Mafic intrusions in northwest Guizhou emplaced along major deep faults and around of lead-zinc mine normally with a small size (~ 0.25 Km2), and the Ermachong and Baiyanqing intrusions located in Maomaochang and Liangshan lead- zinc mine respectively, were studied in this paper. The intrusions mainly consisted of fine-grained gabbros and main rock-forming minerals are plagioclase (labradorite) and clinopyroxene (augite). The SiO2 contents range from 49.60-51.09 wt%, MgO from 3.88-4.27 wt % and TiO2 from 3.69-3.85 wt %. Zircon LA-ICP-MS U-Pb age of Ermachong intrusion shows a result of 268.3±7.4 Ma, and mafic magma emplaced in Permian. Trace elements are characterized with OIB-type, enrichment in LREE, LILE, depletion in HREE, and weak depletion in HFSE (Nb,Ta), with negative anomaly of Sr, Y. (87Sr/86Sr)i=0.706749～0.707069，(143Nd/144Nd)i=0.512313～0.512363，εNd(t)=0.2～1.2, and magma source(s) located in deep garnet lherzolite where from depleted garnet lherzolite (GD) to primitive garnet lherzolite (GP). Both intrusions were the products of 1-3 % of partial melting with fractional crystallization of clinopyroxenes and minor plagioclases, and with weak crust contamination, no obviously AFC processes. The crustal material added to the mantle source was probably the main cause of the mantle enrichment. There are two aspects as to the relationship between the diagenesis and mineralization in the study area. On the one hand is the coupling between tectonic activities, and the other hand is that the mafic rock may play an important role as a chemical barrier in the process of mineralization.