scholarly journals Lower crustal resistivity signature of an orogenic gold system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Graham Heinson ◽  
Jingming Duan ◽  
Alison Kirkby ◽  
Kate Robertson ◽  
Stephan Thiel ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Organic Carbon ◽  
Marine Sediments ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Low Resistivity ◽  
Orogenic Gold Deposits ◽  
Long Period ◽  
Wide Range ◽  
Lower Crustal

AbstractOrogenic gold deposits provide a significant source of the world’s gold and form along faults over a wide range of crustal depths spanning sub-greenschist to granulite grade faces, but the source depths of the gold remains poorly understood. In this paper we compiled thirty years of long-period magnetotelluric (MT) and geomagnetic depth sounding (GDS) data across western Victoria and south-eastern South Australia that have sensitivity to the electrical resistivity of the crust and mantle, which in turn depend on past thermal and fluid processes. This region contains one of the world’s foremost and largest Phanerozoic (440 Ma) orogenic gold provinces that has produced 2% of historic worldwide gold production. Three-dimensional inversion of the long-period MT and GDS data shows a remarkable correlation between orogenic gold deposits with > 1 t production and a < 20 Ω m low-resistivity region at crustal depths > 20 km. This low-resistivity region is consistent with seismically-imaged tectonically thickened marine sediments in the Lachlan Orogen that contain organic carbon (C), sulphides such as pyrite (FeS2) and colloidal gold (Au). Additional heat sources at 440 Ma due to slab break-off after subduction have been suggested to rapidly increase the temperature of the marine sediments at mid to lower crustal depth, releasing HS− ligands for Au, and CO2. We argue that the low electrical resistivity signature of the lower crust we see today is from a combination of flake graphite produced in situ from the amphibolite grade metamorphism of organic-carbon in the marine sediments, and precipitated graphite through retrograde hydration reactions of CO2 released during the rapid heating of the sediments. Thus, these geophysical data image a fossil source and pathway zone for one of the world’s richest orogenic gold provinces.

scholarly journals Texture and Trace Element Composition of Rutile in Orogenic Gold Deposits

2021 ◽  
Vol 116 (8) ◽  
pp. 1865-1892
Author(s):  
Marjorie Sciuba ◽  
Georges Beaudoin
Keyword(s):  
Trace Element ◽  
Trace Element Composition ◽  
Gold Deposits ◽  
Element Composition ◽  
Partial Least Square ◽  
Orogenic Gold ◽  
Orogenic Gold Deposits ◽  
Hydrothermal Deposits ◽  
Wide Range ◽  
Strong Control

Abstract Rutile from a wide range of orogenic gold deposits and districts, including representative world-class deposits, was investigated for its texture and trace element composition using scanning electron microscopy, electron probe microanalysis, and laser ablation-inductively coupled plasma-mass spectrometry. Deposits are hosted in various country rocks including felsic to ultramafic igneous rocks and sedimentary rocks, which were metamorphosed from lower greenschist to middle amphibolite facies and with ages of mineralization that range from Archean to Phanerozoic. Rutile presents a wide range of size, texture, and chemical zoning. Rutile is the dominant TiO2 polymorph in orogenic gold mineralization. Elemental plots and partial least square-discriminant analysis suggest that the composition of the country rocks exerts a strong control on concentrations of V, Nb, Ta, and Cr in rutile, whereas the metamorphic facies of the country rocks controls concentrations of V, Zr, Sc, U, rare earth elements, Y, Ca, Th, and Ba in rutile. The trace element composition of rutile in orogenic gold deposits can be distinguished from rutile in other deposit types and geologic settings. Elemental ratios Nb/V, Nb/Sb, and Sn/V differentiate the rutile trace element composition of orogenic gold deposits compared with those from other geologic settings and environments. A binary plot of Nb/V vs. W enables distinction of rutile in metamorphic-hydrothermal and hydrothermal deposits from rutile in magmatic-hydrothermal deposits and magmatic environments. The binary plot Nb/Sb vs. Sn/V distinguishes rutile in orogenic gold deposits from other geologic settings and environments. Results are used to establish geochemical criteria to constrain the source of rutile for indicator mineral surveys and potentially guide mineral exploration.

A metasedimentary source of gold in Archean orogenic gold deposits

Geology ◽  
2021 ◽  
Author(s):  
Iain K. Pitcairn ◽  
Nikolaos Leventis ◽  
Georges Beaudoin ◽  
Stephane Faure ◽  
Carl Guilmette ◽  
...  
Keyword(s):  
Sedimentary Rock ◽  
Sedimentary Rocks ◽  
Gold Deposits ◽  
Metamorphic Grade ◽  
Orogenic Gold ◽  
Metal Source ◽  
Main Metal ◽  
Metasedimentary Rocks ◽  
Orogenic Gold Deposits ◽  
Archean Orogenic Gold Deposits

The sources of metals enriched in Archean orogenic gold deposits have long been debated. Metasedimentary rocks, which are generally accepted as the main metal source in Phanerozoic deposits, are less abundant in Archean greenstone belts and commonly discounted as a viable metal source for Archean deposits. We report ultralow-detection-limit gold and trace-element concentrations from a suite of metamorphosed sedimentary rocks from the Abitibi belt and Pontiac subprovince, Superior Province, Canada. Systematic decreases in the Au content with increasing metamorphic grade indicate that Au was mobilized during prograde metamorphism. Mass balance calculations show that over 10 t of Au, 30,000 t of As, and 600 t of Sb were mobilized from 1 km3 of Pontiac subprovince sedimentary rock metamorphosed to the sillimanite metamorphic zone. The total gold resource in orogenic gold deposits in the southern Abitibi belt (7500 t Au) is only 3% of the Au mobilized from the estimated total volume of high-metamorphic-grade Pontiac sedimentary rock in the region (25,000 km3), indicating that sedimentary rocks are a major contributor of metals to the orogenic gold deposits in the southern Abitibi belt.

Lithospheric controls on the formation of provinces hosting giant orogenic gold deposits

2006 ◽  
Vol 40 (8) ◽  
pp. 874-886 ◽  
Author(s):  
Frank P. Bierlein ◽  
David I. Groves ◽  
Richard J. Goldfarb ◽  
Benoit Dubé
Keyword(s):  
Gold Deposits ◽  
Orogenic Gold ◽  
Orogenic Gold Deposits

A Tentative Study of Relationship between Mantle Plumes, Supercontinents and Orogenic Gold Deposits

2013 ◽  
Vol 734-737 ◽  
pp. 265-268
Author(s):  
Jun Hao Cui ◽  
Tao Ren
Keyword(s):  
Mantle Plume ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Upper Crust ◽  
Orogenic Gold Deposits ◽  
Orogenic Gold Deposit ◽  
The Earth ◽  
Tectonic Environment ◽  
The Relationship

On the basis of predecessors study, this paper found that outbreak frequency of mantle plume is increase, while scale is reduce. The mantle plume provides ore-forming minerals to orogenic gold deposits, as well as affords force to supercontinent formation and decomposition, for the more controls the global tectonic. Supercontinent is the movement of upper crust that could be cause by combine factors of cold and heat mantle plume. Supercontinent supply suitable tectonic environment for orogenic gold deposits. Further, we discuss the relationship between mantle plume, supercontinent and orogenic gold deposit on space and time. With the evolution of the earth, especially the energy loss, the frequency of orogenic gold mineralization is increasing, while the scale is reducing.

Atmospheric sulfur in the orogenic gold deposits of the Archean Yilgarn Craton, Australia

Geology ◽  
2017 ◽  
pp. G39018.1 ◽  
Author(s):  
Vikraman Selvaraja ◽  
Stefano Caruso ◽  
Marco L. Fiorentini ◽  
Crystal K. LaFlamme ◽  
Thi-Hao Bui
Keyword(s):  
Gold Deposits ◽  
Orogenic Gold ◽  
Yilgarn Craton ◽  
Orogenic Gold Deposits ◽  
Atmospheric Sulfur
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