DISTRIBUTION PATTERN OF HEAVY MINERALS IN THE SURFACE SEDIMENTS ON INNER SHELF, NORTHWEST SOUTH CHINA SEA AND ITS CONTROLLING FACTORS

The heavy minerals of 408 surface sediment samples collected from the inner shelf of the northwest South China Sea were analyzed in 2008.The results suggested that there are three heavy mineral provinces in this region,dominated by Zircon-Ilmenite-Hematite assemblage,Anatase-White Titanium-Epidote assemblage,and Pyroxene-Hornblende-Epidote assemblage respectively.The three provinces have conspicuous differences in depositional environment,hydrodynamic condition,grain size and redox environment,suggesting that the distribution pattern of heavy minerals is controlled by both provenance and hydraulic conditions.From the provinceⅠwith high hydrodynamic condition to the province Ⅲ with relatively low hydrodynamic condition,or from the river estuary and deltas to the inner shelf and semiclosed bays,the stable heavy minerals of high density gradually decrease and those with less density and lower stability increase.The heavy minerals in the study area came from three major sources,i.e.terrestrial,nearshore and autogenetic sources.Terrestrial heavy minerals were mainly from the Hainan island and Yunkai massif.The heavy minerals from erosion of the coastal islands and surrounding lands are mainly distributed by the Pearl River.