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Data cited at:  "Annual Survey of Mining Companies: 2021"@ Fraser Institute   The Fraser Institute Annual Survey of Mining Companies was sent to approximately 4,100 exploration, development, and other mining-related companies around the world. Several mining publications and associations also helped publicize the survey. The survey, conducted from October 9, 2012, to January 6, 2013, represents responses from 742 of those companies. The companies participating in the survey reported exploration spending of US$6.2 billion in 2012 and US$ 5.4 billion in 2011.

The primary World Bank collection of development indicators, compiled from officially-recognized international sources. It presents the most current and accurate global development data available, and includes national, regional and global estimates