On the Origin and Distribution of the Metals in the Major Ore Deposits of the Globe
Noble, James A.
published: Jan 1, 1982
ArtNo. ESP136000201002, Price: 19.00 €
The distribution of all the known major ore deposits of the ten important non-ferrous metals, somewhat over 500 in number for the whole globe, if plotted on a suitable projection and scale, is not random but makes a distinct pattern. This pattern forms a pair of spirals, originating at a point on the equator and spiraling in opposite directions toward the poles in the Northern and Southern Hemispheres, clockwise in the northern, counter-clockwise in the southern. The pattern is incomplete because of extensive ocean cover in the Southern Hemisphere but is complete in the northern. There the shape is a spindle, narrow at the equator, thickening toward the distal end, with most of the occurrences in the last one-third of the distance, splitting toward the end. It makes three full laps and part of a fourth on the globe. It appears that an accident occurred, a one-time event of short duration, at a late stage in the formation of the globe, which at that time consisted of an inner core, probably liquid, and an outer mantle, probably solid, but no crust. A build-up of pressures in the liquid core was relieved by the ejection of a spike or plume of metal-bearing material at a point of weakness on the equator. If for unexplained reasons this plume fell behind the rotation of the globe, it had to split in two and form the opposed spirals described above. The metallic constituents then by gravity returned to the globe and were emplaced on the surface of the mantle. Once a crust is formed, tectonic features of great variety can develop. Those that reach to the mantle and are of suitable character can become ore carriers. An intersection of the spiral belts and the tectonic features is required; neither belts nor tectonic features alone can form an ore deposit. No explanation is proposed here for the formation of the oceanic crust and the continents, but some limitation is put on an explanation. It follows from this discussion that the spiral belts are pre-crustal, yet they have controlled the positions of the ore deposits in the crust throughout geologic time. The crust then was formed by a mechanism that did not destroy the spiral belts; and moreover, the continents have not moved since they were formed. A new metallogenic theory is proposed. The very large bodies of massive sulfides have come almost intact from their pre-crustal places of deposition on the top of the mantle, but the very large low-grade deposits have undergone extreme dilution and dissipation. The ore-forming process in general is one of dissipation rather than concentration.