I figured it out. The corrected code is below (note: In this example, I have the rock textures from the base game copied into my textures folder. If you want to use the base game stone textures prepend the texture name with game:) :
textures: {
all: {
base: "block/stone/rock/{rock}1", blendedOverlays: [{ base: "block/ore/{prop}1", blendMode: "Overlay" }] ,
variants: [
{ base: "block/stone/rock/{rock}2", blendedOverlays: [{ base: "block/ore/{prop}2", blendMode: "Overlay" }] },
{ base: "block/stone/rock/{rock}3", blendedOverlays: [{ base: "block/ore/{prop}3", blendMode: "Overlay" }] }
]
}
},