The Abagong apatite-rich magnetite deposit in the Chinese Altay Orogenic Belt: A Kiruna-type iron deposit

摘要

The Abagong apatite-rich iron deposit is located in the Kelang volcano-sedimentary basin in the southern margin of the Chinese Altay Orogenic Belt (AOB), which is an important polymetallic belt in China. The ore bodies are interbedded with the upper Silurian to Lower Devonian metamorphosed calc-alkaline felsic volcanic rocks that show well-preserved porphyritic and volcaniclastic textures. The ore mineralization is aligned along faults that controlled their emplacement and occurs as lenses, veins, and stratoids bodies that generally cut the host rocks at a high angle and show sharp contacts. The ore bodies and host rocks have undergone greenschist facies metamorphism, deformation and folding. The iron ores have massive, densely disseminated, banded, and brecciated structures. Magnetite from the Abagong deposit is low in Ti (TiO_2 = 0.002-0.129 wt.%) and the apatites from different, ore types (P-poor and P-rich ores) are typical igneous fluorapatites with minor Cl contents. Apatites of different forms and from different ore types show similar rare earth element (REE) and trace element-normalized patterns with weak-to-moderate enrichment in light REE, Th, U, and Pb, depletion in Sr, Ba, Nb, Ta, and Ti, and negative Eu anomalies, indicating a common source and genesis. The similar REE patterns for the magnetite, apatite, and volcanic host rocks suggest their close genetic linkage and support a magmatic origin for the deposit. The Abagong deposit shows the typical characteristics of Kiruna-type deposits with regard to the mineral assemblages, ore texture and structure, and the apatite and magnetite geochemistry. We propose that the Kiruna-type Abagong apatite-rich iron deposit was derived from Fe-P-rich melt through liquid immisci-bility and the activity of hydrothermal fluids.