Puerto Rico volcanogenic Mn

Region East, Southeast
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Defined by Bawiec (1998). Based primarily upon known occurrences, Cretaceous and Tertiary marine volcaniclastic map units, Tertiary marine basalt and chert, and related geochemical signatures associated with these deposits.
Identified resources Historical production of manganese.
Production Juana Diaz mine (1915-1939): ~80,000 tons of ore at an average grade of 60% Mn; production at Gaitti prospect stopped due to flooding.
Status Past mining and exploration.
Estimated resources Unknown.
Geologic maps Cox and Briggs (1973), scale 1:240,000; Briggs and Akers (1965), scale 1:240,000.
Geophysical data Inadequate aeromagnetic, non-existent aeroradiometric data (Bawiec, 1998).
Favorable rocks and structures Manganese deposits in Puerto Rico consist of pyrolusite and psilomelane in pockets that fill irregular chambers within Tertiary limestone units.
Deposits Aguada (MRDS dep_id: 10085418), Gatti prospect (MRDS dep_id: 10100553), Corozal (MRDS dep_id: 10085444), Juana Diaz mine (MRDS dep_id: 10085536).
Evidence from mineral occurrences MRDS.
Geochemical evidence Unknown.
Geophysical evidence Unknown.
Evidence from other sources Geologic mapping, geochemistry.
Comments Limestone fractured by faulting dissolved as ground water and surface waters percolated through the fractures, dissolving CaCO3 and precipitating highly concentrated bodies MnO2 (Bawiec, 19989). There are 14 known occurrences of volcanogenic manganese in Puerto Rico, and three of these occurrences (Juan Diaz mine, Gatti prospect, and Aguada) have been upgraded to known deposits.
Cover thickness and description Exposed, possibly more under cover.
Authors Anjana K. Shah.
New data needs Geophysical data, geologic mapping, and geochemical data.
Geologic mapping and modeling needs Geologic mapping at 1:24,000 scale.
Geophysical survey and modeling needs Rank 2 aeromagnetic and aeroradiometric data; Rank 1 requires helicopter. Aeromagnetic data can assist with mapping volcanogenic terranes. Radiometric data for geochemical variations.
Digital elevation data needs Lidar complete.