LONDON, Oct 11 (Reuters) - Lonmin Plc has made an all-share bid for Ashanti Goldfields Co Ltd but the offer is conditional on resolving the Ghanaian mining company's gold price hedging crisis, industry sources said on Monday.

Ashanti, Africa's third-largest gold producer, gave little away in a brief statement to the London Stock Exchange, saying only that it had received a share-for-share merger offer, subject to certain pre-conditions.

The bidder was not identified but sources familiar with the situation told Reuters that Lonmin's conditional offer had received a green light following a meeting of the Ashanti board in London on Saturday.

They said the offer was likely to be around $5.50-6.00 per share, valuing Ashanti at some $600 million. Ashanti shares were quoted at $4 before being suspended earlier in London.

Lonmin -- formerly Lonrho Plc -- already owns 32 percent of Ashanti, giving it effective first refusal on the group which operates some of the world's richest gold mines in Ghana.

The two firms first discussed a merger a year ago but the issue came to a head this month following massive losses on Ashanti's hedge book due to a sharp rise in bullion prices.

Ashanti announced that it was discussing a possible merger with Lonmin last Tuesday, the same day it revealed that it faced heavy margin calls on its hedge book.

Ghana's mines and energy minister, Fred Ohene-Kena, gave his blessing to a merger between Ashanti and Lonmin last week, telling the pro-government Daily Graphic newspaper that it would improve the gold miner's competitive position.

The government of Ghana owns 20 percent of Ashanti and the minister said he was willing to see this reduce to 10 percent.

Ashanti is a victim of a leap in gold caused by a decision last month by European central banks to cap official sales of the metal. That flipped its derivatives book, designed to protect it against a fall in prices, from profit into loss.

Closing the hedge book at last week's bullion price of $325 per ounce would have meant taking a loss of $570 million, triggering margin calls of $270 million.

Since then the situation has improved somewhat with gold retracing to $318 on Monday.

Ashanti reached a standstill agreement with counterparties last week. Lonmin's offer is conditional on Ashanti reaching a long-term deal to restructure its derivative contracts to reflect the lower country risk of a merged Lonmin-Ashanti.