Mn no issue..Even a 1.3% Mn can be attractive to smelters if it has no other impurities in it. A smelter will seek a zinc conc with low selenium, cadmium, or/and low magnesium, or/and low silica even if it has above average Mn in it.
There are worse things than Mn in a Zn concentrate: Cd, MgO, SiO2, Se, just to name a few. I actually don't know of a zinc concentrate over 50% Zn that is not being sold. Most get penalized, but always sold. Penalties are as necessary as they are profitable. Smelters always penalised miners.. not enough of that all too much of that...
look at Gamsberg in South Africa with zinc concentrate at 2-4% Mn
thanks