Illegal gold mining has expanded significantly in the Amazon in the last decade (Asner et al. 2013; Alvarez-Berríos and Aide 2015; Asner and Tupayachi 2016), up to 18% annually in some regions (Swenson et al. 2011). This expansion is driven by the increase in gold prices in international markets (Alvarez-Berríos and Aide 2015; USGS 2020). In Brazil specifically, since 2018, it is bolstered by political support from the government of President Bolsonaro (Solomon 2020).

The occupation of illegal miners, mostly in search of gold, is encroaching on protected areas (Espejo et al. 2018) and threatening Indigenous peoples’ well-being (CIMI 2018; Souza et al. 2019; Calvimontes et al. 2020; Siqueira-Gay et al. 2020a). Illegal gold mining pollutes water with heavy metals (Lobo et al. 2016; Abe et al. 2019), affecting aquatic (Swenson et al. 2011) and terrestrial ecosystems (Schueler et al. 2011; Asamoah et al. 2017; Dezécache et al. 2017), leading to negative impacts on human health (Castilhos et al. 2015). In addition to local consequences, effects such as water contamination and increased sedimentation can be traced far beyond the mining sites, threatening communities and ecosystems hundreds of kilometers away (Alvarez-Berríos and Aide 2015; Sánchez-Cuervo et al. 2020). These small-scale activities are claimed to cause minor direct adverse impacts on forests (World Bank 2019); however, they can lead to extensive environmental impacts when associated with other drivers of change, such as large infrastructure development (Sánchez-Cuervo et al. 2020). Combined with broader infrastructural interventions, illegal gold mining can cumulatively degrade forests and reduce their area over time (Asner and Tupayachi 2016).

Two satellite monitoring systems are currently used to map the entire Brazilian Amazon (Assis et al. 2019). PRODES provides the annual extent of forest cover and deforestation rates (INPE 2017), and DETER-B (Diniz et al. 2015) issues daily warnings of deforestation to support direct field inspections and control (Assis et al. 2019). Data from DETER-B show that the annual rate of clearing due to illegal mining activities, i.e., the sum of all warnings in a year, increased more than 90% from 2017 to 2020, reaching 101.7 km2 in 2020 compared to 52.9 km2 in 2017, the year before Bolsonaro’s term started (Fig. 1). In contrast, by overlaying deforestation data from PRODES to mining leases from the National Mining Agency (ANM 2020) (Fig. 1), the same trend is not observed inside areas with lease permits (Table S1-S4).

Fig. 1
figure 1

Deforestation in the Brazilian Legal Amazon, industrial mining leases, and deforestation warnings due to illegal mining. In the graph, the gray bars are the annual deforestation rates within mining leases, and the red line features the sum of deforestation warnings per year due to illegal mining

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The types of gold mining in Brazil are twofold: (i) industrial mining, which are required to have a lease permit, and (ii) small-scale (seldom artisanal) mining, known as garimpos, where simplified forms of exploration, extraction, processing, and transportation are used (OECD 2016; Sousa et al. 2011). Several garimpos use heavy machinery to extract gold and are not considered artisanal but small-scale mining (Calvimontes et al. 2020). Most artisanal and small-scale mining of gold in Brazil is illegal (Sousa et al. 2011), but obtaining a garimpo lease is possible. Garimpos are not required to comprehensively assess and mitigate their social and environmental impacts (Ministério Público Federal 2020).

Garimpos not only clear but also degrade forests (Espejo et al. 2018), severely limiting the recovery of ecosystems after disturbance (Kalamandeen et al. 2020) and particularly degrading riparian vegetation. Clearing forest and other native vegetation for industrial mining requires legal authorization and the corresponding adherence to specific terms and conditions, including the commitment to rehabilitate degraded areas. However, deforestation in illegal gold mines is not held to similar conditions, and the mined areas are usually abandoned after the reserves are exhausted, without any rehabilitation (Sousa et al. 2011).

There is growing knowledge and experience around restoring Amazon forests (da Cruz et al. 2020), including after large-scale mining (Gastauer et al. 2019). Post-mining restoration experiences date back to the 1990s (Parrotta and Knowles 2001), but the success of these interventions are highly dependent on how the rehabilitation process is managed (Neri and Sánchez 2010). Key ingredients for successful restoration, such as contextual knowledge, adequate financial resources, and long-time frames necessary to monitor a restoration trajectory (da Cruz et al. 2020; Kalamandeen et al. 2020), are lacking in areas where illegal gold mining occurs.

In order to curb extensive illegal mining deforestation, recommendations are twofold. First, it is critical to track the source of minerals to distinguish gold mined illegally from legal and formalized gold mining, and this can be done through certification schemes. Second, strengthening national and local policies to tackle illegal deforestation is needed. Investigations by the Federal Police and inquiries conducted by the Federal Prosecutor Office found that a significant amount of illegally mined gold is falsely declared as coming from legal sources—i.e., legalized garimpos—in order to be sold to authorized buyers (Solomon 2020). Initiatives such as the Chain of Custody Standard of the Responsible Jewellery Council (RJC 2019), the Minerals Due Diligence of the Responsible Minerals Initiative (RMI 2020), and the Fairmined Standard for Gold (Alliance for Responsible Mining Foundation 2014) have been developed to assist buyers of gold and other precious metals to verify their suppliers’ compliance with environmental and social standards for responsible mining (World Bank 2019) and have potential to contribute to minimize gold trade originated from illegal garimpos.

Although these schemes have limitations (Sippl 2020), certification that is informed by regular audits and inspections could encourage international gold buyers to join international investors in supporting fair enforcement of Brazilian environmental legislation, as a way to curb illegal mining supply chain (World Bank 2019). Promisingly, there is growing awareness around this (Nazareno and Laurance 2020). On April 23 2020, an open letter signed by 30 financial institutions holding more than US$ 3.7 trillion total assets (Harris 2020) warned that “the escalating deforestation in recent years, combined with reports of a dismantling of environmental and human rights policies and enforcement agencies, are creating widespread uncertainty about the conditions for investing in or providing financial services to Brazil” (Storebrand Asset Management et al. 2020).

Since 2004, public policies to tackle deforestation in the Amazon were strengthened by the Action Plan to Prevention and Control of Deforestation in the Legal Amazon (PPCDAm) responsible for the creation of protected areas and regulatory instruments (Silva Junior et al. 2020; Siqueira-Gay et al. 2020b). However, since 2018 (Silva Junior et al. 2020), trust in the government’s willingness to curb deforestation has drastically decreased, given the roll back of environmental protection legislation in Brazil (Abessa et al. 2019; Ferrante and Fearnside 2019) as well as the continuous erosion of most regulations promoted by the Ministry of the Environment (Pereira et al. 2019). In contrast to present moves towards weakening environmental regulations in Brazil, previous initiatives to tackle mining-driven deforestation in the Amazon have demonstrated the importance of local and regional cooperation to support and implement national policies (Dezécache et al. 2017).

Increasing gold prices (Cherringtion et al. 2020) contribute to the prospect of rapidly increasing forest degradation by illegal gold miners in the coming years. Restraining deforestation is unlikely to happen without sustained pressure on investors and consumers for strengthening and expanding international mechanisms to increase traceability of mineral supply chains. Likewise, national support for increasing cooperation between federal and local policies and instruments is needed to restrain the growth of illegal mining and consequent deforestation in the Brazilian Amazon.