Hydrothermal Metasomatism And Its Metallogenic Significance Of The Gongchangling Iron Deposit, Liaoning, China

Located in Anshan-Benxi area, the No.2diggings of the Gongchangling irondeposit makes the most important production of high-grade ores in Anshan-typebanded iron formation. Unlike the widespread low-grade iron ores developed inother banded iron formation of Anshan-Benxi area, these altered rock occurs nearhigh-grade ores in No.2diggings of gongchangling iron deposit.The high-gradeores in No.2diggings of the Gongchangling iron deposit show close geneticrelationship with altered rock. In order to investigate the high-grade ore genesis, thisstudy presents petrological and mineralogical characteristics of the altered rock inNo.2diggings of the Gongchangling iron deposit.The skarnoid can be divided into four types, including garnet-rich type,chlorite-rich type, garnet-chlorite-rich type and magnetite-actinolite-rich type.Electron microprobe data show that the garnet is dominated by almandite, theamphibole is tremolite and the chlorite is prochloriteThe mineralization process of high-grade ores of No.2diggings of theGongchangling iron deposit is divided into the early hydrothermal metasomatismstage,the late hydrothermal metasomatism stage and the quartz veins stage. Theearly hydrothermal metasomatism stage may be the main mineralization stage ofhigh-grade ores.The trace elements of altered rock and ores show relatively enriched HFSE andLILE，but relatively depleted Sr and Hf; the altered rock、poor-ores and rich-oreshave similar PAAS-normalized REE patterns，rightist distribution patterns of relativeloss LREE with a obvious Eu positive anomaly and weak Ce negativeanomaly,REE and Eu positive anomaly increase regularly from poorer-ores、richer-ores to altered rock, which indicate richer-ores and altered rock had inheritedREE patterns of poorer-ores, and superimposing REE geochemical characteristics ofhydrothermal fluid.The SHRIMP U-Pb age of zircons from the altered rock got1840±7Ma, canidentify the cause of high-grade ores;Re-Os model ages of11pyrite samples and1 molybdenite sample got two sets of data:2567～2540Ma,2376～2237Ma and Re-Osisochron ages of1572±140Ma; The Ar-Ar isochron ages of biotite got1250±5.6Maand plateau age of1834±22Ma.The result：the Gongchangling iron deposit sufferedhydrothermal metasomatism of Different period.It can be concluded that the altered rock and high-grade ores were formed byhydrothermal interaction with low-grade ores, both of which were products of thesame hydrothermal activity.