The miner has wanted to sell off the building materials company for years, but waited for the economic recovery to get a good price.
“As we have said, we will divest of Tarmac in a manner and on a timetable that maximises value for Anglo American’s shareholders,” Anglo said.
Marwyn has proposed a “multi-billion pound” transaction under which Anglo would retain a minority shareholding.
As part of the deal, Marwyn would also seek a stock market listingfor Tarmac.
Analysts value Tarmac at $4bn (£2.6bn) to $6bn. HSBC was advising Marwyn on the proposal, to which Anglo has yet to formally respond.
Led by chairman Peter Tom and chief executive Simon Vivian, both industry veterans, AIM-listed Marwyn Materials seeks to buy UK, European and US building-materials companies.
It held off striking any deals last year, but said in March that 2010 was likely to present “numerous further acquisition opportunities” and it was already reviewing some potential takeovers.
In February, Anglo sold some of Tarmac’s European operations for a total of about $400m.