The deposits of gold-bearing gravels in the Inambari River System are the result of the deposition of detritus from the highest geologic layers of the Eastern Andes mountains. Because of its flow volume, the Inambari River is considered among the most important rivers in the Peruvian jungle.
For millions of years, the gold contained in the primary deposits, in veins or in layers (slate and gold-bearing shale) and in particularly the intrusive rocks and slates of the Sandia formation along the Eastern Range of the Andes eroded into the Inambari River System. These rocks have been eroded by mechanical and chemical actions, as well as by wind, rain, heat and cold weather. As the formations were alternately eroded and separated from the host rock, and then carried away to the river system and its tributaries, the gold was transported from the highest parts to the lowest reaches of the Inambari River and then on to the Rio Madre de Dios.
It is easy to suppose that alluvial deposits containing coarse gold have been deposited along this system of rivers, while the gold transported with mud and stone to the lowest part has been triturated, forming the finest particles. (Dr. Estanislao de la Cruz C., Engineer EAP 17027; Sept. 2007).
It is suggested that during the early stages of erosion, the Andes extended eastward, well beyond the current mine site (Dr. Estanislao de la Cruz C., Engineer EAP 17027; Sept. 2007). This would account for the gravels found in terraces many meters above the river levels as we know them today. As the Andes eroded back towards the West, the terraces were left perched and untouched, save for the rivers cutting through the sedimentary formation such as the Carabaya, where the Inambari River deeply incised the rocks at an oblique angle and carved its way down in elevation to its present location.