TY - BOOK

T1 - The formation of Hongge Fe-Ti-V oxide deposit hosted in layered intrusion, Emeishan large igneous province, Southwest China

AU - Wang, Dachuan

N1 - Doctoral thesis

PY - 2023

Y1 - 2023

N2 - The origin of Fe-Ti-V oxide ore layers, especially the monomineralic Fe-Ti-V oxide ores, in layered intrusions remains controversial. To reveal the Fe-Ti-V oxide mineralization processes, we had chosen the giant Hongge Fe-Ti-V oxide deposit in Emeishan Large Igneous Province, Southwest China, to carry out detailed mineralogical, petrological, geochemical and experimental research. Detailed microprobe analyses on cumulus minerals (olivine, clinopyroxene, and plagioclase) from the Hongge drill core samples had shown that a broad normal fraction crystallization trend is largely absent in Hongge intrusion. Instead, from the bottom upwards, the anorthite content (An) of plagioclase and forsterite content (Fo) of olivine show frequent reversals, indicating open magma chamber processes with frequent replenishment of more primitive magmas during the solidification. Crystallization experiments using a high-Ti basaltic composition were conducted under crustal conditions with various temperatures, pressure, oxygen fugacity, and water activity. As a result, the compositions of experimental minerals (olivine, clinopyroxene, and plagioclase) show good agreements with Hongge natural samples, convincing high suitability of high-Ti basalts as parental magmas. Moreover, according to the phase relationships obtained from the experiments, the crystallization conditions of Hongge layered intrusions can be determined at ~1150-1000 °C, 200-300 MPa, QFM-1 to +1, and relatively high water activity. Based on petrological observations and in-situ Fe isotope studies, we proposed a new magmatic-hydrothermal model to explain the formation of monomineralic ore layers. Textural evidence shows that hydrothermal dissolution and re-precipitation of Fe-Ti-V oxides were critical in forming high-grade massive ores. Furthermore, Rayleigh modeling on Fe isotopes indicates that ~20-30 % of Fe from Fe-Ti-V oxides in the lower Units was hydrothermally removed and subsequently re-precipitated into the major ore layers in the MZ, which is expected to significantly increase ore tonnages and grades, forming thick massive or even monomineralic ore layers.

AB - The origin of Fe-Ti-V oxide ore layers, especially the monomineralic Fe-Ti-V oxide ores, in layered intrusions remains controversial. To reveal the Fe-Ti-V oxide mineralization processes, we had chosen the giant Hongge Fe-Ti-V oxide deposit in Emeishan Large Igneous Province, Southwest China, to carry out detailed mineralogical, petrological, geochemical and experimental research. Detailed microprobe analyses on cumulus minerals (olivine, clinopyroxene, and plagioclase) from the Hongge drill core samples had shown that a broad normal fraction crystallization trend is largely absent in Hongge intrusion. Instead, from the bottom upwards, the anorthite content (An) of plagioclase and forsterite content (Fo) of olivine show frequent reversals, indicating open magma chamber processes with frequent replenishment of more primitive magmas during the solidification. Crystallization experiments using a high-Ti basaltic composition were conducted under crustal conditions with various temperatures, pressure, oxygen fugacity, and water activity. As a result, the compositions of experimental minerals (olivine, clinopyroxene, and plagioclase) show good agreements with Hongge natural samples, convincing high suitability of high-Ti basalts as parental magmas. Moreover, according to the phase relationships obtained from the experiments, the crystallization conditions of Hongge layered intrusions can be determined at ~1150-1000 °C, 200-300 MPa, QFM-1 to +1, and relatively high water activity. Based on petrological observations and in-situ Fe isotope studies, we proposed a new magmatic-hydrothermal model to explain the formation of monomineralic ore layers. Textural evidence shows that hydrothermal dissolution and re-precipitation of Fe-Ti-V oxides were critical in forming high-grade massive ores. Furthermore, Rayleigh modeling on Fe isotopes indicates that ~20-30 % of Fe from Fe-Ti-V oxides in the lower Units was hydrothermally removed and subsequently re-precipitated into the major ore layers in the MZ, which is expected to significantly increase ore tonnages and grades, forming thick massive or even monomineralic ore layers.

U2 - 10.15488/13303

DO - 10.15488/13303

M3 - Doctoral thesis

CY - Hannover

ER -