** Century Aluminum's CENX.O shares tumble 12.4% to $28.29 in Tues afternoon trading, and tracking biggest decline in seven months, after report its top holder Glencore GLEN.L cut its stake
** GLEN offloaded 9 mln shares in block trade that generated about $276 mln gross proceeds, Bloomberg News reports
** Block trade handled by Morgan Stanley and priced at $30.65, a 5.1% discount to stock's last close, according to the report
** Chicago-based aluminum smelter's stock on course for steepest daily pct drop since Apr 4; about 7.3 mln shares have changed hands vs stock's 10-DMA of roughly 2 mln shares, per LSEG
** Prior to the transaction, Switzerland-based miner and trader GLEN was CENX's top holder with 40.6 mln shares, roughly 43% of ~93.3 mln shares outstanding - LSEG
** Through Mon close, CENX had gained 77% YTD, aided by U.S. President Trump's tariffs to protect domestic metal supplies from imports
** Before the bell last Thurs, CENX reported Q3 net sales of $632.2 mln, up 17% from $539.1 mln a year ago, and up $4 mln from last qtr
(Lance Tupper is a Reuters market analyst. The views expressed are his own)
((lance.tupper@tr.com 1-646-279-6380))