BUZZ-Cliffs Natural surges 31 pct on results, contract dispute resolution
** Iron ore producer's shares surge 31.5 pct to $5.67, set for their best day ever, amid heavy trading
** Cliffs' Q1 revenue and adjusted EBITDA beat analysts estimates and company says it continues to significantly reduce debt
** Cliffs and Essar Steel Algoma Inc settle a contract dispute, allowing Cliffs to resume supply of iron ore pellets
** Nearly 37 mln Cliffs shares traded, making it the stock's busiest day since April 2015
** Since hitting a near 30-year low of $1.20 on Jan. 12, the stock had gained about 260 percent up to Wednesday's close of $4.31
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