Targeting of Gold Deposits in Amazonian Exploration Frontiers using Knowledge- and Data-Driven Spatial Modeling of Geophysical,Geochemical, and Geological Data

This paper reports the application of weights-of-evidence, artificial neural networks, and fuzzy logic spatial modeling techniques to generate prospectivity maps for gold mineralization in the neighborhood of the Amapari Au mine, Brazil. The study area comprises one of the last Brazilian mineral exploration frontiers. The Amapari mine is located in the Maroni-Itaicaiúnas Province, which regionally hosts important gold, iron, manganese, chromite, diamond, bauxite, kaolinite, and cassiterite deposits. The Amapari Au mine is characterized as of the orogenic gold deposit type. The highest gold grades are associated with highly deformed rocks and are concentrated in sulfide-rich veins mainly composed of pyrrhotite. The data used for the generation of gold prospectivity models include aerogeophysical and geological maps as well as the gold content of stream sediment samples. The prospectivity maps provided by these three methods showed that the Amapari mine stands out as an area of high potential for gold mineralization. The prospectivity maps also highlight new targets for gold exploration. These new targets were validated by means of detailed maps of gold geochemical anomalies in soil and by fieldwork. The identified target areas exhibit good spatial coincidence with the main soil geochemical anomalies and prospects, thus demonstrating that the delineation of exploration targets by analysis and integration of indirect datasets in a geographic information system (GIS) is consistent with direct prospecting. Considering that work of this nature has never been developed in the Amazonian region, this is an important example of the applicability and functionality of geophysical data and prospectivity analysis in regions where geologic and metallogenetic information is scarce.     

从地球物理场信息分析西宁盆地地热地质条件

在对西宁盆地进行可控源音频大地电磁测深(CSAMT)全面探测的基础上,结合以往重力、地震、大地电磁测深、直流电测深等物探资料综合解释,揭示了西宁盆地隆坳构造格局和盆地性状,据地温场分布特征探讨了热储类型,指出西宁盆地中西宁坳陷属张性、张扭性,具有地温场高、地温梯度大的特点,且热储类型具盆地传导兼断裂对流型特征;大通、平安坳陷属压性、压扭性坳陷,地温场、地温梯度相对较低,热储类型为盆地传导型.西宁断陷是地热开发有利地段.     

Geomorphology of the Alluvial Sediments and Bedrock in an Intermontane Basin: Application of Variogram Modeling to Electrical Resistivity Soundings

The study describes a methodology used to integrate legacy resistivity data with limited geological data in order to build three-dimensional models of the near subsurface. Variogram analysis and inversion techniques more typically found in the petroleum industry are applied to a set of 1D resistivity data taken from electrical surveys conducted in the 1980s. Through careful integration with limited geological data collected from boreholes and outcrops, the resultant model can be visualized in three dimensions to depict alluvium layers as lithological and structural units within the bedrock. By tuning the variogram parameters to account for directionality, it is possible to visualize the individual lithofacies and geomorphological features in the subsurface. In this study, an electrical resistivity data set collected as part of a groundwater study in an area of the Peshawar basin in Pakistan has been re-examined. Additional lithological logs from boreholes throughout the area have been combined with local outcrop information to calibrate the data. Tectonic activity during the Himalayan orogeny has caused uplift in the area and generated significant faulting in the bedrock resulting in the formation of depressions which are identified by low resistivity values representing clays. Paleo-streams have reworked these clays which have been eroded and replaced by gravel–sand facies along paleo-channels. It is concluded that the sediments have been deposited as prograding fan-shaped bodies and lacustrine deposits with interlayered gravel–sand and clay–silt facies. The Naranji area aquifer system has thus been formed as a result of local tectonic activity with fluvial erosion and deposition and is characterized by coarse sediments with high electrical resistivities.     

Interpretation of Low Seismicity in the Eastern Anatolian Collisional Zone Using Geophysical (Seismicity and Aeromagnetic) and Geological Data

The eastern Anatolia is a continental collisional zone between the Arabia-Eurasia plates and is currently being accompanied by the westward escape of the Anatolian crustal block to the west-southwest along two major strike-slip fault zones, the NATF and the EATF. Although these major fault zones have experienced historical earthquakes with moderate to high magnitude, notably there is a low seismicity zone on the active EATF between the Bitlis and Pötürge massifs. The low seismicity zone is characterized by thinner crustal structure relative to its environs, the shallow Curie Point Depth (SCPD, ca 12–14 km in between 39–40°E and 38.5–39°N in the easternmost part of the Anatolian plate) and moderate to high b values (more than 0.7). We consider that the shallow CPD and moderate to high b values in the low seismicity zone characterized by thinner crustal area are closely related with the higher thermal structure of the crust, which most probably resulted from crust-hot asthenospheric mantle interactions.     

Satellite Regional Magnetic Anomalies as a Reflection of the Geological and Geophysical Properties of the Lithosphere (According to Champ Data)

Geomagnetism and Aeronomy - The possibilities of the use of satellite data to study lithospheric magnetic anomalies in remote and poorly studied regions are analyzed. The experiment uses data from...     

Geophysical Techniques to Delineate Saturated Alluvial Zones for the Siting of HVDC Power Transmission Return Electrodes

As high-voltage, direct-current (HVDC) electrical power transmission technology advances, the siting and design of the grounded return electrodes become critical factors. Electrode sites should be chosen where surrounding geologic conditions will not unfavorably channel large earth currents and harmfully affect nearby populations. An optimum site allows direct contact between the electrode and a large volume of a stable, low-resistivity material. A saturated alluvial zone between dry surface soils and an underlying crystalline bedrock is an ideal material for containing the current flow from the electrode.
A hydrogeologic investigation was conducted to delineate the saturated zone in several alluvial valleys in the southwestern desert region. Regional ground water flow directions, water quality, and seasonal fluctuations of the water table elevations were determined. The structural shape and topography of the crystalline basement beneath the valleys were interpreted from gravity data. Iterative forward-modeling of the data provided a low-cost means of deducing the volume of the lightweight alluvium. Electrical resistivity surveys were completed to measure the lateral and vertical variations in soil resistivities throughout the valleys. The geophysical data were used to extend the known hydrologic information into areas with no wells.
Composite models of the saturated zones in each valley were produced by integrating gravity interpretations with hydrologic and resistivity results. The composite models were used to predict current density in the ground that would be associated with a HVDC electrode. This methodology proved to be a cost-effective means of siting electrodes in a suitable geologic environment that would minimize their detrimental effects.     

闽西南大排多金属矿区地球物理响应特征与找矿启示

大排多金属矿区位于闽西南坳陷大田—龙岩次级坳陷带南部,政和—大埔深大断裂西侧,是福建省较大的多金属矿产地之一.随着找矿勘查的不断深入,对在该矿区外围和深部寻找隐伏矿床提出了迫切需求,但研究区地表地形崎岖、植被茂密,以往很少进行高精度大比例尺的综合地球物理调查,因此对隐伏的控矿构造、赋矿层位和火成岩体分布的认识远不能满足深部找矿的需求.本文实施了反射地震、可控源音频大地电磁剖面测量和大比例尺航磁面积性测量,在成矿理论和找矿模型的指导下采用反射地震真地表偏移成像技术、可控源音频大地电磁二维带地形反演技术和航磁数据精细处理与三维反演技术,提取识别了剖面浅层逆冲推覆控矿构造和赋矿层位的反射地震特征,与成矿关系密切的燕山期火成岩体的地震、电磁特征,以及控矿构造和隐伏岩体平面分布的航磁异常特征.在地表地质和已知钻孔岩心及物性的约束下,构建了剖面的综合地球物理的地质解释模型,包括浅层推覆构造和控矿地层分布,推断解释大断裂6条,次级断裂16条和3处较大的隐伏岩体分布,为深入认识研究区的矿床成因和分布规律,指导在外围和深部找矿提供了地球物理有效响应特征.

     

Deep Structure of the Zone of Tolbachik Fissure Eruptions (Kamchatka,Klyuchevskoy Volcano Group): Evidence from a Complex of Geological and Geophysical Data

With the use of the method of low-frequency microseismic sounding, the configuration of the magmatic feeding system of the Tolbachinsky Dol—a regional zone of areal basaltic volcanism in the southern part of the Klyuchevskoy volcano group in Kamchatka—is studied. The initial data are obtained by a stepby-step recording of the background microseismic noise in 2010–2015 within a thoroughly marked-out survey area covering the zones of fissure eruptions in 1975–1976 and 2012–2013 and, partly, the edifice of the Ploskii (flat) Tolbachik volcano. The depth sections reflecting the distributions of the relative velocities of seismic waves in the Earth’s crust are constructed. For a more reliable interpretation of the revealed deep anomalies, the results of independent geological and geophysical studies are used. The ascertained low-velocity structures are closely correlated to the manifestations of present-day volcanism. It is shown that the feeding structure of the Tolbachinsky Dol is spatially heterogeneous, incorporating subvertical and lateral pipeshaped magma conduits, closely spaced magma feeding channels, and shallow magma reservoirs. A longlived local transcrustal magma conducting zone is revealed, and regularities in the deep structure of the feeding systems of fissure eruptions are identified. The configuration of the established subvertical magma conduits permits basalts moving to rise to the surface by different paths, which, inter alia, explains the contrasting magma compositions observed during a single eruption. Thus, based on the instrumental data, it is shown that the magmatic feeding structure of the Tolbachinsky Dol has a number of specific peculiarities and is significantly more complicated than has been previously thought about the areal volcanic fields.     

分形滤波(S-A)技术在物探数据异常分解中的应用

分形滤波(S-A)技术能够有效地揭示地球物理场的空间相关性,对背景场以及异常场进行分解。应用分形滤波(S-A)技术分解内蒙古某银矿区地面高精度磁测异常,结果表明:对研究区高精度磁异常进行了有效分解,获得了研究区背景场以及异常场特征,并剖析所获得的异常场,分解异常8处,并据此结合地质情况提出研究区的成矿有利区。     

天水及其南北地区温泉分布的地质—地球物理特征

根据天水及其南北地区温泉分布众多的现象,从分析地质、地球物理场着手,探讨温泉形成的区域与深部地质构造背景以及热缘机制。区内近南北向隐伏断裂发育,中酸性侵入岩、碱性玄武喷发岩构成近南北向岩浆构造带;在深部软流圈埋深变浅,岩石圈减薄、上地幔热物质上涌引起莫霍面上隆;中地壳低速、高导层同步出现;地表热流值增高,温泉呈网格状分布。该区温泉是甘肃省隆起断裂对流型地热资源有利开发地段。     

福建地球物理台网数据跟踪分析探讨

对福建地区不同观测手段仪器的数据进行跟踪分析,总结不同学科仪器观测曲线的变化趋势和观测效能,结果表明:(1)福建地区73.68％的形变观测曲线具有清晰年变动态;(2)重力仪映震效能好,同震响应与地震强度、震中距呈正相关关系;(3)地磁观测年变比较有规律且有一定周期性;(4)福建地区水温观测质量较高,水位受降雨影响不同台...