Gold lockets often enclosing miniature portraits and later photographs were popular, especially in the 18th and 19th centuries.
Did you examine the antique locket carefully using a jewelers loupe? Sometimes the marks are faded and worn and hard to see without 10x loupe magnification.
If there are no visible markings, an opinion or an appraisal would be based on the quality, craftsmenship, finish and design of the locket, by experts on antique jewelry.
Please do not hesitate to contact What It's Worth 2 You. Actually their service has a 100% positive feedback from our visitors.
The measurements of the locket and good, close-up photos would be necessary. You will have to register there first.