Iron ore deposit and skarn alteration was found at Khoa Lek, Amphoe Nong Bao, Changwat Nakhon Sawan. Khao Lek is located in Loei-Petchabun Fold Belt where iron mining was operated from skarn deposited and epithermal deposited. Host rock in this area is volcaniclastics (andesitic sandstone and andesitic breccias) and limestone which are metamorphosed by diorite intrusion. This deposit is iron skarn deposit that comprises of endoskarn and exoskarn. Endokarn is formed in diorite intrusion but it cannot observe in the field because diorite intrusion is completely replaced by magnetite. Exoskarn, prograde skarn, comprises of garnet zone, pyroxene zone, and marble zone. Garnet zone has a red garnet, brownish red garnet, and green garnet which size 1 millimeter to 2 centimeters. Pyroxene zone is located in the south of this area covering approximately 3 meters thick and almost pyroxene in this zone is clinopyroxene. Marble zone is located in northwest of this area and is comprised of calcite. Retrograde skarn, chlorite-epidote vein and calcite vein cross cutting in volcaniclastic rocks, causes low temperature mineral deposit (retrograde mineral) such as epidote, chlorite, calcite, and quartz. From studying iron ore body with reflected light microscopy and electron probe micro-analyzer (EPMA), the ore body comprised of major magnetite and minor pyrite, chalcopyrite, and sphalerite. Paragenesis in iron ore has two stage. The first stage is magnetite which is main mineral. The second stage is pyrite, chalcopyrite and sphalerite veins cross cutting in magnetite.
