Evolution of the ore formation in the history of the earth

Abstract

The formation of the earth's crust proceeded unevenly, mainly during the first 2 milliards of years of the earth (4.6-2.6 mld.). This has led to the inclusion into the early protocrust of the first undifferentiated blocks of the oceanic crust containing effusives of ultrabasic composition of the type of comatiites, which were attended by unique nickel deposits. The presence of large gold ore deposits (Yellowknife, Colar) is characteristic of the same old protocrust. The further geological history of the earth's crust is connected with an intensive erosion of the oldest crust which occurred under conditions of a changing earth atmosphere, of an increase of free oxygen in it and of new conditions of sedimentation. One of the most striking examples of this was the appearance and huge development during the lower Proterozoic (2.6-1.9 mld. of years ago) of big deposits of ferruginous quartzites, jaspilites (Hammersli, Krivoi Rog, KMA, etc.). From this time dates the appearance of the first large uranium deposits (2.6-1.9 mld. of years ago) (Witwatersrand, Atabaska, Singhbum, Alligator River). The following middle and upper Proterozoic (1.9-0.6 mld. of years ago) was characterized by a similar global appearance of large polymetallic deposits being mainly of a stratiform type. The genesis of the deposits was connected with the accumulation of thick carbonate strata enriched in C org (MacArthur, Mount-Isa, Zavar, Sullivan, Sardana, Kholodnenskoye) appearing at that time. The geological history of the earth's crust during the Phanerozoic is distinguished by a further complication of rock composition. Owing to the appearance of numerous linear structures and connected with the latter sediments having been subject to unprecedented sedimentary differentiation, enriched in organic materials, which in their turn were distinguished by accumulation, sorption of rare elements and metals—metallogenic provinces of most different type arose in the earth's crust: tin-bearing provinces (Pacific Ocean zone), tungsten provinces (Middle Asia), germanium provinces (Donbass), uranium ones (Hercynides of Europe), etc. Much favourable to this was the locally displayed magmatism in the same mobile zones which favoured the redeposition of the ore load of sediments and the creation of vein deposits. The irreversible and strictly directed character of the evolution of chemical distribution of elements in the structures of the earth's crust, its relatively slight relation to mantle sources of metals and submission to life development and the laws of organic geochemistry—such are the features which determine the contemporaneous distribution of elements in the earth's crust.