The supergiant Huimin iron deposit is located in the eastern part of the Changning- Menglian suture belt in the Sanjiang compound orogenic belt, which notably features volcanoclastics- hosted, magnetite- siderite association, as well as pervasive hydrothermal alteration. At present, the genesis of the deposit is still debated due to controversy in the age of the ore- bearing strata. Detailed field observations reveal two tectonostratigraphic units separated by an unconformity, both of which belong to the Huimin Formation of the Lancang Group. The lower unit is the Middle to Late Ordovician volcanic- sedimentary rocks with arc affinity, which has been intensely modified by the Paleo- Tethyan subduction, and thus exhibits features of tectonic mélanges. Locally, iron and copper mineralization occurred in the older unit. The upper unit consists of basalt, andesite, crystal- rich tuff and hydrothermal siliceous rocks, where numerous iron- layers occurred. These iron layers form the main orebodies. This volcanic succession contains at least three volcanoclastic cycles with mostly conformity contacts between them. The iron ore bodies are stratiform- like and/or lamellar style in shape, and few are steeply- dipped veins and veinlets. Obviously, the mineralization was syn- sedimentary. New zircon LA- ICP- MS U- Pb dating results show that the ore- hosted volcanic rocks were emplaced during 235 to 214 Ma with the volcanism age peaking at 230 to 225 Ma. The Late Triassic volcanic rocks show arc- signatures geochemically, and likely formed in a forearc basin due to the eastward subduction (at present geographic coordination) of the Paleo- Tethys Ocean. These data, combined with the previously published data, suggest that the supergiant Huimin iron deposit is a volcanic- sedimentary deposit formed owing to subduction- related volcanism during the Early Mesozoic. Our new data and ideas presented in this paper shed light on understanding the mineralization of similar iron deposits in the adjacent regions of the Huimin iron deposit, and are helpful in guiding further prospecting.