How to cite primary source first found in secondary source?
If I'm understanding correctly, you are saying you read a secondary source, which led you to a primary source; then you cited material from the primary source that wasn't discussed in the secondary source; and your question is whether you need to cite the secondary source because it led you to the primary?

If so, I do not think you need to cite the secondary source. It feels polite to do so, sort of like using "via" on Twitter. But in an academic paper I do not think it is required.