以下でアクセス： 01 3月, 2018
Data cited at: "Annual Survey of Mining Companies: 2016"@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.