There are few better descriptions of colonial extraction than this one where Marx eviscerates the Brits in India. He was on the case right till the end, in this case just before he heads off to Africa. Here is part of the letter to Danielson, in case you have not looked at it in a while:
In India serious complications, if not a general outbreak, is in store for the British government. What the English take from them annually in the form of rent, dividends for railways useless to the Hindus; pensions for military and civil service men, for Afghanistan and other wars, etc., etc. – what they take from them without any equivalent and quite apart from what they appropriate to themselves annually within India, speaking only of the value of the commodities the Indians have gratuitously and annually to send over to England – it amounts to more than the total sum of income of the sixty millions of agricultural and industrial labourers of India! This is a bleeding process, with a vengeance!
Marx, Letter to Nikolai Danielson
London, February 19, 1881
See here for Marx in Calcutta