Study On The Mineral Characteristics And Geneses Of Pyrite And Carbonate In The Shallow Water Sediments Around Hainan Island

The dissertation is supported by the Chinese Offshore Investigation and Assessment, the 908 Sub-project. The sampling area is around Hainan Island. In this area the topography and geomorphy is the Continental Shelf and the water depth here is about 5m to 200m. The sample of sediments is content grait, silty sand and argillaceous siltstone. The research in this dissertation is about the mineralogy characteristics and genetic of the pyrite and carbonate in the sediments. And using a series of analyzing methods to research and discuss the morphology feature and chemical components of the pyrite and carbonate.From the observation of the morphology feature of pyrite by stereomicroscope and the surface micro-texture of pyrite by SEM and the research of distribution of trace elements in pyrite by Inductively Coupled Plasma-mass Spectrometry (ICPMS) and the Characteristics of pyrite pyrelectricity, this dissertation found that the pyrite in the offshore sediments around Hainan Island is two types. And the morphology of them is quite different, one is about framboid, framboid assemblies and framboid intergrowth, and the other is cubic crystal form. The framboid form of pyrite is the most significant symbol of the authigenesis. From the standardizing chondrite plotting program of ree pattern, it shows that the negative anomaly of Eu and Ce in pyrite and it indicate that the environment of the authigenesis is a strong reduction environment. Meanwhile given the content of trace element and ree in pyrite, it indicates that the pyrite come from the marine and it can be taken as the symbol of marine genetic. The results of the pyrelectricity test show that the conduction type of the framboid pyrite is the P type and it means that the mineralization environment of the pyrite is the low temperature and sulfur-rich and it accords with the mineralization environment in Shallow Water. However in cubic crystal form, the pyrite is hardly content REE and its pyrelectricity conduction type are almost in N type and it indicates that it mineralization environment is the High-temperature that no related to the marine genetic. So the cubic crystal form is come from the terrigenous sediment.From the observation for the morphology feature of carbonate and using EPMA, itis found that the mainly components of the carbonate is CaCO3 and also little Mg but without Fe and Mn. So the carbonate is the calcium and magnesium carbonate. It is approved that in the shallow water, the carbonate is most about calcium and magnesium carbonate. Meanwhile because of comparing the Ca, Mg is less, it can be estimated that the carbonate is aragonite and calcite and no dolomite. And using results of the LA-ICP-MS test, the content of trace elements and REE in the carbonate sample can be taken as the symbol of autogeny biogenic origin.