| The Liudaowaizi Iron-Copper deposit is located in Yanbian area, east part of theXing’an Mongolian Orogenic Belt. Since Palaeozoic era, this area experiencedsuperposition and conversion of Paleo Asian Oceanic tectonic domain and Circum Pacifictectonic domain, which providing probable ore-forming geological conditions for metallicore deposits including the contact metasomatic iron-copper deposit.The main strata in Liudaowaizi mine are Permian Miaoling Formation and KedaoFormation. The main rock types in Miaoling Formation include sand tuff, tuffaceouscallys, marble and so on. The main type in Kedao Formation is black sand tuff.The early Yanshanian magmatic rocks in the region contain augite diorite, diorite,quartz diorite, granodiorite, K-feldspar granite, and so on. The late Yanshanian intrusionsare mainly located in the south of the ore district, including granite porphyry and granitepegmatite. There occurs skarnization in the contact zone between the Permian marble andaugite diorite, diorite, quartz diorite and K-feldspar granite. The major structures in thearea include the NE-trending Liudaowaizi anticlinorium, compression fractures orcompress-shear faulted with the northwest tensile or compresso-shearing fracture.The metal minerals in iron-copper ore are mainly chalcopyrite and magnetite.followed by pyrite, bornite, chalcocite, tetrahedrite, ilmenite, galena, sphalerite, pyrrhotite,arsenopyrite, silver minerals and so on. The nonmetallic minerals are composed ofalmandine, grossular, enstatite, hypersthene, diopside, epidote, chlorite, quartz and calcite.The main ore textures are xenomorphic-granular texture, panidiomorphic-hypidiomorphicgranular texture, metasomatic texture, unmixing of solid solution texture, banded texture, and so on. The main structures are massive, veinlet-disseminated structure, bandedstructure, cell structure, brecciated structure and so on. Wall-rock alterations includeskarnization, silicification, carbonation, chloritization, sericitization, etc. According tointersections relationship of different veins, ore texture and ore structure, mineralassembles, mineral intergrowth relationship, as well as wall-rock alteration, metallogenicprocess of the Liudaowaizi deposit can be divided into two metallogenic epoches and fivemineralization stages, skarn epoch includes early skarn stage, late skarn stage and oxidestage, quartz-sulphide epoch includes early metal sulfide stage and late metal sulfide stage.The deposit belongs to typical contact metasomatic iron-copper deposit.The homogenization temperature of the two-phase inclusions of polymetallic sulfidestages in Liudaowaizi ranges from148.8℃to266.1℃and mainly from200℃to240℃;the salinity ranges from4.17%NaCl to14.42%NaCl, the density changes from0.83g/cm3to1.02g/cm3. Together with the Raman Spectra analysis of gas phase in fluid inclusions, itcan concluded that the ore-forming fluid belongs to NaCl-H2O-CO2hydrothermal systemwith medium-low temperature, low salinity and density, indicating the ore-forming fluid ismagmatic water.LA-ICP-MS U-Pb dating of the zircon in gabbro-diorite associated withmineralization shows that206Pb/238U ages of zircons are concentrated in196±2Ma to213±1Ma, the weighted average age is204±2.3Ma, indicates that the intrusion emplacedin the early Jurassic (early Yanshanian). The geochemical characteristics of major elements,trace elements and REE of magmatic rock indicate the metallogenic gabbro dioritebelongs to the metaluminous high-sodium calc-alkaline series. Meanwhile, the rock arefeatured by low REE content, high LREE and LREE/HREE ratios, as well as low positiveor negative Eu anomalies. Such geochemical features as relatively enrichment of large ionlithophile element, depletion of high field strength elements show that the gabbro dioritewas derived from the crust-mantle mixed source, meeting the characteristics of northeastI-type granites. Combining the evolution of tectonic background of Northeast China, thethesis holds that both the gabbro diorite and the associated iron-copper mineralization inLiudaowaizi deposit were formed in the island-arc tectonic environment resulted from thesubduction of the Paleo Pacific Plate to the Eurasian Plate at the beginning of the Jurassic period.According to the research of contact zone structure and its relationship withmineralization, and the changes of their shape and occurrence of ore bodies in directionand vertical, the the deposit mineralization enrichment features have been stuided in thisthesis. The result shows that skarnization and iron-copper mineralization are mainlycontrolled by faults and contact zone structure, both in vertical and direction, the orebodyexhibited some variation. In vertical and direction there have local thickening or thinningout reproduction and other features. The orebodyⅠ of north of the mine is lateral plungeto south west, the side-volt angle is about60°, the orebodyⅡof south of the mine islateral plunge to northeast direction, its side-volt angle is about30°.The enrichmentpatterns of orebody are closely related with the contact zone structure. Orebody hassegmented enriched features in vertical, for example, industrial orebodies along strike invein, bonanza ore intervals alternating with poor, segmented enrichment obviously in thedownward extending. Ore bodies has enriched features in sublevel in vertical, they presentas veins, becoming thicker obviously in contact zone structure. There are no ore blocks insome area, bonanza and poor shoot appear in alternate, the interval is70~100m. |
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