The purchase follows the team's decision to strike a royalties deal with London Mining last year, part of a bid to boost the income credentials of the £1.1 billion trust.
Hambro (pictured), who is also chief investment officer of the BlackRock natural resources team, said: 'Following the agreement in July to acquire a 2% revenue related royalty from iron ore from London Mining’s Marampa mine in Sierra Leone, this new investment again demonstrates the trust’s commitment to generate income for investors whilst maintaining exposure to changes in the price of gold and other commodities.'
Banro, a Canadian gold producer, is at a pivotal point in its history and is hoping to use 2013 to make the transition from a smiler scale operation into a mid-tier low cost producer.
It agreed the deal with Hambro and Raw in tandem with a $30 million credit facility with two African banks.
Hambro said the trust's latest investment reflects his view on gold over the longer term, even if investors are currently divided on bullion after its move into a death cross last week.
He said: 'We remain positive on the long-term outlook for gold.
'This investment demonstrates the trust’s ability to assess risk and deploy capital using innovate structures to obtain potentially attractive returns from a well-established mining company operating mines in a key gold production area.'
Broadly, resources firms have been struggling to come by performance, with the HSBC World Mining Index shedding some 4.3% over the 12 months to date.
Hambro and Raw have outperformed this and growth their trust's share price by 11.5% and its net asset value by 1.3%.
Moreover, since seeking out income generative opportunities the trust has seen its discount tighten significantly.
At the end of trade of Friday, BlackRock World Mining Trust shares traded at a 10% discount, a far cry from the 16% discount it has drifted to in recent years.