RE:Question about leachingLeaching is the most common way to extract precious metals. As other posters have stated cyanide is the most common lixiviant and despite being toxic is a proven and reliable solution.
There are a number of "non-cyanide" alternatives that claim to be safer and they typically are to some extent but they are by no means benign.
Every company tries to promote their new alternatives as being safe or a "closed loop" but the fact is other metals (Pb, As etc.) will be extracted into the solution and this will build up over time as the solution is reused and at least a portion of it will need to be bled off and discharged or detoxified.
Aside from the environmental permitting issues the CAPEX for a leach plant would be huge. Currently BHS is just mining, crushing and sorting. Crushing big rocks into little rocks is pretty simple and can be accomplished with a mobile/rental crushing equipment.
Grinding small rocks into dust to be leached is another story and will require the installation of a ball mill which is expensive and requires a ton of diesel/electricity to run. After it is ground fine enough you will need big agitated leach tanks, chemical mixing buildings, solution recovery (Electrowinning, etc.) and finally after you have extracted the silver you have fine chemical tailings slurry that will need a costly rubber lined and constantly monitored tailings dam for storage.
Smelting of the rock should recover just as much if not more silver as the rock is essentially "burned" to extract the silver, the issue is the cost that the smelter passes on to BHS which could be +30% of the contained silver.
Almost every bigger mine has an on site processing plant but this will exponentially increase the CAPEX here.
The unique approach of BHS here is to get into silver production on the cheap without raising $20-50+ million to build a mill.