Geological And Geochemical Characteristics And Ore Genesis Of Shenshan Fe-Cu Deposit In Inner Mongolia

Located in the southern margin of the Siberia Craton and the eastern Xing’an massif, the Great Shenshan deposit of this study is an important Fe-Cu deposit in Zhalaiteqi Inner Mongolia. Paleozoic Paleo-Asia Ocean, Mesozoic Mongol-Okhotsk Ocean and Cenozoic Pacific circle tectonic system all reformed and added on this region. Mesozoic Great Hinggan Mountains volcanic-intrusion belt and metallogenetic mineralization are due to the complex tectonic evolution and the magmatism accompanied.Distributed in the contact zone of Yilite intrusion and Permian Zhesi Formation, the Shenshan Fe-Cu deposit is an important skarn deposit. We got further consensus then established the geodynamic and prospecting modals of the deposit due to the geochemical features, geochronology, fludi inclusion and our detailed fieldwork and synthetic study. The main achievements and results of this paper are as follows.1.Early Cretaceous dykes and Late Jurassic inter-acid intrusion stocks were the main intrusions in the district. The Yilite intrusion which covered an area of 41 Km2 was related to the forming of the Shenshan deposit. Lower Permian Dashizhai formation andesite and middle Permian Zhesi formation carbonate were the major strata in the district, and Zhesi formation limestone was the wall rock of ore bodies. Ore bodies which distributed western and northern in and near the contact zone of the Yilite intrusion mainly occurred in the epidote-garnet skarn zone, with lesser in the layer peel thrust outer contact zone or faults. The ore bodies, with relative high Fe grade, had small size and complicated shapes for instance, beans, layers, lens and strictly controlled by the shape of contact surfaces. Magnetite is the most important metal minerals, with lesser hematite, pyrite, chalcopyrite, sphalerite, galena, tetrahedrite and molybdenite. Granular texture is common in ores while radial texture is rare. Massive and disseminated structure garnet type magnetite ores are predominant, accompanied by copper, molybdenum, Fe-Cu-Mo, Fe-Mo, Fe-Zn, Fe-Cu ores. Skarnized is the most important wall rock alteration, with lesser important silication, epidotization and chloritization.2. Due to our studies on geochemistry and pertrology on the Yilite intrusion, the Si O2 of the intrusion content is 60.60 to 63.33wt%,with an average of 61.92wt% which shows intermedia features. The ∑REE content was 107.1×10-6-132.02×10-6,with an average of 118.33×10-6. The pattern dips to right and with normal Eu content. The Yilite intrusion geochemical feature shows I type granite. The intrusion had high Sr contents and low Yb contents and showed adacatic features. Pyrites and sphalerites from the deposit had nearly same δ34S content, which is-5.54‰ to 0.68, usually in-2.09‰ to 0.68‰. The sulfide Pb isotopes had contents of 37.756-38.191 of 208Pb/204 Pb ratio,207Pb/204 Pb is 15.408 to 15.519 and 206Pb/204 Pb is 17.745 to 18.297. The single stage modal age of sulfide and Yilite granite Pb isotope is 137 to 418 Ma,mainly concentrated in 231-250 Ma and 146-167 Ma two ares.3. Mineralization was constrained by the Paleo-Asian Ocean and Mongol-Okhotsk Ocean tectonic domain and occurred under thickening crust and tectonic activation settings. The tonalitic magma rooted basaltic magma’s underplating progress. Diagenesis and mineralization materials mainly derived from upper mantle or lower crust, with partial upper crustal materials. The early ore-forming fluid mostly derived from magma, while rainfall added in the late stage. Mineralization temperature of the oxide stage is(356-395)℃, with salinity of(5.99-8.13)wt% Na Cl. While mineralization temperature of sulfide stage is(320-350)℃ and filling and metasomatic are the prevalent mineralization.4. Zircon LA-ICPMS U-Pb dating results reveal the Yilite tonalite forming age is(155.7±0.45) Ma, which is consensus with U-Pb age of 155.49 Ma in Houliujiu Cu deposit. Thus the mineralization of the Shenshan deposit occurred in late Jurassic.5. After our study on geology, geochemical and geophysical features of the Great Shenshan deposit, we analysis the prospecting parameters and establish the prospecting model of the deposit. Four prospecting targets and one mineralizing prospecting area were outlined and showed a good metal prospecting in the region, of which the BQ4 is the most important one.