Sulfide Zone Research Articles

Spectral and Chemical Characterization of Copiapite and Rozenite from Padinjarathara in Wayanad, Southern India: Implications for Mars Exploration

Copiapite (Fe2+Fe3+4(SO4)6(OH)2 ∙ 20 H2O) and rozenite (Fe2+(SO4) ∙ 4H2O) are secondary hydrous sulfate minerals, mostly formed because of oxygenation and weathering events of primary sulfides on Earth. Acidophiles, mainly archaea and bacteria, and specifically anaerobic methanogens (methane-producing microorganisms) have been detected in regions where alteration of primary sulfide phases to secondary sulfates are predominant. These secondary sulfate minerals are significant in defining past geological environments on Earth and other rocky planets such as Mars. We discuss here the results of chemical and spectral analyses of copiapite and rozenite found in massive sulfide zones associated with banded iron formations (BIFs) in the Wayanad region in Kerala, southern India. The results from different spectroscopic techniques — VNIR reflectance, TIR (emitted radiation), FTIR, Laser Raman, and X-ray diffraction — were recorded and matched with existing literatures and databases. Different matching algorithms like Spectral Feature Fitting (SFF), Spectral Similarity Value (SSV), Modified Spectral Angle Similarity (MSAS), and Pearsonian Correlation Coefficient (PCC) were utilized in order to quantitatively match the reflectance spectra with the reference spectra (USGS and RELAB). The genesis of copiapite and rozenite in the area is through seasonal and temporary development of an acidic environment, with the high elevations of the Wayanad plateau providing the necessary low-humidity condition during the dry season. Copiapite and rozenite were detected as alteration products in different regions on Mars, which can provide insights into environmental conditions that prevailed during the biogeochemical evolution of Mars. The study of copiapite and rozenite formation in a terrestrial environment will therefore enhance our understanding of similar mineral precipitation, genesis, and fluvial processes on Mars. Future missions to Mars could also use the data obtained from the present study to calibrate similar instruments to detect these secondary sulfate minerals.

Cycling of W and Mo species in natural sulfidic waters and their sorption mechanisms on MnO2 and implications for paired W and Mo records as a redox proxy

Redox-sensitive trace metal concentration patterns have been widely used to track redox conditions in aquatic environments. Among redox-sensitive trace metals, molybdenum (Mo) is of interest owing to its speciation behavior and associated changes in particle reactivity that cause significant changes in concentration patterns in oxic versus sulfidic conditions. However, current understanding of how to use Mo geochemistry of marine sediments as a paleoredox proxy is limited to determining presence or absence of, and in some cases the aerial extent of, sulfidic conditions in the past. Here, we present a combination work of field sampling analysis and experiments to link concentration patterns of another redox-sensitive trace metal, tungsten (W), to Mo in order to provide a framework for using these trace metals to track changes in sulfidic conditions in ancient aquatic environments. We analyzed W and Mo concentrations in the water column and sediment pore waters of the Chesapeake Bay. We found that dissolved Mo/W molar ratios varied under different redox conditions. Because concentrations of these trace metals are controlled by their speciation in solution, we defined three sulfidic zones based on W and Mo speciation and their impacts on particle reactivity: the weakly sulfidic zone (0.2 μM < [H2S] < ∼15 μM); the moderately sulfidic zone (∼15 μM < [H2S] < ∼600 μM); and the strongly sulfidic zone ([H2S] > ∼600 μM). In all sulfidic zones, dissolved W concentrations were positively correlated with dissolved Mn concentrations. In contrast, the dissolved Mo concentrations were negatively correlated with dissolved Mn concentrations. As a result, Mo/W molar ratios were negatively correlated with dissolved sulfide concentrations in the weakly, moderately, and strongly sulfidic zones. Our sorption experiment results indicate that the negative correlation between Mo/W molar ratios and dissolved oxygen concentrations in the oxic zone is likely due to the stronger adsorption of WO42– onto Mn oxide surfaces compared with that of MoO42–. In comparison, the negative correlation between Mo/W ratios and sulfide concentrations in sulfidic waters is attributed to the differences in thiolation processes of W and Mo, with Mo exhibiting a higher degree of thiolation than that of W. Because W and Mo speciation controls their particle reactivities, these results together indicate that both speciation of W and Mo and their particle reactivity with respect to solid phases control the behaviors of Mo/W molar ratios in various reducing environments. Our results also suggest that in both oxic and weakly sulfidic conditions, both WO42– and MoO42– dominate. In contrast, different thiolated anions of W and Mo are likely to be present in the sedimentary records deposited in sulfidic systems. Thus, the results suggest that the dissolved Mo/W molar ratio combined with their speciation information is a strong indicator of redox changes (including oxic and sulfidic changes). Solid phase Mo/W molar ratios increase as sulfide levels increase and thus can be used to track variations in redox conditions (as well as the severity of sulfidic conditions) in ancient oceans.

Unusual Benthic Morphotypes Typical of Permanent Hydrogen Sulfide Zone of the Black Sea: Hypotheses of Their Origin and Perspectives of Study

Benthic morphotypes with an organic shell of unknown systematic affiliation are constantly registered in the bottom sediments of deep-water hydrogen sulfide zone of the Black Sea. The work offers a brief description with illustrations of these morphotypes, which are identified as “Form 3,” “Form 4,” “Form 5,” “Form 6,” and “Form 11.” Hypotheses are proposed concerning their origin. In addition, this paper gives an opinion on the unexplained role of the morphotype accumulations in the formation of deep-sea sediments and the importance of these objects in sedimentology and micropaleontology. The use of the accepted term azoic or lifeless is discussed in relation to the hydrogen sulfide zone of the Black Sea.

Distribution of gold and silver and its relation with hypogene ore minerals in the Esperanza porphyry deposit, Antofagasta Region, Chile

AbstractModes of occurrence of Au‐ and Ag‐bearing phases and their relation with associated hypogene ore minerals were examined with the objective to elucidate Au‐Ag distribution at the Esperanza porphyry deposit in the Eocene Centinela copper belt, using ore‐microscope modal analysis, semi‐quantitative analyses by automated mineralogy, electron probe microanalysis, and secondary ion mass spectrometer. The Esperanza hypogene mineralization is characterized by early‐stage chalcopyrite‐rich veinlets in the potassic alteration zone and later polymetallic stage with tennantite and galena in the chlorite‐sericitic alteration zone. Only the early‐stage chalcopyrite contains fine‐grained electrum (Au68Ag32 ‐ Au81Ag19) and hessite (Ag2Te), and thus yields positive correlations in Cu vs. Au and Cu vs. Ag grades that are clearly recognized in the hypogene sulfide zone. The early‐stage chalcopyrite grains frequently exhibit polysynthetic twinning suggestive of inversion from intermediate solid solution. These features suggest that the fine‐grained electrum and hessite are products exsolved in the cooling process with the intermediate solid solution to chalcopyrite inversion. In contrast, tennantite and galena of the later‐stage mineralization contain no detectable Ag, and it is thus proposed that the early‐stage inverted chalcopyrite is the principal storage of economically important precious metals.

Mineral Inventory of the Algares 30-Level Adit, Aljustrel Mine, Iberian Pyrite Belt, Portugal

Mining activity in Algares (Aljustrel Mine, Portuguese sector of the Iberian Pyrite Belt, IPB) stems prior to Roman times. As the orebody is vertical and relatively thin, mining was carried out mainly along underground adits (galleries). Nowadays, the deposit is considered exhausted and the area is being rehabilitated for a different use. The Algares +30 level adit intersects two volcanic units of the IPB Volcano-Sedimentary Complex. The massive sulphide and related stockwork zone are hosted by the Mine Tuff volcanic unit and are exposed in the walls of the gallery, showing intense hydrothermal alteration. Along the mine adit, the geological sequence is affected by strong oxidation and supergene alteration, giving rise to the formation of secondary minerals through the oxidation of the sulphides. The most common minerals found were melanterite (FeSO4·7H2O) and chalcanthite (CuSO4·5H2O), forming essentially massive or crystalline aggregates, ranging from greenish to bluish colours. Melanterite from the walls revealed to be Cu-rich by opposition to that from stalactites/stalagmites formed below the old ore storage silo revealing the low-copper-grade ores exploited underground. The mineralogy of the efflorescent salts was used to ascertain the processes involved in their formation, and moreover, the inventory of minerals is presented, as well as their principal characteristics.

Using modern low-oxygen marine ecosystems to understand the nitrogen cycle of the Paleo- and Mesoproterozoic oceans.

During the productive Paleoproterozoic (2.4-1.8Ga) and less productive Mesoproterozoic (1.8-1.0Ga), the ocean was suboxic to anoxic and multicellular organisms had not yet evolved. Here, we link geologic information about the Proterozoic ocean to microbial processes in modern low-oxygen systems. High iron concentrations and rates of Fe cycling in the Proterozoic are the largest differences from modern oxygen-deficient zones. In anoxic waters, which composed most of the Paleoproterozoic and~40% of the Mesoproterozoic ocean, nitrogen cycling dominated. Rates of N2 production by denitrification and anammox were likely linked to sinking organic matter fluxes and in situ primary productivity under anoxic conditions. Additionally autotrophic denitrifiers could have used reduced iron or methane. 50% of the Mesoproterozoic ocean may have been suboxic, promoting nitrification and metal oxidation in the suboxic water and N2 O and N2 production by partial and complete denitrification in anoxic zones in organic aggregates. Sulfidic conditions may have composed ~10% of the Mesoproterozoic ocean focused along continental margins. Due to low nitrate concentrations in offshore regions, anammox bacteria likely dominated N2 production immediately above sulfidic zones, but in coastal regions, higher nitrate concentrations probably promoted complete S-oxidizing autotrophic denitrification at the sulfide interface.

Microbial Diversity and Metabolic Potential in the Stratified Sansha Yongle Blue Hole in the South China Sea

The Sansha Yongle Blue Hole is the world’s deepest (301 m) underwater cave and has a sharp redox gradient, with oligotrophic, anoxic, and sulfidic bottom seawater. In order to discover the microbial communities and their special biogeochemical pathways in the blue hole, we analyzed the 16S ribosomal RNA amplicons and metagenomes of microbials from seawater depths with prominent physical, chemical, and biological features. Redundancy analysis showed that dissolved oxygen was the most important factor affecting the microbial assemblages of the blue hole and surrounding open sea waters, and significantly explained 44.7% of the total variation, followed by silicate, temperature, sulfide, ammonium, methane, nitrous oxide, nitrate, dissolved organic carbon, salinity, particulate organic carbon, and chlorophyll a. We identified a bloom of Alteromonas (34.9%) at the primary nitrite maximum occurring in close proximity to the chlorophyll a peak in the blue hole. Genomic potential for nitrate reduction of Alteromonas might contribute to this maximum under oxygen decrease. Genes that would allow for aerobic ammonium oxidation, complete denitrification, and sulfur-oxidization were enriched at nitrate/nitrite-sulfide transition zone (90 and 100 m) of the blue hole, but not anammox pathways. Moreover, γ-Proteobacterial clade SUP05, ε-Proteobacterial genera Sulfurimonas and Arcobacter, and Chlorobi harbored genes for sulfur-driven denitrification process that mediated nitrogen loss and sulfide removal. In the anoxic bottom seawater (100-300 m), high levels of sulfate reducers and dissimilatory sulfite reductase gene (dsrA) potentially created a sulfidic zone of ~200 m thickness. Our findings suggest that in the oligotrophic Sansha Yongle Blue Hole, O2 deficiency promotes nitrogen- and sulfur-cycling processes mediated by metabolically versatile microbials.

The Luanga deposit, Carajás Mineral Province, Brazil: Different styles of PGE mineralization hosted in a medium-size layered intrusion

The Luanga Complex, located in the eastern portion of the Carajás Mineral Province, is part of a cluster of PGE-mineralized layered intrusions, grouped into what is known as the Serra Leste magmatic suite. The Luanga deposit, the largest PGE deposit in South America, has two distinct styles of PGE mineralization. The first type, termed as Sulfide Zone, consists of a 10–50 m thick interval with disseminated base metal sulfides (pentlandite > pyrrhotite >>> chalcopyrite) located along the upper contact of the intrusion's Ultramafic Zone. The Sulfide Zone extends along the entire length of the intrusion (~3 km) and hosts the bulk of PGE resources of the Luanga Complex (i.e., 142 Mt at 1.24 ppm Pt + Pd + Au and 0.11% Ni). The second type of PGE mineralization, termed as low-S-high-Pt-Pd Zones, consists of 2–10 m thick stratabound PGE mineralization within a sequence of interlayered ultramafic and mafic cumulates located above the Sulfide Zone. Host rocks of the low-S-high-Pt-Pd Zones consist mainly of sulfide- and chromite-free harzburgite and orthopyroxenite. These mineralized rocks do not show any distinctive texture or change in modal composition. The Sulfide Zone and low-S-high-Pt-Pd Zons have distinct PGE distribution. The Sulfide Zone has Pt/Pd ratios of 0.52 and a positive correlation between PGE and S. The low-S-high-Pt-Pd Zones have Pt/Pd ratios of 1.2 and depletion in IPGE relative to primitive mantle. The platinum-group minerals (PGM) observed in the Sulfide Zone are predominantly Pt-Pd-bismuthtellurides, stanides and arsenides, mainly enclosed within sulfide minerals. In contrast, the PGM observed in low-S-high-Pt-Pd Zones are mainly Pt-arsenides, stannides and antimonides, mostly enclosed within alteration silicates. Differences in texture, geochemistry and PGM assemblage between these mineralization styles suggest that they originated from distinct geological processes. The Sulfide Zone was formed by a major event of segregation of an immiscible sulfide liquid, whereas the low-S-high-Pt-Pd Zones formed by a sulfide liquid saturation followed by sulfur loss during post-magmatic alteration. The identification of PGE-rich layers in rocks without sulfides or chromite at the Carajás Mineral Province is important as these may have been overlooked during previous exploration programs.

Formation of the main sulfide zone at Unki Mine, Shurugwi Subchamber of the Great Dyke, Zimbabwe: Constraints from petrography and sulfide compositions

AbstractThe major platinum group element (PGE) occurrence in the Great Dyke of Zimbabwe, the main sulfide zone, is a tabular stratabound layer hosted in pyroxenites, and it is broadly similar in form throughout the length of the Great Dyke. We conducted a petrographic and sulfide composition study on a sulfide-enriched zone from the contact of the mafic sequence–ultramafic sequence through the main sulfide zone at Unki Mine in the Shurugwi Subchamber to its underlying footwall rocks to place some constraints on the origin of the rocks.Pyrrhotite, pentlandite, chalcopyrite, and pyrite are the base metal sulfides that were encountered during the study. Pyrrhotite, pentlandite, and chalcopyrite typically occurred as inclusions in both primary (orthopyroxene, plagioclase, and clinopyroxene) and secondary (amphibole and chlorite) silicate phases, whereas pyrite was observed in only three samples, where it occurred in association with pyrrhotite. The concentrations of PGEs in the base metal sulfides were nearly all at or below minimum detection limits. The intercumulus nature of some of these sulfides in the investigated sequence suggests that they were likely formed during the crystallization history of these rocks. The occurrence of pyrite, which we interpret to be an alteration phase, suggests that a late-stage event, likely formed during hydrothermal alteration, helped to concentrate the mineralization at Unki Mine. In some cases, however, these sulfides occur partially surrounding some chromite and silicate phases. Thus, some sulfides in the Unki Mine area were likely formed early in the crystallization history of the Great Dyke, whereas others were formed late during hydrothermal processes. Low concentrations of PGEs such as platinum (Pt), palladium (Pd), and rhodium (Rh) in base metal sulfides imply that the PGEs in the main sulfide zone and Unki Mine are hosted either in silicates and/or platinum group minerals. Very low Co contents in pentlandites in the rocks under investigation are interpreted to imply that very limited Fe substitution by Co, and also of Ni by Co, occurred. Broadly comparable trends, with minor variations of Fe in pyrrhotite, of Co and Ni in pentlandite, and of Cu in chalcopyrite, for example, likely reflect magmatic processes. The concentrations of these metals in base metal sulfides vary sympathetically, indicating that their original magmatic signatures were subsequently affected by hydrothermal fluids. The spiked pattern displayed by the variations in the percent modal proportions of the base metal sulfides across the entire investigated stratigraphic section is interpreted to reflect remobilization of the sulfides during hydrothermal alteration. Depletions in some elements, which occur near the base and at the top of the investigated succession, are likely a result of this hydrothermal alteration.

Микроскопические грибы бассейна Чёрного моря: направления и перспективы исследований

Проанализирован 71 литературный источник, посвящённый изучению микроскопических грибов (микромицетов) Чёрного моря, за период с 1867 по 2018 г. В 1860-е и 1930-е гг. зафиксированы эпидемии морской травы Zostera marina, вызванные грибоподобными организмами рода Labyrinthula. В конце XIX — начале XX века также выявлено несколько случаев локального микоза морской травы. В 1960–2000-е гг. зарегистрированы эпизоотии беспозвоночных животных, вызванные грибами: Hyphochytrium peniliae поражал ветвистоусого рачка Penilia avirostris и вызывал его массовую гибель; гриб Leptolegnia pontica паразитировал на яйцах усоногого рачка Balanus improvisus и существенно сократил плодовитость популяции; вселение Ostracoblabe implexa привело к уничтожению популяций устрицы Ostrea edulis. В настоящее время отмечены единичные случаи поражения грибом O. edulis культивируемой устрицы Crassostrea gigas, спат которой привозят из других стран. На створках C. gigas и Mytilus galloprovincialis выделены грибы-эпибионты. В зрелых ооцитах M. galloprovincialis найдена микроспоридия Steinhausia mytilovum. На рыбах и в их внутренних органах обнаружены гифальные грибы и внутриклеточные паразиты — микроспоридии. На покровах бутылконосых дельфинов выявлены грибы. Проведены работы по изучению микобиоты пелагиали, бентали, целлюлозосодержащих субстратов, пены, перифитона, микро- и макроводорослей, морских трав. В настоящее время в бассейне Чёрного моря известно 435 видов грибов из 212 родов, 84 семейств, 50 порядков, 19 классов, 3 царств. В морской среде зафиксировано 372 вида, в пресной — 196, в гиперсолёных водоёмах — 31. В водной толще обнаружено 230 видов микромицетов (в сероводородной зоне — 21); в донных отложениях — 202 (в сероводородной зоне — 31); на древесине — 70; в перифитоне на стёклах и искусственной каменистой супралиторали (причалы, траверсы) — 30; в морской пене — 46; на/в моллюсках — 50; на коже дельфинов — 18; на макроводорослях — 116; на микроводорослях — 2; на морских травах — 38; на/в рыбах — 69; на/в ракообразных — 14. Количество видов, обнаруженных в прибрежных водах разных районов, составило: Грузии — 8 видов; г. Геленджика (Россия) — 56; полуострова Крым — 276; северо-западной части Чёрного моря — 177; Румынии — 112; Болгарии — 44; Турции — 9; р. Дунай — 238; о-ва Змеиный — 30. В настоящем обзоре рассмотрены работы по оценке способности грибов утилизировать целлюлозу, нефть, нефтепродукты, фенол, серу и вызывать коррозию металлов; проанализированы первые результаты исследований антимикробной активности факультативно и облигатно морских грибов Чёрного моря, а также способности микромицетов к люминесценции. Определены перспективные направления морских микологических исследований.

Stratigraphic setting and timing of the Montagne d’Or deposit, a unique Rhyacian Au-rich VMS deposit of the Guiana Shield, French Guiana

In French Guiana, the Montagne d’Or gold deposit (5 Moz at 1.5 g/t Au) is located in the northern branch of the Rhyacian Paramaca Greenstone Belt. The sulphide deposit is hosted by a south-facing bimodal volcanic and volcaniclastic sequence that is highly strained and affected by a penetrative E-W striking and steeply south-dipping foliation.The volcanic sequence is composed of three members, (1) the Lower unit in the stratigraphic footwall, (2) a bimodal mafic-felsic formation hosting the orebody, and (3) the Upper sedimentary and volcanic rocks unit in the stratigraphic hanging-wall. The bimodal formation is dominated by calc-alkaline felsic volcanic rocks in the west, interbedded/interdigitated with tholeiitic mafic rocks in the east. Pillowed mafic flows and graded-bedded felsic volcaniclastic rocks collectively indicate effusive to explosive volcanic activity in a submarine environment. The mineralization consists of thick and laterally extensive sulphide zones forming (1) stratiform sulphide disseminations, (2) structurally-transposed stringer stockworks, and (3) thin layers of deformed semi-massive sulphides. The gold-rich sulphide mineralization consists mainly of pyrite, pyrrhotite and chalcopyrite with minor sphalerite, magnetite, galena and arsenopyrite, hosted by chlorite-sericite-rich alteration zones mainly developed in the felsic tuff facies.U-Pb zircon geochronology shows that most of the Montagne d’Or volcanic and intrusive sequence has crystallized during a multi-cycle magmatic event, from ca. 2152 Ma to ca. 2130 Ma. A porphyry intrusion crosscutting the ore yields a U-Pb zircon age of 2117.6 ± 5.1 Ma, hence constraining a minimum age for the auriferous sulphide mineralization. This also indicates that the sulphide mineralization was coeval with arc magmatism, demonstrating the volcanogenic nature of the Montagne d’Or gold deposit.

Study of Generation and Underground Flow of Acid Mine Drainage in Waste Rock Pile in an Uranium Mine Using Electrical Resistivity Tomography

Mineral exploration is often associated with the generation of environmental liabilities, whose potential damages might imperil local water quality. An example of these environmental impacts is the acid mine drainage—AMD, caused by sulfides oxidation and production of acid and saline effluents. The analysis of critical areas with generation and spread of contamination plumes becomes more feasible due to the possibility to obtain geophysical models of water systems, especially to identify regions with accumulation of reactive minerals and preferential water flows. The rock-waste pile named BF-04 fits in this context of contamination, and it was studied based on the Electrical Resistivity Tomography technique, inversion models and isosurface models, providing conditions to recognize sulfide zones (> 10.1 mV/V), whereas chaotic high salt content underground flows, along several depths, were identified by low resistivity zones (< 75.8 Ω m). The complex behavior of groundwater flow in this kind of artificial granular aquifer is caused by its granulometric and lithologic heterogeneities, and compacted material. In addition, the results reveled a substantial water infiltration from Consulta creek, however the most critic zones for AMD generation are located at shallow levels where the waste rock material is more exposed to atmospheric O2 and meteoric water infiltration. The bedrock was not associated with significant low resistivity anomalies, which means that its contribution to AMD generation was considered relatively less important. The results will contribute to the environmental remediation management and also to demonstrate the potential applicability of geophysical methods in mining wastes.

О ТОНКОЙ СТРУКТУРЕ И ПРОИСХОЖДЕНИИ ИНТРУЗИЙ ЧЕРНОГО МОРЯ

The process of birth and drift of the Bosporus intrusions as simultaneous temperature and oxygen anomalies in the S-W part of the Black Sea was considered on the basis of data from 2 Argo bio-buoys. The erosion of the amplitude of the anomalies can be traced to a distance of 500 km from the Bosphorus. But in winter, buoys encounter anomalies of temperature and oxygen even further, moreover, both on the periphery of the sea and in the gyres. The parameters of these anomalies are contradictory: increased temperature says that these are Bosphorus intrusions that have been drifting at sea for several months. But they contain up to 20 μM of oxygen in the upper part of the hydrogen sulphide zone, which according to previous data has a life time in such conditions of only about 1 week. This implies local formation of anomalies due to poorly studied processes of winter subsurface water transfer. The author is inclined in favor of the second reason and calls on other researchers to pay attention to this.The process of birth and drift of the Bosporus intrusions as simultaneous temperature and oxygen anomalies in the S-W part of the Black Sea was considered on the basis of data from 2 Argo bio-buoys. The erosion of the amplitude of the anomalies can be traced to a distance of 500 km from the Bosphorus. But in winter, buoys encounter anomalies of temperature and oxygen even further, moreover, both on the periphery of the sea and in the gyres. The parameters of these anomalies are contradictory: increased temperature says that these are Bosphorus intrusions that have been drifting at sea for several months. But they contain up to 20 μM of oxygen in the upper part of the hydrogen sulphide zone, which according to previous data has a life time in such conditions of only about 1 week. This implies local formation of anomalies due to poorly studied processes of winter subsurface water transfer. The author is inclined in favor of the second reason and calls on other researchers to pay attention to this.

The Influence of CO2 on the Solubility of Quartz in Single-Phase Hydrothermal Fluids: Implications for the Formation of Stockwork Veins in Porphyry Copper Deposits

Abstract Porphyry copper deposits consist of low-grade stockwork and disseminated sulfide zones that contain characteristic vein generations formed during the evolution of the hydrothermal systems. The present contribution examines the influence of variable CO2 concentrations on the solubility of quartz in single-phase hydrothermal fluids forming stockwork veins in porphyry deposits at temperatures of 150° to 550°C and pressures ranging from 100 to 2,000 bar at concentrations up to 8 mol % CO2. The calculations demonstrate that quartz solubility in hydrothermal fluids decreases with increasing CO2 content. Retrograde quartz solubility is less pronounced in CO2-bearing fluids and is not observed in single-phase fluids having CO2 concentrations exceeding 6 mol %. Despite the effects of CO2, retrograde quartz solubility plays an important role in the formation of porphyry stockwork veins that contain little or no quartz as a gangue mineral. At high temperatures and lithostatic pressure conditions below 900 bar, early biotite veins can form as a result of quasi-isobaric cooling of single-phase hydrothermal fluids under conditions of retrograde quartz solubility or near-constant quartz solubility. Stock-work veins consisting of molybdenite or hypogene copper sulfide minerals lacking quartz could form at temperatures of up to 450°C under hydrostatic pressures ranging from ~250 to 900 bar. In the presence of CO2, retrograde quartz solubility is shifted toward slightly lower temperatures at constant pressure. At temperatures below ≾375°C, quartz is precipitated during quasi-isobaric cooling irrespective of CO2 content of the hydrothermal fluids, resulting in the formation of late porphyry quartz veins.

Geostatistical estimation to delineate oxide and sulfide zones using geophysical data; a case study of Chahar Bakhshi vein-type gold deposit, NE Iran

Delineation of oxide and sulfide zones in mineral deposits, especially in gold deposits, is one of the most essential steps in an exploration project that has been traditionally carried out using the drilling results. Since in most mineral exploration projects there is a limited drilling dataset, application of geophysical data can reduce the error in delineation of the sulfide and oxide zones. For this purpose, we produced a 3D model of Induced Polarization (IP) data using the ordinary kriging technique. Then the modelling results were compared with the drilling data. The results obtained showed that the 3D geophysical models would properly delineate the sulfide and oxides zones. This work presents a new application of the IP results for separation of these zones. In addition, the conducted variography in this work suggests reducing the profile spacing of dipole-dipole IP arrays down to 25 m. This would properly enrich the integration of geophysical and geological results in the modelling of gold deposits.

Phytoplankton biomass, primary production and chemoautotrophic production of the Western Black Sea in April 2003

Abstract The multilayered surface waters of the Black Sea contain aerobic, suboxic and anoxic layers that support both photoautotrophic (PP) and chemoautotrophic (ChP) biological production. During the R/V Knorr cruise from 15 to 25 April 2003, phytoplankton biomass (represented as chlorophyll-a), photoautotrophic and chemoautotrophic production (ChP) rates were determined in the southwestern Black Sea. Surface Chl-a concentrations ranged from 0.06 and 0.62 μg/ l for the whole study area. These low values suggest post-bloom conditions. Integrated chlorophyll-a concentrations in the euphotic zone were as low as 2.4 mg m−2 in the central gyre, while they were as high as 22 mg m−2 in the Rim current. Integrated photoautotrophic production rates ranged from 70 to 664 mgC m−2 d−1. The lowest values were observed in the western central gyre and the highest values were found at the regions around Sakarya Canyon. Integrated ChP rates were 282 and 1013 mgC m−2 d−1, which were equivalent to 45% and 83% of the overall water-column production for the central gyre and Rim current regions, respectively. Maximum rates are observed in the upper layer of the sulfide zone. The highest values of integrated ChP were in the vicinity of the Sakarya shelf and Rim current region. Extremely high values of ChP can occur in the Black Sea and appear to be driven by oxygen ventilation and redox cycling.

Microthermometric evidence for the formation of Permian VHMS deposits in Tasik Chini area, Central Belt of Peninsular Malaysia

The VHMS deposits of Tasik Chini area are located in the Pahang State of Central Belt, Peninsular Malaysia. The deposits occur in a package of Permian volcanics within mixed volcano-sedimentary sequence, and have been exploited from the Bukit Botol and Bukit Ketaya deposits. They have many similarities with Kuroko-style massive sulfide deposits. The host rocks at both deposits are felsic volcanic rocks of rhyolitic to rhyodacitic composition. Mineralization occurs as distinct ore zonation forming a stringer to massive sulfide zone at the footwall followed by barite lenses and exhalite layers (Fe + Mn ± Si ore) at the stratigraphic top. The sulfide phases are characterized by pyrite as the major sulfide mineral, with subordinate chalcopyrite, sphalerite and rare galena; traces of gold, silver- and Sn-bearing minerals occur in the massive sulfide and barite ores. Primary fluid inclusions within quartz and barite occur as two types: (1) type I: two phase, liquid-vapour inclusions without daughter minerals, and (2) type II: three phase, liquid CO2-bearing carbonic inclusions. These three phase inclusions include liquid H2O, liquid CO2 and vapour CO2, with variable CO2 content, and often decrepitate before complete homogenization. Microthermometric measurements of the type I inclusions show that the temperature of homogenization (Th) varies between 180 °C and 310 °C with salinities ranging from 1.0 to 15.0 wt% NaCl equivalent in the quartz samples. Homogenization temperatures (Th) of 190 °C to 300 °C and salinities between 1.0 and 13.0 wt% NaCl equivalent are recorded from the barite samples. Type II inclusions have an initial melting temperature range of −57.1 °C to −57.5 °C, clathrate melting temperature (Tmclathrate) of 7.4 °C to 8.0 °C and CO2 homogenization temperature (ThCO2) between 30.1 °C and 30.3 °C, and salinity ranging from 4.0 to 5.1 wt% NaCl equivalent. Densities, pressure and depth of ore forming fluids range from 0.711 to 0.970 g/cm3, 12 to 93 bars, and ∼1500 m depth of seawater. Laser Raman spectroscopic analysis shows the presence of CO2 in the carbonic inclusions. The fluid inclusion results suggest that the main ore fluid during the formation of the Tasik Chini VHMS deposit is a seawater-dominated fluid, but contribution from a modified seawater or possibly magmatic origin is also indicated by higher salinities relative to seawater (3.2 wt% NaCl) and the presence of CO2. Taking into account the regional geodynamic evolution, it is also concluded that the formation of VHMS deposits in the Tasik Chini area occurred in a back-arc geotectonic setting.

The Lower Banded series of the Stillwater Complex, Montana: whole-rock lithophile, chalcophile, and platinum-group element distributions

The principal rock types of the Lower Banded series of the Stillwater Complex are gabbronorite and norite with minor troctolite and anorthosite. The whole-rock composition is largely controlled by the cumulate minerals plagioclase and pyroxene (±olivine). The rocks are very poor in incompatible elements, at the 0.1 to 2 times mantle levels, indicating < 10% liquid fraction. The Pd and Pt are enriched in a layer known as the J-M Reef which occurs in a zone containing olivine-bearing rocks (OB I). This zone contains the same rock types as the rest of the Lower Banded series, but troctolite, olivine gabbronorite, and anorthosite are more abundant in OB I. The concentrations of lithophile elements in OB I are similar to the rocks above and below OB I. In particular, the reef rocks show no additional signs of continental crust contamination such as additional Th or LREE enrichment, and the reef rocks are not enriched in incompatible elements. The strongly chalcophile elements Cu, Ni, Se, Bi, and Au all correlate with S, indicating that these elements are controlled by sulfides. The PGE show two trends. The rocks below the J-M Reef and the reef rocks have high PGE+Au to S ratios and fall on a single trend, whereas those above the reef have low metal to S ratios. These low ratios for the rocks above the reef could arise because the magma was depleted in PGE+Au as it had already segregated some PGE+Au-rich sulfides. The relatively high PGE, Au, Cu, and Se concentrations of the rocks below the reef imply that the rocks contain ~ 0.1 wt% cumulate sulfides. However, they have very low S contents (< 300 ppm). The low S/Se ratios of these rocks (< 2000) and most of the rocks outside of the reef suggest that they have lost more than half of their S. The Pd/Pt and Pd/Ir ratios of the reef (~ 3.4 and 800, respectively) are much higher than those of the rocks below and above the reef. The high Pd/Pt and Pd/Ir ratios of the reef imply that the sulfides formed from a fractionated magma; however, there is no correlation between the Pd/Ir and Pd/Pt ratios and the host rock type. These ratios are dissimilar to the Bushveld reefs and the Main Sulfide Zone of the Great Dyke. They more closely resemble the reefs in more fractionated rocks such as the AP Reef of the Penikat Intrusion, the Roby Zone of the Lac des Iles Complex, or the disseminated sulfides of the Noril’sk I intrusion. The very high Pd/S and low Cu/Pd ratios of the J-M Reef require that the sulfides collected Pd from a very large volume of magma. None of the current models is entirely satisfactory; however, we favor a model where at depth the OB1 magma partially melted a komatiitic massive sulfide and then transported the sulfide droplets into the magma chamber at the level of the J-M reef.

On the possible presence of oxygen in the upper sediment layer of the hydrogen sulfide zone in the Black Sea

In the northeastern Black Sea the search was performed for living eukaryotic organisms (micro- and meiobenthos) in hypoxic and anoxic conditions as well as measurement of O2 in the bottom water layer and in the upper layer of sediments. The results have shown the presence of a deep maximum abundance of zoobenthos in a depth range of 215–244 m. This aggregation of benthic fauna occupies a layer of 30 m along the vertical. In general, the proportion of active meiobenthos was no greater than 1.5% of the total number of organisms recorded from the sample.The presence of aerobic benthos near the upper boundary of the H2S zone can be explained by: sliding down of sediments from a higher depth; quasi-periodic O2 supply due to fluctuations in the position of the isopycna and/or sinking of waters downslope in the bottom Ekman layer. Also, in the case of physical entry of oxygen into the bottom layer, it can remain for a relatively long time in the upper part of the H2S zone due to the lack of deep Mn+2 flux and reaction with it.

Geology and Geochemistry of the giant Huoshaoyun zinc-lead deposit, Karakorum Range, northwestern Tibet

The recently discovered giant Huoshaoyun zinc-lead deposit in the Karakorum Range, northwestern Tibet, China, consists of a major zinc-lead carbonate and a minor lead-dominant sulfide mineralization with metal reserves of zinc and lead of over 16 million tonnes. The zinc-lead carbonate mineralization is composed of smithsonite and cerussite, with laminated, massive, veined and botryoidal textures, showing sedimentary and metasomatic structures. The lead-dominant sulfide mineralization is composed mainly of galena and minor sphalerite and pyrite, with laminated, brecciated, and veined textures. The laminated sulfide mineralized zones occur at the top of the deposit, whereas the zinc-lead carbonate mineralized bodies are located below the sulfide zones. Lead-dominant sulfide veins cut the zinc-lead carbonate ores and the host limestone. The sequence of formation of the lead-zinc ores with various mineral colors in thin sections is as follows: (1) light-colored to yellowish, fine- to coarse- and subhedral to euhedral smithsonite; (2) yellowish to reddish, fine- to coarse- and subhedral to euhedral smithsonite; (3) light-colored veined smithsonite; (4) white coarse-grained, xenomorphic cerussite; (5) colorless euhedral to sub-angular quartz crystals; (6) euhedral to anhedral lead-zinc sulfides and gypsum. The mineralization events of the Huoshaoyun deposit are: (1) early hydrothermal sedimentary smithsonite mineralization; (2) hydrothermal replacive smithsonite mineralization; (3) vein-type smithsonite mineralization; (4) open space filling and replacive cerussite mineralization; (5) lead-zinc sulfide mineralization. The fluid inclusions of cerussite indicate that the hydrothermal fluids of the cerussite ore-forming stage are characterized by a temperature range of at least 186–206 °C and low salinities (0.7–1.2 wt% NaCl eq.). The source of oxygen and carbon for the zinc-lead carbonate mineralization is possibly consistent with the involvement of marine water and a magmatic fluid, and is probably dominated by the magmatic fluid. The source of sulfur for the lead-dominant sulfide mineralization is possibly related to a magma reservoir. The zinc-lead-carbonate portion of the deposit represents a primary hypogene non-sulfide mineralization.