Mineralization of the Luis Lopez epithermal manganese deposits in light of fluid inclusion and geologic studies
— David I. Norman, Khosrow Bazrafshan, and Ted L. Eggleston

Manganese minerals are common in hydrothermal deposits. In association with sulfide minerals, manganese occurs in reduced form (Mn+) as a carbonate, silicate, or sulfide: the most common forms are rhodochrosite, rhodonite, and alabandite.

Psilomelane, the principal manganese mineral in the Luis Lopez deposits (Hewitt, 1964; Farnham, 1961), generally occurs in surficial environments or in the shallow, low-temperature part of veins or in thermal spring deposits (Roy, 1981). The possibility that the Luis Lopez district might be the surface expression of an extensive hydrothermal system, with possible economic mineralization at depth, is suggested by the size of the district, the common occurrence of manganese oxides high in hydrothermal systems, the report of anomalous Ag and W in the deposits (Hewitt, 1964; Willard, 1973) and the recognized association of manganese with gold-silver and molybdenum-tungsten mineralization. Because of the possibilty of other mineralization at depth, as well as because there have been few studies of hydrothermal Mn-oxide deposits, the Luis Lopez deposits were studied to determine the nature of the mineralizing system.

Six major occurrences of manganese mineralization (fig. 1, Eggleston and others, this guidebook) were studied by fluid inclusion methods and the paragenesis of the deposits determined.