40Ar-39Ar Dating of Albite and Phlogopite from Porphyry Iron Deposits in the Ningwu Basin in East-Central China and Its Significance

40Ar-39Ar dating of albite from the Meishan and Taocun iron deposits yields plateau ages of 122.90±0.16 Ma and 124.89±0.30 Ma, and isochron ages of 122.60±0.16 Ma and 124.90±0.29 Ma, respectively. Phlogopite from the Zhongshan-Gushan ore field has a plateau age of 126.7±0.17 Ma and an isochron age of 127.21±1.63 Ma. Analysis of regional geodynamic evolution of the middle-lower Yangtze River region suggests that the porphyry iron deposits were formed as a result of large-scale lithosphere delamination and strong sinistral strike-slip movement of the Tancheng Lujiang fault zone. The copper, molybdenum and gold deposit system in the middle-lower Yangtze River region was formed during the stress transition period of the eastern China continent.

Late Mesozoic Ore-forming Events in the Ningwu Ore District, Middle-Lower Yangtze River Polymetallic Ore Belt, East China: Evidence from Zircon U-Pb Geochronology and Hf Isotopic Compositions of the Granodioritic Stocks

Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district （Cretaceous basin） of the middle-lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed： one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic （-granitic） rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization （typically for zircons） ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131-127 Ma. In situ zircon Hf compositions of εHf（t） of the granodiorite are mainly from -3 to -8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.

Geochemistry of Apatite from the Apatite-rich Iron Deposits in the Ningwu Region,East Central China

Four types of apatite have been identified in the Ningwu region. The first type of apatite is widely distributed in the middle dark colored zones （i.e. iron ores） of individual deposits. The assemblage includes magnetite, apatite and actinolite （or diopside）. The second type occurs within magnetite-apatite veins in the iron ores. The third type is seen in magnetite-apatite veins and （or） nodules in host rocks （i.e. gabbro-diorite porphyry or gabbro-diorite or pyroxene diorite）.The fourth type occurs within apatite-pyrite-quartz veins f＇dfing fractures in the Xiangshan Group. Rare earth elements （REE） geochemistry of apatite of the four occurrences in porphyry iron deposits is presented. The REE distribution patterns of apatite are generally similar to those of apatites in the Kiruna-type iron ores, nelsonites. They are enriched in fight REE, with pronounced negative Eu anomalies. The similarity of REE distribution patterns in apatites from various deposits in different locations in the world indicates a common process of formation for various ore types, e.g. immiscibility. Early magmatic apatites contain 3031.48-12080 ×10^-6 REE. Later hydrothermal apatite contains 1958 ×10^-6 REE, indicating that the later hydrothermal ore-forming solution contains lower REE. Although gabbro-diorite porphyry and apatite show similar REE patterns, gabbro-diorite porphyries have no europium anomalies or feeble positive or feeble negative europium anomalies, caused both by reduction environment of mantle source region and by fractionation and crystallization （immiscibility） under a high oxygen fugacity condition. Negative Eu anomalies of apatites were formed possibly due to acquisition of Eu^2＋ by earlier diopsite during ore magma cooling. The apatites in the Aoshan and Taishan iron deposits yield a narrow variation range of ^87Sr/^86Sr values from 0.7071 to 0.7073, similar to those of the volcanic and subvolcaulc rocks, indicating that apatites were formed by liquid immiscibility and differentiation of intermediate and basic magmas.

Ecological Security Assessment in County Area Based on P-S-R Model——A Case Study of Ningwu County,Shanxi Province

To further understand the status quo and change tendency of ecological security in county area, we took the example of Ningwu County, the headstream of Fenhe River, confronting serious eco-environment problem and considerable human impacts. Taking Ningwu as the study area and using variation coefficient method to determine the weights of the indices, we built ecological security pattern based on Pressure-State-Response （P-S-R） Model of Organization for Economic Cooperation and Development. The ecological security status was evaluated by calculating eco-security index （ESI） with socio-economic statistical data of Ningwu during 2001 -2010. The results showed that the situation of eco-security had been improved from heavy alarm to relative safety during 2001 -2010. It reflected that the ecological economic system in Ningwu County tended to be relaxed constantly after experienced a sharp conflict between ecological environment and economic growth. The ecological safety awareness was growing, however, by force of the objective requirements of population growth and economic development, the situation of ecological security was still unstable.

Geochemical characteristics and genesis of volcanic and sub-volcanic rocks from porphyrite-type iron deposits in Ningwu metallogenic province,eastern China:Constraints from elements

Ningwu porphyrite-type iron deposits are located in Ningwu Mesozoic volcanic basin,which belongs to the middle and lower reaches of the Yangtze River metallogenic province.The volcanic rocks can be divided into Longwangshan,Dawangshan,Gushan and Niangniangshan Formations from early to late.All these volcanic rocks are rich in alkali,and show the similar patterns in rare earth element(REE) distribution.However,some differences can be found in the trace elements and REE patterns.The study of petrology and REE geochemical characteristics shows that these rocks are derived from the underplating of the lithospheric mantle and are contaminated by crustal materials,undergo AFC process during the magmatic evolution.

宁芜矿集区多阶段火山作用岩浆源区的转变:来自侵入岩锆石Hf-O同位素特征的记录

宁芜玢岩型铁矿矿集区是中国东部重要的铁矿矿集区之一。宁芜矿集区在早白垩世135~126 Ma间连续发育了成分和源区相似的4组火山作用旋回,并伴随有两大类侵入岩发育:一类为辉石闪长玢岩-闪长玢岩,与玢岩型铁矿床的形成密切相关,主要发育于大王山火山旋回晚期(约131 Ma);另一类为花岗岩类侵入岩,形成于铁矿化之后,成岩时代与姑山和娘娘山火山旋回相近(130~126 Ma)。两类侵入岩源区的差异与联系目前尚未揭露。本次研究通过对两类侵入岩锆石年代学、Hf-O同位素特征的研究,区分了不同侵入岩源区差异。结果表明,与成矿母岩同旋回侵入岩锆石的δ^(18)O集中于6.0‰~6.5‰,εHf(t)集中于-6.0~-5.0;成矿后形成的花岗岩类侵入岩锆石的δ18O集中于7.0‰至8.0‰,ε_(Hf)(t)分布于-8.7~-1.2。结合前人研究,区内岩浆活动存在有富集地幔、太古代地壳和新元古代地壳3个岩浆源区,4个火山作用旋回的岩浆源区在130 Ma左右发生了改变。130 Ma之前的龙王山和大王山火山旋回的岩浆岩源区主要为受太古代地壳混染的富集地幔,而130 Ma之后的姑山和娘娘山火山作用旋回的岩浆岩源区主要为受新元古代地壳混染的富集地幔。多阶段火山作用中只有大王山旋回的闪长玢岩与玢岩型铁矿的形成有关。相比较其他火山旋回,大王山旋回具有更高的富集地幔组分以及更少的新元古代地壳的混染。因而,岩浆中较高比例的富集地幔含量是控制玢岩型铁矿形成的关键因素之一。

宁武盆地南部深部煤层气临界深度与成藏特征

近年来,随着深部煤层气勘探开发技术的不断突破,深部煤层气已逐渐成为中国油气资源重要的勘探开发新领域。但是,关于煤层气深度界线的科学内涵、深部煤层气藏的地质特征、煤层气富集模式等基础科学问题仍处于初期探索阶段。为此,以宁武盆地宁武南区块上石炭统太原组9号煤层为研究对象,基于区块20余口煤层气井的钻井、测井及试井资料等,联合等温吸附、气体同位素等实验测试手段,探讨了宁武南区块深部煤层气临界深度与成藏特征。研究结果表明:①研究区深部煤层气临界深度为1200 m,临界深度以深,深部煤层气藏具有煤层厚度大、热演化程度高、含气量及含气饱和度高、煤体结构好和孔隙度低的地质特征。②地温梯度和热演化程度是影响研究区深部煤层气临界深度及煤层气成藏条件的重要因素。结论认为,该盆地的宁武南区块深部煤层气地质特征与鄂尔多斯盆地大宁—吉县、临兴、延川南等深部煤层气区块具有可比性,展现出宁武盆地深部煤层气良好的勘探开发前景。

SHRIMP dating of volcanic rocks from Ningwu area and its geological implications

The SHRIMP U-Pb ages are reported for two volcanic rocks from the Longwangshan and the Dawangshan formations respectively, Ningwu area, Jiangsu Province. The Dawangshan formation (NB-01) is dated at (127 3) Ma, and the Longwangshan formation (NL-01), (131 4) Ma. Besides, a few Archean zircons are also found in the Longwangshan formation, which suggests a possible Archean basement in the region.

宁芜盆地娘娘山早白垩世黝方石响岩中黑云母逆反应边结构:岩浆混合触发火山喷发的矿物学证据

矿物的不平衡结构是岩浆混合、不平衡结晶以及岩浆-流体交代等过程的重要指标。在长江中下游宁芜盆地娘娘山破火山口的早白垩世娘娘山组黝方石响岩中,黑云母斑晶发育了罕见的逆反应边结构,即在黑云母边部出现由角闪石及辉石等镁铁质矿物组成的反应边,但对其成因长期以来缺少深入研究。文章通过详细的岩相学研究和电子探针分析等手段,查明宁芜盆地娘娘山组黝方石响岩中具逆反应边结构的黑云母具有核-幔-边结构,其核部为原生黑云母,靠近逆反应边的幔部为高温熔蚀再平衡结晶成因的黑云母,边部为角闪石。黑云母及角闪石的温压计算及其地球化学特征表明,黑云母结晶温度为807~862℃,压力为231~369 MPa;相比之下,“逆反应边”中的角闪石结晶温度为920~949℃,压力为271~309 MPa,其寄主岩浆化学组成类似于亚碱性系列的基性岩浆,较黑云母寄主岩浆更偏基性。黑云母与“逆反应边”中角闪石结晶的物理化学条件差异表明,这种特殊的“逆反应边”结构是早期碱性岩浆与晚期基性亚碱性岩浆混合的结果。矿物CSD计算表明,反应边的形成可能仅先于火山喷发一个月左右,暗示岩浆混合可能是导致火山喷发的重要诱因。

宁武盆地深部煤储层地温场特征及其对含气性的影响

温度是影响深部煤储层含气性的重要因素,继而影响深部煤层气的开发效果。因此,明确煤储层地温条件及其对深部煤储层含气性的影响是系统认识深部煤层气富集特征及生产规律的关键。宁武盆地太原组9号煤层埋深大于1000 m的面积占比超过90%,盆地腹部煤层埋深基本大于1500 m,最大埋深超过2500 m,属于典型的深部煤层气。以宁武南区块为例,基于井温测井数据、实验测试数据、录井资料及试井资料,确定宁武南煤储层地温场特征及其对含气性的影响效应。结果显示,宁武南区块9号煤储层温度为15.5~40.1℃,与煤层埋深具有显著的正相关性,地温梯度为1.27~1.95℃/hm,平均为1.52℃/hm,显示出低地温场特征。研究区煤储层含气饱和度为40.1%~93.7%,平均为71.7%,显示出深部煤储层低含气饱和度的特征。随着埋藏深度的增加,较低的地温梯度使得研究区煤储层温度增加缓慢,导致在相似埋深下,温度对研究区深部煤储层吸附能力的负效应显著低于大宁-吉县、临兴等深部煤层气区块,使得研究区煤储层吸附气向游离气的转换深度加深且转换比例降低。低地温条件是影响研究区深部煤层含气性的重要因素之一,继而影响其可开采程度。在深部煤层气的勘探开发中应重视煤储层地温条件的研究。

2000-2020年山西省宁武县生态系统服务价值时空动态研究

生态系统服务价值(ESV)时空动态研究对生态修复工程的评价、生态修复空间的准确识别和生态安全格局建设具有重要意义。收集宁武县2000-2020年5期的土地覆被类型数据,应用价值当量因子法量化ESV,运用网格分析法、热点分析法研究其时空变化规律,同时运用相关性分析法分析ESV变化影响因素。结果表明:(1)宁武县近20 a年均ESV为169032.41万元,2000-2020年ESV增加了5.80%;5期ESV总体呈现先下降后上升波动变化,2020年4个一级生态服务功能指标都有增加,比例为调节服务(20.23%)>文化服务(18.63%)>支持服务(18.36%)>供给服务(14.56%);(2)14个乡镇5期ESV空间分布较为一致,呈聚集型,高值集中分布在县域西部和东北部山区,低值分布在县域中间的汾河及恢河流域;(3)2000-2020年,ESV变化的冷点区和热点区分别占研究区面积的10.14%和9.30%。冷点区主要分布在汾河流域和恢河流域中部,热点区分布在县域中部及东部,在生态修复中应予以重视。此外,热点区所占比例呈上升趋势,表明各类生态修复项目的生态功能逐步提升;(4)相关性分析表明,针叶林、灌木、灌草和湿地这4类土地覆被类型对提升宁武县ESV有重要意义,自然因素中坡度、高程、降水与ESV呈显著正相关。

宁武县汾河流域矿山环境生态修复理论及实践研究

宁武县地处汾河上游,煤炭资源丰富,开采历史悠久,但开采方式粗放,导致地质灾害频发、环境破坏,影响水资源补给体系和区域植被生境。本文结合现状问题调查结果,从治理策略和工程措施实践两个方面总结宁武县汾河流域矿山环境生态修复的方法,以期为我国流域矿山修复提供借鉴。

Ningwu——An Ancient Pass On The Plateau

Ningwu situated on the Loess Plateau in north of Shanxi Province is one of the three passes along the Great Wall. The other two are the Pian Pass in the west and the Yanmen Pass in the east. In the ancient times, it had been a key military town in the northern Chinese borders.

Activation of northern margin of the North China Craton in Late Paleozoic:Evidence from U-Pb dating and Hf isotopes of detrital zircons from the Upper Carboniferous Taiyuan Formation in the Ningwu-Jingle basin

LA-MC-ICPMS U-Pb dating has been performed on detrital zircons from the Upper Carboniferous Tai-yuan Formation (N-8) in the Ningwu-Jingle Basin, west of the North China Craton (NCC). The ages of 72 detrital zircon grains are divided into three groups: 303―320 Ma (6 grains), 1631―2194 Ma (37 grains, peaked at 1850 Ma), 2318―2646 Ma (29 grains, peaked at 2500 Ma). Detrital zircons of Group 2 and Group 3 were likely derived from the basement of the NCC. Group 1 zircons exhibit 176Hf/177Hf ratios ranging from 0.281725 to 0.282239, with corresponding negative εHf(t) values of -12.4―-30.3 and old Hf model ages of 1.4―2.2 Ga. These characteristics show a strong resemblance to those of Carboniferous igneous zircons from the Inner Mongolia Paleo-uplift (IMPU) on the northern margin of the NCC, but differ significantly from those of the Xing-Meng Orogenic Belt, suggesting that the source of the Tai-yuan Formation partly came from the IMPU. All detrital zircons of Group 1 have relatively high Th/U ratios (> 0.67), indicating a magmatic origin. The mean age (304 ± 6 Ma) of the two youngest grains is close to the depositional age of the Taiyuan Formation, suggesting a strong tectonic uplift and magmatism in the IMPU during the Late Carboniferous. This paper provides important geological evidence for the activation of the northern margin of the NCC in the Late Paleozoic.

宁芜盆地大岭岗金铜矿床地质特征及找矿前景

宁芜盆地发育一系列与火山—岩浆侵入作用有关的热液脉型金铜矿床(点),大岭岗金铜矿床属区内该类矿床。矿体主要赋存于NNW向张扭性断裂带中,呈脉状、复脉状、透镜状产出。大岭岗金铜矿床的蚀变和矿化划分为三个阶段:早期石英阶段、中期石英碳酸盐硫化物阶段和晚期石英碳酸盐重晶石阶段。大岭岗金铜矿床与燕山晚期岩浆活动有着密切的联系,岩浆发展的晚期阶段,从次火山岩(闪长玢岩)中分离出来的富含S、Cu、Fe、Co、Au等元素热液沿着断裂带及其派生的次生裂隙流向各方,与安山质火山岩中的水溶液或下渗的大气水混合,萃取地层成矿物质,使之活化转移,在有利的环境中富集成矿。大岭岗金铜矿床属次火山岩中低温热液脉型金铜矿床。大岭岗金铜矿区成矿地质背景良好,成矿条件优越,通过攻深找盲,寻找新的工业矿体的潜力巨大。

宁武盆地及周缘岩体裂变径迹对山西地块中——新生代构造演化的约束

宁武盆地及周缘岩体的抬升剥蚀对于山西地块中—新生代构造演化具有重要的指示意义。本文对宁武盆地及周缘岩体进行裂变径迹分析,磷灰石裂变径迹年龄97~47 Ma,锆石裂变径迹年龄161~141 Ma。裂变径迹记录了早白垩世早期(145~125 Ma)、晚白垩世(85~70 Ma)、古新世晚期—始新世早期(59~53 Ma)和渐新世晚期(28 Ma)的4次抬升剥蚀事件。综合分析山西地块的裂变径迹数据,表明隆起区晚古生代以来发生了多期抬升剥蚀事件。山西地块中—新生代构造演化具有时空差异。周缘岩体样品的裂变径迹年龄大于盆地内沉积地层样品的年龄,指示了周缘山体先于盆地抬升剥蚀。晋东北抬升剥蚀时限早于晋西南。山西裂谷系西南端裂开较早。裂谷系发育具有由南向北扩展的特征,这与地层保留记录相一致。山西地块现今地貌格局是在中生代发育一系列雁行状排列的复背斜和复向斜构造基础上发展而成的。

宁武煤田2号煤中镓的富集与赋存特征

宁武煤田是我国典型的煤伴生资源丰富的煤炭基地。为研究煤中Ga的成矿规律,从宁武煤田2号煤中采集了117个煤样,通过工业分析、X射线衍射、扫描电子显微镜、X射线荧光光谱、电感耦合等离子体质谱和逐级化学提取实验对样品进行测试分析。结果表明宁武煤田2号煤中Ga的平均含量为30.93μg/g,整体上属于轻度富集—富集。逐级化学提取的结果显示煤中Ga的赋存以残渣态为主,占比87~92%,其次为有机态,占比6%~10%。由煤中Ga与煤质和常量元素的相关性分析认为,高岭石、勃姆石等黏土矿物是煤中Ga的主要矿物载体,黏土矿物对Ga的吸附是2号煤中Ga富集的主要原因。

芜湖市夏家庄铁矿床矿化特征及成因分析

夏家庄铁矿床是宁芜矿集区西南部雍镇矿田内的代表性铁矿床,但有关夏家庄矿床的成因研究目前还比较薄弱,阻碍了对雍镇矿田的认识。通过该区内区域地质特征、矿床地质特征及其他找矿信息的阐述,结合矿区地质工作成果,详细分析了成矿物质来源和成矿环境,总结了矿床成因。研究发现,岩浆岩与围岩接触带构造中的岩凹构造是本区主要的控矿构造;膏盐层为后期矿质沉淀提供有利空间,是研究区重要成矿特征;寻找下接触带磁铁矿体是本区下一步找矿方向之一。

宁芜火山岩盆地及周缘重磁场多尺度边缘检测与地质意义

宁芜火山岩盆地位于长江中下游成矿带,在盆地内发育了以玢岩型铁矿为主的宁芜矿集区,是中国重要的铁矿资源基地。经过多年勘探和开发,浅部矿床基本已经查明,深部找矿已经成为解决接替资源这一突出问题的主要方向。但受火山岩和第四系覆盖,宁芜盆地隐伏构造和隐伏岩体还未完全查明,制约了找矿预测。利用覆盖宁芜盆地及周缘的重力和航磁数据,通过多尺度边缘检测方法,增强和提取了地下地质体的边界。结合地质资料综合分析,厘定15条断裂构造,推测8个隐伏岩体,为宁芜矿集区找矿预测提供了支撑。

煤系页岩有机质特征及有机碳含量预测:以宁武南区块为例

宁武盆地石炭-二叠系太原组-山西组地层广泛发育,但其煤系页岩气勘探程度尚低。基于宁武南区块多口钻井页岩样品的扫描电镜观测、有机碳含量测试、岩石热解测试及系列测井数据探讨了宁武南区块煤系页岩展布特征、有机质微观赋存特征和有机质丰度预测方法。结果表明:宁武南区块太原组-山西组煤系页岩连续泥岩厚度达到30 m以上,有机质丰度平均达到2.6%,有机质类型以Ⅲ型干酪根为主,显微组分以惰质体与镜质体为主,有机质孔隙主要发育于固体沥青,镜质体与惰质体中零星可见。构建了基于改进ΔlgR法、多元线性回归和神经网络的有机碳含量预测模型,对比预测精度认为反向传播(back propogation,BP)神经网络模型更适用于研究区煤系页岩有机碳含量预测。利用构建的BP神经网络模型对宁武南区块太原组和山西组总有机碳(total organic carbon,TOC)进行预测,指出研究区东北部煤系页岩有机质丰度高(TOC>3%),具有较好的勘探前景。