scholarly journals Supergene gold enrichment in the Castromil-Serra da Quinta gold deposit, NW Portugal

2018 ◽  
Vol 82 (S1) ◽  
pp. S307-S320 ◽  
Author(s):  
C. Cruz ◽  
F. Noronha ◽  
P. Santos ◽  
J. K. Mortensen ◽  
A. Lima
Keyword(s):  
Gold Deposit ◽  
Gold Deposits ◽  
Northwestern Part ◽  
Gold Particles ◽  
Weathering Processes ◽  
Quartz Veins ◽  
Free Gold ◽  
Gold Enrichment ◽  
Upper Level ◽  
Variscan Granites

ABSTRACTSeveral gold deposits hosted mainly by Variscan granites and Precambrian to Palaeozoic metasediments occur in the northwestern part of Portugal. Most of these deposits were mined by the Romans (in the period I BC to II AD) as open pits and surface galleries. The Castromil-Serra da Quinta gold deposit is an important example of such a mined site; it occurs in the Dúrico-Beirã Au province located in the Central Iberian Zone (CIZ) in the western branch of European Variscan belt, mainly on the eastern flank of the Valongo anticline. Open pits and underground galleries at Castromil-Serra da Quinta exploited the gossan formed from the weathering of primary mineralization. The gossan is composed essentially of goethite, scorodite and clay minerals. A recent drilling campaign at Castromil-Serra da Quinta has provided samples of the primary mineralization below the oxidation level. Different modes of gold occurrence are defined based on metallographic studies of both the gossan and drill cores. Gold I occurs encapsulated in primary sulfide minerals, mainly arsenopyrite and pyrite; Gold II is also associated with the main primary sulfides, but occurs along grain boundaries and in microfractures of the sulfides or in associated quartz veins; and Gold III occurs as free gold particles in iron oxides within the gossan. In the gossan samples, it is difficult to distinguish whether the gold particles hosted in oxides correspond to Gold I, Gold II, or both, so these particles are described as Gold I–II and they are commonly surrounded by very much smaller particles of Gold III. Scanning electron microscope (SEM) and electron probe microanalysis (EPMA) data for the different gold particles reveal that Gold I is poorer in Ag (~15.5–39.76%) than Gold II (37.46–51.45%), whereas Gold III corresponds to native gold (<16.11% Ag). Gold III is thought to reflect gold enrichment in the upper level of the deposit, resulting from weathering processes that affected the primary Au (Bi) mineralization.

Characterization of heavy mineral concentrates and detrital gold particles from the Bigorne granite-hosted gold deposit in the Iberian Variscan Belt

2021 ◽  
pp. SP516-2020-217
Author(s):  
Sara Leal ◽  
Alexandre Lima ◽  
Fernando Noronha
Keyword(s):  
Gold Deposit ◽  
Gold Deposits ◽  
Heavy Mineral ◽  
Local Source ◽  
Variscan Belt ◽  
Alluvial Deposits ◽  
Gold Particles ◽  
First Results ◽  
Ore Minerals ◽  
Variscan Granites

AbstractThe Bigorne gold deposit, located in the Iberian Variscan belt, is a gold-bearing vein system, which crosscuts Variscan granites. The hypogene mineralization corresponds to sheet-veins parallel to the late-Variscan Penacova-Régua-Verín fault.A combined study was undertaken of gold particles from hypogene mineralization and locally derived eluvial material, as well as gold from alluvial deposits in local drainages, to assess possible source(s) of the alluvial gold.The geochemistry and mineralogy of heavy mineral concentrates revealed a similar signature as the hosted granites and hypogene mineralization, which indicates a local source for the surficial materials, with limited contribution from surrounding rocks.Hypogene and detrital gold particles at Bigorne area are entirely primary in origin and correspond essentially a Au-Ag alloy (< 22 wt.% Ag), locally with minor amounts of Cu. The compositional range of Ag and Cu is a consequence of variation in parameters formation of the deposit, such as temperature. Our study highlights the first results on gold detrital particles chemistry for granite-hosted gold deposits in Iberian Variscan belt and has provided a platform for further work to characterize gold from this environment such that it may be used as a generic indicator mineral together with other resistant ore minerals.

scholarly journals Tourmaline from Late Quartz Veins of the Murtykty Gold Deposit, Republic of Bashkortostan

2020 ◽  
Vol 6 (1) ◽  
pp. 69-83
Author(s):  
M.A. Rassomakhin ◽  
E.V. Belogub ◽  
K.A. Novoselov ◽  
P.V. Khvorov
Keyword(s):  
Gold Deposit ◽  
Sedimentary Rocks ◽  
Gold Deposits ◽  
Sulfide Mineralization ◽  
Porphyry Deposits ◽  
Quartz Veins ◽  
Orogenic Gold Deposits ◽  
Eastern Zone ◽  
Republic Of Bashkortostan ◽  
Intermediate Member

Tourmaline, an intermediate member of the oxyschorl–oxydravite–oxymagnesio-foitite-bosiite series with a predominance of the oxy-dravite-bosiite end-member, was studied from late calcite-quartz veins in the eastern zone of the Murtykty gold deposit (Republic of Bashkortostan). Sulfide mineralization in veins includes rare chalcopyrite, pyrite, sphalerite and galena. Accessory minerals are xenotime-(Y), vanadium-containing rutile and fine high-fineness gold. Supergene mineralization resulted from decomposition of carbonates, sulfides and rock-forming silicates includes kaolinite, hydroxides of Mn (chalcophanite, psilomelane) and Fe (goethite and limonite ochers), mainly developed in vein cavities ; chalcopyrite is replaced by cuprite and malachite. The composition of tourmaline is close to metamorphic dravite of orogenic gold deposits and tourmaline of gold-porphyry deposits, transitioning from porphyry to epithermal. Two possible B sources for the formation of tourmaline are considered: sedimentary rocks of the paleoisland-arc complex and granodiorites of the Mansurovo pluton. Figures 9. Table 1. References 36. Key words: tourmaline, boron, gold, xenotime-(Y), Murtykty deposit, Republic of Bashkortostan.

scholarly journals Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C-H-O-S Isotopes

2019 ◽  
Author(s):  
Kai Zhao ◽  
Huazhou Yao ◽  
Jianxiong Wang ◽  
Ghebsha Fitwi Ghebretnsae ◽  
Wenshuai Xiang ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Meteoric Water ◽  
Gold Mineralization ◽  
Early Stage ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Quartz Veins ◽  
Three Phase ◽  
Igneous Origin ◽  
Ne Africa

The Koka gold deposit is located in the Elababu shear zone between the Nakfa terrane and the Adobha Abiy terrane, NW Eritrea. Based on the paragenetic study two main stages of gold mineralization were identified in the Koka gold deposit: 1) an early stage of pyrite-chalcopyrite-sphalerite-galena-gold-quartz vein; and 2) a second stage of pyrite-quartz veins. NaCl-aqueous inclusions, CO2-rich inclusions, and three-phase CO2-H2O inclusions occur in the quartz veins at Koka. The ore-bearing quartz veins formed at 268℃, from NaCl-CO2-H2O(-CH4) fluids averaging 5 wt% NaCl eq. The ore-forming mechanisms include fluid immiscibility during stage I, and mixing with meteoric water during stage II. Oxygen, hydrogen and carbon isotopes suggest that the ore-forming fluids originated as mixtures of metamorphic water, meteoric water and magmatic water, whereas sulfur isotope suggest an igneous origin. Features of geology and ore-forming fluid at Koka deposit are similar to those of orogenic gold deposits, suggesting the Koka deposit might be an orogenic gold deposit related to granite.

scholarly journals Mineralizing Events of the World-Class Volta Grande Gold Deposit, Southeastern Amazonian Craton, Brazil

2021 ◽  
Vol 6 (1) ◽  
pp. 19
Author(s):  
Hugo Paiva Tavares de Souza ◽  
Carlos Marcello Dias Fernandes ◽  
Ricardo de Freitas Lopes ◽  
Stéphane Amireault ◽  
Marcelo Lacerda Vasquez
Keyword(s):  
Gold Deposit ◽  
Native Gold ◽  
Gold Deposits ◽  
Quartz Veins ◽  
The World ◽  
Intrusive Rocks ◽  
Amazonian Craton ◽  
World Class ◽  
High Level ◽  
Southeastern Region

The southeastern region of the Amazonian Craton has been the target of several metallogenetic surveys, which recently led to the identification of the world-class Volta Grande gold deposit with gold reserves of ~3.8 Moz at 1.02 g/t. This deposit is located ~60 km southeast of Altamira city, Pará state, and is hosted by the Três Palmeiras intrusive greenstone belt that is located in the northern Bacajá tectonic domain (2.24–2.0 Ga). The mineralization is hosted by a high-level intrusive and mylonitized suite. Local kinematic indicators suggest dip-slip movement in which the greenstone moves up relative to the intrusive rocks. Native gold mostly occurs as isolated grains in centimeter-wide quartz veins and veinlets associated with pervasive carbonate alteration that was synchronous with dynamic metamorphism. Part of the gold is also associated with disseminated sulfides in this generally low-sulfide mineralization. These relationships are compatible with orogenic lode-type gold systems elsewhere. New petrographic studies from core samples along a stratigraphic profile reveal the presence of lava flows and dykes of rhyodacite, rhyolite, and plutonic rocks such as quartz monzonite, granodiorite, monzodiorite, and subordinate microgranite crosscutting an earlier style of mineralization. These rocks are characterized by potassic, propylitic, intermediate argillic, and/or carbonate hydrothermal alterations in selective, pervasive, or fracture-controlled styles. Within the hydrothermal volcano-plutonic sequence, gold occurs as disseminated isolated grains or replacing sulfides. Both native gold and sulfides are also present in centimetric quartz veinlets. Such features of the deposit are similar to those from porphyry-type and low- to intermediate-sulfidation epithermal systems already identified in the Amazonian Craton. The Volta Grande deposit data suggest a second mineralizing event, common in large-tonnage gold deposits, and can represent a new exploration guide.

Thermoluminescence of quartz from Shihu gold deposit, western Hebei province, China: some implications for gold exploration

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
Ye Cao ◽  
Shengrong Li ◽  
Meijuan Yao ◽  
Huafeng Zhang
Keyword(s):  
Gold Deposit ◽  
Cross Sections ◽  
North China Craton ◽  
North China ◽  
Mineral Exploration ◽  
Gold Deposits ◽  
Quartz Veins ◽  
The North ◽  
Indicator Mineral ◽  
Gold Bearing

AbstractThermoluminescence (TL) of monomineralic separates have been widely used in various geosciences fields in order to trace the thermal history and aid in prospecting for gold deposits. Quartz is a ubiquitous mineral in the Shihu gold deposit, which is situated in the northern part of the Taihang orogenic belt in the North China craton (NCC). The deposit is hosted by ductile-brittle faults within an Archean metamorphic core complex of the Fuping Group. This deposit is characterized by gold-bearing quartz-polymetallic sulfides and quartz veins. New TL results have been obtained for quartz, in which four type-TL glow curves were identified. The gold-bearing quartz present type III glow curves that consist of two peak glow curves at the middle and high peak temperatures with the similar TL intensity. In addition, the cross-sections of peak temperatures and TL intensity highlight the valuable area where the Au-bearing quartz present weak TL intensity and low-middle peak temperatures. Our results significantly enhance the usefulness of quartz in metallogenic studies of the North China craton and as an indicator mineral in mineral exploration of the Taihang Mountain region.

Chapter 34: The Paleoproterozoic (Rhyacian) Gold Deposits of West Africa

2020 ◽  
pp. 735-752
Author(s):  
Nicolas Thébaud ◽  
Andrew Allibone ◽  
Quentin Masurel ◽  
Aurélien Eglinger ◽  
James Davis ◽  
...  
Keyword(s):  
Sedimentary Basins ◽  
Shear Zones ◽  
Gold Deposits ◽  
Gold Deposition ◽  
Quartz Veins ◽  
Free Gold ◽  
High K ◽  
Refractory Gold ◽  
Close Relationship ◽  
Transcurrent Deformation

Abstract Paleoproterozoic terranes of the Man-Leo Shield in the southern part of the West African craton host one of the world’s largest gold provinces with an overall endowment &gt;10,000 metric tons (t). Although gold deposition commenced by ca. 2170 Ma, most deposits formed later, either during the inversion and metamorphism of intraorogenic sedimentary basins between ca. 2110 and 2095 Ma, or during later transcurrent deformation and associated widespread high K plutonism following docking of Archean and Paleoproterozoic domains within the craton at ca. 2095 Ma. Deposits formed between ca. 2110 and 2095 Ma include those with free gold in quartz veins and refractory gold in arsenopyrite and/or pyrite, and are associated with halos of carbonate, sericite, chlorite, and albite alteration. Most are located in bends and intersections between shear zones, minor faults, folds, and entrained blocks of relatively reactive igneous rock. Conglomerate-hosted gold deposits of the Tarkwa district formed early in the 15-m.y.-long period. Gold deposits that formed subsequently between ca. 2095 and 2060 Ma have a wider variety of styles, geologic settings, and metal assemblages. District-scale albite, carbonate, and tourmaline alteration, hydrothermal breccias, and a close relationship to high K granitoids characterize some of these deposits, whereas others are more typical orogenic gold deposits that are similar to those formed earlier during the craton evolution.

Geology of the Hammer Down mesothermal gold deposit, Newfoundland Appalachians, Canada

1996 ◽  
Vol 33 (2) ◽  
pp. 335-350 ◽  
Author(s):  
Damien Gaboury ◽  
Benoît Dubé ◽  
Marc R. Laflèche ◽  
Kathleen Lauzière
Keyword(s):  
Gold Deposit ◽  
High Strain ◽  
Volcanic Rocks ◽  
Gold Deposits ◽  
Quartz Veins ◽  
Younger Age ◽  
Two Generations ◽  
Brittle Faulting ◽  
Host Rocks ◽  
Actual Geometry

The Hammer Down gold deposit is one of the most significant mesothermal vein-type gold deposits in the Canadian Appalachians. It is located within a complex sequence of Ordovician, mafic-dominated tholeiitic and calc-alkalic and arc-related volcanic rocks, which was intruded by Silurian felsic porphyry dykes. The host rocks have undergone complex polyphase deformation. At least three deformational events influenced vein emplacement and overall geometry of the deposit. A Taconian deformation (D1–2) was responsible for the development of a 250 m wide zone of high-strain deformation (HSZ1) at the interface between two blocks of Ordovician rocks: the Catcher's Pond Group and the Lush's Bight Group. Rocks included within the HSZ1, represent "exotic" slabs of volcanic rocks that were tectonically juxtaposed, intensively foliated (S1), and folded (F2). Gold occurs in high-grade, sulfide-rich, fault-fill quartz veins that occur within the HSZ1. At the outcrop scale, these veins are hosted by discrete centimetre- to metre-wide ductile–brittle D3 high-strain zones (HSZ3) of Silurian or younger age. The development of the gold-hosting structures (HSZ3) is genetically related to layer anisotropy induced by intrafolial F2 folds, and most importantly by the presence of felsic porphyry dykes, which were competent compared to the intensively foliated and incompetent mafic volcanic rock sequence. A postmineralization D4–5 deformation, which included two generations of folds (F4 and F5) and late brittle faulting, is responsible for the actual geometry of the deposit.

scholarly journals Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 201 ◽  
Author(s):  
Kai Zhao ◽  
Huazhou Yao ◽  
Jianxiong Wang ◽  
Ghebsha Fitwi Ghebretnsae ◽  
Wenshuai Xiang ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Gold Mineralization ◽  
Early Stage ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Quartz Veins ◽  
Second Stage ◽  
Three Phase ◽  
Igneous Origin ◽  
Ne Africa

: The Koka gold deposit is located in the Elababu shear zone between the Nakfa terrane and the Adobha Abiy terrane, NW Eritrea. Based on a paragenetic study, two main stages of gold mineralization were identified in the Koka gold deposit: (1) an early stage of pyrite–chalcopyrite–sphalerite–galena–gold–quartz vein; and (2) a second stage of pyrite–quartz veins. NaCl-aqueous inclusions, CO2-rich inclusions, and three-phase CO2–H2O inclusions occur in the quartz veins at Koka. The ore-bearing quartz veins formed at 268 °C from NaCl–CO2–H2O(–CH4) fluids averaging 5 wt% NaCl eq. The ore-forming mechanisms include fluid immiscibility during stage I, and mixing with meteoric water during stage II. Oxygen, hydrogen, and carbon isotopes suggest that the ore-forming fluids originated as mixtures of metamorphic water and magmatic water, whereas the sulfur isotope suggests an igneous origin. The features of geology and ore-forming fluid at the Koka deposit are similar to those of orogenic gold deposits, suggesting that the Koka deposit might be an orogenic gold deposit related to granite.

scholarly journals Alteration Alteration, Mineralization and Geochemistry of Metamorphic Rocks Hosted Hydrothermal Gold Deposit at Rumbia Mountains, Bombana Regency, Southeast Sulawesi, Indonesia

2019 ◽  
Vol 4 (2) ◽  
pp. 83
Author(s):  
Hasria Hasria ◽  
Arifudin Idrus ◽  
I Wayan Warmada
Keyword(s):  
Gold Deposit ◽  
Inductively Coupled Plasma ◽  
Field Work ◽  
Gold Deposits ◽  
Metamorphic Rocks ◽  
Inductively Coupled ◽  
Quartz Veins ◽  
Three Stages ◽  
Primary Gold ◽  
Gold Bearing

In Indonesia, gold is commonly mined from porphyry, epithermal and skarn type deposits that are commonly found in volcanic/magmatic belts. However, were recently numerous gold prospects discovered in association with metamorphic rocks. This paper is intended to describe an alteration and ore mineralogy hosted by metamorphic  rocks at Rumbia mountains, Bombana regency, Southeast Sulawesi province, Indonesia. The study area is found the placer and primary gold hosted by metamorphic rocks. The placer gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). This study is conducted in three stages, three stages including desk study, field work and laboratory analysis. Desk study mainly covers literature reviews. Field work includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rocks types, altered rocks and gold-bearing veins. Laboratory analysis includes the petrologic observation of handspecimen samples, petrographic analysis of the thin section and ore microscopy for polished section, XRD (X-ray diffraction), ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy), ICP-MS (Inductively Coupled Plasma Emission Mass Spectrometry and FA/AAS (Fire Assay/Atomic Absorbtion Spectophotometry) analysis. The results shows that the alteration characteristics of hydrothermal gold deposits in Mendoke and Rumbia mountain consist of 3 (three) alterations namely sericitic, argillic dan propylitic. Characteristics of mineralization hydrothermal gold deposits in the research area are generally p related to gold-bearing quartz veins/veinlets consist of chalcopyrite, pyrite, chrysocolla, covellite, cinnabar, magnetite, hematite and goetite in rocks categorized into greenschist facies. There are three generations of veins identified including the first is parallel to the foliations, the second crosscut the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage. The  quartz veins commonly deformed, segmented, massive, laminated,   irregular, brecciated, and occasionally sigmoidal. The veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18,4000 at found in third generation veins which are laminated quartz±calcite in argillic alteration. ppm. The protoliths of metamorphic rocks in Rumbia Mountain, which comes from sedimentary rocks, spesifically pelitic rocks and graywacke. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposits type. The orogenic gold deposit is one of the new targets for exploration in Indonesia.

scholarly journals Quartz Rb-Sr Isochron Ages of Two Type Orebodies from the Nibao Carlin-type Gold Deposit, Guizhou, China

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 399 ◽  
Author(s):  
Zheng ◽  
Yang ◽  
Gao ◽  
Chen ◽  
Liu ◽  
...  
Keyword(s):  
Low Temperature ◽  
Gold Deposit ◽  
Fluid Inclusions ◽  
Large Scale ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Quartz Veins ◽  
Golden Triangle ◽  
Mineralization Age ◽  
Gold Bearing

The Nibao gold deposit, which includes both fault-controlled and strata-bound gold orebodies, constitutes an important part of the Yunnan–Guizhou–Guangxi “Golden Triangle” region. Defining the mineralization age of these gold orebodies may provide additional evidence for constraining the formation ages of low-temperature orebodies and their metallogenic distribution in South China. Petrographic studies of gold-bearing pyrites and ore-related quartz veins indicate that these pyrites coexist with quartz or filled in vein-like quartz, which suggests a possible genetic relationship between the two from Nibao gold deposit. Minerals chemistry shows that Rb and Sr are usually hosted in fluid inclusions in quartz ranging from 0.0786 to 2.0760 ppm and 0.1703 to 2.1820 ppm, respectively. The Rb–Sr isotopic composition of gold-bearing quartz-hosted fluid inclusions from the Nibao gold deposit were found to have Rb–Sr isochron ages of 142 ± 3 and 141 ± 2 Ma for both fault-controlled and strata-bound orebodies, respectively, adding more evidence to previous studies and thus revealing a regional gold mineralization age of 148–134 Ma. These results also confirm the Middle-Late Yanshanian mineralizing events of Carlin-type gold deposits in Yunnan, Guizhou, and Guangxi Provinces of Southwest China. In addition, previous studies indicated that antimony deposits in the region which were formed at ca. 148–126 Ma have a close affinity with gold deposits. This illustrates that the regional low-temperature hydrothermal gold mineralization is related in space and time to the Yanshanian (ca. 146–115 Ma) magmatic activity. Specifically, the large-scale gold and antimony mineralization are considered to be inherently related to mantle-derived mafic and ultramafic magmatic rocks associated with an extensional tectonic environment. Based on the initial 87Sr/86Sr ratios of 0.70844 ± 0.00022 (2σ) and 0.70862 ± 0.00020 (2σ) for gold-bearing quartz veins from fault-controlled and strata-bound gold orebodies, respectively, at the Nibao gold deposit, as well as the C, H, O, and S isotopic characteristics of gold deposits located in the Golden Triangle region, we suggest that the mantle-derived material can be involved in the formation of the Nibao gold deposit and that the ore-forming fluid can be derived from a mixed crust–mantle source.

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