Potassium Enrichment Research Articles

Petrology and geochemistry of volcanic rocks from the island of Panarea: implications for mantle evolution beneath the Aeolian island arc (southern Tyrrhenian sea)

Major, trace element and radiogenic isotope (Sr, Nd, Pb) data are reported for a suite of rocks from the Panarea volcano, a large structure that is largely hidden below sea level and outcrops only as a group of small islands between Lipari–Vulcano and Stromboli in the eastern Aeolian arc. The exposed rocks mostly consist of high-potassium calc-alkaline (HKCA) andesites, dacites and some rhyolites; shoshonitic basalts have been collected from submarine centres; mafic calc-alkaline (CA) rocks occur as thin layers of late-erupted strombolian scoriae. Major and trace element data are scattered, but define generally linear trends on inter-element diagrams; Sr-isotope ratios do not display significant increase with evolution, although rough positive trends of 87Sr/86Sr versus SiO2 and Rb/Sr can be recognised within some units. The mafic rocks display varying enrichment in potassium, from CA to shoshonitic compositions, and are characterised by variable abundances of incompatible trace elements, which increase with potassium. There is an increase of 87Sr/86Sr ratios and a decrease of 143Nd/144Nd and 206Pb/204Pb ratios from CA to HKCA and shoshonitic mafic rocks. The scattered and incomplete nature of the outcrops make it difficult to constrain magmatic evolution at Panarea; geochemical and isotopic data suggest that AFC and mixing were important evolutionary processes. However, geochemical modelling does not support the possibility that the first-order compositional variations observed in the mafic rocks are the result of these processes, and suggests a genesis in a heterogeneous mantle source. Recent studies have highlighted strong differences in terms of incompatible trace element ratios and isotopic signatures, between the western-central and the eastern Aeolian arc. Rocks from the western islands (Alicudi, Filicudi, Salina, Vulcano) have typical magmatic arc geochemical signatures and relatively unradiogenic Sr-isotope compositions. By contrast, the eastern island of Stromboli has a more radiogenic Sr-isotope signature, and shows trace element abundances and ratios that are intermediate between arc and intraplate compositions. Panarea mafic rocks have geochemical and isotopic signatures that are intermediate between those observed in the two sectors of the arc. The late-erupted CA scoriae of Panarea have trace element and isotopic compositions similar to those of the mafic rocks from the western islands of Filicudi and Alicudi, whereas the HKCA and shoshonitic mafic rocks have isotopic and trace element signatures that are closer to those of Stromboli. This reflects the particular position of Panarea, which is sited midway between the western-central arc and Stromboli. According to some recent views, subduction of the Ionian sea plate is actively occurring beneath the eastern Aeolian arc, with rollback of the subduction zone toward the southeast. The Tindari–Letoianni–Malta Escarpment fault zone is considered to be the boundary between the active subducting plate in the east and the African plate and western Aeolian arc in the west. It is suggested that the rollback of the Ionian plate generated inflow of mantle material from below the western arc into the mantle wedge above the subducting Ionian slab. This situation generated a hybrid mantle beneath Panarea, which resulted in a mixture of western-type and resident eastern-arc mantle materials; the latter had a composition akin to the source of Stromboli magmas. Early HKCA and shoshonitic magmatism tapped such a hybrid source, whereas the younger CA activity has been derived from melting of unmodified western-type mantle material. The late eruption of CA rocks with a composition similar to western arc can be explained by assuming that a continuing inflow process had increased the amount of western-type mantle with time, thus favouring the late appearance of CA magmas. This hypothesis accounts for the overall decrease of potassium with time, which is the opposite of the trend observed in other Aeolian islands.

Geochemical and Petrological Characteristics of the Kale (Gümüshane) Volcanic Rocks: Implications for the Eocene Evolution of Eastern Pontide Arc Volcanism, Northeast Turkey

The Kale (Gumushane) volcanic rocks crop out in the southern zone of the eastern Pontide arc, and consist mainly of agglomerate, andesite, minor basalt, and tuff associated with sediments (limestone, marl, siltstone, sandstone) deposited in a shallow basin environment. The volcanites show mainly porphyritic, hyalo-porphyritic, and rare fluidal and glomeroporphyritic textures. These volcanic rocks consist predominantly of plagioclase, augite, hornblende, and lesser biotite, magnetite, and quartz, and secondary products of chloritization, carbonation, sericitization, and epidotization. In general, they show disequilibrium textures, possibly reflecting magma-mixing processes. The volcanic rocks are mainly calc-alkaline in composition, and show moderate potassium enrichment. Most of the major- and trace-element variations reflect the significant role of fractional crystallization during the evolution of the volcanic suite. The fractionating phases are dominantly hornblende and augite, minor plagioclase, and magnetite. The rocks have high LILE and LREE enrichments, but are relatively depleted in HFSE relative to MORB. Moreover, incompatible trace-element distributions show similarities to those of an E-type MORB source. The rocks have moderately fractionated REE patterns with (La/Lu)N = 2–12. Geochemical data suggest that the volcanites evolved by shallow-level fractional crystallization and magma-mixing contamination of a parental magma derived from metasomatized upper mantle by partial melting after thickening of the Pontide arc during the Paleocene-Eocene. Furthermore, differentiation took place in a magma chamber situated in the thickened arc crust within an extensional tectonic regime.

Isotopic constraints on the genesis and age of autochthonous glaucony in the Oligo‐Miocene Torquay Group, south‐eastern Australia

The Oligo‐Miocene Torquay Group at Bird Rock in south‐eastern Australia comprises a sequence of fine‐grained skeletal carbonates and argillaceous and glauconitic sandstones, deposited in a cool‐water, mid‐shelf environment. The Bird Rock glaucony is autochthonous and consists predominantly of randomly interstratified glauconitic smectite, which constitutes bioclast infills and faecal pellet replacements. The results of Rb–Sr and oxygen isotopic analysis of samples taken from a single glauconitic horizon (the BW horizon) indicate that the glaucony developed through a series of simultaneous dissolution–crystallization reactions, which occurred during very early diagenesis in a closed or isochemical system, isolated from the ambient marine environment. The constituent ions of the glaucony were derived primarily from terrigenous clay minerals, but considerable potassium may have been sourced indirectly from sea water, through potassium enrichment of clay precursors. The pore fluids associated with glauconitization were marine derived, but progressively modified by the dissolution–crystallization of detrital clay minerals and autochthonous glaucony. Rb–Sr data for the BW horizon indicate that dating glauconies may be somewhat problematic, as co‐genetic glauconitic minerals can show a range of initial strontium compositions, which reflect the incorporation of strontium derived from mineralogical precursors and/or contemporaneous sea water. Rb–Sr isochrons indicate that the glaucony of the BW horizon formed at 23 ± 3 Ma. This age is in good agreement with both the established biostratigraphy and a 87Sr/86Sr age for the horizon (23 ± 1 Ma), but could only be determined using the independent age constraint and the estimate of the 87Sr/86Sr ratio of contemporaneous sea water provided by analysis of associated biogenic carbonate.

Tracing Nitrate Transport and Environmental Impact from Intensive Swine Farming using Delta Nitrogen‐15

Natural-abundance delta15N showed that nitrate generated from commercial land application of swine (Sus scrofa domesticus) waste within a North Carolina Coastal Plain catchment was being discharged to surface waters by ground water passing beneath the sprayfields and adjacent riparian buffers. This was significant because intensive swine farms in North Carolina are considered non-discharge operations, and riparian buffers with minimum widths of 7.6 m (25 ft) are the primary regulatory control on ground water export of nitrate from these operations. This study shows that such buffers are not always adequate to prevent discharge of concentrated nitrate in ground water from commercial swine farms in the Mid-Atlantic Coastal Plain, and that additional measures are required to ensure non-discharge conditions. The median delta15N-total N of liquids in site swine waste lagoons was +15.4 +/- 0.2% vs. atmospheric nitrogen. The median delta15N-NO3 values of shallow ground water beneath and adjacent to site sprayfields, a stream draining sprayfields, and waters up to 1.5 km downstream were + 15.3 +/- 0.2 to + 15.4 +/- 0.2%. Seasonal and spatial isotopic variations in lagoons and well waters were greatly homogenized during ground water transport and discharge to streams. Neither denitrification nor losses of ammonia during spraying significantly altered the bulk ground water delta15N signal being delivered to streams. The lagoons were sources of chloride and potassium enrichment, and shallow ground water showed strong correlation between nitrate N, potassium, and chloride. The 15N-enriched nitrate in ground water beneath swine waste sprayfields can thus be successfully traced during transport and discharge into nearby surface waters.

The nature of maskelynite in shocked meteorites: not diaplectic glass but a glass quenched from shock-induced dense melt at high pressures

Maskelynite, an important constituent of shocked meteorites, once thought to be diaplectic plagioclase glass formed by shock-induced solid-state transformation. Our systematic investigation of shocked L-chondrites and SNC meteorites indicates that maskelynite does not contain inherited fractures or cleavage, and shock-induced fractures. We found no evidence for models calling for melting that initiated in PDFs and affected the whole crystals. Maskelynite grains are smooth and display radiating cracks emerging from their surfaces into neighboring pyroxene. This is indicative of shock-induced melting and quenching of the dense melt at high pressure, thus erasing the inherited and shock-induced fractures. This was followed by relaxation of the dense plagioclase glass, which induced the expansion cracks in pyroxene and olivine. Enrichment in potassium, deviation from stoichiometry, degradation of igneous zoning, the presence of offshoots of maskelynite in pyroxene, the lack of vesiculation in the melt pockets, melt veins and molten mesostasis are clear evidence for melting and quenching under high pressure. Our investigations present unequivocal evidence that maskelynite in meteorites is not diaplectic plagioclase glass formed by solid-state transformation, but a dense quenched glass. The duration of the shock pulse in natural events can be several orders of magnitude longer than in shock experiments. Since kinetic effects are crucial factors in promoting phase transitions, vitrification and melting, experimentally induced solid-state vitrification of plagioclase produced in dynamic experiments is inadequate for calibration of peak shock pressures in maskelynite-bearing natural samples.

Potassium enrichment in shale—fluid transport or provenance?

Shale composition shows increasing potassium content with depth, generally attributed to one or both of potassium metasomatism or original variation in depositional composition. The compositional variations of shale through time suggest that depositional variations in composition are significant. Weathered cratonic rocks and volcanic rocks provide two end-members, which may be mixed to produce variations observed in potassium concentration. Bulk rock and clay fraction isotope compositions are consistent with mixing of these two end members. If K-enrichment is caused by fluid transport, the source of potassium metasomatizing fluids is enigmatic. Formation waters in clastics have low potassium contents, only carbonates have waters with high potassium. Deep “geothermal” waters are likely to have K contents less than 1000ppm and Na/K set by feldspar equilibrium. Reaction path models suggest the time required to double K concentration of a shale approach hundreds of millions of years.

Characteristics of Regolith developed on basalt in Pahang, Malaysia

The characteristics and degree of weathering in a deep regolith developed on basalt were investigated. A representative 15m deep regolith of soil‐saprolite‐rock sequence, located in Pahang state, Malaysia, was selected. The intensity of weathering in this deep regolith was assessed by various weathering indices as well as changes in the physicochemical properties and clay mineralogy of the regolith. The values of all weathering indices and other assessments gave strong evidences of intense weathering during saprolite formation. The low CËC and base cation values even in the saprolite layers were accounted By the extreme depletion of major elements such as potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg), and significant enrichment of aluminum (Al), iron (Fe), titanium (Ti), copper (Cu), and niobium (Nb) occurred during saprolitization. The extreme weathering pattern of basalt differed from those described in granite and metamorphic rocks found in Peninsular Malaysia.

Illitization in a Paleozoic, peat-forming environment as evidence for biogenic potassium accumulation

Potassium enrichment is common in surface horizons of many paleosols and has been attributed to the formation of authigenic illite from smectites during burial diagenesis. In such cases, the presence of primary smectite is key to the illitization process, which then results in potassium enrichment as a byproduct. Potassium enrichment in paleosols where no primary smectite was present, however, requires a different process of accumulation. A Lower Pennsylvanian, tropical Ultisol from the Southern Anthracite Field in Pennsylvania is enriched in potassium in the surface horizon and formed in an environment unfavorable for smectite accumulation. Kaolinite dominates clay mineral fractions of soils that form in such highly weathering environments. In the absence of primary smectite to scavenge potassium during illitization, there should be no potassium enrichment during burial diagenesis. However, in Lykens Valley paleosol, the pattern of potassium concentration, organic matter distribution and authigenic illite growth suggests that organic matter may have provided an important source of potassium for illite formation. Illitization of kaolinite in the organic-rich surface horizon is complete but, illite coexists with kaolinite in the B horizon. Within the paleosol matrix, illitization is more complete in areas of high organic concentration where organic fragments often have illite haloes with illite whorls growing from their edges. We propose that the potassium enrichment both in the soil profile and in the overlying coal is the result of the luxury uptake of potassium by peat-forming plants (nutrient intake at rates exceeding metabolic requirements). Further, potassium immobilized by adsorption on the peat provided interlayer cations for illite authigenesis to begin. If, as we suggest, luxury nutrient uptake during peat formation sequestered sufficient potassium to promote later illite formation, the pattern and extent of illitization within the paleosol profile reflects early biogenic nutrient accumulation. Thus, illite, in some paleosols, may represent fossil evidence for a biological process: the luxury uptake of potassium.

Miocene potassium metasomatism, Whipple Mountains, southeastern California: A datable tracer of extension-related fluid transport

Research Article| March 01, 1999 Miocene potassium metasomatism, Whipple Mountains, southeastern California: A datable tracer of extension-related fluid transport Kathi K. Beratan Kathi K. Beratan 1Department of Geology and Planetary Science, 321 EH, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kathi K. Beratan 1Department of Geology and Planetary Science, 321 EH, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1999) 27 (3): 259–262. https://doi.org/10.1130/0091-7613(1999)027<0259:MPMWMS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kathi K. Beratan; Miocene potassium metasomatism, Whipple Mountains, southeastern California: A datable tracer of extension-related fluid transport. Geology 1999;; 27 (3): 259–262. doi: https://doi.org/10.1130/0091-7613(1999)027<0259:MPMWMS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Potassium enrichment within the upper plate of the Whipple detachment fault, southeastern California, occurred as a discrete pulse between 18.5 and 14 Ma, following the most intense extension and prior to the last episode of movement on the detachment fault. This timing is not consistent with a hydrothermal model for K enrichment in which the K is derived from propylitic alteration of lower-plate rocks. Instead, the temporal and spatial distribution of K enrichment supports a diagenetic model in which the K was derived from leaching of Tertiary alkalic volcanic rocks and dissolution of rhyolitic ashes by alkaline-saline brines in a lake and circulating ground water. The most intense alteration is commonly associated with mapped upper-plate faults, although not all mapped faults display evidence of K metasomatism. Fracture porosity present along active faults may have provided a conduit for K-bearing fluids, thus marking a set of faults as coeval and cogenetic. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemistry of Organic-Rich Black Shales Overlying the Natural Nuclear Fission Reactors of Oklo, Republic of Gabon

The organic-rich black shales of the Franceville Series' FB Formation overlying the uranium ores and natural nuclear fission reactors of Ohio, Gabon, are not notably metalliferous. Chromium, gold, silver, and barium are slightly enriched in average Ohio black shale (AOK) relative to black shale standard SDO-1. Geochemical variations among the black shale samples of the sedimentary sequence include enrichment in potassium, barium, chromium, and silver in the four lowermost samples, the presence of a bleached zone depleted in organic carbon lowermost in the sequence, and elevated rare earth element (REE) content in samples closest to the Oklo reactor zones. Hydrothermal activity has influenced the geochemistry of the black shale but is evidently not linked to reactor-driven processes. Chondrite-normalized REE patterns of Oklo black shale samples show slight enrichment in light REE and slight depletion in heavy REE, especially in the sample closest to the reactor zone. However, comparison of REE content with various petrographic facies in and near the Oklo reactors shows no apparent enrichment in fission product (intermediate) REE. With few exceptions, reactor facies all contain more REE than AOK The chondrite-normalized REE pattern of AOK resembles that of greywacke-shale turbidites of Archean greenstone belts. The paucity of uranium and manganese in AOK is a curious anomaly in an area of world class uranium and manganese deposits.

Geochemistry and depositional environment of the gold-mineralized Proterozoic Koolpin Formation, Pine Creek Inlier, Northern Australia: a comparison with modern shale sequences

The Paleo- to Mesoproterozoic Koolpin Formation is a lithologically distinct sequence in the sedimentary pile of the Pine Creek Inlier in Northern Australia. This succession hosts several gold deposits such as the Cosmo Howley Gold Mine (Matthäi et al., 1995a). Part of the Koolpin Formation has been referred to as ‘iron formation’ and interpreted as an ‘exhalative’ deep water sediment. By analogy with the Homestake gold deposit (South Dakota), a syn-sedimentary origin of the gold-enrichment has been proposed for Cosmo Howley. This paper presents a detailed investigation of the sedimentology, petrography, and geochemistry of the Koolpin Formation at and in the vicinity of Cosmo Howley. It is shown that the sequence consists mainly of metamorphosed shales with narrow intercalations of formerly carbonate-bearing mudstones in which chert-concretions formed during periods of subaerial weathering. In the hanging wall, the sequence grades into carbonaceous slates which formerly contained diagenetic dolomite. Depositional structures indicate that the older part of the Koolpin Formation at Cosmo Howley formed in a low-energy, inter- to supra-tidal environment dominated by detrital input of terrestrial provenance. The younger carbonaceous slates seem to reflect a transition to shallow-marine conditions. The chemical character of the metasediments and their REE-signatures are comparable to modern-day analogs, despite potassium enrichment and Ca-, Na-depletion which is inferred to be a consequence of fluid flow during mineralization and contact metamorphism. Iron formations as defined by James (1954) are not present at Cosmo Howley. Iron enrichment to present values (⩽ 27 wt.% total Fe) is shown to have occurred from a weakly diagenetically enriched protolith due to silica loss during nodule formation, volatile loss during metamorphism, and epigenetic sulfide precipitation during retrograde alteration. No gold enrichment can be demonstrated for the protolith. Similar conclusions may be reached for the iron-rich metasediments which host gold mineralisation at Homestake, South Dakota.

Technology of Production of Fine Pottery Excavated on a Western Greek Site Investigated by Scanning Electron Microscopy Coupled with Energy-Dispersive X-ray Detection

Scanning electron microscopy (SEM) coupled with energy-dispersive x-ray detection was used to study fragments of fine pottery excavated on the archaeological site at Locri Epizephiri (Southern Italy). The fragments analysed were specimens of black coated ware and included pieces suspected to have been produced on the site in the course of the fourth and third centuries BC and suspected imports from foreign centres of production. Comparison between the composition of slip and body of the samples indicated that selection and refinement of clays led to silicon and calcium depletion and aluminium, iron and potassium enrichment in the coating. In addition, pronounced depletion of magnesium was observed in the slip of the imported wares and the earlier local products, but not of the later local wares; this might account for the low quality of some 3rd century products with respect to the earlier pieces. Examination of SEM images indicated that the thickness of the surface slip reaches up to about 20-25 μm on the imported sherds, but measures ca. 10-20 μm on most of the local products.

Evaluation of the role of Cambrian granites in the genesis of world class VHMS deposits in Tasmania

An analysis of the distribution, composition and alteration zonation of Cambrian granites which intrude the Mt Read Volcanics of western Tasmania provides evidence that there may have been a direct input of magmatic fluids containing Fe, Cu, Au and P to form the copper-gold volcanic-hosted massive sulphide (VHMS) mineralisation in the Mt Lyell district. Interpretation of regional gravity and magnetic data indicates that a narrow discontinuous body of Cambrian granite (2–4 km wide) extends along the eastern margin of the Mt Read Volcanic belt for over 60 km. The Cambrian granites are altered magnetite series types which show enrichment in barium and potassium, and contrast markedly with the fractionated ilmenite series Devonian granites related to tin mineralisation elsewhere in the Dundas Trough. Copper mineralisation occurs in a linear zone above the apex of the buried Cambrian granite body at the southern end of the belt, from Mt Darwin to the Mt Lyell district over a strike length of 25 km. Gold and zinc mineralisation are concentrated higher in the volcanic stratigraphy more distant from the granite. Overlapping zones of alteration extend from the granite into the surrounding volcanic rocks. An inner zone of K-feldspar alteration is overprinted by chlorite alteration, which passes outwards into sericite alteration. Magnetite ± pyrite ± chalcopyrite ± apatite mineralisation is concentrated in the chlorite alteration zone as veins and low grade disseminations. The Mt Lyell copper-gold stringer and disseminated mineralisation is hosted in felsic volcanic rocks 1 to 2 km west of the interpreted buried granite position. Magnetite-apatite ± pyrite veins in the Prince Lyell deposit at Mt Lyell are very similar to the veins in the halo of the granite, further south, and provide evidence for magmatic fluid input during the formation of the copper-gold VHMS deposits. A model involving deeply penetrating convective seawater, mixing with a magmatic fluid released from the Cambrian granites, best explains the features of VHMS mineralisation in the Mt Lyell district.

Aerosol emissions by tropical forest and savanna biomass burning: Characteristic trace elements and fluxes

Aerosol particles were collected during the dry season in the amazonian forest and in African and Brazilian savannas. Sampling was performed inside the plumes of vegetation fires and in the local background atmosphere. Samples were analysed for their elemental composition by Particle Induced X‐Ray Emission (PIXE). Enrichment factors relative to the local background were calculated. Savanna fire aerosols are characterised by enrichments in elements like K, P, Cl, Zn, and Br, whereas forest fire emissions are enriched in Si and Ca. The unexpected low potassium enrichment factor for the forest fires could be due to the prevailing smoldering conditions, whereas the high values of potassium enrichment factor during savanna fires could be associated with the predominant flaming conditions. This result indicates that potassium may be considered a good tracer of the flaming phase of fires only. Emission factors of P, S, Cl, K, Ca, Mn, Zn, Br and total particulate matter were calculated for African savanna fires. Our estimates of the annual potassium and zinc emissions by tropical savanna fires indicate that the contribution of this source should be taken into account to understand the biogeochemical cycle of these elements.

Convection of saline brines in enclosed lacustrine basins: A mechanism for potassium metasomatism

Metasomatic potassium enrichment is found in a number of different geologic environments. One type of metasomatism that is often spatially and temporally associated with volcanism and sedimentation is found in ancient closed lacustrine basins. We propose that metasomatizing fluids may have been plumes driven by instabilities inherent in evaporation-induced density stratification found beneath saline lakes. For instabilities to occur, the hydraulic conductivity of the stratigraphic section should be greater than ∼10 −7 m/s. Metasomatized Tertiary volcanic and sedimentary rocks near Socorro, New Mexico, and in the Harcuvar Mountains, Arizona, show potassium enrichment by a factor of two or more. In both areas, the stratigraphic section is estimated to have an overall vertical hydraulic conductivity larger than ∼10 −7 m/s, sufficient for ground-water convection and potassium transport. In contrast, data from Searles Lake and Lake Tecopa in eastern California show little or no net addition of potassium. Lithology of these sediments suggests initial vertical hydraulic conductivities to range from 10 −8 to 10 −10 m/s, insufficient to sustain salinity-driven convection. Vertical convective transport of potassium was therefore unlikely at Searles Lake and Lake Tecopa.

Características geoquímicas de las rocas volcánicas del sistema geotérmico Los Humeros, Puebla y su relación con la mineralogía de alteración

Las rocas volcánicas presentes en el sistema geotérmico Los Humeros varían de andesitas-basálticas a riolitas con diferentes grados de alteración hidrotermal. Los estudios petrográficos realizados, aunados con análisis de difracción de Rayos X, permitieron determinar que los minerales de alteración son de diversos tipos; sin embargo, éstos se presentan en asociaciones paragenéticas indicadoras de temperaturas que varían de 150°a más de 300° C. Este rango de temperaturas coincide con el gradiente actual del sistema. La composición de elementos mayores y traza de las diversas unidades litológicas permite proponer que las rocas volcánicas de Los Humeros siguen un comportamiento evolutivo calcoalcalino con un ligero enriquecimiento en potasio. Ciertos elementos químicos (Zr, V, Ti o P), considerados como relativamente inmóviles bajo la acción hidrotermal, fueron utilizados en la estimación de la transferencia de masa ocurrida dentro de las rocas volcánicas del sistema. El uso de relaciones isotópicas 87Sr/86Sr como indicadores de la procedencia de ciertos constituyentes químicos puede ser de gran utilidad. En el caso de Los Humeros las rocas volcánicas y las calcitas hidrotermales presentan valores isotópicos similares (0.70414 promedio), lo cual indica que los constituyentes químicos del tipo Ca y Sr fueron derivados de fuentes magmáticas similares. Dichos valores isotópicos contrastan con los valores encontrados en las rocas carbonatadas del basamento (0.70730).

Batholithic, K-Rich Silicic Magmatism in East-Central Asia: Evidence for a Mantle Source for Progressive Regional Crustal Potassium Enrichment

Granitoid nmgmatism in East-Central Asia Granitoid magmatism has occurred on a vast scale in Transbaikalia, East Central Asia during the Phanerozoic. Within this huge and geologically complex region, many hundreds of individual plutons of syenite, quartz syenite, and K-rich granite have been intruded within NE-SW-oriented belts 200-400 km wide and 2000-3000 km long. These belts are superimposed upon and cut across more ancient tectonic structures (including basement blocks of different age and composition). The intrusive activity was accompanied by extrusion of the volcanic counterparts of these magmas. The composition of intrusive and extrusive magmas was absolutely independent of local country-rock composition (Leontiev eta/., 1981; Zanvilevich et a/., 1985; Litvinovsky et al., 1993.) Five main stages of intrusive activity are distinguished (see Table 1), and each suite of

The Lac Troilus gold-copper deposit, northwestern Quebec; a possible Archean porphyry system

The Lac Troilus gold-copper deposit is located approximately 120 km north of Chibougamau, Quebec, within the northeastern part of the Evans-Frotet greenstone belt, an Archean, bimodal, supracrustal sequence of mafic to felsic volcanic flows and tuffs. Volcanic rocks in the vicinity of the deposit form an overturned sequence of porphyritic intermediate tuffs and flows and mafic lapilli tuffs. These rocks were intruded, post-tilting, by syn- to late tectonic felsite and feldspar porphyry dikes and sills. The bulk of the copper-gold mineralization is hosted within a zone of in situ breccia along the contact between the intermediate and mafic volcanic rocks. The Lac Troilus deposit has a drill-indicated geologic resource totaling approximately 60 million metric tons containing over 2.5 million oz gold, 3 million oz silver, and 60,000 metric tons copper.Mineralization consists of 2 to 3 percent sulfides with localized areas of up to 7 percent sulfides. The sulfides are principally chalcopyrite, pyrite, and pyrrhotite, with rare sphalerite. The sulfides form disseminations, tiny veinlets, and narrow semimassive seams and are controlled by both foliation and fractures. Gold generally occurs as electrum, although native gold and calaverite have been recognized. The electrum occurs as discrete grains, generally from 20 to 100 mu m in diameter, along sulfide grain boundaries and along fractures within the sulfides.The Lac Troilus deposit shows strong mineral and chemical zonation. The core area of wall-rock alteration, characterized by a zone of strong biotite alteration, is centered on a large felsic dike situated in the immediate structural footwall to the deposit. Moving outward, there is a decrease in the intensity of biotite alteration and an increase in plagioclase, epidote, and calcite alteration. Data currently available indicate that the zonation is asymmetric and is best developed upward into the hanging wall. Chemical zonation is indicated by strong potassium enrichment in the footwall which grades into a more sodium-enriched zone in the hanging wall. Calcium is depleted in all altered rocks adjacent to the copper-gold mineralization.The copper and iron sulfide minerals and gold show similar zoning patterns. The core area is characterized by a chalcopyrite-pyrrhotite-rich assemblage. Proceeding toward the structural hanging wall, there is a gradual decrease in chalcopyrite and pyrrhotite contents and a relative increase in pyrite. The potassic footwall rocks are primarily copper-bearing whereas the hanging-wall, sodium-enriched rocks tend to be gold rich and copper poor. The zone of brecciation, which has both sodium and potassium enrichment, is both gold and copper rich.Considering the size and nature of the wall-rock alteration zones, the metal zoning, grades, and characteristics of the host rocks, the Lac Troilus deposit is similar to, and may have formed in a manner analogous to, porphyry copper-gold deposits in the Phanerozoic, such as Island Copper, in British Columbia.

Effect of nutrition on susceptibility of cucumber, eggplant, and pepper crops to Botrytis cinerea

Parthenocarpic cucumbers were grown in polyethylene tunnels under commercial conditions and fertilized with N – P – K 7:3:7%. During two winter seasons when nitrate level in the fertilizer was low, the addition of potassium to the fertilizer significantly reduced the incidence of fruit grey mould caused by Botrytis cinerea Pers.:Fr. by 27 – 33%, whereas adding calcium generally reduced grey mould by 35 – 50%. The fungicide treatments, diethofencarb and carbendazim (at 0.25 g∙L−) reduced grey mould by 39 and 50%, respectively. In the 2nd year stem infection with B. cinerea was decreased by 50, 50, or 60% by treatment with potassium, fungicide, or calcium, respectively. Only the calcium treatment was significantly different from the basic fertilizer control. Calcium treatments were effective on cucumber crops only under high relative humidity at two out of four sampling dates. The effect of calcium could not be separated from high nitrate level associated with its use in cucumber plantings. Potassium enrichment reduced natural incidence of downy mildew (Pseudoperonospora cubensis). Neither ion reduced incidence of powdery mildew (Sphaerotheca fuliginea) in cucumber crops. Disease reduction and increased yield of an eggplant crop were obtained by the addition of calcium to the fertilizer. Grey mould of pepper was reduced by 50 – 60% by adding calcium, but pepper yield was not increased. A single application of calcium sulphate alone or with calcium dihydrogen phosphate to glasshouse plants resulted in a reduction of grey mould in pepper and eggplant artificially inoculated with B. cinerea. Key words: Botrytis cinerea, Pseudoperonospora cubensis, Sphaerotheca fuliginea, calcium, nitrate, potassium.

The origin of the potassic rock suite from Batu Tara volcano (East Sunda Arc, Indonesia)

atu Tara is an active potassic volcano in the eastern Sunda arc. Its leucite-bearing rock suite can be subdivided into two groups, one less evolved with Th<20 ppm, the other more evolved with Th>20 ppm. 87Sr/ 86Sr, δ 18O and trace-element systematics in the less evolved group suggests that existence of parental magmas with different mantle origins. The mantle below Batu Tara is most likely heterogeneous and several source components are involved in magma genesis. Trace element and isotopic compositions of Batu Tara and adjacent volcanoes are consistent with the involvement of a subducted sedimentary/crustal component as well as MORB and OIB mantle, the latter with geochemical characteristics comparable to the mantle underlying Muriah (Java). Melt extraction from this complex mixture is envisioned as a two-stage process: partial melts of the crust-contaminated MORB mantle mix in the mantle wedge with partial melts of OIB domains. Different mixtures of these two melts provide the parental magmas that enter the volcanic plumbing system, where crystallization, hybridization and refilling processes occur. The calcalkaline volcanoes in the arc segment show stronger signatures for a subducted crustal component than Batu Tara, which displays a greater influence from the OIB mantle source. The potassium enrichment can therefore be attributed to contributions both from the enriched mantle and from subducted crustal material. Mantle-type δ 18O values of the Batu Tara magmas indicate that the mantle wedge below potassic orogenic volcanoes is not necessarily strongly enriched in 18O.