Fool's Gold (Pyrite)

Located in Mondulkiri Province, Cambodia

1- Why pyrite form as a vein between quartz vein and host rock (sedimentary rock)?

2- what kind of this deposit?

3- What kind of tectonic setting that control it?

Sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time. The amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter, dissolved sulfate, and reactive detrital iron minerals. Organic matter appears to be the major control on pyrite formation in normal (non-euxinic) terrigenous marine sediments where dissolved sulfate and iron minerals are abundant. By contrast, pyrite formation in non-marine, freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic-rich fresh water shales from marine shales. Under marine euxinic conditions sufficient H 2S is produced that the dominant control on pyrite formation is the availability of reactive iron minerals. Calculations, based on a sulfur isotope model, indicate that over Phanerozoic time the worldwide average organic carbon-to-pyrite sulfur ratio of sedimentary rocks has varied considerably. High C/S ratios during Permo-Carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time. Low C/S ratios, compared to today, during the early Paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean. The latter could have been due to lower oceanic oxygen levels and/or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time.Often mistaken for gold, pyrite is easily recognizable by its metallic luster and brass-yellow color. Pyrite forms into cubic crystals or as a mass of shapeless grains within sedimentary nodules, coal seams, or other rock veins. It is commonly associated with gold . 


Pyrite is called fool's gold because its colour may deceive... ... rocks, in vein deposits with quartz and sulfide minerals, and in sedimentary rocks, such as shale, coal, and limestone. Pyrite occurs in large deposits in contact metamorphic rocks.

Explained by Mosul University, Faculty of Science _ Department of Earth Sciences