Animals and mineralization of phosphorus ore forming mechanism of phosphorites

Filed under: Food

Quan S., 1987: Animals and mineralization of phosphorus ore forming mechanism of phosphorites. Acta Geologica Sinica: 72-81

Guano, or insular phosphate, commonly containing a P2o5 content of 10-35%, is one of the sources of phosphatic manures. As an example of modern phosphate of the Xisha Islands, China, this paper discusses the mechanism of mineralization of phosphate and the important contribution of animals in this process. Phosphate occurs in the middle part of carbonate sand clay of coral reef. The clay is surrounded by the longshore dam and has a dish-form in relief. The surface is covered by yellow-brown to black-brown in colour and it is thick-bedded and of sand-gravel texture. Its grains are cemented by colloidal cement of collophanite and are partly replaced by carbonate-apatite. The mechanism of mineralization is as follows: The average content of phosphorus in the seawater is only 0.07 ppm. Because of the sea food chain concentration, phosphorus is concentrated to a high content. The phytoplanktons, as producers, suck up phosphorus from the sea water. The primary consumer-zooplanktons-obtain phosphorus through eating phytoplanktons. Then phosphorus is further concentrated by the second and third consumers, including zooplanktons and fishes. As third consumers, the sea birds by way of eating fishes concentrate and transport the phosphorus to the carbonate sand clay. Thus under the arbores (high forest) layers of guano are deposited. In the tropic climate with high temperature and high rainfall, the guano is solved and moves down to the deeper horizon. In alkaline groundwater, with a pH greater than 7.0, the phosphoritization takes place. Bioclastics are cemented and replaced by collophanite or carbonate-apatite. Finally the phosphorus is fixed and phosphate is formed.

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