Remarkable folded dacitic dikes at Mina Ragra, Peru
Peru has a very unusual historic vanadium deposit called Mina Ragra that was produced from a small open pit located right along a dacitic dike that intruded into the latest Cretaceous-early Paleocene Casapalca Formation. The vanadium mineralization was described as being along a NS-striking “vein”, but the mining and geology of this deposit is poorly documented given the time in which it was extracted by the Vanadium Corporation of America in the early twentieth century. This is the only meaningful vanadium occurrence in Peru, and it stands out as being a unique deposit in the Andes. The mine is located at -10.861169S, -76.572055W. I have not had the chance to visit this mine, which is located well west of Lago Junín at an elevation of 4,703 meters above sea level, but I have made an exciting air photo interpretation map using Google Earth that may suggest a genetic relationship between a series of dacitic intrusions and the mine. And for Peru, and the Andes, what is especially remarkable is that these never before dated dacitic dikes are folded.
The mineralization at Mina Ragra consists of black asphalt-like ore of patronite (VS4) with the gangue minerals of anhydrite and pyrite. Mina Ragra is the type locality for patronite. More exotic rare minerals, mostly supergene varieties, from this mine are listed on www.mindat.org have an additional eight others that share having a type locality distinction or being first described from Mina Ragra. Two of these are hydrous nickel-sulfates that mark Ragra has having bizarre metallogeny. Mineralization was discovered here in 1905. Early production in 1906 had high-grade ore carried overland by llamas. Later the Jumasha processing plant was built to the east along the shore of Lago Punrun. A rail line once connected the mine and plant. Mina Ragra had ores running up 7 percent vanadium, and once accounted for nearly 50% of the world’s production for the early twentieth century. The mine closed in 1955.
Over the last 52 weeks the price of vanadium has varied between 19 and 35 dollars per kilo; or during the last seven years averaged at about 10 dollars per pound. When Mina Ragra was first discovered vanadium prices were extraordinary at $4,000 USD per pound. After the mine reached consistent production the price dropped to $1.86 USD per pound. Mina Ragra is known for being the world’s first industrial-scale producer of vanadium. Total production numbers from Mina Ragra are not well reported; unconfirmed total production varies between 36 and 42 Mt of vanadium. For reference, modern annual vanadium production/consumption averages at 75Mt. Russia, China, and South Africa supply about 85% of the world´s vanadium, which generally comes from magnetite deposits. The South Africa production comes from magnetite sands and the Bushveld Complex. Vanadium products are sold as ferrovanadium and vanadium pentoxide.
The Ragra mine lies in a relatively gentle sloping area where the Casapalca Formation is covered by tundra like fields, making tracing out the structure of the bedding difficult. The number or folds in this area is likely far greater than shown in area geology map. The dikes, however, boldly crop out due to being more weathering resistant. The small open pit, which has a pit lake in the bottom, measures in size at 122 by 254 meters. Mine dumps are scattered about northeast of the pit. It is unclear whether or not the mine had some underground production. A prominent rib on the east highwall appears to be a dike.
“Vanadium Corporation of America. “Campamento De Arriba,” October 25, 1911. Vanadium Corporation of America Photograph Collection, Box 2. Science History Institute. Philadelphia. https://digital.sciencehistory.org/works/3t945r32x.”
The dikes make a WNW-striking pattern in the map, and are spatially related to a couple of NS-elongate dacite plugs. In detail, it is certain that the dikes are crosscutting bedding in the Casapalca Formation red beds, and that they define a folded map pattern. The dikes have about 5-km strike length, and are up 20-50 meters thick. They must be post-Early Paleocene in age, and likely older than the late Miocene (perhaps young enough to have crosscut older folds made during the 47-48 Ma Incaic shortening event and old enough to have been folded by the regional circa 17.5 Ma Quechua 1 folding event). The dikes are suspected to be comprised of dacite as based on spatial relation with the plugs, and from the general color aspect of the dike and their massive thickness. The scale of the dikes and number of folds bending them are enough to make them perhaps one of the best examples of folded dikes in the Andes. This may be explained by the incompetent nature of the host rocks, and that the dikes were emplaced in a nearly EW-direction which made them ideal for the subsequent EW-directed contraction to develop the folds. EW-striking veins and dikes are common in the Andes and relate to regional stress conditions with sigma 1 being horizontal oriented EW, sigma 2 vertical, and sigma 3 lying NS, providing for vein-like dilation in Mode 1 fractures.
The folded dikes, and the Ragra mine occurrence, were mapped during many years long regional compilation work I have been doing on Andean dikes. Out of the 23,232 number of dikes mapped in the Andes to date, the folded Ragra dikes makes just one of numerous interesting stories that could use additional research to more fully understand the geology. None of the dikes were marked on the INGEMMET 100k-scale geological quadrangle map covering the Oyon sheet. We are left with the questions of whether or not the dikes played a role sourcing the metals at Mina Ragra, or if they intruded post-mineral. It would appear that a vanadium-sulfide deposit would be difficult to form in oxidizing continental sandstone, which would then argue another genetic motivator is required. If the Ragra deposit did form through igneous activity, then the mapped folded dikes would make a part of the exploration guide in the search for any new resources in this area. New significant resources of vanadium from this district are really not expected, but the area has not seen any modern exploration. The deposit lies 620 meters west of a large dacite plug. The dikes and plugs need to be dated, their composition field checked, and their relationship the mineralization studied.
James M. Wise, May 2018
References
Bravo, J.J., 1906, El vanadio de mine Ragra: Sociedad Ing. Peru Bol., v. 8, p. 171-185.
Hewett, D.F., 1909, Vanadium deposits in Peru: American Institute of mining Engineers (A.I.M.E.) Transactions: 40: 274.
Hillebrand, W.F., 1907, The vanadium sulfide patronite and its mineral associates from Minas Ragra, Peru: American Journal of Science, v. 24, p. 141-151.
Hillebrand, W.F., Merwin, H.E., and Wright, F.E., 1914, Hewettite, Metahewettite and Pascoite, Hydrous Calcium Vanadates: Proceedings of the American Philosophical Society: vol. 53, n° 213, 31-54.
Lindgren, W., 1921, Melanovanadite, A New Mineral from Mina Ragra, Pasco, Peru: Proceedings of the National Academy of Sciences: 7(8): 249-251.
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