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Geological, mineralogical, and oxygen isotope studies of the Chandmani Uul iron oxide–copper–gold deposit in Dornogobi Province, Southeastern Mongolia
Author(s) -
Oyunjargal Luvsannyam,
Hayashi Kenichiro,
Maruoka Teruyuki
Publication year - 2020
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/rge.12232
Subject(s) - geology , sericite , magnetite , geochemistry , pyrite , banded iron formation , epidote , chlorite , calcite , quartz , mineral , ore genesis , mineral redox buffer , isotopes of oxygen , chalcopyrite , andesite , mineralogy , sedimentary rock , volcanic rock , fluid inclusions , copper , paleontology , chemistry , organic chemistry , volcano , mantle (geology)
The Chandmani Uul deposit is located in Dornogovi province, Southeastern Mongolia. Iron oxide ores are hosted in the andesitic rocks of the Shar Zeeg Formation of Neoproterozoic to Lower‐Cambrian age. Middle‐ to Upper‐Cambrian bodies of granitic rocks have intruded into the host rocks in the western and southern regions of the deposit. The wall rocks around the iron oxide ore bodies were hydrothermally altered to form potassic, epidote, and sericite–chlorite alteration zones, and calcite and quartz veinlets are ubiquitous in the late stage. Since granitic rocks also underwent potassic alteration, the activity of the granitic rocks must have a genetic relation to the ore deposit. The ore mineral assemblage is dominated by iron oxides such as mushketovite, euhedral magnetite with concentric and/or oscillatory zoning textures, and cauliflower magnetite. Lesser amounts of chalcopyrite and pyrite accompany the iron oxides. Among all these products, mushketovite is dominant and is distributed throughout the deposit. Meanwhile, euhedral magnetite appears in limited amounts at relatively shallow levels in the deposit. By contrast, cauliflower magnetite appears locally in the deeper parts of the deposit, and is associated with green‐colored garnet and calcite. Sulfide minerals are ubiquitously associated with these iron oxides. The oxygen isotope (δ 18 O) values of all types of magnetite, quartz, and epidote were found to be −5.9 to −2.8‰, 10.5 to 14.9‰, and 3.6 to 6.6‰, respectively. The δ 18 O values of quartz–magnetite pairs suggest an equilibrium isotopic temperature near 300°C. The calculated values of δ 18 O for the water responsible for magnetite ranged from 2 to 10‰. All the data obtained in this study suggest that the iron oxide deposit at the Chandmani Uul is a typical iron oxide–copper–gold deposit, and that this deposit was formed at an intermediate depth with potassic and sericite–chlorite alteration zones under the oxidized conditions of a hematite‐stable environment. The δ 18 O range estimated implies that the ore‐forming fluid was supplied by a crystallizing granodioritic magma exsolving fluids at depth with a significant contribution of meteoric water.