318 Economic Geology (Posters)

Wednesday, 28 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

GEOLOGICAL AND GEOCHEMICAL STUDY ON VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN WESTERN MONGOLIA

Paper number: 318-4
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Recent mineral exploration and geological researches in western Mongolia reveal several volcanogenic massive sulfide (VMS) deposits and their occurrences. These VMS deposits mostly occurin Mongol-Altai and Gobi-Altai VMS belts, and some deposits in Han Hohii VMS belt.In this paper, we focus on the Dulaan Khar VMS deposit with comparative study for some VMSDs in those belts. The Dulaan Khar VMS deposit occurs in the margin of a volcano-tectonic caldera containing the Early to Middle Devonian Dulaan Khar formation that consists of rhyolitic tuffs and lava flows, sandstone, rhyo-dacitic porphyries, and basaltic dikes in Mongol-Altai belt.

Ore minerals in this deposit are mainly sphalerite, galena chalcopyrite and pyrite. Framboidal pyrite and chalcopyrite disease textures in sphalerite are remarkable in the ores. The alteration processes of the host rocks are silicification, chloritization, sericitization and carbonatization. The δ34S values of sulfide minerals for sphalerite, galena and framboidal pyrite of the Dulaan Khar VMS deposit range from +4.3‰ to +5.6‰.

Geochemistry of the host rocks is discussed from the data of 34 volcanic rocks in Dulaan Khar and in some other deposits in western Mongolia. Those data show clear compositionally bimodal characteristics ranging from 43.7 to 52.3% SiO2, and from 55.1 to 74.6% SiO2. Chondrite normalized patterns of REEs and other trace elements show relatively lightly LREE-rich characterisitics with some negative Ti anomalies. LREE concentration of the Dulaan Khar rhyolites is higher than others rhyolite and similar to dacite from Ezuri Kuroko deposit, Japan. All mafic rock data are plotted on the Zr/Y-Ti/Y discrimination diagram suggesting plate margin basalt field.

Least altered felsic rock samples are mostly plotted in calc-alkaline rhyo-dacites (FII) and rhyolites (FIIIa) field of Lesher et al. (1986), those two fields suggested to the higher potential for VMS deposits. From our geochemical research we conclude that those western Mongolian belts have a higher mineralization potential for VMS deposits.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-284718

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