The understanding of the geological processes behind the formation of mineral systems has advanced remarkably over the past two decades and has initiated a re-think with respect to the optimal geophysical methods required to both target and delineate economic ore bodies. The mineral system concept of McCuaig and Hronsky (2014) proposes four critical elements that must combine in various scales over space and time: whole lithosphere architecture, transient favourable geodynamics, fertility, and preservation of the primary depositional zone. They conclude that “[the mineral system concept] focuses mineral exploration strategies on incorporating primary datasets that can map the critical elements of mineral systems at a variety of scales, and particularly the regional to camp scales needed to make exploration decisions.”

With exploration evolving to take a holistic view of the complete mineral system in targeting, geophysics has adapted to making greater use of techniques that can explore scales ranging from deposit to lithospheric. While the geophysical toolbox is filled with many techniques, only a few of them are capable of the depth investigation required to expand our view past the deposit scale: active- and passive-seismics, and methods that make use of the Earth’s natural gravitational, magnetic, and EM fields. Gravity and magnetics are ubiquitous in datasets ranging from continental to prospect scales and the use of seismic techniques in mineral exploration is growing. But nothing compares to natural field EM methods if the goal is 3D conductivity imaging to kilometres depth combined with ease of data collection. Over the past decade, these have become mainstream in mineral exploration, and recent advances in the joint inversion of ground and airborne data are making natural field EM methods an even more powerful tool for resolving complete mineral systems.

Examples of natural field EM techniques applied to a variety of mineral systems over the past decade are presented, beginning with a crustal scale MT transect across the Gawler Craton and the super-giant Olympic Dam IOCG deposit of South Australia, and followed by illustrations from porphyry systems (Collahuasi, Pebble, El Salvador, Los Bronces, Cobre Panama, Resolution, Santa Cecilia, and Morrison) that dominate this paper owing to the economic significance of porphyry copper-gold deposits globally and because of their amenability to large-scale conductivity imaging. Further applications to sedimentary copper (Frontier and Kansanshi), magmatic polymetallic sulphide (Voisey’s Bay), and unconformity-related uranium (McArthur River) deposits are also presented. Together these examples demonstrate the value that natural field EM geophysics can bring to the exploration decision making process when interpreted in context of mineral systems.