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We undertook Zr isotope measurements on zircon, titanite, biotite, amphibole, and whole rocks from the La Posta pluton (Peninsular Ranges, southern California) together with trace element analyses and U-Pb age measurements to understand the controls on Zr isotope fractionation in igneous rocks, including temperature, crystallization sequence, and kinetic effects. We find large (>0.6‰) Zr isotope fractionations (expressed as δ⁹⁴/⁹⁰Zr) between titanite and zircon forming at approximately the same temperature. Using equilibrium fractionation factors calculated from ionic and ab initio models, we infer the controls on Zr isotope evolution to include the relative order in which phases appear on the liquidus, with titanite fractionation resulting in isotopically lighter melt and zircon fractionation resulting in isotopically heavier melt. While these models of Zr fractionation can explain δ⁹⁴/⁹⁰Zr variations in zircon of up to ∼1.5‰, crystallization order, temperature and presence of co-crystallizing phases do not explain all aspects of the intracrystalline Zr isotopic distribution in zircons in the La Posta pluton or the large range of Zr isotopic values among zircons (>2‰). Without additional constraints, such as knowledge of co-crystallizing phases and a better understand of the true causes of Zr isotope fractionation, Zr isotopes in zircon remains an ambiguous proxy of magmatic evolution.

The association of MgII clays with dolomite is common in ancient and modern lacustrine environments, although, the role of microbial activity in their precipitation remains a challenge. In this study, microbial culture experiments provide the first evidence of saponite and dolomite precipitation on diatom-bearing photosynthetic microbial mats. Microbial strains were isolated from photosynthetic microbial mats collected from Caballo Alba lake in Segovia, Spain. The microbial communities´ growth and mineral precipitates varied function of the type of media used, semi-solid or liquid, respectively. The prokaryotic composition identified from cultures was dominated by Cyanobacteria and Proteobacteria. Bacteroidetes were the most abundant heterotrophic bacteria. Saponite, aragonite, and dolomite crystals were closely attached to the phytoplanktonic communities grown in liquid cultures. Diatoms are replaced by saponite and dolomite in liquid cultures where diatoms are unprovided of protection of extracellular polymeric substances (EPS). Saponite grew around the diatom frustules, as dissolution of the biogenic silica occurs in a medium depleted in silica, replacing diatoms by saponite pseudomorphs. To a lesser extent, cyanobacterial cell walls were also covered by saponite crystals. In addition, amorphous silica of the frustules also provided a suitable template for the nucleation of dolomite crystals. Alternatively, MgII-rich aragonite crystals with fibrous morphologies precipitated within saponite crystal aggregates, suggesting that clay minerals enhanced the nucleation and precipitation of dolomite. In the semi-solid medium, where calcite precipitated in association with Cyanobacteria, diatoms were capable of developing a sheet of EPS which protected their frustules from dissolution. Here, we suggest that, in alkaline lakes phytoplanktonic diatoms might have contributed to the precipitation of clay minerals and carbonates since the Jurassic.

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.

International audience; Diagenesis has been recognized for decades to significantly alter the trace elements biogenic signatures in fossil tooth enamel and bone that are routinely used for paleobiological and paleoenvironmental reconstructions. This signature is modified during diagenesis according to a complex continuum between two main processes, addition and substitution. For an additive-like, or early diagenesis, the trace elements biogenic profiles can be restored by leaching secondary minerals, but this technique is inefficient for a substitutive-like, or extensive diagenesis for which secondary trace elements are incorporated into the biogenic mineral. This scheme is however unclear for Ca, the major cation in tooth enamel and bone hydroxylapatite, whose stable isotope composition (δ44/42Ca) also conveys biological and environmental information. We present a suite of leaching experiments for monitoring δ44/42Ca values in artificial and natural fossil enamel and bone from different settings. The results show that enamel δ44/42Ca values are insensitive to an additive-like diagenesis that involves the formation of secondary Ca-carbonate mineral phases, while bone shows a consistent offset toward 44Ca-enriched values, that can be restored to the biogenic baseline by a leaching procedure. In the context of a substitutive-like diagenesis, bone exhibits constant δ44/42Ca values, insensitive to leaching, and shows a REE pattern symptomatic of extensive diagenesis. Such a REE pattern can be observed in fossil enamel for which δ44/42Ca values are still fluctuating and follow a trophic pattern. We conclude that Ca isotopes in fossil enamel are probably not prone to extensive diagenesis and argue that this immunity is due to the very low porosity of enamel that cannot accommodate enough secondary minerals to significantly modify the isotopic composition of the enamel Ca pool.

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.