Windygriff:
If in future you're looking for a lubricant that dust won't stick to at all, then go to any locksmith and buy some graphite powder.
NEVER ever never use any kind of oil inside a lock. The dust sticks to the oil and gums up the internal workings of the lock. Also, in cold weather the increase in viscosity of the oil can make the lock difficult to work. The ONLY lubricant to use inside any sort of lock is graphite powder. Graphite is a natural lubricant, that dust won't stick to and whose lubricating properties are unaffected by temperature. You can also buy "Dry Graphite" in aerosol spray cans (so named because the propellant fluid evaporates completely leaving only the dry graphite powder behind) in hardware stores.
(The reason why graphite is a natural lubricant is because it forms sheets with the carbon atoms arranged in hexagonal shapes, kinda like a Buckeyball split open and spread out flat. The distance between these sheets is far enough so that they can slide over each other without the atoms in neighboring sheets hitting each other. Graphite is kinda like a new deck of playing cards.)