Although it is possible to identify the potential controls on mineralization, the problem remains to identify the critical factors. Very large mineral deposits are rare occurrences in the geological record and are likely to have resulted from the combination of an unusual set of circumstances. When attempting to understand the mineralization processes that occurred to form a major ore deposit in the geological past, especially the reasons why the deposit formed at a particular time and location within an evolving orogenic system, it is instructive to look at mineralization in modern, active subduction complexes. There it is possible to measure and quantify the rates at which both tectonic and mineralizing processes occur. In a complex subduction system, regions of extension develop. For example, subduction hinge retreat is a process that creates extension and generates heat from the upwelling of hot asthenosphere ahead of the retreating slab, producing partial melting, magmatism and associated mineralization. Seismic tomography not only images mantle as it is now, but subduction slab anomalies can be interpreted in terms of the past history of subduction. This can be used to test tectonic plate reconstructions. Tectonic and magmatic events occur rapidly and are of short duration so that many are ephemeral and will not be preserved. Furthermore, they can be diachronous as is the case with the lithospheric slab tear clockwise around the Carpathian Arc during the Neogene.
If the tectonic setting is paramount in determining the onset of the mineralization process and generation of mineralizing fluids, the fluid transport system that localizes the mineralization in space and time and concentrates the metal charge is the key to finding when and where the ore deposits occur. Fault and fracture networks in the crust provide various mechanisms for the localized expulsion of fluid in pulses of short duration. Excess surface water flow following large earthquakes in the Basin and Range region of USA offers a modern analogue to quantify fluid flow related to extensional faulting. Evidence from the Woodlark basin, east of Papua New Guinea, suggests that similar conditions pertain in the oceanic environment. Whilst there are limits to the use of regions of active tectonism as modern analogues to explain the mineralization of ancient orogenic systems, they do provide the best opportunity to understand the mechanisms of mineral processes and the controls on the location and timing of major ore deposits.
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The Timing and Location of Major Ore Deposits in an Evolving Orogen
As an outcome of the European Science Foundation scientific programme, GEODE, on geodynamics and ore deposit evolution, this book examines the underlying geodynamic processes that lead to the formation of ore deposits in order to discover what controls the timing and location of major ore deposits in an evolving orogen.
A collection of 19 research papers examines various aspects of ore genesis in the context of the geodynamic processes occurring within an evolving orogen. Although the majority of papers relate to Europe, their findings have a global significance for metallogenesis.
The book will be of interest to all those involved in research or mineral exploration concerned with metallogenesis. In addition, ore deposits provide new evidence about magmatism associated with transient, rapid changes in plate motions and subduction processes in unusual tectonic settings, and are therefore of interest to those involved in both the magmatic and tectonic processes of orogenesis.