Geological characteristics and age of the Dahongliutan Fe-ore deposit in the Western Kunlun orogenic belt, Xinjiang, northwestern China

Abstract

The large-scale Dahongliutan hematite-rich Fe deposit in the Tianshuihai terrane (Western Kunlun orogenic belt), Xinjiang, northwestern China, contains proven Fe ore reserves exceeding 100Mt at an average grade of 35wt.% Fe(t) (maximum 53wt.%). The deposit is hosted in the Neoproterozoic Tianshuihai Group, a suite of neritic, siliciclastic and sedimentary carbonate rocks subjected to greenschist-facies metamorphism. The Fe orebodies are laminate, stratoid, lenticular and interlayered with marbles and schists. Ore minerals mainly contain hematite, with minor siderite and limonite and rare sulfides, whereas gangue minerals mainly comprise quartz, dolomite, ankerite, calcite, muscovite and chloritoid. Most Fe ores display lepidoblastic, blastopsammitic, crystalloblastic and metasomatic textures with massive or banded structures. Based on mineral assemblages, the Fe ores are divided into four types, namely: (1) Quartz–hematite; (2) Quartz–dolomite–calcite–muscovite–hematite; (3) Quartz–ankerite–hematite; (4) Quartz–siderite–hematite.Zircon U–Pb analyses on the marbles and schists yielded a Neoproterozoic age (Ediacaran; 593±7Ma), whereas those on the ore-intruding medium-grained porphyritic biotite-quartz monzonite, medium to fine grained biotite-quartz monzonite and metagabbro yielded Cambrian–Early Ordovician ages (i.e., 484.5±2.7, 527.9±2.8 and 532.3±3.1Ma), which altogether constrain the ore formation to the Late Neoproterozoic to Early Cambrian (532–593Ma). In addition, the 163 detrital zircon analyses on the Dahongliutan marble and schist define five major age populations, namely: 2561–2329, 2076–1644, 1164–899, 869–722 and 696–593Ma. Provenance studies show that the detritals at Dahongliutan were mainly sourced from the North Kunlun and Tianshuihai terranes.Comparison with typical BIF deposits in the world, we infer that the deposit belongs to Neoproterozoic (Ediacaran) BIF-related sedimentary metamorphic type iron deposit and resembles Superior-type BIF, probably reflecting the recurrence of anoxic ferruginous conditions in the Neoproterozoic–Early Cambrian deep sea.