Geological Issues

Редакцийн бүрэлдэхүүн, гарчиг болон өмнөх үг

Редакцийн зөвлөл — 2024-02-05

Геологийн асуудлууд 22 №01

Редакцийн бүрэлдэхүүн, гарчиг болон өмнөх үг

БАРУУН МОНГОЛЫН ЮРЫН ХУРДСЫН НАС, ЭРТНИЙ УУР АМЬСГАЛ, ПАЛЕОЛАНДШАФТ: ПАЛИНОЛОГИЙН СУДАЛГААНЫ ШИНЭ ҮР ДҮН

Н.ОДГЭРЭЛ — 2024-02-05

The age of Jargalant Formation in western Mongolia is changed to the middle Jurassic by Quadraeculina, Uvaesporites, main types of palynomorph group of middle Jurassic. The dominance of pollen Coniferalis (Inaperturopollenites, Quadraeculina), Cycadales (Cycadopites, Ginkgocycadoptes), Shpagnaceae (Leiotriletes), and Zygnematacea (Ovoides) in palynomorph groups indicates a warm-temperate, relatively humid seasonal climate during the deposition of Jargalant formation. Four palynomorph groups have defined as upland, lowland, riverside and aquatic conditions. Based on the palynomorph group definition of ancient plants accumulated in intracontinental, intermontane lowland along banks of riverlake system in seasonally dry-humid climate, we reconstruct the flattened paleolandscape. Western Mongolia had a humid and warm environment during the Mesozoic (until the early Cretaceous), therefore fluvial erosion and accumulation were predominantly responsible for basin sedimentation.

ТЭЛМЭН НУУРЫН МОРФОМЕТРИЙН ОНЦЛОГ, ХОТГОРЫН МОРФОЛОГИ, ГАРАЛ ҮҮСЭЛ

Э.АЛТАНБОЛД — 2024-02-05

Studies of paleoclimate change based on the sediments of Lake Telmen have been conducted. We present the morphometric characteristics, depression origin of the Telmen Lake, Western Mongolia. In the study, the morphometric analysis, spatial improvement method, hypsometric curve method, Geophysical magnetic mapping, and AWEI index were used to determine the pattern of lake depressions. The depression of the Telmen Lake formed as a blocksubsidence by faults. Lake water is likely to relate to underground water, which level cutted by fault. Climate change and permafrost studies show that water area and volume of the Telmen Lake are not changed through Central Asia warming and drying in last two decades.

БОРЗОНГИЙН ГОВЬ-50 ТӨСЛИЙН ТАЛБАЙН ХАЛЗАН-УУЛ БҮРДЛИЙН U-PB (SHRIMP IIe) НАСНЫ СУДАЛГАА

Б.ЭНХБАТ — 2024-02-05

The Khalzan-Uul granite complex occurs in the western part of the Tsagaan Uul block, South Mongolia, intruding the Permian Lugiingol Formation, which is mainly composed of terrigenous sedimentary rocks. The granite complex occupies an area of 60 km2 with an oval outline and consists mainly of leucocratic granite, biotite granite, and alkali granite. The main constituent minerals of the granitic rocks are K-feldspar, quartz, plagioclase, and mica, and accessory phases are titanite, apatite, zircon and opaque minerals. Sericite, pelite, albite, chlorite, and epidote are secondary phases. A granite sample is selected for the SHRIMP IIe zircon U-Pb age dating. The zircon sample was photographed in SEM images, back-scattered (BSE) and cathodoluminescence (CL) images that are used to examine the internal texture of the analyzed zircons and with petrographic observations guided the selection of analytical spots, using a JEOL JSM-6610LV scanning electron microscope at KBSI (Korea Basic Science Institute). High-precision data on U and Th contents and Th/U ratios of zircon were obtained using a SHRIMP IIe housed at KBSI.

A total of 24 spot analyses were made on 20 zircon grains. 15 spots of them analysed yield a weighted mean 206Pb/238U age of 223.3±2.3 Ma (MSDW=3.3) which correspond to the late Trassic Т3 (Norian). The igneous origin zircons have Th/ U>0.30 ratios (Hoskin and Schaltegger, 2003), and the zircon SHRIMP U–Pb dating results are listed in Table 1, and related concordant diagrams are shown in Fig. 5. The sample images on the CL have an oscillatory zone that is narrow. It indicates that zircons were formed in the felsic rocks.

УВС АЙМГИЙН ӨНДӨРХАНГАЙ СУМАНД ОРШИХ ДЭЛТИЙН CU-NI-ИЙН ИЛРЭЛИЙН БОДИСЫН БҮРЭЛДЭХҮҮНИЙ СУДАЛГАА

Э.НАРАНГЭРЭЛ — 2024-02-05

A newly discovered the Delt occurrence cropping out in the northwestern part of the Zavkhan terrane nappefold megazone, composed of NW trending small tectonic blocks of amphibolite, granite-gneiss, schist, intruded by small reddish granite and diorite bodies and dykes of gabbro, gabbro-diorite. The main constituent minerals of the gabbro are plagioclase (40-45%), pyroxene (20-25%), olivin olivine (15-20%), amphibole (5%), biotite (5%), opaque minerals are magnetite, pyrrhotite, pentlandite, chalcopyrite, chromite, chalcocite, covellite, hematite, and accessory phases are apatite. The analysis was made using an X-ray Diffraction Instrument at Panalytical X’pert pro and Olympus BX-53, Motic BA310-pol at the the Geological Center for Research and Analysis and the Department of Geology and Geophysics of the School of Arts & Sciences, National University of Mongolia. The gabbro has Fe, Ni Cu, and Cr ore mineralization. The samples contain magnetite, pyrrhotite, pentlandite, chalcopyrite, chromite, and small amounts of sphalerite, covellite, and hematite as inclusions in host rocks or gangue minerals. Wide and narrow small veins and small discontinuous inclusions of second-type magnetite are formed around the serpentinized olivine. Based on the ore microscopic study, we can conclude that there is Fe, Ni Cu, Cr ore mineralization associated with ultramafic and mafic rocks.

ХОЙД ЭЛДЭВИЙН ОРДЫН НҮҮРСНИЙ ПЕТРОГРАФИЙН НАЙРЛАГА, ЧАНАРЫН СУДАЛГАА

Б.ЦЭРЭНБАТ — 2024-02-05

North-Eldev coal deposit is located in ChoirNyalga coal-bearing basin of the eastern Mongolia. Coal seams are hosted in middle Jurassic sediments. This study presents geological setting, deposit coal quality and petrograph study of North Eldev coal deposit. The results show that the coal of North Eldev deposit composed of three microlitotypes including 74.6-94.0% vitrinite, 1.5-12.5% inertinite, 0.1-1.8% liptinite and of 0.6-13.5% inorganic matters. Vitrinite reflectance (Rr) of coal is ranged from 0.38 % to 0.45%. Moisture is 8.34 to 10.12%, ar basis and volatile matter content 33.3 to 49.7%, daf basis. Ash content of Seam IV ranges from 25.6 to 29.5% (ar basis), whereas that of Seam II, III are low, ranging from 28.04-34.04 to 31.25% (ar basis). The calorific values of Seam II, III, IV range from 4926.18-5292.06, 4792.37, 4975.95-5198.95 to kcal/kg (ar basis). Total sulphur contents of the all three seams are low (1.34 to 2.35%, ad basis). The coal of North-Eldev deposit is classified as Long Flame coal according to Mongolian standard.