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GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 256-4
Presentation Time: 9:00 AM-6:30 PM

GEOLOGICAL, GEOCHEMICAL AND ORE GENETIC STUDY OF CHANDMANI UUL IRON OXIDE COPPER GOLD (IOCG) DEPOSIT IN DORNOGOBI PROVINCE, SOUTHEASTERN MONGOLIA


LUVSANNYAM, Oyunjargal1, HAYASHI, Ken-ichiro2 and MARUOKA, Teruyuki2, (1)Department of Earth and Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8572, Japan, (2)Department of Earth and Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8572, Japan

The Chandmani Uul IOCG deposit locates in south segment of the Siberian craton, and at the south rim of the Idermeg terrane. The deposit lays along SWS-NEN direction with ~1.5 km in length and consists of several lenticular ore bodies that extends 100-250 m in length and 10-30 m in thickness.

Magnetite ores are hosted in andesitic rocks of Shar Zeeg formation from Neoproterozoic to Lower-Cambrian in age. Middle- to Upper- Cambrian bodies of granitic rocks intruded into andesitic rocks. Wall rocks around magnetite ore body were hydrothermally altered to form potassic, epidote and sericitic-chloritic alteration zones and calcite and quartz veinlets.

The ore mineral assemblage is dominated by mushketovite, zoned (concentric and oscillatory) magnetite and cauliflower-shaped magnetite with minor chalcopyrite and pyrite. Among them, mushketovite is the most dominant iron ore mineral and shows prismatic aggregate with grain sizes of 0.2-3 mm. Mushketovite can be observed in whole parts of the deposit. Concentric and oscillatory zoned magnetite grains appear limitedly at relatively shallow levels of the deposit are composed from fine-grained euhedral crystals. Cauliflower-shaped magnetite grains exist locally in the deeper parts of deposit to associate with andradite and calcite. Sulfide minerals ubiquitously associate with iron oxides.

Oxygen isotope values of all types of magnetite, quartz, epidote were obtained. Delta 18O values are -5.9 to 2.8 ‰ for all types of magnetite, 10.5 to 14.9 ‰ for quartz, 3.6 to 6.6 ‰ for epidote. Delta 18O for water responsible for all type of magnetite were calculated at temperature of 3000C and values are ranging from 2 to 10 ‰.

Geological, mineralogical and geochemical data obtained in this study suggest that iron oxide deposit at the Chandmani Uul corresponds to the one of the typical occurrences of world IOCG deposits. This deposit was formed at the intermediate depth to form potassic and sericitic-chloritic alteration zones under an oxidized condition of hematite stable environment. The ore-forming fluid was supplied from granodioritic magma with significant contribution of meteoric water.

Session No. 256--Booth# 10

T46. Investigations of Hydrothermal Systems: Advances and Challenges (Posters)
Wednesday, 25 September 2019: 9:00 AM-6:30 PM
Hall AB, North Building (Phoenix Convention Center)
Geological Society of America Abstracts with Programs. Vol. 51, No. 5
doi: 10.1130/abs/2019AM-332847
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