A search in Google on Zinc and Process* lead me to the following websites (amongst thousands others):
http://www.britannica.com/EBchecked/topic/657347/zinc-processing/82100/Extraction-and-refining I would use this site since it is from a respected publication.
http://en.wikipedia.org/wiki/Zinc_smelting I will not use this site (prefer Britannica) BUT I may look at the references that are used at the end of the entry and evaluate if they are authoritative.
http://www.madehow.com/Volume-2/Zinc.html This is a famous site but does not show the author. May or may not use it.
http://www.youtube.com/watch?v=x3DP5JNmFOE Good visual but not sure who made this video so will not use it.