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 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.

scholarly journals Genesis of the Late Cretaceous Longquanzhan Gold Deposit in the Central Tan-Lu Fault Zone, Shandong Province, China: Constraints from Noble Gas and Sulfur Isotopes

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 250
Author(s):  
Chuanpeng Liu ◽  
Wenjie Shi ◽  
Junhao Wei ◽  
Huan Li ◽  
Aiping Feng ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Fault Zone ◽  
Late Cretaceous ◽  
Genetic Model ◽  
Gold Mineralization ◽  
Sulfur Isotopes ◽  
Noble Gas ◽  
Gold Deposits ◽  
Shandong Province ◽  
Magma Sources

The Longquanzhan deposit is one of the largest gold deposits in the Yi-Shu fault zone (central section of the Tan-Lu fault zone) in Shandong Province, China. It is an altered-rock type gold deposit in which ore bodies mainly occur at the contact zone between the overlying Cretaceous rocks and the underlying Neoarchean gneissic monzogranite. Shi et al. reported that this deposit formed at 96 ± 2 Ma using pyrite Rb–Sr dating method and represents a new gold mineralization event in the Shandong Province in 2014. In this paper, we present new He–Ar–S isotopic compositions to further decipher the sources of fluids responsible for the Longquanzhan gold mineralization. The results show that the δ34S values of pyrites vary between 0.9‰ and 4.4‰ with an average of 2.3‰. Inclusion-trapped fluids in ore sulfides have 3He/4He and 40Ar/36Ar ratios of 0.14–0.78 Ra and 482–1811, respectively. These isotopic data indicate that the ore fluids are derived from a magmatic source, which is dominated by crustal components with minor mantle contribution. Air-saturated water may be also involved in the hydrothermal system during the magmatic fluids ascending or at the shallow deposit site. We suggest that the crust-mantle mixing signature of the Longquanzhan gold deposit is genetically related to the Late Cretaceous lithospheric thinning along the Tan-Lu fault zone, which triggers constantly uplifting of the asthenosphere surface and persistent ascending of the isotherm plane to form the gold mineralization-related crustal level magma sources. This genetic model can be applied, to some extent, to explain the ore genesis of other deposits near or within the Tan-Lu fault belt.

CALCITE U-Pb DATING UNRAVELS THE AGE AND HYDROTHERMAL HISTORY OF THE GIANT SHUIYINDONG CARLIN-TYPE GOLD DEPOSIT IN THE GOLDEN TRIANGLE, SOUTH CHINA

2021 ◽  
Vol 116 (6) ◽  
pp. 1253-1265
Author(s):  
Xiao-Ye Jin ◽  
Jian-Xin Zhao ◽  
Yue-Xing Feng ◽  
Albert H. Hofstra ◽  
Xiao-Dong Deng ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Early Cretaceous ◽  
South China ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Late Triassic ◽  
Gold Deposition ◽  
Golden Triangle ◽  
Icp Ms ◽  
Carlin Type Gold Deposits

Abstract The ages of Carlin-type gold deposits in the Golden Triangle of South China have long been questioned due to the general lack of minerals unequivocally linked to gold deposition that can be precisely dated using conventional radiogenic isotope techniques. Recent advances in U-Pb methods show that calcite can be used to constrain the ages of hydrothermal processes, but few studies have been applied to ore deposits. Herein, we show that this approach can be used to constrain the timing of hydrothermal activity that generated and overprinted the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle. Three stages of calcite (Cal-1, Cal-2, and Cal-3) have been recognized in this deposit based on crosscutting relationships, cathodoluminescence colors, and chemical (U, Pb, and rare earth element [REE]) and isotope (C, O, Sr) compositions. Cal-1 is texturally associated with ore-stage jasperoid and disseminated Au-bearing arsenian pyrite in hydrothermally altered carbonate rocks, which suggests it is synmineralization. Cal-2 fills open spaces and has a distinct orange cathodoluminescence, suggesting that it precipitated during a second fluid pulse. Cal-1 and Cal-2 have similar carbonate rock-buffered chemical and isotopic compositions. Cal-3 occurs in veins that often contain realgar and/or orpiment and are chemically (low U, Pb, and REE) and isotopically (higher δ13C, lower δ18O and Sri values) distinct from Cal-1 and Cal-2, suggesting that it formed from a third fluid. U-Pb isotope analyses, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for U-rich Cal-1 and Cal-2 and by LA-multicollector (MC)-ICP-MS for U-poor Cal-3, yield well-defined age constraints of 204.3 to 202.6, 191.9, and 139.3 to 137.1 Ma for Cal-1, Cal-2, and Cal-3, respectively. These new ages suggest that the Shuiyindong gold deposit formed in the late Triassic and was overprinted by hydrothermal events in the early Jurassic and early Cretaceous. Given the association of Cal-3 with orpiment and realgar, and previous geochronologic studies of several other major gold deposits in the Golden Triangle, we infer that the latest stage of calcite may be associated with an early Cretaceous regional gold metallogenic event. Combined with existing isotopic ages in the region, these new ages lead us to propose that Carlin-type gold deposits in the Golden Triangle formed during two metallogenic episodes in extensional settings, associated with the late Triassic Indochina orogeny and early Cretaceous paleo-Pacific plate subduction. This study shows that the calcite U-Pb method can be used to constrain the timing of Carlin-type gold deposits and successive hydrothermal events.

The Mineral Characteristics and Occurrence of Gold in Nali Gold Deposit, Guangxi

2014 ◽  
Vol 936 ◽  
pp. 2383-2388
Author(s):  
Zhi Wen Li ◽  
Cheng Dong Liu ◽  
Xuan Qing Zhao ◽  
Jian Hui Lu ◽  
Guo Lin Guo
Keyword(s):  
Gold Deposit ◽  
Mineral Composition ◽  
Electron Probe ◽  
Mining Area ◽  
Optical Microscope ◽  
Analysis Techniques ◽  
Mineral Characteristics ◽  
Ore Minerals

Using the analysis techniques of polarizing optical microscope and electron probe, mineral composition, ore texture and structure and the occurrence of Au in the primary ore are studied. The research shows that the main ore minerals in the ore include realgar, pyrite and arsenopyrite etc. Sulfur-stibarsen is the main carrier of Au, and is the major associated mineral of realgar, surrounded mainly by realgar, and partly is the associated mineral of arsenopyrite. The existence of visible gold and microscopic gold in the ore of this mining area can be excluded, and the gold might exist mainly in the form of inclusion gold, which is the so-called “nanoAu”.

scholarly journals A NEW GOLD ORE REGION IN TANZANIA

2018 ◽  
pp. 55-59
Author(s):  
V. Mykhailov ◽  
А. Tots
Keyword(s):  
Gold Deposit ◽  
Shear Zone ◽  
Gold Mineralization ◽  
Lake Victoria ◽  
Gold Deposits ◽  
Mobile Belt ◽  
Gold Content ◽  
Gold Ore ◽  
Metallogenic Zone ◽  
The Republic

Tanzania is one of the leading gold mining countries in the world and the discovery of new gold resources on its territory is an actual task. Known gold deposits are concentrated mainly in the northwest of the country, in the metallogenic zone of Lake Victoria, where they are associated with the Archean greenstone belts, and to a lesser extent – in the southwest, in the ore regions of Lupa and Mpanda, confined to the Ubendian Paleoproterozoic mobile belt. With regard to the eastern regions of Tanzania, where the Proterozoic structures of the Uzagaran mobile belt are developed, until recently in this region any significant manifestations of gold mineralization were not known. As a result of our research in the northern part of the Morogoro province of the Republic of Tanzania, a new previously unknown gold deposit Mananila was discovered. It is represented by a large volume, up to 400–450 m long, up to 60–80 m thick, mineralized shear zone over intensely leached and schistosed migmatites, gneisses, amphibolites, penetrated by echelon systems of quartz veins and veinlet, steeply dipping bodies of quartz breccia up to 1.0–1.5 m thick. Gold contents range from 0.61 to 8.11 g/t, the average zone content is 2.5–3.0 g/t. Parallel to the main zone, similar structures are developed on the site, although they are of lower thickness. The forecast resources of the deposit are estimated at 20 tons of gold. 2.8 km to the east from the Mananila field, the recently discovered Mazizi gold deposit is located, and a number of small occurrences of gold are also known in the region. All these objects are located within a large shear zone of the northeastern strike, up to 4–5 km width, over 20 km in length. This serves as the basis for the identification of a new gold ore region in the northern part of the Morogoro province of the United Republic of Tanzania, within the Proterozoic mobile belt of Usagaran, the possible gold content of which has never been previously discussed in geological literature.

A Non-local Source of Irish Chalcolithic and Early Bronze Age Gold

2015 ◽  
Vol 81 ◽  
pp. 149-177 ◽  
Author(s):  
Christopher D. Standish ◽  
Bruno Dhuime ◽  
Chris J. Hawkesworth ◽  
Alistair W. G. Pike
Keyword(s):  
Bronze Age ◽  
Lead Isotope ◽  
Ore Deposits ◽  
Local Source ◽  
Geochemical Data ◽  
Early Bronze Age ◽  
Element Analysis ◽  
Alluvial Deposits ◽  
Study Region ◽  
South West

Lead isotope analyses of 50 Irish Chalcolithic and Early Bronze Age gold artefacts favour a gold source in southern Ireland. However when combined with major element analysis, the artefacts are not consistent with any Irish gold deposit analysed to date. Understanding the lead isotope signatures of ore deposits within a study region allows informed inferences to be drawn regarding the likelihood that an unanalysed ore deposit was exploited in the past. If an Irish gold source is assumed, then the gold is most likely to have originated from deposits hosted by Old Red Sandstone in the Variscan ore field of south-west Ireland. However, based on our current understanding of mineralisation in the region, this scenario is considered unlikely. A non-Irish source for the gold is therefore preferred – a scenario that may favour cosmologically-driven acquisition, ie, the deliberate procurement of a material from distant or esoteric sources. Available geochemical data, combined with current archaeological evidence, favour the alluvial deposits of south-west Britain as the most likely source of the gold.

Seismic structure of the Cheb Basin from high resolution surveying – data quality assessment and first results

2021 ◽  
Author(s):  
Natalia Banasiak ◽  
Florian Bleibinhaus
Keyword(s):  
High Resolution ◽  
Earthquake Activity ◽  
Seismic Structure ◽  
North West ◽  
The North ◽  
Eger Rift ◽  
First Results ◽  
Ground Roll ◽  
Variscan Granites ◽  
Cheb Basin

&lt;p&gt;&lt;span&gt;&lt;span&gt;In this study we present data and preliminary results from several shallow high-resolution seismic surveys in the Cheb Basin, CR, a small intracontinental basin in the North-West Bohemian Massif, located at the Western end of the Cenozoic Eger Rift. The area is well known for its intense earthquake activity, with the largest instrumentally recorded magnitude of M&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;sub&gt;&lt;span&gt;L&lt;/span&gt;&lt;/sub&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;=4.6. Macroseismic reports of local seismicity date back to the early 19&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;sup&gt;&lt;span&gt;th&lt;/span&gt;&lt;/sup&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; century, with magnitudes possibly above 5. Quaternary volcanoes, CO&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;-rich moffettes, and the swarm-like occurrence of the earthquakes suggest they are being triggered by crustal fluids. In contrast, most focal mechanisms show a dominant strike-slip component, indicative of tectonics. Investigating the role of fluids in triggering those earthquakes is one of the objectives of an ongoing ICDP program.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We expect high-resolution images of the basin structure to provide additional constraints regarding the importance of tectonic faulting. To that end, we surveyed several up to 3-km-long reflection and refraction profiles in the basin center across the putative Po&amp;#269;&amp;#225;tky-Plesn&amp;#225; Fault, and at its edge, across the basin-bounding Mari&amp;#225;nsk&amp;#233; L&amp;#225;zn&amp;#283; Fault. The up to 350-m-thick basin sediments are mostly of Miocene and Quaternary origin, overlying Paleozoic Variscan units and post-Variscan granites. The main reflectors are around 200-400 ms. The data were collected with a 500-m-long split-spread of single geophones at 2 m spacing, and the raw shots are dominated by ground roll. In this presentation, we will show an overview of the field campaigns and present first results.&lt;/span&gt;&lt;/p&gt;

Geology of the Liese Zone, Pogo Property, East-Central Alaska

SEG Discovery ◽  
1999 ◽  
pp. 1-21
Author(s):  
MOIRA SMITH ◽  
JOHN F.H. THOMPSON ◽  
JASON BRESSLER ◽  
PAUL LAYER ◽  
JAMES K. MORTENSEN ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Gold Mineralization ◽  
Geochemical Data ◽  
East Central ◽  
Gold Silver ◽  
Ore Minerals ◽  
Middle Paleozoic ◽  
Deposit Type ◽  
Alteration Minerals ◽  
Native Bismuth

ABSTRACT The Liese zone is a recently discovered high-grade gold deposit on the Pogo claims, approximately 90 miles (145 km) southeast of Fairbanks. A conservative geologic resource for the Liese zone is 9.98 million tons at an average grade of 0.52 oz/t, for a total of 5.2 million contained ounces. The region is underlain by highly deformed, amphibolite-grade paragneiss and minor orthogneiss of the Late Proterozoic(?) to middle Paleozoic Yukon-Tanana terrane, which has been intruded by Cretaceous felsic granitoid bodies thought to be related to gold mineralization in the Fairbanks area and elsewhere along the Tintina gold belt. The Liese zone is hosted primarily in gneiss, and lies approximately 1.5 km south of the southern margin of the Late Cretaceous Goodpaster batholith. Mineralization occurs in three or more tabular, gently dipping quartz bodies, designated L1 (uppermost), L2, and L3 (lowermost). The thickness of the quartz bodies ranges from 1 to 20 m, averaging approximately 7 m. The quartz contains approximately 3 percent ore minerals, including pyrite, pyrrhotite, loellingite, arsenopyrite, chalcopyrite, bismuthinite, various Ag-Pb-Bi ± S minerals, maldonite, native bismuth, and native gold. Early biotite and later quartz-sericite-stockwork and sericite-dolomite alteration are spatially associated with the Liese zone, which shows characteristics of both vein and replacement styles of mineralization. Geochemical data indicate a strong correlation between gold and bismuth, and weaker correlations between gold, silver, and arsenic. Based on U-Pb dating of intrusive rocks, the Liese zone was formed between 107 and 94.5 m.y. ago, although 40Ar/39Ar cooling ages on alteration minerals return younger ages of 91 Ma, suggesting a protracted or multiphase thermal history. The Liese zone may represent a deep-seated manifestation of the "intrusion-related" gold deposit type.

scholarly journals Genesis of Carbonate Breccia Containing Invisible Gold in Taebaeksan Basin, South Korea

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1087
Author(s):  
Sang-Gun No ◽  
Maeng-Eon Park ◽  
Bong-Chul Yoo ◽  
Seung-Han Lee
Keyword(s):  
South Korea ◽  
Carbonate Rock ◽  
Gold Deposits ◽  
Invisible Gold ◽  
Gold Particles ◽  
X Ray ◽  
Taebaeksan Basin ◽  
The Matrix ◽  
Backscattered Electron

The Yemi breccia developed and is distributed within the Paleozoic carbonate rock (Maggol Formation) in the central part of the Taebaeksan Basin, South Korea. Explanation for the genesis of the Yemi breccia has been controversial. We investigated the petrological and mineralogical properties of the breccia and the matrix materials at 60 outcrops. The Yemi breccia is divided into crackle, mosaic, and chaotic breccias based on morphology. In addition, these are divided into blackish, reddish, grayish, and white to pinkish matrix breccias according to the materials of the matrix. Quartz, calcite, pyrite, hematite (after pyrite), and minor epidote, chlorite, and opaque materials mainly comprise the matrix materials. The pyrite grains from the Yemi breccia can be divided into two types based on the mineral texture: diagenetic and hydrothermal. We analyzed the chemistry of pyrite and hematite (after pyrite) from the Yemi breccia with an electron probe X-ray microanalyzer (EPMA). Invisible gold was detected within the pyrite grains by EPMA and disseminated micron-sized isolated gold particles were discovered by backscattered electron (BSE) images. The texture of Au-bearing pyrite and gold particles in the Yemi breccia is especially well matched with pyrite and gold from the Shuiyindong Carlin-type hydrothermal gold deposits, China. Therefore, we suggest an important role of hydrothermal fluid in karstification within the Paleozoic carbonate rock.

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