I am trying to create chainlink surface. I have 2 textures; a standard map which has the metallic look of the metal links with a white background (diffuse):

I also have an alpha map:

I am trying to apply both of these to a MeshBasicMaterial without luck:
var chainlinkMask = THREE.ImageUtils.loadTexture('textures/chainlink_Large-Panels_mask.png');
chainlinkMask.wrapS = THREE.RepeatWrapping;
chainlinkMask.wrapT = THREE.RepeatWrapping;
chainlinkMask.repeat.set( 2, 2 );
var chainlinkDiffuse = THREE.ImageUtils.loadTexture('textures/chainlink_Large-Panels_Diffuse.png');
chainlinkDiffuse.wrapS = THREE.RepeatWrapping;
chainlinkDiffuse.wrapT = THREE.RepeatWrapping;
chainlinkDiffuse.repeat.set( 2, 2 );
material.map = chainlinkMask;
material.alphaMap = chainlinkDiffuse;
material.transparency = true;
material.side = THREE.DoubleSide;
This gives me the following:

As you can see, the alpha map isn't being applied.
Why not?
Any help appreciated.