Petrogenesis and Fe fertility of intrusive complexes in the Han–Xing region, North China Craton: constraints from apatite geochemistry
Xian Liang^1,2, Fang-Yue Wang^1,2*, Ju-Quan Zhang^3,4*, Long Zhang^1,2, Jun-Wu Zhang⁵
1. Ore Deposit and Exploration Center, School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China
2. Anhui Province Engineering Research Center for Mineral Resources and Mine Environments, Hefei 230009, China
3. College of Earth Sciences, Hebei GEO University, 136Huaiandong Road, Shijiazhuang 050031, China
4. Hebei Key Laboratory of Strategic Critical Mineral Resources, Hebei GEO University, Shijiazhuang 050031, China
5. Mongolia Zhengyuan Co., Ltd, Jinan 250101, China

The Han-Xing (Handan-Xingtai) region is famous for its endowment of skarn iron deposits in China. These deposits are mainly spatially and genetically associated with diorite rocks, but these rocks show different Fe ore potential. Major and trace elements composition of apatite from the Kuangshan and Fushan diorite complexes were investigated to explore the potential of apatite as a proxy of petrogenesis and Fe fertility of these rocks. All the investigated apatite grains are identified as fluorapatite, which is typical for magmatic apatite. The Sr, Y, Mn, and HREE contents of apatite in the Kuangshan diorite complex are positively correlated with the increase of melt SiO₂ content compared to that in the Fushan diorite complex. Our apatite geochemical data indicate that the Fushan and Kuangshan complexes were primarily formed through amphibole fractional crystallization during deep processes, whereas the magma for the Kuangshan complex experienced extensive plagioclase fractional crystallization during shallow processes, which is more favorable for the formation of iron deposits. The F, Cl and S content of the Kuangshan complex estimated by apatite volatile (F = 2632 ppm, Cl = 4100 ppm, SO₃ = 140 ppm) is significantly higher than that of the Fushan complex (F = 2488 ppm, Cl = 3400 ppm, SO₃ = 90 ppm). The Eu, Ce anomalies, Mn, and SO₃ contents of apatite show that both of the two complexes have higher oxygen fugacity, but the oxygen fugacity of the Kuangshan complex calculated by Mn and SO₃ content (Δ FMQ + 2.41) is higher than that of the Fushan complex (Δ FMQ + 1.77), which may also be one of the reasons for the great difference in ore-forming scale between the two complexes. Our results suggest that the high volatile contents and oxidation states of magma estimated by apatite, as well as the lower Sr/Y in apatite reflect favorable conditions for skarn iron mineralization. Therefore, our study shows that magmatic apatite geochemistry may be a useful tool to distinguish the Fe fertility of plutonic rocks related to skarn deposits. 
 

apatite; Han-Xing iron deposits; magma evolution; Fe fertility; diorite complexes