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Geochemical characteristics and Cr metallogenic potential evaluation of the middle section of the northern margin of the Qaidam Basin |
CHEN Xi1( ), AN Zhao2( ), ZHANG Wen-Quan2, XU Yun-Fu3, MA Ying4, SHI Lian-Chang2, TAO Zhi-Hua5 |
1. No.1 Bureau of China Metallurgical Geology Bureau, Sanhe 065201, China 2. Qinghai Provincial Geological Survey Bureau, Xining 810100, China 3. Qinghai Geological Survey Institute, Xining 810100, China 4. The Fifth Geological Exploration Institute of Qinghai Province, Xining 810100, China 5. The Second Bureau of Qinghai Nonferrous Metals Geological Exploration, Xining 810100, China |
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Abstract This study extracted 59238 pieces of original data on different scales (1:50000 stream sediment surveys and 1:25000 geochemical surveys) of the middle section of the northern margin of the Qaidam Basin. Based on these data, this study conducted the superposition analysis of mathematical index statistics and multivariate statistics, aiming to discover the element association relationship and determine the major metallogenic elements in the region and provide basic support for subsequent mineral work. According to the statistics, the mathematical indexes of Au, W, and Cr in the study area show great metallogenic potential. Combined with the multivariate statistical analysis and existent metallogenic facts, the authors of this study believed that the study area has the great potential for the prospecting of chromium deposits associated with ultramafic rocks besides tectonic altered rock-type and hydrothermal gold deposits. Owing to the relatively high overall background value of local chromium (Cr) element, the traditional method using X+2σ (129×10-6) or the cumulative frequency 85% (142.9×10-6) used to delineate the anomaly threshold cannot meet the requirement for delineating local anomalies in the study area. Therefore, this study improved the anomaly threshold using the 1/4 concentration grading value (234×10-6). As a result, many anomalies exhibiting significant zonal distribution in the concentration center were delineated, and most weak anomalies were eliminated. Based on the geological, geophysical, and geochemical results, this study inferred zones favorable for the further exploration of chromium deposits and determined four favorable metallogenic zones and five prospecting areas.
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Received: 26 September 2021
Published: 27 April 2023
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Regional tectonic unit in the northern margin of Qaidam Basin (a) and geological map of the region(b) 1—Quaternary sediments; 2—Paleogene-Neogene; 3—lower Cretaceous Quanyagou formation; 4—lower-middle Jurassic Dameigou formation; 5—lower-middle Triassic Longwuhe formation; 6—lower Carboniferous Huaitoutala formation; 7—upper Devonian Maoniushan formation; 8—Cambrian-Ordovician Tanjianshan group; 9—Nanhua period Quanji group; 10—middle Proterozoic Wandonggou group;11—Paleoproterozoic Dakendaban group; 12—Paleoproterozoic Hualong group; 13—the Permian rock mass; 14—the Devonian rock mass; 15—the Silurian rock mass; 16—the Ordovician rock mass; 17—the Ordovician gabbro; 18—the Paleoproterozoic ringspot granite; 19—place names; 20—road;21—stratigraphic boundary;Ⅰ—the southern margin of Lajiishan-middle Qilian fault; Ⅱ—Zongwulong-Qinghainanshan fault;Ⅲ—Wulan-Yuka fault; Ⅳ—the fault of the north Chaidamu basin; Ⅴ—Altun strike-slip fault
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参数 | Ag | As | Au | Co | Cr | Cu | Mo | Ni | Pb | Sb | W | Zn | 青海省丰度[18] | 70.00 | 16.89 | 1.38 | 10.05 | 53.13 | 20.24 | 0.70 | 24.09 | 24.03 | 0.92 | 1.67 | 59.85 | 柴北缘丰度[18] | 69.00 | 6.04 | 1.45 | 10.93 | 72.34 | 24.89 | 0.60 | 25.98 | 25.00 | 0.34 | 1.34 | 55.80 | 最大值 | 10100 | 1668 | 11300 | 222 | 27567 | 1358 | 95 | 16212 | 6457 | 382 | 735 | 10283 | 丰度X1 | 49.77 | 7.23 | 1.92 | 15.59 | 113.20 | 30.75 | 0.85 | 40.80 | 21.37 | 0.38 | 1.89 | 61.33 | 标准差S1 | 70.40 | 16.45 | 54.00 | 11.00 | 438.50 | 27.00 | 1.32 | 107.10 | 41.40 | 1.69 | 9.14 | 71.33 | 变异系数CV1 | 1.41 | 2.28 | 28.13 | 0.71 | 3.87 | 0.88 | 1.55 | 2.63 | 1.94 | 4.45 | 4.84 | 1.16 | 背景值X2 | 45.42 | 4.11 | 0.88 | 14.45 | 55.90 | 26.50 | 0.60 | 24.90 | 18.71 | 0.26 | 0.98 | 58.43 | 标准差S2 | 11.88 | 2.47 | 0.45 | 8.50 | 34.60 | 17.00 | 0.32 | 16.40 | 6.87 | 0.14 | 0.52 | 23.42 | 变异系数CV2 | 0.26 | 0.60 | 0.51 | 0.59 | 0.62 | 0.64 | 0.53 | 0.66 | 0.37 | 0.54 | 0.53 | 0.40 | 剔除数Nh | 2423 | 7449 | 6481 | 1728 | 6303 | 3175 | 5650 | 5600 | 2136 | 6195 | 6262 | 1027 | 剔除比率R | 0.04 | 0.13 | 0.11 | 0.03 | 0.11 | 0.05 | 0.10 | 0.09 | 0.04 | 0.10 | 0.11 | 0.02 | 浓集系数N1 | 0.71 | 0.43 | 1.39 | 1.55 | 2.13 | 1.52 | 1.21 | 1.69 | 0.89 | 0.41 | 1.13 | 1.02 | 浓集系数N2 | 0.72 | 1.20 | 1.32 | 1.43 | 1.56 | 1.24 | 1.42 | 1.57 | 0.85 | 1.12 | 1.41 | 1.10 | 叠加强度D | 6.49 | 11.72 | 261.8 | 1.40 | 25.66 | 1.84 | 5.84 | 10.70 | 6.88 | 17.64 | 33.90 | 3.20 |
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Statistical table for superposition analysis of mathematical indexes of original data
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Fitting curves of concentration coefficient,abundance and rejection ratio
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The diagram of rich quantile
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Fitting graph of variation coefficients
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Superposed intensity(a) and cluster tree(b)
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元素 | F1 | F2 | F3 | F4 | F5 | F6 | Ag | 0.573 | 0.004 | 0.471 | -0.049 | 0.000 | -0.062 | As | 0.155 | -0.018 | 0.793 | 0.144 | 0.151 | 0.156 | Au | -0.060 | 0.027 | 0.868 | -0.038 | -0.054 | -0.014 | Co | 0.025 | 0.573 | 0.004 | 0.726 | -0.006 | -0.012 | Cr | 0.010 | 0.853 | -0.001 | 0.032 | -0.003 | 0.004 | Cu | 0.068 | 0.027 | 0.037 | 0.927 | 0.016 | -0.001 | Mo | 0.113 | -0.160 | 0.179 | 0.344 | 0.497 | 0.098 | Ni | 0.005 | 0.846 | 0.012 | 0.085 | 0.002 | 0.007 | Pb | 0.901 | -0.010 | 0.021 | -0.064 | 0.059 | 0.036 | Sb | 0.075 | 0.011 | 0.087 | 0.002 | 0.011 | 0.981 | W | -0.009 | 0.088 | -0.033 | -0.104 | 0.897 | -0.040 | Zn | 0.829 | 0.032 | -0.025 | 0.243 | 0.012 | 0.102 | 特征值 | 2.468 | 2.036 | 1.379 | 1.181 | 1.025 | 0.951 | 方差贡献率/% | 20.563 | 16.964 | 11.495 | 9.843 | 8.539 | 7.923 | 累积方差贡献率/% | 20.563 | 37.528 | 49.023 | 58.866 | 67.405 | 75.328 |
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Principal components of rotation factor analysis
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Factor measurement charts a—F1 factor (Pb-Zn-Ag) score chart;b—F2 factor (Cr-Ni) score chart;c—F3 factor (Au-As) score chart;d—F4 factor (Ca-Co) score chart;e—F5 factor (W-Mo) score chart;f—F6 factor (Sb) score chart;1—the Saishitengshan copper depsosit; 2—the Yeluotuoquan gold-cobalt deposit; 3—the Hongliugou gold deposit; 4—the Qinglonggou gold deposit; 5—the Longbaigou gold deposit; 6—the Tanjianshan gold deposit; 7—the Xijinggou gold deposit; 8—the Luofengpo chromitite deposit; 9—the Shuangkoushan Pt-Ag-Zn deposit; 10—the Xitieshan Pt-Zn deposit
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Geochemical map of chromium
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3D topography and geophysical section plan of abnormal area
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地区 | 靶区 | 地质特征 | 化探特征 | 物探特征 | 已发现的矿化点 | 成矿评价 | 马海 | 1号 | 大面积分布的滩间山岩群与牦牛山组呈断层接触,强蚀变橄辉岩、辉长岩大面积发育,发育多组北西向断裂构造 | 圈定2处Cr为主的异常,伴生有Ni、Au等,峰值达803×10-6,均具3级浓度分带,规模大,规律性强,重砂异常显示有铬铁矿重晶石的出现 | 极值在-344~554nT之间,化极延伸不强 | 暂未发现 | 具蛇纹石化、褐铁矿化的强蚀变橄辉岩的出现是引起物化探异常的主要原因,是铬镍成矿的有利地段 | 马海北 | 1号 | 大面积分布的滩间山岩群与牦牛山组呈断层接触,发育多组NW—SE向断裂构造,第四系覆盖较厚,偶见辉绿玢岩脉发育,第四系覆盖较厚 | 圈定7处Cr为主的异常,伴生有Ni、Au等,异常峰值在(2000~5455)×10-6之间,3级浓度分带,规模大,沿NE向次级断裂展布 | 极值达2000nT,化极上延 1000m仍有异 常反应 | 暂未发现 | 物化探异常峰值高、规模大,整体随构造方向呈现明显的规律性,地表偶见的超基性岩株出露,推断深部可能存在一条NW向的基性—超基性岩韵律层,是寻找深部超基性岩型铬铁矿的有利地段 | 2号 | 基性辉长岩大面积侵入于万洞沟群千枚岩段中,发育一条长约9.3km、宽约100~200m的超基性蛇纹石化橄榄岩,韵律明显,NW向构造为主,NE向次级断裂次之 | 圈定6处Cr为主的异常,伴生有Ni、Au、As、Hg、Ag、W、Pb等,峰值在(2000~3441)×10-6之间,3级浓度分带,规模大 | 极值-138~ 1549nT之间,强度高,梯度陡,化极上延1000m仍有反映 | 2处石棉矿化点,1处铬铁矿化点 | 断裂构造发育,热液活动强烈,成矿物质来源丰富,是寻找超基性岩型铬铁矿的有利地段 | 落凤坡 | 1号 | 辉长岩、辉橄岩大面积侵入于达肯达坂岩群中,NW向断裂发育,NE向次之 | 圈定2处Cr为主的异常,伴生有Cu、Co、Ni、Pb、W、Bi等,峰值达8591×10-6,3级浓度分带,规模大 | 2处物探磁异常显示-2179~1104nT,化极上延800m仍有反映 | 1处铬铁矿点 | 蛇纹石化的辉长岩、辉橄岩反应的规模强度均较高的物化探异常,显示了该区是寻找超基性岩型铬矿的有利地段 | 黑石山 | 1号 | 侵入到滩间山岩群之中的辉长岩大面积发育,西侧与达肯大坂岩群呈断层接触,接触带上见有超镁铁质岩呈不连续的脉状产出,多见玄武岩包体和蛇纹石化辉石橄榄岩包体 | 圈定的9处Cr异常伴生有W、Mo、Bi、Hg、Au等异常,异常峰值达1729×10-6,具三级浓度分带,规模大 | 幅值在-2179~1104nT之间,正磁异常 | 金、铜、铬铁、石棉等矿(化)点5处 | 成矿物质较为丰富,区域构造作用对成矿形成了促进到破坏再到促进的循环模式,不仅热液型元素成矿潜力较大,铬镍等基性—超基性元素成矿也较为有利 |
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Division of prospecting target areas of chromium element in the study area
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1:5 000 geophysical (a),geochemical (b) and geological (c) profile of Mahaibei No.1 target area
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