SULFIDE RECRYSTALLIZATION AND GOLD REMOBILIZATION DURING THE 2.0 GA STAGE OF THE MINAS OROGENY: IMPLICATIONS FOR GOLD MINERALIZATION IN THE QUADRILÁTERO FERRÍFERO AREA, BRAZIL

2021 ◽  
Author(s):  
Mariana Brando Soares ◽  
David Selby ◽  
Laurence Robb ◽  
Atlas Vasconcelos Corrêa Neto
Keyword(s):  
Thermal Effects ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Coarse Grained ◽  
Gold Deposition ◽  
Mining District ◽  
Mean Square ◽  
Fine Grained ◽  
Tectonic Events ◽  
Quadrilátero Ferrífero

Abstract The historic Quadrilátero Ferrífero mining district in Brazil is a polydeformed Archean terrane recording several tectonic events. This history has hampered the accurate dating of its important gold deposits, given that most of the geochronological clocks have been affected by multiple thermal events. To determine an accurate time constraint for the mineralizing events in this region, we provide the first Re-Os dating for a gold deposit in the Quadrilátero Ferrífero, obtained from 13 mineral separates of disseminated sulfide phases (pyrrhotite, coarse-grained arsenopyrite, fine-grained arsenopyrite, and pyrite) at the recently discovered São Sebastião deposit (northwest Quadrilátero Ferrífero). Three distinct successive sulfidation stages are interpreted at the deposit. The final stage, texturally associated with gold, is marked by fine-grained arsenopyrite and pyrite (assemblage III) and is associated with high-temperature (~600°C) features. A Re-Os errorchron is obtained when considering the data of all samples collectively; however, a comprehensive Re-Os isochron age of 1987 ± 72 Ma (2σ; n = 4; IsoplotR model 3; initial 187Os/188Os = 2.1 ± 0.7) is obtained from assemblage III. A 187Re-187Osr isochron at 1988 ± 56 Ma (mean square of weighted deviates = 0.1, initial 187Osr = –0.1 ± 2.6 ppt; n = 4) is obtained if an initial 187Os/188Os composition of ca. 2.1, is used, this being consistent with the fact that the 187Os in the sulfides in assemblage III is largely radiogenic (187Osr). Earlier assemblages (I and II) individually show variable initial 187Os/188Os, indicative of disturbance to the Re-Os systematics at ~2.0 Ga. This age is considered the best estimate for the timing of gold mineralization at São Sebastião, being coincident with the waning stages of the Minas orogeny, the thermal effects of which are restricted to the southern Quadrilátero Ferrífero. Hence, we consider that the hot fluids from which assemblage III crystallized were responsible for resetting the Re-Os systematics in assemblages I and II and were central to Paleoproterozoic gold deposition in the region. This ~2.0 Ga age challenges previous notions of a late Archean, ~2.7 Ga mineralizing event in the Quadrilátero Ferrífero and makes it possible that gold remobilization occurred elsewhere in the region, particularly in areas representing deeper crustal levels.

Chapter 16: Giant Carlin-Type Gold Deposits of the Cortez District, Lander and Eureka Counties, Nevada

2020 ◽  
pp. 335-353
Author(s):  
Mark A. Bradley ◽  
L. Page Anderson ◽  
Nathan Eck ◽  
Kevin D. Creel
Keyword(s):  
Great Basin ◽  
Genetic Model ◽  
Gold Mineralization ◽  
Late Eocene ◽  
Gold Deposits ◽  
Gold Deposition ◽  
Lower Paleozoic ◽  
Fine Grained ◽  
Siliciclastic Rocks ◽  
Carlin Type Gold Deposits

Abstract The Cortez district is in one of the four major Carlin-type gold deposit trends in the Great Basin province of Nevada and contains three giant (>10 Moz) gold orebodies: Pipeline, Cortez Hills, and Goldrush, including the recently discovered Fourmile extension of the Goldrush deposit. The district has produced >21 Moz (653 t) of gold and contains an additional 26 Moz (809 t) in reserves and resources. The Carlin-type deposits occur in two large structural windows (Gold Acres and Cortez) of Ordovician through Devonian shelf- and slope-facies carbonate rocks exposed through deformed, time-equivalent lower Paleozoic siliciclastic rocks of the overlying Roberts Mountains thrust plate. Juxtaposition of these contrasting Paleozoic strata occurred during the late Paleozoic Antler orogeny along the Roberts Mountains thrust. Both upper and lower plate sequences were further deformed by Mesozoic compressional events. Regional extension, commencing in the Eocene, opened high- and low-angle structural conduits for mineralizing solutions and resulted in gold deposition in reactive carbonate units in structural traps, including antiforms and fault-propagated folds. The Pipeline and Cortez Hills deposits are located adjacent to the Cretaceous Gold Acres and Jurassic Mill Canyon granodioritic stocks, respectively; although these stocks are genetically unrelated to the later Carlin-type mineralization event, their thermal metamorphic aureoles may have influenced ground preparation for later gold deposition. Widespread decarbonatization, argillization, and silicification of the carbonate host rocks accompanied gold mineralization, with gold precipitated within As-rich rims on fine-grained pyrite. Pipeline and Cortez Hills also display deep supergene oxidation of the hypogene sulfide mineralization. Carlin-type mineralization in the district is believed to have been initiated in the late Eocene (>35 Ma) based on the age of late- to postmineral rhyolite dikes at Cortez Hills. The Carlin-type gold deposits in the district share common structural, stratigraphic, alteration, and ore mineralogic characteristics that reflect common modes of orebody formation. Ore-forming fluids were channeled along both low-angle structures (Pipeline, Goldrush/Fourmile) and high-angle features (Cortez Hills), and gold mineralization was deposited in Late Ordovician through Devonian limestone, limy mudstone, and calcareous siltstone. The Carlin-type gold fluids are interpreted to be low-salinity (2–3 wt % NaCl equiv), low-temperature (220°–270°C), and weakly acidic, analogous to those in other Carlin-type gold deposits in the Great Basin. The observed characteristics of the Cortez Carlin-type gold deposits are consistent with the recently proposed deep magmatic genetic model. Although the deposits occur over a wide geographic area in the district, it is possible that they initially formed in greater proximity to each other and were then spatially separated during Miocene and post-Miocene regional extension.

Gold distribution in the Val-d'Or Formation and a model for the formation of the Lamaque–Sigma mines, Val-d'Or, Quebec

1991 ◽  
Vol 28 (5) ◽  
pp. 706-720 ◽  
Author(s):  
Mehmet F. Taner ◽  
Pierre Trudel
Keyword(s):  
Gold Mineralization ◽  
Regional Metamorphism ◽  
Analytical Techniques ◽  
Shear Zones ◽  
Gold Deposits ◽  
Mining District ◽  
Volcanic Complex ◽  
Geothermal Systems ◽  
Gold Mines ◽  
Geothermal Activity

Recent lithogeochemical studies by accurate analytical techniques (e.g., instrumental and radiochemical neutron-activation analyses) have been used to explore the possibility of using gold distribution in the research for new gold deposits; these show that anomalous gold distribution occurs in some parts of the Val-d'Or Formation in the Val-d'Or mining district of Quebec. Gold lithogeochemistry in the Val-d'Or Formation has shown that it is possible to distinguish: (i) background values (1.4–3.5 ppb Au); (ii) zones of primarily anomalous gold values around the Lamaque–Sigma mines (median: 15 ppb Au); (iii) enrichment halos around gold orebodies (median: 70 ppb Au); and (iv) secondary gold enrichment in shear zones. We conclude that the Val-d'Or Formation is auriferous, i.e., anomalously rich in gold at least in some of its parts and contains the Lamaque – Sigma gold mines, representing 68% of the total gold production in the district. The Val-d'Or Formation is part of a central volcanic complex within an island-arc system. The centre of this complex is located in the main Lamaque plug, and this environment may be compared to high-temperature active geothermal systems that are commonly responsible for the formation of epithermal gold deposits. Gold mineralization at Sigma and Lamaque is considered to be related to a late hydrothermal phase or a retrograde phase of regional metamorphism. For the formation of the gold deposits, two distinct and successive events are postulated: (i) a gold-rich synvolcanic geothermal activity and (ii) a late remobilisation from the host rocks followed by deposition of gold ore within favourable structures.

scholarly journals Role of the Environment in the Placement of Apocarbonate Gold Mineralization Chakylkalyan Megablock (Southern Uzbekistan)

2021 ◽  
Vol 7 (6) ◽  
Author(s):  
T. Yarboboev ◽  
Sh. Sultanov ◽  
I. Ochilov
Keyword(s):  
Carbonate Rocks ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Gold Deposition ◽  
Sufficient Detail ◽  
Available Information ◽  
Gold Bearing ◽  
Geochemical Specialization

Analysis of the available information and the results of many years of research on gold deposits in Uzbekistan made it possible to identify the main unconventional types of deposits. Among them, the most interesting are apocarbonate, crustal, sulfide-carbonaceous and apovolcanogenic quartzite (Upper-Kattakashkasai ore occurrence). The apocarbonate type is widespread in Uzbekistan, has been studied in sufficient detail and information is provided on it in this article. The article examines the existence, distribution and genesis of ores of Karlin type gold deposits. The generalizing characteristics of the Karlin type gold mineralization are given. The issues of geochemical specialization of the Paleozoic strata of the Chakylkalyan megablock are considered, the most favorable stratolevel for the localization of mineralized zones is determined, and the features of carbonate rocks in the process of gold deposition during reactions with silicic solutions are characterized. Based on the materials of regional geochemical profiling, the behavior of the main ore-forming elements in the rocks of both carbonate and volcanogenic-terrigenous strata is analyzed. As a result of the analysis, subclarkic contents of the main ore-forming elements (As, Co, Ni, Pb, Cu, Ag, V, Cr, Sc) were revealed, which create increased concentrations in gold-bearing pyrites of both apocarbonate gold mineralization and related formations.

The Paleoproterozoic Kombolgie Subgroup (1.8 Ga), McArthur Basin, Australia: Sequence stratigraphy, basin evolution, and unconformity-related uranium deposits following the Great Oxidation Event

2021 ◽  
Vol 59 (5) ◽  
pp. 1049-1083
Author(s):  
Eric E. Hiatt ◽  
T. Kurtis Kyser ◽  
Paul A. Polito ◽  
Jim Marlatt ◽  
Peir Pufahl
Keyword(s):  
Large Scale ◽  
Sedimentary Basins ◽  
Uranium Mineralization ◽  
Coarse Grained ◽  
Uranium Deposits ◽  
Burial Diagenesis ◽  
Fine Grained ◽  
Braided Rivers ◽  
Tectonic Events ◽  
Regional Tectonic

ABSTRACT Proterozoic continental sedimentary basins contain a unique record of the evolving Earth in their sedimentology and stratigraphy and in the large-scale, redox-sensitive mineral deposits they host. The Paleoproterozoic (Stratherian) Kombolgie Basin, located on the Arnhem Land Plateau, Northern Territory, is an exceptionally well preserved, early part of the larger McArthur Basin in northern Australia. This intracratonic basin is filled with 1 to 2 km-thick, relatively undeformed, nearly flat-lying, siliciclastic rocks of the Kombolgie Subgroup. Numerous drill cores and outcrop exposures from across the basin allow sedimentary fabrics, structures, and stratigraphic relationships to be studied in great detail, providing an extensive stratigraphic framework and record of basin development and evolution. Tectonic events controlled the internal stratigraphic architecture of the basin and led to the formation of three unconformity-bounded sequences that are punctuated by volcanic events. The first sequence records the onset of basin formation and is comprised of coarse-grained sandstone and polymict lithic conglomerate deposited in proximal braided rivers that transported sediment away from basin margins and intra-basin paleohighs associated with major uranium mineralization. Paleo-currents in the upper half of this lower sequence, as well as those of overlying sequences, are directed southward and indicate that the major intra-basin topographic highs no longer existed. The middle sequence has a similar pattern of coarse-grained fluvial facies, followed by distal fluvial facies, and finally interbedded marine and eolian facies. An interval marked by mud-rich, fine-grained sandstones and mud-cracked siltstones representing tidal deposition tops this sequence. The uppermost sequence is dominated by distal fluvial and marine facies that contain halite casts, gypsum nodules, stromatolites, phosphate, and “glauconite” (a blue-green mica group mineral), indicating a marine transgression. The repeating pattern of stratigraphic sequences initiated by regional tectonic events produced well-defined coarse-grained diagenetic aquifers capped by intensely cemented distal fluvial, shoreface, eolian, and even volcanic units, and led to a well-defined heterogenous hydrostratigraphy. Basinal brines migrated within this hydrostratigraphy and, combined with paleotopography, dolerite intrusion, faulting, and intense burial diagenesis, led to the economically important uranium deposits the Kombolgie Basin hosts. Proterozoic sedimentary basins host many of Earth's largest high-grade iron and uranium deposits that formed in response to the initial oxygenation of the hydrosphere and atmosphere following the Great Oxygenation Event. Unconformity-related uranium mineralization like that found in the Kombolgie Basin highlights the interconnected role that oxygenation of the Earth, sedimentology, stratigraphy, and diagenesis played in creating these deposits.

Gold mineralization in Lower Cambrian McNaughton Formation, Athabasca Pass, Canadian Rocky Mountains: structural, mineralogical, and temporal relationships

1990 ◽  
Vol 27 (4) ◽  
pp. 477-493 ◽  
Author(s):  
Robert P. Shaw ◽  
Roger D. Morton
Keyword(s):  
Rocky Mountains ◽  
Lower Cambrian ◽  
Gold Mineralization ◽  
White Mica ◽  
Gold Deposits ◽  
Process Models ◽  
Gold Deposition ◽  
Canadian Rocky Mountains ◽  
Gold Stage ◽  
Gold Bearing

Gold-bearing quartz veins were recently discovered in archimetamorphic quartzite–rudite and quartzite–pelite sequences of the Lower Cambrian McNaughton Formation in the main ranges of the central Canadian Rocky Mountains. There are two distinct vein types: an early syntectonic, syn- to postmetamorphic, auriferous, bedding-parallel type, generated during repeated northeast-directed compressive tectonism; and a late, postpenetrative deformational discordant type, which contains only minor gold (<500 ppb Au). Gold emplacement and discordant veining were confined to the onset of late compression leading to development of the Chatter Creek Fault.The spatial distribution and dimensions of the veins attest to mechanically founded lithologic anisotropy. Bedding-parallel veins are confined to less competent, volumetrically minor pelitic rock types. Discordant veins are confined to competent quartzitic units.Bedding-parallel vein filling took place in two paragenetic stages: a protracted, pre-gold stage (quartz ± minor white mica and pyrite) depositing over 90% of vein material; and a late gold-bearing–post-gold stage (quartz–pyrite–gold–galena ± white mica and Fe carbonate). Gold usually occurs in association with brecciated pelites and penecontemporaneous sulfides. Discordant veins (quartz ± minor pyrite) record a single stage of vein filling broadly coeval with gold deposition. Minor hydrothermal alteration (pyrite ± white mica ± carbonate) of adjacent wall rocks accompanied gold emplacement and is mineralogically congruent with the regional archimetamorphic and bedding-parallel vein assemblages.In terms of their setting and morphology, the Athabasca Pass gold lodes are viewed as a siliciclastic-hosted analogue of the turbidite-hosted class of gold deposits. Principle geochemical differences from published process models for turbidite-hosted gold deposits are a function of the mineralogical maturity of the siliciclastic host strata in the Athabasca Pass.

40Ar/39Ar age constraints on the thermal history of the Archean Abitibi greenstone belt and the Pontiac Subprovince: implications for terrane collision, differential uplift, and overprinting of gold deposits

1992 ◽  
Vol 29 (7) ◽  
pp. 1389-1411 ◽  
Author(s):  
R. Feng ◽  
R. Kerrich ◽  
S. McBride ◽  
E. Farrar
Keyword(s):  
High Temperature ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Coarse Grained ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Thermal Activity ◽  
Thermal Event ◽  
Southern Volcanic Zone ◽  
Differential Uplift

40Ar/39Ar mineral age spectra of granitic and metamorphic rocks, in conjunction with existing conventional zircon geochronology, indicate that at least two major late Archean thermal events affected tectonic blocks of the Abitibi Southern Volcanic Zone (SVZ) and the juxtaposed Pontiac Subprovince. The earlier thermal activity (2690–2670 Ma) was accompanied by the intrusion of voluminous syntectonic plutons and caused low-pressure, greenschist-facies metamorphism in the SVZ and intermediate-pressure metamorphism in the Pontiac Subprovince. The second thermal event (2660–2630 Ma) was coeval with the emplacement of syncollisional, S-type garnet–muscovite granites in the Pontiac Subprovince and the higher grade Lacorne block of the Abitibi SVZ, and reset the K–Ar systems in preexisting rocks.Magmatic amphibole from the syntectonic Round Lake batholith (~2695 Ma U–Pb zircon age) of the Abitibi SVZ has a slightly disturbed Ar release spectrum with an upper plateau age of 2669 ± 6 Ma, signifying that the low-grade Round Lake block cooled through 500 °C at a slow rate. Amphiboles in syntectonic batholiths from the higher grade Lacorne block and the Pontiac Subprovince have substantially disturbed Ar release spectra, with high-temperature steps giving apparent ages of 2681 ± 4 to 2679 ± 4 Ma; these overlap zircon ages of 2690–2670 Ma, indicating relatively rapid cooling through the amphibole blocking temperature.Metamorphic rocks (amphibolites) from the Lacorne block and the Pontiac Subprovince contain amphiboles with substantially disturbed 40Ar/39Ar release spectra and higher temperature step ages of 2677 ± 6 to 2670 ± 5 Ma, representing the minimum formation age. Fine-grained muscovite and biotite (180–250 μm) from mica schists also have disturbed Ar release patterns, but much younger apparent ages at high-temperature release steps (2581–2523 Ma for muscovite, 2562–2455 Ma for biotite) than the amphiboles.Coarse-grained muscovites from pegmatites associated with syncollision, S-type garnet–muscovite granites (2644 ± 13 Ma) in the Lacorne block and Pontiac Subprpvince show undisturbed or slightly disturbed Ar release spectra and magmatic δ18Oquartz–muscovite = 1.8–3.5‰, with total integrated ages of 2615 ± 10 to 2594 ± 7 Ma (Lacorne) and 2572 ± 6 Ma (Pontiac), respectively, indicating different uplift rates for the two terranes. Amphiboles (~2680 Ma) from metamorphic rocks in the Lacorne block and Pontiac Subprovince and from the Round Lake batholith are disturbed, whereas coarse-grained muscovites from the pegmatites (2644 ± 13 Ma) are relatively undisturbed. This indicates that the disturbance of the amphiboles may have been caused by a thermal event that preceded or was coeval with the emplacement of the garnet–muscovite granite suite, rather than being a grain-size effect.These results are consistent with a model whereby early subduction of oceanic lithosphere beneath the Abitibi SVZ (2740–2680 Ma), and separately under the Pontiac Subprovince, was responsible for syntectonic batholiths and the first thermal event. Collision with the Abitibi SVZ and local underthrusting of the Pontiac Subprovince at about 2670–2630 Ma caused the second major thermal event and partial melting of the underthrust Pontiac-type metasediments to form the garnet–muscovite granites. Later differential uplift exposed the entire Pontiac Subprovince and the Lacorne block as a tectonic window of underthrust Pontiac in the Abitibi SVZ. Resetting of several isotopic systems, including apparent younger ages of gold mineralization, is probably related to this late collisional, tectonothermal overprinting event. Fluid and (or) thermal events at ≥275 °C influenced the Kirkland Lake – Cadillac fault down to 2513 ± 10 Ma, as indicated by a plateau age of postkinematic biotite in the fault. The fault was intermittently reactivated over a period of 440 Ma, from ~2690 Ma to ≤2250 Ma.

Sulphur isotopic composition of sulphides from the Beaver Dam and other Meguma-Group-hosted gold deposits, Nova Scotia: implications for genetic models

1989 ◽  
Vol 26 (8) ◽  
pp. 1617-1629 ◽  
Author(s):  
Daniel J. Kontak ◽  
Paul K. Smith
Keyword(s):  
Nova Scotia ◽  
Gold Mineralization ◽  
Source Region ◽  
Gold Deposits ◽  
Genetic Models ◽  
Gold Deposition ◽  
Published Data ◽  
Sulphide Mineral ◽  
Beaver Dam ◽  
Wide Range

Sulphur isotopic compositions were determined for sulphide mineral phases in Meguma-Group-hosted gold deposits, Nova Scotia, in order to resolve (i) potential source regions for sulphur in these deposits, (ii) prevailing ambient physiochemical conditions during sulphide (and gold?) deposition, and (iii) possible implications of δ34S values on genetic models. The Beaver Dam deposit was selected as a test case, and results (± 1σ) from 32 sulphides analyzed for δ34S are as follows (‰): pyrite, 9.9 ± 1.1 (n = 16); pyrrhotite, 9.9 ± 0.2 (n = 4); arsenopyrite, 10.5 ± 0.4 (n = 11); and 9.4 for a single galena. The strikingly narrow range for sulphur isotope data and the sulphide mineral assemblage together are interpreted as implying that the prevailing chemical conditions during sulphide deposition remained at or below the H2S-SO4 buffer and constant relative to it, thus δ34Smineral is a good approximation of δ34Sfluid. Considering that the sulphide minerals analyzed represent a wide range in paragenesis and mode of occurrence, the uniform values suggest a homogeneous sulphur composition in the fluid, with little if any influence of local wall rocks during sulphide deposition. This is consistent with extensive alteration zones (i.e., silicification) throughout the deposit, indicating both high fluid/rock ratios and disequilibrium conditions. Data for an additional seven Meguma Group gold deposits (arsenopyrite only) indicate for δ34S a total range of about 9–25‰; however, the intradeposit variation is consistently small (2–3‰). These results are confirmed by previously published data for a variety of sulphide phases from three other deposits.Comparison of the results for Meguma-hosted deposits with a wide range of both similar and dissimilar gold deposits of variable age indicates that the large positive values (i.e., >9–10‰) are unique to the deposits examined. Two possible explanations are offered: first, the δ34S values originally may have been similar to those of other deposits (i.e., around 0‰ or slightly enriched) and then modified during transport to the site of deposition, or second, the source region of the fluids contained sulphur in an oxidized form (e.g., evaporites). The former hypothesis is currently favoured.Potential reservoirs for sulphur in the Meguma Zone include the Meguma Group metasedimentary rocks and younger peraluminous granitoid batholiths. The sulphur isotopic data are inconsistent with an unmodified magmatic source, and if the Meguma Group is favoured, then the dominant contribution was from the greywacke component. In the latter case, results for the Beaver Dam deposit may represent relatively unmodified fluid, whereas deposits characterized by enriched sulphur may reflect increasing amounts of greywacke-derived sulphur.The data somewhat constrain the possible genetic models for Meguma Group gold deposits. Syngenetic and magmatic models are considered unlikely; instead, a metamorphogenic origin is favoured. However, the ultimate source for mineralizing fluids is considered as lying beneath the Meguma Group, with variable amounts of contamination of this fluid during passage through Meguma Group strata. The relationship between gold mineralization and sulphur isotopic signatures of the associated sulphides is unclear, although a metamorphic protolith is probable.

scholarly journals Structural Evolution of the Rio das Velhas Greenstone Belt, Quadrilátero Ferrífero, Brazil: Influence of Proterozoic Orogenies on Its Western Archean Gold Deposits

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 983
Author(s):  
Orivaldo Ferreira Baltazar ◽  
Lydia Maria Lobato
Keyword(s):  
Greenstone Belt ◽  
Gold Mineralization ◽  
Structural Evolution ◽  
Shear Zones ◽  
Gold Deposits ◽  
Normal Faults ◽  
Small Scale ◽  
Crenulation Cleavage ◽  
Quadrilátero Ferrífero ◽  
Tectonic Transport

The Quadrilátero Ferrífero region is located in the extreme southeast of the Brasiliano São Francisco craton, Minas Gerais state, Brazil. It is composed of (i) Archean TTG granite-gneaissic terranes; (ii) the Archean Rio das Velhas greenstone belt; (iii) the Proterozoic metasedimentary and metavolcano-sedimentary covers. The Rio das Velhas rocks were deposited in the synformal NW–SE-directed Nova Lima basin. The Archean deformation converted the Nova Lima basin into an ample synclinorium with an eastern inverted flank. Archean orogenic gold mineralization within the Rio das Velhas greenstone belt rocks is controlled by NNW–SSE-directed, Archean regional shear zones subparallel to the strata of the Nova Lima synclinorium borders. Transamazonian and Brasiliano orogenies are superposed onto the Archean structures that control gold mineralization. In the eastern domain, Brasiliano fold-and-fault belts prevail, whereas in the western domain Archean and Transamazonian structures abound. The present study focus mainly is the western domain where the Cuiabá, Morro Velho, Raposos, Lamego and Faria deposits are located. Gold orebodies plunge to the E–NE and are tectonically controlled by the Archean D1–D2 deformation. The D3 Transamazonian compression—Which had a SE–NW vector sub-parallel to the regional mineralized Archean foliation/bedding—Buckled these structures, resulting in commonly open, synformal and antiformal regional folds. These are well documented near the gold deposits, with NE–SW axial traces and fold axes plunging to E–NE. Such folds are normal to inverted, NW-verging, with an axial planar foliation dipping moderately to the SE. The Transamazonian compression has only been responsible for the reorientation of the mineralized Archean gold ores, due to coaxial refolding characterized by an opposite tectonic transport. It has therefore not caused any other significant changes. Thrust shear zones, sub-parallel to the strong Transamazonian foliation, have given rise to localized metric segmentation and to the dislocation of gold orebodies. Throughout the region, along the towns of Nova Lima to Sabará, structures pertaining to the Brasiliano Araçuaí orogeny are represented only by gentle folding and by a discrete, non-pervasive crenulation cleavage. Thrust-shear zones and small-scale normal faults have caused, at most, metric dislocations along N–S-oriented planes.

scholarly journals Petrography, microthermometry, and isotopy of the gold veins from Vetas, Santander (Colombia)

2020 ◽  
Vol 24 (1) ◽  
pp. 5-18
Author(s):  
Sonia Rojas Barbosa ◽  
Juan Carlos Molano ◽  
Thomas Cramer
Keyword(s):  
Fluid Inclusions ◽  
Gold Mineralization ◽  
Coarse Grained ◽  
Fine Grained ◽  
Quartz Veins ◽  
Low Salinity ◽  
Second Stage ◽  
The Third ◽  
Jurassic Rocks ◽  
Low Sulfidation

The gold mineralization located in Vetas, Santander, consists of auriferous quartz veins hosted in Bucaramanga gneiss rocks, intrusive Jurassic rocks, and intrusive to porphyritic Miocene rocks. This study identified four mineralizing events: (1). Sericite, carbonate (ankerite and calcite?), massive and microcrystalline quartz, sphalerite, adularia, albite, galena, thin pyrite, pyrrhotite, chalcopyrite. The age for this stage is 10.78 ±0.23Ma (Ar/Ar on sericite). (2). Molybdenite, magnetite with exsolution of ilmenite, As-pyrite, sphalerite, fine-grained pyrite and little chalcopyrite quartz with huge, feathery, fine mosaic, flamboyant and microcrystalline textures and, tourmaline and sericite. (3). Gold and tennantite associated with sphalerite, fine- and coarse-grained pyrite, As-pyrite, chalcopyrite like inclusions, and quartz with flamboyant, mosaic, massive and “comb” textures, and tourmaline. Stage 2 and 3 happened from 7.58 ±0.15 Ma to 6,89±0,41Ma (Ar/Ar on sericite). (4). Thick, thin, and pyrite with arsenic, hematite and microcrystalline quartz (forming breccia texture), and sericite. The age for this stage is 5.24 ±0.10 (Ar/Ar on sericite). Post-mineral: quartz comb, alunite, halloysite, kaolinite, and ferrum hydroxides. The stable isotopes, ∂18O, ∂D, and ∂34S and fluid inclusions analysis infer that fluids were producing a mixture of meteoric and magmatic fluids with low salinity and minimum trapping temperatures between 200°C to 390°C. The mineralogy association, and fluid inclusions, in the first event show characteristic of low sulfidation epithermal. The second stage was hottest and with more magmatic signature over printed an intermediate sulfidation system; show a little more salinity on the fluids and more mineralogical diversity, the third and four events, could show an evolution of this fluid, where it was cooling and impoverishing on metals. Two initials stages are contemporaneous with two magmatic Miocene pulses on the area: the first one of granodiorite composition 10, 9± 0.2 Ma (U/Pb zircon), and the other one rhyodacite with 8.4 ±0.2 y 9.0 ± 0.2 Ma.

scholarly journals Structural Control of Ore Deposits: The Role of Pre-Existing Structures on the Formation of Mineralised Vein Systems

Minerals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 56 ◽  
Author(s):  
Chauvet A.
Keyword(s):  
Structural Control ◽  
Shear Zones ◽  
Iberian Pyrite Belt ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Gold Mines ◽  
Existing Structures ◽  
Tectonic Events ◽  
Quadrilátero Ferrífero

The major role played by pre-existing structures in the formation of vein-style mineral deposits is demonstrated with several examples. The control of a pre-existing decollement level on the formation of a crustal extension-related (collapse) gold deposit is first illustrated in the Quadrilátero Ferrífero from Brazil. Shear zone and decollement structures were also examined and shown to control veins formation by three distinct processes: (i) re-aperture and re-using of wrench shear zones in the case of Shila gold mines (south Peru); (ii) remobilisation of metal in volcanic-hosted massive sulphide (VHMS) deposit by subsequent tectonic events and formation of a secondary stockwork controlled by structures created during this event (Iberian Pyrite Belt, Spain); (iii) formation of economic stockwork by contrasting deformation behaviours between ductile black schist versus brittle more competent dolomite (Cu-Ifri deposit, Morocco). Two examples involve changing of rheological competence within zones affected by deformation and/or alteration in order to receive the mineralisation (case studies of Achmmach, Morocco, and Mina Soriana, Spain). The last case underscores the significance of the magmatic–hydrothermal transition in the formation of mesothermal gold deposits (Bruès mine, Spain). All these examples clearly demonstrate the crucial role played by previously formed structures and/or texture in the development and formation of ore deposits.

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