REE geochemistry of the Mengku iron deposit,Xinjiang,and its indication for iron mineralization.

The large Mengku iron deposit,Fuyun County,Xinjiang,is hosted in the metamorphosed volcaniclastic-sedimentary rocks of the Lower Devonian Kangbutiebao Formation.The orebodies in the deposit occur as beds or lenses.There are skarns in the orebodies,but they do not occur in a contact zone of the intrusion.Epidote,garnet and ores have similar chondrite-normalized REE distribution patterns and are enriched in light REE(LREE)with a moderate Eu positive anomaly but no Ce anomaly,implying that there is genetic relation between ores and skarns.Garnet has kick-down-line-shaped REE distribution patterns with a pronounced Eu positive anomaly.Three types of fluid inclusion,namely melt inclusions,melt-fluid inclusions and two-phase aqueous type inclusions,have been recognized in garnet.The combined REE geochemistry and fluid inclusion studies imply that the garnet skarn is of magmatic origin and hydrothermal origin.The garnet skarn formed in the magmatic-hydrothermal transitional stage in which the crystal,melt and fluid phases coexist.The geological characteristics and REE geochemistry of skarn minerals and ores suggest that the Mengku iron deposit is best classified as a skarn-type iron deposit.