Is this platinum ore?
The rock you have is most likely not platinum ore.  It appears to be sulfide ore most likely composed of galena, pyrite, and maybe copper sulfides such as bornite.

It is more likely that your specimen is silver ore rather than platinum ore.
Mexico has a long history of silver mining.  

There is a platinum deposit in southern mexico and it appears to similar to the Bushveld igneous complex deposit.  Ref: Mindat.

Layered chromtite ore looks significantly different.  Reference.


USGS report on Platiunum
Article on current silver mining in Mexico.