Mechanism of formation of superdeep sedimentary basins: lithospheric stretching or eclogitization?

The superdeep North Caspian, South Caspian, and Barents basins have their sedimentary fill much thicker and the Moho, correspondingly, much deeper than it is required for crustal subsidence by lithospheric stretching. In the absence of large gravity anomalies, this crustal structure indicates the presence under the Moho of a thick layer of eclogite which is denser than mantle peridotite. Crustal subsidence in the basins can be explained by high-grade metamorphism of mafic lower crust. The basins produced by lithospheric stretching normally subside for the first ～100 myr of their history, while at least half of the subsidence in the three basins occurred after that period, which is another evidence against the stretching formation mechanism. According to the seismic reflection profiling data, stretching can be responsible for only a minor part of the subsidence in the Caspian and Barents basins. As for the South Caspian basin, there has been a large recent subsidence event in a setting of compression. Therefore, eclogitization appears to be a realistic mechanism of crustal subsidence in superdeep basins.     

Digital mapping in structural geology — Examples from Namibia and Greece

Many problems in geology, especially structural geology, can only be solved by detailed mapping. Presently, mapping is still mainly carried out on paper using techniques from the 19^th Century. However, tools are now available to carry out most mapping tasks on microcomputers in the field without any need of paper. This speeds up geological mapping and reduces the errors involved in the mapping process. Digital mapping also allows work in featureless areas and areas of great structural complexity that would not be possible using paper maps. We present two practical examples of the new technology of digital mapping using microcomputers, from Namibia and Greece.     

Delineation of mineralization zones in porphyry Cu deposits by fractal concentration–volume modeling

The purpose of this study was to identify the various mineralization zones especially supergene enrichment and hypogene in two different Iranian porphyry Cu deposits, based on subsurface data and by using the proposed concentration–volume (C–V) fractal method. The Sungun and Chah-Firuzeh porphyry Cu deposits, which are situated in NW and SE Iran, respectively, were selected for this study. Straight lines fitted through log–log plots showing C–V relations for Cu were employed to separate supergene enrichment and hypogene zones from oxidation zones and barren host rocks in the two deposits and to distinguish a skarn mineralized zone from the hypogene zone in Sungun deposit. In the proposed C–V fractal method, the identification of mineralization zones is based on power–law relationships between Cu concentrations and the volume of rocks hosting porphyry Cu mineralization. Separate subsurface data from the two deposits were analyzed by C–V fractal method and the results have been compared with geological models which included alteration and mineralogical models. The comparison shows that the interpreted zones based on the C–V fractal method are consistent with the geological models. The proposed C–V method is a new approach to defining zones in a mineral deposit and there was no commercial software available to perform the relevant calculations; therefore, a fractal concentration–volume (FCV) software was designed by the authors to achieve this goal.     

Pesticides and other micro-organic contaminants in freshwater sedimentary environments—a review

A wide range of issues relating to the presence and fate of pesticides and other micro-organic contaminants (MOCs) in surface freshwater sedimentary environments is reviewed. These issues include the sources, transport and occurrence of MOCs in freshwater environments; their ecological effects; their interaction with sedimentary material; and a range of processes related to their fate, including degradation, diffusion in bed sediments, bioturbation and slow contaminant release. An emphasis is placed on those processes—chemical, physical or biological—in which sediments play a role in determining the fate of micro-organics in freshwater environments. The issues of occurrence, source and transport, and the ecological effects of micro-organics are introduced more briefly, the focus where these aspects are concerned being largely on pesticides. In the concluding section, key points and issues relating to the study of micro-organics in freshwater environments are summarised and areas where initial or further research would be welcome are highlighted. It is hoped that this paper will both form a useful reference for workers in the field of micro-organic contaminants, and also stimulate new work in the freshwater environment and beyond.     

Evolution of oil and gas generation in the Earth’s history and petroleum prediction in sedimentary basins

Oil and gas generation is a basic problem of geology and natural sciences, which is associated with energy resources as well as with the origination of life on the Earth. The evolution of hydrocarbons is controlled by the evolution of the biosphere and is an issue of phylogeny. Organic matter (OM) buried in sediments since the Early Precambrian consists mostly of phytoplankton, the main carrier of lipids producing hydrocarbons. Organic matter accumulates in marine sediments according to the law of periodicity. Middle Paleozoic fossilized OM is largely composed of zooplankton. Zooplanktonic OM, classified as sapropelites, had interfered with the process of oil and gas generation since its origin, e.g., tentaculites of the Domanik formation increased oil content. The inception of low-lipid macrophytes gave rise to introduction of humic OM into water bodies and formation of mixed-type OM. The larger the humic component in OM, the higher its gas potential. However, instead of replacing oil generation, enhanced gas generation had come on the scene since the Mesozoic, and their scales were approximately equal. The actual oil/gas ratio in sedimentary basins depends both on phylogenetic factors and on the evolution of each separate basin.     

On formation mechanisms of deep sedimentary basins: Is there enough evidence for eclogitization?

This is a critical comment on the model of basin formation by eclogitization of mafic crust suggested by E. Artyushkov. The eclogitization model bears uncertainties in average parameters (thickness, density, pressure) of lithospheric mantle, crust, and sediments, which may bias the estimates of subsidence magnitude. Main pitfalls, however, lie in high-pressure petrology: The lithostatic pressure is insufficient for eclogite to form in the lower crust beneath deep basins. It is shown that linear extrapolation of laboratory data on the gabbro-to-eclogite transition onto the field of relatively low pressures and temperatures in the lithosphere is incorrect. The hypothesized role of hot mantle fluids in the gabbro-eclogite transformation appears doubtful in terms of both petrology and kinetics of metamorphic reactions. Eclogite volumes in none of well known eclogitic sites agree with those required for eclogitization-driven subsidence. Artyushkov’s criticism of the extension basin formation model is not quite just. There are recent models of a two-layer lithosphere that imply a possibility of brittle and ductile deformation at different crust rheologies. The models we refer to predict most of extension to occur in mantle lithosphere rather than in the crust, this extension being able to produce deep continental basins.     

Anomalous iron distribution in shales as a manifestation of “non-clastic iron” supply to sedimentary basins: relevance for pyritic shales,base-metal mineralization,and oolitic ironstone deposits

In previous investigations, nearshore pyritic shale horizons in the Mid-Proterozoic Newland Formation were interpreted to be due to non-clastic colloidal iron supply by streams. New data on the chemical composition of shales in the Newland Formation support this interpretation. In these shales, Fe and Al show a positively correlated trend that intercepts the Fe axis above the origin. These relationships suggest control of Fe by clays (via iron oxide coatings on clay minerals), and the presence of an additional, non-clastic iron component. Shales from stratigraphic intervals during which pyritic shale horizons were deposited plot above the Fe/Al trend typical for the remainder of the Newland Formation.Pyritic shale horizons in sediments are favourable hosts for base-metal deposits of the pyrite-replacement type. Fe/Al relationships as found in the Newland Formation may help to identify stratigraphic horizons in other sedimentary basins that contain pyritic shale horizons and potentially base-metal mineralization.     

Multistage gold mineralization at the Lapa mine, Abitibi Subprovince: insights into auriferous hydrothermal and metasomatic processes in the Cadillac–Larder Lake Fault Zone

The Lapa gold deposit contains reserves of 2.4 Mt at 6.5 g/t Au and is one of the few deposits located directly within the Cadillac–Larder Lake Fault Zone (CLLFZ), a first-order crustal-scale fault that separates the Archean Abitibi Subprovince from the Pontiac Subprovince to the south. Gold mineralization is predominantly hosted in highly strained and altered, upper greenschist–lower amphibolite facies mafic to ultramafic rocks of the Piché Group. Auriferous ore zones consist of finely disseminated auriferous arsenopyrite–pyrrhotite?±?pyrite and native gold disseminated in biotite- and carbonate-altered wall rocks. Native gold, which is also present in quartz ± dolomite–calcite veinlets, is locally associated with Sb-bearing minerals, especially at depth ≤1 km from surface where the deposit is characterized by a Au–Sb–As association. At vertical depth greater than 1 km, gold is associated with arsenopyrite and pyrrhotite (Au–As association). The mineralogy and paragenesis of the Lapa deposit metamorphosed ore and alteration assemblages record the superposition of three metamorphic episodes (M1, M2, and M3) and three gold mineralizing events. Spatial association between biotitized wall rocks and auriferous arsenopyrite indicates that arsenopyrite precipitation is concomitant with potassic alteration. The predominant Au–As association recognized across the deposit is related to gold in solid solution in arsenopyrite as part of a pre-M2 low-grade auriferous hydrothermal event. However, the occurrence of hornblende?+?oligoclase porphyroblasts overprinting the biotite alteration, and the presence of porous clusters and porphyroblasts of arsenopyrite with native gold and pyrrhotite indicate an auriferous metasomatic event associated with peak M2 prograde metamorphism. Late retrograde metamorphism (M3) overprints the hornblende–oligoclase M2 assemblage within the host rocks proximal to ore by an actinolite–albite assemblage by precipitation of free gold and Sb–sulfosalts at lower P–T. The complex relationships between ore, structural features, and metamorphic assemblages at Lapa are related to the tectonometamorphic evolution of the Cadillac–Larder Lake Fault Zone at different times and crustal levels, and varying heat and fluid flow regimes. The Lapa deposit demonstrates that early, low-grade gold mineralization within the Cadillac–Larder Lake Fault Zone has benefited from late gold enrichment(s) during prograde and retrograde metamorphism, suggesting that multi-stage processes may be important to form gold-rich orogenic deposits in first order crustal-scale structures.     

Redox problems in the “metallogenic specialization” of magmatic rocks and the genesis of hydrothermal ore mineralization

Considering the history and current state of the problem of the so-called metallogenic specialization of magmatic rocks, the paper places emphasis onto various aspects of the genesis of ore mineralization depending on the redox state of magmas (as a logical continuation of S. Ishihara’s works), fluids, and host rocks. These problems were inadequately poorly explored and discussed by researchers dealing with ore deposits. Various possible variants of ore-forming redox processes for different types of mineral deposits, with ore mineralization affiliated to granites (Ta, Sn, W, Mo, and Be) and mafic magmas (Au, Ag, U, Cu, Zn, Pb, As, Sb, and Hg) and, accordingly, to crustal and mantle origin, are discussed. On the basis of analyzed geological data, including those published over the past three decades, it is shown that the redox state of ore-producing magmas commonly significantly impacted not only the ore potential of magmatic complexes but also the genetic type of the ore mineralization. The redox state of the fluids predetermined the transport and precipitation speciation of metals. Influence mechanisms of hydrocarbons from sedimentary country rocks and gaseous products of their pyrolysis on ore deposition of various metals are considered. Understanding these mechanisms can be helpful for predicting the possible precipitation sites of ore mineralization of noble, radioactive, and chalcophile metals.     

The Guelb Moghrein Cu–Au deposit: Neoarchaean hydrothermal sulfide mineralization in carbonate-facies iron formation

The Guelb Moghrein copper–gold deposit in the Islamic Republic of Mauritania reopened in 2006 and has produced copper concentrate and gold since then. The deposit is hosted in Neoarchaean–Palaeoproterozoic Fe–Mg carbonate-dominated metamorphic rocks interpreted as carbonate-facies iron formation. It forms tabular orebodies controlled by shear zones in the hanging wall and footwall of this meta-iron formation. Copper and gold are hosted in a complex sulfide ore in tectonic breccia replacing Fe–Mg carbonate and magnetite. Hydrothermal monazite dates the mineralization at 2492 ± 9 Ma. Two types of aqueous fluid inclusions suggest fluid mixing at 0.75–1.80 kbar and ~ 410 °C as the mineralization and precipitation mechanism, which is temporally coincident with regional retrograde metamorphism at 410 ± 30 °C (garnet-biotite). Distal alteration zones are enriched in K, Rb and Cu, whereas orebodies are depleted in K, Rb, Sr and Ba. The copper–gold mineralization at Guelb Moghrein formed during retrograde shearing in metamorphic rocks and contemporaneous hydrothermal alteration. The stable isotope signature of alteration and ore minerals suggest an external crustal fluid source. Fluids were focused in the reactive and competent meta-iron formation. Potassium alteration, magnetite and copper–gold mineralization suggest an IOCG mineral system akin similar deposits in Australia and Brazil.     

Research achievements and application in anaerobic treatment of organic solid wastes—— A review

1 IntroductionSolid wastes (SW) refer to all the wastes derivedfrom human and animal activities, which are normallysolid and are discarded as useless or unwanted (Juha-Heikki Tanskanen, 2000 ). Generally, the organicfraction accounts for more than 50% -60…     

Malinovka deposit—A new type of gold mineralization in Primorye,Russia: Geology,mineralogy, and genesis

Original data on the ore composition are obtained by studying samples from mining workings. In terms of mineral composition, gold-productive veinlets are subdivided into three types: sulfide–quartz, sulfide–carbonate–quartz, and sulfide. The wall-rock metasomatites and typomorphic features of the minerals are studied and the genetic problems of the ores and deposit are discussed. It is established that the Malinovka deposit is ascribed to the gold–tourmaline type (gold–quartz formation), which is identified for the first time in Primorye. In terms of many parameters, the ores of this type are close to those of the large deposits from the Transbaikalian and Amur regions (Klyuchevsky, Kariy, Kirov, Darasun, and others), which are genetically related to granitoid magmatism.     

Geology and mineralization of the Dayin’gezhuang supergiant gold deposit (180 t) in the Jiaodong Peninsula,China: A review

The Dayin’gezhuang gold deposit is located in the central part of the Zhaoping Fault metallogenic belt in the Jiaodong gold province —the world ’s third-largest gold metallogenic area. It is a typical successful case of prospecting at a depth of 500‒2000 m in recent years, with cumulative proven gold resources exceeding 180 t. The main orebodies (No. 1 and No. 2 orebody) generally have a pitch direction of NNE and a plunge direction of NEE. As the ore-controlling fault, the Zhaoping Fault is a shovel-shaped stepped fault, with its dip angle presenting stepped high-to-low transitions at the elevation of −2000‒0 m. The gold mineralization enrichment area is mainly distributed in the step parts where the fault plane changes from steeply to gently, forming a stepped metallogenic pattern from shallow to deep. It can be concluded from previous studies that the gold mineralization of the Dayin’gezhuang gold deposit occurred at about 120 Ma. The ore-forming fluids were H₂O-CO₂-NaCl-type hydrothermal solutions with a medium-low temperature and medium-low salinity. The H-O isotopic characteristics indicate that the fluids in the early ore-forming stage were possibly magmatic water or mantle water and that meteoric water gradually entered the ore-forming fluids in the late ore-forming stage. The S and Pb isotopes indicate that the ore-forming materials mainly originate from the lower crust and contain a small quantity of mantle-derived components. The comprehensive analysis shows that the Dayin ’gezhuang gold deposit was formed by thermal uplifting-extensional tectonism. The strong crust-mantle interactions, large-scale magmatism, and the material exchange arising from the transformation from adakitic granites to arc granites and from the ancient lower crust to the juvenile lower crust during the Early Cretaceous provided abundant fluids and material sources for mineralization. Moreover, the detachment faults formed by the rapid magmatic uplift and the extensional tectonism created favorable temperature and pressure conditions and space for fluid accumulation and gold precipitation and mineralization.©2022 China Geology Editorial Office.     

Mineral chemistry of gersdorffite – A powerful tool in the differentiation of hydrothermal systems

Gersdorffite from two mineralization types (post-Variscan vein deposits, strata-bound mineralization) was investigated in the Niederberg area Rhenish Massif. In the ternary Ni–Co–Fe space gersdorffite from post-Variscan vein deposits displays a tight cluster with the highest Ni-contents ranging from 0.825 to 0.962 atoms per formula unit (a.p.f.u.). As/S ratios comprise a narrow range from 0.875 to 1.012. In contrast gersdorffite from the strata-bound mineralization displays a substitutional trend. Co and Fe substitute for Ni in a ± fixed ratio. Ni ranges between 0.494 and 0.836 a.p.f.u. As/S ratios (1.025–1.211) display a wider range and indicate higher As-contents relative to gersdorffite from post-Variscan vein deposits. Based on these results, two different hydrothermal fluid systems can be identified in the Niederberg area forming gersdorffite in both mineralization types. The hydrothermal fluids circulating in the post-Variscan vein deposits were homogeneous (high Ni-activities, lower As fugacities) and mixing occurred far away from the site of deposition whereas the fluids of the strata-bound mineralization were more heterogeneous (decreasing Ni-activities) with moderate elevated As fugacities. With respect to the post-Variscan vein deposits in the Niederberg area the results are compatible with earlier findings.Comparison with available gersdorffite analyses from adjacent areas (borehole Viersen, Ramsbeck deposit) reveal that gersdorffite compositions provide a reliable tool in distinguishing between different hydrothermal systems on a regional scale in the northern Rhenish Massif. However, gersdorffite compositions cannot be used to discriminate between Variscan and post-Variscan deposits with confidence.The country rocks in the Niederberg area are possible sources for Ni, Co and Fe during gersdorffite formation of the strata-bound mineralization. However, due to the remarkable homogeneity of gersdorffite compositions of the post-Variscan vein deposits irrespective of age and composition of the immediate adjacent host-rocks it is assumed that these host-rocks are not the source of the metals. Reduced Zechstein sulfate is assumed to be the source of sulfur. The As source remains unknown.Due to conflicting experimental data concerning the gersdorffite solid solution field it is not possible to derive reliable formation temperatures for the strata-bound mineralization. However, gersdorffite compositions of the post-Variscan vein deposits are compatible with low formation temperatures (<300 °C) in accordance with earlier findings.     

Reconsideration of the structural relationship between the Parnassus–Ghiona and Vardoussia geotectonic zones in central Greece

The relationship between the geotectonic zones of the Hellenides orogen is important for understanding its geological evolution. The Parnassus–Ghiona geotectonic zone in central Greece has long been interpreted as thrust over the Vardoussia subzone. On the basis of detailed geological mapping, supported by a stratigraphic study and tectonic observations, no evidence of an overthrust of the Ghiona limestones on the Vardoussia flysch was found. The new data show that the transition of the Ghiona limestones to the Vardoussia flysch is a sedimentary passage and at certain places the base of the flysch is marked by a basal conglomerate formation. The entire deformation of the Ghiona is related to a large-scale anticline of the limestone series, presenting a highly inclined western limb, overlain by the flysch strata, which were deposited in a common basin between Ghiona and Vardoussia mountains. Consequently, questions concerning the geotectonic position of the Vardoussia subzone and the role of the Parnassus–Ghiona zone to the orogenic evolution of the eastern External Hellenides are raised.     

Melt inclusions in detrital spinel from the SE Alps (Italy–Slovenia): a new approach to provenance studies of sedimentary basins

Detrital spinel is a widespread heavy mineral in sandstones from the Maastrichtian–Middle Eocene sedimentary basins in the SE Alps. Chemistry of detrital spinels from the Claut/Clauzetto and Julian Basins (N Italy and NW Slovenia) is used to constrain petrological and geochemical affinities and tectonic provenance of the source rocks. In addition, we have analysed melt inclusion compositions in the detrital volcanic spinels to better constrain the nature of their parental magmas. This is the first study of melt inclusions in detrital spinels. Two principal compositional groups of detrital spinels are recognised based on their TiO₂ and Fe²⁺/Fe³⁺; one derived from peridotites, the other from basaltic volcanics. Peridotitic spinels are more abundant and have TiO₂ < 0.2 wt% and high Cr/Cr + Al (40–90), characteristic of suprasubduction zone harzburgites. Significant chemical variations among volcanic spinels (TiO₂ up to 3 wt%, Al₂O₃ 12–44 wt%) suggest multiple sources, with geochemically distinct characteristics, including MORB-type and backarc basin basalts, subduction-related magmas and tholeiites produced during early continental rifting. Compositions of homogenised melt inclusions in spinels with TiO₂ > 0.2 better distinguish the differences between the compositions of their host spinels and help to further clarify the geodynamic provenance of extrusive source rocks. Several compositional groups of melt inclusions have been recognised and represent diverse magmatism of marginal basins, including MORB- and subduction-related geochemical types, as well as magmas characteristic of early continental rifting. These results, combined with the data on regional ophiolitic complexes and tectonic reconstructions favour the Internal Dinarides of Yugoslavia as a possible source area for the SE Alps sediments. Received: 20 January 2000 / Accepted: 25 April 2000