2010 Vol. 16, No. 4

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GEOLOGICAL CHARACTERISTICS AND METALLOGENIC MODEL OF SUPER-LARGE PORPHYRY COPPER DEPOSIT IN AKTOGAI ORE FIELD, KAZAKHSTAN
CHEN Xuanhua, YANG Nong, CHEN Zhengle, HAN Shuqin, WANG Zhihong, SHI Wei, YE Baoying
2010, 16(4): 325-339.
Abstract (313) HTML (128) PDF (2038KB)(17)
Abstract:
The Aktogai ore field consists of a group of porphyry Cu-Mo-Au deposits, such as Aktogai, Aidarly, and Kyzylkia deposits, in the Balkhash Metallogenic Belt of the Central Asian Metallogenic Domain. They are formed in the Balkhash volcanic arc of the north-central margin of Kazakhstan Orocline due to the large left-leteral strike-slip movement of the Ural-Tianshan Fault System and lateral crust-growth in the Late Paleozoic. Among them, the Aktogai deposit is a superlarge porphyry Cu-Mo-Au deposit. All of them are porphyry deposits with typical zoning of wallrock alterations and mineral assemblages. The metallogenesis is mainly related to the silicification of the early-stage alkaline alteration and the redeposition in the acid alteration stage. The occurrence of ore-bodies is controlled by the E-W, ENE, and WNW trending faults. The SHRIMP zircon dating of granodiorite has given the Aktogai deposit a metallogenic age of 327.5 ± 1.9 Ma in the late period of the Early Carboniferous. The deposit model of the porphy deposits in the Aktogai ore field is concluded as "granodiorite" type in the hypabyssal porphyry copper system.
GEOLOGICAL CHARACTERISTICS AND METALLOGENIC AGE OF BORLY PORPHYRY CU DEPOSITS IN BALKHASH METALLOGENIC BELT, KAZAKHSTAN
ZHAO Hengle, CHEN Xuanhua, QU Wenjun, YANG Yi, LI Xuezhi, YANG Nong, CHEN Zhengle, HAN Shuqin
2010, 16(4): 340-348.
Abstract (182) HTML (75) PDF (806KB)(15)
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The Balkhash Metallogenic Belt in Kazakhstan, with the output of many large and superlarge porphyry Cu-Mo deposits and some quartz-vein greisen W-Mo deposits, is a very famous porphyritic Cu-Mo metallogenic belt in Central Asian Metallogenic domain. In this paper, the geological characteristics of the Borly Porphyry Cu Deposit are briefly introduced, and 2 molybdenite samples from the deposit are selected for Re-Os isotopic dating. The molybdenites from porphyritic Borly Cu-Mo deposit give average model Re-Os ages of 315.9 Ma. The Re-Os model ages of the deposit suggest that Late Carboniferous porphyry granitoid and pegmatite magmatism during Late Hercynian movement. Comparing to the Juggar-East Tianshan porphyry Cu metallogenic belt in northwestern China, the time of the Cu-Mo metallogenesis in Balkhash metallogenic belt, is between that of Tuwu-Yandong and Baogutu porphyry Cu deposits in East Tianshan and west Junggar.
GEOLOGICAL CHARACTERISTICS AND RE-OS ISOTOPIC DATING OF AKSHATAU GREISEN-TYPE W-MO DEPOSIT IN BALKHASH METALLOGENIC BELT
LI Yong, CHEN Xuanhua, QU Wenjun, WANG Zhihong, YANG Nong, CHEN Zhengle, HAN Shuqin
2010, 16(4): 349-358.
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The Akshatau disseminated Be-W-Mo deposit is a large-scale greisen-type deposit in the Balkhash metallogenic belt of Central Asian Metallogenic Domain, with typical mineral compositions, wall rock alterations, ore body shapes, and ore texture and structures of greisen-type deposit. The ore field has yielded pegmatites and quartz feldspar veins, bearing W-Mo minerals, quartz and topaz greisen. In this paper, an average molybdenite model age of 289.3 Ma has been obtained through Re-Os isotopic dating for the molybdenite samples from Akshatau W-Mo deposit, suggesting greisen-type W-Mo mineralization in the Early Permian. The Akshatau greisen-type W-Mo mineralization is considered to be the continuation of the Late Carboniferous large-scale porphyry copper-molybdenum mineralization in the Central Asian Metallogenic Domain and a product of the Late Hercynian tectono-magmatic activity in the Central Asia Orogeny.
TISSION-TRACK DATING FOR ACTIVITY OF THE LONGMENSHAN FAULT ZONE AND UPLIFTING OF THE WESTERN SICHUAN PLATEAU
YANG Nong, ZHANG Yueqiao
2010, 16(4): 359-371.
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Twelve samples of tectonites, metasediments and granites taken from the western Sichuan Plateau were dated in this study by apatite fission track dating method. The results are used to reconstruct uplifting history and fault activity of the Longmenshan tectonic belt in eastern margin of the Tibetan Plateau. It is shown that the recent activity of the two major boundary faults:the Wenchuan-Maowen fault and the Yingxiu-Beichuan fault, occurred in early Pleistocene (FT ages of 1.2~1.3 Ma); the Miyaluo fault developed in the interior of the plateau was strongly active in middle Pleistocene (around 0.5 Ma); the back Longmenshan tectonic zone started to uplift in Miocene; and the interior of the plateau began rapid uplift in latest Pliocene to Middle Pleistocene. The uplifting of the plateau caused formation of deep-incised river morphology.
MAGNETIC SUSCEPTIBILITY OF HEQING DRILL CORE AND ITS PALAEOENVIRONMENTAL IMPLICATIONS
XU Xinwen, QIANG Xiaoke, AN Zhisheng, LI Xubin, LI Peng, SUN Yufang
2010, 16(4): 372-382.
Abstract (129) HTML (49) PDF (666KB)(8)
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Located in southwestern China, the Heqing Basin received continuous lacustrine sediments of great thickness, which could be an excellent continental record for Indian monsoon. In this study, we choose the lake sediments from Heqing drill core to analyze the paleoenvironmental significance of magnetic susceptibility. By analyzing the magnetic susceptibility in combination with the response of carbonate content, Loss on Ignition (LOI), and grain size to paleoenvironmental changes, we get some useful information:1) magnetic susceptibility increase when carbonate and LOI decrease; 2) magnetic susceptibility increase with increase of < 4μm grains in lacustrine clayey sediments, and with increase of middle grain size in sections containing sands and pebbles. Based on comparison between these proxies, we conclude that magnetic minerals got into the lake mainly together with clay-sized terrestrial detritus, and magnetic susceptibility is related to the vegetation cover and rainfall in the watershed and therefore could be considered to be a good indicator for monsoon-induced erosion around lake catchments. In the warm-humid interglacial periods, due to well-developed vegetation cover in the catchment area, erosion is relatively weak and clay-sized terrestrial detritus transported into the lake are reduced, so sediments have low concentration of magnetic minerals and low magnetic susceptibility. In the cold-arid glacial periods, however, because of the vegetation development is restricted, erosion is relatively strong and more clay-sized sediments are transported into the lake, the sediments have high concentration of magnetic minerals and high magnetic susceptibility.
GEOMORPHOLOGY OF THE FUXIANHU DRAINAGE BASIN AND ITS STRUCTURAL IMPLICATION
CHENG San-you, LI Ying-jie
2010, 16(4): 383-392.
Abstract (105) HTML (194) PDF (711KB)(10)
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We took adavage of ArcGIS software platform to obtain the data of geometrical shapes and boundaries of 61 sublevel individual watersheds in the Fuxianhu drainage With SRTM-DEM as the basic data, 34 in the ridges east to Xiaojiang fault, 27 in the ridges west to the Xiaojiang fault. Afterwards, we calculated the watershed areas, perimeters, river lengths, shape indexs, average slopes, relative height differences, elevation-area integral values, the drainage branching ratios and the level of the 61 watersheds. The results show some differences between the east and west ridges. These features indicates the difference in Late Cenozoic tectonic activity on both sides of the Fuxianhu drainage and reflects the uneven uplift on east and west sides of the Xiaojiang fault zone. The activity of the Xiaojiang fault zone imposed a control over the rapid uplift of the Fuxianhu drainage during the Late Cenozoic basin, and the rapid uplift of the Central Yunnan Plateau and the difference in activity of interior of the Xiaojiang fault zone are the leading factors causing the different topographies on east and west sides of the Fuxian drainage.
PRETREATMENT METHODS FOR ANALYZING THE TOTAL ORGANIC CARBON AND NITROGEN CONTENTS OF HEQING CORE SEDIMENTS AND THEIR ENVIRONMENTAL SIGNIFICANCES
Lu Feng-yan, An Zhi-sheng
2010, 16(4): 393-401.
Abstract (53) HTML (25) PDF (555KB)(8)
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Total organic carbon content (TOC), Total organic nitrogen content (TN) and their ration (C/N) of lacustrine sediments have been widely used in the Quaternary palaeoenvironment researches. Before measuring the TOC and TN of the sediments, the first important step is to effectively remove the inorganic carbonate, and preserve organic carbon well at the same time, which is the guarantee to good experiment results and accurate palaeoenvironment reconstruction. In order to apply a proper experimental procedure to the Heqing core sediments in Yunnan province, different lithological sediment samples from different depths are used to examine the influence of pretreatment methods, including grain size, the concentration of hydrochloric acid (HCl), and the method of washing the residual acid, on the analysis of total organic carbon content. According to the results of TOC, TN, C/N, and the total inorganic carbonate content (TIC), the pretreatment procedure of Heqing core sediments prior to TOC analysis is established as the followings:under normal condition, a sediment sample is grinded to be uniform and fine (no sieving process), which reacts with enough HCl whose concentration is 2mol/L for 24 hours; then centrifugal acceleration method is employed to cleaning the treated sample by acid to be neutral. This procedure can effectively remove the inorganic carbonate from the sediments, and the results of TOC and TN show good stability and reproducibility. The obtained sequences of TOC, TN, and C/N show good correlation, which all imply the intensity changes of the southwest monsoon.
QUANTITIVELY PARTITION OF EOLIAN AND HYDROMORPHIC COMPONENTS IN LACUSTRINE SEDIMENTS: AN EXAMPLE FROM LAKE QINGHAI
DONG Jibao, AN Zhisheng, LU Fengyan
2010, 16(4): 402-411.
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This paper reports a cluster analysis on sources of Lake Qinghai sediments, and a grainsize analysis on the surface sediments of Lake Qinghai and its adjacent typical aeolian loess Based on the results, we have fitted the typical grain size distributions of the lake sediments and evaluated the proportions of eolian and fluvial components by using the grain size distributions of given end members, i. e., taking the aeolian loess sediments around the lake as eolian end-member and the surface lake sediments as fluvial end-member. The fitting result shows that the grain size distributions of Lake Qinghai sediments can be grouped into three types:1) dominated by fluvial components; 2) dominated by eolian components (aeolian loess); 3) mixture of both with different proportions. It is hopeful that this method will provide a new way for quantitively partition of different components in lake sediments and for understanding of paleoenvironment. in the future researches.
PALAEOMAGNETIC STUDY OF THE LATE CENOZOIC STRATA IN THE CENTRAL TARIM BASIN:IMPLICATION ON THE EVOLUTION OF TAKELIMAKAN DESERT
WANG Xin, SUN Donghuai, Wang fei, WU Sheng, LI Baofeng
2010, 16(4): 412-422, 411.
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High resolution magnetostratigraphy study and paleoenvironment analysis were developed to the parallel section in the central of Tarim basin. The results indicate that dry land environment with relative warm and humid climate pattern dominant in the area between 4.2~3.4Ma. The oldest in-situ eolian dun sands formed in 3.4Ma, which in turn indicate the age of Taklimakan desert. The dry climate significant intensified by 2.8Ma, consequently forming the extremely dry environment like those of present. We argue that the retreat of Para-Tethys, uplift of Tibet Plateau and evolution of Northern Hemisphere glaciations are all played key roles in the desertification of interior Asian.