Scientists have developed a revolutionary drug test that experts claim will soon be used to trace a batch of seized heroin back to its exact source - even to the field in which the opium was cultivated. Police say the research advance will prove a formidable weapon in the fight against imports of drugs, which are escalating - especially from southern China and Hong Kong. The No 4 brand, imported from Hong Kong, is the most common heroin in use in Australia. The Australian Government Analytical Laboratories has developed the technique after discovering that each batch of heroin has a tell-tale chemical fingerprint. The new test is said to be able to pinpoint the minerals in the soil in which the opium poppy was grown. Scientist Dr Bob Wells said the breakthrough had unlimited potential, especially as magnesium, nickel and copper - all essential minerals in the soils of the Golden Triangle - could now be readily identified. Experts say there is a high possibility of linking an end-batch of heroin to a certain drug baron's favoured heroin brand. Tests have been done on 110 recent seizures, confirming that No 4 heroin from Hong Kong dominates the Australian market. In a police report, Chinese were labelled as the kings of Australia's heroin trade.