Earthquake is currently one of the biggest concerns in Vietnam, especially, when a number of earthquakes recorded by seismometers in recent years imply the danger of earthquake in the country. In Vietnam, the recorded earthquakes were pinpointed as the consequence of stratigraphic movements along active fault zones. Identifying of the activities of fault is mainly based on tectonics, geomorphology and observation techniques utilizing geophysical methods with data on seismic waves of earthquakes. However, determining the active fault intervals is generally a difficult task which is of the interest of many domestic and worldwide scientists. One of the methods of identifying the active intervals of faults that has been applied in many countries is studying authigenetic clay mineral forming in fault planes and cataclasites due to fault activities. The movement of fault surface will create fault gouges formed at low temperature, the typical of which is illite mineral. In order to date active phases of faults, K-Ar dating of illite mineral is now proved to be an effective method. Based on the successful studies on modern fault activities using the method of K-Ar dating of authigeneticillite, and with the goal of having a general view on the activities of Red Rive Fault, Vietnam and more information on earthquakes caused by this fault, the authors have conducted a study on characteristics of the authigenetic clay minerals formed by fault activities, accordingly identifying their formation periods using K-Ar dating method. Based on the recorded ages, we hope to be able to explain the active fault intervals and its relationship with earthquake activity in the surround areas. In this paper, we are presenting the initial results about characteristics of clay minerals in gouges of the Red River fault zone, Vietnam. Several gouges amples were collected from the Red River fault zone. Then, they were separated into four grain-size fractions (<0.1, 0.1 - 0.4, 0.4 - 1.0, and 1-2µm) using standard gravitational settling and high-speed centrifuging techniques based on a preliminary analysis. The samples after separating were characterized by using FTIR spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The results indicated that authigenetic clay minerals forming in fault planes due to fault activities such as illite, illite/smectite is in samples with significant amounts. These are important results in defining modern active time of Red River fault zone using method of K-Ar dating for authigenetic clay minerals.
Studying sediment provenance in the marine environment particularly plays an important role in interpretation of paleoclimate, lithology of the source regions as well as tectonism controlling weathering, erosion, transportation, and deposition processes (source-to-sink analysis). However, defining sediment sources and controlling elements require quantitative data and micro-analysis as they are influenced significantly by many factors such as lithology, tectonics, and climate condition in the source regions as well as sea-level changes, oceanic circulation, and their differential setting in the sea. A number of methods are employed to elucidate sediment provenance, but not all of them are useful in the East Sea. In this study, clay mineralogy and Sr-Nd isotope of sediment cores and surrounding river sediments in this region from previous studies are reused to evaluate their effectiveness in determining sediment provenance. In comparison between sediment cores and river sediments indicates that clay mineral assemblages and Sr-Nd isotopic composition of river sediments frequently contain feature information of the source regions that are preserved in marine sediments well, implying they contain valuable information of sediment provenance. Thus, these methods have been widely utilized to identify sediment provenance in the East Sea. This study displays that sediment provenance methods based on clay mineralogy and Sr-Nd isotope are effective tools in elucidating sediment provenance in the East Sea.
Ban Lim area in Cao Bang province has proposed a high potential of lead-zinc resources, which have occurred in different rocks of geological formation. The paper-based on collecting, synthesizing, and geological processing data. In addition, mathematical methods were also applied to recognize studied objects of the exploration process using a quantitative description. The results how that the lead-zinc orebodies in Ban Lim area mainly occurred in lens-shaped and distributed in layered surfaces of the dolomitized limestone of Coc Xo formation. The average lead-zinc content of the orebodies is in a range from 3.27% to 8.33%; its coefficient of variation (Vc) is in a range from 13.71% (evenly) to 137.92% (very unevenly). Generally, the lead-zinc contents of the orebodies in Ban Lim area mainly comply with the standard normal distribution. The average thicknesses of the orebodies are in a range from 0.92 m to 6.48 m, its coefficient of variation (Vm) is in the range from 8.7% (stable) to 132.95% (very unstable). Quantitative calculation results have shown that Ban Lim lead-zinc deposit belongs to group III of deposits. For the exploration of this type of minerals, it is recommended to use a linear grid pattern. Appropriate exploration grid pattern for the 122 category reserve is (60÷80) m × (30÷40) m. These calculated results are well- documented foundations that allow suggesting a mining group of deposit and an exploration grid pattern for lead-zinc ore in Ban Lim area and other lead-zinc deposits occurring in similar geological settings.
One of the most important achievements of applying radioactive isotope in the geological study is to determine the age of mineralization. Based on the synthesis, comparison, and evaluation of the popular isotopic systems in dating mineralization, the Rb - Sr, Re - Os, and Ar - Ar dating methods are discussed in this study. The results show that the Rb - Sr dating method is likely to be successfully applied to sulfide mineralization. If the mineralization contains little or no sulfide minerals, then the method is applied to other minerals in an ore mineral association. The Re - Os dating method has shown great success when it is applied to hydrothermal deposits, especially for the molybdenite - bearing vein deposits. The limitation of the method is that when the concentration of the Os element in molybdenite is low, it is difficult to establish the Re/Os ratio in a single mineral. The Ar - Ar isotope system for dating mineralization often uses mica or feldspar minerals, which are minerals with blocking temperatures ranging from 150÷350 0C, and later metamorphic periods have higher than 350 0C often overprinted these minerals. Generally, tectonic, magmatic, and metamorphic events, which occur after mineralization, can cause difficulty in determining the age of mineralization and collecting analysis samples.
Tuong Duong area, Nghe An province is considered as a high potential area of gold deposits such as the Yen Na - Yen Tinh, Ban Bon, Xieng Lip, and Na Khom gold occurrences. Based on synthesizing, geological processing data, analysis and complement of the 15 thin sections, 10 thick sections, 02 scanning electron microscope and 05 ICP - MS samples, results show that the gold mineralization has fomed from hydrothermal activities at low - moderate temperature, belonging to quartz - sulfur - gold mineral deposit type. The gold contents in orebodies vary from medium to high values, with average contents ranging from 0.8÷6.55 (g/ton). Results also provide an overview of the prospect of gold resources, serving as a basis for determining the Au prospective areas in Tuong Duong, Nghe An province. The direct calculation method for metallization parameters and Huvo methods are applied in this paper to estimate gold resources in the study area, resulting in 2.21 tons of Au - metal.
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