Mica Alteration Research Articles

Rochas portadoras de glauconita como fonte alternativa de potássio para fertilizantes por processamento térmico com aditivos

Glauconite (K,Na) (Fe,Al,Mg) 2 (Si,Al) 4 O 10 (OH) 2 is a green, potassium and iron hydrated phyllosilicate, monoclinic mineral. It is a secondary mineral formed from the alteration of iron-rich micas, such as biotite. It is a potential source of potassium, but still not commercialized due to lack of commercial technology that makes the business viable. The objective of this work was to evaluate the reactivity, in relation to the release of potassium, from a glauconite-containing rock, subjected to thermal alteration, with additives, at two temperatures: 800°C &900°C. The source of glauconite was the Verdete that occurs in Serra da Saudade, in the region of the municipality of Cedro de Abaete, state of Minas Gerais, Brazil. The following additives were used:CaSO 4 .2H 2 O, CaCO 3 and Na 2 SO 4 ,at the mass ratio with respect to the rock: (1.0: 0.2: 0.3: 0.2). Thermal alteration was performed at 800°C&900°C. After thermal alteration, the calcined samples were leached with 20% sulfuric acid (m/m). The final product was a solution containing K 2 SO 4 . At the temperature of 800°C, the potassium released reached only 11.2%. Increasing the temperature to 900°C, the extraction incresed to 40%. There was a tendency for increased potassium release at temperatures higher than 900°C. These findings highlight gave the potential forglauconite to be exploited as an alternative source of potassium for the production of fertilizer, by thermal processing with sulfating compounds.

Provenance and diagenesis of Guamá Sandstone, northeastern Pará, Brazil: A Silurian link between the Amazonas and Parnaíba basins

The Guamá Sandstone, exposed in small isolated outcrops in the northeastern region of the State of Pará (Brazil), which are surrounded by Cenozoic sediments, represents a Silurian relic of the Amazonas and Parnaiba basins connected during the Paleozoic and separated only since the Triassic period through the development of the Marajó Basin. Previous outcrop-based studies showed that the Guamá Sandstone is a fine to medium-grained quartzarenite, with high compositional and textural maturity, which was deposited in a coastal marine setting (foreshore/shoreface), correlatable with the environment of the Silurian Nhamundá Formation of the Amazonas Basin. The principal primary sources of the sandstone are associated with rocks formed during the Transamazonico and Brasiliano Cycles according to isotopic dating of zircon. In order to better understand provenance and diagenesis of the Guamá Sandstone core samples of a 50 m deep bore hole, located 6 km north of the town of São Miguel do Guamá, have been studied. The sandstone is usually bioturbated and massive, but planar stratification (foreshore) and cross bedding (shoreface), the latter in the lower part of the profile, are also present indicating a transgressive to regressive coastline. In addition to quartz, the Guamá Sandstone is composed of the following detrital accessory minerals: zircon, tourmaline, rutile, epidote, mica, ilmenite and chromite while kamacite occurred only sporadically indicating, at least for the latter, origin from Fe-Ni-meteorites. Provenance data obtained from the composition of zircon and tourmaline grains, as well as from internal textures of zircon, point to primary igneous and metamorphic source rocks of the Guamá Sandstone. While zircon is principally of magmatic origin, tourmaline grains are derived dominantly from metapelitic, metapsammitic and granitoid rocks. However, pre-existing sediments probably represent, to a lesser extent, the ultimate direct source as suggested by the well-rounded grains of the quartz arenite and worn tourmaline overgrowths. The diagenetic phases of the sandstone include syntaxial quartz overgrowths, microquartz, kaolinite booklets, illite and anatase. The quartz overgrowths are pseudo-zoned and engulf parts of the kaolinite booklets. These may be surrounded by microquartz which usually replaced quartz overgrowths. Illite, which is rare, is probably the product of replacement of kaolinite, and anatase may be related to partial dissolution of ilmenite. The main diagenetic processes including precipitation of quartz and kaolinite began during eodiagenesis, in shallow burial conditions, and proceeded through mesodiagenesis as suggested by multi-episodic quartz zoning and formation of illite. The early precipitation of kaolinite is related to alteration of feldspar and mica caused through flushing of meteoric water during forced marine regression and uplift, probably still in Silurian time. The sources for quartz cementation may include kaolinitization of feldspar and pressure dissolution, the latter associated to concavo-convex and sutured grain contacts, although these types of contact are relatively rare. Therefore, external silica-rich solutions likely occurred.

Application of SWIR spectrometry to the determination of biotite compositions in hydrothermally altered units of the Yangyang iron-oxide-apatite (IOA) deposit, South Korea

The Yangyang iron oxide-apatite deposit in South Korea has gone through multiple events for igneous activity, structural evolution, hydrothermal alteration, and mineralization. Trioctahedral mica is indicative of potassic alteration in the Yangyang IOA deposit and its mineral chemistry is quite variable. The variability can be described in terms of biotite colors and short wavelength infrared (SWIR) reflectance spectra. Brown to greenish brown biotite displays lower values of Mg# (0.48–0.58) than green biotite (0.62–0.78), whereas colorless phlogopite related to Fe–P mineralization has the highest values of Mg# (0.85–0.95). To compare Mg# values with the positions and intensities of absorption in the trioctahedral micas, we used three types of spectrum: reflectance, hull quotient, and Gaussian. Brown biotite produces a short Mg–OH peak near 2340 nm, green biotite has a peak near 2330 nm, and colorless phlogopite displays an absorption peak near 2310 nm. These positional variations are consistent with compositional changes. A mica alteration index (MAI) represents the ratio of Fe–OH and Mg–OH peak absorption intensities for trioctahedral micas. From brown to green biotite and colorless phlogopite, the MAI values gradually increase with decreasing Fe–OH intensity. Correlation coefficients for plots of Mg–OH absorption values vs. Mg# vary from 0.89 for the reflectance method, to 0.93 for the hull quotient method, and 0.93 for the Gaussian method, and for plots of MAI vs. Mg# they vary from 0.91 for the reflectance method, to 0.92 for the hull quotient method, and 0.92 for the Gaussian method. Analyses using our new SWIR spectroscopic methods confirm that the abundance of indicator minerals and the Fe:Mg ratios in trioctahedral micas vary systematically as a function of hydrothermal fluid chemistry and mineral composition within the altered lithologies. SWIR spectroscopy of trioctahedral micas could provide a useful tool for mapping vectors of alteration in the Yangyang IOA system.

Mapping white mica alteration associated with the Jiama porphyry-skarn Cu deposit, central Tibet using field SWIR spectrometry

Field measurement of the short-wave infrared (SWIR) reflectance from drill hole samples proved to be an effective method to map variations in white mica composition (Tschermak substitution) associated with hydrothermal alteration zonation of the Jiama porphyry-skarn Cu deposit, Tibetan Plateau, China. This SWIR mineral spectral information provides geological insights into: (a) the possible nature of the related magmatic intrusions. (b) the physicochemistry of the associated hydrothermal fluids; (c) the interactions between these fluids and country rocks; and (d) potential vectors to economic mineralization. The results suggest that the Al-OH band wavelength of white mica can used as an indicator in the subsequent steps of prospecting.

Diagenesis of tight oil sand reservoirs: Upper Triassic tight sandstones of Yanchang Formation in Ordos Basin, China

Upper Triassic sandstones in the Ordos Basin, northern‐central China, comprise tight oil reservoirs. Using a combination of thin sections, SEM, BSE, EDS, XRD, and fluid inclusion analyses, 24 core samples from 13 wells were collected to study the petrology, paragenesis, and diagenetic processes and implications for reservoir quality. Quartz cement usually occurs as overgrowths or euhedral quartz. Extensive dissolution and albitization of K‐feldspar can be observed. Five types of carbonate cements, ferrocalcite, ankerite, dolomite, calcite, and siderite, occur during different diagenetic stages. Two main types of illite and 5 main habits of chlorite are observed in this study. Kaolinite mainly occurs as booklets and vermicular aggregates. Diagenetic illite, chlorite, biotite, mixed‐layer illite/smectite (I/S), and other minor minerals are also observed. The diagenetic processes include compaction, alteration of volcanic materials and mica, clay mineral transformation, cementation (silica, aluminosilicate, and carbonate), and dissolution of feldspars and rock fragments. Compaction was a significant porosity‐reducing agent, and the presence of carbonate cement exerts a dominant impact on the reduction of porosity. Quartz cement and authigenic clays are less important; however, it is worth mentioning that pore‐lining clays are conducive to porosity preservation. In this study, most of the porosity variation is caused by a combination of compaction, carbonate cements, quartz cement, and authigenic clays. This study gives insights into diagenetic alterations within tight sandstones and has implications for reservoir quality prediction in similar settings.

Mapping of diagenetic processes in sandstones using imaging spectroscopy: A case study of the Utrillas Formation, Burgos, Spain

Imaging spectroscopy is applied to sandstone formation to study diagenetic processes in sedimentary deposits. The study was carried out on the upper member of the Utrillas Formation in Spain. Shortwave infrared and visible near-infrared Specim® hyperspectral cameras were used to scan near-vertical and well-exposed outcrop walls. Reflectance spectra from close-range hyperspectral imaging was compared with high-resolution laboratory spectra, hyperspectral imagining data, thin sections, and results of previous sedimentological studies to analyze geochemical variations and quantify facies and diagenetic mineral abundances.Distinctive characteristics of the absorption features of clay minerals were used to develop a kaolinite crystallinity index to identify detrital kaolinite and authigenic kaolinite in the Utrillas Formation. Results show that poorly ordered kaolinite is only present in floodplain deposits, whereas well-ordered authigenic kaolinite is related to paleochannel deposits and organic-rich irregular patches. Meteoric water flux probably induced feldspar and mica alteration, as well as authigenic clays precipitation. Contemporary microbial degradation of organic matter in the subsurface might be the cause of authigenic clay formation at the alteration areas. This study provides new data and interpretation on diagenetic alterations of the Utrillas Formation. Results of this work may have important implications in the mining industry as a methodology to evaluate mining areas of interest.

Multiple Gold Mineralizing Styles in the Northern Pataz District, Peru

Gold production from the northern Pataz district in the eastern Andean Cordillera of Peru has been sourced mainly from mesothermal quartz-carbonate-sulfide veins hosted by the Mississippian Pataz batholith. Gold is also found in basement-hosted veins underlying the batholith, in the Vijus-Santa Filomena area of the district. Both are located within a central horst; similar vein mineralogy and proximal phengitic white mica alteration are common to both. However, comb-textured quartz, the chemical compositions of bulk ore and sulfide minerals, and the presence of barite and siderite veins suggest that the basement-hosted veins formed at a shallower crustal level. Similar expressions of hydrothermal alteration associated with anomalous gold, As, Sb, and Tl are also present in the adjacent Lavasen graben, where alteration is intimately associated with volcanic processes that deposited the Mississippian Lavasen Volcanics. K-Ar and 40 Ar- 39 Ar ages for hydrothermal illite from all three locations range between Mississippian and Late Triassic but are consistent with a single Mississippian hydrothermal event, if the data record a minimum age for original illite formation. The geologic setting, mineralization styles, and chemical data suggest a range of crustal depths, ranging from mesothermal batholith-hosted veins through shallow to intermediate depths for the Vijus-Santa Filomena area to a near-surface epithermal setting for the Misquichilca area. Telescoping of this 10- to 13-km crustal range into a 3-km topographic section of the Andes is attributed to syn- and postmineralization uplift and erosion. Sulfide-rich high-grade ore shoots and moderately saline fluid inclusions in the batholith-hosted veins are inconsistent with the original orogenic gold model and suggest a magmatic source component for the ore fluid, consistent with stable isotope (O, H, C, and S) compositions of quartz, illite, carbonates, and sulfides. The isotopic data suggest a mixed magmatic-meteoric ore fluid in the basement-hosted deposits of the Vijus-Santa Filomena area and the volcanic-hosted Misquichilca area. Both the Pataz batholith and the Esperanza Subvolcanic Complex are of the same Mississippian age as the hydrothermal alteration and mineralization. The Esperanza Subvolcanic Complex, comagmatic with the Lavasen Volcanics, contains cognate mineral clots from which a subjacent magma chamber can be inferred. It exhibits potassic, calc-silicate, and argillic alteration, and evidence for the evolution of an Fe-rich volatile phase. The Lavasen-Esperanza magma suite is ferroan and weakly alkaline, with A-type affinities. These features provide a conceptual genetic link with hydrothermal alteration associated with gold mineralization, including Fe (±As) sulfides, phengitic white mica, celadonite, Fe-rich carbonates, and less common Fe oxides. An oxidized intrusion-related model is proposed for gold and hydrothermal alteration in the northern Pataz district.

Genesis of smectite in siliciclastics and pyroclastics of the Eocene İslambeyli Formation in the Lalapaşa region, NW Thrace, Turkey

AbstractThe Eocene İslambeyli Formation in the Lalapaşa region (NW Thrace, Turkey) consists predominantly of siliciclastic clayey clastics at the bottom and of claystone, tuff and tuffaceous claystone/ sandstone/limestone in the middle and uppermost parts of this formation. Some tuff-tuffaceous beds of the middle–upper parts of the formation are economically viable bentonite depoits. The İslambeyli Formation exhibits vertical variations in the mineralogy, elemental compositions, and smectite-forming processes. Smectite was formed by weathering and diagenetic processes in the fluvial-shore environments in the lower part and by diagenetic alteration in a shallow-marine environment in the middle–upper parts of the formation. Ca-smectite flakes were formed by two processes: direct precipitation; and by means of a dissolution-precipitation mechanism from feldspar and mica. Dissolution-precipitation was most prevalent in the siliciclastic lower part of the formation. The amounts of Al, Fe, Mg and Ca required to form smectite and accessory illite were supplied mainly from the alteration of feldspars, mica and glass shards. The origin of smectite can also be explained by the inferred solution compositions given the parent phases in this formation, and the devitrification of glass shards in pyroclastic-rich middle–upper parts of the formation. In the upper beds, the observed decrease of K and Fe in the smectite structure coincided with both the increase in the amount of smectite and the increase in solution pH suggesting that precipitation of smectite developed over a prolonged period and under arid conditions.

Gold mineralisations in the Canan area, Lepaguare District, east-central Honduras: Fluid inclusions and geochemical constraints on gold deposition

Gold mineralisations in the Canan area (Honduras) occur within altered metamorphic rocks crossed by quartz veins which filled the fractures where the hydrothermal fluids carrying gold flowed. Quartz crystals of the veins contain abundant fluid inclusions which have been divided into four main types on the basis of the petrographic features and microthermometric data. The association of L-rich and V-rich inclusions with the same major components supports boiling at the time of entrapment. The trapped hydrothermal fluid consists of an aqueous solution (0.9–4.8wt.% NaCl equivalent) plus a CO2–CH4-bearing bubble. Some fluid inclusions contain graphite of hydrothermal origin. Microthermometric and spectroscopic data on fluid inclusions indicate that hydrothermal fluids carrying gold were at T=300°C, P=500–1400bar, log fO2~−37.6±2.5 and with a pH value of 2.9±0.4. Large amounts of sulphides (mainly pyrite) are associated with gold. We infer that Au was transported as Au–S complex, in particular as Au(HS)°. The activity of sulphur in the hydrothermal fluids was at least 10−2. The precipitation of gold can be related to several processes that reduced the stability of AuHS°: 1) boiling and vapour loss following the pressure drop caused both by fracture opening and fluid uprise, 2) sulphidation as a result of the presence of Fe2+ (and other metal cations) from the mineralogical alteration (mainly of biotite and chlorite) in the wall-rocks and 3) hydrothermal alteration of feldspars and micas into kaolinite and diaspore with increase in pH of the hydrothermal fluids. The mineralogical, petrological, geochemical features and the geological setting are broadly consistent with those of orogenic-type gold deposits.

Rio Tinto (Iberian Pyrite Belt): a world-class mineral field reopens

The deposits of Rio Tinto are located in the Spanish segment of the Iberian Pyrite Belt and are hosted within felsic porphyritic volcanic rocks and tuffs. The orebodies comprise a spectrum from sedimentary exhalative (San Antonio) to sub-sea floor replacement of the volcanic host rocks (Filon Norte); the two largest masses (San Dionisio and Filon Sur) are closely associated with black shale and probably formed by partial replacement of these units in an anoxic setting. Alteration associated with ore deposition is typified by marginal sericitic (white mica) alteration, and central chloritisation and silicification in a multi-phase alteration history. Structures formed during initial plate convergence may have acted as controls on ore deposition, and evidence of such controls is retained in the distribution of various elements in the sulphide deposits. Tectonism followed the mineralisation, and overprinted previous extensional events and resulted in the development of slaty cleavage in the pelitic rocks with partial remobilisation of sulphides, and tight folds with associated shearing of the southern limb.

Strain accumulation and fluid–rock interaction in a naturally deformed diamictite, Willard thrust system, Utah (USA): Implications for crustal rheology and strain softening

Structural and geochemical patterns of heterogeneously deformed diamictite in northern Utah (USA) record interrelations between strain accumulation, fluid–rock interaction, and softening processes across a major fault (Willard thrust). Different clast types in the diamictite have varying shape fabrics related to competence contrasts with estimated effective viscosity ratios relative to micaceous matrix of: ∼6 and 8 for large quartzite clasts respectively in the Willard hanging wall and footwall; ∼5 and 2 for less altered and more altered granitic clasts respectively in the hanging wall and footwall; and ∼1 for micaceous clasts that approximate matrix strain. Within the footwall, matrix X–Z strain ratios increase from ∼2 to 8 westward along a distinct deformation gradient. Microstructures record widespread mass transfer, alteration of feldspar to mica, and dislocation creep of quartz within matrix and clasts. Fluid influx along microcracks and mesoscopic vein networks increased westward and led to reaction softening and hydrolytic weakening, in conjunction with textural softening from alignment of muscovite aggregates. Consistent Si, Al, and Ti concentrations between matrix, granitic clasts, and protoliths indicate limited volume change. Mg gain and Na loss reflect alteration of feldspar to phengitic muscovite. Within the hanging wall, strain is overall lower with matrix X–Z strain ratios of ∼2 to 4. Microstructures record mass transfer and dislocation creep concentrated in the matrix. Greater Al and Ti concentrations and lower Si concentrations in matrix indicate volume loss by quartz dissolution. Na gain in granitic clasts reflects albitization. Large granitic clasts have less mica alteration and greater competence compared to smaller clasts. Differences in strain and alteration patterns across the Willard thrust fault suggest overall downward (up-temperature) fluid flow in the hanging wall and upward (down-temperature) fluid flow in the footwall.

Paragenesis, Stable Isotopes, and Molybdenite Re-Os Isotope Age of the Lala Iron-Copper Deposit, Southwest China

The Lala Fe-Cu deposit in the Kangdian iron oxide copper-gold (IOCG) metallogenic province, SW China, is hosted in the Paleoproterozoic Hekou Group. This volcanic-sedimentary sequence has undergone upper greenschist-lower amphibolite facies metamorphism at ~850 Ma. The deposit contains more than 200 million metric tons (Mt) of Fe-Cu ores with an average grade of 13 wt % Fe and 0.92 wt % Cu. Orebodies are roughly strata bound but occur along foliation, lithologic contacts, and shear zones. The paragenetic sequence of the Lala deposit includes metamorphosed (I, II, and III) and unmetamorphosed (IV and V) stages. Stage I is characterized by extensively pervasive Na alteration, forming abundant albite but minor scapolite. Stage II occurs as massive and banded replacements, consists of Ti-V–poor magnetite and apatite with minor disseminated sulfide minerals, and was associated with pervasive K-Fe alterations forming K-feldspar, chlorite, and actinolite. Stage III occurs predominantly as bands and disseminations confined along foliations with minor veinlets cross-cutting hosting rocks. This stage is characterized by abundant Fe-Cu-Mo sulfides intergrown with angular magnetite and minor titanite and allanite and is associated with alteration of carbonate, quartz, fluorite, and mica. Stage IV has an assemblage dominated by chalcopyrite with variable pyrite and bornite, occurring as veins of sulfides + quartz + calcite + biotite ± muscovite ± fluorite. Stage V occurs chiefly as veins of hematite ± calcite ± quartz and also results in extensive hematization. Stages II and III have fluids with high δ 18 O (7.2–11.7‰) and δ 34 S values (0–4‰), indicative of a magmatic-hydrothermal origin. However, the stage III fluids have δ 34 C values (~0.5‰) close to the least altered marble (0–2‰) of the hosting rocks, indicating a possible contribution of strata-sourced carbon. The stage IV fluids have δ 34 C values similar to and δ 18 O (4.1–6.7‰) lower than the stage III fluids, and a wider range of δ 34 S values (−9.0 to +10.5‰), consistent with significant contributions of strata-sourced sulfur. Fluids of the late barren vein stage (V) have relatively low δ 34 C (−4.0 to −2.4‰) and δ 18 O values (−2.9 to +0.6‰), indicative of significant contributions of meteoric and oxidized fluids. Molybdenite from stage III has an Re-Os isotope age of 1086 ± 8 Ma, providing tight constraints on the timing of the main stage of mineralization. This age indicates that the Lala deposit is coeval with the ~1100 Ma intraplate magmatism in the western Yangtze Block. We propose that the majority of the Fe-Cu deposits in the Kangdian IOCG metallogenic province may have formed in an intraplate extensional setting, although it is possible that some of the deposits may have involved in multiple events including modification by the Neoproterozoic metamorphism forming the mineral assemblages of stage IV.

Influence of pH and temperature on the early stage of mica alteration

Mineral dissolution and precipitation reactions actively participate in controlling fluid chemistry during water–rock interaction. In this study, the changes in the biotite and muscovite basal surface nano-morphology were evaluated during interaction with fluids of different pH (pH = 1.1, 3.3 and 5.7) at different temperatures (T =2 5, 120, and 200 C). Results show that at the nanometre scale resolution of the atomic force microscope (AFM), dissolution generates etch pits with a stair-shaped pattern over the (0 0 1) surface. The flux of dissolved elements decreases when pH increases. However, at pH 5.7, a change was found in the flux after 42 h of reaction when abundant gibbsite and kaolinite coat the dissolving mineral surface. This phenomenon was widely observed at edges of the etch pits by AFM. It was also found that an increase in temperature produces an enhancement in the elemental flux in both micas. Dissolution regime changes after less than one day of interaction at high temperature because of abundant coating formation over the etch pits and edges. The results demonstrate the key role of nanometre size neogenic phases in the control of elemental flux from mica surfaces to solution. The formation of nanometre size coatings, blocking the sites active for dissolution, appears to control the alteration of phyllosilicates even at the early stage of the interaction.

Effects of extreme cold and aridity on soils and habitability: McMurdo Dry Valleys as an analogue for the Mars Phoenix landing site

AbstractThe McMurdo Dry Valleys are among the driest, coldest environments on Earth and are excellent analogues for the Martian northern plains. In preparation for the 2008 Phoenix Mars mission, we conducted an interdisciplinary investigation comparing the biological, mineralogical, chemical, and physical properties of wetter lower Taylor Valley (TV) soils to colder, drier University Valley (UV) soils. Our analyses were performed for each horizon from the surface to the ice table. In TV, clay-sized particle distribution and less abundant soluble salts both suggested vertical and possible horizontal transport by water, and microbial biomass was higher. Alteration of mica to short-order phyllosilicates suggested aqueous weathering. In UV, salts, clay-sized materials, and biomass were more abundant near the surface, suggesting minimal downward translocation by water. The presence of microorganisms in each horizon was established for the first time in an ultraxerous zone. Higher biomass numbers were seen near the surface and ice table, perhaps representing locally more clement environments. Currently, water activity is too low to support metabolism at the Phoenix site, but obliquity changes may produce higher temperatures and sufficient water activity to permit microbial growth, if the populations could survive long dormancy periods (∼106years).

Mineralogy, geochemistry and genesis of the Taşoluk kaolinite deposits in pre-Early Cambrian metamorphites and Neogene volcanites of Afyonkarahisar, Turkey

AbstractThe Taşoluk kaolinite deposits of Afyonkarahisar (western Anatolia) are hosted by both pre-Early Cambrian sericitic mica-chlorite schists and Neogene volcanites, the latter comprising tuffs and agglomerates. These units have been affected by hydrothermal alteration controlled by faults resulting in complex, irregular, lateral mineralogical zonation. The occurrence of a siliceous cap on altered schists and in claystone, of quartz veins in schists and tuffs, and the development of explosion cones and pit fillings indicate that alteration in both the schists and the volcanites is due to hydrothermal processes. Altered schists have generally large (locally small) Fe contents, and claystones are generally silicified and have small Fe contents. Kaolinite predominates south and west of Taşoluk, whereas high (Fe+Ti)-bearing illite + kaolinite predominate in other altered sections. The kaolinite exhibits a stacked micromorphology within altered schists, and the altered volcanites recordin situprecipitation, derived from a mechanism of paired dissolution and precipitation. Illite fibres coexist with kaolinite, smectite, chlorite, mica and sericitized feldspar in markedly altered schists, revealing that the illite formed either authigenically or by conversion of smectite to illite. A relative increase in Cr+Ni and decrease in Sr+Ba in the kaolinite deposits and their schistose host rock relative to the upper level of the kaolinite deposits and their volcanic parent rocks came about by the alteration of chlorite, mica and feldspar in the sericitic mica-chlorite schists, and feldspar, glass shards and schist fragments in the volcanites as a result of extensive faulting, fracturing and hydrothermal activity during Late Miocene-Pliocene volcanism, which contributed to the development of kaolinite deposits under acidic environmental conditions. With regard to industrial applications, the low-Fe kaolinized schists are suitable for use in refractories and paper coatings, while the claystone is suitable for use in ceramics and in the white-cement industry.

Size-exclusion chromatography can identify faster-associating protein complexes and evaluate design strategies

BackgroundWe previously developed a set of rationally designed mutant MICA protein ligands for the NKG2D immunoreceptor in which MICA was mutated at residues that do not contact NKG2D. Some of these MICA mutants, predicted by RosettaDesign to be destabilized, bound NKG2D with affinities enhanced by more than an order of magnitude when evaluated by surface plasmon resonance (SPR).FindingsSmall-zone size-exclusion chromatography (SEC) detected persistent high-affinity MICA mutant-NKG2D complexes in solution as early-eluting peaks. The SEC binding assay used standard protein purification instrumentation to evaluate complex stability, qualitatively paralleled the SPR results, and successfully discriminated among complexes that differed only in on-rates. We used the SEC binding assay, along with SPR, to assess the results of a follow-up design strategy targeting the non-interfacial redesigned region. Both SEC and SPR agreed that these mutations did not enhance affinity as much as previous mutants. When the SEC binding assay was run in 1 M urea, only the highest affinity complex was detected.ConclusionThis SEC binding assay provides a correlation with SPR results for protein complex affinities, detecting changes in complex on-rates, and tunable to lower sensitivity with 1 M urea. The SEC binding assay is complementary to other protein design evaluation methods, can be adapted to the undergraduate research laboratory, and may provide additional structural information about changes in hydrodynamic radii from elution times. Our assay allowed us to conclude that further alteration of MICA at non-contacting residues is unlikely to further enhance NKG2D affinity.

Extensive dickitization of the permo-triassic fluvial sandstones from the eastern Iberian Range, Spain

AbstractDiagenetic kaolin minerals are very common in the Permo-Triassic succession from the SE Iberian Range, Spain. The morphology and crystal structure of kaolin minerals has been examined in four size fractions (<1 µm, <2 µm, <6.3 µm and <20 µm) of sandstone samples by means of scanning electron microscopy, X-ray diffraction, infrared spectroscopy, differential thermal analysis and thermogravimetry. Experimental data reveal that dickite is the dominant kaolin-type mineral in the entire range of size fractions, whereas small amounts of kaolinite coexists with dickite in all size fractions. Dickite appears typically as booklets of pseudo-hexagonal plates with blocky habit. The increase in size fraction is concomitant with the increase in the amount of dickite and the progressive improvement of its structural order. The extensive dickitization is attributed to the high paleogeothermal gradient recorded in the studied area and the increase in H+, presumably resulting from the flux of organic acids derived from the underlying Carboniferous rocks and/or the late Permian succession. These conditions are more likely to be associated with the late Cretaceous post-rift thermal stage of the eastern Iberian Basin. Lately, during the maximum burial depth, the fine crystalline kaolin minerals were slightly illitized. Given the very small feldspar content in the studied sequence, the results reflect the important contribution of mica alteration to the early diagenetic formation of kaolinite as well as the late conversion to dickite.

Textural Features and Chemical Evolution in Tantalum Oxides: Magmatic Versus Hydrothermal Origins for Ta Mineralization in the Tanco Lower Pegmatite, Manitoba, Canada

Tantalum, a key element in the electronics industry, is produced mainly from rare element granitic pegmatites. Although their internal structure, mineralogy, and petrogenesis have been extensively investigated, the processes that control tantalum mineralization remain poorly understood, in particular the role of fluids in the crystallization of tantalum ore. One of the major problems arises from the difficulty in distinguishing primary magmatic from secondary, hydrothermal textures in such complex rocks. In the Tanco pegmatite, Manitoba, Canada, tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite. Eight different families of tantalum oxides occur in various associations and compositions. The Tanco Lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration. Tantalum mineralization in the Tanco Lower pegmatite occurs as three different styles. Facies 1 is hosted by the wall zone and hosts primary magmatic Ta oxides with simple textures (progressive and oscillatory zoning). Facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite. Facies 3 is hosted by the central zone, which is affected by mica alteration. In this latter facies, the oxides show particularly complex textures evident from X-ray mapping. By combining information obtained from textural observations and chemical analyses, we are able to determine the paragenesis for each Ta oxide-bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes. In complex associations, we observe relics of primary Ta phases that are replaced or overgrown by secondary Ta phases. We propose the paragenetic sequence: columbite group minerals + microlite (early primary magmatic) → columbite + wodginite group minerals + microlite (late primary magmatic) → wodginite group minerals + microlite (secondary magmatic) → ferrotapiolite (secondary magmatic). In addition, chemical variations were identified in the columbite and wodginite group minerals, both at the crystal scale and at the pegmatite scale. Columbite and wodginite group minerals show the typical Ta* = Ta/(Ta + Nb) and Mn* = Mn/(Mn + Fe) (atomic ratios) increase from earlier to later zones. At the crystal scale, the increase in Ta* and Mn* with fractionation in the columbite group is explained by the higher solubility of the Ta end member relative to the Nb end member and the crystallization of other minerals that shift the melt composition toward Mn* enrichment. The fractionation trend in the wodginite group shows Fe enrichment, which is consistent with experimental results that show a higher solubility of the Fe end member relative to the Mn end member in columbite group minerals. Considering the available experimental data, as well as the intimate association of Ta oxides with zircon observed in this study, we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin. Fluids are attributed an indirect role only, as they could have brought minor elements (Fe, Mn, or Ca) into the melt, which resulted in the crystallization of secondary Ta phases. Textural evidence shows that the late secondary phases were formed at the same time as mica alteration. We suggest that mica alteration was due to a late melt, rather than a hydrothermal fluid, that reacted with the blocky K-feldspar of the central zone. During the alteration event, tantalum was remobilized from primary phases and incorporated in new, secondary Ta oxide species.

Conditions of kaolin illitization in the Permo-Triassic sandstones from the SE Iberian Ranges, Spain

Kaolin is a widespread authigenic clay mineral in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin. However, relatively more extensive illitization of kaolin occurs in the SW basin margin compared with the slight occurrence in the NE margin. SEM analysis of sandstones reveals that illite replaced small kaolinite crystals while blocky dickite remained unaltered. Kaolin illitization is suggested to take place in relation to the maximum burial depth reached during Late Cretaceous post-rift stage. Vitrinite reflectance data denotes a maximum burial temperature of 118 °C and 144 °C in the NE basin margin and in the SW basin margin, respectively. Thus, the extent of illitization in the SW margin is attributed to the higher T peak reached by the Permo-Triassic succession. Regarding the lack of K-feldspars observed in the sandstones and interbedded mudrocks, the source of K + is mainly related to the alteration of detrital mica.

Short Wavelength Infrared Spectral Characteristics of the HW Horizon: Implications for Exploration in the Myra Falls Volcanic-Hosted Massive Sulfide Camp, Vancouver Island, British Columbia, Canada

Short wavelength infrared (SWIR) spectrometry has been used to identify previously unmapped hydrothermal alteration zones around volcanic-hosted massive sulfide (VHMS) orebodies at Myra Falls, Vancouver Island, British Columbia. Hydrothermal alteration assemblages are uniformly dominated by fine-grained white mica, with poor development of mineralogical zonation. SWIR spectrometry is an ideal exploration tool for characterizing this fine-grained hydrothermal alteration. At Myra Falls, SWIR spectrometry has identified subtle shifts in the wavelengths of the AlOH absorption feature of white mica, corresponding to compositional changes in altered rhyolite distal and proximal to ore. AlOH absorption occurs at shorter wavelengths (<2,198 nm) and corresponds to lower Fe, Fe + Mg, and Si/Al and higher Na/(Na + K) in strongly altered samples proximal to ore (slightly sodic muscovites). AlOH absorption occurs at longer wavelengths (>2,206 nm) and corresponds to higher Fe, Fe + Mg, and Si/Al and lower Na/(Na + K) in samples distal to ore (nonsodic slightly phengitic muscovites). White mica in siltstone within a meter of VHMS ore has higher Zn, V, Fe, and Mg contents than white mica distal to these altered samples. Chlorite compositions, identified by SWIR, also show systematic changes with intensity of alteration and distance from ore. The average wavelength of the FeOH absorption feature for chlorite in rhyolitic samples proximal to ore is 2,241 nm (intermediate Mg chlorite), whereas wavelengths in background samples average 2,247 nm (intermediate Fe chlorite). Similar changes are observed in footwall and hanging-wall andesites, with samples near the Battle mine containing muscovite to phengitic muscovite (average wavelength of the AlOH absorption feature of 2,200 nm) and Mg-rich chlorite (average wavelength of the FeOH absorption feature of 2,245 nm) to regional andesite samples with phengitic muscovite (average wavelengths of the AlOH absorption feature of 2,209 nm) and Fe-rich chlorite (average wavelength of the FeOH absorption feature of 2,249 nm). In weakly altered rocks white mica compositions also vary with host lithology. The AlOH absorption feature occurs at longer wavelengths in white mica in dacite and andesite compared to adjacent rhyolitic rocks, suggesting that higher Fe and Mg in the host lithology affects the composition of white mica. Two zones of intense hydrothermal alteration above the Battle and HW orebodies have distinctive SWIR spectral characteristics, with the AlOH and FeOH features occurring at shorter wavelengths (<2,197 and <2,240 nm, respectively). Small anomalous zones of alteration were also identified in the Thelwood Valley area, where minor mineralized zones are present. As broad zones of fine-grained white mica (sericite) alteration are ubiquitous throughout the Myra Falls property, alteration proximal to ore cannot be identified simply by visual logging of drill core. Alteration zonation may be determined by subtle shifts in white mica spectral characteristics. This study indicates that SWIR analysis may be an effective field-based exploration tool for quantifying the intensity of alteration associated with VHMS orebodies, and that trends in mineral compositions, even in very fine grained rocks, can be used as mine-scale vectors to ore.