The manganese deposits in Bani, Tinambac, Camarines Sur are tabular to lenticular ore bodies occurring within a sequence of thermally metamorphosed volcanic and sedimentary rocks with associated jasper. The manganese ore minerals are predominantly braunite and pyrolusite, the former mineral making up the bulk of the deposits. Piedmontite, barite, calcite and quartz are associated in minor amounts.

To judge from the various features of the deposits and those of the enclosing rocks, it is believed that the deposits are to a large degree of syngenetic or sedimentary origin. Small scale replacement observed in the deposits is thought to be contemporaneous with sedimentary ore deposition. Deposition of the ores and jasper took place during or shortly after the extrusion of the volcanic rocks under a marine environment. The source of the manganese and silica was most probably from warm springs related to the same volcanic activity responsible for the extrusion of the volcanic rocks. The Bani deposits may fall under the "volcanic sedimentaries" type proposed by P. Routhier to the manganese deposits in New Caledonia.