I think of two possibilities :

1. PyroGenesis is in the last moments of an important agreement and asked iiroc to halt the stock to prevent news leaking. That to ensure a fair trading of the stock. 
2. The news is very important and iiroc is asking PyroGenesis some clarification. PyroGenesis won't be able to release the news until it complies with iiroc rules. PyroGenesis might have to give more details. Sometimes, this begins a long back and forth messaging between iiroc and the halted company. It could get long. 

When the news will be on the wire, the halt will be lifted an hour or more after.

GLTA,

TomCam