Mumbai, June 19 -- Equity benchmarks Sensex and Nifty on Tuesday closed in the green on emergence of buying in metal, energy and IT counters, but gains were capped by a caution among investors ahead of the crucial US Federal Reserve meeting. Snapping its four-day losing streak, the 30-share Sensex settled the day at 39,046.34, 0.22% or 85.55 points higher. The index swung over 300 points in a highly volatile session. Similarly, the 50-stock NSE Nifty ended at 11,691.50, up 0.17% or 19.35 points. Sentiments turned a bit optimistic towards the fag-end of the session in view of lower crude oil prices and strengthening rupee....