The Yulong ore deposit is a superlarge porphyry copper-molybdenum deposit in the Sanjiang region. These data indicate that the source rook or source region of the Yulong porphyry copper-molybdenum belt might have been the depleted upper mantle. Combined with geophysical data, the authors hold that, along with the asthenosphere upwelling, the Yulong porphyry rocks might have been derived from the partial melting of the thickened crust resulting from the underplating.