On some of our sites, we now have several thousand pages that dilute our website's keyword density. The website is an MVC site with SEO routing.

If I submit a new sitemap with say only the 2000 or so pages that we want indexed, even though navigating to the diluting pages still works, will Google re-index the site with only those 2000 pages, dropping the superfluous ones?

For example, I want to keep roughly 2000 of the following:

www.mysite.com/some-search-term-1/some-good-keywords
www.mysite.com/some-search-term-2/some-more-good-keywords

And remove several thousand of the following that have already been indexed.

www.mysite.com/some-search-term-xx/some-poor-keywords
www.mysite.com/some-search-term-xx/some-poor-more-keywords

These pages are not actually "removed" as navigating to these URL's still renders a page. Even though there are potentially hundreds of thousands of pages, I only want say 2000 to be re-indexed and retained. The others removed (without having to do these manually).

Thanks.