Characteristics And Origin Of The Tugurige Gold Deposit In Inner Mongolia,China And Its Geological Significance

The Tugurige gold deposit, in the northeastern margin of the North China Craton (NCC) and western part of the Xing’an-Mongolia Orogenic Belt (XMOB), is a large tonnage quartz-vein type deposit with a resource of ～24 t at about 4 g/t Au. Gold mineralization is hosted by porphyritic syenogranite and controlled by NW-trending faults. Depending on the nature of the host rocks, the gold mineralization can be divided into sulfide quartz-vein and altered hostrock types.In order to determine the geological setting, characteristics, ages of the intrusive rocks and gold mineralization, origin and genetic model of the Tugurige gold deposit, In this paper, we describe the geology of this deposit and present Re-Os isotope age data for pyrite,40Ar-39Ar isotope age data of sericite, U-Pb zircon age and petrological-geochemical data of the intrusive rocks, Sr-Nd-Pb-S-O-H isotopic and fluid inclusion data of the deposit, proposed a tentative genetic model, and evaluated gold potential in the XMOB.The zircons from syenogranite, granite, horablendite, diorite and biotite granite in Tugurige gold deposit yield weighted mean 206Pb/238U ages of 275.8±1.5Ma-264.5±1.4Ma (two samples),278.7±1.0Ma (n=19, MSWD=0.34),280.6±1.3Ma (n=19, MSWD=0.39),288.0±2.6Ma (n=13, MSWD=1.7), and 415.1±2.1Ma (n=14, MSWD=0.41) respectively. The Re-Os dating of six pyrite separates from the deposit yields an isochron age of 268±15 Ma. The 40Ar-39Ar dating of sericite from the deposit yields an isochron age of 259.2±2.9 Ma (MSWD=5.4). The results show that the ages of syenogranite and gold mineralization are the same within error. Furthermore, geological and geochronological evidence indicate that the syenogranite and gold mineralization have very close genetic relationships.Sr-Nd-Pb isotopes of the intrusions show that they have initial 87Sr/86Sr ratios of 0.70629-0.70799, eNd(t) values of -6.6±3.8,206Pb/204Pb ratios of 18.113-18.392, 207Pb/204Pb ratios of 15.535-15.594, and 208Pb/204Pb ratios of 38.133-38.473. The isotope composition indicates that these intrusions are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust.The ore-forming fluids of the Tugurige gold deposit are characterized by moderate to high temperature and moderate to low salinity, consistent with formation from magmatic hydrothermal fluids. Hydrogen (-108.8‰～-87.4‰) and oxygen (1.1‰～ 6.9%o) isotope data indicate that ore-forming fluids were dominated by magmatic water mixed with minor meteoric water. Sulfur (-7.5～-3.5) and lead isotope data indicate that some sulfur and lead came from themagmatic fluid.In summary, The Tugurige gold deposit is a magmatic-hydrothermal gold deposit related to Permian syenogranite. The intrusions and gold mineralization in the Tugurige area formed in an post-collisional extensional setting, and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere. The Permian tectono-magmatism and associated hydrothermal activity remobilized gold and drove ore-forming fluids to the favorable depositional environment. The Late Paleozoic is an important period in which economic gold mineralization was deposited in the XMOB.