<p>In the D&#250;rico-Beir&#227;o mining district, several occurrences of Sb-Au are... more <p>In the D&#250;rico-Beir&#227;o mining district, several occurrences of Sb-Au are known, which were exploited since the Roman occupation in Iberia until mid-last century. This region is located in the Central Iberian Zone of the Iberian Massif, part of the Ibero-Armorican Arc. The country rocks in the area consist of folded metasedimentary rocks from Cambrian to Carboniferous surrounded by syn- to post-orogenic Variscan granites. The Ribeiro da Serra Sb-Au mine, intensively exploited in the 19<sup>th</sup> century, occurs west of the western limb of the Valongo Anticline, a major ante-Stephanian structure with NW-SE trend. This Sb-Au deposit consist mainly of stibnite-bearing quartz veins hosted by slates, quartzites and conglomerates of the Schist-Greywacke Complex in a possible spatial relationship with dolerite dykes. These mafic dykes are emplaced in sub-parallel shear zones to the sinistral Douro Shear Zone and their presence may suggest the existence of mafic/ultramafic bodies at depth, which contributed to the occurrence of Sb-Au deposits.</p><p>This study aims to describe the dolerite dykes present through the region (petrographic composition, weathering, distribution, and dimension) considering a possible contribution for the Sb-Au occurrence. Dolerites are greyish-green colored and are intensely weathered. The samples surface shows a few millimeters of brownish supergenic alteration. The petrographic study highlighted an intense chloritization and saussuritization of plagioclase, whose tabular form and twinning are still preserved. The primary igneous texture is better preserved than the primary mineralogy. The texture is ophitic to sub-ophitic although the interstitial mass of the pyroxene is totally altered. &#160;Chlorites occur as fresh, green-colored patches, sometimes with radiated fibrous textures. Frequent polycrystalline quartz lenses and veins occur, also as consequence of the hydrothermal/metamorphic alteration. The opaques, not yet identified, occur in a great modal percentage, and are frequently associated with titanite. They do not seem to have a special concentration related to quartz veins and lenses. Apatite is a frequent accessory phase and appears to be preferentially associated with opaque minerals.</p><p>The knowledge of the petrographic characteristics of these dolerite dykes, associated with geochemical data, can be a great contribution to the understanding of the distribution of Sb mineralization and corroborate the hypothesis of non-outcropping mafic/ultramafic bodies.</p><p>&#160;</p><p><strong>Acknowledgment</strong></p><p>The work was financial supported within the compass of the ERA-MIN/0005/2018&#8212;AUREOLE project, FEDER through operation POCI-01-0145-FEDER-007690 funded by the Programa Operacional Competitividade Internacionaliza&#231;&#227;o&#8212;COMPETE2020 and by National Funds through FCT within the ICT (reference UIDB/04683/2020).</p>
A geological based remote sensing study was carried out over the Chaves License in northern Portu... more A geological based remote sensing study was carried out over the Chaves License in northern Portugal. In this study, Landsat 8 imagery was used in order to map hydrothermal alteration associated with gold mineralization. The Chaves license is an area acquired by Medgold resources Corp. for gold exploration. This license is located in the Trás-os-Montes region, in Portugal, covering an area over 600 Km, where gold exploration dates back to the Roman era with several mining and exploration works. Geologically, this study area is within the Galician Trásos-Montes Zone, and it’s composed of Hercynian granites that intruded and metamorphozed Silurian sediments. Gold mineralization consists in quartz veins with disseminated sulfides or in massive sulfide veins, where gold is generally associated with the arsenopyrite and pyrite as native gold or electrum. These mineralized structures are NE trending and are usually found within altered granite. Different remote sensing techniques, such as...
Mapping hydrothermal alteration minerals and structural lineaments using Landsat 8 multispectral ... more Mapping hydrothermal alteration minerals and structural lineaments using Landsat 8 multispectral imagery provides valuable information for mineral exploration. In northern Portugal, there are several known gold occurrences, but there is the potential to identify new anomalous areas. Gold mineralization occurs in the form of quartz veins and veinlets associated with hydrothermal alteration halos. Fractures are interpreted as conduits for mineralizing fluids, where the interaction between the wall rock and hydrothermal fluids induces compositional variations. Identifying these features is one of the key indicators for targeting new prospective zones of orogenic gold mineralization in the Boticas–Chaves region. Remote sensing image processing methods such as band combinations, band ratios, and principal component analysis (PCA) were implemented to the visible, near-infrared, and shortwave infrared bands of Landsat 8. The results of this investigation demonstrate the capability of the applied imagery enhancement methods in distinguishing different features and identifying hydrothermally altered rocks. Selective PCA proved to be the most effective and reliable method to identify iron oxides and hydroxyl-bearing minerals, compared to other methods, where a simple imagery analysis has a strong influence of noise and is more challenging to interpret. Enhanced imagery allowed the identification of physiographic characteristics and extracted structural features. The combination of mapped hydrothermal alteration minerals and extracted structural features allowed us to predict potential areas for the mineralization occurrence. This investigation proves that remote sensing can be a cost-efficient and time-saving technique for mineral exploration, and its application in new areas can accurately map hydrothermal alteration and outline potential new exploration targets.
&amp;amp;lt;p&amp;amp;gt;In the D&amp;amp;amp;#250;rico-Beir&amp;amp;amp;#227;o m... more &amp;amp;lt;p&amp;amp;gt;In the D&amp;amp;amp;#250;rico-Beir&amp;amp;amp;#227;o mining district several paragenetic associations have been described in gold mineralizations, including Sb-Au. The objective of this research was the study of the Sb-Au mineralization in the Rates area, from field reconnaissance of the mineralized structures by soil sampling to the petrographic and mineralogical study of the parageneses associated with this gold mineralization, mined by the Romans.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The portable XRF was used to measure Sb and As in farms and forest soils. The observed Au-Sb-As anomalies in the Rates area must be linked to Lagoa Negra mine by the same north-western trend fault. Historical mining works have been identified both in Lagoa Negra and in Rates, where rock-chip sampling returned results up to 30 g/t Au from the Rates prospect.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Some rock samples from Rates were studied by geochemical and petrographic analyses and were analysed in detail by scanning electron microscopy. The results indicate that the paragenetic association in Rates is Sb-Au, with stibnite as primary Sb sulfide mineral, valentinite as alteration mineral, and gold in native and granular form.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;&amp;amp;lt;strong&amp;amp;gt;Acknowledgment&amp;amp;lt;/strong&amp;amp;gt;&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The work was financial supported within the compass of the ERA-MIN/0005/2018&amp;amp;amp;#8212;AUREOLE project, FEDER through operation POCI-01-0145-FEDER-007690 funded by the Programa Operacional Competitividade Internacionaliza&amp;amp;amp;#231;&amp;amp;amp;#227;o&amp;amp;amp;#8212;COMPETE2020 and by National Funds through FCT within the ICT (reference UIDB/04683/2020).&amp;amp;lt;/p&amp;amp;gt;
<p>In the D&#250;rico-Beir&#227;o mining district, several occurrences of Sb-Au are... more <p>In the D&#250;rico-Beir&#227;o mining district, several occurrences of Sb-Au are known, which were exploited since the Roman occupation in Iberia until mid-last century. This region is located in the Central Iberian Zone of the Iberian Massif, part of the Ibero-Armorican Arc. The country rocks in the area consist of folded metasedimentary rocks from Cambrian to Carboniferous surrounded by syn- to post-orogenic Variscan granites. The Ribeiro da Serra Sb-Au mine, intensively exploited in the 19<sup>th</sup> century, occurs west of the western limb of the Valongo Anticline, a major ante-Stephanian structure with NW-SE trend. This Sb-Au deposit consist mainly of stibnite-bearing quartz veins hosted by slates, quartzites and conglomerates of the Schist-Greywacke Complex in a possible spatial relationship with dolerite dykes. These mafic dykes are emplaced in sub-parallel shear zones to the sinistral Douro Shear Zone and their presence may suggest the existence of mafic/ultramafic bodies at depth, which contributed to the occurrence of Sb-Au deposits.</p><p>This study aims to describe the dolerite dykes present through the region (petrographic composition, weathering, distribution, and dimension) considering a possible contribution for the Sb-Au occurrence. Dolerites are greyish-green colored and are intensely weathered. The samples surface shows a few millimeters of brownish supergenic alteration. The petrographic study highlighted an intense chloritization and saussuritization of plagioclase, whose tabular form and twinning are still preserved. The primary igneous texture is better preserved than the primary mineralogy. The texture is ophitic to sub-ophitic although the interstitial mass of the pyroxene is totally altered. &#160;Chlorites occur as fresh, green-colored patches, sometimes with radiated fibrous textures. Frequent polycrystalline quartz lenses and veins occur, also as consequence of the hydrothermal/metamorphic alteration. The opaques, not yet identified, occur in a great modal percentage, and are frequently associated with titanite. They do not seem to have a special concentration related to quartz veins and lenses. Apatite is a frequent accessory phase and appears to be preferentially associated with opaque minerals.</p><p>The knowledge of the petrographic characteristics of these dolerite dykes, associated with geochemical data, can be a great contribution to the understanding of the distribution of Sb mineralization and corroborate the hypothesis of non-outcropping mafic/ultramafic bodies.</p><p>&#160;</p><p><strong>Acknowledgment</strong></p><p>The work was financial supported within the compass of the ERA-MIN/0005/2018&#8212;AUREOLE project, FEDER through operation POCI-01-0145-FEDER-007690 funded by the Programa Operacional Competitividade Internacionaliza&#231;&#227;o&#8212;COMPETE2020 and by National Funds through FCT within the ICT (reference UIDB/04683/2020).</p>
A geological based remote sensing study was carried out over the Chaves License in northern Portu... more A geological based remote sensing study was carried out over the Chaves License in northern Portugal. In this study, Landsat 8 imagery was used in order to map hydrothermal alteration associated with gold mineralization. The Chaves license is an area acquired by Medgold resources Corp. for gold exploration. This license is located in the Trás-os-Montes region, in Portugal, covering an area over 600 Km, where gold exploration dates back to the Roman era with several mining and exploration works. Geologically, this study area is within the Galician Trásos-Montes Zone, and it’s composed of Hercynian granites that intruded and metamorphozed Silurian sediments. Gold mineralization consists in quartz veins with disseminated sulfides or in massive sulfide veins, where gold is generally associated with the arsenopyrite and pyrite as native gold or electrum. These mineralized structures are NE trending and are usually found within altered granite. Different remote sensing techniques, such as...
Mapping hydrothermal alteration minerals and structural lineaments using Landsat 8 multispectral ... more Mapping hydrothermal alteration minerals and structural lineaments using Landsat 8 multispectral imagery provides valuable information for mineral exploration. In northern Portugal, there are several known gold occurrences, but there is the potential to identify new anomalous areas. Gold mineralization occurs in the form of quartz veins and veinlets associated with hydrothermal alteration halos. Fractures are interpreted as conduits for mineralizing fluids, where the interaction between the wall rock and hydrothermal fluids induces compositional variations. Identifying these features is one of the key indicators for targeting new prospective zones of orogenic gold mineralization in the Boticas–Chaves region. Remote sensing image processing methods such as band combinations, band ratios, and principal component analysis (PCA) were implemented to the visible, near-infrared, and shortwave infrared bands of Landsat 8. The results of this investigation demonstrate the capability of the applied imagery enhancement methods in distinguishing different features and identifying hydrothermally altered rocks. Selective PCA proved to be the most effective and reliable method to identify iron oxides and hydroxyl-bearing minerals, compared to other methods, where a simple imagery analysis has a strong influence of noise and is more challenging to interpret. Enhanced imagery allowed the identification of physiographic characteristics and extracted structural features. The combination of mapped hydrothermal alteration minerals and extracted structural features allowed us to predict potential areas for the mineralization occurrence. This investigation proves that remote sensing can be a cost-efficient and time-saving technique for mineral exploration, and its application in new areas can accurately map hydrothermal alteration and outline potential new exploration targets.
&amp;amp;lt;p&amp;amp;gt;In the D&amp;amp;amp;#250;rico-Beir&amp;amp;amp;#227;o m... more &amp;amp;lt;p&amp;amp;gt;In the D&amp;amp;amp;#250;rico-Beir&amp;amp;amp;#227;o mining district several paragenetic associations have been described in gold mineralizations, including Sb-Au. The objective of this research was the study of the Sb-Au mineralization in the Rates area, from field reconnaissance of the mineralized structures by soil sampling to the petrographic and mineralogical study of the parageneses associated with this gold mineralization, mined by the Romans.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The portable XRF was used to measure Sb and As in farms and forest soils. The observed Au-Sb-As anomalies in the Rates area must be linked to Lagoa Negra mine by the same north-western trend fault. Historical mining works have been identified both in Lagoa Negra and in Rates, where rock-chip sampling returned results up to 30 g/t Au from the Rates prospect.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Some rock samples from Rates were studied by geochemical and petrographic analyses and were analysed in detail by scanning electron microscopy. The results indicate that the paragenetic association in Rates is Sb-Au, with stibnite as primary Sb sulfide mineral, valentinite as alteration mineral, and gold in native and granular form.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;&amp;amp;lt;strong&amp;amp;gt;Acknowledgment&amp;amp;lt;/strong&amp;amp;gt;&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The work was financial supported within the compass of the ERA-MIN/0005/2018&amp;amp;amp;#8212;AUREOLE project, FEDER through operation POCI-01-0145-FEDER-007690 funded by the Programa Operacional Competitividade Internacionaliza&amp;amp;amp;#231;&amp;amp;amp;#227;o&amp;amp;amp;#8212;COMPETE2020 and by National Funds through FCT within the ICT (reference UIDB/04683/2020).&amp;amp;lt;/p&amp;amp;gt;
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