Genesis of As-Pb-Rich Supergene Mineralization: The Tazalaght and Agoujgal Cu Deposits (Moroccan Anti-Atlas Copperbelt)

2020 ◽  
Vol 115 (8) ◽  
pp. 1725-1748
Author(s):  
Michèle Verhaert ◽  
Atman Madi ◽  
Abdelaziz El Basbas ◽  
Mohamed Elharkaty ◽  
Abdellah Oummouch ◽  
...  
Keyword(s):  
Sulfide Deposits ◽  
Host Rocks ◽  
Evolution With Time

Abstract In the Moroccan Anti-Atlas, sulfide deposits hosted by Neoproterozoic to Cambrian formations underwent significant weathering, leading to the formation of supergene profiles. In the Tazalaght Cu-As deposit, three mineralogical steps are distinguished: (1) the replacement of hypogene sulfides (chalcopyrite, pyrite, tennantite) by supergene sulfides (bornite, chalcocite) in the large cementation zone; (2) the formation of oxidized minerals (malachite, azurite, olivenite, and chenevixite, mainly) in a more oxidizing and neutral environment; and (3) the precipitation of goethite, hematite, and quartz in the gossan. In the Cu-As-Pb-V deposit of Agoujgal, the mineralogical units are spatially less confined than at Tazalaght. The narrow cementation zone hosts chalcocite, resulting from the weathering of hypogene chalcopyrite, pyrite, tennantite and galena, while the much more extended and diversified oxidized zone is rich in Cu and Pb carbonates, arsenates, sulfates, phosphates, vanadates, and oxides. Goethite, hematite, mottramite, and late calcite occur in the gossan. Both deposits are characterized by As-rich secondary ores that were formed through similar processes, despite some mineralogical and chemical variations highlighting the influence of the host rocks on weathering. The restricted oxidized mineralization at Tazalaght and the Agoujgal cementation zone most likely arise from the contrasting omnipresence of quartzite at Tazalaght that could not enable a fast and effective neutralization of the fluid’s acidity, and the large amounts of dolomitic host rocks that could be dissolved at Agoujgal. At both sites, the weathering of tennantite through a boxwork texture records the transition from the cementation zone (chalcocite), the oxidized zone (arsenates), and the gossan, and reflects the fluids evolution with time.

Massive sulfide deposits of the Noranda area, Quebec. III. The Ansil mine

1991 ◽  
Vol 28 (11) ◽  
pp. 1699-1730 ◽  
Author(s):  
T. J. Barrett ◽  
W. H. MacLean ◽  
S. Cattalani ◽  
L. Hoy ◽  
G. Riverin
Keyword(s):  
Hanging Wall ◽  
Volcanic Rocks ◽  
Massive Sulfide ◽  
Hydrothermal Activity ◽  
Sulfide Deposit ◽  
Sulfide Deposits ◽  
Almost All ◽  
Host Rocks ◽  
Low K ◽  
General Range

The Ansil massive sulfide deposit occurs at the contact of the underlying Northwest Rhyolite and the overlying Rusty Ridge Andesite, in the lower part of the Central Mine sequence of the Blake River Group. The orebody, which is roughly ellipsoidal in outline and up to 200 m × 150 m across, contained reserves of 1.58 Mt of massive sulfide grading 7.2% Cu, 0.9% Zn, 1.6 g/t Au, and 26.5 g/t Ag. Production began in 1989. Least-altered host rocks are low-K basaltic andesites and low-K rhyolites. These rocks have Zr/Y ratios of ~5 and LaN/YbN ratios of ~2.3, typical of tholeiitic volcanic rocks, although their major-element chemistry is transitional between tholeiitic and calc-alkaline volcanic rocks.The Ansil deposit, which dips ~50° east, is a single orebody comprising two main massive sulfide lenses (up to ~35 m thick) connected laterally via a thinner blanket of massive sulfides, with thin discontinuous but conformable massive magnetite units at the base and top of the orebody. Sulfide ore consists of massive to banded pyrrhotite–chalcopyrite. In the downplunge lens, up to 10 m of massive magnetite are capped by up to 10 m of massive sulfide. Finely banded cherty tuff, with sphalerite–pyrite–chalcopyrite, forms a discontinuous fringe to the deposit.The two main lenses of massive sulfide have the highest contents of Cu, Ag, and Au and are thought to have formed in areas of major hydrothermal input. Altered feeder zones contain either chlorite + chalcopyrite + pyrrhotite ± magnetite, or chlorite + magnetite ± sulfides. Footwall mineralization forms semiconformable zones ~5–10 m thick that directly underlie the orebody and high-angle pipelike zones that extend at least 50 m into the footwall. Ti–Zr–Al plots indicate that almost all altered footwall rocks were derived from a homogeneous rhyolite precursor. Hanging-wall andesites were also altered. Despite some severe alteration, all initial volcanic rock compositions can be readily identified, and thus mass changes can be calculated. Silica has been both significantly added or removed from the footwall, whereas K has been added except in feeder pipes. Oxygen-isotope compositions up to at least 50 m into the hanging wall and footwall are typically depleted in δ18O by 2–6‰. These rocks have gained Fe + Mg and lost Si. Altered samples in general range from light-rare-earth-element (REE) depleted to light-REE enriched, although some samples exhibit little REE modification despite strong alkali depletion. Mineralized volcanic rocks immediately below the orebody are enriched in Eu (as are some Cu-rich sulfides in the orebody).Contact and petrographic relations generally suggest that the main zone of massive magnetite formed by replacement of cp–po-rich sulfides, although local relations are ambiguous. Magnetite formation may reflect waning hydrothermal activity, during which fluids mixed with seawater and became cooler and more oxidized. Cu-rich feeder pipes that cut magnetite-rich footwall indicate a renewal of Cu-sulfide mineralization after magnetite deposition. Chloritic zones with disseminated sulfides occur up to a few hundred metres above the orebody, attesting to continuing hydrothermal activity.

Compositional peculiarities of the host rocks and ores of the Lazursky ore field, Zmeinogorsk ore region of the Rudny Altai minerogenic zone

2021 ◽  
pp. 36-47
Author(s):  
Tatyana SERAVINA ◽  
Svetlana KUZNETSOVA ◽  
Ludmila FILATOVA
Keyword(s):  
Massive Sulfide ◽  
Ore Deposits ◽  
Sulfide Ores ◽  
Volcanogenic Massive Sulfide ◽  
Sulfide Deposits ◽  
Ore Bodies ◽  
Ore Minerals ◽  
Copper Pyrite ◽  
Host Rocks ◽  
Volcanogenic Massive Sulfide Deposits

The article describes composition of the host rocks and ores of the Lazursky and Maslyansky polymetallic volcanogenic massive sulfide deposits of the Lazursky ore field located within the Zmeinogorsk ore region of the Rudny Altai minerogenic zone. The ore field is composed of various facies of the Devonian (Late Givetian – Frasnian) ore-bearing siliceous-terrigenous basalt-rhyolite formation containing horizons of synvolcanic metasomatites. All rocks of the ore field were subjected to folding and schistosity with zones of tectonic brecciation. Hydrothermal alterations are represented by carbonatization and chloritization. The ore bodies exposed at the Lazursky and Maslyansky ore deposits are represented by copper-pyrite, copper, and zinc-copper-pyrite massive sulfide ores and other varieties. The major ore minerals of the deposits are chalcopyrite, pyrite, sphalerite, marcasite, and pyrrhotite.

Isotopic studies of ore-leads of the circum-Kisseynew volcanic belt of Manitoba and Saskatchewan

1978 ◽  
Vol 15 (7) ◽  
pp. 1112-1121 ◽  
Author(s):  
D. F. Sangster
Keyword(s):  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Massive Sulfide ◽  
Good Evidence ◽  
Lake Area ◽  
Sulfide Deposits ◽  
North West ◽  
The North ◽  
Isotopic Abundances ◽  
Host Rocks

Volcanic rocks, distributed to the north, west, and south of the Kisseynew gneissic belt in Manitoba and Saskatchewan, define a crescent-shaped belt herein informally referred to as the 'circum-Kisseynew volcanic belt'. Field relationships lead to the conclusion that the flanking volcanics are correlative with, and grade basinward to, greywackes and shales.Nearly 30 volcanogenic massive sulfide deposits, interpreted as coeval with their host rocks, are distributed throughout the circum-Kisseynew volcanic belt. Lead isotopic abundances in a representative number of these deposits are, apart from 204-error, relatively homogeneous in composition and model lead ages determined from these isotopic ratios fall, for the most part, between 1700 and 1900 Ma. This is regarded as good evidence that the circum-Kisseynew volcanic belt, as well as its greywacke equivalent, is largely Aphebian in age.Model lead ages for sulfide deposits from the entire circum-Kisseynew volcanic belt, with one exception, agree well with recent Rb–Sr and U–Pb age determinations from the southern portion of the belt. Reasons for the exception, in the Hanson Lake area, are discussed in some detail.

The Petrochemistry of Altered Volcanic Rocks Surrounding the Louvem Copper Deposit, Val d'Or, Quebec

1975 ◽  
Vol 12 (11) ◽  
pp. 1820-1849 ◽  
Author(s):  
Guy Spitz ◽  
Richard Darling
Keyword(s):  
Volcanic Rocks ◽  
Copper Deposit ◽  
Massive Sulfide ◽  
Original Compositions ◽  
Pyroclastic Rock ◽  
Calc Alkaline ◽  
Genetic Classification ◽  
Sulfide Deposits ◽  
Host Rocks

The Louvem copper deposit, a carrot-shaped body of mineralized silicic pyroclastic rock, appears generally conformable with surrounding, steeply dipping volcanic rocks, but otherwise closely resembles the cross-cutting feeder pipes that underlie many Archean stratiform volcanogenic massive sulfide deposits. It is, like many such deposits, associated with peraluminous and calc-alkaline rocks in the felsic upper portion of a volcanic sequence.Naming of the Louvem volcanic host rocks by means of their chemical composition is rendered difficult by intense local alteration which has changed their original compositions. Of the four classification schemes tried, that based on sample SiO2 content appears to provide results that are least affected by this alteration and which therefore reflect most clearly the original compositions of the rocks surrounding the ore deposit.The calc-alkaline nature of Louvem volcanic rocks is apparent even for very altered near-ore samples. This is revealed by Ol–Ne–Qz and AFM diagrams, which appear to be suitable for the genetic classification of such altered rocks.The chemical nature of the wallrock alteration in and around the deposit is revealed by certain petrologic diagrams. All rocks in the study area show magnesium enrichment, but no petrologic diagram illustrates this very clearly. Outside the orebody, the alteration consists mainly of Na and Ca depletion, and those diagrams which show such depletion are the most useful. Of these, the AKF, AFM, and ACF plots appear to be most practical.

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