The Ordovician volcanic rocks in Kaladawan area are composed of alkali basalts and tholeiites, and the alkali basalts geochemically similar to OIB were derived from asthenospheric mantle. The tholeiites show enrichment of LILE, LREE and Th-U, and depletion of HFSE and Nb-Ta, similar to characteristics of island arc tholeiite, suggesting that they were derived from subduction modified lithospheric mantle. The existence of the two rock types in the same geological section implies that they jointly represented a regional early Paleozoic back-arc basin magmatism. Combining regional geological data with the authors’ findings, it is held that the Kaladawan iron ore district is a reformed volcanic-sedimentary type deposit formed in a back-arc basin tectonic setting.