the European Roundtable of Industrialists (ERT) in May 2018, the Global CEO Council in Beijing in June 2019, the Business Council of Australia in November 2019 and the US Business Council in January 2020.