Editor’s Notes
Total Results: 1697
Volume 105 : November 2020 Issue
Trace elements in sulfides from the Maozu Pb-Zn deposit, Yunnan Province, China: Implications for trace-element incorporation mechanisms and ore genesis
https://doi.org/10.2138/am-2020-6950
To understand the genesis of Pb-Zn deposits in the Sichuan-Yunnan-Guizhou Metallogenic Province (SYGMP), the trace elements in different sulfides (sphalerite and galena) from the Maozu Pb-Zn deposit, which is a representative Pb-Zn deposit in the SYGMP, were analyzed by Li et al. via LA-ICP-MS. Compared with trace elements in sulfides from the different genetic types of Pb-Zn deposits, the Maozu Pb-Zn deposit is characterized by enrichment of Ge, Fe, Mn, and Co in sphalerite and Ag, Sb, Cd, and Se in galena, which is similar to the composition of typical Mississippi Valley Type (MVT) deposits and different from those of SEDEX, VHMS, and skarn type Pb-Zn deposits, suggesting that the Maozu deposit is a MVT deposit.
New pressure-induced phase transition to Co2Si-type Fe2P
https://doi.org/10.2138/am-2020-7574
The phase relations and elastic properties of Fe alloys with light elements under relevant high-pressure and high-temperature conditions are the keys to understanding the nature of planetary metallic cores. Phosphorous is one of the candidates for core light elements. Here, Nakajima et al. discovered a new phase transition in Fe2P from Co2P-type (C23) to Co2Si-type (C37) structure at 42 GPa based on in-situ high pressure-high temperature X-ray diffraction measurements. The results indicate that the new C37-type Fe2P phase can be stabilized as the most iron-rich phosphide phase under planetary core conditions where the pressure is higher than 42 GPa. Moreover, the present study reveals that (Fe,Ni)2(S,Si,P) could have wide solid solution and constitute planetary cores.
Effects of small crystallite size on the thermal infrared (vibrational) spectra of minerals
https://doi.org/10.2138/am-2020-7602
The infrared spectra of minerals change when their crystallite sizes approach the wavelength of light. Hamilton et al. show that these changes can be used to recognize small crystallite sizes in samples lacking other indicators of this characteristic. Such small crystallite sizes are commonly associated with abbreviated crystal growth and reflect a potentially important aspect of the sample's geologic history.
Volume 105 : October 2020 Issue
The effects of solid-solid phase equilibria on the oxygen fugacity of the upper mantle
https://doi.org/10.2138/am-2020-7162
Terrestrial magmas and peridotites display large variations in oxygen fugacity, typically attributed to differences in the redox state of multivalent elements in the mantle or to processes acting on segregated melts. Using thermodynamic models, Stolper et al. show that the oxygen fugacity of subsolidus mantle peridotite of a fixed composition can vary by 1.5 log units in the upper ~100 km of the mantle due to the same reactions that produce transitions from plagioclase-spinel-garnet lherzolite and variations in Al in pyroxenes. These effects of phase equilibria on peridotite oxygen fugacity are likely to be superimposed on variations due to bulk composition and should be considered in efforts to understand variations in the oxygen fugacities of magmas and their mantle sources.
Structural and spectroscopic study of the kieserite-dwornikite solid-solution series, (Mg,Ni)SO4·H2O, at ambient and low temperatures, with cosmochemical implications for icy moons and Mars
https://doi.org/10.2138/am-2020-7287
Talla et al. present new detailed data on the behavior of the kieserite-Ni-kieserite solid solution series. The study documents changes in the crystal structure along the binary join, as well as variations in the IR and Raman spectral band positions in relation to the changing chemical and structural properties. These sulfate phases are of cosmochemical importance, as they occur in considerable amounts on some planetary objects in our solar system.
Mineral compositions and thermobarometry of basalts and boninites recovered during IODP Expedition 352 to the Bonin forearc
https://doi.org/10.2138/am-2020-6640
IODP Expedition 352 to the Bonin forearc recovered tholeiitic forearc basalt (FAB) and slightly younger basaltic, low-Si and high-Si boninite. Using mineral compositions and thermobarometry, Whattam et al. determined the conditions of crystal growth and differentiation for Expedition 352 lavas and compared these conditions with those recorded in lavas from mid-ocean ridges, forearcs, and ophiolites.
An evolutionary system of mineralogy. Part II: Interstellar and solar nebula primary condensation mineralogy (>4.565 Ga)
https://doi.org/10.2138/am-2020-7447
The evolutionary system of mineralogy relies on varied physical and chemical attributes, including trace elements, isotopes, solid and fluid inclusions, and other information-rich characteristics, to understand processes of mineral formation and to place natural condensed phases in the deep-time context of planetary evolution. This paper by Hazen and Morrison considers the formation of primary crystalline and amorphous phases by condensation in interstellar molecular clouds and the earliest period of solar nebula evolution-environments that increased mineralogical diversity and distribution prior to the accretion of planetesimals greater than 4.5 billion years ago.
Swelling capacity of mixed talc-like/stevensite layers in white/ green clay infillings (“deweylite”/ “garnierite”) from serpentine veins of faulted peridotites, New Caledonia
https://doi.org/10.2138/am-2020-6984
Fonteneau et al. describe the occurrence of stevensite in vein-infillings of reactivated faults from peridotitic formations, New Caledonia. Five samples of white (deweylite) and bluish green (garnierite) clay infillings were selected from a large set of vein infillings to investigate their swelling ability and crystal chemistry. They belong to the ultimate phases of clay infillings, which are predominantly made of 2:1 layer silicates. Different treatments were used to link the gradual increase of the swelling capacity to charge deficiency and structural defects in mixed S and TL phases.
Experimental observations of TiO2 activity in rutile-undersaturated melts
https://doi.org/10.2138/am-2020-7391
Over the past decade, trace-element thermobarometry (e.g., Ti-in-quartz, Ti-in-zircon) has emerged as a powerful tool to determine the thermal and barometric histories of igneous and metamorphic rocks. In many instances, the application of these tools requires an accurate estimate of Ti activity when rutile is not present. In this study, Ackerson and Mysen utilized two methods (a rutile-saturation model and a Ti-in-tridymite solubility calibration) to calculate Ti activity in rutile-undersaturated melts, and demonstrate that rutile-saturation model estimates consistently over-predict Ti activity. When applied to natural systems, this over-prediction will lead to an under-estimation of magmatic temperatures.
Direct evidence for the source of uranium in the Baiyanghe deposit from accessory mineral alteration in the Yangzhuang granite porphyry, Xinjiang Province, northwest China
https://doi.org/10.2138/am-2020-7383
Zhang et al. provide new insights into ore sources and enrichment processes of post-magmatic hydrothermal uranium deposits. This study also provides an example illustrating the application of primary versus altered U-bearing mineral-assemblages and their trace element abundances and textures to trace the source of uranium for uranium deposits. The results highlight the potential of element mapping in obtaining direct evidence for uranium leaching from source rocks and in tracing the source of uranium in ore deposits.
Extraction of high-silica granites from an upper crustal magma reservoir: Insights from the Narusongduo magmatic system, Gangdese arc
https://doi.org/10.2138/am-2020-7369
Although the magma dynamics for the genesis of crystal-poor high-SiO2 rhyolites has been a subject of many studies, the dynamics for the formation of high-silica granites are poorly understood. Yang et al. provide a scarce case that kilometer-scale high-silica granite bodies are the extracted products from a shallow magma reservoir. These high-silica granites can be regarded as failed eruptions of high-SiO2 rhyolites. The work addresses a broad range of issues concerning silicic magmatism, such as the behaviors of shallow magmatic systems, the volcanic-plutonic connections, and, particularly, the capability and efficiency of crystal-melt separation in upper crustal reservoirs.
“EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry” by Angel et al. (2017)—Discussion
https://doi.org/10.2138/am-2020-7267
EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry by Angel et al. (2017)—Discussion
“EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry”—Reply to Zhong et al.
https://doi.org/10.2138/am-2020-7616CCBY
“EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry” —Reply to Zhong et al
Synthesis and crystal structure of Pb-dominant tourmaline
https://doi.org/10.2138/am-2020-7457
Vereshchagin et al. synthesized a Pb-dominant tourmaline (up to 14.7 wt% PbO) at 700 °C and 200 MPa using a hydrothermal method. Structural analysis shows that tourmaline can incorporate significant amounts of Pb2+ (up to 0.71 apfu) in its X-site, which means that natural Pb-rich tourmalines belong to a Ca-dominant group. Similarities between (1) the paragenesis of Minh Tien tourmaline and (2) the observed, final experimental phase assemblage indicate comparable P-T conditions of formation.
Element loss to platinum capsules in high-temperature– pressure experiments
https://doi.org/10.2138/am-2020-7580
Wang et al. investigate the loss behavior of 45 elements in high-temperature-pressure experiments and find (1)15 elements including V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Cd, In, Sn, W, and Mo lose significantly from the sample by alloying with Pt at reducing condition; (2) Graphite- and Re-lined Pt capsules can prevent the loss of V, Cr, Mn, Fe, Zn, Ga, Ge, Cd, In, Sn, W, and Mo, but can barely reduce the loss of Ni and Cu; (3) Element loss can be reduced effectively at the oxidizing condition, and all the elements except Cu are retained at Ru-RuO2 buffered condition. The results provide several viable capsule assemblies that are capable of preventing or reducing element loss, which may prove useful in determining precise phase diagrams and accurate partition coefficients in HTP experiments.
NEW MINERAL NAMES
https://doi.org/10.2138/am-2020-NMN1051022
New Mineral Names
Volume 105 : September 2020 Issue
How American Mineralogist and the Mineralogical Society of America influenced a career in mineralogy, petrology, and plate pushing, and thoughts on mineralogy’s future role
https://doi.org/10.2138/am-2020-7382
This reflection by W.G. Ernst was a part of the recent yearlong centennial celebration of the MSA that took place at the 2019 GSA annual meeting in Phoenix. One day’s activities featured invited talks by extant MSA presidents. Most speakers described exciting new mineralogic studies in progress, whereas Dr. Ernst took a “walk down memory lane” -- a chronicle of 65 years of scientific studies and a few lessons learned from them, as well as concerns regarding the future habitability of the Earth. Dr. Ernst’s goals involved the integration of mineralogy, petrology, and geochemistry with regional geology and plate tectonics.
Petrographic and spectral study of hydrothermal mineralization in drill core from Hawaii: A potential analog to alteration in the martian subsurface
https://doi.org/10.2138/am-2020-7125
This is the first analysis of alteration in basaltic materials obtained from the subsurface that can provide a unique analog for alteration environments on Mars. The paper by Calvin et al. describes the initial analysis of spectra taken of drill core in the field used to investigate a set of cut sections that represent the mineralogical diversity present. Petrography and infrared spectroscopy identify similar minerals and show that field spectra can be a useful reconnaissance tool for subsequent higher resolution and more time-consuming analysis in the lab.
Characterizing low-temperature aqueous alteration of Mars-analog basalts from Mauna Kea at multiple scales
https://doi.org/10.2138/am-2020-7131
Rasmussen et al. characterized the low-temperature aqueous alteration of core samples documenting the shield-building phase of Mauna Kea’s formation. Trioctahedral Mg-Fe smectites and multiple zeolites make up the bulk of the alteration mineralogy, providing an opportunity to spectrally characterize these minerals in geologically realistic mixtures. Spectral characterization of these minerals and understanding their environment of formation are fundamental in the pinpointing of Martian alteration conditions.
Archean to Paleoproterozoic seawater halogen ratios recorded by fluid inclusions in chert and hydrothermal quartz
https://doi.org/10.2138/am-2020-7238
Halogens are critical elements for sustaining life on Earth and control the salinity of the oceans. Changes in past ocean halogen compositions are largely unknown, especially for the least abundant halogen, iodine. Burgess et al. determine Cl, Br, and I abundances in chert from the 2.5 Ga Hamersley Banded Iron Formation and hydrothermal quartz from the 3.5 North Pole area, both in Australia. Comparable results from both imply that ancient oceans had Br/Cl and I/Cl about 30% and 30 times higher, respectively, relative to modern seawater. The higher I/Cl indicates a smaller organic reservoir in the ancient oceans.
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