People who are often silent are usually deep thinkers?

Well that's a statement rather than a question.

Would you care to clarify your point.

Silent people could be deep in thought.

Or they could be clueless and have nothing to say.

Is this what you want do discuss ?

I agree with your statement. However, a talkative person could be an equally deep thinker. The two types just have different methods of thinking. The talkative one thinks by discussing and collaborating with others. The quiet one thinks by formulating his own ideas. I am personally around the middle, leaning towards quiet.