烟台市牟平区磨山金矿床成矿规律和找矿远景分析

磨山金矿床位于著名的牟平乳山金成矿带西侧。矿体直接产出于玲珑花岗岩体内,受控于NNE向压扭性断裂构造。赋矿岩性主要为黄铁绢英岩化花岗质碎裂岩。磨山金矿床探求金金属量15t,为新发现的中型矿床,其深部及外围尚有很大的找矿前景,及时总结其成矿规律,可为进一步勘查提供可靠的参考地质依据。     

基于地质统计学的地震反演冲积扇相研究——以新疆C油藏为例

新疆C油藏属于开发早期区块,井资料少、井距较大,采用地震反演等数据进行沉积相研究,可提高研究精度。采用约束稀疏脉冲反演和地质统计学反演两种方法进行地震反演研究,前者受到地震分辨率的限制,纵向上分辨率不能够满足研究需求;而后者可提高反演纵向上的分辨率。本文采用地质统计学反演的储层厚度分布图进行沉积相分析,得到沉积相平面展布图,并总结了沉积相模式,解决了勘探阶段沉积相难以描述等问题,并取得了较好的效果。     

Geochronologic Constraints on the Magmatic Underplating of the Gangdisê Belt in the India-Eurasia Collision: Evidence of SHRIMP II Zircon U-Pb Dating

1 Introduction Mo et al. (2005) determined that magma mixing and mingling took place extensively in the Gangdisê magmatic belt around 50 Ma, and argued that magma mixing was genetically related to underplating of mantle-derived magmas beneath that belt. Underplating, as one of the major mechanisms for crustal growth, can occur in the environments of convergent plate boundaries, subduction and collision zones, and in intra-plate settings such as continental flood basalt provinces (Wilson, 19…     

Geochronologic Constraints on the Magmatic Underplating of the Gangdise^ Belt in the India-Eurasia Collision： Evidence of SHRIMP II Zircon U-Pb Dating

Abstract  Abundant small mafic intrusions occur associated with granitoids along the Gangdisê magmatic belt. In addition to many discrete gabbro bodies within the granitoid plutons, a gabbro‐pyroxenite zone occurs along the southern margin of the Gangdisê belt to the north of the Yarlung Zangbo suture. The mafic intrusion zone spatially corresponds to a strong aeromagnetic anomaly, which extends ～1400 km. The mafic intrusions consist of intermittently distributed small bodies and dikes of gabbro and dolerite with accumulates of pyroxenite, olivine pyroxenite, pegmatitic pyroxenite and amphibolite. Much evidence indicates that the Gangdisê gabbro‐pyroxenite assemblage is most likely a result of underplating of mantle‐derived magma. Detailed field investigation and systematic sampling of the mafic rocks was conducted at six locations along the Lhasa‐Xigazê segment of the mafic intrusive zone, and was followed by zircon SHRIMP II U‐Pb dating. In addition to the ages of two samples previously published (47.0±1 Ma and 48.9±1.1 Ma), the isotopic ages of the remaining four gabbro samples are 51.6±1.3 Ma, 52.5±3.0 Ma, 50.2±4.2 Ma and 49.9±1.1 Ma. The range of these ages (47–52.5 Ma) provide geochronologic constraints on the Eocene timing of magma underplating beneath the Gangdisê belt at ca. 50 Ma. This underplating event post‐dated the initiation of the India‐Eurasia continental collision by 15 million years and was contemporaneous with a process of magma mixing. The SHRIMP II U‐Pb isotopic analysis also found several old ages from a few zircon grains, mostly in a range of 479–526 Ma (weighted average age 503±10 Ma), thus yielding information about the pre‐existing lower crust when underplating of mafic magma took place. It is believed that magma underplating was one of the major mechanisms for crustal growth during the Indian‐Eurasia collision, possibly corresponding in time to the formation of the 14–16 km‐thick “crust‐mantle transitional zone” characterized by Vp = 6.85–6.9 km/s.     

鄂尔多斯周缘地区中强震发生前地震矩加速释放时空特征

为研究鄂尔多斯周缘地区中强地震发生前地震矩加速释放时空特征,选取去丛集后的地震目录,基于地震矩释放程度m值,对1981年以来鄂尔多斯周缘地区10例MS≥5.5中强地震进行二维时空扫描,提取与地震矩加速释放特征相关的时空尺度作为矩释放程度时空扫描模型参数,以3个月为扫描步长,对震前12个月m值及累积Benioff应变释放进行拟合计算。结果显示,震前破裂成核点附近存在显著的AMR现象,7次震例存在累积Benioff应变加速释放特征,说明鄂尔多斯周缘地区MS≥5.5地震发生前AMR现象存在一定普遍性,应用矩加速时空扫描方法具有一定优势,但仍需结合其他方法进行综合分析。     

胶东型金矿床控矿构造及成矿模式

胶东型金矿床受断裂构造控制，断裂控矿规律一直是地质勘查和研究的重点问题。为深入研究断裂对金成矿的控制作用，本文基于大量矿床勘查和地质调查资料，通过对典型断裂剖面和断裂与矿体空间关系的构造解析，判断了成矿期断裂的性质和应力状态，讨论了断裂产状变化的控矿机理，提出了胶东型金矿新的构造成矿模式。将胶东主要控矿断裂分为Ⅰ级缓倾角断裂、Ⅱ级陡倾角断裂和Ⅲ级陡倾角张裂脉，三者分别控制了破碎带蚀变岩型、复合类型和石英脉型金矿床。金矿体主要赋存于断裂产状转折部位，蚀变岩型矿体赋存于断裂的倾角变缓部位，石英脉型矿体赋存于断裂倾角变陡部位。缓倾角断裂控制的矿体具有总体侧伏角小、富矿柱侧伏角大的“双向”侧伏特征。矿体产状与断裂产状的关系指示，三山岛、焦家和招平三条控矿断裂成矿期均属右行正滑或右行张扭性，金牛山断裂具有左行正滑特征。根据金矿体产状分析的胶西北金成矿小区区域构造应力场σ1为294°∠82°和269°∠78°，焦家断裂的σ1为300°∠67°、311°∠78°和321°∠81°，招平断裂北段σ1为130°∠65°和138°∠69°，反映了胶西北玲珑花岗岩体分布区域总体以垂向主压应力为主，其东、西两侧的边界断裂处的主压应力方位分别沿SE向和NW向指向岩体，成矿期断裂处于NW—SE向拉张状态。胶东东部邓格庄金矿田的σ1为287°∠0°，以水平主压应力为主。综合分析认为，产状变化的具张扭性质的断裂是金的有利赋矿构造，断裂的产状变化对金矿体具有明显的控制作用，断裂结构和流体性状的变化是金矿阶梯成矿的关键因素，断裂沿走向和倾向的产状转折联合控制了金矿体的侧伏。胶东地区早白垩世深部大量岩浆岩快速侵位，导致地壳强烈隆升产生伸展构造，来自不同深度和层次岩浆房及不同源区的岩浆梯次上侵，为深部含金流体活化、迁移提供了热动力条件和流动通道，含金流体到达地壳浅部在断裂产状变化的减压扩容空间卸载成矿。     

An Effective Model to Retrieve Soil Moisture from L- and C-Band SAR Data

This study investigated an appropriate method for soil moisture retrieval from radar images and coincident ground measurements acquired over bare soil and sparsely vegetated regions. The adopted approach based on a single scattering integral equation method (IEM) was developed to establish the relationship between backscatter coefficient and surface soil parameters including volumetric soil moisture content and surface roughness. The performance of IEM in 0–7.6 cm is better than that in 0–20 cm. Moreover, IEM can simulate correctly the backscatter coefficients only for the root mean square (RMS) height s < 1.5 cm at C-band and s < 2.5 cm at L-band by using an exponential correlation function and for s > 1.5 cm at C-band and s > 2.5 cm at L-band by using Gaussian function. However, due to the difficulties involved in the parameterization of soil surface roughness, the estimated accuracy is not satisfactory for the inversion of IEM. This paper used a combined roughness parameter and Fresnel reflection coefficient to develop an empirical model. Simulations were performed to support experimental results and to highlight soil moisture content and surface roughness effects in different polarizations. Results showed that a good agreement was found between the IEM simulations and the SAR measurements over a wide range of soil moisture and surface roughness characteristics. The model had a significant operational advantage in soil moisture retrieval. The correlation coefficients were 77.03 % at L-band and 81.45 % at C-band with the RMSEs of 0.515 and 0.4996 dB, respectively. Additionally, this work offered insight into the required application accuracy of soil moisture retrieval at a large area of arid regions.     

广西大瑶山西部一带勘查（新）区构造叠加晕法研究及应用

构造叠加晕找盲矿法在“攻深找盲”勘查中具有不可替代的作用,勘查（新）区构造叠加晕法的提出拓宽了其应用范围。为探索如何运用勘查（新）区构造叠加晕法对广西大瑶山1∶5万航磁异常桂C-2014-104进行异常查证和评价,本次研究引入元素相关性分析,并提出适用于勘查（新）区的分带方法。在李惠教授等总结的“参照实用理想模型”的基础上,建立了本研究区成矿预测的“参照实用模型”。利用“参照实用模型”对研究区内化探异常进行了评价和预测,最终,预测了3处较典型的成矿有利部位,并对这些部位进行了排序。研究表明,主成矿元素的分带对建立预测模型较为关键,对预测结果影响较大。此外,勘查（新）区构造叠加晕法的应用结果表明该方法具有较高的预测准确性和实用性,可以为相关找矿评价工作提供可靠的地球化学依据。     

藏南米拉山地区林子宗火山岩LA-ICP-MS锆石U-Pb年龄和起源

大规模的林子宗火山岩呈带状展布于拉萨地体中南部地区,记录了新特提斯洋壳晚期俯冲和随后印度—欧亚大陆碰撞的重要信息,因而受到广泛关注,但迄今对区域性的林子宗火山岩仍然缺乏可靠的年龄数据约束。为此,本文对南部拉萨地体东部米拉山地区林子宗火山岩中的含角砾流纹岩样品进行了LA-ICP-MS锆石U-Pb定年和Hf同位素、全岩地球化学测试。获得了60.1±0.9Ma的锆石206Pb/238U年龄,与林周盆地典中组底部安山质岩浆活动的时代相当。测试样品以亏损中稀土元素和低的重稀土元素丰度为特征,锆石εHf(t)为正值(+8.5~+18.8),可能来源于较厚新生下地壳物质在角闪岩相/榴辉岩相过渡条件下的部分熔融。目前还很难论证呈带状分布的约60Ma林子宗火山岩稀土元素含量差异的构造含义。     

Genesis of the Weiquan Ag–Polymetallic Deposit in East Tianshan, China: Evidence from Zircon U–Pb Geochronology and C–H–O–S–Pb Isotope Systematics

The Weiquan Ag-polymetallic deposit is located on the southern margin of the Central Asian Orogenic Belt and in the western segment of the Aqishan-Yamansu arc belt in East Tianshan,northwestern China. Its orebodies, controlled by faults, occur in the lower Carboniferous volcanosedimentary rocks of the Yamansu Formation as irregular veins and lenses. Four stages of mineralization have been recognized on the basis of mineral assemblages, ore fabrics, and crosscutting relationships among the ore veins. Stage I is the skarn stage(garnet + pyroxene), Stage Ⅱ is the retrograde alteration stage(epidote + chlorite + magnetite ± hematite 士 actinolite ± quartz),Stage Ⅲ is the sulfide stage(Ag and Bi minerals + pyrite + chalcopyrite + galena + sphalerite + quartz ± calcite ± tetrahedrite),and Stage IV is the carbonate stage(quartz + calcite ± pyrite). Skarnization,silicification, carbonatization,epidotization,chloritization, sericitization, and actinolitization are the principal types of hydrothermal alteration. LAICP-MS U-Pb dating yielded ages of 326.5±4.5 and 298.5±1.5 Ma for zircons from the tuff and diorite porphyry, respectively. Given that the tuff is wall rock and that the orebodies are cut by a late diorite porphyry dike, the ages of the tuff and the diorite porphyry provide lower and upper time limits on the age of ore formation. The δ~(13)C values of the calcite samples range from-2.5‰ to 2.3‰, the δ~(18)O_(H2 O) and δD_(VSMOW) values of the sulfide stage(Stage Ⅲ) vary from 1.1‰ to 5.2‰ and-111.7‰ to-66.1‰, respectively,and the δ~(13)C, δ~(18)O_(H2 O) and δD_(V-SMOW) values of calcite in one Stage IV sample are 1.5‰,-0.3‰, and-115.6‰, respectively. Carbon, hydrogen, and oxygen isotopic compositions indicate that the ore-forming fluids evolved gradually from magmatic to meteoric sources. The δ~(34)S_(V-CDT) values of the sulfides have a large range from-6.9‰ to 1.4‰, with an average of-2.2‰, indicating a magmatic source, possibly with sedimentary contributions. The ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb ratios of the sulfides are 17.9848-18.2785,15.5188-15.6536, and 37.8125-38.4650, respectively, and one whole-rock sample at Weiquan yields~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb ratios of 18.2060, 15.5674, and 38.0511,respectively. Lead isotopic systems suggest that the ore-forming materials of the Weiquan deposit were derived from a mixed source involving mantle and crustal components. Based on geological features, zircon U-Pb dating, and C-H-OS-Pb isotopic data, it can be concluded that the Weiquan polymetallic deposit is a skarn type that formed in a tectonic setting spanning a period from subduction to post-collision. The ore materials were sourced from magmatic ore-forming fluids that mixed with components derived from host rocks during their ascent, and a gradual mixing with meteoric water took place in the later stages.