China visas are affixed in your passport on the pages specifically marked for them, and countries require that visa stamps be placed on those pages that do not contain any other stamps.

Can a visa be issued on a blank amendment page at the back of my passport?

No, amendment pages at the back of passports are specifically for changes and endorsements to a passport after initial issuance. Chinese Embassy and Consulates generally refuse to recognize the usability of an amendment page for visas.