The Ore-forming Fluid And Mineralization Of Skarn Fe Deposits In Handan-Xingtai Area, South Hebei

Tectonically located in the middle of the North China plateform, Handan-Xingtai area is an important locality for skarn iron deposits. Currently ,more than 100 ore deposits have been discovered. With diverse shapes and different scale, the ore bodies were hosted along the contact belt between the intrusives and carbonate rocks. Folds are the dominating ore control and host structures. The ore type is monotonous magnetite. The mineralization and alteration are characterized by obvious zoning.The intermediate-acid intrusives that related to skarn Fe deposits formed two complexs: Fushan complex and Wuan complex. Fushan complex belongs to the positive emplacement mechanisrn. Within the pluton, the ore bodies show themselves as xenoliths, and there is still deep-seated metallogenic potential far away from the contact zone between the intrusives and the carbonate rock. Wu'an complex belongs to the passive emplacement mechanisrn. The xenoliths seldom occurred within the pluton, and the iron deposits are mainly hosted along the contact zone while a minority within the carbonate country rocks. The anticlines formed under the condition of the positive emplacement are the important host structure.The melt-fluid inclusions and the melt inclusions in skarn minerals were firstly discovered in this region, and their phase state, homogenization temperatures and salinity were observed and tested. The origin of these two kinds of inclusions were discussed: they were produced by the re-melting of the skarn that formed due to the original contact metasomatism.Theδ18Ovalues of the skarn minerals range from 5.3‰to 8.5‰, with 13CV–PDB values from–2‰to 11.2‰,δDV-SMOW values from–80‰to -109‰,and correspondingδ18OH2O values from 0.84‰to 8.62‰. Theδ18Ovalues of the magnetite range from from 3.7‰to 5.1‰, with 13CV–PDB values from -5.6‰to -24.9‰,δDV-SMOW values from–79‰to -156‰,and correspondingδ18OH2O values from 10.61‰to 11.41‰. It suggested that the ore-forming materials were mainly mantle-derived with a little hybridization of crustal materials.Through chronological study of Xishimen iron deposit, the 40Ar-39Ar age ofphlogopite that coexisted with magnetite shows that the main metallogenic stage occurred around 133 Ma.Plutons related to iron deposits were formed by multiple magmatic pulses. The early intrusions provided ore-forming materials during albitization, The magmatic hydrothermal solutions produced by the later intrusions were the carrier of ore-forming materials, and the compressive stress produced by hydrothermal solutions gave dynamism for the migration of ore-forming materials. Based on the mentioned above, an ore-forming model was builded.