Volcanic Stratigraphy, Geochronology, and Gold Deposits of the Archean Hope Bay Greenstone Belt, Nunavut, Canada

2012 ◽  
Vol 107 (5) ◽  
pp. 991-1042 ◽  
Author(s):  
R. L. Sherlock ◽  
A. Shannon ◽  
M. Hebel ◽  
D. Lindsay ◽  
J. Madsen ◽  
...  
Keyword(s):  
Greenstone Belt ◽  
Gold Deposits ◽  
Volcanic Stratigraphy ◽  
Hope Bay

scholarly journals Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 966
Author(s):  
Baptiste Madon ◽  
Lucie Mathieu ◽  
Jeffrey H. Marsh
Keyword(s):  
Oxygen Fugacity ◽  
Greenstone Belt ◽  
Inductively Coupled Plasma ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Chemical Diversity ◽  
Temporal Association ◽  
Volatile Content ◽  
Abitibi Subprovince

Neoarchean syntectonic intrusions from the Chibougamau area, northeastern Abitibi Subprovince (greenstone belt), may be genetically related to intrusion related gold mineralization. These magmatic-hydrothermal systems share common features with orogenic gold deposits, such as spatial and temporal association with syntectonic magmatism. Genetic association with magmatism, however, remains controversial for many greenstone belt hosted Au deposits. To precisely identify the link between syntectonic magmas and gold mineralization in the Abitibi Subprovince, major and trace-element compositions of whole rock, zircon, apatite, and amphibole grains were measured for five intrusions in the Chibougamau area; the Anville, Saussure, Chevrillon, Opémisca, and Lac Line Plutons. The selected intrusions are representative of the chemical diversity of synvolcanic (TTG suite) and syntectonic (e.g., sanukitoid, alkaline intrusion) magmatism. Chemical data enable calculation of oxygen fugacity and volatile content, and these parameters were interpreted using data collected by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The zircon and apatite data and associated oxygen fugacity values in magma indicate that the youngest magmas are the most oxidized. Moreover, similar oxygen fugacity and high volatile content for both the Saussure Pluton and the mineralized Lac Line intrusion may indicate a possible prospective mineralized system associated with the syntectonic Saussure intrusion.

Oxidized and reduced mineral assemblages in greenstone belt rocks of the St. Ives gold camp, Western Australia: vectors to high-grade ore bodies in Archaean gold deposits?

2007 ◽  
Vol 43 (3) ◽  
pp. 363-371 ◽  
Author(s):  
Peter Neumayr ◽  
John Walshe ◽  
Steffen Hagemann ◽  
Klaus Petersen ◽  
Anthony Roache ◽  
...  
Keyword(s):  
Western Australia ◽  
Greenstone Belt ◽  
Gold Deposits ◽  
High Grade ◽  
Ore Bodies ◽  
Mineral Assemblages

Laser ablation ICP MS trace element composition of native gold from the Abitibi Greenstone belt, Timmins Ontario.

2021 ◽  
Author(s):  
John D. Greenough ◽  
Alejandro Velasquez ◽  
Mohamed Shaheen ◽  
Joel Gagnon ◽  
Brian J. Fryer ◽  
...  
Keyword(s):  
Trace Elements ◽  
Laser Ablation ◽  
Trace Element ◽  
Greenstone Belt ◽  
Native Gold ◽  
Internal Standard ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Abitibi Greenstone Belt ◽  
Icp Ms

Trace elements in native gold provide a “fingerprint” that tends to be unique to individual gold deposits. Fingerprinting can distinguish gold sources and potentially yield insights into geochemical processes operating during gold deposit formation. Native gold grains come from three historical gold ore deposits; Hollinger, McIntyre (quartz-vein ore), and Aunor near Timmins, Ontario, at the western end of the Porcupine gold camp and the south-western part of the Abitibi greenstone belt. Laser-ablation, inductively-coupled plasma mass spectrometry (LA ICP MS) trace element concentrations were determined on 20 to 25 µm wide, 300 µm long rastor trails in ~ 60 native gold grains. Analyses used Ag as an internal standard with Ag and Au determined by a scanning electron microscope with an energy dispersive spectrometer. The London Bullion Market AuRM2 reference material served as the external standard for 21 trace element analytes (Al, As, Bi, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Pd, Pt, Rh, Sb, Se, Si, Sn, Te, Ti, Zn; Se generally below detection in samples). Trace elements in native gold associate according to Goldschmidt’s classification of elements strongly suggesting that element behavior in native Au is not random. Such element behavior suggests that samples from each Timmins deposit formed under similar but slightly variable geochemical conditions. Chalcophile and siderophile elements provide the most compelling fingerprints of the three ore deposits and appear to be mostly in solid solution in Au. Lithophile elements are not very useful for distinguishing these deposits and element ABSTRACT CUT OFF BY SOFTWARE

The application of the mise-a-la-masse electrical technique in Greenstone belt gold exploration

1989 ◽  
Vol 20 (2) ◽  
pp. 113
Author(s):  
L.G.B.T. Polomé
Keyword(s):  
Greenstone Belt ◽  
Electrical Potential ◽  
Gold Deposits ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Current Electrode ◽  
Barberton Greenstone Belt ◽  
A Current ◽  
Ore Zones ◽  
Gold Bearing

Most of the gold deposits in the Barberton Greenstone belt of South Africa are relatively small and in structurally complex geological areas.The mise-a-la-masse electrical technique, where a current electrode is earthed in a mineralised zone, was used on one of our exploration projects consisting of a sulphides/gold-bearing carbonaceous banded iron formation within a succession of mafic, ultramafic and sedimentary rocks. The technique was successful in delineating individual mineralised units within a broad lithological sequence. During the survey, electrical potential measurements were recorded on surface, in underground drives and in twenty five boreholes. Measurements were also repeated by earthing the mineralised zone in a number of boreholes. Major discontinuities were recognised within the ore zones and used to interpret geological structures. These were then used to define specific units for ore reserve calculations and the application of selected mining techniques.

Gold Remobilization: Insights from Gold Deposits in the Archean Swayze Greenstone Belt, Abitibi Subprovince, Canada

2020 ◽  
Vol 115 (2) ◽  
pp. 241-277 ◽  
Author(s):  
Evan C.G. Hastie ◽  
Daniel J. Kontak ◽  
Bruno Lafrance
Keyword(s):  
Greenstone Belt ◽  
Inductively Coupled Plasma ◽  
Native Gold ◽  
Gold Deposits ◽  
Coarse Grained ◽  
High Grade ◽  
Northern Ontario ◽  
Inductively Coupled ◽  
Abitibi Subprovince ◽  
Plasma Mass Spectrometry

Abstract Recognizing if and how Au is remobilized, in solid, melt, or fluid state, is critical for understanding the origin of high-grade ore zones in Au deposits. When evidence for Au remobilization can be demonstrated, then primary versus secondary processes can be distinguished, resulting in a more complete understanding of Au deposit formation. To address this, samples from two Au deposits, Jerome and Kenty, in the Archean Swayze greenstone belt of northern Ontario, Canada, together with archived samples from 39 high-grade Au deposits from the Abitibi greenstone belt across Ontario and Quebec, were geochemically characterized using integrated scanning electron microscopy-energy dispersive spectroscopy and electron microprobe imaging and analyses in addition to laser ablation-inductively coupled plasma-mass spectrometry elemental mapping. These data provided the basis to develop a model for Au remobilization and upgrading of Au that is widely applicable to orogenic gold settings. Data for the Jerome deposit indicate that Au uptake into early pyrite was not due to pulsing of different fluids, but instead was predominantly controlled by S availability, whereby the oscillatory/sector zoning in pyrite resulted from the substitution of As into S sites during rapid growth due to local chemical disequilibrium. In addition, Au-bearing pyrite from both the Jerome and Kenty deposits records textures, such as porosity development coincident with the presence of native gold and accessory sulfide phases, that are strongly suggestive of coupled dissolution-reprecipitation (CDR) reactions that liberated Au and associated elements from earlier auriferous (100–5,000 ppm Au) pyrite. During the remobilization process, Au and Ag were decoupled, which resulted in (1) a change in Au/Ag ratios of 0.5 to 5 in early pyrite to ≈9 in the new native gold (900 Au fineness) and (2) incorporation of Ag into cogenetic secondary mineral phases (e.g., chalcopyrite, tetrahedrite, and galena). Evidence for an association of low-melting point chalcophile elements (LMCE; Hg, Te, Sb, and Bi) with Au at the Jerome, Kenty, and many (>50%) of the 39 historic deposits sampled, along with native gold filling structurally favorable sites in vein quartz in all samples, indicates a fluid might not have been the only factor contributing to remobilization. This systematic Au-LMCE association strongly supports a model whereby Au is released by CDR reactions and is then remobilized by fluid-mediated, LMCE-rich melts that began to form at 335°C and/or by local, nanoparticle (nanomelt?) transport during deformation and metamorphism. Conclusions drawn from this study have implications for Au deposits globally and can account for the common presence of coarse-grained, commonly crystalline, native gold filling fractures in quartz and the paragenetically late-stage origin of gold in veins. They can also better explain the inability of Au in solution remobilization models to account for locally high gold grades, given the relatively low solubility of Au in hydrothermal fluids.

Brazil's premier gold province. Part II: geology and genesis of gold deposits in the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero

2001 ◽  
Vol 36 (3-4) ◽  
pp. 249-277 ◽  
Author(s):  
Lydia Maria Lobato ◽  
Luiz Cláudio Ribeiro-Rodrigues ◽  
Frederico Wallace Reis Vieira
Keyword(s):  
Greenstone Belt ◽  
Gold Deposits ◽  
Quadrilátero Ferrífero

The role of fluids during formation and evolution of the southern Superior Province lithosphere: an overview

2000 ◽  
Vol 37 (2-3) ◽  
pp. 135-164 ◽  
Author(s):  
Robert Kerrich ◽  
John Ludden
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Greenstone Belt ◽  
Meteoric Water ◽  
Gold Deposits ◽  
Lode Gold ◽  
Magmatic Fluids ◽  
Abitibi Subprovince ◽  
Lode Gold Deposits ◽  
Archean Basement

Models for fluid flow and hydrothermal alteration for the Abitibi greenstone belt are reviewed in the light of Lithoprobe results in the region. In the Abitibi greenstone belt, eruption of volcanic sequences over 2750-2700 Ma was accompanied by pervasive low-temperature hydrothermal alteration at high water/rock ratios, giving systematic 18O-enrichment. Archean ambient ocean water bottom temperatures were likely ca. 30°C, and δ18O ~0 ± 1‰. Chert-iron formations precipitated from low temperature hydrothermal discharge. Base metal massive sulphide deposits formed at or near the seafloor from focussed discharge of high-temperature (~300-400°C) fluids in convective cells sited above subvolcanic intrusions. The ore fluids were evolved seawater that had undergone compositional and isotopic evolution by high-temperature, low water/rock exchange with the volcanic pile to NaCl (3-7 wt.%) or CaCl2-NaCl (up to 30 wt.%) brines of δ18O = 0-8‰. These volcanic associated hydrothermal deposits are associated with greenstone belt asemblages in the northern Abitibi subprovince that were emplaced as a series of thrust slices over the Opatica plutonic belt. In the southern Abitibi subprovince the hydrothermal deposits were associated with a series of rift basins (Noranda, Val d'Or, etc.), formed on top of accreted oceanic assemblages comprising primitive arcs and plateaus, or in protoarcs, and associated with oblique convergence. Contemporaneous erosion of emergent arcs and the older cratonic provenance terrane of the Pontiac subprovince by orographic rainfall, and submarine weathering, fed first-cycle vol cano genic sediments to depositional basins in the Abitibi, but siliciclastic sediments of mixed old 3 Ga continent and 2.7 Ga arc provenance in the Pontiac subprovince. Abitibi subprovince turbidites were more weathered and 18O-enriched than Pontiac subprovince equivalents. Subduction-accretion assembly of the Opatica-Abitibi and Pontiac terranes involved allochthonous thrusting of the Abitibi subprovince over the Pontiac subprovince. There were several pulses of granitoid magmatism during accretionary assembly over 2695 to 2674 Ma. Syn- to late-tectonic tonalites were generated by melting of hot young hydrous ocean crust in a shallow-dipping intraoceanic subduction zone. The intrusions exsolved small quantities of magmatic fluids that formed Cu-Zn showings. Late-tectonic shoshonites formed at [Formula: see text]80 km in subarc mantle wedge by slab dehydration-wedge melting. This late-stage of arc development involved transfer of significant quantities of gas-rich alkaline magmas 80+ km through the lithosphere along the accretionary terrane bounding structures, and produced small phosphorus and barite deposits. Synmagmatic metamorphism was of the high-temperature low-pressure type, and occurred in several pulses; water/rock ratios were generally low distal from structures. Tens of thousands of cubic kilometres of fluids generated by dehydration reactions at the base of the subduction-accretion complex, during thermal relaxation following collision and the main granitoid pulses, advected up terrane boundary structures and locally generated lode gold deposits. At the highest structural levels these fluids mixed with Archean meteoric water where δ18O < 0. A second metamorphism (M2) occurred over 2645 to 2611 Ma leading to melting of Pontiac sediments and formation of S-type granites. Deposits of Mo, Th, and P were precipitated from magmatic fluids of δ18O 8-9‰. M2 variably reset radiogenic and stable isotope systems in nonrobust minerals of vol canogenic massive sulphide and lode gold deposits. Hypersaline CaCl2 formation brines evolved in Paleoproterozoic glaciogenic sediments; these penetrated into the Archean basement where they redistributed gold and are pervasively present as low-temperature secondary brine inclusions. The Matachewan (2.5 Ga) and Hearst dyke swarms drove higher temperature advection of the brines, and Ag-Co-Ni sulpharsenide deposits formed by thermal evolution of the brines driven by the Nipissing diabase dyke swarm at ~2219 Ma. Local resetting of 40Ar/39Ar spectra between 2550 and 2200 Ma was the product of tectonic pumping of fluids along reactivated Archean structures, possibly due to coupling of the 200 km thick mantle lithosphere to Archean crust. Seismic evidence for late overprinting of the lower crust and growth of 2450 Ma zircon rims in lower crustal assemblages were associated with this event. There was also fluid activity at 1950 to 1850 Ma due to the Hudsonian orogen induced Kapuskasing event. Hypersaline CaCl2-rich brines formed in the Paleozoic sedimentary cover (~500 Ma), penetrated deep (>5 km) into the Archean basement, and comprise vast reservoirs of hypersaline brines deep in the Shield. The brines precipitated prehnite-laumontite veins that record hundreds of increments of dilation. Subglacial 18O-depleted fluids penetrated to shallow ([Formula: see text]1 km) depths in the Quaternary; they form mixing lines with the hypersaline end member. Extremely D-depleted (-400 to -100‰) CH4 and H discharge in mining districts of the Shield. The depleted H may form by radiolysis of H2O and (or) by a Fischer-Tropsch type process. The hypersaline brine end-member was shifted to the left of the meteoric water line by exchange with D-depleted H.

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