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The environment model is used to describe the location of carbonate in nine carbonated apatites containing varied percentages of carbonate and Na+, K+, or NH4+ ions. Unlike the traditional model for carbonate substitution, which identifies different locations and orientations of the carbonate ion in the apatite structure, the environment model utilizes the different structural surroundings to describe the different types of carbonate. The A-type carbonate environment is assigned to channels lined only with calcium ions (A-channel configuration = Ca6) or to channels containing one Na+ or a vacancy (A′-channel configuration = Ca5Na or Ca5☐), and the B-type carbonate environment is the surroundings of the replaced phosphate ion. The assignments are made by peak-fitting the carbonate asymmetric stretch region (ν3) of the IR spectrum, following previously published criteria. These assignments lead to the conclusion that the percentage of channel carbonate (A- and A′-environments) is greater than that of B-type for each of these carbonated apatites. In general, the use of triammonium phosphate as the phosphate source in the synthesis produces apatites with larger amounts of channel carbonate (A- and A′-environments), while the use of sodium-containing phosphate reagents produces smaller amounts of channel carbonate. The environment model provides explanations for the differences within IR and NMR spectra obtained for apatites containing a range of total carbonate content. The B-type appearance of the carbonate ν3 region of the IR spectrum is found primarily in apatites containing sodium, which allows increased amounts of carbonation via co-substitution of Na+ with carbonate and creation of A′-environments with populations equal to that of B-type carbonate. The presence of ammonium or alkali metal salts with cations larger than Na+ results in the utilization of a charge-balance mechanism that produces vacancies rather than cation substitution in the channel. The carbonated apatites formed with primary utilization of the vacancy mechanism generally contain greater percentages of carbonate in the A-environment and carbonate IR spectra that contain an obvious high-frequency peak at about 1550 cm–1. The multiple peaks in the solid state 13C NMR spectra previously observed for carbonated apatite are attributed to substitution in the A-, A′-, and B-environments rather than different stereo-chemical orientations of the carbonate ion.

The A.M. breccia is part of the Giant Copper porphyry deposit in southern British Columbia. It is the only well-defined zoned tourmaline breccia pipe in the Canadian Cordillera. Tourmaline is a common alteration mineral within the A.M. breccia and is spatially associated with Cu mineralization. Observed changes in tourmaline chemistry range from alkali (schorlitic-dravitic) to calcic (feruvitic-uvitic). Tourmaline subspecies vary based on their spatial location within the A.M. breccia. Tourmaline outside of the pipe contains higher concentrations of Mg, whereas tourmaline preferentially incorporates Fe within the pipe. These chemical variations are indistinguishable in hand specimens. Spectral reflectance data were collected from 587 tourmaline grains to determine if discerning chemical changes in tourmaline can be made field-based and thus more cost-effective. Spectral reflectance differentiates tourmaline associated with mineralization and breccia textures from tourmaline occurring distal to the pipe contact or within barren tourmaline breccia pipes. Fe-rich tourmaline within the A.M. breccia shows spectral characteristics of end-member schorl (Fe-rich) spectra. Tourmaline distal to the A.M. breccia and within barren pipes demonstrates spectra of end-member dravite (Mg-rich). This grouping suggests that tourmaline subspecies can be inferred by spectral reflectance, enhancing the efficiency of tourmaline as a mineral vector. Tourmaline was also identified via airborne spectral surveys. However, the airborne spectral survey did not identify the end-member spectral properties identified by in situ analysis. Airborne spectral surveys can rapidly identify tourmaline breccia pipe exposures and expedite early stages of exploration in ore districts where tourmaline is a known gangue mineral.

Porphyry, epithermal, and volcanogenic massive sulfide (VMS) deposits can form together in the same mineral district in convergent margin environments. Their spatial association and superposition indicate evolving tectonic settings. The Artvin Au-Cu district is one of the major clusters of VMS bimodal-felsic, porphyry, and epithermal deposits in the Eastern Pontides belt in northeast Turkey. Whereas ore-forming processes, timing, and tectonic setting of VMS mineralization are well defined in Artvin, those for porphyry and epithermal mineralization remain less constrained. Our district-scale field study focused on the Hod gold corridor in the Artvin district, which is defined by the NE-trending alignment of the recent Au-Cu mineral discoveries (~205 t Au; ~0.33 Mt Cu; e.g., Hod Maden, Ardala-Salinbaş, and Taç-Çorak) that include Au-rich porphyry, highand intermediate-sulfidation epithermal, carbonate-replacement, and hybrid VMS-epithermal mineralization styles. Our new U-Pb, 40Ar/39Ar, and Re-Os geochronological results interpreted with previously compiled data show that magmatism in the Artvin district formed in the Carboniferous (358–325 Ma), Jurassic (182–174 Ma), Late Cretaceous (92–78 Ma), Eocene (51–40 Ma), and Oligocene (30 Ma). Porphyry and epithermal mineralization along the Hod gold corridor peaked in the Early (~113 Ma; Berta prospect) and Late Cretaceous (~86.5-82 Ma; e.g., Taç and Çorak deposits) and Eocene (~50 Ma; e.g., Ardala deposit), whereas VMS bimodal-felsic mineralization only formed in the Late Cretaceous (~91–85 Ma). Therefore, we interpret that the Hod gold corridor was a long-lived, deep crustal-scale structural feature along which the successive magmatic and mineralization events were emplaced. In addition, the timing of porphyry Cu-Mo mineralization can significantly (>20 Ma) postdate the crystallization age of the intrusive host rocks in the Artvin district, such as at Berta and Balcılı camp, which emphasizes the importance of dating mineralization directly to correctly attribute the tectonic setting. The distribution of Late Cretaceous mineral occurrences suggests a possible eastward temporal evolution from VMS (~91–85 Ma) to epithermal-porphyry systems (~86.5–82 Ma), transitioning from back-arc to arc settings at the onset of the Northern Neotethyan oceanic slab rollback and accompanied by increasingly elevated gold content eastwards across the Artvin district.

Stratabound ore has been recognized as an end-member of porphyry copper systems, but pyrite chemistry has not been widely applied to linking stratabound ore with the related porphyry and skarn system. Stratabound ore is commonly developed around porphyry-skarn systems in eastern China, and is characterized by abundant colloform pyrite; however the origin of the colloform pyrite has been contentious. Xinqiao deposit is ideal for study of pyrite geology and geochemistry with the aim of elucidating formation of the stratabound ore and to decipher the evolution of pyrite compositions in a porphyry-skarn environment. The colloform pyrite paragenesis and S isotopes indicate that it formed during early skarn mineralization, based on its occurrence in stockwork veins cutting skarn minerals, and that it is replaced by later hypogene sulfides; the δ34S of colloform pyrite (average 6.12‰) is close to the δ34S value of both porphyry-(average 5.06‰) and skarn-type pyrite (average 4.65‰). The colloform texture formed as an aggregate of nanometer- or micrometer-sized ( Co, Ni, and Se enrichment in porphyry- and proximal skarn-type pyrite suggests they formed at relatively high temperature, whereas the colloform pyrite shows trace element contents (Cu, Pb, Zn, Ag, and Bi) similar to those in distal skarn pyrite, suggesting that they may have formed in the same fluid environment. The trace element variations in pyrite from stratabound, skarn and porphyry ore probably resulted from decreasing fluid temperature and increasing pH away from the source. Our data, combined with previous studies, show that Co and Ni in pyrite increase toward porphyry and skarn ore, whereas As, Sb, Pb, Ag, and Bi are enriched in pyrite in distal stratabound ore, which extends for 1–2 km away from the intrusion. A plot of As/Se vs. Co discriminates the three ore types that occur associated with porphyry-skarn Cu systems in the Middle and Lower Yangtze belt (MLYB). These results indicate pyrite chemistry can be effective in discriminating the genesis of different deposit types related to porphyry-skarn systems and can potentially be used as a vectoring tool during exploration in the MLYB and elsewhere.

The thermal behavior of 15 natural tourmaline samples has been measured by X-ray powder diffraction from room temperature to ~930 °C. Axial thermal expansion is generally greater along the c crystallographic axis (αc 0.90–1.05 × 10–5/K) than along the a crystallographic axis and the symmetrically equivalent b axis (αa 0.47–0.60 × 10–5/K). Ferro-bearing samples show lower expansion along a than in other tourmalines. In povondraite the thermal expansion along the c axis is higher than in other tourmalines, whereas along a it is lower [αa = 0.31(2) and αc = 1.49(3) × 10–5/K]. Volume expansion in the tourmaline-supergroup minerals is relatively low compared with other silicates such as pyroxenes and amphiboles. Volume also exhibits a relatively narrow range of thermal expansion coefficients (1.90–2.05 × 10–5/K) among the supergroup members. An interpretation for the small changes in thermal expansion in a compositionally heterogeneous group like tourmaline is that all members, except povondraite, share a framework of dominantly ZAlO6 polyhedra that limit thermal expansion. Povondraite, with a framework dominated by ZFe3+O6 polyhedra, displays thermal expansion that is different from other members of the group. Unit-cell dimensions of tourmalines having significant Fe2+ deviate from linearity above 400 °C on plots against temperature (T); along with the resulting substantial reduction in unit-cell volume, these effects are likely the result of deprotonation/oxidation processes. Lithium-rich and Fe2+-free tourmalines deviate similarly at T > 600 °C. In Li- and Fe2+-free tourmalines, no such deviation is observed up to the highest temperatures of our experiments. It is not clear whether this is due to cation order-disorder over Y and Z sites that occurs during the highest temperature measurements, a phenomenon that is apparently inhibited (at least in the short term) in Li-free/Mg-rich samples. If so, this must occur at a relatively rapid rate, as no difference in unit-cell values was detected at 800 °C after heating in both one- and 12-h experiments on Na-rich rossmanite.

The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins. There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with –4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.

Understanding past and present aqueous activity on Mars is critical to constraining martian aqueous geochemistry and habitability, and to searching for life on Mars. Assemblages of minerals observed at or near the martian surface include phyllosilicates, sulfates, iron oxides/hydroxides, and chlorides, all of which are indicative of a complex history of aqueous activity and alteration in the martian past. Furthermore, features observed on parts of the martian surface suggest present-day activity of subsurface brines and at least transient liquid water. Terrestrial analogs for younger and colder (Hesperian–Amazonian) martian geologic and climatic conditions are available in the McMurdo Dry Valleys (MDV) of Antarctica and provide opportunities for improved understanding of more recent aqueous activity on Mars. Here, we study the VXE-6 intermittent brine pond site from Wright Valley in the MDV region and use coordinated spectroscopy, X-ray diffraction, and elemental analyses to characterize the mineralogy and chemistry of surface sediments that have evolved in response to aqueous activity at this site. We find that brine pond activity results in mineral assemblages akin to aqueous alteration products associated with younger sites on Mars. In particular, surficial chlorides, a transition layer of poorly crystalline aluminosilicates and iron oxides/hydroxides, and a deeper gypsum-rich interval within the upper 10 cm of sediment are closely related at this Antarctic brine pond site. Activity of the Antarctic brine pond and associated mineral formation presents a process analog for chemical alteration on the martian surface during episodes of transient liquid water activity during the late Hesperian and/or more recently. Our results provide a relevant example of how aqueous activity in a cold and dry Mars-like climate may explain the co-occurrence of chlorides, clays, iron oxides/hydroxides, and sulfates observed on Mars.

Tourmaline-cemented breccia bodies host much of the ore in the Río Blanco-Los Bronces porphyry Cu-Mo deposits. We determined the chemical and B isotope composition of tourmaline as well as S isotope ratios of anhydrite and sulfide minerals to shed light on the composition and origin of mineralizing fluids. Also, the utility of tourmaline as an indicator mineral was tested by comparing mineralized and barren breccias. Tourmaline in mineralized samples has a narrow Mg range (1.5–2 apfu) and variable, generally low Al contents (4–6.5 apfu). A strong negative correlation of Al with Fe indicates monovalent substitution of Al and Fe3+, implying relatively oxidizing fluids. In contrast, tourmaline from barren breccias has a narrower Al range (6–7 apfu), lower and more variable Mg (0.2–2.5 apfu), and a strong negative Mg-Fe correlation, suggesting more reduced fluids with a dominance of Fe2+. These features and the implications of redox contrast may have exploration significance. Tourmaline from all breccia samples yielded δ11B values from 1.8 to 7.9‰. A magmatic source of boron is concluded from the identical B isotope values of granite-hosted tourmaline in the district (1.2–7.7‰) and from the similar range of regional volcanic and porphyry rocks in the Central Andes. The δ34S values of coexisting anhydrite (11.6–14.5‰) and chalcopyrite (–1.5 to –0.2‰) in mineralized breccia give S isotope exchange temperatures of 377° to 437°C, consistent with fluid inclusion temperatures. Total sulfur δ34Sfluid estimates between 1.4 ± 3.9 and 8.8 ± 1.3‰ are broadly consistent with a magmatic source but not well constrained. However, published O and H isotope ratios of quartz and tourmaline from the Río Blanco-Los Bronces breccias have a clear magmatic signature, so this is the preferred scenario. Mass balance simulations of the boron budget show that typical magma flux rates, water contents, and boron concentration for the Central Andes could produce the estimated 107 tons of boron in the Río Blanco-Los Bronces breccias within the 4-m.y. duration of porphyry intrusions if (1) magma accumulated and evolved at midcrustal levels before emplacement and (2) boron partitioned strongly to the fluid phase (DBfluid/melt > 3).

Rozenite (FeSO4·4H2O) is a candidate mineral component of the polyhydrated sulfate deposits on the surface and in the subsurface of Mars. To better understand its behavior at temperature conditions prevailing on the Martian surface and aid its identification in ongoing and future Rover missions, we have carried out a combined experimental and computational study of the mineral’s structure and properties. We collected neutron powder diffraction data at temperatures ranging from 21–290 K, room-temperature synchrotron X-ray data and Raman spectra. Moreover, first-principles calculations of the vibrational properties of rozenite were carried out to aid the interpretation of the Raman spectra. We found, in contrast to a recent Raman spectroscopic study, that there are no phase transitions between 21 and 290 K. We confirm the heavy atom structure reported in the literature (space group P21/n) to be correct and present, for the first time, an unconstrained determination of the H atom positions by means of high-resolution neutron powder diffraction, and report the complete crystal structure at 290 and 21 K. The anisotropy of the thermal expansion of the lattice vectors is αa:αb:αc = 1.00:2.19:1.60 at 285 K. Subsequent analysis of the thermal expansion tensor revealed highly anisotropic behavior as reflected in negative thermal expansion approximately ||〈101〉 and ratios of the tensor eigenvalues of α1:α2:α3 = −1:3.74:5.40 at 285 K. Lastly, we demonstrated how combining Raman spectroscopy and X-ray diffraction of the same sample sealed inside a capillary with complementary first-principles calculations yields accurate reference Raman spectra. This workflow enables the construction of a reliable Raman spectroscopic database for planetary exploration, which will be invaluable to shed light on the geological past as well as in identifying resources for the future colonization of planetary bodies throughout the solar system.

New petrographic and microanalytical studies of mineral inclusions in the Purang ophiolitic chromitites (SW Tibet) are used to scrutinize the evolution of the associated Cretaceous sub-oceanic lithospheric mantle section. Silicate inclusions in the chromite grains include composite and single-phase orthopyroxene, clinopyroxene, amphibole, and uvarovite. Most inclusions are sub-rounded or globular, whereas a few inclusions exhibit cubic/octahedral crystal morphologies. The latter are randomly distributed in the large chromite grains, though discrete aggregates are consistently confined to the grain centers. Abundant micrometer-scale, clinopyroxene inclusions are topotaxially aligned along crystallographic planes. Less-abundant sulfide, wüstite, apatite, and uvarovite inclusions are observed in some samples. The trace element geochemistry of the Purang chromitite evoke parental MORB- and boninite-like melts, consistent with the supra-subduction zone setting. The δ26Mg values of the high-Cr and high-Al chromitites range from –0.25 to –0.29‰ and –0.05 to –0.32‰, respectively. The associated harzburgite has nearly overlapping δ26Mg values of –0.13 to –0.37‰, but pyroxenite sills show distinct δ26Mg values (–0.61 to –0.67‰). The variable Mg isotope signatures, combined with abundant exotic, ultrahigh-pressure and super reduced (UHP-SuR) mineral inclusions in the chromite grains, suggest that recycling and recrystallization under different mantle conditions played an important role in the genesis and evolution of these rocks. Furthermore, discrete silicate, sulfide, and metal alloy inclusions in the Purang chromitites are comparable to those reported in other Tethyan ophiolites, and collectively suggest a common geodynamic evolution.

The solubility, speciation, and local atomic environment of chlorine have been determined for aluminoborosilicate glasses equilibrated with various sources of chlorine (NaCl and PdCl2) at high pressure (0.5–1.5 GPa) and high temperature (1350–1400 °C). The Cl solubility reaches up to 11 mol% in borosilicate glass and appears to be strongly influenced by the concentration of network-modifying cations (Ca and Na) and increases with increasing CaO + Na2O content. The Cl solubility is enhanced in Ca-bearing rather than Na-bearing borosilicate glass, suggesting a higher affinity of chlorine for alkaline-earth cations. Cl K-edge XANES and Cl 2p XPS spectra reveal that chlorine dissolves in glasses only as chloride species (Cl–) and no evidence of oxidized species is observed. Using PdCl2 as a chlorine source leads to a pre-edge signal for PdCl2 in the XANES spectra. The EXAFS simulations show that the Cl– local environment is charge compensated by Na+ or Ca2+ at a distance to first neighbor on the order of 2.7 Å, which is comparable to the observed distances in crystalline chloride compounds. The coordination to charge compensating cation is lower in the case of Ca2+ (~1.1) than Na+ (~4.3).

The Taurus porphyry Cu-Mo district contains four mineralized porphyry centers in the eastern interior of Alaska. All four centers were emplaced during a magmatic episode that spanned from ca. 72 to 67 Ma, with seven distinct igneous suites. Each igneous suite resulted in hydrothermal alteration and mineralization, with younger pulses overprinting older pulses. Each magmatic-hydrothermal system is not present at all four mineralized centers. Apart from the Dennison occurrence, each mineralized center records pulses of repeated intermediate-silicic magmatism and associated alteration and mineralization. Laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon crystallization ages indicate that an early quartz porphyry dike swarm ranges in age from ca. 71 to 70 Ma and is associated with potassic, sericitic, and propylitic alteration. Quartz latite intrusions were emplaced at ca. 69 Ma and exhibit early sodiccalcic alteration overprinted by potassic, sericitic, and propylitic alteration. The Taurus monzonite suite is cut by quartz latite but yielded an ca. 70 Ma emplacement age and exhibits the largest footprint of potassic and sericitic alteration. Feldspar porphyry dikes were emplaced ca. 69 Ma and have significant tourmaline-bearing potassic and sericitic alteration. This suite was followed by development of an igneous breccia with a monzonitic igneous matrix. Sodic-calcic alteration was associated with the igneous brecciation. A small stock of monzonite was emplaced at ca. 68 Ma causing locally pervasive sericite-tourmaline-pyrite alteration. The youngest suite of magmatism dated in the district is a series of granodiorite porphyry dikes with weak sodic-calcic and propylitic alteration that truncates earlier alteration assemblages. Mineralization in the district consists of chalcopyrite and molybdenite associated with sugary quartz veins with potassium feldspar and biotite alteration envelopes (A veins). Less common banded quartz-molybdenite veins (B veins) occur with potassium feldspar envelopes. Gold occurs throughout the district and is strongly correlated with copper grade. Sericitic alteration contains lower copper contents and is predominantly associated with quartz-pyrite veins with sericite envelopes (D veins). Pyrrhotite and local arsenopyrite are present in sericitic assemblages. Pyrrhotite also occurs as inclusions in pyrite within D veins. Magmas across the district exhibit oxidized characteristics, evidenced by the presence of abundant magnetite, rare titanite, and elevated Eu/Eu* and Ce/Ce* in zircon. Zircon Th/U and Yb/Gd compositions suggest a fractionation path controlled by apatite, titanite, and hornblende. Zircon rare earth element ratios and trace element data indicate two distinct batches of magma evolved from mafic parental compositions to monzonite and granodioritic compositions via fractional crystallization. In the early pulse of magma (ca. 72–69 Ma), fractional crystallization was key to ore formation. Earlier, better mineralized suites evolve to less negative Eu anomalies (Eu/Eu* > 0.7), indicating more oxidized and higher-water-pressure conditions evidenced by the suppression of plagioclase crystallization, compared to later, more poorly mineralized suites. The temporal and spatial evolution of the district was determined from mapping and U-Pb and Re-Os geochronology. Mapping of igneous and hydrothermal assemblages indicates that the locus of the intrusive suites and hydrothermal systems shifted spatially over time, based on the presence of high-temperature (K-silicate–dominant) alteration, which is coincident with the highest Cu and Au grades. The earliest hydrothermal system was centered at Bluff and East Taurus and transitioned to West Taurus during emplacement of the second magmatic suite. Emplacement of the third magmatic suite was centered back at East Taurus, and the fourth and fifth suites were centered at West Taurus. The latest suites were widespread without a core of high-temperature alteration marking a central locus. East Taurus contains the overlap of six of the seven magmatic and hydrothermal suites and has the highest intersected grades and tonnages in the district. The Bluff and Dennison occurrences exhibit fewer igneous suites and hydrothermal assemblages with weak mineralization. Sodic-calcic alteration, common on the deep and distal flanks of porphyry systems, is only present at West Taurus and is indicative of a localized source of high-salinity nonmagmatic fluids.

The UV/Vis single-crystal absorption spectra of two almandine-bearing and several spessartine garnets were measured and their respective Fe2+ and Mn2+ spin-forbidden electronic transitions analyzed. Spin-forbidden bands of Fe3+ are also considered, because many aluminosilicate garnets contain some Fe3+. The spectra of the almandine-bearing garnets were recorded at room temperature between about 10 000 and 30 000 cm–1. The spectrum of a nearly end-member spessartine (97 mol% Mn32+Al2Si3O12) was measured between about 15 000 cm–1 and 30 000 cm–1 at room temperature and 78 K, the latter for the first time. The 78 K spectrum shows absorption features not observed at room temperature. Five additional spessartine-rich garnets with different Mn2+/(Mn2+ + Fe2+) ratios, and two with unusual chemistries, were recorded up to 26 000 cm–1. The spectra of the two almandine-bearing garnets agree well with published results and show several overlapping Fe2+/3+ bands located between about 14 000 and 25 000 cm–1. The spectra were deconvoluted to gain more insight into the electronic transition behavior. These results, together with an analysis of other measured spectra, reveal several absorption features that were previously unrecognized or misassigned. The spectrum of spessartine shows several Mn2+ bands, and most are clearly spaced from one another. A synthesis of various UV/Vis spectroscopic results is made and assignments for the Fe2+/3+ and Mn2+ bands are attempted. The intensities of the Mn2+ spin-forbidden bands and the ligand → metal charge edge observed in the various spessartine spectra are discussed. Spectra of almandine and spessartine have been interpreted using Tanabe-Sugano diagrams that are constructed for cations in octahedral coordination, point symmetry Oh. However, such analysis does not appear to be fully successful because Fe2+ and Mn2+ in garnet have triangular dodecahedral coordination with point symmetry D2. The interpretation of the spectrum of spessartine is especially problematic. An analysis shows that published model calculations of Fe2+ electronic transition energies in garnet are not in good agreement with each other and are also not in full agreement with experimental spectra. First principles calculations are needed to better understand the spin-forbidden transitions of Fe2+, Fe3+, and Mn2+ in garnet.

The Sukari gold deposit (>15 Moz Au) in the Eastern Desert of Egypt is hosted by a deformed granitoid stock (Sukari tonalite-trondhjemite intrusion) and mainly occurs as a network of crosscutting sulfide-bearing quartz (± carbonate) veins and intensely sulfidized-silicified-sericitized wall rock. Emplacement of the Sukari intrusion into a tectonized Neoproterozoic accretionary complex was controlled by a system of NE- to NNE-trending oblique faults that are related to a deep-seated positive flower structure. A robust genetic model has been hampered by the poorly understood relationships between gold mineralization and host rocks. In this study, zircon U-Pb ages of three samples from the Sukari intrusion define a crystallization age of ~695 ± 2 Ma. In contrast, hydrothermal sericite from the ore zone yields an 40Ar/39Ar age of ~625 ± 3 Ma, which coincides with the onset of major sinistral transpression in the region. Features including sigmoidal morphology of gold quartz veins and abundant subhorizontal tension gashes alongside widespread brecciation and recrystallization suggest that quartz veining occurred during renewed shortening and exhumation through the brittle-ductile transition. Petrographic and micro-X-ray fluorescence (µXRF) studies indicate that disseminated gold and sulfides, commonly associated with sericite and carbonate alteration, are mostly confined to stylolitic bands in the quartz veins. Oscillatory and sector zoning patterns, irregular As-rich bands, and truncations between early- and late-genetic pyrites reflect variations in temperature and mechanism of ore deposition, demonstrated by variable As/S and Co/Ni ratios in the different pyrite generations. Laser ablation-inductively coupled plasma-mass spectrometry analysis pinpoints the covariance of gold and arsenic contents in pyrite, but free milling gold inclusions in microfractures consistently have a mercury-bearing electrum composition, depicting different ore formation stages. Ore fluids with δ34SH2s values of –1.9 to –3.0‰, modeled from gold-associated pyrite and arsenopyrite assemblages with nearly identical δ34S values, suggest a likely single source of sulfur. Alternatively, multisourced sulfur could have extensively mixed and equilibrated by fluid reaction with carbonaceous wall rock. Gold deposition was triggered by abrupt changes in fluid pH and fO2. As an implication for future exploration, sites of maximized strain gradients adjacent to granitoid bodies along extensive transpression zones in the district could be highly prospective targets, particularly where imprinted by sericite-carbonate ± graphite alteration.

Aluminosilicate garnet is an excellent phase to research solid-solution behavior in silicates. Natural almandine-pyrope, {Fe3x2+,Mg3–3x}[Al2](Si3)O12, and almandine-spessartine, {Fe3x2+,Mn3−3x2+}[Al2](Si3)O12, crystals were measured by UV/Vis/NIR (~29 000 to 10 000 cm–1) optical absorption spectroscopy using a microscope. The spectra and changes in energy of several Fe2+ and Mn2+ spin-forbidden electronic transitions of different wavenumber were analyzed as a function of garnet composition across both binaries. The spectra of Alm-Pyp garnets are complex and show several Fe2+ and Fe3+ transitions manifested as overlapping absorption bands whose intensities depend on composition. There are differences in energy behavior for the various electronic transitions, whereby lower wavenumber Fe2+ transitions decrease slightly in energy with increasing pyrope component and those of higher wavenumber increase. The spectra of Alm-Sps solid solutions show both Fe2+ and Mn2+ spin-forbidden bands depending upon the garnet composition. The variations in energy of the different wavenumber Fe2+ transitions are unlike those observed in Alm-Pyp garnets. The three lowest wavenumber electronic transitions appear to vary the most in energy across the Alm-Sps join compared to those at higher wavenumber. Four narrow and relatively intense Mn2+ spin-forbidden bands between 23 000 and 25 000 cm–1 can be observed in many Sps-Alm garnets. Their transition energies may increase or decrease across the join, but scatter in the data prohibits an unequivocal determination. A consistent crystal-chemical model and Fe2+-O bond behavior, based on published diffraction and spectroscopic results, can be constructed for the Alm-Pyp binary but not for the Alm-Sps system. The spectra of the former garnets often show the presence of high-wavenumber spin-forbidden bands that can be assigned to electronic transitions of Fe3+ occurring at the octahedral site. The most prominent band lies between 27 100 and 27 500 cm–1 depending on the garnet composition. Fe3+-O2– bonding is analyzed using Racah parameters. State-of-the-art electronic structure calculations are needed to understand the precise physical nature of the electronic transitions in garnet and to interpret better UV/Vis/NIR spectra.

The Hyuga-nada region is located in the southwestern part of the Nankai Trough in the Pacific Ocean, where M7 class interplate earthquakes have been repeatedly occurring because of the subduction of the Philippine Sea Plate. The largest earthquake recorded in history for the Hyuga-nada region was the Hyuga-nada earthquake of 1662, which occurred off Miyazaki Prefecture in the southeastern area of Kyushu region, Japan, generating a tsunami. The region is also an area where slow earthquakes are active at the shallow part of the plate boundary. It is confirmed by the 2011 Tohoku earthquake that the active area of shallow slow earthquakes also became a tsunami source area. We hypothesize that the unusually large tsunami of 1662 was caused by the coseismic slipping of the active source area of shallow slow earthquakes. We constructed the fault model of the 1662 Hyuga-nada earthquake based on recent geophysical observations. A numerical simulation of the tsunami was carried out using the fault model constructed based on hypotheses. The total seismic moment was 9.8 × 10²⁰ Nm (Mw 7.9) estimated from the fault model. The estimated fault model can explain the distribution of the likely tsunami event deposits which were recognized in this study and also have been reported by other studies and tsunami heights in historical records. Hypotheses based on geophysical findings have been found to be correct., 1662年日向灘地震の新たな断層モデルを構築 --地球物理学と地質学の検証に基づく初の成果--. 京都大学プレスリリース. 2023-01-24.

Hydrothermal rutile (TiO2) is a widely distributed accessory mineral in hydrothermal veins or alteration assemblages of porphyry deposits and provides important information for further understanding hydrothermal fluid signatures. This study determines the geochemical composition and U-Pb dates of hydrothermal rutile from the Yulong porphyry Cu-Mo deposit in east Tibet, China. Three types of TiO2 polymorphs have been identified based on their Raman spectroscopic, textural, and chemical characteristics. (1) Brookite and anatase pseudomorphs after titanite in a fine-grained matrix, indicating low-temperature hydrothermal fluids destabilizing primary Ti-bearing minerals during argillic alteration (type-I). (2) Elongated and prismatic rutile present in hydrothermal veins or in clusters in accompanying alteration envelope characterized by weak zoning (type-II). And (3) rutile intergrown with sulfides in hydrothermal veins, characterized by well-developed patchy and sector zoning (type-III). In contrast to the type-I and type-II TiO2 polymorphs, tungsten is enriched in backscattered bright patches and sector zones in type-III rutile, which is due to the substitution of W6+ in the Ti4+ octahedral site. The mechanism of the enrichment of tungsten is effectively driven by the halogen-rich (F, Cl) aqueous fluids during hydrothermal mineralization. In situ U-Pb dating of the type-III rutile yields a lower intercept age of 41.8 ± 1.2 Ma, which brackets the timing of the Cu-Mo mineralization. The relationship between rutile textures and composition indicates that W-bearing rutile can serve as a recorder of hydrothermal processes in porphyry Cu deposits.

Niobium is a critical metal in high demand because of technological advances and the supply risk created by the fact that over 90% of its production is by a single country (Brazil). In this paper, we review the geology of the deposits that are currently being mined and other potentially economic deposits as well as develop models for their genesis. With the exception of the Lovozero deposit (Russia), which is hosted by a layered silica-undersaturated alkaline igneous complex, all the deposits that are currently being mined for niobium are hosted by carbonatites, and most of the deposits with economic potential are also hosted by these rocks. Niobium owes its concentration in carbonatites and alkaline silicate rocks to its highly incompatible nature and the small degree of partial melting of the mantle required to generate the corresponding magmas. The primary control on the concentration of niobium to economic levels in alkaline silicate magmas is fractional crystallization, partly prior to but mainly after emplacement. In the case of silica-undersaturated magmas, the final residue saturates in minerals like eudialyte and loparite to form niobium-rich horizons in the layered complexes that crystallize from these magmas. The final residue, in the case of silica-saturated magmas, crystallizes the pegmatites that are the hosts to the economic niobium mineralization, which commonly takes the form of pyrochlore. In contrast, carbonatitic magmas undergo little to no fractional crystallization prior to emplacement. Moreover, fractional crystallization on emplacement has minimal impact on the concentration of niobium to economic levels. Instead, we propose that the metasomatic interaction of the carbonatitic magmas with their hosts to form rocks like phlogopitite (glimmerite) consumes much of the magma, leaving behind a phoscoritic residue from which pyrochlore crystallizes in amounts sufficient to form economic deposits. Although many niobium deposits display evidence of intense hydrothermal alteration, during which there can be major changes in the niobium mineralogy, the extremely low solubility of niobium in aqueous fluids at elevated temperature precludes significant mobilization and, thus, enrichment of the metal by hydrothermal fluids. However, weathering of carbonatite-hosted niobium deposits leads to supergene enrichment (due largely to the dissolution of the carbonate minerals) that can double the niobium grade and make subeconomic deposits economic. Pyrochlore is the principal niobium mineral in these laterite-hosted deposits, although its composition differs considerably from that in the primary mineralization. This paper evaluates the processes that appear to be responsible for the genesis of niobium ores and provides a framework that we hope will guide future in-depth studies of niobium deposits and lead to more effective strategies for their successful exploration and exploitation.

Apatite containing 14 wt% TREO (total rare earth oxide) and coexisting with calciobritholite with 37.2 wt% TREO has been synthesized at 800 °C and 10 kbar from a felsic melt with the addition of NaCl. The analysis of the experimental products with regression analysis of time-resolved (RATR) laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data allowed to estimate the composition of the coexisting phases. The results suggest that equilibrium has been established during the run and both apatite and calciobritholite contained REE in [Si4+REE3+] to [Ca2+P5+] solid solution, whereas the coupled substitution [Na1+REE3+] to [2Ca2+] was insignificant despite crystallization from an alkaline, Na-rich melt. The coexistence of the apatite and calciobritholite and available experimental data allowed the miscibility gap to be constrained between apatite and calciobritholite, and suggest complete miscibility between apatite and britholite above 950 °C. The melt that produced coexisting apatite and calciobritholite was characterized by a significant Cl content of (0.51 wt%) and elevated REE (526 ± 19 ppm Ce) and low-P content (112 ± 49 ppm). The change of the accessory mineral association from monazite to apatite and calciobritholite with the addition of NaCl illustrates the importance of halogens for mineral associations. The partition coefficients of britholite are similar to those of apatite and are distinguished mainly by a higher preference for REE and Th. Henry’s law was not acting for the total REE content in the melt because of the buffered system; however the partition coefficients could still be used for the prediction of the relative REE patterns for melts that generated high-REE apatite and/or calciobritholite. These results have implications for the interpretation of the phosphate associations in alkaline volcanic and plutonic rocks.

Magnetic contributions have the potential to significantly influence predicted phase stability within alloy and mineral mixing phase diagrams, yet have been historically challenging to incorporate due to a significant increase to phase space sampling. In this work, we employ a computational protocol that includes spin orientation as an additional configurational component within multi-component cluster expansions between magnetic and non-magnetic metal oxide alloys [calculated using density functional theory (DFT) and the generalized gradient approximation]. This approach was used to determine the effect of magnetic contributions to corundum-eskolaite and corundum-hematite phase equilibria from first principles. Two-component cluster expansions of the magnetic components of eskolaite and hematite were first performed showing the ability of this method to properly calculate their respective magnetic properties. Two-component cluster expansions were then performed for non-magnetic Al(III) and ferromagnetic Cr(III) and Fe(III), and phase diagrams were calculated for later comparison. Finally, a non-magnetic Al(III) and “up” and “down” magnetic configurations for anti-ferromagnetic Cr(III) and Fe(III) were performed. Magnetic contributions to the calculated phase diagram for the corundumeskolaite system were shown to be inconsequential but are vital for accurate determination of the corundum-hematite solvus.

The Morelos district, located in the center of the Guerrero gold belt, Guerrero State, southern Mexico, has been the site of several recent gold ± copper skarn discoveries (total of ~8.5 Moz Au) associated with Upper Cretaceous-Paleocene granodiorite intrusions. The Limon, Guajes, and Media Luna skarn deposits developed along the contact of the El Limon granodiorite and the sedimentary host rocks. Native gold is associated with retrograde alteration of garnet-pyroxene skarn and is accompanied by native bismuth as well as telluride and sulfide minerals. The Media Luna deposit is characterized by a distinct magnesium-rich skarn mineralogy and contains an average of ~1 wt % Cu, in addition to gold and silver. This distinguishes it from the other gold-only skarn deposits in the Guerrero gold belt. This observation suggests that skarns in the Guerrero gold belt, which replaced magnesium-rich sedimentary protoliths, may host significant copper resources in addition to gold. Uranium-lead laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon ages of the El Limon granodiorite range from 66.86 ± 0.40 to 65.88 ± 0.79 Ma. Preskarn molybdenite-quartz veins cut through the El Limon granodiorite and yield Re-Os molybdenite ages between 66.63 ± 0.22 and 65.55 ± 0.25 Ma. A series of pre-, syn-, and postskarn porphyritic dikes intruded the El Limon granodiorite, having zircon ages ranging from 65.9 ± 1.1 to 64.68 ± 0.38 Ma. The timing of skarn formation at Limon and Media Luna was constrained to 64.6 ± 1.2 to 63.2 ± 1.0 Ma, applying U-Pb LA-ICP-MS to garnet. The ubiquitous presence of garnet in skarn deposits and the time- and cost-efficiency of in situ geochronology are striking advantages of this method to constrain the timing of mineralization.

Stratiform to stratabound replacement of a mixed siliciclastic-carbonate host rock is a defining characteristic of many sediment-hosted base metal deposits. Mineralized rocks in clastic-dominated (CD-type) Zn-Pb ore deposits, which represent our highest value base metal resources, are generally thin (101 m), laterally extensive (103 m), and stratiform to stratabound in fine-grained siltstone and mudstone facies. At the recently discovered Teena CD-type Zn-Pb deposit (Proterozoic Carpentaria province, Australia), the host rock was undergoing burial diagenesis when altered and mineralized by hydrothermal fluids that moved up to 2 km lateral to the fluid input conduit (growth fault) through intraformational intervals. In much of the deposit, carbonate dissolution was an important reaction permeability control, although significant amounts of mineralization also occur in carbonate-free siliciclastic beds. In this study, transmission electron microscopy (TEM) data has been generated on a drill core sample that preserves a sharp reaction front between mineralized and unmineralized domains of the fine-grained siliciclastic compositional end member (carbonate free). Petrographic and mineralogical data provide evidence that oxidized hydrothermal fluids moved through the protolith via reaction permeability that developed from feldspar dissolution. The nature of reactive fluid flow was determined by reactions that took place at the fluid-mineral interface. Pyrite formation during the earliest stage of the hydrothermal paragenesis increased the mineral reactive surface area in the protolith. Acidity was then generated in situ via self-sustaining reactions involving pyrite oxidation, transient Fe sulfate formation, and sphalerite precipitation, which provided positive feedbacks to enhance porosity creation and further fluid infiltration and mineralization. In the absence of carbonate, however, ore fluid pH was buffered by K-feldspar dissolution (~4.5), thereby ensuring sphalerite precipitation was not inhibited under more acidic conditions. All CD-type deposits in the Carpentaria province are hosted by a protolith comprising carbonate, K-feldspar, pyrite, and organic matter; these phases set the boundary conditions for the development of self-sustaining reactions during ore formation. Importantly, these self-sustaining reactions represent a Goldilocks zone for ore formation that is applicable to other sediment-hosted deposits that formed via replacement of mixed siliciclastic-carbonate host rocks (e.g., stratiform Cu).

Administrative support is concerned with the provision of secretarial and administrative services to students, faculty, and other customers of educational institutions. In effect, any assistance provided by administrative staff to students and faculty that benefits the institution's overall well-being constitutes an administrative support service. Despite their complementary role in the teaching and learning process, it appears from the literature that administrative support services receive little attention when it comes to students’ evaluation of university services for quality assurance. This article reviews digitally available scholarly research on administrative support services in higher education. The purpose of the review was to justify the inclusion of administrative support in students' evaluations of university services for quality assurance. To do this, the study reviewed scholarly works on administrative support services in higher education. In all, 43 research articles were analyzed in terms of six criteria, namely 1) nature of administrative support in higher education 2) administrative support as service 3) customers of higher education administrative support 4) quality as necessity in administrative support 5) justification for quality assuring administrative support service 6)justification for use of students’ to evaluate administrative support services. The study found that administrative support and teaching services have a direct symbiotic relationship. Quality assurance of teaching services without the same being done for administrative support services does not provide a complete picture of the overall service quality and well-being of higher education. Again, the study found that a lot of resources go into the recruitment and maintenance of administrative staff. To ensure efficiency effectiveness and accountability of this staff, there is the need for frequent evaluation. The study recommends periodic student satisfaction surveys to ascertain students’ level of satisfaction with administrative support services.

Health management information system (HMIS) has been implemented in many countries to promote evidence-based decision making. The aim of this study was to generate information that will help the Ministry of Health (MOH) to improve the use of HMIS data at district level in southern region, Lesotho. This was a descriptive cross-sectional study which employed explanatory mixed methods approach. Quantitative data were collected through records reviews while qualitative data were collected through interviews and records reviews. The findings have shown that DHMTs and district hospitals are using HMIS data quite satisfactorily. Also, data demand by managers and possession of HMIS skills influences the use of data. In conclusion, the main enablers to a satisfactory level of HMIS data use in the southern region were ability of managers to demand data from their subordinates and improved data quality because of intensive interventions aimed at strengthening Lesotho’s HMIS by external donors.

Seismic speckle noise is the primary factor causing severe reflection distortions caused by small-scale near-surface scattering. As in optics and acoustics speckle, deterministic velocity model-building techniques cannot recover these heterogeneities which are much smaller than a wavelength. Conventional processing techniques struggle to perform if multiplicative noise remains unsuppressed. Although local and global stacking mitigates the effects of speckle noise, it leads to a severe loss of higher frequencies reducing the vertical resolution of the seismic data. The foundation for attacking speckle noise is a recently proposed mathematical model that includes two concurrent random multiplicative noise types: type 1 defining residual statics and type 2 describing random frequency-dependent phase perturbations that mimic small-scale near-surface scattering. Using this model, we have developed seismic time-frequency masking to suppress speckle noise on prestack data. The time-dependent and nonsurface-consistent nature of scattering noise dictates window-based approaches borrowed from local stacking techniques. Separate manipulation of phase and amplitude spectra is achieved through modified time-frequency masking inspired by speech processing. A beamformed data set from local stacking is used as a guide for designing phase and amplitude masks that are directly applied to raw data in the time-frequency domain. The phase mask allows the restoration of coherency by repairing phase distortions caused by near-surface scattering. The amplitude mask corrects power spectrum (PS) distortions caused by multiplicative and additive noises. An amplitude mask is implemented using a data-driven minimum statistic approach that estimates the noise PS in each local window. The minimum statistics approach is adapted from speech processing using beamformed data as an initial signal estimate and as a guide to designing an improved amplitude mask. Synthetic and field data examples suggest significant improvements in coherency and signal-to-noise ratio after the suppression of multiplicative noise, which makes the data processable by conventional techniques afterward.

This study aims to evaluate the prevalence of type 2 diabetes mellitus among the adults from 30 years of age and above and to assess the association between the risk factors and type 2 diabetes. A total of 522 patients diagnosed with diabetes at Federal Medical Centre (FMC) Asaba from August 2022 to February 2023 were collected for the study. We employed the method of logistic multinomial regression to assess the association between the risk factors and the type 2 diabetes mellitus, descriptive statistics to ascertain the prevalence of type 2 diabetes mellitus, and the likelihood ratio test to check which of the risk factors is significant. The female was taken as a reference category. The results showed that the prevalence of type 2 diabetes mellitus was higher in females (284, 54.4%) and also in the age group 45-64 years of age. Risk factors that had a significant association with type 2 diabetes mellitus are age (Chi-square = 10.589, p = 0.005), BMI (chi-square = 1.038, p = 0.092), hypertension (chi-square = 1.370, p = 0.042), alcohol consumption (chi-square = 73.319, p = 0.000), and smoking (chi-square = 142.096, p = 0.000). The results further revealed that with female patients as the reference category, a male patient in the age bracket 45-64 years (p = 0.028, AOR = 0.538, 95% C.I: 0.310 – 0.935), a male that is obese (p = 0.090, AOR = 0.962, 95% C.I: 0.524 – 1.765), male with hypertension (p = 0.044, AOR = 1.362, 95% C.I: 0.810 – 2.292), male that consumes alcohol (p = 0.000, AOR = 0.129, 95% C.I: 0.077 – 0.214), and male that smokes (p = 0.000, AOR = 0.014, 95% C.I: 0.005 – 0.042) had 72.3% fewer odds, 3.8% fewer odds, 36.2 higher odds, 87.1 fewer odds, and 98.6% fewer odds of having type 2 diabetes mellitus compared to a female patient. This study suggests appropriate actions for community awareness of regular blood sugar testing and preventive measures.

The reservoir brittleness index can characterize the relative brittleness of shale oil and gas reservoirs, which provides guidance for hydraulic fracturing in the later stage of oil and gas exploration and development. It is a significant index to evaluate the sweet spot of oil and gas reservoirs. Most research on the brittleness index is about laboratory measurements and petrophysical quantitative analysis, but few studies directly predict the reservoir brittleness index from prestack seismic data. The Markov chain Monte Carlo (MCMC) probabilistic algorithm incorporating the delayed rejection adaptive Metropolis (DRAM) strategy has been developed to invert the reservoir brittleness index directly. The different brittleness index is analyzed and compared by the constructed rock-physics model of the shale gas exploration area to select the most sensitive one. Based on the chosen brittleness index, the approximate equation of the PP-wave reflection coefficient for the brittleness index is deduced, and the correctness and achievability of the modeling operator are indicated by theoretical analysis. To analyze the uncertainty of the brittleness index and enhance computational efficiency, an improved MCMC probabilistic inversion algorithm is introduced, which aims to optimize the sampling process of the general MCMC algorithm by delayed rejection and adaptive Metropolis strategies. Our study finds that the DRAM strategy improves the efficiency of the algorithm by nearly 30%. Synthetic examples and field seismic data verify the applicability and effectiveness of our inversion method.

Background: Similar to other African countries, life expectancy of people living with HIV infection has improved due to access to antiretroviral therapy (ART) in Rwanda. However, both HIV infection and use of ART are associated with cardiovascular disease (CVD) risks, due to adverse changes in some biomarkers, causing dyslipidemia and other metabolic imbalances. Biomarkers for CVD risk in HIV-infected individuals taking ART, has not been well characterized in Rwanda. We evaluated the association between the use and duration of ART and biomarkers of CVD risk among HIV infected adults in Rwanda. Methods: A total of 150 participants (18-45 years) from HIV clinics in public Health Center in Kigali included n=30 HIV-uninfected (HIV-) and n=120 HIV-infected (HIV+) adults. Among the HIV+ adults, n=40 participants were ART-naïve. Cross-sectional data were collected on healthrelated behaviors and biochemical markers of CVD risk. We compared CVD-related biomarkers between HIV-, HIV+ ART-naïve, and HIV+ on ART groups. Results: The majority of participants were women (60%) and HIV- were younger (35 ± 6 vs. 31 ± 6 years). Total cholesterol and triglycerides concentrations were associated with ART usage. Serum triglycerides concentrations were lower in HIV+ ART-naïve compared to HIV+ on ART (76.6 ± 38.9 mg/dl vs. 85.0 ± 38.3 mg/dl; p< 0.01). While total cholesterol concentrations were higher in HIV+ on ART than HIV+ ART-naïve (136.0 ± 45.1 mg/dl vs. 130.0 ± 36.5 mg/dl; p

Seismic fluids prediction under the machine-learning framework is of great significance for the exploration and development of oil and gas resources, geothermal energy exploitation, carbon dioxide sequestration monitoring, and groundwater management. Data-driven supervised machine-learning algorithms often rely heavily on the characteristics of the data (number of labels and data distribution). The disparity in the number of different labels for the majority and minority samples can hinder the generalization ability of the machine-learning model, especially weakening the predicting power for minority groups (e.g., hydrocarbon-bearing rocks) which are often of essential interest to us. For a clastic reservoir exhibiting a typical class imbalance (the ratio of gas sandstone to other lithofluids is significantly low), under the framework of a supervised convolutional neural network, we investigate and compare various class-rebalance methods to enhance the model’s prediction ability for gas-bearing sandstones. To achieve the purpose of class rebalance, we mainly use sampling methods to obtain class-balanced data sets and cost-sensitive learning methods to modify loss functions. The crosswell blind tests indicate that the ensemble-based undersampling method of BalanceCascade is found to be most effective in enhancing the prediction performance, increasing the F1 score of gas sandstone by as much as 15%. We also propose the combination of Balance Cascade and focal-loss (FL) methods, which can further improve the F1 score of gas-bearing sandstone in several wells compared with using BalanceCascade or FL alone. By incorporating class-rebalance strategies into model building, we finally obtain more reliable seismic prediction results for gas-bearing sandstone.

We develop a new 3D ambient noise tomography (3D ANT) method for geotechnical site characterization. It requires recording ambient noise fields using a 2D surface array of geophones, from which experimental crosscorrelation functions (CCFs) are then extracted and directly inverted to obtain an S-wave velocity ([Formula: see text]) structure. The method consists of a forward simulation using 3D P-SV elastic wave equations to compute the synthetic CCF and an adjoint-state inversion to match the synthetic CCFs to the experimental CCFs for extraction of [Formula: see text]. The main advantage of the presented method, as compared with conventional passive-source seismic methods using characteristics of Green’s function (GF), is that it does not require equal energy on both sides of each receiver pair or far-field wavefields to retrieve the true GF. Instead, the source power spectrum density is inverted during the analysis and incorporated into the forward simulation of the synthetic CCFs to account for source energy distribution. After testing on synthetic data, the 3D ANT method is applied to 3 h of ambient noise recordings at the Garner Valley Downhole Array (GVDA) site in California, using a surface array of 196 geophones placed on a 14 × 14 grid with 5 m spacing. The inverted 3D [Formula: see text] model is found to be consistent with previous invasive and noninvasive geotechnical characterization efforts at the GVDA site.

Geophysical and geologic data, e.g., results obtained using rock cores, outcrops, and borehole images, reveal the presence of multiple sets of fractures in rock. To analyze how fracture interactions affect seismic anisotropy and dispersion, we consider an effective model that contains two sets of orthogonal fractures. In seismic amplitude analysis, we focus on the case of subsurface target zones containing a fracture network composed of primary and secondary fracture sets. Focusing on gas-bearing rocks with small fracture densities, we formulate simplified stiffness parameters in terms of two groups of fracture weaknesses, which are related to the primary and secondary fractures, respectively. Using the simplified stiffness parameters, we derive the PP-wave reflection coefficient and the azimuthal elastic impedance (AEI) as functions of the two groups of normal and tangential fracture weaknesses. Based on the derived PP-wave reflection coefficient and AEI, we propose a method and workflow in which the azimuthal variations of the partial incidence-angle-stacked seismic data are used to estimate the AEI and differences in AEI (which we refer to as DEI) is input to a nonlinear inversion for two groups of fracture weaknesses. In the nonlinear inversion, the initial values of fracture weaknesses are obtained based on a two-term approximation of the PP-wave reflection coefficient. First- and second-order derivatives of DEI with respect to fracture weakness parameters are calculated to generate the update in the unknown parameter vector. Synthetic seismic gathers with varying signal-to-noise ratios are used to validate the robustness of the estimation. Applying the inversion method to a real data set, we obtain what we interpret to be reliable fracture weakness estimates that produce azimuthal amplitude differences matching those extracted from real seismic data. The results provide a potential tool for determining if two sets of fractures have developed in a reservoir.

Time-reversal imaging is a powerful method for localization of microseismic events. Conventional time-reversal imaging methods like auto-correlation imaging or grouped cross-correlation imaging may suffer from imaging artifacts, e.g., caused by less refined velocity models, noise-contaminated data, and data acquired from sparse receiver networks. These artifacts typically reduce imaging quality and may cause subsequent misinterpretation leading to false positives. To address these issues, we propose a new imaging condition that comprises three steps for each time step: Firstly, we divide the back-propagated wavefield into parts according to their maximum-absolute amplitudes. Secondly, the amplitudes of the back-propagated wavefield are weighted by a Gaussian function with the spatial extent of the prevailing wavelength of the event, centered at the absolute maximum of the part of the wavefield. Finally, we zero-lag cross-correlate these weighted wavefields at each space point to obtain an image for this time step. The final image is gained by summing the images for each time step. This process collects all energy concentrations along the back projection process, and the energy on the wavefront overlap and collapse at the hypocenter leading to high resolution images displaying little to no imaging artifacts. Numerical examples using the Marmousi-II and the 3D SEG overthrust models, and a 3D field data example show the performance of the proposed method. High-resolution low-noise source images allow unique identification of sources even for source clusters, noisy data, and sparse acquisitions. The source localization errors are smaller than the dominant wavelength of the signal, where a smooth model with a mean velocity error of about 5% was considered in the synthetic examples and a homogeneous model was used in the field data example.

As an alternative method for the compensated neutron porosity measurement method, the neutron-gamma porosity measurement method is widely used in cased holes. However, the neutron-gamma porosity measurement method has some problems, such as the lack of detailed theoretical analysis and low sensitivity in high-porosity formations. The purpose of this paper is to clarify the theory of neutron-gamma porosity measurement, improve the measurement sensitivity, and eliminate the effects of environmental factors. Based on the neutron diffusion theory and the gamma transport theory, the distribution of capture gamma rays is described. A new neutron-gamma porosity measurement method is developed based on inelastic and capture gamma-ray distribution. The applicability of the new method in different environments is analyzed using the Monte Carlo method, and the effectiveness of this method is verified using the synthetic model. The results indicate that the capture gamma-ray ratio is only related to the source-detector distance, gamma-ray attenuation length, and neutron migration length. By combining density, different neutron cross sections, inelastic gamma-ray count ratio, and capture gamma-ray count ratio, the parameter secondary gamma-ray hydrogen index (SGH) related to hydrogen index can be extracted. The dynamic range of SGH is much higher than thermal neutron count ratio and the capture gamma-ray count ratio. The errors in porosity calculation by this method under different borehole and lithologic conditions are generally less than 2 pu. The calculation error of this method is close to that of the compensated neutron porosity measurement method. In addition, the applicability of the new method is analyzed without density data, and the results indicate that the calculation results are basically consistent with the results of calculation with density data. The new method has great potential for extensive applications in cased holes or open holes as an alternative for the compensated neutron porosity logging measurement method.

Seismic imaging methods like Phase Shift Plus Interpolation achieve computational efficiency by reducing the associated P-wave velocity model to a small set of reference values. Anisotropy complicates this reduction because multiple parameters characterize an anisotropic model, and they do not necessarily correlate in space. Rather than attempting to find reference parameters for potentially uncorrelated anisotropic models, I find a set of reference traveltimes based on the spatial variation of horizontal slowness at the evanescent boundary. Strong changes in that horizontal slowness mark zones of strong changes in anisotropic parameters simultaneously, and I use these zones to define the set of reference traveltimes. Based on traveltime comparisons and impulse responses, I show that reference traveltimes rather than reference parameters return greater accuracy with a more reasonable computational cost.

Cement-bond evaluation is of great significance in oil/gas development, geothermal production, and CO2 storage. Advanced ultrasonic pitch-catch measurement exhibits poor performance in determining a cement-formation interface due to weak reflections from the cement-formation interface (third interface echo) in nonaxisymmetric complex ultrasonic environments. To deal with this issue, we use a reverse time migration (RTM) approach for ultrasonic pitch-catch measurements to image the cased-hole structure, especially for the cement-formation interface. To further enhance cased-hole RTM feasibility, a phase-shift interpolation technique is applied to reconstruct ultrasonic array waveforms from limited receivers in the pitch-catch measurement. Synthetic examples demonstrate that RTM is capable of imaging the cement-formation interface with a high resolution under various eccenterings of casings and tools. This study illustrates that small errors introduced by phase-shift interpolations do not greatly degrade the imaging result of RTM. Furthermore, tests for inclined cement-formation interfaces demonstrate that the RTM is able to recover the true position and geometry of the cement-formation interface when a smoothed velocity model is available. In addition, although RTM is sensitive to the velocity perturbation, it is possible to image the cased-hole structure by using a multistep strategy assuming that the position and thickness of the steel casing are unknown.

SUMMARY The massive eruption of the Hunga Volcano on 15 January 2022 provides an ideal test case for reviewing established methods to discriminate and analyse source processes. Discriminating source mechanisms and identifying their origins is a key task when analysing suspicious events in the frame of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Earthquakes and explosions can be distinguished in some cases using well established methods such as inversion for the seismic moment tensor. In more complex cases the combination of analyses of the seismic, infrasonic and hydroacoustic waveform content can be of help. More challenging is the discrimination of the specific kind of explosive source such as a nuclear test and a volcano eruption based on the data from the three waveform technologies alone. Here, we apply standard techniques destined to analyse relevant events in the frame of the CTBT, that is all three waveform technologies (seismology, infrasound and hydroacoustic) and atmospheric transport modelling of radionuclides. We investigate the potential of standard analysis methods to discriminate a source and identify their possible weaknesses. We show that the methods applied here work very well to identify, investigate and discriminate an explosive event. During discrimination we could not only exclude a shear-source (i.e. earthquake) but also distinguish the volcanic explosion in contrast to a man-made explosion. However, some tasks remain difficult with the available methods. These tasks include the reliable estimation of the strength of a non-shear event and thereupon a yield estimation of a possibly CTBT relevant event. In addition to evaluating our methods, we could relate our results with specific phases of the eruption process providing a more detailed insight of what happened. Our investigations of the eruption details only provide a starting point for further in-depth analysis. However, they underline the importance of the Hunga eruption event for science. The huge amount of observations provide a unique opportunity for knowledge gain in several subdisciplines of the geosciences. In addition, although not being a nuclear test, it also provides a useful and important data set for further developing multitechnology analyses in the frame of the CTBT.

The increasing global interest in geologic carbon storage as a feasible way of reducing CO2 atmospheric levels requires extensive onshore high-resolution seismic investigations to characterize suitable storage sites, for example, close to major CO2 emitters. To partly address this challenge and to acquire quality data at shallower and greater depths in a cost and time-effective approach, a tailored acquisition scheme was adopted and tested at a candidate site in Stenlille, Denmark. The survey aims at understanding whether an anticline reservoir structure known to exist at a 1000 m depth can serve for long-term CO2 storage and presents the structural integrity for this purpose. The data were recorded using a combination of nodal arrays, spaced at 10 m in a fixed geometry, and a set of more closely (2 m) spaced digital recorders, mounted on a landstreamer, which was moved at each shot location. Two 12 t mini vibrators were used as seismic sources. The nodal and landstreamer data sets are compared and combined into a unique data set for reflection imaging purposes along five profiles with a total length of approximately 12 km. The seismic sections obtained using this tailored combination of different recorders provide images of the entire shallow and deeper structures with an unprecedented resolution at the different depth levels necessary to assess the full potential of the suggested CO2 storage reservoir. The results significantly increase the existing knowledge of the extent and structural closure of the reservoir as well as a possible fault, all of which are critical for future risk analysis and planning of the storage.

Theoretical studies predict that a slow compressional wave propagating in a fluid-saturated porous medium can produce a coseismic electric field due to the electrokinetic effect, but the experimental proof is still lacking. Laboratory experiments are conducted to measure such a seismoelectric conversion inside a synthetic rock. Fluid pressure signals are recorded by using mini hydrophones 1.6 mm in diameter, and then electric field signals generated at the liquid-solid interface and inside the rock sample based on the seismoelectric effect are recorded by electrode arrays, respectively. The seismoelectric waves induced by fast and slow compressional waves can be clearly identified in the recorded electric signals and their attenuation property are analyzed at an ultrasonic frequency, which confirms that the seismoelectric signals induced by fast/slow compressional waves are measurable in the experiments. To support our explanation of the experimental observation, theoretical simulations are conducted according to the experimental model, and then compared with the recorded experimental data. The results find that the simulated wavefields are in excellent agreement with those signals measured in the measurements, which proves the theoretical prediction of the seismoelectric signal accompanying the slow compressional wave and suggests a feasible way for detecting the slow compressional wave property with seismoelectric conversions in field measurements.

Seismic samples are generally designed to be placed on perfect Cartesian coordinates, that is, on-the-grid. However, sampling geometry is disturbed by obstacles in field applications. Large obstacles result in missing samples. For small obstacles, geophones or sources are placed at an available off-the-grid location nearest to the designed grid. To achieve simultaneous off-the-grid regularization and missing data reconstruction for 3D seismic data, we develop a new mathematical model based on a new combined sampling operator, a 3D curvelet transform, and a fast projection onto convex sets (FPOCS) algorithm. The sampling operator is combined with a binary mask for on-the-grid samples reconstruction and a barycentric Lagrangian (BL) operator for off-the-grid samples regularization. A 2D BL operator is obtained using the tensor product of two 1D BL operators. The inversion problem is efficiently solved based on FPOCS. This method is tested on synthetic and field data sets. The reconstruction results outperform the methods based on the binary mask in terms of signal-to-noise ratio and visual effect.

We present PySulfSat, an open-source Python3 tool for modeling sulfide and anhydrite saturation in magmas. PySulfSat supports a variety of data types (spreadsheets, Petrolog3 outputs, MELTS tbl files). PySulfSat can be used with alphaMELTS for Python infrastructure to track sulfur solubility during fractional crystallization within a single Jupyter Notebook. PySulfSat allows far more customization of calculations than existing tools. For example, the SCSS2− could be calculated with one model using the sulfide composition from a parameterization released with a different SCSS2− model. There are also functions for calculating the proportion of S6+/STot, allowing modeled SCSS and SCAS values to be converted into total S solubility to compare to natural data. We also contain functions for modeling mantle melting in the presence of sulfides using a variety of SCSS and KD models. Extensive documentation and worked examples are available at ReadTheDocs (https://bit.ly/PySulfSatRTD) along with narrated YouTube videos (https://bit.ly/PySulfSatYouTube).

Seismic waves always suffer from amplitude dissipation and phase distortion and such attenuation-induced effects will degrade the quality of seismic data. Therefore, a slew of researches on attenuation compensation have been proposed to correct the attenuation effects and improve the resolution of original data. In recent years, geophysicists have paid more attention on prestack compensation because prestack data contains more information of subsurface medium. However, it is challenging to implement prestack compensation for which the traveltime of prestack data is hard to be determined unless an accurate velocity model is available. Furthermore, prestack data usually behaves lower signal to noise ratio (SNR), which is more prone to noise amplification during compensation. In order to improve the performance of prestack compensation, we propose a robust structure-oriented multichannel prestack compensation method. We incorporate additional adaptive structure regularization to stabilize the processing of compensation. We refer the proposed structure constrained multichannel prestack compensation method as SCMPC. With the help of adaptive structure regularization, the proposed method has a superior ability to suppress those artifacts caused by ambient noises and enhance the consistency of effective signals during compensation. Compared with classic single-channel prestack compensation methods (SPC), the proposed SCMPC method can provide a better result with higher accuracy and SNR. We adopt synthetic and field examples to further validate the well performance of the proposed method.

Convolutional Neural Network (CNN)-based seismic interpolation methods recover the missing traces by feeding the corrupted data to a trained neural network, whose parameters are obtained by training pairs of corrupted data and their complete labels. Compared to traditional reconstruction approaches, these methods require less human-computer interaction and computation time, therefore, CNNs approaches have been popular for 2D/3D seismic interpolation. 5D seismic data interpolation methods recover missing traces simultaneously in five dimensions, considering all the physical coordinates with high-accuracy. Unfortunately, existing deep learning frameworks (such as Tensorflow and Pytorch) only provide low-dimensional convolution operators (no more than 3D), which makes it difficult to generalize to 5D seismic reconstruction directly. To this end, we propose an effective 5D-CNN by cascading low-dimensional convolution to deal with 5D seismic interpolation, referred as CCNet-5D. First, based on the definition of convolution and the theory of tensor decomposition, 5D convolution operator is approximated by the sum of multiple cascading of low-dimensional convolution operators. Then, we demonstrate the CNN architecture for 5D convolutional operators by cascading of 3D and 2D convolutional layer, termed as CC-3D2D module. The final CCNet-5D is constructed by stacking the four resulting CC-3D2D modules. In our setup, 5D-CNN outperforms the existing 5D traditional method and 3D CNN-based method.

Least-squares reverse time migration (LSRTM) has shown great potential to improve the amplitude-fidelity and spatial resolution of reverse time migration (RTM) image. However, the main disadvantage is that it requires significant computational resources for the iterative solution. To ameliorate this problem, the image-domain least-squares reverse time migration (IDLSRTM) approach through point-spread functions (PSFs) has been proven to be a viable and alternative technique to deconvolve the standard RTM image. In this paper, we present a tutorial for the numerical implementation of IDLSRTM through PSFs. The Hessian matrix in the standard IDLSRTM approach is estimated through the spatial interpolation of precomputed PSFs on the fly, where the PSFs are computed by one-round forward modeling and migration. However, the resulting IDLSRTM scheme is highly ill-conditioned, because of the incomplete acquisition condition, irregular subsurface illumination, and band-limited data. To stabilize inversion and improve the inverted image, we suggest that the PSFs and RTM image should be deblurred by applying a deblurring filter. The deblurring PSFs can reduce the condition number of the standard Hessian matrix and make the inverse problem more well-conditioned, thus improving imaging quality and accelerating convergence. Furthermore, the regularization operators should be imposed to produce a reasonable inverted image and avoid the overfitting of the image-matching term. Based on several examples with synthetic and field data, we can conclude two significant points. The first point is that the standard IDLSRTM approach through the conventional PSFs can only recover a similar reflectivity image to the deblurring RTM and non-stationary matching filter (NMF) approaches. The second point is that the deblurring IDLSRTM approach through the deblurring PSFs can retrieve the reflectivity image with higher resolution and better amplitude-fidelity than the standard IDLSRTM approach and the standard RTM approach with the deblurring filter or NMF.

The free-surface boundary condition is a crucial aspect in numerical modeling of (visco)elastic wave equations, especially when using a finite-difference (FD) method in the presence of surface topography. The parameter-modified method is a widely used approach to solve this problem. In this regard, the adaptive Poisson's ratio parameter-modified (APM) method has proven to be effective in accurately simulating seismic surface waves within the FD discretization framework. Based on the equivalent medium theory, vacuum approximation, and mathematical limit, we developed a viscoelastic parameter-modified (VPM) method for the implementation of the free-surface boundary condition in the three-dimensional (3D) viscoelastic wave equation. Our approach modifies the viscoelastic constitutive relation and density at the free surface and provides a formulation in terms of displacement and stress. We demonstrated that our VPM method is more general than the viscoelastic stress-image (VSI) method as it includes the latter as a limit case when Poisson's ratio equals zero. The presented free-surface method is represented implicitly within the FD grid, and we provide implementation details when simulating surface waves with topography in the standard staggered-grid FD scheme. We support our theory' feasibility and accuracy through numerical examples.

SUMMARY A new approach is proposed for measuring the dispersion relation of surface waves in weakly anisotropic media using a single station, which consists of translational displacement and rotation or strain. The azimuth-dependent surface wave dispersion curve can be directly obtained by using the amplitude ratio of translational displacement to rotation or strain. Using observations from earthquakes from a variety of azimuths allows us to characterize the anisotropy of subsurface media. The amplitude ratio gives the localized azimuth-dependent dispersion relations of the formation beneath a receiver without requiring knowledge of the source or structure along the path. The theory shows that in anisotropic media the coupled quasi-Rayleigh wave and quasi-Love wave will result in elliptically polarized rotational motions. In addition, rotational motion information allows the determination of backazimuth even in general anisotropic media. We carry out numerical experiments, investigate the effects of noise and degree of anisotropy and demonstrate the potential for field studies.

Detecting the presence of gaseous formation fluids, estimating the respective volumes, and characterizing their spatial distribution is important for a wide range of applications, notably for geothermal energy production. The ability to obtain such information from remote geophysical measurements constitutes a fundamental challenge, which needs to be overcome to address a wide range of problems, such as the estimation of the reservoir temperature and pressure conditions. With these motivations, we compute the body wave velocities of a fractured granitic geothermal reservoir formation with varying quantities of steam to analyze the seismic signatures in a partial saturation context. We employ a poroelastic upscaling approach that accounts for mesoscale fluid pressure diffusion (FPD) effects induced by the seismic strain field, and, thus, describes the governing physical processes more accurately than standard representations. Changes in seismic velocities due to steam saturation are compared with changes associated with fracture density variations, as both are plausible results of pressure changes in geothermal reservoirs. We find that steam saturation has a significant impact on P-wave velocities while affecting S-wave velocities to a significantly lesser extent. This contrasting behavior allows to discriminate between fracture density and steam saturation changes by means of P- and S-wave velocity ratio analyses. To evaluate the potential of seismic methods to provide this information, a canonical geothermal reservoir model is employed to compute Rayleigh wave velocity dispersion and seismic reflection amplitude vs angle (AVA) curves. These studies reveal that AVA analyses allow to differentiate changes in fracture density from changes in steam saturation. We also note that Rayleigh-wave-based techniques are much less sensitive to steam content changes than to fracture density changes. Comparisons with elastic approaches show that including FPD effects through the use of a poroelastic model is crucial for the reliable detection and characterization of steam in fractured geothermal reservoirs.