Gold Occurrences Research Articles

In Situ Trace Element and S-Pb Isotope Study of Pyrite from the Denggezhuang Gold Deposit in the Jiaodong Peninsula—Insights into the Occurrence of Gold and the Source of Ore-Forming Materials

The Jiaodong gold province is one of the most important gold fields globally and the largest in China. The Denggezhuang gold deposit is situated in the eastern portion of the Muping metallogenic belt, within the Jiaodong gold province. Despite many recent investigations, detailed mineralogical studies, particularly on auriferous minerals such as pyrite, are lacking. Therefore, further constraints on the occurrence mode and source of gold are necessary for this deposit. This study employed in situ laser ablation (multi-collector) inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) trace element and sulfur-lead isotopic analyses on pyrite at different stages. The aim was to reveal the occurrence status of various trace elements within Denggezhuang pyrite and to trace the complete evolution process of multi-stage fluids at Denggezhuang, elucidating the sources of gold mineralization. Four generations of pyrite in chronological order, Py-1, Py-2a, Py-2b, and Py-3, were identified via petrographic and backscattered electron (BSE) image analyses. Using in situ LA-MC-ICP-MS, we found that Co and Ni are most abundant in Py-1, while Py-2b is rich in As, Au, Ag, Pb, and Zn, reflecting the evolution of the mineralizing fluids in different mineralization stages. Py-2b contains a significant amount of invisible lattice gold, which migrates and precipitates within fluids rich in As. The in situ LA-MC-ICP-MS S-Pb isotopic analysis of pyrite indicates a relatively consistent source of ore-forming materials across different stages. Additionally, the S-Pb isotope characteristics resemble those of widely distributed coeval mafic dikes. Therefore, we propose that a water-rich, fertile, and deep-seated mafic magmatic system might have provided fluids, materials, and heat for mineralization.

Radiometric characteristics of some metallic ores and nonmetallic deposits: an example, Wadi Al-Allaqi, South Eastern Desert, Egypt

Hydrothermal alteration processes are connected to many mineral formations, particularly auriferous deposits. In this study, airborne gamma-ray spectrometry (GRS) data and the analysis of radioactive materials (eU, eTh, and K) are applied to search for regions with hydrothermal alteration activity. An example is presented from Wadi Al-Allaqi, South Eastern Desert, Egypt. GRS was used to analyse various radiometric data to address potential mineral deposit areas, to map regions potentially showing metallic ore mineralisation, and to point out new geological mineral resources. The Kd (potassium deviation), “F” parameter and Th-normalisation of the K and eU anomalies were calculated, and locating new exploratory targets in the study area that exhibit high F-parameter, Kd, and K/eTh values was recommended. Additionally, the research region has a few isolated enriched spots of (K). Therefore, GRS data was used to characterise and estimate potential metallic ores, nonmetallic deposits, and gold ore zones associated with the alteration zones. Results show that most of the known mineral deposits and gold occurrences in the area, according to the metallogenic map of Egypt, are located in zones with a ratio value of (0.25–0.30) (K%/(U or Th ppm)) maps which may suggest a moderate degree of alteration. Also, most mineral deposits and gold occurrences are found in intermediate altered zones, or K-enriched sites, with a Kd% of (0.2. The work represents an attempt to map hydrothermal alteration zones associated with mineral deposits in the Wadi Al-Allaqi area. Generally, natural radiation characteristics and attributes suggest criteria that can be used globally for regional mineral exploration.

In situ illite Rb-Sr dating indicates the coevality of Carlin-type gold deposits inside and around the isolated carbonate platform in western Guangxi, China

The western Guangxi is a crucial component of the Guizhou–Yunnan–Guangxi “Golden Triangle”(hereafter referred to as the Golden Triangle) of South China. The most discovered Carlin-type gold deposits in this region are primarily situated at the periphery of isolated carbonate platforms. The ore bodies are vein-like in form controlled by faults, and the wall rock are Triassic carbonate-bearing terrigenous clastic rocks. Recently, some gold deposits have been discovered in the interior of isolated carbonate platforms. The ore bodies are primarily stratiform hosted in sedimentary unconformities. The mineralized strata span from the Cambrian to the Permian, and the host rock include sandy and muddy dolostones, as well as a combination of sandstone, mudstone, tuff, and chert. The geological and geochemical characteristics suggest that these stratiform deposits in the interior of isolated carbonate platforms share common characteristic with Carlin-type gold deposits in China and USA. However, it remains uncertain whether these deposits are products of the one mineralization system and are coeval with those vein deposits at the periphery of the isolated platforms. To address this question, we conducted geological and isotopic dating studies on the Longhuo gold deposit and the De'e gold occurrence in the interior of isolated platforms. The Longhuo stratiform gold deposit occurs along a parallel unconformity in the Carboniferous/Devonian composed of sandstone, shale, tuff, and chert. Hydrothermal illite, quartz and auriferous pyrite fill along joints and fissures, implying that illite formed during the main ore-forming stage and its age could represent the age of gold mineralization. The stratiform orebodies of De'e gold occurrence are hosted in Cambrian sandy and muddy dolostones. Gold occurs as invisible Au in zoned pyrite and arsenopyrite, with a dominant alteration assemblage of silicification, carbonate alteration, and illitization. Hydrothermal quartz, illite and dolomite often aggregate with zoned auriferous pyrite and arsenopyrite in the most intensely altered zones, suggesting that illite formed during the main ore-forming stage and its age could also represent the age of gold mineralization. Illite LA-ICP-MS Rb-Sr dating was performed on both deposits, yielding ages of 184.16 ± 3.14 Ma for the Longhuo gold deposit and 191.21 ± 6.76 Ma for the De’e gold occurrence.Previous studies have indicated that Carlin-type gold deposits in the Golden Triangle exhibits two distinct age clusters, one ranging from 184 to 235 Ma and the other from 134 to 148.4 Ma. These dual age clusters suggest the potential occurrence of two mineralization events. The obtained ∼ 190 Ma mineralization ages for the Longhuo and De'e gold deposits in this study indicate that the Carlin-type gold mineralization within the isolated platform took place during the Early Jurassic. This aligns with the early mineralization event of gold deposits along the platform's edge, implying that gold deposits inside and around the isolated carbonate platform are products of the same mineralization system, influenced by post-Indosinian extensional events. The interior of the isolated carbonate platform holds substantial exploration potential, making it a novel direction for prospecting Carlin-type gold deposits in western Guangxi.

Deformational and metasomatic transformations of detrital gold in the course of placer formation

The richest gold placers periodically mined since 1838 are known in the north of the Republic of Tyva, within the basin of the Amyl and Sistig-Khem rivers. Ag-Au gold is the most common, and cuprous and mercuric varieties are presented in small quantities. Lode gold occurrences are confined to quartz veins and have no economic value. Detrital gold in the placer deposits has the typical typomorphic features of placer gold: roundness, compositional heterogeneity, the presence of rims and intergranular veinlets of high-fineness gold, and particle deformation structures. We have considered the transformation mechanisms of detrital gold within the mentioned placers due to the deforming interaction of transported particles in the sedimentogenic environment at the stage of motogenesis, as well as crystallophysical effects at the stage of syngenesis – early diagenesis during heterogeneous metasomatic recrystallization of endogenous gold under conditions of differential mobility of the main mineral-forming elements of gold, Au, Ag,
 Cu, and Hg. As a result, compositionally polyphase structures formed in the particle, they are high-fineness rims along the periphery of the particles, intergranular veins of high-fineness gold, deformation structures, and increased fineness in the particle kernels.

Prospects of the Bug mining district as an agglomeration of ore and non-ore mineral deposits for the reconstruction of the national economy of Ukraine in the post-war period

The role and capabilities of Ukrainian geological science, production and investment capital in the reconstruction of the national economy of Ukraine during the war and post-war period are considered here using the example of the Bug mining district (BMD) of the Ukrainian Shield (USh).
 BMD is characterized by an extremely wide range of deposits and ore of minerals relatively close to the surface, among which the most important ones are graphite, iron ore and iron-manganese, nickel-chromium-cobalt deposits, deposits and ore occurrences of gold discovered by geologists and geophysicists for many years. Numerous deposits of building materials and kaolin are also known here. There are prospects for obtaining local agrochemical raw materials based on the development of apatite-containing ores and calcifers.
 The article lists and shows the location of mineral deposits and ore occurrences which arethe most well-prepared for industrial development and investments. The composition of ores and the content of useful substances are given for some of them.
 Two powerful industrial enterprises are located on the BMD square, i.e., the Zavallye graphite factory and the Bug ferronickel plant (currently repurposed for other products). They can be used to process the above-mentioned ore raw materials, with some improvement of technological processes. In this regard, the possibility and practicality of creating two centers (clusters) of integrated mining and industrial development of these useful resources were considered. One of them can be created on the basis of nickel-cobalt and iron ore deposits of BMD with an orientation towards the Bug ferronickel plant. The second center can be created based on the enrichment of iron-manganese oxide ores using the technical capabilities of the Zavallye graphite plant.
 In case of realization of the entire economic potential of the industrial development of graphite ores of the region, Ukraine could become a world leader in this field and receive significant funds to reconstruct the industry disrupted by the war.
 The BMD also meets all the geological and economic prerequisites to become the first region on the Ukrainian Shield for industrial gold mining.

Deep Structure of Epithermal Deposits in Youxi Area: Insights from CSAMT and Dual-Frequency IP Data

Epithermal deposits represent a significant category of gold occurrences, with their subsurface structure playing a key role in reserve assessments. Fujian Province, characterized by extensive Mesozoic volcanic activities, stands out as a noteworthy region for shallow hydrothermal mineralization in China. This paper focus on the Youxi area within Fujian Province, employing the dual-frequency induced polarization method (DFIP) and controlled-source audio-frequency magnetotelluric method (CSAMT) to investigate the target ore. The DFIP results revealed predominant northeast-oriented zones with high polarizability and notable apparent resistivity. The CSAMT data were inverted using the SCS2D software. Two-dimensional resistivity profiles reveal a three-layer electrical structure, comprising subsurface banded rhyolites influenced by fault zones, intermediate-low resistivity sandstone layers, and deep-seated high-resistivity conglomerates. The resistivity gradient zones and highly polarizable locations align closely with known local faults. We interpreted these resistivity gradient zones as prospective target areas for mineralization, a hypothesis subsequently validated by drilling results. Combining geochemical analyses of epithermal gold deposits with the electrical resistivity structure, we propose an explanatory model for the mechanism of the formation of epithermal gold–silver deposits in the Youxi area. The magmatic hydrothermal fluids ascended along the fault, underwent convection-driven interaction with meteoric waters, and subsequently metasomatized the host rocks. This integrated approach provides valuable insights into the geological processes governing epithermal gold–silver deposit formation in the Youxi region.

Petrogenesis of the Morobe Granodiorite and their shoshonitic mafic microgranular enclaves in Maramuni arc, Papua New Guinea

Abstract The Miocene tectonics of Papua New Guinea, where subduction, arc-continent collision, and changes in subduction direction are considered to have occurred, is very complex and various tectonic models have been proposed. The Maramuni arc, active in the Miocene, is composed of a chain of granitoid bodies. As the chain-like distribution indicates the generation of igneous activities in a wide range of the same tectonic settings, the study of the Maramuni arc magmatism is important for elucidating the geologic events of the time. We provide data on the petrological and geochemical characteristics of the Morobe Granodiorite that form part of the Maramuni arc. The Morobe Granodiorite consists of metaluminous I-type granitoids, belonging to the medium-K to high-K series. The whole-rock major element variations in the granitoids can be explained by the fractionation of hornblende and plagioclase. They are generally within the composition range of experimental partial melts of amphibolites, and the whole-rock trace element compositions have characteristics of slab failure magma rather than arc. This suggests that the granitoids were generated by partial melting of the torn slab after slab failure. The mafic microgranular enclaves (MMEs) in the granitoids are classified as shoshonite, and their trace element compositions suggest that they were formed by partial melting of phlogopite-bearing mantle. The occurrences of native gold and barite within the MME show that MMEs transport Au from the mantle metasomatized by slab-derived sediment melt and/or fluid to the crustal magma chamber.

Typification of gold occurences in the Phuoc Thanh - Phuoc Son area, Central Vietnamccurences in the Рhuoc Тhanh — Рhuoc Son area, Сentral Vietnam

Background. Substantiation for the expediency of typification of gold occurrences in the Phuoc Thanh–Phuoc Son area, Central Vietnam.Aim. To classify and evaluate the prospects of gold mineralization in the Phuoc Thanh–Phuoc Son area, Central Vietnam.Materials and methods. The data of geological mapping and exploration of 20 deposits and ore occurrences in the Phuoс Son and Phuoc Thanh ore fields, collected in the 2001–2019 period, were analyzed.Results. The deposits and ore occurrences of gold-sulfide-quartz and low-sulfide gold-quartz formations of the Late Mesozoic age were established to be common within the Phuoc Thanh– Phuoc Son area. These deposits differ in terms of reserves, ore body morphology, gold-silver ratio, and gold fineness. Conclusion. The results obtained can be used when forecasting the largest gold deposits in Central Vietnam.

Geochemistry, mineral paragenesis and geothermal conditions of oreforming fluids from the Ain El Bey Cu–Fe deposit: potential occurrence of native gold and precious metal traces (North African orogenic belt, Northern Tunisia)

Geochemistry, mineral paragenesis and geothermal conditions of oreforming fluids from the Ain El Bey Cu–Fe deposit: potential occurrence of native gold and precious metal traces (North African orogenic belt, Northern Tunisia)

Endogenic Gold Occurrences in the Sedimentary Cover of the Voronezh Anteclise

Endogenic Gold Occurrences in the Sedimentary Cover of the Voronezh Anteclise

Prediction of gold mineralization zones using spatial techniques and geophysical data: A case study of the Josephine prospecting licence, NW Ghana

In this study, predictive models that characterize gold potential zones within the Josephine Prospecting Licence (PL) Area of Northwestern Ghana have been created by data-driven methods comprising frequency ratio and information value. These predictive models were evaluated using known locations of gold (Au) occurrence datasets and compared to each other. The mineral prospectivity models (MPMs) of gold occurrence areas within the Josephine PL Area were constructed by determining the spatial correlation between known locations of Au occurrences and eight mineralization related factors. The locations of these known Au occurrences, which characterize regions of anomalously high Au geochemical concentration and regions of previous or ongoing artisanal mining operations were identified by using geographic positioning systems (GPS). Eight mineralization related factors (geoscientific thematic layers) over the entire study area composed of analytic signal, lineament density, uranium-thorium ratio, uranium, potassium-thorium ratio, potassium, reduction-to-equator and geology were used to generate the MPMs. The predictive capacity of each of the MPMs generated was determined by employing the area under the receiver operating characteristics curve (AUC). The AUC score obtained for the predictive models produced based on the information value and the frequency ratio approaches were respectively 0.794 and 0.815. The AUC scores generated indicate that the MPMs produced are good predictive models (with an AUC greater than 0.7) and can therefore assist in narrowing down the highly prospective zones of mineral occurrences within the study area. However, the overall predictive potential of the frequency ratio approach was better than the model produced by the information value approach.

Типоморфизм рентгеноструктурных характеристик золота (на примере россыпей и рудопроявлений Тимано-Североуральского региона)

The results of the study of native gold of the Timan-Northern Ural region using X-ray diffraction analysis (Debye-Scherrer diffractometric method, single crystal registration) have been presented. It was established that the structural characteristics of gold were different depending on the nature of gold-bearing objects. The structure of typical placer gold was an aggregate of randomly distributed microcrystallites. In this case, only solid annular lines of reflexes of the planes of the crystal lattice of gold were visible on the photodebagrams. The formation of this microcrystalline structure in gold was conditioned by exogenous mechanical deformations resulting from its occurrence in dynamic environments (water, wind activity, etc.).
 The structure of the autigenic gold of ore occurrences was characterized by a suboriented ordering of crystals (texturization). On the photodebagrams of this gold, intermittent dashed lines and nodes of reflections from the planes of the crystal lattice of the metal were observed. The frequency of occurrence of gold with this structure on primary ore objects varied from several units to several tens of percent. According to the authors, the findings of native gold with the structures of the ordering of its grains as part of accretions or aggregates of microcrystallites were a sign of the extreme proximity of this gold to its root source, which was important at predicting of gold content and searching for gold deposits.

The gold mineral systems of the West Qinling orogen, central China: New insight from the Baguamiao gold deposit

The Baguamiao gold deposit is the first large deposit discovered in the West Qinling orogen in central China in the 1990 s. However, the occurrence of invisible gold in the deposit has not been reported. There is also no consensus on whether magmatic activity is involved in the gold mineralization, the style of mineralization, and the mechanism of gold precipitation. In this study, the in-situ trace elements, and chemical mapping of pyrite and pyrrhotite in the Baguamiao gold deposit were carried out for the first time. These data combined with the C-H-O isotope data of quartz, ankerite and calcite were used to determine mineralization process. In the Baguamiao gold deposit, five types of pyrite (Py0 to Py4) and pyrrhotite (Po0 to Po4) were identified, corresponding to the sedimentary-diagenetic period and four stages of mineralization (Stage I to Stage IV), respectively. From stage I to stage IV, gold mineralization in pyrite and pyrrhotite occurs as either visible or invisible crystals. The latter occurs dominantly as lattice-bound solid solutions (Au+) and is related to the content of Cu and Te. Co and Ni contents and Co/Ni ratios indicate that pyrite and pyrrhotite are magmatic-hydrothermal origin and affected by fluid-rock interaction. The change of Se and Te concentrations in pyrite and pyrrhotite indicates that oxygen fugacity (ƒO2) was increased from stage I to stage II, and then decreased during stage III and stage IV. In addition, the δ18O values of quartz, calculated δ18OH2O values of the ore-forming fluids and δ13C values range from 16.9 to 20.3 ‰, 7.7 to 12.9 ‰, and − 19.3 to + 0.2 ‰, respectively. Such isotopic signature records typical characteristics of orogenic gold deposit. The ore-forming fluid is a mixed hydrothermal solution involving metamorphic water, magmatic water, and meteoric water, and mixed with marine carbonate and sedimentary organic matter. Gold was precipitated by phase separation, fluid-rock interaction, and fluid mixing. Combined with the tectono-magmatic evolution, metamorphic deformation, and gold mineralization age of the West Qinling orogen, it can be concluded that with the closure of the Mianlue portions of the East Paleo-Tethys Ocean, the Baguamiao gold deposit was formed in the post-collisional extensional environment between the South China Block and the North China Block in the Late Triassic and is an orogenic gold deposit reference to the crustal continuum model.

Quartz-tourmaline metasomatites in gold deposits in Aktyuz-Boоrdinsky ore district (Northern Tien Shan, Kyrgyzstan)

In the Aktyuz-Boordinsky ore district in the Northern Tien Shan, numerous deposits and ore occurrences of gold, rare and rare earth metals and base metals are discovered. Gold deposits are characterized by the presence of a number of metasomatites: beresites, listvenites, K-feldspatites, etc. Many of them are also characterized by quartz-tourmaline gold-bearing metasomatites. A mineralogical and petrographic description of the metasomatic zoning of quartz-tourmaline metasomatites from weakly to highly altered zones is given. Quartz-tourmaline metasomatites form vein-like bodies and metasomatic breccias, where they act as cement, and the fragments can consist of intrusive rock, beresites, K-feldspatites, and listvenites. For the Aktyuz-Boordinsky ore district, quartz-tourmaline metasomatites are a prospecting feature for gold, and for other areas they are a prospecting criterion.

Polygenic gold mineralization in quartz-pebble formations on the Takyr-Kaljir site of the Southern Altai, East Kazakhstan Region

Purpose. The research purpose is to study the forms of gold occurrence in the Takyr graben alluvial-proluvial deposits in order to develop a low-waste resource-saving processing technology. Methods. At the first stage, in the course of field studies, the geological structure of the site is specified, samples are taken for mineralogical-technological analysis, which includes the following procedures: studying granulometric and mineral composition of detrital material; fractional gravitational beneficiation of the source material; fractional beneficiation of material pre-processed in the autogenous mill (AG mill); studying free (native) and bound gold in beneficiation products, their quantitative assessment. The samples are processed under the three-stage scheme using an autogenous mill for sample preparation. Findings. For the first time, the geological structure of the site has been specified with the identification of the deposits in the Turangi and Tuzkabak suites within its boundaries, as well as granulometric and petrographic composition of gold-bearing deposits, and the specifics of gold bearing. The detrital material, represented by quartz with a sharply subordinate amount of quartzite, quartz diorites and jasperoids, is practically identical in all fractions. Originality. For the first time, various types of gold mineralization have been identified in placer sands: clastogenic, newly-formed hypergene, newly-formed hydrothermal and residual. Fractional beneficiation makes it possible to estimate the gold content in each fraction and gravitational beneficiation products, as well as the ratio of free and bound native gold in different fractions. The largest amount of free native gold has been revealed in fractions of -0.25 + 0.1 mm (60%) and -0.074 + 0.044 mm (~40%). Gold is high-grade (96.5%) with an admixture of silver and iron. Together with gold, ilmenite, zircon, scheelite, native bismuth, as well as barite, galena, sphalerite, and dolomite have been identified. Practical implications. The research results make it possible to reassess the prospects of similar objects, to adjust the scheme and methodology for processing stream-sediment samples, to solve the issues of productive sand processing technology, as well as to improve the efficiency of geological exploration and eliminate the “underestimation” of gold deposits. The results obtained can be recommended for implementation by both domestic and foreign organizations specializing in the exploration and mining of gold deposits.

Structure and Distribution of the Gold-Related Quartz Vein Systems in the Southwestern Part of the Barberton Greenstone Belt (South Africa, Eswatini)

This study investigates the structural control of the numerous gold occurrences in the southern part of the Barberton Greenstone Belt in the Malolotja and Steynsdorp areas. The gold-bearing event distribution is studied using field structural geology associated with a petrological and microstructural analysis. Three major tectonic events have been identified in quartz veins and direct country rocks. The first event (De) created a regional schistosity (Se), probably associated with an early thrusting event. The second event (Df) is related to a large-scale folding, which formed the anticline at Steynsdorp and synform at Malolotja. It resulted from a main E–W direction of shortening and is responsible for the folding of the Se schistosity. It formed a N–S-striking axial planar cleavage (Sf), observed and associated with the emplacement of the main gold-bearing veins. The mineralised system exhibits a complex vein network, in which shallow dipping veins have developed coevally with steep west- and east-dipping veins. A third deformation event (Dl) produced by NE–SW shortening is related to the late barren hydrothermal quartz vein formation. Mineralogically, the veins are filled with abundant quartz, and scarce tourmaline and feldspars. Alteration halos composed of neoformed tourmaline and plagioclase within a talc and white mica matrix developed specifically during the late Dl event. A model of regional deformation giving rise to large-scale folds and quartz vein formation formed in response to E–W and NE–SW directions of shortening globally is proposed and discussed in this paper.

Formation Model of the Gold-Sulfide Deposits of the Western Kalba and Its Main Forecast and Search Criteria

The West Kalba Gold ore Belt (WKB), located within the Greater Altai, is a unique gold ore province on a global scale. It contains about 500 known gold occurrences and deposits. The main industrial type for the WKGB are gold-bearing sulfide deposits. The article presents a model for the formation of gold sulfide deposits in West Kalba. The main predictive-search criteria are considered, which make it possible to assess the prospects of areas for the presence of potential gold-sulfide objects within the described territory. The aim of the work is to clarify the main predictive and prospecting criteria specific to the considered field model. The given data is highlighted using descriptive analytics methods.

Geological Structures Controlling Au/Ba Mineralization from Aeromagnetic Data: Harrat ad Danun Area, Saudi Arabia

Positive and negative magnetic anomalies occupied the total aeromagnetic (TM) map of the Harrat ad Danun area, Saudi Arabia. Reduction to the pole (RTP) maps display the range of magnetic values (−312.4 to 209.4 nT) that vary in shape, size, and magnitude. These anomalies generally follow the NNW–SSE (Red Sea axis trend), NE–SW, and NNE–SSW trends. The NNW-SSE linear negative and positive magnetic anomalies could be brought on by buried faults, shear zones, or subsurface dikes. In the central part, the position of Au and Ba mineralization was connected to this trend. It is concluded that the principal structures are represented by the NNW–SSE, NE–SW, and NNE–SSW tendencies. Based on gridded RTP magnetic data, the 2-D power spectrum was computed and revealed the frequency of the near-surface and deep magnetic components. It is believed that the depths of the shallow and deep magnetic sources are typically 80 m and 570 m, respectively. Additional negative and positive magnetic anomalies with varied amplitudes and frequencies, trending in the NNW–SSE, ENE–WSW, and NE–SW directions, are seen when the high-pass and low-pass maps are closely examined. Many faults in various directions cut into these anomalies. The occurrence of negative linear magnetic anomalies (−36.6 nT to −137.3 nT) at this depth (80 m) is also confirmed by this map. The TDR filter and the Euler deconvolution method were used to identify the horizontal variations in magnetic susceptibility as well as the source position and depth of magnetic sources. The linear clustering rings are thought to be caused by contacts or faults with depths between 1 m to 474 m that are oriented WNW–ESE, NNE–SSW, and NNW–SSE. These faults or contacts are thought to be particularly prominent in the western, eastern, southern, northern, and central zones. The majority of felsic and mafic dikes are found to be connected to subsurface structures, showing that three structural trends—WNW–ESE, NNE–SSW, and NNW–SSE—affect the studied area. This demonstrates that important features and shear zones control the majority of Saudi Arabia’s gold deposits. A negative magnetic anomaly that is centered in the area, trending NNW–SSE and crossing the NNE–SSW fault, is connected to the plotted gold and barite mineralization in the study area. This may imply that these two tendencies are responsible for mineralization. This result raises the possibility of mineralization in the NNW negative magnetic feature located in the western part of the area. The occurrence of gold and barite was significantly impacted by the NNW–SSE and NNE–SSW structural lineaments.

Geophysical Mapping by Electromagnetic Induction of Gold Occurrences in Birimian Formations of Liptako: Case of Sorbon Haoussa Sector (Souhwest Niger)

The survey zone corresponds to the Sirba greenstone belt, one of Liptako Birimian Formations (LBF) of Niger. Previous aeromagnetic and geochemical works reveal the significant gold occurrences. The present study integrates geophysical mapping of these occurrences by electromagnetic induction on field. A multi-frequencies system of 10 frequencies was used for depth and subsurface investigation of resistive anomalies. The interpretation of obtained results shown two types of resistive anomalies, corresponding to the conductive units: deep anomalies obtained with low frequencies and subsurface anomalies detected with high frequencies. The subsurface anomalies were detected around the 15 meters and the deep anomalies were recorded beyond 80 meters. All of the detected resistive anomalies are in a lenticulars shapes oriented N-S or E-W. The analysis of combined resistivity map from all frequencies shown three zones of resistive anomaly presenting a high potential in conductive metals: The first zone Z1 (most important), located in Eastern studied zone covering, covering a surface of 3.5 Km2, the second zone Z2 is located in West and covers an area of 2.9 Km2 and the third anomaly zone Z3 is located in South with a surface of 0.96 Km2. On field, these conductive units correspond to auriferous quartz veins and/or highly altered manganese schists, exploited by using the artisanal mining wells, up to 20 meters in depth.

Role of Integrated Magnetics and Geology in Tracking and Exploring Complex Structures Controlling Gold Mineralization. Example from the Fawakheir-Atalla Gold Prospects, Eastern Desert, Egypt

Gold mineralisation is spatially and chronologically correlated with fault/shear zones in many of the world-class gold mines. Hence, the indirect exploration for Au mineralisation is linked with shearing and complex structures in many areas. Hence, in general, the need for a rapid, effective and new technology for gold exploration that reflects the structure set-up, shear zones, faults and related structural elements is crucial in the gold industry. In this article, we present an example of an integrated approach to gold exploration in the Fawakheir-Attala gold mining prospect in the eastern desert of Egypt. Remote sensing is used to test for rock differentiation; intensive field geological investigations were conducted along several traverses. Petrographic and geochemical analysis of selected samples confirmed Au content in some localities. Moreover, magnetic methods are used extensively (either aeromagnetic or measured land profiles) to investigate the magnetic signature of the different reported rock units and their relationship with gold occurrences and deposits. Normalised source strength transformation, magnitude magnetic transforms and subsurface modelling are used to explore the inherent relation between the surface and subsurface magnetic susceptibilities. The magnetic signature of the talc-carbonate rocks is determined. The gradational contact against the serpentinite is explained. Because three current Au mines are associated with contacts/fractures, the clear relation between the contacts/fractures and the magnetic data and the comparison with the contact occurrence density COD (heat) magnetic filtered map, the present analysis workflow can now be used to suggest new locations for Au occurrences.