Geological Characteristics And Genesis Of Iron Poiymetallic Orefield In Ergu Area, Heilongjiang Province

Ergu iron polymetallic orefield is located at40km southeast of Yichun City,Heilongjiang Province. Geotectonic position of the orefield is at the overlappedparts of the Mongolia-Okhotsk orogenic belt and the outer edge of the Pacificsubduction zone, the east of the so called central Heilongjiang microplat, the centrolportion of the Yichun-Yanshou fold belt and the central portion of theTangwanghe-Guansongzhen uplift. The east of Yichun-Yanshou fold belt is boundedby the Jiamusi terrane and their boundary is the NS Mudanjiang fault. The west ofYichun-Yanshou fold belt is bounded by the Songneng terrane and their boundary isthe NS Xunke-Tieli-Shangzhi fault. The Ergu iron lead and zinc orefield includesErgu Xishan iron lead and zinc deposit, Xiangshuihe lead-zinc deposite and Ergudongshan iron lead and zinc deposit. Ergu orefield was found by Aeromagneticanomaly and ground inspection in the1960s. The deposits of Ergu orefield are typicalskarn deposits. Although the number of the researchers who studed in Ergu ironpolymetallic orefield is larger, but because of covering serious, so there was not largernumber of research data. Based on collecting and summarizing predecessors’ data,The paper had the following understandings by the researching on the mineralizationstages, the geochemisty of ore-forming rock, chronology, mineral sources etc.(1) The ore-forming surrounding rock of the Ergu orefield is Qianshan formation(1q) enrich magnesium carbonate. The ore-forming rock of Ergu orefield isgranodiorite, The rock occur in rock strains, The mineralization surrounding rockmainly are garnet skarn, diopside skarn, epidote skarn and hornfels. The ore metalmineral mainly are Magnetite, pyrrhotite, galena, sphalerite. Ore textures mainly aremetasomatic texture、filling texture and separation of the solid solution. Ore structuresmainly are massive structure, banded structure, lumps and veins. The mineralizationstages of the Ergu orefield’s deposite are nearly same to the typical skarn deposits’, itscharacteristics is two minerogenetic stages and five periods.(2) The ore-forming rock granodiorite is the I-type granite rocks and high-Kcalc-alkaline series.The REE patterns of the intrusive rocks in the Ergu orefield aresimilar. All of them are enrichment in LREE, depletion of HREE; They enrich inLILE, relative depletment in HFSE for example Ba、Nb、P、Ti、Ta、U et al and LILEfor example Sr、Ba. The intrusive rocks of Ergu orefield have the characteristics ofactive continental margin and material source mainly to crust source.(3) The Geological characteristics and the geochemisty characteristics of thehost granite, MME and catagenesis rock dyke show that the formation of theore-forming magmatic rocks is influenced by the underplating of Mantle-derivedmafic magma. The chorismitization possibility is the main diagenetic mechanism.(4) The zircon LA-ICP-MS U-Pb dating of granodiorite in Ergu Xishan ironlead and zinc deposit is186.5±5Ma and in Xiangshuihe iron lead and zinc deposit is191.4±2.2Ma.The model age of molybdenite in Ergu Dongshan deposite is182.2±2.7Ma from Re-Os isotopic dating. The granodiorite of Ergu ore field is mineralizationmagmatite in chronology; the w(Re) reveal that there is the characteristics ofcrust-mantle migmatization in metallogenic material of deposit; these evidence furtherdemonstrated that the underplating of basic magma provided a part of metallogenicmaterial to the forming of deposit in Ergu ore field.(5) The standard curve chondrite of rare earth element of granodiorite, griotteand ore-bearing skarn reveals some comparable characteristics. The average of everyore-forming element of granodiorite in Ergu ore field is much higher than the averageof every ore-forming element of granodiorite in Xingan-Jihei orogenic belt in Inner Mongolia. Therefor the source of metallogenic material of deposit in Ergu ore field isthe granitic magma of early Yanshanian in tihis ore field.(6)The ore-forming model in Ergu ore field is that: after the subduction ofPacific Plate to Eurasian Plate in Early-Middle Jurassic. The underplating of basicmagma provided heat and a part of metallogenic material to migmatization ofIndosinian-early Yanshan epoch in this area. The high temperature mixed magma,which contained many metallogenic material and volatile, risen and intruded along thelithospheric fault; due to the changes in temperature and pressure, they dissociatedinto high MME contained granitic magma and ore-forming hydrotherm rich involatiles. The intrusion of granitic magma breaking, extruding and capturing theoverlying stratum formed the beneficial metallogenic geological environment. Theore-forming hydrothermal replaced and filled the favourable metallogenic rocks formineralization.