Once you make a claim through the physical damage coverage portion of your insurance policy, the claims adjuster will investigate the damage to your vehicle from the chain hitting your vehicle and determine under what part of your policy this would fall under.

It would appear from the description you provided of the incident that this would most likely fall under your comprehensive coverage but again your insurance company will tell you for certain what they determine. For repairs to be made you will need to pay the deductible you chose when you set up your physical damage coverage.