Models and Exploration Methods for Major Gold Deposit Types

Gold occurs as primary commodity in a wide range of gold deposit types and settings. In the last decade, significant progress has been made in the classification, definition and understanding of the main gold deposit types. Three main clans of deposits are now broadly defined, each including a range of specific deposit types with common characteristics and tectonic settings. The orogenic clan has been introduced to include vein-type deposits formed during crustal shortening of their host greenstone, BIF or clastic sedimentary rock sequences. Deposits of the new reduced intrusion-related clan share an Au-Bi-Te-As metal signature and an association with moderately reduced equigranular post-orogenic granitic intrusions. Oxidized intrusion-related deposits, including porphyry, skarn, and high-sulfidation epithermal deposits, are associated with high-level, oxidized porphyry stocks in magmatic arcs. Other important deposit types include Carlin, low-sulfidation epithermal, Au-rich VMS and Witwatersrand deposits. The key geology features of the ore-forming environments and the key geologic manifestations of the different deposit types form the footprints of ore systems that are targeted in exploration programs. Important progress has been made in our ability to integrate, process, and visualize increasingly complex datasets in 2D GIS and 3D platforms. For gold exploration, important geophysical advances include airborne gravity, routine 3D inversions of potential field data, and 3D modeling of electrical data. Improved satellite-, airborne- and field-based infrared spectroscopy has significantly improved alteration mapping around gold systems, extending the dimensions of the footprints and enhancing vectoring capabilities. Conventional geochemistry remains very important to gold exploration, while promising new techniques are being tested. Selection of the appropriate exploration methods must be dictated by the characteristics of the targeted model, its geologic setting, and the surficial environment. Both greenfield and brownfield exploration contributed to the discovery of major gold deposits (>2.5 moz Au) in the last decade but the discovery rates have declined significantly. Geologists are now better equipped than ever to face this difficult challenge, but geological understanding and quality field work were important discovery factors and must remain the key underpinnings of exploration programs.