The Huoshenmiao intrusion, which is located in the western section of the Luanchuan ore cluster district, southern margin of the North China Craton (NCC), comprises quartz diorite, monzo- granite and granite porphyry. The quartz diorite distributed mainly in the periphery is the main part of the intrusion. Four major rock- forming minerals including plagioclase, K- feldspar, amphibole and biotite were analyzed using electron microprobe to constrain the formation process and physicochemical conditions of the quartz diorite, and to reveal the genesis of the Huoshenmiao Mo deposit. Mineralogical study shows that plagioclase belongs to andesine, which can be divided into three types including normally zoned, reverse zoned and oscillatory zoned; K- feldspar is orthoclase; amphibole is magnesium amphibole; and biotite belong to magnesium biotite and iron biotite. The formation process of quartz diorite experienced multiple- stage magma evolution: the early stage of magma evolution, at which plagioclase was crystallized with An=30~35; the middle stage, at which increased water content in magma gave rise to the formation of plagioclase with An=39~42; the late stage, at which magma with less water was stabely crystallized to form plagioclase with An=42~28. The quartz diorite formed under the conditions of high- temperature (798℃ to 830℃), high- pressure (198～242MPa) and high- oxygen fugacity (-14～-13). Therefore, the high oxygen fugacity, temperature and Cl contents of mafic magma are directly related to the formation of the Huoshenmiao Mo deposit.