Aluminium hit a month high and copper also gained on Tuesday as speculators bought up metals on a weakening dollar that came under pressure from signals that U.S. interest rates would remain on hold.

Nickel, however, resisted the stronger trend as investors had second thoughts about the impact of a environmental audit of mines in the Philippines.

The dollar index slid to a seven-week low after a U.S. Federal Reserve policymaker argued that central banks might have to raise inflation targets, focus more on growth and back much looser fiscal policy in future.

“The main drivers seem to be currency and macro today rather than any sudden real changes in fundamentals,” said analyst David Wilson at Citi in London.

Speculators were likely buying back short positions in copper to lock in profit after the metal shed about 5 percent since touching a peak of $5,032 on July 13, he added.

“Copper’s been under pressure for the past month, so maybe there’s a bit of profit taking from shorts and the currency is also helping.”

London Metal Exchange benchmark copper had gained 0.4 percent to $4,786 a tonne by 1430 GMT after closing slightly firmer on Monday and touching a one-month low of $4,750.50 on Friday.

Three-month LME aluminium rose 0.7 percent to $1,688, the highest since July 15, while lead added 0.2 percent to $1,870 after touching $1,874.50, its strongest since July 21.

Aluminium was targeting its July peak of $1,703, Commerzbank technical analyst Axel Rudolph said in a report. “We will retain our medium term bullish view while no unexpected drop below the $1,592/$1,588 late June and July lows is seen.”

Recent gains in the two metals have triggered buy signals for CTA (Commodity Trade Advisor) funds, many of which use algorithms based on momentum and other technical signals.

LME nickel shed 1.7 percent to $10,310 following gains of 1.8 percent on Monday. Trade has been especially volatile in recent days, with traders watching for developments on the Philippines’ mining crackdown. The results of an environmental audit of the sector are due this month.

“Most of the big miners in the Philippines appear to be unaffected by this audit so far, so the impact on nickel ore availability has been minimal at best. Maybe a sense of reality is coming back into play,” Wilson said.

LME nickel stocks MNISTX-TOTAL rose 4,944 tonnes to 373,992 tonnes on Tuesday, highlighting good availability of inventories to supply the market.

Zinc fell 0.7 percent to $2,249.50 and tin was flat at $18,240.

PRICES

Three month LME copper

Most active ShFE copper

Three month LME aluminium

Most active ShFE aluminium

Three month LME zinc

Most active ShFE zinc

Three month LME lead

Most active ShFE lead

Three month LME nickel

Most active ShFE nickel

Three month LME tin

Most active ShFE tin

Source: Reuters (Additional reporting by Melanie Burton in Melbourne; editing by Susan Thomas and David Evans)