Application of 3D Euler deconvolution of aeromagnetic data and pseudogravity transforms in mineral exploration: a case study of the pegmatite-rich zones of Lafiagi,Central Nigeria

Structural evaluation of the pegmatite-rich zones in a part of Lafiagi (Sheet 203), Central Nigeria, was carried out. It was aimed at identification of the structures responsible for the rich mineralization of the area. This work involved the qualitative and quantitative analysis of aeromagnetic data and pseudogravity transforms by using Oasis Montaj? software. The 3D Euler deconvolution results from acquired aeromagnetic data and pseudogravity transforms augmented with geological information obtained from reliable sources were employed in the structural interpretation work. The results have shown that the abundance of 2D and 3D structures that are commonly associated with gemstones and precious minerals explain why the study area is rich in mineral deposits.     

内蒙古自治区额济纳旗红石山南锑金矿地质特征及找矿前景分析

红石山南锑、金矿位于阿木乌苏—鹰嘴红山金、锑、铁、钨Ⅳ级成矿带中段南部,赋存于长城系古硐井岩群近东西向脆韧性断裂（韧性剪切带）之中,按锑、金矿（化）带的相对位置划分为东部锑、金矿（化）带和西部金矿（化）带。东部锑、金矿（化）带圈定三个锑矿（化）体,西矿段金矿化带发育两条规模较大的含金构造蚀变带,带内金矿以构造蚀变岩型和韧性剪切带型为主,次为石英脉型。金矿（化）体呈斜列式排列,与主构造线方向一致。通过对红石山南锑、金矿地质特征、矿（化）体特征及化探异常特征的综合分析研究,总结了控矿因素和找矿标志。在综合研究区域成矿规律的基础上,运用＂类比＂原理,指出研究区Au、Sb矿具有较好的找矿潜力。     

Aeromagnetic data analysis of the Southern Aravalli Fold Belt: Its implications in understanding the inter-relationship among the migmatites and Gneissic Rocks,Aravalli supracrustals and Godhra granite

The Southern Aravalli Fold Belt represents a geologically complex terrain comprising migmatites, gneisses, low-grade metasediments and intrusive granites. Processing and interpretation of the existing aeromagnetic data using modern techniques has helped in understanding the geological complexity of the area. High quality aeromagnetic maps — total intensity, vertical derivative, analytic signal and 3D Euler depth — have been produced from the digitally processed data to augment visualisation and interpretation of the data. Strong east-west to northeast-southwest long strike-length anomalies in the southern part within the gneissic/granitic terrain indicate presence of narrow bands of high-susceptibility (magnetic) materials probably along regional lineaments. The thick sequence (> 1 km) of magnetically transparent sedimentary cover in the Rajgad basin is better visualised in the analytic signal and Euler Depth maps. The sediments in the northern part of the basin are deposited in a grabben formed by a northwest-southeast trending marginal fault in the north and an intrabasinal east-west fault in the south as demonstrated in the Euler 3D map. The Lunavada and Champaner Groups are separated by a shear zone comprising en-echelon shears clearly indicated in the shaded relief and vertical derivative maps. Interpretation of magnetic relief of the aeromagnetic data reveals that the area comprises of five distinct litho-tectonic units. This study demonstrates that the old aeromagnetic data acquired few decades back can provide valuable geological information, if processed using modern techniques.     

西秦岭温泉—中川一带金属矿床的成矿规律及找矿预测

西秦岭温泉—中川一带实施的1:5万矿产地质调查项目,共圈定1:5万局部高磁异常33处,1:5万地球化学综合异常11处,发现矿点2处,矿化点5处,矿种有金、钼、铁、铜、铷等。通过分析研究区成矿地质条件、1:5万地球物理和地球化学综合异常特征、矿(化)点特征及分布规律等,阐明了该区成矿时空分布规律和矿产共生组合规律,划分成矿远景区9处,提交找矿靶区6处。对其中2处找矿靶区进行槽探验证的结果为: 关子镇幅玉杨观找矿靶区圈定了4条含铷矿化伟晶岩脉和多处铁矿化破碎蚀变带,具有形成伟晶岩型铷矿的潜力; 礼县幅李坝金矿床南侧百叶沟—河西沟找矿靶区圈定了14条蚀变破碎带,在矿化蚀变带内圈定了11条金矿(化)体,具有形成构造蚀变岩(微细粒浸染状)型金矿床的潜力。     

The role of aeromagnetic data analysis (using 3D Euler deconvolution) in delineating active subsurface structures in the west central Arabian shield and the central Red Sea,Saudi Arabia

In this paper, we present a case study of structural mapping by applying the 3D Euler method to the high-resolution aeromagnetic data that was collected in the west central Arabian Shield region and the coastal region of the central Red Sea in Saudi Arabia. We show the 3D Euler deconvolution algorithm and apply it to magnetic potential field data from the west Central Arabian Shield and the Central Red Sea. The solution obtained with 3D Euler deconvolution gives better-focused depth estimates, which are closer to the real position of sources; the results presented here can be used to constrain depth to active crustal structures (volcanisms) for the study area. The results indicated that the area was affected by sets of fault systems, which primarily trended in the NNW–SSE, NW–SE, EW, and NE–SW directions. Moreover, estimated Euler solution map from aeromagnetic data delineated also the boundaries of shallow, small, and confined magnetic bodies on the offshore section of the study area. These nearly exposed basement intrusions are most likely related to the Red Sea Rift and may be associated with structures higher up in the sedimentary section. These volcanic bodies are extended to the continental part (onshore) of the west central Arabian Shield, particularly beneath both sides of the Ad Damm fault zone. This extension verifies that the fault was largely contemporaneous with a major period during the extension of the Red Sea Basin. Moreover, according to the distribution of circular magmatic-source bodies (circular-shaped ring dikes) that resulted from this study, we can state that the clustering of most earthquakes along this fault may most likely be attributed to the active mantle upwelling (volcanic earthquakes), which are ultimately related to volcanic processes. Furthermore, the oceanic crustal structures near and in the Red Sea offshore regions were also estimated and discussed according to the ophiolite occurrences and further opening of the Red Sea. Our results are largely comparable with studies of previous crustal sections, which were performed along the Red Sea Rift and the Arabian Shield. As a result, the areas above these anomalies are highly recommended for further geothermal study. This example illustrates that high-resolution aeromagnetic surveys can greatly help delineating the subsurface active structures in the west central Arabian Shield and the middle coastal region of the Red Sea of Saudi Arabia.     

Subsurface structural features of the basement complex and mineralization zone investigation in the Barramiya area,Eastern Desert of Egypt,using magnetic and gravity data analysis

In the Barramiya area, the majority of gold deposits are generally related with the quartz veins that associated with shear zones cutting the crystalline basement rocks. The quartz vein system is controlled by shear zone and general faults. The present study is to delineate the general faults, shear zones, geological limits, and basement rock relief, using airborne magnetic and gravity data analysis at the Barramiya gold mine and surrounding area, Eastern Desert of Egypt. To achieve our goal, we have applied on magnetic and gravity data the following techniques: reduction to pole (RTP), analytical signal, tilt derivative, total horizontal derivative, 3D Euler deconvolution, downward continuation, and source parameter imagining power spectrum techniques. The analytical signal used to map the types of rock boundaries. Tilt derivative and total horizontal derivative filters helped to delineate fractures and the contact zones of the formations that host the main Barramiya shear zone. 3D Euler deconvolution techniques helped to delineate the fault trends which represented at the following direction: NNE–SSW and NNW–SSE. The average depths of both regional and residual causes have been estimated by applying downward continuation, source parameter imagining, and power spectrum techniques. According to the results of the present study, the depth of the basement rocks is relatively high (~?80-m depth) in the western part of the study area and the basement rocks cropped out in the surface at the rest of the area. Our results are coinciding with the previous geological studies.     

The geology and Re–Os geochronology of the Palaeoproterozoic Vaikijaur Cu–Au–(Mo) porphyry-style deposit in the Jokkmokk granitoid, northern Sweden

The Vaikijaur Cu–Au–(Mo) deposit is located in the ca. 1.88 Ga calc-alkaline Jokkmokk granitoid near the Archaean–Proterozoic palaeoboundary within the Fennoscandian shield of northern Sweden. The Skellefte VMS district lies immediately to the south and the northern Norrbotten Fe-oxide–Cu–Au deposits to the north. The Vaikijaur deposit occupies an area of 2×3 km within the Jokkmokk granitoid and includes stockwork quartz-sulphide veinlets and disseminated chalcopyrite, pyrite, gold, molybdenite, magnetite, and pyrrhotite. Porphyritic mafic dykes were emplaced along fractures in a ring dyke pattern. The Jokkmokk granitoid, dykes, and the mineralized area are foliated, indicating that mineralization predated the main regional deformation. The mineralized area is characterized by strong potassic alteration. Phyllic and propylitic alteration zones are also present. A pyrite-rich inner core is surrounded by a concentric zone with pyrite, chalcopyrite, and gold. Molybdenite is distributed irregularly throughout the chalcopyrite zone. Geophysical data indicate a strongly conductive central zone in the mineralized area bordered by conductive and high magnetic zones. Five high precision Re–Os age determinations for three molybdenite occurrences from outcrop and drill core samples constrain the age of porphyry-style Cu–Au–(Mo) mineralization to between 1889±10 and 1868±6 Ma. A younger molybdenite is associated with a much later metamorphic event at about 1750 Ma. These data suggest that primary porphyry-style mineralization was associated with calc-alkaline magmatism within the Archaean–Proterozoic boundary zone at ca. 1.89–1.87 Ga.     

内蒙古赤峰柴胡栏子金矿及周边地区构造形迹的“米字型”分布及其控矿特征

柴胡栏子金矿位于中国东部大兴安岭北北东向构造带与华北地块北缘近东西向构造带的交汇部位。该交汇区经历了多期构造-岩浆活动,产出了柴胡栏子、莲花山、红花沟等多个大-中型金矿床。航磁和遥感资料解译结果表明,矿田内发育北北西向、北西西向、北北东向和北东东向共4个方向的构造形迹,呈现“米字型”结构的展布特点,分别控制了晚古生代岩浆岩(脉岩)和主要金矿床的展布。在柴胡栏子金矿区,4个方向的构造形迹也组成了“米字型”结构,控制了矿体(矿化带)和化探异常的展布。矿田和矿区级别的构造形迹均呈现“米字型”分布特点,是新华夏构造体系分级控岩控矿规律的具体表现。上述认识为矿床成因研究和矿田成矿预测提供了重要的依据。     

陕西周户长地区金矿成因初探

陕西周(至)户(县)长(安)金成矿区位于华北板块与扬子板块的结合地带，已发现大型金矿床2处，中小型矿床(点)20余处。它们分属金牛坪-库峪贵、多金属成矿带和沙梁子-丰北河贵金属成矿带。本区金矿成矿物质来源可能与围岩有关；硫来源较为复杂，总体表现为混合硫特征；成矿流体总体表现为混合流体特征；成矿物化环境为中低温、低压、弱酸性的浅部还原条件。本区金矿矿床类型属于蚀变岩型和石英脉型。     

辽宁省抚顺棋盘山矿区物化探地质特征及找矿方向浅析

本文论述了辽宁省抚顺棋盘山矿区的地质、物化探及、矿化体特征,指出花岗斑岩体具有良好的分带性,是低阻高极化体且与土壤地球化学异常吻合。分析了Au、Mo矿化体的空间分布规律、原生晕的分带规律以及矿化体与蚀变之间的关系,指出Au矿化体多产于岩体内部的断裂带内,且与硅化、褐铁矿化、黄体矿化关系密切;而Mo矿化体呈矿化带产于岩体的外接触带中,与硅化关系密切;原生晕在轴向上具有Pb-Ag-Zn-Au-Mo-Cu的分带特征。根据矿区的地质、物化探异常以及蚀变,概括了可能的找矿标志,认为物化探异常地段以及岩体接触带应是今后找矿的重点方向。     

西准噶尔成矿带金矿异常识别及其不确定性分析

西准噶尔成矿带地处中亚成矿域核心区,伴随着古生代强烈的构造岩浆活动,发生了广泛的金成矿作用,形成了一系列金矿床、矿点及矿化点,如萨尔托海、哈图、包古图等金矿床,已成为我国重要的黄金开发基地之一.基于该成矿带水系沉积物地球化学数据,采用集成序贯指示模拟技术和多重分形局部奇异性分析方法,开展金异常信息识别及其不确定性定量模拟,有效突出局部异常和弱缓异常,实现金元素富集异常在空间上的概率分布与量化表达.研究结果显示,金奇异性指数小于2的条件下,金元素富集异常的高概率区与已知金矿产地在空间分布上非常吻合,该研究可为西准噶尔成矿带金矿勘查及其不确定性风险评估提供决策依据.      

陕西镇安县桂林沟钼矿成矿特征及成矿要素分析

潼关—柞水—宁陕区域性北东向构造岩浆岩带控制了矿区岩浆岩体、矿区构造和钼矿化带的产出及其规模,矿区次级断裂构造为成矿物质聚集提供了有利的储存空间,中酸性岩浆活动及其热液蚀变控制了成矿物质的迁移、富集.区域性北东向构造岩浆岩带具有良好的找矿前景,应引起相关矿产勘查工作的高度重视.     

陕西镇安县太白庙一带金矿地质特征及控矿因素

镇安县太白庙一带金矿以显微金与明金颗粒为特征,矿床由三个近东西向展布的含金石英脉体密集带构成,由南向北可划分为Ⅰ、Ⅱ、Ⅲ三个含矿带。赋矿地层为泥盆系星红铺组,金矿矿(化)体分布受地层、构造双重控制。     

青海巴颜喀拉地区高精度航磁异常查证及金矿找矿效果

中国冶金地质总局地球物理勘查院在青海巴颜喀拉地区开展了1∶5万高精度航磁测量,项目组通过总结测区内的岩(矿)石磁性规律,分析磁场特征及研究区域成矿模型,精选了部分航磁异常来开展地面查证,取得了较好的金矿找矿效果。本文研究了在青海巴颜喀拉地区、利用高精度航磁测量成果快速高效找寻金矿及有色金属矿的技术方法,总结出不同区域的磁场背景与岩(矿)石磁性特征,其构造破碎蚀变带引起的磁异常并不相同,可能是负磁异常,也可能是正磁异常,并认为研究一个地区的磁异常特征,首先要研究区内的岩(矿)石磁性参数特征。     

湖南锡田钨锡多金属矿床成矿地质特征及成矿模式

通过对锡田钨锡多金属矿床地质特征的研究,认为锡田矿区钨锡多金属矿体的形态、产状及空间展布严格受岩体接触带及断裂构造控制;矿床类型主要为矽卡岩型,其次为破碎带蚀变岩型、云英岩型等;钨锡多金属成矿作用与岩浆活动密切相关:印支期花岗岩浆侵位形成矽卡岩型钨锡矿(化)体;燕山期花岗岩浆侵位导致早期矿化矽卡岩发生叠加矿化,同时在构造破碎带中形成云英岩型锡矿或破碎带蚀变岩型钨锡多金属矿体,是形成规模巨大的钨锡多金属工业矿床的必要条件.此外,提出了锡田矿区钨锡多金属矿的成矿模式.     

New data on the correlation of skarn and gold mineralization at the Tardan deposit (northeastern Tuva)

Gold mineralization of the Tardan deposit is of different spatial occurrences and is related to different hydrothermal-metasomatic formations, the main ones being skarn-magnetite bodies, metasomatites of mineralized crush zones, and metasomatites of argillizitic-rock association. The formation of gold mineralization was a multistage process related to the repeated magmatism of the Tannu-Ola complex. It took place in a wide temperature range (400–150 °C), which determined the diversity of produced mineral assemblages. The gold mineralization associated with magnetite bodies shows a spatial correlation with magnesian and calcareous skarns and is localized in plagiogranites and gabbro-diorites of the Tannu-Ola complex intruded in the Late Ordovician. Gold mineralization that occurs in crush zones and along the fault sutures in moderate- and low-temperature hydrothermal-metasomatic rocks (propylites, beresites, serpentinites, and argillizites) formed somewhat later than skarns as a result of the intrusion of granite dike bodies. Comparative analysis of different types of gold mineralization showed both a change of mineral assemblages of the gold mineralization during the ore formation and some geochemical difference between gold and gold-bearing ores. In passing from early to late occurrences of native gold, its fineness decreases, the contents of admixtures correspondingly increase, and the gold composition changes. Gold of high-temperature rocks is rich in Cu (up to 17%), and gold of low-temperatures rocks has higher contents of Ag and Hg.     

Biogeochemical studies of areas of sulphide mineralization in Northern Greece

Biogeochemical and geobotanical studies have been carried out in several areas of sulphide mineralization in northern Greece. In porphyry copper areas, mineralized zones can be delineated by mapping the distribution of Minuartia verna, or by measuring the copper content of Rumex acetosella and Thymus sibthorpii. Elevated levels of molybdenum in the soil are indicated by higher concentrations of this element in T. sibthorpii. In an area of barite mineralization, biogeochemical methods were not useful in showing the barium distribution, but did provide an indication of the associated lead mineralization. The appearance of the nickel accumulator Alyssum murale near a zone of antimonite mineralization seems to be related to sporadic occurrences of ultrabasic rocks nearby.     

Metallogenic regularity and mineral prediction of metallic deposits in Baiyin mine field and its periphery of Gansu Province

Through the mineral prospecting project in Baiyin mine field and its periphery of Gansu Province, the authors have delineated twelve 1:50 000 aeromagnetic anomaly areas, seven 1:50 000 high magnetic anomaly areas and sixty-four 1:50 000 geochemical prospecting anomaly areas. Besides, four mineral occurrences and six mineralized spots were found, including copper, lead, zinc etc. The temporal and spatial distribution of mineralization and the paragenesis and combination rules of mineral resources were also expounded, after a comprehensive study of the metallogenic geological conditions, 1:50 000 geochemical and geophysical anomalies and the characteristics of mineral occurrence distribution. The “multi-type” prospecting prediction model was concluded in the study area. Nine key metallogenic prospective areas were delineated, including three type A, two type B and four type C prospective areas. Four target prospecting areas were delineated, including one type A, one type B and two type C target prospecting areas.     

西藏勒青拉铁矿床地质特征及其找矿意义

笔者对勒青拉铁矿床形成的地质背景、矿床地质特征、成矿机制和找矿前景进行了研究。研究结果表明,矿床位于冈底斯岛弧造山带东段北矿带,矿体产出部位严格受碳酸盐岩层位及其层间破碎带的控制,矿体主要为层状。容矿岩石主要为矽卡岩、矽卡岩化灰岩。矿石类型简单,主要为磁铁矿矿石。矿化富集与喜马拉雅早期居布札日花岗闪长岩密切相关,矿床类型属矽卡岩型矿床。勒青拉铁矿床潜在资源量巨大,外围地区具有相同类型铁矿床的找矿远景。     

3-D magnetic inversion and satellite imagery for the Um Salatit gold occurrence,Central Eastern Desert,Egypt

The Um Salatit is a gold occurrence situated in the Central Eastern Desert of Egypt. The studied area is characterized by an intensive imbrication zone of serpentinites and metavolcanic rocks. The integrated use of aeromagnetic and spectral reflectance remote sensing data has proved effective for mapping geology related to ore deposits. Spectral reflectance maps have been produced to discriminate various rocks, such as serpentinites, gabbros, and metavolcanic rocks. 3-D inversion of aeromagnetic data acquired over the Um Salatit study area produced a 3-D magnetic susceptibility model showing magnetic bodies surrounded by less magnetic host rock. The magnetic features are elongated ENE-WSW parallel to the major thrust fault and mapped the Um Salatit serpentinized rocks. Remote sensing data allow investigating surficial geological features and mapping the mineralized areas. Remote results, in conjunction with 3-D inversion of aeromagnetic data, demonstrate that gold occurrence in the study area was effectively restricted to the highly magnetic zone interpreted as host rocks.