NE-SW-orientation Gossan-8 formed in stages and close to the contact of...

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Aug 2023

Like the Eastern Hemisphere, the cultures of the Americas developed a rich tradition of metallurgy millennia ago. The Andes were an independent center of innovation, arriving at the similar technologies and end products in the absence of direct or indirect contact. It is fascinating that human ingenuity and experimentation arrived at similar industrial processes in at least two areas of the world. In this paper we review the great metallurgy traditions in the Pre-Columbian Andes with an emphasis on copper.KeywordsAndesMetallurgyCultural evolutionPyrotechnologyCopper

Mapping hydrothermal alteration zone throughaster data inGadag Schist Belt ofWestern Dharwar Craton ofKarnataka, India

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Dec 2020
ENVIRON EARTH SCI

Alteration zones are developed in a wide range of geological milieus such as volcano-plutonic rocks. Hydrothermal alteration zones are considered an important guide for mineral exploration and can act as a potential zone of mineralization. The minerals in alteration zones have very diagnostic absorption features in visible–near infrared (VNIR) and shortwave infrared (SWIR) regions of the electromagnetic spectrum. The Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) data have the potential to identify mineral assemblages in different hydrothermal alteration zones because of its 14 spectral bands which cover a wide spectral range. In the present article, FCC, band ratio, and SPCA techniques were applied to map the hydrothermal alteration zones in Gadag Schist Belt (GSB) of Western Dharwar Craton (WDC) of Karnataka. FCC has highlighted lithology, alteration zones, and given a fair idea about the lithological control and alteration occurrences in the area. Band ratio technique for muscovite, kaolinite, chlorite, iron oxide gossan, and silica alteration have yielded promising results. SPCA analysis successfully mapped hydrothermal alteration and delineated phyllic, argillic, and propylitic zones in the area. These results were verified through the existing geological map and by geological fieldwork in the area and these results are satisfactory. The total area, altered by different alteration process, was also calculated. In the GSB, iron alteration zone, phyllic, argillic, propylitic, and silica alteration zones were effectively mapped with the help of ASTER data.

Mapping hydrothermal alteration zone through aster data in Gadag Schist Belt of Western Dharwar Craton of Karnataka, India

Article

Nov 2020

Alteration zones are developed in a wide range of geological milieus such as volcano-plutonic rocks. Hydrothermal alteration zones are considered an important guide for mineral exploration and can act as a potential zone of mineralization. The minerals in alteration zones have very diagnostic absorption features in visible–near infrared (VNIR) and shortwave infrared (SWIR) regions of the electromagnetic spectrum. The Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) data have the potential to identify mineral assemblages in different hydrothermal alteration zones because of its 14 spectral bands which cover a wide spectral range. In the present article, FCC, band ratio, and SPCA techniques were applied to map the hydrothermal alteration zones in Gadag Schist Belt (GSB) of Western Dharwar Craton (WDC) of Karnataka. FCC has highlighted lithology, alteration zones, and given a fair idea about the lithological control and alteration occurrences in the area. Band ratio technique for muscovite, kaolinite, chlorite, iron oxide gossan, and silica alteration have yielded promising results. SPCA analysis successfully mapped hydrothermal alteration and delineated phyllic, argillic, and propylitic zones in the area. These results were verified through the existing geological map and by geological fieldwork in the area and these results are satisfactory. The total area, altered by different alteration process, was also calculated. In the GSB, iron alteration zone, phyllic, argillic, propylitic, and silica alteration zones were effectively mapped with the help of ASTER data.

Integration of Selective Dimensionality Reduction Techniques for Mineral Exploration Using ASTER Satellite Data

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Apr 2020

There are a significant number of image processing methods that have been developed during the past decades for detecting anomalous areas, such as hydrothermal alteration zones, using satellite images. Among these methods, dimensionality reduction or transformation techniques are known to be a robust type of methods, which are helpful, as they reduce the extent of a study area at the initial stage of mineral exploration. Principal component analysis (PCA), independent component analysis (ICA), and minimum noise fraction (MNF) are the dimensionality reduction techniques known as multivariate statistical methods that convert a set of observed and correlated input variables into uncorrelated or independent components. In this study, these techniques were comprehensively compared and integrated, to show how they could be jointly applied in remote sensing data analysis for mapping hydrothermal alteration zones associated with epithermal Cu–Au deposits in the Toroud-Chahshirin range, Central Iran. These techniques were applied on specific subsets of the advanced spaceborne thermal emission and reflection radiometer (ASTER) spectral bands for mapping gossans and hydrothermal alteration zones, such as argillic, propylitic, and phyllic zones. The fuzzy logic model was used for integrating the most rational thematic layers derived from the transformation techniques, which led to an efficient remote sensing evidential layer for mineral prospectivity mapping. The results showed that ICA was a more robust technique for generating hydrothermal alteration thematic layers, compared to the other dimensionality reduction techniques. The capabilities of this technique in separating source signals from noise led to improved enhancement of geological features, such as specific alteration zones. In this investigation, several previously unmapped prospective zones were detected using the integrated hydrothermal alteration map and most of the known hydrothermal mineral occurrences showed a high prospectivity value. Fieldwork and laboratory analysis were conducted to validate the results and to verify new prospective zones in the study area, which indicated a good consistency with the remote sensing output. This study demonstrated that the integration of remote sensing-based alteration thematic layers derived from the transformation techniques is a reliable and low-cost approach for mineral prospectivity mapping in metallogenic provinces, at the reconnaissance stage of mineral exploration.

Mapping of real Gossan in oxidant deposits using multi-source images and deep learning

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Full-text available

Feb 2024

Gossans serve as a rapid and efficient means of exploring subsurface resources, essentially manifesting mineral zones on the Earth's surface. Specifically, Gossans harboring significant mineral resources like copper and gold are denoted as true Gossans. This study aimed to discern true Gossans in compact exploration areas, presenting an algorithm for deep convolutional Gossan identification. The proposed algorithm initiates with preprocessing steps, including geometric and spectral correction, restoration, satellite image segmentation into smaller units, and augmentation of training data to prepare RGB input for the network. The designed Convolutional Neural Network (CNN) adopts an encoder-decoder structure, extracting diverse and effective features at various scales during encoding, while combining these features during decoding to estimate Gossan regions. The algorithm was then implemented for images of the exploration area named "TalBargah" in Darab city, successfully extracting Gossan regions. To field-evaluate the results, the network outcomes were juxtaposed with the copper orthodontic interpolation map of the region. Comprehensive lithological reviews, cross-referencing with actual Gossans, and statistical accuracy parameters were considered, revealing a sensitivity of 0.957, an F1 score of 0.457, a rock detection accuracy of 92%, and an average copper grade exceeding 4% in the identified areas. These findings underscore the effectiveness and reliability of the proposed algorithm in pinpointing true Gossans. Keywords: Gossan, Geochemistry, Copper deposit, Remote sensing, Deep learning. Introduction Gossan, in general, refers to a collection of iron oxides and hydroxides resulting from the weathering and oxidation of sulphide minerals near the Earth's surface. This process involves surface water washing away soluble elements, as well as secondary iron oxide, hydroxide minerals (such as goethite and hematite), and sulphate oxides (associated with the Jarosite group), which form in proximity to massive sulphide deposits. The presence of gossans on the surface serves as a valuable indicator for exploring sulphide deposits at greater depths. The abundance of iron oxide in Gossans can be readily identified through satellite imagery, making them a useful tool in sulphide deposit exploration. In this context, a deep learning network has been employed to discern and categorize Gossan variations due to its well-suited characteristics. The primary objective of this research is to employ a CNN deep learning neural network to accurately identify immature Gossans. Alongside mineralogical studies, the concentrations of valuable elements, including gold, silver, lead, zinc, and copper, have been assessed in various horizons of the Gossan. The findings from this study can serve as valuable data for conducting comprehensive explorations and contribute to the development of mineralization models in the quest for concealed sulphide deposits. Methodology and Materials In previous studies, the precise and accurate identification of crucial alterations in copper deposit areas, specifically Gossans, has been inadequately explored, as has the examination of the geometrical structure and formation position of these alterations. The alterations investigated in these prior research efforts, observable in remote sensing images, lack distinct geometric features individually; however, their collective presence gives rise to a meaningful structure. Consequently, a robust methodology is imperative not only to pinpoint these changes effectively but also to incorporate ground methods for result verification and interpretation. Proposed Method In this study, a suitable dataset of input and output images was curated using RGB images. To train the deep learning network, Gossan variations were meticulously separated and extracted from other variations in the mining area, establishing them as the target class. Following the training of the proposed network, the images of the study area underwent processing, revealing the distribution of Gossans within the region as identified by the network. Drawing on the mineral metal sources associated with Gossan, the theory suggests the accumulation of valuable metallic minerals such as copper, gold, lead, zinc, chromium, etc., in the vicinity of Gossan. Consequently, to assess the operational accuracy of the network's results in delineating Gossan boundaries, a comparative analysis was conducted. This involved comparing the lithology results and the geochemical anomaly map of the region—indicating the surface dispersion of copper and other valuable metals—with the outcomes produced by the proposed network. Datasets and Study Area The Talbargah copper deposit is situated in the eastern part of Fars province, approximately 57 kilometers northwest of Hajiabad city. Positioned on the southern margin of the Sanandaj-Sirjan zone, the deposit is delineated on the Darab 1:250,000 and Sargdar 1:100,000 geological maps. Figure 1 provides an overview of this geographical area. The central coordinates of the designated region are approximately 55°22'15" E longitude and 28°31'13" N latitude. This deposit is categorized as one of the copper deposits within the melange ophiolite group in the country, aligning with the Faryab to Neyriz ophiolites. Notably, the area has a history of ancient mining activities, evident from the presence of substantial excavations and mineral slag. The prevalence of extensive pits and mineral remnants attests to the considerable scale of past mining operations in this region. Results and Discussion In this study, a convolutional deep learning network was employed to distinguish authentic Gossans within the exploratory region of Talbargah, situated southeast of Darab city. RGB images from Google Earth sources and ASTER sensor images were utilized to construct the training dataset. Following several iterations of trial and error, the optimal parameters for the network were determined, as outlined in Table 1. The optimized network was then applied to the images of the study area, yielding statistical results related to two crucial parameters in its error matrix: sensitivity (0.957) and F1 score (0.461). Upon extracting the network's prediction results corresponding to the actual Gossan locations, field operations were conducted to validate these outcomes through lithological and geochemical analyses. The results of these analyses are presented in Figures 9 and 2. In the lithological assessments of the studied area, Gossans were identified with an accuracy of 92%. Additionally, the geochemical interpolation map, based on the copper element grades in 75 rock samples from the region, revealed that the recognized Gossans exhibited an average copper grade of 4%. This economically significant finding further substantiates the authenticity of the Gossans in the region. Table 1. The results of convolutional network parameters extraction in the identification of real gossans Figure 1. Orthophoto map of Talbargah exploration area Figure 2. Interpolation map of copper element distribution in the study area References Beiranvand Pour. and A.. Hashim. M.. 2012. The application of ASTER remote sensing data to porphyry copper and epithermal gold deposits. Ore Geology Reviews, 44 (2012) 1–9. Gossan Tar RGB RGB RGB RGB Input 200 100 50 20 Epoch 0.00001 0.00001 0.00001 0.00001 L-r 0.5 0.5 0.5 0.5 D-o *4 *4 *4 *4 D-a 75 75 75 75 Train 0.1 0.1 0.1 0.1 Val-S 2 2 2 2 Test 2 2 2 2 B_s 0.882 0.957 0.911 0.846 Sen 0.436 0.461 0.445 0.423 F1 100 50 25 10 TIME (m) Beiranvand Pour. A.. Hashim. M.. and Marghany. M.. 2013. Exploration of gold mineralization in a tropical region using Earth Observing-1 (EO1) and JERS-1 SAR data: a case study from Bau gold field, Sarawak, Malaysia. Arab J Geosci 7, 2393–2406. Bhadra. B. K.. Kumar. A.. Karunakar.G.. Meena. H.. Rehpade. B.. and Srinivasa Rao. S.. 2021. Integrated remote sensing and geophysical techniques for shallow base metal deposits (Zn, Pb, Cu) below the gossan zone at Kalabar, Western Aravalli Belt, India. Journal of Applied Geophysics, 191. 104365. Gahlan. H.. and Ghrefat. H.. 2018. ‏Detection of Gossan Zones in Arid Regions Using Landsat 8 OLI Data: Implication for Mineral Exploration in the Eastern Arabian Shield, Saudi Arabia‏. Natural Resources Research, 27(1):109-124. Ioffe. S.. and Szegedy. C.. ‏2015. Batch normalization: Accelerating deep network training by reducing internal covariate shift,‏ arXiv preprint arXiv:1502.03167. Karimpour. M. H.. Malekzadeh Shafaroudi.A.. Esfandiarpour. A.. and Mohammadnezhad. H.. 2012. ‏Neyshabour turquoise mine: the first Iron Oxide Cu-Au-U-LREE (IOCG) mineralized system in Iran‏. Journal of Economic Geology, 3(2), 193-216. LeCun. Y.. Bengio. Y.. and Hinton. G.. ‏2015.Deeplearning,‏ Nature, vol. 521, pp. 436-444. Ozdemir. A.. and Sahinoglu. A.. 2018. Important of Gossans in Mineral Exploration: A Case Study in Northern Turkey. Int J Earth Sci Geophys, 4:019. Pirouei. M.. Kolo. K.. and Kalaitzidisc. S. P.. 2020. Hydrothermal listvenitization and associated mineralizations in Zagros Ophiolites: implications for mineral exploration in Iraqi Kurdistan. Journal of Geochemical Exploration, 208. 106405. Rajendran. S.. and Nasir. S.. 2017. ‏Characterization of ASTER spectral bands for mapping of alteration zones of volcanogenic massive sulphide deposits‏. Ore Geology Reviews, 88:317-335.

Mineralogical and textural evolution of the Alvo 118 copper-bearing gossan: Implications for supergene metallogenesis in Carajás Mineral Province, Brazil

Article

Nov 2022
J S AM EARTH SCI

The Carajás Mineral Province is home to one of the most extensive copper-gold belts globally, where hypogene orebodies were partially transformed into gossans. The Carajás Mountains host mature gossan profiles modified by lateritization. Conversely, the surrounding denuded landscape holds deep immature gossans characterized by generation mechanisms that remain poorly understood. Alvo 118 is a typical deposit from this area, with numerous drill cores available for evaluation. Mineralogical, textural, and mineral chemistry investigations showed that the hypogene mineralization, consisting of massive and disseminated chalcopyrite with minor nukundamite, was partially oxidized. The resulting gossan comprises a range of copper-bearing minerals, including malachite, pseudomalachite, cuprite, tenorite, native copper, ramsbeckite, chrysocolla, and libethenite, with relics of a secondary sulfide zone represented by chalcocite. The host rocks are relatively well-preserved from supergene alteration near the gossan due to the chalcopyrite's low acidifying potential and the deep occurrence of the gossan orebody, resulting in an immature profile. The gossan orebody is sectioned into four zones; the mineral succession of each zone indicates independent evolution, with a general transition from slightly acidic to alkaline conditions and increasing oxidation potential, with local oscillations related to water table fluctuations. This environment was established by the interaction of acid solutions derived from sulfide dissolution with gangue minerals (calcite and apatite) and secondarily with host rocks (chloritites and granodiorites), leading to system buffering. Ti, Mn, Zn, Ni, V, and Co were incorporated into the gossan mainly by goethite, while malachite contains Ba, Ca, Cr, Mn, and Zn. Gold and Pb were detected in goethite, cuprite, tenorite, and native copper. This set of mineralogical zones and mineral successions record an important and unique stage of the supergene evolution of the Carajás Mineral Province, with prominent copper-gold mineralization showing no effects from lateritization.

Geochemistry, Mineralography and Rare Earth Elements Distribution of Gossans related to Volcanogenic Massive Sulfide Deposit, Case Study: Ghaleh-Rigi, Southwest of Jiroft, South of Iran

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Full-text available

Nov 2020
ECON GEOL

Introduction Erosion and oxidation of massive sulfides when uplifted and exposed to the surface, commonly lead to the formation of gossans. In this process, surface water will dissolve soluble elements, and oxides and hydroxides of iron (goethite and hematite) will form on top of the volcanogenic massive sulfide (VMS) deposits. The main tectonic settings for Iranian VMS deposits are magmatic arcs, which can be subdivided into volcanic primitive arc, arc/intra-arc rift, and back-arc settings and Sanandaj-Sirjan zone is one of the structural zones that host many VMS deposits in Iran (Mousivand et al., 2018).The study area is located southwest of Jiroft, Kerman province. The main rock units include vitric tuff, pelagic sediments, volcano-sedimentary rocks, gabbro and intermediate to mafic dykes. Mineralization has occurred in volcanosedimentary beds. The pelagic sediments which are composed of limestone, shale, sandstone, siltstone and interlayers of pillow lava, are the main hosts for mineralization. Surface oxidation of mineralized zones has led to conversion of primary sulfides to iron oxides and hydroxides to form gossan. This study contributes to mineralogical and geochemical composition and mineralization of gossans to demonstrate how surface oxidation of primary sulfides can play a role in locating VMS mineralization at depth. Materials and methods A geological map with a scale of 1:5000 was prepared during field and laboratory studies. Twenty polished section were studied to identify mineral distributions and textures, and some of them were chosen for scanning electron microscopic (SEM) examinations. Fifteen rock samples from the gossan horizons were chosen for geochemical studies. The samples were taken from across the mineralized horizon. Six rock samples were taken from old mining site outcrops to compare the geochemistry of gossans with other surface mineralization. All samples were sent to the laboratory for analysis by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES). The rare earth element (REEs) values were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). X-ray diffraction (XRD) spectroscopy was used to identify mineralogy of 30 rock samples. All analyses were performed in the central laboratory of the Geological Survey and Mineral Exploration of Iran, in Tehran and Karaj. Results The ore and gangue minerals have massive, layered, disseminated, veinlet, breccia and replacement textures. Based on mineralography, XRD and SEM studies, the main minerals are hematite, goethite, quartz, and jarosite-group minerals. The upper horizon of gossan, with 13 meters thickness has large volume of hematite and gothite minerals. The enrichment of gold, arsenic, antimony, silver, lead and bismuth were observed in this zone. The lower horizon, with a thickness of about 1.5 meters show anomalies of copper and zinc elements. The highest amount of gold and silver were measured about 18.5 and 120 g/ton, respectively. The highest amount of lead element is 1.3 wt.%, which shows a positive correlation with silver variations. The other values are copper 0.16 wt.%, arsenic 0.61 wt.%, bismuth 580 g/ton, and antimony 280 g/ton. Discussion Trace and REEs geochemistry are useful in identifying gossans and probable sources (Scott et al., 2001). Geochemical studies also can be used to separate mature from immature gossans. Although the composition of gossans is influenced by early composition of the ore, gossans with high content of Pb (more than 4 wt.%) are usually considered immature. The average Pb measured in the studied gossans is about 2210 g/ton. The Ag content is also low (less than 150 g/ton) and there is a relatively linear relationship between increasing Ag and Pb content. High values of copper often refer to a lower degree of maturity. In the studied gossans, the average amount of Cu is about 2900 g/ton, which is much lower than the immature gossans with average 1.6 wt.%. Therefore, the results of chemical analysis indicate that these gossans are in the category of mature ore bearing gossan. The REE from La to Lu, is relatively consistent with the shape of REE profiles for volcanogenic massive sulfide mineralization and concurrent massive sulfide gossans (Peter et al., 2003; Volesky et al., 2017; Gieré, 1993). The pattern of distribution of REEs shows small positive Eu enrichment and zoning of precious mineral elements confirms the possibility of orebody under the gossans. Further exploration of volcanogenicmassive sulfide deposits is recommended for this area.

Evaluación de metales preciosos (Au y Ag) en zonas de oxidación al noroeste de Artemisa (Cuba) Evaluation of precious metals (Au and Ag) at the oxidation zone northwest of Artemisa (Cuba)

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Full-text available

Jan 2021

La determinación de contenidos de metales preciosos (Au y Ag) en las zonas de oxidación, alteración hidrotermal y cizallamiento presentes en la zona metalogénica Bahía Honda, al noroeste de Artemisa, fue el objetivo primordial de la investigación. La mayoría de estas zonas se localizan sobre y en los alrededores de los yacimientos y/o prospectos cupro – sulfurosos que se extienden desde el macizo de Cajálbana, hacia el oeste, hasta Buena Vista, hacia el este. El motivo fundamental para emprender la tarea ha sido el creciente interés que ha habido en Cuba a partir del descubrimiento de yacimientos de oro en zonas de oxidación (gossan) de los depósitos de sulfuros tipo sedex, VMS y epitermales, entre los que se encuentran Oro Castellanos, Cobre Mantua, Loma de Hierro y Golden Hill, además de que la inmensa mayoría de los depósitos de cobre y metales base de Cuba son portadores de Au y Ag. La metodología se basó en la realización de itinerarios geológicos, el muestreo y la documentación de los principales afloramientos y muestras de testigos de pozos, además del análisis y la reinterpretación de la información geofísica y geoquímica de los trabajos anteriores. Las muestras fueron analizadas en el laboratorio “José Isaac del Corral” (LACEMI), determinándose mediante análisis combinado de docimasia con espectrometría de absorción atómica los contenidos de Au y Ag. Se realizó también análisis químico por espectrometría de masas con plasma inductivamente acoplado (ICP – MS) a un grupo de elementos acompañantes. Como resultado de estos trabajos se pudo determinar la presencia de valores significativos de Au en todas las zonas evaluadas, oscilando entre 0,05 – 2,24 g/t, lo cual permitió realizar el cálculo de los recursos hipotéticos. Los valores de la concentración de Ag fueron muy bajos en todas las zonas estudiadas.

NE-SW-orientation Gossan-8 formed in stages and close to the contact of metamorphics of Akgöl Formation and ophiolites of Elekdağ near Kirenlice-Çamlıköy.

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