According to a study by Colombia's intelligence service, the DAS, and seen by El Espectador, up to 50 percent of Colombia's mines are unlicensed. Many of them are a source of funding for armed groups like the Rastrojos or the Revolutionary Armed Forces of Colombia (FARC).

Since 2010, the government has been engaged in a nationwide push to shut down unlicensed mines, seize machinery and reform the laws which dictate how the offense should be prosecuted. But the campaign has been a difficult one.

One problem is that not all criminal groups have the same relationship to unlicensed mining. This means that even though the security forces talk of fighting "illegal" mining, not all illegal mining is the same and it is unclear that the government has mapped out the various strategies needed to address this.

In some cases, criminals tax the machiney -- backhoes and trommels -- used for alluvial mining. In northern Antioquia, for example, the FARC charges at least three million pesos (about $1,650) for a machine to enter their territory. The guerrillas then charge a monthly "maintanance" tax per machine, and destroy the equipment belonging to miners who don't make payments on time.

In municipalities like Timbiqui and Santander de Quilichao in Cauca, where the DAS counts almost 70 backhoes, this would represent significant profits for the FARC.

In this scenario, criminal groups earn most of their profits from Colombia's mechanized mining. The more traditional gold panners -- who often work in the rivers with the most basic equipment -- are not the principle targets of extortion. The FARC are taxing the machinery, not the workers themselves. In Putumayo, the FARC are believed to charge three million pesos a month on machinery.

In other cases, criminal bands (known by the government as BACRIMs) and guerrilla groups directly control mines and tax the amount of material produced. In this case, gold panners are directly affected. In Valle del Cauca, panners have to pay 10 percent of their earnings to a Rastrojos faction, according to a DAS report. The FARC charge a similar fee in Guainia, where gold and coltan miners pay a 10 percent tax on their daily profits.

Based on the El Espectador report, InSight Crime has mapped the areas where there are concentrations of mines controlled -- both directly and indirectly -- by criminal groups.

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