Yes, you can increase silica purity by removing iron oxide and...

Yes, you can increase silica purity by removing iron oxide and alumina by wet sieving, attrition techniques, magnetic separation, reverse floatation and etc. However, I'd imagine this would add on a fair bit to the CAPEX and OPEX costs. I'm not an expert on the matter and there's no readily available information on how costly this would be - but this would reduce IND's profitability and mine feasibility.

My question is - can it be done cheaply enough that it falls within the current AU$26-33 per tonne margin (going off VRX's projected OPEX) and current FOB (Free on Board) spot price for 99.5% SiO2 sand, and still leave enough for IND? Beneficiation process is unlikely to be outsourced due to shipping costs, so can they also fund that and be sustainable?

Noted you're saying only 10% of the prospective area has been drilled - but it'd be almost impossible for any company to gather the debt funding required on such a mine, in addition to a beneficiation plant - where the NPV based on "Indicated and referred resource" may not even cover the CAPEX & OPEX to pull out the proven resource.

IND also don't have an offtake partner, or pre-feasibility study completed (let alone DFS/BFS). I couldn't locate an estimated CAPEX from their Stockyard announcements either. Without mining development plans, BFS or DFS - I don't see how they could even get FID to go ahead at this stage even if the price for 98.9% SiO2 sand was high enough.

I don't feel it's a reasonable comparison between Stockyard and ASN. Based on current open market prices for 99.5% SiO2 which reflects ASN updated BFS - my view is that ASN is feasible.

IMO and DYOR