Abstract The Mann Intrusive Complex is one of several large, mafic-ultramafic complexes located in the southwestern part of the Abitibi greenstone belt. The intrusive complex occurs within the Stoughton-Roque-maure assemblage, which closely resembles the Kidd-Munro assemblage and contains similar proportions of mafic and ultramafic intrusive and extrusive igneous rocks. A clinopyroxenite unit within the Mann Intrusive Complex contains anomalous PGE mineralization but only trace sulfides. The clinopyroxenite unit is a medium-grained clinopyroxene adcumulate between 14 and 30 m thick and>500 m long. Mineralization in the clinopyroxenite is characterized by (1) Pt + Pd up to 1.1 ppm with local high Pt/Pd ratios, (2) low sulfide content (<0.1 wt % S), (3) low Ni, Cu, and Co, and (4) platinum-group minerals that are intimately associated with chlorite + secondary clinopyroxene ± spinel alteration of hydrothermal origin. The Pt/Pd and Pd/Ir ratios in clinopyroxenite range widely from 0.45 to 48 and 3 to 1,370, respectively. This style of mineralization contrasts with the komatiite-hosted, Ni-Cu PGE occurrences found in the Kidd-Munro assemblage. The strong concentrations of Ir, Rh, Pt, and Pd in the clinopyroxenite cannot be explained by chromite or Ni-Cu sulfide accumulation or by concentration in a residual intercumulus liquid. Instead, the PGE mineralization is most likely the product of local hydrothermal alteration of the clinopyroxenite. Petrographic and mineral chemistry studies of the mineralization confirm that Ir, Rh, Pt, Pd, and Au were mobile during alteration of the intrusive complex and suggest that the PGE were introduced by a hydrothermal fluid. Pt and Pd have comparable solubilities, but locally Pt is deposited in preference to Pd. Ir and Rh also have similar solubilities but are less soluble than Pt and Pd. Apparent controls on the transport and deposition of PGE are similar to those of other PGE deposits of hydrothermal origin, such as the platiniferous pipes of the Bushveld Complex, and may represent a new style of PGE mineralization in this part of the Abitibi.