Whether or not you would be doing original research depends on whether the cited work can be replicated. If the cited work is unable to be replicated, and you

Whether or not you would be doing original research depends on whether the cited work can be replicated. If the cited work is unable to be replicated, and you try to replicate but get different results, then you would be doing original research, and then you can base further work on your initial original study that came to a different result. On the flip side, if you are able to replicate it, then you are doing extra work initially, but after replicating the work you've cited, the work you've done is more likely to be reproducible by someone else. The amount of citations needed to require replication could itself be a function of how easy it is to replicate work across an entire field. A field where there's a high rate of success in replicating work could have a higher threshold for requiring replication compared to a field where it's difficult to replicate work.