Ground motions, recorded both underground and on the surface in two of the South African Gold mining districts, were inverted to determine complete moment tensors for 10 mining-induced tremors in the magnitude range 1.9 to 3.3. The resulting moment tensors fall into two separate categories. Seven of the events involve substantial coseismic volumetric reduction-Δ V together with normal faulting entailing shear deformation Σ AD, where the summation is over fault planes of area A and average slip D. For these events the ratio-Δ V/Σ AD ranges from 0.58 to 0.92, with an average value of 0.71. For the remaining three events Δ V is not significantly different from zero; these events are largely double-couple sources involving normal faulting. Surprisingly, the two types of source mechanism appear to be very distinct in that there is not a continuous distribution of the source mix from Δ V=0 to-Δ V≈Σ AD. Presumably, the coseismic closure indicates substantial interaction between a mine stope and adjacent shear failure in the surrounding rock, under the influence of an ambient stress for which the maximum principal stress is oriented vertically.