NEW APPLICATION OF MANGANESE OXIDE MINERALIZATION AS A PATHFINDER TO MAGMATIC-HYDROTHERMAL SULFIDE MINERALIZATION
Three mining districts that contain both sulfide and complex MnOx deposits were studied to evaluate the mineralogical and temporal relationships of these two types of mineralization. These districts included: Magdalena (NM), Lake Valley (NM), and Santa Eulalia (Chihuahua, Mexico). All districts displayed similar manganese mineral assemblages. Detailed study of the MnOx paragenesis was essential for locating datable K-bearing minerals; found most commonly at the transition of Mn oxide mineralization to calcite precipitation. Age dating of the MnOx mineralization was accomplished by 40Ar/39Ar dating of minerals from the coronadite group, specifically the K-bearing phases, cryptomelane and todorokite.
In none of the districts studied did the age of MnOx mineralization correlate to the age of igneous rocks associated with sulfide mineralization. In most cases, the manganese oxides were more than 10 million years younger than the inferred ages of the sulfide ores (sulfide age/MnOx age): Magdalena (28-29 Ma/8-14 Ma), Lake Valley (28-35 Ma/14 Ma), Santa Eulalia (33 Ma/ 2-10 Ma). Obviously the MnOx deposits are produced by a process independent of the magmatic-hydrothermal system. A broad survey of MnOx deposits suggests weathering or remobilization of metals by younger hydrothermal or groundwater systems could to be responsible for observed MnOx mineralization. Although temporally unrelated, the geologic relationships and proximity of MnOx to sulfide mineralization suggest they can be used for exploration; albeit using a different geological paradigm than has been employed historically.