THE market capitalisation of Western Australian listed companies crashed to a 20-month low during September, falling 21 per cent to $127 billion, according to the Deloitte WA Index. The figure compares to an 11.2 per cent decline by the All Ordinaries index over the same period. ?The Deloitte WA Index lost $34 billion in the month of September, considerably worse than other major indices,? Deloitte Perth managing partner Keith Jones said. ?The stocks in the mining industry recorded the most significant falls with a cumulative fall of 27.62 percent within the index.? Among those in positive territory for the month were Portman Ltd and Extract Resources Ltd. Portman Limited recorded a gain of 14.21 per cent in market capitalisation in September, driven by a takeover offer by majority shareholder Cleveland-Cliffs, while Extract posted a 19.8 per cent gain. Last month, Extract announced a friendly merger with West Perth-based Kalahari Minerals plc. Included in the top 10 WA stocks for the index were Woodside Petroleum Ltd, Wesfarmers Ltd, Fortescue Metals Group Ltd, Aquila Resources Ltd, and West Australian Newspapers Holdings Ltd. Major world indices fell significantly in September. The US S&P 500 fell 14.94 per cent, while the Nikkei and the FTSE 100 recorded losses of 13.87 per cent and 13.34 per cent respectively