The role of mantle-rooted structural discontinuities in concentration of metals
published: Jan 1, 1996
ArtNo. ESP136000503001, Price: 19.00 €
The author's studies, performed in different geological environments on five continents show that an important role in major concentration of metals belongs to mantle-rooted structural discontinuities, especially in places where they intersect plate margins, rift structures, orogenic belts, or deep-seated intraplate boundaries of other trends. Some of these discontinuities are poorly expressed in surface geology, but can be detected by geophysical methods. When projected over the surface geology, they extend across boundaries of crustal blocks, modern stress provinces, or across allochthonous terranes. Mutual intersection of such structural discontinuities delineates major lithospheric blocks, rooted in the upper mantle, of a size several hundred kilometers across. Recognition of such a pattern, its projection onto geological maps and comparison with surface or subsurface structures is of a great importance for compilation of mineral prognosis maps to be used in outlining target areas having high potential for the discovery of giant ore deposits. The author's studies in the western United States, using different geophysical data and showing concentration of large ore deposits near the corners of major lithospheric blocks, are used as the main example demonstrating the above approach. In the second part of the paper, the author applies his methodology to the Czech part of the Bohemian Massif. A major E-W trending discontinuity, named the Fifty-north Fracture Zone is defined and its transregional character described. The Upper Silesian-Cracovian Zn-Pb district in Poland, as well as a group of ore deposits of the Erzgebirge Mts. at the Czech/Germany border, including the "five-element formation" deposits of Jachymov and Johanngeorgenstadt occur within a belt following the 50° N discontinuity. The position of the 50° N discontinuity is set in the context of major latitudinal structures of Central and Western Europe, comparing it with the east-west axes of the North-German and North-Danish Basins, with a spacing of about 300 km. Possible metallogenic role of the intersections of these east-west structures with the rifts is recommended for detailed investigation.