The Economic Potential of Terrestrial Impact Craters

Abstract

Like concentrations of economic resources, terrestrial impact structures are the result of relatively rare geologic events. Economic resources occur in a number of terrestrial impact structures. After providing a context by briefly summarizing the salient points of the terrestrial impact record and the characteristics of impact craters, the relationship between impact craters and economic resources is explored. Approximately 25% of the known terrestrial impact craters are associated with some form of economic resources and ∼ 12% currently are exploited or have been exploited in the recent past. The resources range from world-class ore deposits to relatively localized occurrences of materials. The larger economic deposits are discussed under the genetic classification of progenetic, syngenetic, and epigenetic. The progenetic deposits include the iron and uranium ore exposed at Ternovka, Russia, and Carswell (Saskatchewan), Canada, which are exploitable because of uplift in the center of complex impact structures. Progenetic deposits also include most of the gold and uranium deposits in the Witwatersrand Basin, South Africa, which have been protected from erosion by structures associated with the Vredefort impact structure. Syngenetic deposits include the occurrence of impact diamonds at several impact structures and the Cu-Ni- PGM ores of the Sudbury Igneous Complex, which is interpreted as part of the impact melt system of the Sudbury Structure, Ontario, Canada. Epigenetic deposits include various deposits resulting from post impact hydrothermal and sedimentary activity. They also include hydrocarbon deposits. One of several examples is at Ames (Oklahoma), USA, where hydrocarbons are recovered from several lithologies, including crystalline basement. At Ames, the impact structure not only provided the necessary structural trap but also was instrumental in localizing the source rock, which was local post-impact oil shales. The current worth of economic materials produced from impact structures worldwide is unknown, but is estimated at $5 billion per year for North America. As the known record of terrestrial impact cratering is far from complete, there remain many impact structures (and, therefore, potentially economic deposits) to be found. As such deposits are highly varied in type and impact structures are random in both geologic time and terrestrial location, it is difficult to develop an overall exploration strategy, although some generalized guidelines can be provided. Once an economic deposit has been located, however, the relatively fixed morphology and structure of impact structures of a given diameter can considerably simplify further exploration and exploitation.