Ann: Calidus buys Nullagine Gold Project & enhances cash position, page-46

Treating refractory sulphide ore is usually done by one of three methods , which are roasting, pressure oxidation, or bio oxidation. All are expensive in terms of initial capital cost, and operating costs, necessitating high grades. Usually a flotation section/ or fine grinding and flotation, precedes the above processes in order to produce a much smaller volume of higher grade concentrate, which means lower unit cost.There are indeed major environmental concerns with roasters , as they produce large volumes of sulphuric dioxide , which cannot any longer be released to atmosphere, the gases must be scrubbed to high standard first.
Another option which might work for Calidus without major capital expenditure might ? Be to produce a high grade flotation concentrate, and then sell that concentrate to a smelter for gold credits . This avoids the large upfront processing costs. The viability of this would depend on the flotation response of the ore , how much it can be upgraded into what volume and with what recovery. And whether they could find an operation that would buy it. Other mines around the world have done this successfully.
It circumvents many of the problems others have outlined .
Just a thought .