Would a mercury amalgam filling deteriorate faster if it was in contact with a gold crown?
The answer is basically yes, if the dental procedures are done improperly. Here is a good answer from a DDS:
Galvanic current is a term that has been used in dentistry for over 100 years. It is a condition created by the presence of dissimilar metals in the oral cavity of the teeth and gums, with saliva serving as the electrolyte. Have you ever felt a “shock” to your teeth caused by a piece of tin foil or a spoon that touches a sliver or mercury filling in your mouth? If you answer yes to this question, you’ve experienced a galvanic event.
There are several different types of galvanism: 1) A silver/mercury filling is placed in opposition or adjacent to a tooth restored with gold. These dissimilar metals in conjunction with saliva and body fluids constitute an electric cell. When brought into contact, the circuit is shorted, the flow of electrical current passes through the pulp, and the patient experiences pain. 2) Dissimilar metals coming into contact when the upper and lower teeth come together and touch each other. 3) Two adjacent teeth are restored with dissimilar metals. The current flows from metal to metal through the dentine, bone and tissue fluids of both teeth resulting in discomfort and tooth sensitivity.
Additionally, from the same site:
Metals will not necessarily always cause the galvanic effect in the mouth. It depends on the specific metal and alloy being used along with quantity and placement in the mouth.
In other words the amalgam filling and the gold cap may form a weak galvanic cell. The proximity of the amalgam to tooth nerves creates a situation in which only a very weak cell current is required in order for the resulting sensation be perceived. The rate of degradation could thus be very small, or if the filling and capping procedures are done correctly there will be no galvanic affect at all.