Discussion The Genesis Of Makeng Iron Ore-deposit,fujian Province

Makeng iron deposit which lies in Wuyishan metallogenic belt and northeast Late Paleozoic secondary longzhang basement fault depression belt is the largest iron deposit of Western Fujian,or even South China, and its genesis has gotten much attention for a long time.Since 1950 s, a lot of previous research work has been done on Makeng iron deposit,but there do not reach an agreement so far.Based on valuable collection of previous materials,through field observation and laboratory test and analysis,this paper reveals that the ore-bearing horizon of Makeng major orebody is P1q-P1 w. The orebody shape as anticline and syncline is obvious controlled by structures,and may form through the breaking of overturned anticline by later fault.The characteristics of skarns of Makeng iron deposit show that the zonage is an inverted zoning, and the main orebody shows quartz type magnetite-tremolite type magnetite-diopside type magnetite-garnet type magnetite ores from top to bottom,it is inferred this zoning phenomenon is also the product of overturned anticline.Filed observations indicate the skarns show falut contact with rock mass,as the same time,underground observations also display granite veins fill into scarms,and these evidences reveal the formation time of this ore body is earlier than Juzhou and Dayang pluton.Molybdenite veinlets have genetic relationship with Juzhou and Dayang pluton,which fill in the cracks of the plutons, it shows that iron ore forms earlier than molybdenum. LA-ICP-MS U-Pb age of diabase dike is 141 Ma, which cuts through skarn, it determines that metallogenic period of the Makeng Iron ore is earlier than141 Ma. Skarn has flow structure, magnetite veins contact with marble directly,magnetite veins make marble become plastic, and a large number of melt inclusions are found in skarn minerals, these facts show that the origin of skarn is molten lava skarn,and the genesis of magnetite is ore pulp. On the basis of the relations betweent skarms and magnetites,combining the petrography, electron probe analysis and oxygen isotope analysis of magnetites,it is determined that magnetites form in iron skarn magma with abundant of volatiles,being transformed by gabbro-diabase magmas and granitic magmas during later period.Moreover,the transformation dominates by gabbro-diabase,granitic transformation only occurs in the parts closing to ore bodies.