The presence of magmatic ore mineralization in igneous and metamorphic rocks in the crest of a mid-oceanic ridge (MOR) suggests that the recycling model is not adequate enough to be used as a basic genetical scheme of ore formation in MOR magmatic systems. On the basis of analogy of magmatic mineralization in basalts and other igneous rocks of the Earth’s crust of the MOR crest with that in layered basic and basic-ultrabasic plutons, a qualitative model has been constructed for the orthomagmatic ore-forming system of a magmatic chamber and related fluid magmatogenic system of the MOR. Three successive stages of evolution for quickly spreading ridges are distinguished: (1) A cumulus zone forms in a shallow magmatic chamber under differentiation, where a sulfide liquid released in the process of subliquidus decomposition of a basic melt is segregated in the adcumulus melt. Also, subliquidus immiscibility develops in a freely convecting volume of magma as well as in the process of crystallization of the residual liquid, which is saturated with volatiles. (2) Ore and petrogenic components are actively transported by a volatile phase from the zone of ore melt segregation to the upper part of the chamber and out of it. This stage develops upon reaching the volume saturation of the adcumulus melt with volatiles. A mixed magmatogene fluid system forms over the zone where magmatic gases and interstitial solutions mix. Hydrothermal solutions from this zone may discharge on the sea bottom. The interstitial solutions create hydrothermal recycling cells in the side parts of these magmatogene fluid systems. (3) Upon complete crytallization of a shallow magmatic chamber, a recycling fluid system forms and functions. It dies out after the Earth’s crust temperature anomaly has disappeared. Similar phenomena must also occur in the mantle magmatic chambers. With the quasistationary feeding of shallow magmatic chambers from deeper ones, the third stage does not take place in some segments of MOR. In slowly spreading ridges, with no large shallow-depth chambers in the recent magmatic systems, the above-mentioned processes run in intermediate mantle magmatic chambers. The third stage of the evolution of magmatogene ore-forming systems is not expressed in them because there are no conditions appropriate for its development in the mantle.

First Page Preview

First page of ORE-FORMING MAGMATIC SYSTEMS OF MID-OCEANIC RIDGES
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.