Firstly, I'm a different Mike Zarate to who is mentioned in the earlier posts. I'm in Australia.
My lolo(First name - Nemesio) is from Calauan, Laguna, and my dad told me the majority of Zarates in the Philippines came from there. I was also told some Zarates from Laguna moved to Pangasinan, not sure from which generation.
Not sure how accurate this is, so just passing on what was told to me.
There was 15 in my dads family and my lolo owned the Zarate Rice Mill in Calauan, Masiit. A couple of years after my lolo passed away the mill was just rented out.
Hope this helps in any way, and I too would love to know more about our surname.