One of the most remarkable placer gold fields in the world is found in the Andean piedmont in the department of Madre de Dios in southern Peru. Gold was discovered in the 1970s in the District of Huepetuhe, where a small stream that drains into the Río Inambari, approximately 20 kilometers downstream from the narrow gorge where the Inambari exits the Andean foothills. The current channel did not exist until a few tens of thousands of years ago, because it was blocked by a low ridge that deflected the main channel 90º west into the precursor of the Huepetuhe.

This diversion created a near-perfect sediment trap for the gold being carried out of the Andes. Eventually, the river eroded a channel through the outlying ridge and created a depositional plain south of Madre de Dios, creating a mega gold field that stretches from the Río Colorado (West) to the city of Puerto Maldonado.

Enormous amounts of alluvial gold have been funnelled into the Inambari due to the tectonic peculiarities of the Altiplano and the climatic history of the Quaternary Period. The headwaters span a 260-kilometer swath of the Andean highlands that constitute the northern border of the Altiplano, which was formed by a process known as ‘crustal shortening’ where a section of the South American plate was chipped off (rather than subducted) and relocated on top of the South American plate.

Essentially an exaggerated phase of the Andean orogeny, this phenomenon was associated with magmatism that created numerous gold-bearing ore bodies in the eastern cordillera. Subsequently, this section of the Andes was completely glaciated during the Pleistocene, causing massive amounts of gold-bearing rocks to be pulverized and released into the Inambari watershed.

Climate also played a role. This region is often referred to as the ‘Elbow of the Andes,’ because it is oriented west to east, rather than north to south, which ensures the Amazon-facing slopes experience exceptionally high levels of rain because they sit astride a low-level jet stream flowing along the base of the Andes. Mean annual precipitation exceeds 10,000 mm per year, leading to high rates of erosion in the cloud forest section of the Inambari watershed where colluvial gold is associated with paleo-placers located within Tertiary conglomerates.

In synthesis, the gold fields of the Madre de Dios are remarkable because they receive gold from multiple different primary sources and concentrate it in the sediments in the Huepetuhe Valley and the adjacent alluvial fan of the Río Inambari. There is no published estimate of total gold reserves in Madre de Dios, but the alluvial fan covers about 500,000 hectares (1.23 million acres) and if the average gold concentration is 5 kg/ha, then the region should have contained about 2,500 tonnes of gold. Assuming miners have exploited the richest deposits, then perhaps half of that total has been extracted, which would value the remaining reserves at ~US$75 billion, a conservative estimate.

By 2020, the total area of placer-mine tailings in Madre de Dios exceeded 150,000 hectares (370,658 acres) with annual increments that vary between 4,000 and 10,000 hectares (9884 to 24,710 acres) (Figure 5.28). Estimates of the amount of gold extracted from the region range between 15 and 35 tonnes per year, which translates into equally imprecise estimates of gross revenues between ~US$500 million in 2015 to more than US$1.6 billion in 2019. Placer gold mining is the most important economic activity in southeast Peru. By way of comparison, the nearby coca fields in the cloud-forest region generated between US$60 and $US100 million annually over the same period, while the total value for legal farming is a mere US$4 million per year. The estimated number of individuals working or providing services to the gold fields varies between 50,000 and 75,000.

The government initiated an effort to establish a legal and regulatory presence in 2014 with the creation of the Fiscalía Especializada en Materia Ambiental (FEMA), which are prosecutors charged with enforcing environmental law. As in Brazil, they work via periodic ‘law and order’ campaigns that mobilize multi-agency task forces, which also include environmental agents, police and the military. The first campaign in 2015 destroyed 86 mining camps that had encroached upon the Tambopata y Amarakaeri protected areas. This was followed by the Operación Harpia in 2018 to collect data and display their technological prowess; and the Operación Mercurio, which expelled 25,000 miners from Tambopata Reserve in 2019. Subsequent efforts by wildcat miners to invade the reserve have been similarly shut down and included the confiscation and destruction of their machinery and vehicles.

Authorities are less inclined to confront illegal mining on public lands not located within a protected area. They have started collecting royalties, however, and in 2020 the ministry for mines and energy reported that 245 concessionaires produced 1.1 tonnes of gold, up from about 500,000 kilograms in 2015 and 10,000 kilograms 2011. Although greatly improved, these numbers represent less than 5% of the estimated production from the Madre de Dios.

The La Paz Yungas and the Río Beni

The gold fields of the Bolivian Yungas are similar to the Inambari system. They are linked to primary magmatic intrusions located in glaciated terrain of the Cordillera Real and paleo-placer deposits in the foothills. Gold has been mined in the foothills for decades, but a gold rush has exploded across the intermontane valleys that have functioned as logistical corridors between the Altiplano and the Amazon lowlands since before the Inca Empire. The Yungas is traditionally divided into two subregions: Nor Yungas and Sur Yungas, each of which are drained by half a dozen rivers that all feed into the Río Beni, which, like the Inambari, exits the Andes through a narrow gorge.

Apparently, the depositional landscape of the alluvial plain created by the Río Beni is not conducive to the formation of a sediment trap and, as of 2022, placer mining below the gorge has been limited to dredges mounted on barges. The use of dredges was introduced into Bolivia from Brazil in the 1980s and, in addition to the Río Beni, are a common sight on the Madre de Dios, as well as the Orton and Manuripi rivers, both of which are paleochannels of the Madre de Dios.

The Bolivian gold-mining industry is almost completely dominated by miners operating as cooperatives. However, the use of this identifier disguises a sector that is actually dominated by unscrupulous individuals who use the associative framework to avoid the labor and environmental regulations applied to the private sector. The sector is highly decentralized and democratically organized: an estimated 140,000 miners are employed by 1,300 cooperative-affiliated enterprises that are incorporated into four separate federations. Altogether they produce 94% of Bolivia’s gold; 76% originating in the Yungas of La Paz and from the dredge barge operations in the department of the Beni and Pando.

Starting in about 2010, the government and the mining cooperatives organised a process to register miners and collect mineral royalties, which are returned to local governments to finance infrastructure and basic services. The devolution of royalties explains, in part, the willingness to report production values that obligate them to pay the 4% royalty tax. Nonetheless, the system continues to tolerate other forms of tax evasion and ignores environmental regulations. Despite numerous commitments to control the importation and use of mercury, the government has failed to act because authorities are reticent about antagonizing a group of highly organized and militant cooperative miners. Like other mining landscapes across the Pan Amazon, murder, extortion and armed robbery are common, as are multiple different forms of social and labor exploitation.
In 2021, the Bolivian mining ministry reported production of 45 tonnes of gold with an estimated value of US$ 2.5 billion, up from two tonnes and US$94 million in 2010. Bolivia’s economy benefited from the formalisation of gold exports by creating a significant new source of foreign exchange at a time when the country’s balance of payments was suffering from a decline in revenues from the export of natural gas (see below). It is unlikely, however, that 100% of the gold harvest is being reported to authorities and independent analysts estimate that as much as 50% of the gold produced in Bolivia is sold via intermediaries from Peru.

The Alto Marañon

There are multiple reports in the Peruvian press about illegal gold mining in the highlands and valleys of the Andes, particularly in the upper valley of the Río Marañon where gold mining has existed since before the Inca empire. The most heavily impacted section is a 100-kilometer stretch in the department of La Libertad where miners have exploited gold veins using underground and surface mining technology for about 100 years. In 2022, three Peruvian companies were operating several underground mines with others under development; they produced ~20 tonnes of gold with a nominal value of US$1 billion in 2022. Known as the Pataz mining district, it has numerous environmental liabilities, including eroded hillsides scarred by hydraulic mining, abandoned placer tailings, and cyanide-laced tailing storage facilities and leaching pads.

The Alto Marañón drains both the Cordillera Oriental, the source of most of its water, and the Cordillera Occidental, which is home to six massive open-pit gold mines that have initiated operations after 2005. All apply the heap-leach concentration technology that minimizes the use of water and avoids the use of tailings ponds. Their production sums to about ten tonnes of gold, and they will probably operate for a couple of more decades by opening other pits in adjacent ore bodies and expanding via brownfield investments.

Further north in Cajamarca is Yanacocha, the largest and most lucrative corporate gold mine in Peru, which has produced more than 1,200 tonnes of gold and 950 tonnes of silver over its thirty-year lifespan. The mine complex, which ceased operations in 2021, encompasses seven open pits, surrounded by hillocks composed of waste rock and tailing heaps that cover more than 30,000 hectares (74,100 acres). The operator, Newmont Corporation, had hoped to open a second facility on a nearby mountain (Conga Project); however, opposition by communities forced the company to abandon those plans. Apparently, the US$1.2 billion spent on community development and the 1,600 jobs was insufficient to convince the region’s inhabitants that a second similar mine would benefit the region.

Although the gold-mining operation has closed, reclamation efforts are still underway with at least 5,000 hectares (12,350 acres) of area scheduled for some sort of active remediation. Newmont is evaluating the feasibility of exploiting two copper-ore bodies with an underground mine, which could prolong operations for another 20 years.

Cordillera del Condor and the Northern Andes

The Río Marañón also receives runoff from the Cordillera del Condor, a unique mountain range on the border between Ecuador and Peru that is home to a surprising number of endemic plants and animals. The area was sheltered from development throughout most of the twentieth century due to a border conflict between the two countries. Upon resolution of that dispute, the area became the focus of conservation advocates and geological prospectors attracted by the region’s mineral resources. Much of the area has been set aside as a protected area or Indigenous territory, but there are still large areas open to mining, particularly in Ecuador where multinational corporate miners are investing in both copper and gold mines.

In Ecuador there are two dedicated gold mines: Fruta del Norte, which has been operating since 2015, and the Condor Project, which is still at the development stage. Together, they hold an estimated 320 tonnes of gold with a nominal value of about US$16 billion in 2022. In addition, several copper mines are operating (one) or under development (five); all six will produce significant amounts of gold. All are located on the western slope of the Cordillera del Condor where wildcat miners have exploited alluvial gold in the headwaters of the Río Zamora, a tributary of the Rio Santiago since about 2010.

Nearby on the cloud forest slopes of the Andean Cordillera, is the Nambija gold district, a historical site dating from the Inca empire. An old Spanish mine was rediscovered in the 1980s, triggering a ‘gold rush’ when 25,000 wildcat miners poured into the area seeking their fortunes at one of 75 different mine sites. Chaos and ad hoc engineering led to an avalanche that killed 300 miners in 2000, while leaving a legacy of unstable underground mines and unremediated tailings heaps that are laced with mercury. The area continues to be a locus for dozens of small and medium-scale mines, which are operated by domestic companies that are, apparently registered with national mining authorities. Downstream, the Santiago flows north until it exits the cordillera through a narrow gorge and then back south into Peru where wildcat miners have been active since about 2016.

Wildcat miners also have been reported on the Río Cenepa, a tributary of the Marañón that drains the eastern slope of the Cordillera del Condor, where 39 placer mines were exploiting the river bed and adjacent beaches in 2021. This part of Peru falls within the territory of the Awajún, a well-organized Indigenous nation, whose representative organizations have denounced the illegal activity. Not all Awajún are opposed to the activity, however, and many of the miners, perhaps most, are residents who view placer mining as a legitimate economic activity that can generate resources for the families.

Both Ecuador and Colombia are renowned for their volcanos, and gold is commonly found associated with volcanic rocks. With the exception of Nambija, there are no industrial-scale mines operating on the Amazonian slopes of the Cordillera Oriental in either country – yet; nonetheless, there is undoubtedly gold in those mountains, otherwise there is no reasonable explanation for the alluvial gold that has been discovered (and exploited) on the floodplains of the Napo, Putumayo and Caquetá rivers. Further evidence is being gathered by corporate miners exploring copper porphyries in Mocoa, Colombia and the Bonito project in Succumbios, Ecuador.

Banner image: Devastation caused by an open-pit gold mine in the Peruvian Amazon. Image by Rhett A. Butler.

“A Perfect Storm in the Amazon” is a book by Timothy Killeen and contains the author’s viewpoints and analysis. The second edition was published by The White Horse in 2021, under the terms of a Creative Commons license (CC BY 4.0).

To read earlier chapters of the book, find Chapter One here, Chapter Two here, Chapter Three here and Chapter Four here.

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Amazon MiningCopperDeforestationGeologyGold MiningIllegal MiningIndigenous CommunitiesNatural ResourcesRiversThreats To The AmazonBoliviaColombiaEcuadorLatin AmericaPeruSouth America

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