Darcy did initially approach Elizabeth for conversation at the beginning of the Netherfield ball. The description is embedded in the third paragraph of chapter 18:

This part of his intelligence, though unheard by Lydia, was caught by Elizabeth, and as it assured her that Darcy was not less answerable for Wickham's absence than if her first surmise had been just, every feeling of displeasure against the former was so sharpened by immediate disappointment, that she could hardly reply with tolerable civility to the polite inquiries which he directly afterwards approached to make. Attention, forbearance, patience with Darcy, was injury to Wickham. She was resolved against any sort of conversation with him, and turned away with a degree of ill humour which she could not wholly surmount even in speaking to Mr. Bingley, whose blind partiality provoked her.