Zhou J.,China University of Geasciences |
Luo Z.,China University of Geasciences |
Pan Y.,China University of Geasciences |
Li X.,China University of Geasciences
Acta Petrologica Sinica | Year: 2013
Magmatic iron deposit is not only one of the most important tvpies of iron resources in China, but also an intimate component of the Emeishan mantle plume. However, the metallogenic mechanism of magmatic iron deposit is still controversial. We investigate the vein-type iron orebody in the Heishan iron deposit as an example, and aim to unravel the genesis of vein-type iron orebody in magmatic iron deposit by zircon mineral geochemistry. Using Ti-in-zircon geothermometer and δCe-in-zircon oxygen geobarometer, the metallogenic temperature and oxygen fugacity of vein-type iron orebody are 631 ∼ 768 °C (average = 681 °C] ) and -25. 7 ∼ - 15. 6 ( average = -20. 8 ) , respectively. It is much lower than the saturation of ferro-rich magma about 400°C , and higher than the temperature of hvdrothermal fluid, which imply the "iron ore magma" is in the state of supercritical fluid dissolving numerous metal material. This conclusion is further confirmed by the CL images, discriminant diagrams of (Sm/La)N vs. La and Ce/Ce *vs. ( Sm/La)Nfor zircons. Being enriched with fluid component would effectively reduce the viscosity and density of "iron ore magma" and be beneficial to its injection, which could well interpret its irregular-shaped vein occurrence and wall-rock alteration. Based on previous studies, chemical components of the fluid component in the "iron ore magma" comprise C-H-O-S, which are enriched by magma fractional crystallization and addition of transmagmatic and surface fluid. Phase separation after injection of the "iron ore magma" triggers crystallization of Fe-Ti oxide and ore-formation. This fluid geological process is recorded by Eu anormaly in zircon. The metallogenic mechanism of the vein-type iron orebody in the Heishan iron deposit may be comparable to that of other magmatic iron deposits, including the Panzhihua-type iron deposits.