Stan,
The WD-40 does have a mineral oil component but the solvent in it that allows it to evaporate so well and fairly quickly eliminates its lubricant properties. The W D stands for water dispersant, as I am sure you know. (40 was the 40th formulation evaluated.) I just hate to see riders have a chain ruined by depending on it for a lubricant. It had no film properties that can be measured so the metal isn't protected like a chain lube can. A mineral oil won't adhere to the plates and pins well enough even if it wasn't diluted by the other components.

As a "Light lubricant" with no evaporation or dilution it is okay but the stresses in a bicycle's drive are more than it can hope to achieve. As a motorcycle mechanic when I was young and an MX racer I have seen too many chains and sprockets ruined by riders that thought the WD-40 they used to clean their chain and figured the oily feeling was enough to serve as a lubricant.

Hope this sheds a little light on the WD-40 debate, I swear by it as a dispersant after I clean my motocross motorcycle or my road bicycle. best wishes and great riding to you! have a good Sunday.

Bill