EPOCHS OF VOLCANIC-HOSTED MASSIVE SULFIDE ORE FORMATION IN THE EARTH'S HISTORY

Abstract

Massive sulfide ore formation is one of the oldest ore-forming processes on the Earth and has accompanied volcanism for the last 3.5 Ga. At least four short epochs are distinguished in the planet's history, during which most of the resources and the majority of massive sulfide deposits were formed: these are the intervals of 2.69-2.72 Ga; 1.77-1.90 Ga; the Devonian-Early Carboniferous, which is the most notable peak of massive sulfide ore formation in the Phanerozoic history of the Earth; and the Cambrian-Early Ordovician, a less important peak. Processes of massive sulfide ore formation were cyclic in nature due to the general trend of tectonic evolution and the existence of tectonic cycles which included both the convergence of continental masses and the formation and subsequent breakup of supercontinents. In the course of each cycle, different types of massive sulfide deposits appeared in a certain sequence, which varied to some extent in particular ore provinces. Though many indications of the oldest massive sulfide deposits do persist in their younger analogs, some important distinctions gradually appear in them in later epochs. These distinctions depend on the state of the lithosphere, hydrosphere, atmosphere, and biosphere typical of that epoch. In the course of geological history, the intensity of processes of massive sulfide ore formation increased, the geography of deposit settings extended, larger and larger deposits formed, the variety of their new types grew, irreversible changes took place in the composition of ores, wallrock alterations and relevant hydrothermal-sedimentary associations, in the isotope composition of sulfide sulfur, and in many other indicators.