Zimbabwe's coloured gemstone endowments - A regional geological overview

Zimbabwe hosts a varied array of coloured gemstones. With the exception of emerald deposits and several world-class pegmatites, few of the gemstone occurrences have received detailed attention from the scientific or mineral exploration communities. In the present contribution we summarize the status of knowledge of the gemstone deposits and occurrences in Zimbabwe, paying particular attention to the geological settings in which they were formed. Synthesis of this regional geological approach reveals that there may be significant exploration potential for further gemstone occurrences, particularly in the extensive pegmatite fields and in Al-enriched orogenic belts that have undergone greenschist to granulite facies metamorphism. Further socio-economic and developmental initiatives will aid in optimizing the value generation from this important sub-sector

A rest potential study of impurity (As, Au, Ni and Co) bearing synthetic pyrite in alkaline flotation conditions

Pyrite is an important mineralogical component of most sulphide ore deposit classes, where it commonly forms part of the gangue mineralogy, but may also represent an important ore mineral (i.e., auriferous pyrite). Effective and efficient separation of pyrite is thus a crucial step during most ore processing operations, and this is in part influenced by the pyrite mineral chemistry. Here, electrochemical measurements were used to study the reactivity of a series of well-characterised synthetic trace-element substituted pyrite samples under alkaline conditions relevant to industrial flotation. The presence of metals and metalloid impurities (As, Au, Co, and Ni) in pyrite were tested using rest potential measurements to infer oxidation and associated hydrophobicity. In the absence of any collector phases, pure- and Ni-substituted pyrite have the highest rest potential, followed by Co-substituted pyrite and couple-substituted (Co + Au) pyrite, whilst As-substituted pyrite has the lowest measured rest potential. Importantly, the degree of oxidation at the mineral surface correlates linearly with the concentration of each of the substituents, with the largest effect observed when As is the substituent. These results correspond to the semiconducting properties and noble character of each pyrite sample, with n-type pyrite (Au-, Co- and Ni-substituted) associated with noble character and high rest potential, whereas p-type As-substituted pyrite associated with least noble character and lowest rest potential. With the addition of a potassium amyl xanthate collector, the mineral chemistry further had an impact on the probability of dixanthogen formation. Increased substituent concentration in the pyrite lattice decreased the probability of dixanthogen formation, except in a sample where high Au (and moderate Co) was incorporated. These results highlight the importance of developing improved understanding of the impacts of substitution mechanisms on the surface reactivity and flotability of pyrite. Such an understanding will form the foundation for further improved (and engineered) approaches towards reagent design and mixture. This will serve to optimise separation of both gangue and valuable pyrite by using fundamental knowledge to target specific collector bands and flotation domains. © 2023 The AuthorsMinistry of Education and Science of the Russian Federation, Minobrnauka; Universiteit Stellenbosch, US; DSI-NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis, CIMERA; Institute of Experimental Mineralogy, Russian Academy of Sciences, IEM, RAS: NSh-2394.2022.1.5The authors are grateful to the DSI-NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis (CIMERA) for providing funding for this research. Special thanks to the Russian Academy of Science's Institute of Experimental Mineralogy for facilitating this collaboration and assisting with the synthesis of the pyrite crystals used in this study. In addition, Dr. Chareev acknowledges the state financial support of the leading scientific schools of the Russian Federation No. NSh-2394.2022.1.5 and the research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program) that helped establish the experimental lab used to generate synthetic samples for this study. The authors would also like to express their gratitude to the colleagues at Stellenbosch University's Central Analytical Facilities (CAF) for their excellent assistance with the SEM and LA-ICP-MS evaluations. Thanks to Remy Bucher at Ithemba Labs for his help with the XRD analysis of our samples. Additionally, the authors would like to thank the editor and reviewers for reading and evaluating our manuscript

Connectivity between marine reserves and exploited areas in the philopatric reef fish Chrysoblephus laticeps (Teleostei: Sparidae)

"No-take‟ Marine Protected Areas (MPAs) are successful in protecting populations of many exploited fish species, but it is often unclear whether networks of MPAs are adequately spaced to ensure connectivity among reserves, and whether spillover occurs into adjacent exploited areas. Such issues are particularly important in species with low dispersal potential, many of which exist as genetically distinct regional stocks.The roman, Chrysoblephus laticeps, is an overexploited, commercially important fishery species endemic to South Africa. Post-recruits display resident behavior and occupy small home ranges, making C. laticeps a suitable model species to investigate connectivity in marine teleosts with potentially low dispersal ability. We used multilocus data from two types of highly variable genetic markers (mitochondrial DNA control region and microsatellites) to clarify patterns of genetic connectivity and population structure in C. laticeps using samples from two MPAs and several moderately or severely exploited regions. Despite using analytical tools that are sensitive to detect even subtle genetic structure, we found that this species exists as a single, well-mixed stock throughout its core distribution. This finding lends supports to the status of MPAs as an adequate tool for managing overexploited marine teleosts. Even though adult dispersal out of MPAs is limited, the fact that the large adults in these reserves produce exponentially more offspring than their smaller counterparts in exploited areas makes MPAs a rich source of recruits. We nonetheless caution against concluding that the lack of structure identified in C. laticeps and several other southern African teleosts can be considered to be representative of marine teleosts in this region in general. Many such species are represented in more than one marine biogeographic province and may be comprised of regionally-adapted stocks that need to be managed individually

Identification of stomach contents from a Shepherd's beaked whale Tasmacetus shepherdi stranded on Tristan da Cunha, South Atlantic

Shepherd’s beaked whale Tasmacetus shepherdi is one of the most poorly known cetaceans, whose diet has created some speculation given that its dentition differs greatly from that of most other beaked whales that are primarily teuthophagous. The few stomachs examined previously have given seemingly conflicting dietary information. In this paper the stomach contents of a freshly stranded adult female on Tristan da Cunha have been examined through identification of trace elements and genetic analysis of soft parts. At least 13 cephalopod and 8 fish species were identified from beaks and otoliths respectively, but only undigested fish remains were present in the stomach and identified genetically as Beryx splendens. Reconstituted masses totaled 8809 g for cephalopods and 17,554 g for fish, with four species (Histioteuthis atlantica, Taningia danae, Ommastrephes bartrami and Pholidoteuthis ‘A’) comprising 78.6% of the cephalopods and one species (B. splendens) comprising 87.4% of the fish eaten. It is concluded that Tasmacetus may alternately exploit fish and cephalopods, depending on the time of day and access to seamount or continental slope areas.P.B.B. and M.J.S. acknowledge support from the National Research Foundation, South Africa, and S.v.d.H. thanks the Stellenbosch University Discretionary Fund for financial assistance.http://journals.cambridge.org/action/displayJournal?jid=mbi2015-09-30am201

Ubiquitous Presence of Fe(II) in Aquatic Colloids and Its Association with Organic Carbon

Despite being thermodynamically less stable, small ferrous colloids (60 nm to 3 μm in diameter) remain an important component of the biogeochemical cycle at the Earth’s surface, yet their composition and structure and the reasons for their persistence are still poorly understood. Here we use X-ray-based Fe L-edge and carbon K-edge spectromicroscopy to address the speciation and organic–mineral associations of ferrous, ferric, and Fe-poor particles collected from sampling sites in both marine and freshwater environments. We show that Fe(II)-rich phases are prevalent throughout different aquatic regimes yet exhibit a high degree of chemical heterogeneity. Furthermore, we show that Fe-rich particles show strong associations with organic carbon. The observed association of Fe(II) particles with carboxamide functional groups suggests a possible microbial role in the preservation of Fe(II). These finding have significant implications for the behavior of Fe(II) colloids in oxygenated waters, and their role in different aquatic biogeochemical processes

Reviewing evidence of marine ecosystem change off South Africa

Recent changes have been observed in South African marine ecosystems. The main pressures on these ecosystems are fishing, climate change, pollution, ocean acidification and mining. The best long-term datasets are for trends in fishing pressures but there are many gaps, especially for non-commercial species. Fishing pressures have varied over time, depending on the species being caught. Little information exists for trends in other anthropogenic pressures. Field observations of environmental variables are limited in time and space. Remotely sensed satellite data have improved spatial and temporal coverage but the time-series are still too short to distinguish long-term trends from interannual and decadal variability. There are indications of recent cooling on the West and South coasts and warming on the East Coast over a period of 20 - 30 years. Oxygen concentrations on the West Coast have decreased over this period. Observed changes in offshore marine communities include southward and eastward changes in species distributions, changes in abundance of species, and probable alterations in foodweb dynamics. Causes of observed changes are difficult to attribute. Full understanding of marine ecosystem change requires ongoing and effective data collection, management and archiving, and coordination in carrying out ecosystem research.DHE

Multi-model seascape genomics identifies distinct environmental drivers of selection among sympatric marine species

Background As global change and anthropogenic pressures continue to increase, conservation and management increasingly needs to consider species’ potential to adapt to novel environmental conditions. Therefore, it is imperative to characterise the main selective forces acting on ecosystems, and how these may influence the evolutionary potential of populations and species. Using a multi-model seascape genomics approach, we compare putative environmental drivers of selection in three sympatric southern African marine invertebrates with contrasting ecology and life histories: Cape urchin (Parechinus angulosus), Common shore crab (Cyclograpsus punctatus), and Granular limpet (Scutellastra granularis). Results Using pooled (Pool-seq), restriction-site associated DNA sequencing (RAD-seq), and seven outlier detection methods, we characterise genomic variation between populations along a strong biogeographical gradient. Of the three species, only S. granularis showed significant isolation-by-distance, and isolation-by-environment driven by sea surface temperatures (SST). In contrast, sea surface salinity (SSS) and range in air temperature correlated more strongly with genomic variation in C. punctatus and P. angulosus. Differences were also found in genomic structuring between the three species, with outlier loci contributing to two clusters in the East and West Coasts for S. granularis and P. angulosus, but not for C. punctatus. Conclusion The findings illustrate distinct evolutionary potential across species, suggesting that species-specific habitat requirements and responses to environmental stresses may be better predictors of evolutionary patterns than the strong environmental gradients within the region. We also found large discrepancies between outlier detection methodologies, and thus offer a novel multi-model approach to identifying the principal environmental selection forces acting on species. Overall, this work highlights how adding a comparative approach to seascape genomics (both with multiple models and species) can elucidate the intricate evolutionary responses of ecosystems to global change

Environmental Barcoding Reveals Massive Dinoflagellate Diversity in Marine Environments

Rowena F. Stern is with University of British Columbia, Ales Horak is with University of British Columbia, Rose L. Andrew is with University of British Columbia, Mary-Alice Coffroth is with State University of New York at Buffalo, Robert A. Andersen is with the Bigelow Laboratory for Ocean Sciences, Frithjof C. Küpper is with the Scottish Marine Institute, Ian Jameson is with CSIRO Marine and Atmospheric Research, Mona Hoppenrath is with the German Center for Marine Biodiversity Research, Benoît Véron is with University of Caen Lower Normandy and the National Institute for Environmental Studies, Fumai Kasai is with the National Institute for Environmental Studies, Jerry Brand is with UT Austin, Erick R. James is with University of British Columbia, Patrick J. Keeling is with University of British Columbia.Background -- Dinoflagellates are an ecologically important group of protists with important functions as primary producers, coral symbionts and in toxic red tides. Although widely studied, the natural diversity of dinoflagellates is not well known. DNA barcoding has been utilized successfully for many protist groups. We used this approach to systematically sample known “species”, as a reference to measure the natural diversity in three marine environments. Methodology/Principal Findings -- In this study, we assembled a large cytochrome c oxidase 1 (COI) barcode database from 8 public algal culture collections plus 3 private collections worldwide resulting in 336 individual barcodes linked to specific cultures. We demonstrate that COI can identify to the species level in 15 dinoflagellate genera, generally in agreement with existing species names. Exceptions were found in species belonging to genera that were generally already known to be taxonomically challenging, such as Alexandrium or Symbiodinium. Using this barcode database as a baseline for cultured dinoflagellate diversity, we investigated the natural diversity in three diverse marine environments (Northeast Pacific, Northwest Atlantic, and Caribbean), including an evaluation of single-cell barcoding to identify uncultivated groups. From all three environments, the great majority of barcodes were not represented by any known cultured dinoflagellate, and we also observed an explosion in the diversity of genera that previously contained a modest number of known species, belonging to Kareniaceae. In total, 91.5% of non-identical environmental barcodes represent distinct species, but only 51 out of 603 unique environmental barcodes could be linked to cultured species using a conservative cut-off based on distances between cultured species. Conclusions/Significance -- COI barcoding was successful in identifying species from 70% of cultured genera. When applied to environmental samples, it revealed a massive amount of natural diversity in dinoflagellates. This highlights the extent to which we underestimate microbial diversity in the environment.This project was funded by Genome Canada and the Canadian Barcode of Life Network. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Biological Sciences, School o