Co–Ni arsenide deposits, with accessory gold, in ultramafic rocks from Morocco

1986 ◽  
Vol 23 (10) ◽  
pp. 1592-1602 ◽  
Author(s):  
Marc Leblanc
Keyword(s):  
Upper Mantle ◽  
Carbonate Rocks ◽  
Ultramafic Rocks ◽  
Hydrothermal Solutions ◽  
Average Content ◽  
Mantle Origin ◽  
Upper Proterozoic ◽  
Mantle Peridotites ◽  
Gold Bearing

A type of Co–Ni arsenide deposit with accessory gold and no silver can be recognized in ultramafic massifs of upper mantle origin. The Bou Azzer deposits (50 000 t Co) are distributed along the borders of serpentinite massifs in an Upper Proterozoic ophiolite (Anti-Atlas, Morocco). They consist of quartz–carbonate lenses with Co (Ni–Fe) arsenides. Gold is related to the skutterudite (8–15 ppm average content). In the Alpine lherzolite massif of Beni Bousera (Rif, Morocco) are found small chromite–Ni arsenides veins (300 t Ni) with accessory gold. They are associated with late orthopyroxene–vermiculite dikes. Several occurrences of As, arsenides, and gold-bearing carbonate rocks are found in serpentinites from various ophiolites. It is proposed that gold was leached by As- and Co2-rich hydrothermal solutions related to the serpentinization of mantle peridotites.

scholarly journals Physicochemical Model of Formation of Gold-Bearing Magnetite-Chlorite-Carbonate Rocks at the Karabash Ultramafic Massif (Southern Urals, Russia)

Minerals ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 306 ◽  
Author(s):  
Valery Murzin ◽  
Konstantin Chudnenko ◽  
Galina Palyanova ◽  
Aleksandr Kissin ◽  
Dmitry Varlamov
Keyword(s):  
Carbon Dioxide ◽  
Carbonate Rocks ◽  
Southern Urals ◽  
Ultramafic Rocks ◽  
Physicochemical Model ◽  
The Southern Urals ◽  
Model Calculations ◽  
Ultramafic Massif ◽  
Copper Gold ◽  
Gold Bearing

We present a physicochemical model for the formation of magnetite-chlorite-carbonate rocks with copper gold in the Karabash ultramafic massif in the Southern Urals, Russia. The model was constructed based on the formation geotectonics of the Karabash massif, features of spatial distribution of metasomatically altered rocks in their central part, geochemical characteristics and mineral composition of altered ultramafic rocks, data on the pressure and temperature conditions of formation, and composition of the ore-forming fluids. Magnetite-chlorite-carbonate rocks were formed by the hydrothermal filling of the free space, whereas chloritolites were formed by the metasomatism of the serpentinites. As the source of the petrogenic and ore components, we considered rocks (serpentinites, gabbro, and limestones), deep magmatogenic fluids, probably mixed with metamorphogenic fluids released during dehydration and deserpentinization of rocks in the lower crust, and meteoric waters. The model supports the involvement of sodium chloride-carbon dioxide fluids extracting ore components (Au, Ag, and Cu) from deep-seated rocks and characterized by the ratio of ore elements corresponding to Clarke values in ultramafic rocks. The model calculations show that copper gold can also be deposited during serpentinization of deep-seated olivine-rich rocks and ore fluids raised by the tectonic flow to a higher hypsometric level. The results of our research allow predicting copper gold-rich ore occurrences in ultramafic massifs.

scholarly journals Water contents of nominally anhydrous orthopyroxenes from oceanic peridotites determined by SIMS and FTIR

2021 ◽  
Author(s):  
Kirsten T. Wenzel ◽  
Michael Wiedenbeck ◽  
Jürgen Gose ◽  
Alexander Rocholl ◽  
Esther Schmädicke
Keyword(s):  
Upper Mantle ◽  
Secondary Ion Mass Spectrometry ◽  
Spinel Peridotite ◽  
Structural Water ◽  
Major Element Composition ◽  
Mantle Peridotites ◽  
History Of ◽  
Polarized Ftir ◽  
Water Contents ◽  
Forearc Region

AbstractThis study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic reference orthopyroxenes from spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al2O3 ranges between 4.02 and 5.56 wt%, and Cr2O3 ranges between 0.21 and 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the water contents of the eleven reference orthopyroxenes vary from dry to 249 ± 6 µg/g H2O. Using these reference grains, a set of orthopyroxene samples obtained from variably altered abyssal spinel peridotites from the Atlantic and Arctic Ridges as well as from the Izu-Bonin-Mariana forearc region was analyzed by SIMS and FTIR regarding their incorporation of water. The major element composition of the sample orthopyroxenes is typical of spinel peridotites from the upper mantle, characterized by Mg#s between 0.90 and 0.92, Al2O3 between 1.66 and 5.34 wt%, and Cr2O3 between 0.62 and 0.96 wt%. Water contents as measured by SIMS range from 68 ± 7 to 261 ± 11 µg/g H2O and correlate well with Al2O3 contents (r = 0.80) and Cr#s (r. = -0.89). We also describe in detail an optimized strategy, employing both SIMS and FTIR, for quantifying structural water in highly altered samples such as abyssal peridotite. This approach first analyzes individual oriented grains by polarized FTIR, which provides an overview of alteration. Subsequently, the same grain along with others of the same sample is measured using SIMS, thereby gaining information about homogeneity at the hand sample scale, which is key for understanding the geological history of these rocks.

Experimental investigation of the composition of incipient melts in upper mantle peridotites in the presence of CO2 and H2O

Lithos ◽  
2021 ◽  
pp. 106224
Author(s):  
Zsanett Pintér ◽  
Stephen F. Foley ◽  
Gregory M. Yaxley ◽  
Anja Rosenthal ◽  
Robert P. Rapp ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Upper Mantle ◽  
Mantle Peridotites

Upper mantle origin for Harding County well gases

Nature ◽  
1987 ◽  
Vol 325 (6105) ◽  
pp. 605-607 ◽  
Author(s):  
Thomas Staudacher
Keyword(s):  
Upper Mantle ◽  
Mantle Origin

On the Vp/Vs–Mg# correlation in mantle peridotites: Implications for the identification of thermal and compositional anomalies in the upper mantle

2010 ◽  
Vol 289 (3-4) ◽  
pp. 606-618 ◽  
Author(s):  
Juan Carlos Afonso ◽  
Giorgio Ranalli ◽  
Manel Fernàndez ◽  
William L. Griffin ◽  
Suzanne Y. O'Reilly ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Mantle Peridotites

A suite of alkali basalts and gabbros associated with the Hare Bay Allochthon of western Newfoundland

1977 ◽  
Vol 14 (3) ◽  
pp. 346-356 ◽  
Author(s):  
R. A. Jamieson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Upper Mantle ◽  
Ultramafic Rocks ◽  
Alkali Basalts ◽  
Crust And Upper Mantle ◽  
Bay Area ◽  
Close Proximity ◽  
Thrust Sheets

The Hare Bay Allochthon of northwestern Newfoundland consists of a series of sedimentary, volcanic, metamorphic, and ultramafic rocks which was emplaced over a Cambro-Ordovician continental margin as several thrust sheets. It probably represents a continental margin sequence overridden by oceanic crust and upper mantle. The Partridge Point gabbro, Cape Onion volcanics, and Ireland Point Volcanics, which now occur in the Maiden Point, Cape Onion, and St. Anthony tectonic slices respectively, appear to be closely related on petrographic and chemical grounds. Olivine, titanaugite, kaersutite, and plagioclase indicate that these rocks formed as a single suite of hydrous alkali basalts, possibly as part of a seamount near a continental margin. This relationship provides a link between the lower sedimentary and the upper igneous-metamorphic structural slices of the allochthon and implies that most of the transported rocks in the Hare Bay area evolved in close proximity to each other.

Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

2019 ◽  
Vol 57 (5) ◽  
pp. 677-706
Author(s):  
Isabel Ribeiro da Costa ◽  
Frederick Joseph Wicks ◽  
Fernando J.A.S. Barriga
Keyword(s):  
Upper Mantle ◽  
Hydrothermal Activity ◽  
Isotopic Data ◽  
Geochemical Characterization ◽  
Textural Evolution ◽  
Mantle Peridotites ◽  
Carbonate Deposition ◽  
Mid Atlantic Ridge ◽  
Ree Patterns

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

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