Petrogenesis of Cu-Ni sulphide ores from O’okiep and kliprand, Namaqualand, South Africa : constraints from chalcophile metal contents

The petrogenesis of sulphide ores in the O’okiep district has remained controversial. Based mainly on the concentration of chalcophile metals (PGE, Cu, Ni), it is proposed that the sulphides segregated from a basaltic magma generated during melting of sub-continental lithospheric mantle. Sulphide saturation of the magma was delayed due to relatively high fO2 until crustal contamination occurred during the advanced stages of differentiation. The immiscible sulphide melt was entrained and fractionated in dynamic magma conduits. Sulphides enriched in monosulphide solid solution (mss) component precipitated at depth in the Kliprand area of southern Namaqualand to form the Hondekloof deposits, whereas the O’okiep ores crystallised at shallower levels from highly fractionated residual sulphide liquids enriched in intermediate solid solution (iss). Sulphides of intermediate composition occur at Ezelsfontein. In the context of this model, the O’okiep intrusions could represent the proximal magmatic members of an IOCG suite of deposits, raising the prospect for additional IOCG deposits elsewhere in southern Africa. The model also predicts an enhanced potential at O’okiep for undiscovered Ni sulphide ores at depth

A scale-integrated exploration model for orogenic gold deposits based on a mineral system approach

Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model. Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model. Plausible models involve metamorphic fluids, but the fluid source has been equivocal. Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits, and numerous Chinese provinces, including Jiaodong, where the only feasible fluid source is sub-crustal. If all orogenic gold deposits define a coherent mineral system, there are only two realistic sources of fluid and gold, based on their syn-mineralization geodynamic settings. These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or release from mantle lithosphere that was metasomatized and fertilized during a subduction event, particularly adjacent to craton margins. In this model, CO2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ​°C. This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales. Within these settings, it is then possible to define the critical gold mineralization processes in the system: fertility, architecture, and preservation. The geological parameters that define these processes, and the geological, geophysical and geochemical proxies and responses for these critical parameters can then be identified. At the geodynamic to province scales, critical processes include a tectonic thermal engine and deep, effective, fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin. At the district to deposit scale, the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems, with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps. Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.David I. Groves, M. Santosh, Liang Zhan

Discovery and fine-mapping of glycaemic and obesity-related trait loci using high-density imputation

Reference panels from the 1000 Genomes (1000G) Project Consortium provide near complete coverage of common and low-frequency genetic variation with minor allele frequency ≥0.5% across European ancestry populations. Within the European Network for Genetic and Genomic Epidemiology (ENGAGE) Consortium, we have undertaken the first large-scale meta-analysis of genome-wide association studies (GWAS), supplemented by 1000G imputation, for four quantitative glycaemic and obesity-related traits, in up to 87,048 individuals of European ancestry. We identified two loci for body mass index (BMI) at genome-wide significance, and two for fasting glucose (FG), none of which has been previously reported in larger meta-analysis efforts to combine GWAS of European ancestry. Through conditional analysis, we also detected multiple distinct signals of association mapping to established loci for waist-hip ratio adjusted for BMI (RSPO3) and FG (GCK and G6PC2). The index variant for one association signal at the G6PC2 locus is a low-frequency coding allele, H177Y, which has recently been demonstrated to have a functional role in glucose regulation. Fine-mapping analyses revealed that the non-coding variants most likely to drive association signals at established and novel loci were enriched for overlap with enhancer elements, which for FG mapped to promoter and transcription factor binding sites in pancreatic islets, in particular. Our study demonstrates that 1000G imputation and genetic fine-mapping of common and low-frequency variant association signals at GWAS loci, integrated with genomic annotation in relevant tissues, can provide insight into the functional and regulatory mechanisms through which their effects on glycaemic and obesity-related traits are mediated

Discovery and Fine-Mapping of Glycaemic and Obesity-Related Trait Loci Using High-Density Imputation

Reference panels from the 1000 Genomes (1000G) Project Consortium provide near complete coverage of common and low-frequency genetic variation with minor allele frequency ≥0.5% across European ancestry populations. Within the European Network for Genetic and Genomic Epidemiology (ENGAGE) Consortium, we have undertaken the fi

Composition of Fluids Responsible for Gold Mineralization in the Pechenga Structure-Imandra-Varzuga Greenstone Belt, Kola Peninsula, Russia.

This study presents the first fluid inclusion data from quartz of albite–carbonate–quartz altered rocks and metasomatic quartzite hosting gold mineralization in the Pechenga structure of the Pechenga– Imandra–Varzuga greenstone belt. A temperature of 275–370°C, pressure of 1.2–4.5 kbar, and the fluid composition of gold-bearing fluid are estimated by microthermometry, Raman spectroscopy, and LA-ICP-MS of individual fluid inclusions, as well as by bulk chemical analyses of fluid inclusions. In particular, the Au and Ag concentrations have been determined in fluid inclusions. It is shown that albite–carbonate–quartz altered rocks and metasomatic quartzite interacted with fluids of similar chemical composition but under different physicochemical conditions. It is concluded that the gold-bearing fluid in the Pechenga structure is similar to that of orogenic gold deposits

Novel Loci for Adiponectin Levels and Their Influence on Type 2 Diabetes and Metabolic Traits : A Multi-Ethnic Meta-Analysis of 45,891 Individuals

J. Kaprio, S. Ripatti ja M.-L. Lokki työryhmien jäseniä.Peer reviewe

The Not-So-Boring Billion: A metallogenic conundrum during the evolution from Columbia to Rodinia supercontinents

Following the commencement of assembly of Columbia at ca. 2.0 to 1.8 Ga with its normal convergent margin metallogeny rich in orogenic gold and VMS Cu-Zn-Pb systems, the Earth entered the Boring Billion phase from 1800 to 800Ma from Late Paleoproterozoic to the dawn of the Neoproterozoic, a transitional period prior to the assembly and breakup of Rodinia. The Boring Billion is considered as a static period in terms of the evolution of global tectonics, the atmosphere, oceans, and life itself. Unlike the history of previous supercontinents, there is limited evidence of extensive breakup and continental drift during the transition from breakup of Columbia to the assembly of Rodinia. The low strain accordion-style tectonic regime appears to have been typified by intermittent periods of variable degrees of extension, rifting, and asthenosphere upwelling followed by compression and closure of extensional basins. The anomalous accordion-type tectonics resulted in the formation and preservation of an equally anomalous but richly endowed metallogeny. Varying degrees of rifting, asthenospheric upwelling, intermittent magmatism derived both from mantle melting, and induced hydrothermal circulation resulted in a variety of giant mineral deposits that were preserved on the margins of buoyant lithosphere during mild compression. In accordance with their inferred relationship to accordion tectonics, the metallogeny was episodic with peaks at ca. 1.7–1.6, 1.4, and 1,1 Ga. The world’s largest IOCG, carbonatite REE, lamproite diamond, unconformity U, SEDEX, and BHT deposits represent a metallogenetic bonanza during this period. The more intensively metal endowed blocks within Columbia were smaller blocks with largely Paleoproterozoic lithosphere, particularly Central Australia, and the North American Craton with its myriad of internal blocks. These appear to have been most susceptible to rifting under relatively low strain accordion-style tectonism due to their high density of lithosphere margins relative to their surface area. Overall, it appears that it was the relative lack of tectonic activity and continental drift in the Boring Billion that was responsible for the not-so-boring but, rather spectacular and unique, metallogeny of that period of Earth’s history.M. Santosh, D.I. Grove

Use of noise to augment training data: A neural network method of mineral–potential mapping in regions of limited known deposit examples

One of the main factors that affects the performance of MLP neural networks trained using the backpropagation algorithm in mineral-potential mapping isthe paucity of deposit relative to barren training patterns. To overcome this problem, random noise is added to the original training patterns in order to create additional synthetic deposit training data. Experiments on the effect of the number of deposits available for training in the Kalgoorlie Terrane orogenic gold province show that both the classification performance of a trained network and the quality of the resultant prospectivity map increasesignificantly with increased numbers of deposit patterns. Experiments are conducted to determine the optimum amount of noise using both uniform and normally distributed random noise. Through the addition of noise to the original deposit training data, the number of deposit training patterns is increased from approximately 50 to 1000. The percentage of correct classifications significantly improves for the independent test set as well as for deposit patterns in the test set. For example, using ±40% uniform random noise, the test-set classification performance increases from 67.9% and 68.0% to 72.8% and 77.1% (for test-set overall and test-set deposit patterns, respectively). Indices for the quality of the resultant prospectivity map, (i.e. D/A, D × (D/A), where D is the percentage of deposits and A is the percentage of the total area for the highest prospectivity map-class, and area under an ROC curve) also increase from 8.2, 105, 0.79 to 17.9, 226, 0.87, respectively. Increasing the size of the training-stop data set results in a further increase in classification performance to 73.5%, 77.4%, 14.7, 296, 0.87 for test-set overall and test-set deposit patterns, D/A, D × (D/A), and area under the ROC curve, respectively

Formation of Bushveld PGE Reefs due to magma chamber subsidence and mobility of cumulate slurries

The Bushveld magmas were strongly sulfide undersaturated during emplacement, leading to accumulation of S-poor ultramafic cumulates of the Lower and Lower Critical zones. The magmas in the chamber eventually reached sulfide saturation in response to differentiation, forming sulfide-bearing noritic cumulates of the Upper Critical Zone and gabbonoritic cumulates of the Upper Zone. Prior to complete solidification of the rocks, the Main Zone was injected as the last major magma addition into the pile of cumulate mushes. This caused subsidence of the chamber, mobilization and mixing of semi-consolidated cumulate mushes and, in places, gravity-driven, mechanical un-mixing of crystals and liquid leading to the formation of distinct layers, plugs and pipes enriched in olivine, pyroxene, plagioclase, chromite, magnetite, and sulfides, particularly in more centrally located portions of the Bushveld Igneous Complex