* China refined zinc demand weakens in August * ECB expected to unveil debt-purchasing scheme on Thursday * Coming up; U.S. ISM Manufacturing PMI USPMI=ECI at 1400 GMT By Susan Thomas LONDON, Sept 4 (Reuters) - Copper dipped on Tuesday on signs of flagging growth in top metals consumer China, but hopes that central bankers in Europe and the United States will take steps to tackle struggling economies helped to limit losses. The European Central Bank is expected to unveil details of a long-awaited debt-buying scheme to tackle the region's debt crisis at its policy meeting on Thursday, where it may also cut rates to stimulate growth and head off a euro area recession. "The politicians and central banker have been promising a lot over the summer and now it's time to deliver. The markets have rallied on anticipation that we now have some sort of policy framework," Natixis head of commodity research Nic Brown said. "But there is still scope for disappointment, there are still enormous problems besetting peripheral economies." Three-month copper on the London Metal Exchange was down 0.1 percent at $7,668 per tonne at 1041 GMT from a last bid $7,678 on Monday, when it hit a one-week high of $7,700. Prices are reaching the top of a range held since late July, with a break above $7,720, the Aug. 23 peak, likely to spark further chart-based buying. After Thursday, markets will turn their attention to the U.S. Federal Reserve's policy-making meeting next week where it will consider whether further monetary easing is warranted. "Apparently, market participants have high hopes for further monetary easing by the ECB and Fed," Credit Suisse said in a research note. "However, as long as economic data fails to improve, we think the current price rally stands on fragile ground." CHINA There are also growing expectations that the People's Bank of China (PBOC) would need to take more decisive action to spur growth, which would help to boost demand for industrial metals. China's vast manufacturing sector has been badly hit by slowing new orders, two complementary surveys showed in recent days, a sign that the pace of growth in the world's second-largest economy will weaken well into the third quarter. China's demand for refined zinc also weakened further in August from July, traders said on Tuesday, diluting hopes for a fourth-quarter rise in consumption in the world's top consumer of the metal. Three-month zinc was up 0.5 percent at $1,884 per tonne at 1033 GMT from $1,875 at the close on Monday. Still, zinc has fallen nearly a sixth from the year's high struck in January. In other metals tin was down 0.4 percent at $19,670 per tonne from $19,750 on Monday, battery material lead was at $2,008 from a last bid of $1,999, aluminium was $1,947 from $1,927 and nickel was $16,232 from $16,220. Metal Prices at 1042 GMT Comex copper in cents/lb, LME prices in $/T and SHFE prices in yuan/T Metal Last Change Pct Move End 2011 Ytd Pct move COMEX Cu 347.70 1.90 +0.55 344.75 0.86 LME Alum 1946.75 19.75 +1.02 2020.00 -3.63 LME Cu 7668.25 58.25 +0.77 7600.00 0.90 LME Lead 2007.00 42.00 +2.14 2034.00 -1.33 LME Nickel 16231.00 11.00 +0.07 18650.00 -12.97 LME Tin 19638.00 -112.00 -0.57 19200.00 2.28 LME Zinc 1883.25 8.25 +0.44 1845.00 2.07 SHFE Alu 15490.00 60.00 +0.39 15845.00 -2.24 SHFE Cu* 56080.00 -140.00 -0.25 55360.00 1.30 SHFE Zin 14825.00 15.00 +0.10 14795.00 0.20 ** Benchmark month for COMEX copper * 3rd contract month for SHFE AL, CU and ZN SHFE ZN began trading on 26/3/07

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