The increase in the price of gold, due to a shift to safe investments during the global economic crisis, has led to a rapid expansion of gold production. Alongside legal gold mines, wildcat gold mining has developed in French Guiana since the early 2000s. This phenomenon, with its social, environmental and economic consequences, is at the heart of the environmental governance of this territory. However, its difficult quantification is the subject of multiple controversies. Environmental governance is increasingly dependent on metrological regimes aimed at quantifying political action in order to objectify it. This article examines the role of metrology in implementing environmental policies in sparsely populated regions via the example of wildcat gold mining in French Guiana. Based on the study of two observatories, one managed by public authorities, the other by an NGO, we deconstruct their maps and counter-maps of wildcat gold mining. To do so, we make a distinction between measurement, commensuration and its diffusion. This focus on “measurement-commensuration-diffusion” allows us to identify three key phases in the production of nature statistics. We argue that the critical analysis of metrological processes through this three-step framework reveals methodological controversies that reflect different and even divergent political visions. The article also shows that metrological systems for environmental protection are the focus of targeted political disputes. It reports on the current disagreements—not only between the State and NGOs but also within the State itself—on the proposed solutions for fighting the impacts of wildcat gold mining in French Guiana and the broader issues of data production in Amazonia.