Jan 16 (Reuters) - ** Shares in Toronto-listed Sigma Lithium SGLML.V plunge for a second day after Brazil's Labor Ministry shut down three waste piles at the firm's flagship mine in Minas Gerais state
** The ministry pointed out a "grave and imminent" risk to workers and the local community to justify the move, according to documents seen by Reuters
** The order added to Sigma's struggle to restart the lithium mine, Brazil's largest, even though it said the restrictions do not affect its schedule for resuming production
** Bank of America last week downgraded the firm's shares, citing a lack of clarity on when production would resume
** Sigma's shares dive 15% in Toronto trading, following a 12.5% drop on Thursday
(Reporting by Fernando Cardoso)
((fernando.cardoso@thomsonreuters.com;))
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