Large-area iron-manganese mineralization is developed in Ajile-Ulan-Bogen Obo area of Dong Ujimqin Banner in Inner Mongolia. The in-situ measurement of soil and rock outcrops in this area by means of X-ray fluorescence instrument revealed the consistency between the anomaly concentration centers of quite a few elements and the known ore veins, the trenching performed over anomalies outside the ore veins led to the delineation of new ore bodies, and the drill hole intersected several layers of veined and stockwork ore bodies. If rational methods and techniques are adopted to correct the matrix effect, and the influence of the humidity effect and the geometric effect can be overcome as much as possible, the measurement result of the portable X-ray fluorescence instrument can reflect the reality of the ore district, which is hence of great practical significance for rapid delineation of ore prospective areas, tracing and verification of anomaly points (zones) and direct delineation of ore bodies in anomalous areas where values of ore-forming elements are higher than their ore grades.