BEIJING, Sept 28 (Reuters) - Shanghai aluminium prices dropped for a fourth session on Friday and were on course for their steepest monthly drop since March after China decided not to impose blanket cuts on industrial output in 28 northern cities this winter. The production cuts are to be determined by local authorities and the market expects less restrictions on aluminium supply. The London base complex was broadly higher, however, with copper adding 0.4 percent amid thin trade before China shuts down for a week-long holiday. "If you look at the regional macro cues they are all higher. Ahead of the holidays maybe people don’t want to be short," said Matt France, head of Asia institutional metal sales at Marex Spectron in Singapore. "It’s just a general drift higher so far as we head into the last SHFE trading session before Golden Week." FUNDAMENTALS * ALUMINIUM: Shanghai aluminium fell as much as 1.5 percent to 14,275 yuan ($2,073.02) a tonne, the lowest since July 23 and stood at 14,335 yuan at the mid-session interval. The metal is headed for a 4.1 percent drop in Shanghai in September. London Metal Exchange aluminium was flat at $2,029.50 a tonne. * LME COPPER: Three-month copper on the London Metal Exchange was up 0.4 percent to $6,214.50 a tonne, as of 0345 GMT, snapping four straight sessions of declines. Copper has fallen 2.4 percent this week, putting it on course for its steepest weekly fall in six, although it is also heading for a 4 percent gain over September, which would be its best month since December 2017. * SHFE COPPER: The most-traded November copper contract on the Shanghai Futures Exchange fell 0.5 percent to 50,140 yuan a tonne. * GRASBERG: Global mining giants Freeport McMoRan Inc and Rio Tinto have struck a binding accord to sell a majority stake in the world's second-biggest copper mine, Grasberg, to Indonesia's state mining company, Inalum for $3.85 billion.