The effect of temperature on the development of Nephus includens (Kirsch) and Nephus bisignatus (Boheman) (Coleoptera: Coccinellidae), predators of Planococcus citri Risso (Hemiptera: Pseudococcidae)

The effect of temperature οη the development of the predators Nephus includens (Kirsch) and Ν. bisignatus (Boheman) (Coleoptera: Coccinellidae), was studied. The development time of immature stages and the pre-oviposition period of adult females for the two predators was recorded at eight constant temperatures (10, 15, 20, 25, 30, 32.5, 35 and 37.5°C). The beetles were reared on eggs, nymphs and female adults of Planococcus citri (Risso) (Homoptera: Pseudococcidae) that had developed on squash (Cucurbita pepo) and on sour orange leaves (CΊtrus aurantium). Using the linear model for the biological cycle of Ν. includens on squash and on sour orange leaves, the developmental zeros (lower temperature thresholds) were estimated to be 10.9 and 11.0°C respectively and the thermal constants, 490.5 and 472.8 day-degrees respectively. Using the Lactin model the lower thresholds were estimated to be 11.1 and 11.2°C respectively and the upper thresholds 36.1 and 36.0°C respectively. For the biological cycle of Ν. bisignatus, using the linear model, the lower thresholds were estimated to be 9.4°C on squash and 9.3°C on sour orange leaves and the thermal constants were 614.3 and 647.9 day-degrees respectively. Using the Lactin model the lower thresholds were estimated to be 9.9 and 1O.0°C respectively and the upper thresholds, 34.7 and 35.0°C respectively. The survival rate of Ν. includens in­stars at 10, 15, 20, 25, 30, 32.5, 35 and 37.5°C on squash and on sour orange leaves was respectively 0.0, 34.9, 63.2, 70.6, 63.3, 54.5, 19.8, 0.0, and 0.0, 32.2, 61.0, 68.0, 68.3, 56.6, 17.6, 0.0%. The survival rate of Ν. bisignatus instars at 10, 15, 20, 25, 30, 32.5 and 35°C on squash and on sour orange leaves was respectively, 0.0, 39.9, 61.1, 60.7, 47.2, 26.4, 0.0 and 0.0, 35.7, 65.7, 68.0, 44.2, 29.1, 0.0%. The results show that Ν. includens has a shorter biological cycle than Ν. bisignatus, whereas the latter species has lower temperature thresholds

Palladium, platinum and gold concentration in porphyry copper systems of Greece and their genetic significance

Compilation of new and published data on precious metal and associated trace-element contents in mineralized porphyry copper intrusions of Greece indicates that the Pd content in the potassic-propylitic zone of the Skouries deposit is relatively high, ranging between 60 and 200 ppb (average 110 ppb), whereas in the porphyry copper intrusions of Gerakario and Pontokerasia, it is very low (3 ppb Pd). The oxidized zone of Fissoka (OP-65) exhibits low Pd and Cu contents, but higher Au, Te, As, Pb and Zn contents. The Pt content is much lower than Pd in the porphyry copper intrusions studied. The Pd/Pt ratio in the Skouries deposit ranges from 9 to 60, while it is much lower (< 2) in the mineralized samples from Fissoka, Gerakario and Pontokerasia. A decrease of the Pd content and Pd/Pt ratio with increasing Te, As, Pb and Zn content may indicate that the Pd distribution in porphyry copper systems is effected by the evolution of the magma-hydrothermal system. Also, mineralogical and geochemical data on the Skouries deposit, coupled with textural relations between base metal sulphides, PGM and Au-Ag tellurides, indicate that the main Pd-bearing mineral, merenskyite, is associated with the vein-type chalcopyrite or bornite, and was deposited during the main stage of mineralization. The high magmatic oxidation state and the magmatic features of the hydrothermal system (limited participation of meteoric portion) in the Skouries intrusion may be a strong control of its Pd potential. Assuming that Pd is mainly associated with chalcopyrite in the porphyry copper deposits, the calculated Pd (from measured Pd) contents in chalcopyrite (average 3300 ppb Pd) are relatively high, and comparable to that in the chalcopyrite concentrate made after the processing of large composite drill-hole samples (2400 ppb Pd to 21 wt.% Cu). It is considered to be an encouraging economic factor for Pd as a by-product, probably along with Au, although the main product is Cu. (C) 2000 Elsevier Science B.V. All rights reserved

Trace element distribution in magnetite separates of varying origin: Genetic and exploration significance

Magnetite is a widespread mineral, as disseminated or massive ore. Representative magnetite samples separated from various geotectonic settings and rock-types, such as calc-alkaline and ophiolitic rocks, porphyry-Cu deposit, skarn-type, ultramafic lavas, black coastal sands, and metamorphosed Fe–Ni-laterites deposits, were investigated using SEM/EDS and ICP-MS analysis. The aim of this study was to establish potential relationships between composition, physico/chemical conditions, magnetite origin, and exploration for ore deposits. Trace elements, hosted either in the magnetite structure or as inclusions and co-existing mineral, revealed differences between magnetite separates of magmatic and hydrothermal origin, and hydrothermal magnetite separates associated with calc-alkaline rocks and ophiolites. First data on magnetite separates from coastal sands of Kos Island indicate elevated rare earth elements (REEs), Ti, and V contents, linked probably back to an andesitic volcanic source, while magnetite separated from metamorphosed small Fe–Ni-laterites occurrences is REE-depleted compared to large laterite deposits. Although porphyry-Cu deposits have a common origin in a supra-subduction environment, platinum-group elements (PGEs) have not been found in many porphyry-Cu deposits. The trace element content and the presence of abundant magnetite separates provide valuable evidence for discrimination between porphyry-Cu–Au–Pd–Pt and those lacking precious metals. Thus, despite the potential re-distribution of trace elements, including REE and PGE in magnetite-bearing deposits, they may provide valuable evidence for their origin and exploration. © 2019 by the authors. Licensee MDPI, Basel, Switzerland

Geochemical and mineralogical characteristics of Fe-Ni- and bauxitic-laterite deposits of Greece

Contiguous vertical sample profiles from Ni-laterite deposits with in situ features (Kastoria, Profitis Ilias, and Tsouka) and allochthonous Ni- and bauxitic-laterite deposits in contact with basement limestone (Nissi) and bauxitic-laterites lying on peridotite (Parhari) were analyzed for major, trace (including Th and U), rare earth and platinum-group elements (REE and PGE, respectively). In addition, minerals with emphasis to chromite grains found as residual components in these laterites, inherited from the ophiolitic parent rocks, were analyzed by microprobe. Low Al2O3, TiO2, REE, Th and U contents are common features of the Kastoria, Bitincka and Tsouka deposits. In contrast, elevated REE contents are present in the karst-type bauxitic- and Ni-laterite ores of Nissi and bauxitic-laterites of Parhari. The bauxitic-laterite deposit of Nissi attains REE contents of thousands parts per million in samples from the contact between the lowest part of the bauxitic-laterite and the footwall limestone. Highest contents of Th and U are found in the bauxitic-laterites, with Th ranging from 4 to 28 ppm and U from 4 to 66 ppm. In general, increasing Al contents are accompanied by elevated Ti, REE, Th and U contents at the Parhari and Nissi laterite deposits. Goethite, is the dominant mineral in all Ni-laterite profiles studied, while boehmite co-existing with goethite is common in the bauxitic-laterites at Nissi and Parhari. Goethite exhibits variable Al contents, while the Al/Fe ratio increases towards the top of the profiles. The PGE concentrations are generally low, ranging from less than 100 ppb to a few hundred parts per billion. The lowest values - lower than in the bedrock - were recorded in the saprolite zone. A certain enrichment in Pt (up to 48 ppb), Pd (7 ppb), and Au (16 ppb) is recorded in the reddish altered peridotite overlying the saprolite zone at Profitis Ilias. The Fe-Ni ore overlying the reddish altered peridotite has the highest Os values (14 ppb), Ir (32 ppb), Ru (66 ppb), Rh (20 ppb), Pt (86 ppb), and Pd (186 ppb). Gold contents are below 36 ppb. An increasing Pt/Pd ratio from 3.0 in Fe-Ni-laterites to 6.0 in bauxitic-laterites is apparent. Both whole rock compositions and mineral chemistry of laterites indicate that major controlling factors of the composition of the bauxitic-laterites are the conditions during transportation/deposition of the weathered material and during diagenesis/metadiagenesis stage rather than parent mafic ophiolitic rocks. The comparison between the primary composition of chromite in the saprolite zone and the overlying Fe-Ni ore may provide evidence for the discrimination between Fe-Ni ore linked to in situ weathering and ore derived by transportation to some extent of clastic and chemical material. (C) 2000 Elsevier Science B.V. All rights reserved

Platinum-group element distribution in chromite ores from ophiolite complexes: Implications for their exploration

Compilation of some new data on ophiolites for Greece and Yugoslavia, and published data from previous studies, indicate that platinum-group element (PGE) and gold concentrations in chromite ores are generally low, ranging from less than 100 ppb to a few hundred ppb. However, samples from several ophiolite complexes exhibit an enrichment (of a few ppm) (a) only in Os, Ir and Ru,(b) only in Pt and/or Pd or (c) in all PGE. This enrichment (up to 10s ppm) is mainly related with chromitites hosted in supra-Moho dunites and dunites of the uppermost stratigraphic levels of the mantle sequence and it seems to be local, independent of the chromitite major element composition and the chromite potential of the ophiolite complexes. The contents of PGE combined with less chalcophile elements (Ni, Co, Cu), the ratios of incompatible/compatible elements, and PGE-patterns provide evidence for discrimination between chromitites derived from primitive magmas and those derived from partially fractionated magmas, although they have a similar major element composition. Thus, they can be used for a stratigraphic orientation in the mantle sequence, and therefore for exploration targets. Moreover, PGE data offer valuable information for the evaluation of the chromite potential in ophiolite complexes. The most promising ophiolites seem to be those which apart from the petrological and geochemical characteristics indicating extensive degree of partial melting in the mantle source contain only one chromite ore type (the other type being only in small proportion) of limited compositional variation, in both major elements and PGE, low ratios of Pd/Ir, while PGE-enriched chromitites in the mantle sequence are only occasionally present. In contrast, ophiolites which contain both high-Cr and -Al chromitites, and where their chalcophile element data implies relatively extensive fractionation trend are not good exploration targets for chromite ores, although they are related with a SSZ environment

Mineralogical and geochemical constraints on the origin of mafic–ultramafic-hosted sulphides: The pindos ophiolite complex

Sulphide ores hosted in deeper parts of ophiolite complexes may be related to either primary magmatic processes or links to hydrothermal alteration and metal remobilization into hydrothermal systems. The Pindos ophiolite complex was selected for the present study because it hosts both Cyprus-type sulphides (Kondro Hill) and Fe–Cu–Co–Zn sulphides associated with magnetite (Perivoli-Tsoumes) within gabbro, close to its tectonic contact with serpentinized harzburgite, and thus offers the opportunity to delineate constraints controlling their origin. Massive Cyprus-type sulphides characterized by relatively high Zn, Se, Au, Mo, Hg, and Sb content are composed of pyrite, chalcopyrite, bornite, and in lesser amounts covellite, siegenite, sphalerite, selenide-clausthalite, telluride-melonite, and occasionally tennantite–tetrahedrite. Massive Fe–Cu– Co–Zn-type sulphides associated with magnetite occur in a matrix of calcite and an unknown (Fe,Mg) silicate, resembling Mg–hisingerite within a deformed/metamorphosed ophiolite zone. The texture and mineralogical characteristics of this sulphide-magnetite ore suggest formation during a multistage evolution of the ophiolite complex. Sulphides (pyrrhotite, chalcopyrite, bornite, and sphalerite) associated with magnetite, at deeper parts of the Pindos (Tsoumes), exhibit relatively high Cu/(Cu + Ni) and Pt/(Pt + Pd), and low Ni/Co ratios, suggesting either no magmatic origin or a complete transformation of a preexisting magmatic assemblages. Differences recorded in the geochemical characteristics, such as higher Zn, Se, Mo, Au, Ag, Hg, and Sb and lower Ni contents in the Pindos compared to the Othrys sulphides, may reflect inheritance of a primary magmatic signature. © 2020 by the authors

Apatite and Mn, Zn, Co-enriched chromite in Ni-laterites of northern Greece and their genetic significance

The SEM-microprobe investigation of pseudo-autochthonous Fe-Ni deposits from the areas east Vermion, Edessa and Olympos, northern Greece, reveals the presence of apatite, and a significant Mn, Zn and Co enrichment in chromite, up to 14.0, 3.3 and 4.1 wt.%, respectively, due to the substitution for Mg2+ and Fe2+ by Mn, Zn and Co in the chromite lattice. Despite the significant Mn, Zn and Co contents (whole ore analysis) of some Ni-laterite deposits of the Balkan peninsula, Mn, Zn and Co enrichment in chromite is restricted to certain deposits, and its level seems to be a characteristic feature of each deposit. This may indicate that the Mn ± Zn ± Co enrichment has taken place after the re-deposition of the weathered material rather than during serpentinization and weathering of parent rocks. Mn ± Zn ± Co enrichment is commonly higher in the ferrian-chromite zone of chromite grains, and in high-Cr than high-Al chromite. The availability of Mn2+ ± Zn2+ ± Co2+ in solution during the diagenesis-metadiagenesis stage, due probably to the decomposition of organic matter, and the Eh-pH conditions may be major controlling factors for the incorporation of Mn, Zn or Co in the lattice of chromite. Apatite occurs as fine grained crystals (< 10 to 50 μm) dispersed throughout the matrix of the ore and as inclusions within zoned crystals of chromite, between chromite core and magnetite rim. It is associated with Fe-oxides (goethite, hematite, magnetite), chamosite, and quartz. A salient feature of the apatite is its poikiloblastic texture (with inclusions of quartz and iron oxides). The apatite crystals exhibit both plastic and brittle deformation textures. The composition of apatite is homogeneous, either in different apatite types or within crystals themselves. Apatite is Cl-free and corresponds to the fluor-hydroxyl-apatite type with the following average composition: 51.35 wt.% CaO, 2.80 wt.% FeO, 41.4 wt.% P2O 5 and 5 wt.% (F + H2O). The inclusions of apatite between chromite core and magnetite rim and the inclusions of magnetite and quartz dispersed throughout apatite suggest that these minerals crystallized at the same time. The association of apatite with Fe-chlorite and magnetite points to their formation during the diagenesis-metadiagenesis stage, while the gradual dissolution of apatite crystals dispersed throughout the matrix suggests that it was unstable during a subsequent stage of its formation. © 2003 Elsevier Science B.V. All rights reserved

Platinum-group minerals and tetraauricupride in ophiolitic rocks of Skyros island, Greece

In the serpentinized ophiolitic rocks from Skyros island, two distinct assemblages of base metal sulphides (BMS) and platinum-group minerals (PGM) occur. The first (early) generation is associated with chromitites which are enriched in platinum-group elements (PGE). The highest values were recorded in samples from Achladones (Ru 1210, Ir 780, Os 630, Rh 228, Pt 208, Pd 22; all values in ppb). Mineral inclusions in chromite consist of Ni-Fe sulphides and Os-rich laurite, and crystallized at high sulphur fugacity (fS2) during chromite formation. The second (late) generation is closely associated with Au-rich, PGE-poor magnetite ores which host a complex assemblage of inclusions consisting mainly of graphite, Cu-Fe- and pure Cu sulphides, sperrylite and tetraauricupride. Their accompanying hydrous silicates are Cl-bearing. It is assumed that this mineral assemblage was deposited by hydrothermal processes during serpentinization. © 1992 Springer-Verlag

Distribution of selenium in the soil–plant– groundwater system: Factors controlling its bio-accumulation

Selenium (Se) is an essential micronutrient for humans and animals, but both Se excess and deficiency can cause various health risks. Since Greece is among the European countries where people have very low Se-serum, the present study is focused on the Se distribution in cultivated and non-cultivated plants and relative soil coming from the Neogene basins of Greece (Assopos-Thiva and Attica), aiming to define potential Se-source/es and factors controlling Se bio-accumulation and enrichment in food. The dry weight Se values are relatively low (0.1–0.9 mg/kg) with the highest Se contents in garlic, beet and lettuce from the Assopos basin, where the translocation percentage [(mplant/msoil) × 100] for Se, P and S is much higher compared to non-cultivated Attica basin. There is a diversity between the Se source in soil and coastal groundwater which is used for irrigation in the cultivated Assopos–Thiva basin. The soil pH and oxidizing conditions (Eh) are considered the main driving force to make Se available for plant uptake. Potential sources for Se in Greece are Fe-Cu-Znsulphide ores and peat deposits in northern Greece, with a Se content ranging from decades to hundreds of mg/kg. Application of the leaching testing protocol is necessary to select the most appropriate proportion of additives to improve the Se deficiencies in agricultural soil. © 2020 by the authors. Licensee MDPI, Basel, Switzerland