Richard L. Burger, Kris Lane, and Colin Cooke (Reference Burger, Lane and Cooke2016) mistakenly claim that Huancavelica was the only source of vermilion pigment in prehispanic Peru. Cinnabar was also mined in southern Ecuador in the province of Cañar. There are ample historical records of the mines, beginning with their discovery about 1558 by Gil Ramírez Dávalos, the founder of Cuenca (Newson Reference Newson1995:229). Owing to the complete lack of any archaeological investigation in this area, we know nothing concerning precolumbian use of the mines, although a local Cañari apparently showed them to Ramírez. The official claim (estanco) of 1561, issued by the viceroy to establish royal monopoly over the cinnabar mines of Cuenca (Azogues was within the jurisdiction of Cuenca during the colonial period) and Huamanga, Peru (Archivo General de Indias, Seville ES.41091.AG/29.7.16.4/Patronato, 188, R.21), survives, as does 250 more years of documentation of the mines.

This source was important enough that the adjoining town was named San Francisco de Peleusí de Azogues after both the local indigenous chiefdom and the local cinnabar mines. Multiple documents show that the mines flourished for approximately a decade until Huancavelica in Peru started full production. The Spanish government officially closed all cinnabar mines except Huancavelica in 1570 (to limit tax evasion), but Loma Guashon continued intermittent production until the beginning of the nineteenth century.

In 1799, a detailed drawing/map of Loma Guashon showing the 10 sequentially used mine tunnels was made (Supplementary Figure 1). Shortly thereafter, the cinnabar source was exhausted and the mines completely abandoned. Our original article was based on a visit to Loma Guashon in 1996 (Truhan et al. Reference Truhan, Burton and Bruhns2005). It was only in 2013, when a track was bulldozed down the deep gully called Quebrada San Marcos, that we visited the mines themselves; they appear exactly as shown in the 1799 drawing, although the Loma is now covered with a eucalyptus plantation (Supplementary Figure 2).

In October 2016, we took geological samples from the well-preserved 1799 El Boquerón mine (Supplementary Figures 3, 4, and 5). Standard geochemical sampling (inductively coupled plasma) of the altered sandstones at Cerro Guashon gave 11.8–113.3 ppm Hg (Supplementary Table 1), consistent with mining that would have long since removed the high-grade cinnabar ore, leaving only trace amounts of disseminated cinnabar in the sediments adjacent to the north-south vein. Occurrence of mercury in association with the sedimentary rocks is somewhat similar to the geologic setting of Almadén, Spain, where the ore is also strata-bound, disseminated cinnabar with some native mercury (Rytuba Reference Rytuba, Cox and Singer1986:180). The geochemical signature at Guashon includes As (9–75 ppm) and Sb (10–54 ppm), much like the geochemical signature at cinnabar occurrences such as Almadén. The amount of sulfur (182–7262 ppm S) may be related to the sulfur held in cinnabar, but other sulfur-bearing minerals may also be present. There is no field evidence to suggest that Guashon is a hot-spring mercury occurrence. We dismiss Cooke's coring in the Cajas National Park since the prevailing winds of Azogues are north-northwest, not south. Likewise, we dismiss the conjecture, based on an inaccurate translation of the Relaciones Geográficas de Indias (Gallegos Reference Gallegos and de la Espada1965 [1881]), that the Loma Guashon mines were sources of red ceramic clay. The clay sources are 5–7 km to the southeast (Supplementary Table 2).

We suggest that Burger and colleagues’ conclusion that the only precolumbian cinnabar source was Huancavelica is premature. Georg Petersen mentions 20 cinnabar sources in Peru; 19 remain unsampled (Petersen Reference Petersen and Brooks2010 [1975]:29). Moreover, not a single Ecuadorian precolumbian pigment was analyzed. Given the close precolumbian trade connections between northern Peru and southern Ecuador, one might expect the use of cinnabar there. Whether it was locally mined or traded in from any Peruvian source has yet to be established. We thank them for posing some questions that may be settled with the publication of our new research.