Chapter 3: The Power of a Systems Approach to Mineral and Petroleum Exploration in Sedimentary Basins
T. Campbell McCuaig, Sonia Scarselli, Timothy O’Connor, Stephen Busuttil, Niall McCormack, 2018. "The Power of a Systems Approach to Mineral and Petroleum Exploration in Sedimentary Basins", Metals, Minerals, and Society, Antonio M. Arribas R., Jeffrey L. Mauk
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Petroleum systems (conventional and unconventional) and hydrothermal sedimentary rock-hosted copper, lead-zinc (clastic-dominated and Mississippi Valley-type), and uranium systems can be described in a common system framework comprising the critical processes of (1) establishing the fertility of source(s) of the commodity of interest and the transporting fluid, (2) geodynamic triggers for commodity movement and accumulation, (3) establishing an architecture for fluid movement, (4) accumulation by deposition of the commodity, and (5) preservation. To translate these commodity system models to effective exploration targeting models, they must correspond to business decisions. Exploration is an exercise in scale reduction and has a number of natural business decision points that map to scale:
Regional-scale targeting—what basin has the potential of hosting a substantial mineral or petroleum system?
Play-scale targeting—where within the basin could a number of deposits be clustered?
Prospect scale targeting—where is there a deposit of sufficient quality within the play?
Marrying the systems to the decision points involves identifying (1) constituent processes relevant at each scale, (2) the geology that can map the evidence of the processes occurring, and (3) the data or interpretative products that are best used as spatial proxies to map the evidence and guide area selection at the appropriate scale. A common change in focus is noted across spatial scales for all commodities: in basin selection, fertility is key, with lesser focus on other aspects of the system; in play analysis within a basin, all elements of the mineral system are fully considered; in prospect delineation the focus shifts toward accumulation and preservation. The similarity in the targeting workflow highlights that similar key data sets, tools, and interpretative products are required to assess each mineral system across scale, albeit looking for different features within those products, dependent upon the system being targeted.
There are several key differences between mineral and petroleum systems. First, petroleum systems involve a mass trapping process with the transporting fluid as the commodity, whereas mineral systems involve mass scrubbing processes, with the transporting fluid having low concentrations of the commodity, thus requiring much fluid throughput. Second, petroleum systems require the entire system to remain reduced to maintain high-quality hydrocarbon, whereas most copper, lead-zinc, and uranium systems require the systems to remain oxidized until the site of deposition.
Consideration of these commodity systems in the context of the Earth’s evolving atmosphere-hydrosphere-biosphere-lithosphere highlights the power of paleotectonic, paleogeographic, and paleoenvironmental reconstructions in the critical step of basin selection. Such consideration also highlights common gaps in understanding the commodity systems. These knowledge gaps constitute high-value research paths that would provide greatest leverage in area selection at the basin and play scales. These include improved knowledge of paleogeographic and paleoenvironmental reconstructions, basin hydrodynamics, and timelines of mass and energy flow through basins. For metal systems, better understanding is required of how metal extraction efficiency, solubility, mineral precipitation, permeability, and pressure and temperature gradients dynamically interact along flow paths during the evolution of basins.