* Neither mine nor scrap supply expected to balance market LONDON, April 21 (Reuters) - Supplies of copper scrap will jump this year due to decade high prices, but are unlikely to come fast enough to meet robust demand, leaving shortages that are expected to trigger stock draws and further price gains. Copper prices around $9,400 a tonne are close to $9,617 hit in February, the highest since August 2011 and more than double the levels seen in March last year, when manufacturing activity crashed due to COVID lockdowns. Scrap typically accounts for about a third of global copper supplies at around 30 million tonnes, but quantities tend to vary according to prices.