Metal sources for the Katanga Copperbelt deposits (DRC) insights from Sr and Nd isotope ratios

The ore deposits of the Central African Copperbelt formed during a multiphase mineralisation process. The basement underlying the Neoproterozoic Katanga Supergroup that hosts the ore, demonstrates the largest potential as metal source. Various ore deposits that formed during different mineralisation phases are taken as case studies, i.e. Kamoto, Luiswishi, Kambove West, Dikulushi and Kipushi (Democratic Republic of Congo, DRC). The Sr and Nd isotopic compositions of gangue carbonates associated with these deposits is determined and compared with those of rocks from several basement units, bordering or underlying the Copperbelt, to infer the metal sources. The mineralising fluid of diagenetic stratiform Cu-Co mineralisation interacted with felsic basement rocks underlying the region. The Co from these deposits is most likely derived from mafic rocks, but this is not observed in the isotopic signatures. Syn-orogenic, stratabound Cu-Co mineralisation resulted mainly from remobilisation of diagenetic sulphides. A limited, renewed contribution of metals from felsic basement rocks might be indicated by the isotope ratios in the western part of the Copperbelt, where the metamorphic grade is the lowest. The mineralising fluid of syn- and post-orogenic, vein-type mineralisations interacted with local mafic rocks, and with felsic basement or siliciclastic host rocks

Genesis of the Eugui sparry Magnesite deposit (Western Pyrenees, Spain): Evidence from fluid inclusions and isotope geochemistry

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Diagenetic origin of the stratiform Cu-Co deposit at Kamoto in the Central African Copperbelt

International audienceSediment-hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny. This controversy concerns the formation of many world-class sediment-hosted ore deposits such as in the Central African Copperbelt. Here we present Re-Os dating results for disseminated and stratiform Cu-Co sulfide pseudomorphs after anhydrite in nodules and layers from the Copperbelt. Results demonstrate that at least some of the ores formed at around 800 Ma during rifting and basin development, and thus predate the Pan-African Lufilian orogeny. Younger Re-Os ages, i.e., between 682 +/- 28 and 230 +/- 36 Ma, may be due to the replacement of the early Cu-Co sulfides by younger sulfide phases. Alternatively, these younger ages may result from the disturbance or resetting of the Re-Os system during recrystallization/metamorphism or the transition of chalcocite from its high- to its low-temperature polymorph

From Pixels to Deposits: Porphyry Mineralization With Multispectral Convolutional Neural Networks

Mineral exploration is essential to ensure a sustainable supply of raw materials for modern living and the transition to green. It implies a series of expensive operations that aim to identify areas with natural mineral concentration in the crust of the Earth. The rapid advances in artificial intelligence and remote sensing techniques can help in significantly reducing the cost of these operations. Here, we produce a robust intelligent mineral exploration model that can fingerprint potential locations of porphyry deposits, which are the world's most important source of copper and molybdenum and major source of gold, silver, and tin. We present a deep learning pipeline for assessing multispectral imagery from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) with the objective of identifying hydrothermal alterations. Our approach leverages a convolutional neural network (CNN) to analyze the high-resolution images, overcoming computational challenges through a patch-based strategy that involves an overlapping window for partitioning the images into fixed-size patches. Through the utilization of manually labeled patches for image classification and identification of hydrothermal alteration areas, our results demonstrate the remarkable ability of CNN to accurately detect hydrothermal alterations. The technique is adaptable for other ore deposit models and satellite imagery types, providing a revolution in satellite image interpretation and mineral exploration

Postorogenic origin of the stratiform Cu mineralization at Lufukwe, Lufilian Foreland, Democratic Republic of Congo

The Central African Copperbelt, which stretches across the border between Zambia and the Democratic Republic of Congo, is one of the largest sediment-hosted stratiform Cu-Co provinces in the world. The triangular-shaped Lufilian foreland is located to the northeast of the Copperbelt. Recently sediment-hosted stratiform copper occurrences have been explored in the foreland, including the Kinkumbi prospect in the Lufukwe anticline. Although the stratiform copper mineralization in the Copperbelt is mainly concentrated in the Roan Group sedimentary rocks, where it is commonly associated with cobalt, the Lufilian foreland copper mineralization occurs in sedimentary rock units of the Nguba and Kundelungu Groups where it is mainly associated with silver. This paper examines the metallogenesis of the stratiform copper mineralization at Lufukwe. The Lufukwe anticline is situated in the eastern part of the Lufilian foreland and is composed of Neoproterozoic sedimentary rocks belonging to the Katanga Supergroup. The Kinkumbi prospect, a sediment-bosted stratiform copper-silver occurrence, is located in the northern part of the western flank of the anticline. This part of the anticline is characterized by disseminated copper-silver mineralization hosted in the lower 10 to 15 in of the Monwezi Sandstone (Nguba Group). A comparison between the location of high copper grades in surface samples and boreholes and the location of structural lineaments visible on ASTER images indicates that the mineralization is spatially related to northeast-southwest to east-northeast-west-southwest strike-slip faults. These faults are nearly perpendicular to the strike of the host rock and postdate both the Lufilian folding and deposition of the entire Katanga Supergroup. The Monwezi Sandstone was subjected to strong compaction and silica cementation (authigenic quartz overgrowths), followed by intense feldspar dissolution, which resulted in a well-developed secondary porosity represented by dissolution cavities. Copper sulfides are mainly, concentrated in these cavities and partially replace the detrital grains. The copper mineralization is both hypogene (chalcopyrite, bornite, and chalcocite) and supergene (digenite, covellite, and minor native copper), with malachite and chrysocolla as the main oxidation products. Point counting and grain size measurements demonstrate that the sandstone horizons with high copper content (>1.25% Cu) are those with a detrital grain size larger than 175 p in, more than 35 percent altered feldspars and little or no fine-grained matrix. Microthermometry of fluid inclusions indicates that the authiogenic quartz overgrowths precipitated from a moderate-temperature (80 degrees-1.30 degrees C), high-salinity (18.8-23.4 wt % CaCl2 equiv) H2O-NaCl-CaCl2 fluid. The hypogene copper-silver mineralization was deposited from a hot (120 degrees-180 degrees C) and low- to moderate-salinity (1.9-7.7 wt % NaCl equiv) H2O-NaCl fluid with a general trend of increasing homogenization temperatures with increasing salinities. The interpretation of the available structural, stratigraphic, petrographic, and fluid inclusion microthermometric data constrain the timing of the mineralization to a time after the Lufilian folding and deposition of the entire Katanga Supergroup. The data presented Support a postorogenic fluid-mixing model in which the mineralization is related to the mixing of a copper-rich mineralizing fluid with a temperature >= 180 degrees C and salinity >= 7.7 wt percent NaCl equiv, likely migrating upward along northeast-southwest- to east-northeast-west-southwest-oriented strike-slip faults with a colder, low-salinity, reducing fluid in the Monwezi Sandstone. The location and distance between the northeast-southwest to east-northeast-west-southwest,est faults strongly influenced the spatial distribution of the copper mineralization in the anticline, and the variability in grain size and composition of the Monwezi Sandstone caused the preferential lateral migration of the mineralizing fluid through the lower 10 to 15 m. Copper precipitation was possibly induced by reduction by preexisting noncopper sulfides (pyrite and arsenopyrite) and hydrocarbons and by the drop in fluid temperature and salinity Based oil this research the areas with dominant northeast-southwest to east-northeast-west-southwest structural lineaments are considered favorable sites for further copper exploration in the Lufilian foreland, especially where these lineaments cut previously deformed Katanga sediments. Coarse-grained sandstones with no fine matrix that underwent intense feldspar dissolution are the most promising host rocks for the late disseminated stratiform copper mineralization in the Lufilian foreland. Airborne gamma-ray spectrometric surveys could be used as a powerful exploration tool for targeting ore-related, K-depleted zones in these sandstones

Diagenetic origin of the stratiform Cu-Co deposit at Kamoto in the Central African Copperbelt

© 2015, Springer-Verlag Berlin Heidelberg. Sediment-hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny. This controversy concerns the formation of many world-class sediment-hosted ore deposits such as in the Central African Copperbelt. Here we present Re–Os dating results for disseminated and stratiform Cu–Co sulfide pseudomorphs after anhydrite in nodules and layers from the Copperbelt. Results demonstrate that at least some of the ores formed at around 800 Ma during rifting and basin development, and thus predate the Pan-African Lufilian orogeny. Younger Re–Os ages, i.e., between 682 ± 28 and 230 ± 36 Ma, may be due to the replacement of the early Cu–Co sulfides by younger sulfide phases. Alternatively, these younger ages may result from the disturbance or resetting of the Re–Os system during recrystallization/metamorphism or the transition of chalcocite from its high- to its low-temperature polymorph.status: publishe

Dolomitization of the Latemar buildup (Dolomites, northern Italy)

ABSTRACT This study focuses on the spatial distribution and genesis of dolomite in the Latemar Formation and the underlying Contrin Formation in the Latemar buildup (Dolomites, Northern Italy). The Contrin Formation is completely dolomitized. From this formation several dolomitized pipe-like structures up to 100 m in diameter occur that extend into the Latemar Formation. In addition large dolomite bodies (50-100 m) occur scattered. The origin of these massive dolomite structures and their relation to crosscutting mafic dikes and the nearby Predazzo Intrusion is a part of this ongoing petrographical, geochemical (stable C- and O-isotopes, Sr- & Mg-isotopes) and petrophysical (poroperm) study. Keywords: Dolomitization, Latemar, Predazzo Intrusionstatus: publishe

Contribution to the understanding of the Ionian Basin sedimentary evolution along the eastern edge of Apulia during the Late Cretaceous in Albania

Integrated in the peri-Adriatic domain, the Ionian Basin extended along a NW-SE direction during the Late Cretaceous, limited on its sides by the Apulian and the Kruja platforms. The basinal/slope succession was studied in seven outcrops exposed in the Albanian fold-and-thrust belt. Sedimentological investigations, supported by bio- and chronostratigraphy were performed on calcareous Upper Cretaceous hemipelagites, gravity-flow deposits and slumps. The western part of the basin was studied, revealing a strong influence of the Apulianmargin, alternatively shedding sediment basinward, by means of a tectonically controlled edge. The Late Albian to Cenomanian period is characterized by the settling of muddy debrites along themargin. A deep basinal environment characterizes this period which prolongs until the Santonian, with no significant influx of the platform basinward. This sedimentary setting abruptly changed at the end of the Santonian, with an important influx derived from both platforms. Coarsening and thickening upward sequences show a progressive increase in sediment shedding during the Campanian. The Late Campanian-Early Maastrichtian period points out a major change on the resedimentation processes with the settling of several slumped units reworking thick sediment packages. The latter can be traced along the Apulian margin, testifying of instabilities along the edge of Apulia.status: publishe

Meter-scale cycles as a proxy for the evolution of the Apulian Carbonate Platform during the late Cretaceous (Llogara Pass, Albania)

© 2015, Springer-Verlag Berlin Heidelberg. Sedimentological investigations have revealed ten facies in Upper Cretaceous platform carbonates (1220 m thick) at Llogara Pass in southern Albania that can be grouped into four facies associations. These reflect specific environmental conditions, ranging from intertidal to subtidal. The facies form small-scale patterns attesting to high-frequency/low-amplitude cyclicity characteristic of relative sea-level fluctuations. Meter-scale cycles have been classified into six distinct types and characterized on the basis of diagnostic surfaces, diagenetic features, and reservoir properties. A closer look at diagenetic and petrophysical features revealed a drastic porosity reduction at each cycle top (i.e., cycle boundary). This underlines a strong interconnection of facies types and reservoir properties at the cycle scale, thus impacting the whole carbonate succession. The cycle stacking pattern is a reflection of the sedimentary evolution during the late Cretaceous in this southern part of the Apulian Platform. (1) Meter-scale peritidal cycles suggest that the Cenomanian was characterized by stable shallow-water conditions. (2) Thick stromatolitic-dominated cycles typify Turonian deposits. Although the nature of the deposits indicates inner platform conditions, the long-term hiatus documented from Italy (Turonian bauxites) is not evidenced in Llogara. (3) The thin (a few tens of meters) Coniacian–Santonian interval suggests the onset of a significant tectonic control over the sedimentary dynamics, likely accompanied by morphological changes on the Apulian Platform and an emergence of rudist-dominated cycles. (4) Peritidal-subtidal cycles persist during the Campanian, accompanied by a broad development of rudist organisms that evidence significant and repeated relative sea-level rise. These data allow refinement of the general sedimentological evolution during the late Cretaceous on the Apulian Platform.status: publishe

Genesis of sediment-hosted stratiform copper–cobalt mineralization at Luiswishi and Kamoto, Katanga Copperbelt (Democratic Republic of Congo)

The sediment-hosted stratiform Cu-Co mineralization of the Luiswishi and Kamoto deposits in the Katangan Copperbelt is hosted by the Neoproterozoic Mines Subgroup. Two main hypogene Cu-Co sulfide mineralization stages and associated gangue minerals (dolomite and quartz) are distinguished. The first is an early diagenetic, typical stratiform mineralization with fine-grained minerals, whereas the second is a multistage syn-orogenic stratiform to stratabound mineralization with coarse-grained minerals. For both stages, the main hypogene Cu-Co sulfide minerals are chalcopyrite, bornite, carrollite, and chalcocite. These minerals are in many places replaced by supergene sulfides (e.g., digenite and covellite), especially near the surface, and are completely oxidized in the weathered superficial zone and in surface outcrops, with malachite, heterogenite, chrysocolla, and azurite as the main oxidation products. The hypogene sulfides of the first Cu-Co stage display delta S-34 values (-10.3aEuro degrees to +3.1aEuro degrees Vienna Canyon Diablo Troilite (V-CDT)), which partly overlap with the delta S-34 signature of framboidal pyrites (-28.7aEuro degrees to 4.2aEuro degrees V-CDT) and have a dagger S-34(SO4-Sulfides) in the range of 14.4aEuro degrees to 27.8aEuro degrees. This fractionation is consistent with bacterial sulfate reduction (BSR). The hypogene sulfides of the second Cu-Co stage display delta S-34 signatures that are either similar (-13.1aEuro degrees to +5.2aEuro degrees V-CDT) to the delta S-34 values of the sulfides of the first Cu-Co stage or comparable (+18.6aEuro degrees to +21.0aEuro degrees V-CDT) to the delta S-34 of Neoproterozoic seawater. This indicates that the sulfides of the second stage obtained their sulfur by both remobilization from early diagenetic sulfides and from thermochemical sulfate reduction (TSR). The carbon (-9.9aEuro degrees to -1.4aEuro degrees Vienna Pee Dee Belemnite (V-PDB)) and oxygen (-14.3aEuro degrees to -7.7aEuro degrees V-PDB) isotope signatures of dolomites associated with the first Cu-Co stage are in agreement with the interpretation that these dolomites are by-products of BSR. The carbon (-8.6aEuro degrees to +0.3aEuro degrees V-PDB) and oxygen (-24.0aEuro degrees to -10.3aEuro degrees V-PDB) isotope signatures of dolomites associated with the second Cu-Co stage are mostly similar to the delta C-13 (-7.1aEuro degrees to +1.3aEuro degrees V-PDB) and delta O-18 (-14.5aEuro degrees to -7.2aEuro degrees V-PDB) of the host rock and of the dolomites of the first Cu-Co stage. This indicates that the dolomites of the second Cu-Co stage precipitated from a high-temperature, host rock-buffered fluid, possibly under the influence of TSR. The dolomites associated with the first Cu-Co stage are characterized by significantly radiogenic Sr isotope signatures (0.70987 to 0.73576) that show a good correspondence with the Sr isotope signatures of the granitic basement rocks at an age of ca. 816 Ma. This indicates that the mineralizing fluid of the first Cu-Co stage has most likely leached radiogenic Sr and Cu-Co metals by interaction with the underlying basement rocks and/or with arenitic sedimentary rocks derived from such a basement. In contrast, the Sr isotope signatures (0.70883 to 0.71215) of the dolomites associated with the second stage show a good correspondence with the Sr-87/Sr-86 ratios (0.70723 to 0.70927) of poorly mineralized/barren host rocks at ca. 590 Ma