According to the alberta geological survey, diamondiferous kimberlite pipes fall under metallic minerals. Why?

Answer 1

No Geological Survey would classify diamondiferous Kimberlite pipes into metallic minerals. Neither diamonds nor Kimberlite falls under the category of metallic minerals geologically speaking per se.

But, for sake of granting lease for prospecting, production etc. sometimes minerals are grouped into various categories to bring them in a group of minerals covered under already existing rule, regulations or mining laws by state. Sometimes a particular rock is mined or prospected for a particular mineral commodity or metal and latter on becomes a source of altogether different mineral commodity. To avoid legal complications, the source rock of the new mineral commodity can be kept under the previous set of rules and category and the cess, royality etc. can be charged on the new mineral commodity separately.
Sometimes such grouping is not compatible or is in conformity to geological classification of minerals based on their properties or use (economic geology).
Perhaps this could be the reason for the situation pointed out by you.
You can always discuss it with their geologists, remember geologists are very open people world over and I am sure he would give you the right explanation, better than mine.
thnks

Answer 2

After looking at the site, my impression is that kimberlites are grouped with the metallic minerals on the site primarily because of the organization of the survey (and kimberlites being among the "hardrock" group), and perhaps the organization of the permitting rules and regulations. I do not believe they meant to imply that diamonds are metallic.