Geological Characteristics and Ore-Prospecting Criteria of the Ulandler Porphyry Molybdenum Deposit in Sonid Left Banner,Inner Mongolia

The Ulandler ore deposit is a medium-size porphyry molybdenum deposit discovered during the land survey in Inner Mongolia.The ore deposit with typical porphyritic mineralization characteristics shows two mineralization shapes exhibited respectively in the upper part and the lower part.The ore bodies in the upper part exhibit multilayered veinlike and stockwork forms and are hosted in the fractures of early intruded quartz diorite and granodiorite,with molybdenite assuming large foliated lamellae and small-scaly aggregates.The ore bodies in the lower part constitute the main ore bodies,assume thick layers of veinlets and disseminations,and are hosted in the intrusive contact zone between mineralizing parent fine-grained adamellite and early intruded quartz diorite.There exist typical porphyry hydrothermal alterations in the wall rocks such as potassic alteration(biotite),beresitization,greisenization and silicification,which are genetically related to the mineralization.Geochemical exploration re-veals that there are obvious concentration zones and centers of geochemical anomalies,characterized by extensive and high intensities of metallogenic elements Mo,Cu,W and Bi.High precision magnetic survey shows that the mineralization-related quartz diorite and pyritized granodiorite have strong magnetism,whereas the wall rocks biotite granite and altered granite have no or only weak magnetism.The induced electrical medium gradient survey shows that the mineralization-related fine-grained adamellite and altered granite have high excitation rate and low resistance,which can serve as the indicators in ore prospecting.The SHRIMP zircon U-Pb age of the mineralization-related fine-grained adamellite is 131.3 ± 1.6 Ma,and the Re-Os age of molybdenite in the ore deposit is 134.1 ± 3.3 Ma,suggesting that the ore deposit was formed in Lower Cretaceous.The geological,geochemical and geophysical ore-prospecting criteria and the mineralization age of the Ulandler molybdenum porphyry deposit are important clues to further ore prospecting work in this region.