Sulphide textures and compositions associated with the hydrothermal/magmatic system of the Twangiza gold deposit (South Kivu, DRC)

Twangiza mine is a gold deposit situated in the eastern Democratic Republic of Congo. The rock types at the Twangiza Mine consist of black shale, including carbonaceous mudstone and thin intercalated layers of siltstone, and feldspar-rich granitoid intrusive sills, referred to as albitite, folded into a major antiformal structure. The gold mineralization at the mine is commonly found associated with sulphides. The sulphide textures and compositions of mineralized and unmineralized samples of black shales, albitite sills and hydrothermal veins in the mine are considered for the understanding of the spatial association of gold with sulphides and gold mineralization history of the mine. The sulphides within the Twangiza mine consist of pyrite, arsenopyrite, pyrrhotite, chalcopyrite and rare cobaltite. The primary pyrite texture occurs in unmineralized black shale and is interpreted to be diagenetic. It consists of fine-grained anhedral pyrite crystals aggregating into spherical nodules and formed in replacement of organic material during the diagenesis process. The secondary pyrite textures resulted from the hydrothermal fluids activity and include (i) aggregates of annealed anhedral crystals into sulphide-rich lenses; (ii) elongated anhedral pyrite in the form of short stringers; (iii) fine-grained subhedral to euhedral pyrite randomly distributed within the rock matrix; (iv) euhedral zoned pyrite crystals occurring within veins; (v) aggregations of fine-grained anhedral pyrite, locally distributed in the matrix; (vi) abundant dissemination of fine-grained subhedral to anhedral pyrite crystals within the vein selvedge in the host rock; (vii) and coarse-grained massive pyrite bodies. The pyrite major elemental composition does not vary significantly in the different textures and sample types. The Fe content ranges from 44.57 to 46.40 wt. %, and the S content ranges from 53.75 to 55.25 wt. %. Pyrite from mineralized black shale and hydrothermal veins contains relatively higher concentrations of As (~ 1 wt. %) than pyrite from other sample types. The arsenopyrite commonly occurs as fine-grained anhedral crystals as inclusions within pyrite, medium-grained crystal intergrowing with pyrite and/or as coarse-grained massive arsenopyrite bodies in the massive sulphide veins. The arsenopyrite composition is uniform in all textural and sample type with Fe content ranging from 33.44 to 35.20 wt. %, S content ranging from 21.13 to 22.55 wt. % and As content ranging from 42.20 to 43.97 wt. %. In mineralized black shale and unmineralized black shale, the arsenopyrite shows, however, minor concentrations of Ni with 0.39 and 0.70 wt. % respectively. The pyrrhotite occurs as fine-grained anhedral patchy crystals randomly distributed within the rock matrix of unmineralized black shale and unmineralized granitoid, and / or as inclusions within pyrite in mineralized granitoid. The pyrrhotite shows a uniform composition in all samples and textural types, though minor concentrations of Ni (2.06 wt. %) content are reported in unmineralized granitoid. Chalcopyrite occurs as fine-grained crystals in inclusions within pyrite; and cobaltite occurs as rare fine-grained anhedral crystals occasionally disseminated in the albitite sill matrix. The chalcopyrite composition does not vary considerably in all sample and textural types, and cobaltite shows minor concentrations of Ni (4.55 wt. %) and Fe (3.45 wt. %). Native gold grains are commonly found associated with the secondary pyrite texture especially within the sulphide-rich lenses and in the massive sulphide veins, and are almost pure with ~97 wt. %. A Na-rich hydrothermal fluid from low-grade metamorphism associated with the E-W compressive tectonic event, which caused formation of the antiform structure which control the mineralization in the deposit area, led to the albitization of the deposit rocks and specially the alteration of the granitic assemblage to form albitite, and the deposition of aggregates of fine-grained anhedral crystals and growth and annealing of pyrite in sulphide-rich lenses. Afterward, the CO2-rich hydrothermal fluids influx circulated through reactivated structures, including quartz veins, and led to the precipitation of dolomite, ankerite, siderite and magnesite. They also led to the precipitation of pyrite of secondary textures as well as arsenopyrite, chalcopyrite and formation of pyrrhotite from the desulphurization of early pyrite. The CO2-rich hydrothermal fluids probably leached gold and other trace elements such as As, Co, etc. from the sedimentary host rocks and deposited them into suitable traps, such as the sulphide-rich lenses and massive sulphide bodies, preferably within the hinge zone of anticline axis constituting a hydrothermal fluid pathway

La espontaneidad en el derecho

Les Comités de gouvernances des ressources naturelles (CGRN) sont des structures impliquant les services publics de l’État et divers acteurs et organisations non étatiques. Il s’agit d’un dispositif de gestion concertée des ressources naturelles au niveau des entités locales en République Démocratique du Congo. Cet article porte sur la conformité ou non de ces structures émergentes au droit administratif congolais et propose des pistes de réflexion pour leur fonctionnement harmonieux.The Committees of Natural Resources Governance (C.G.R.N.) are the structures involving public services of the state and various actors and non state-controlled organizations. It is about a device of concerted management of the natural resources to the level of the local entities in R.D.C. This article debates on conformity or non-conformity of these emergent structures to the Congolese administrative right and propose tracks of reflection for their harmonious working

Language endangerment and language documentation in Africa

Non peer reviewe

Kajian potensi ekstrak bilberi sebagai penunjuk pH untuk memantau kesegaran makanan secara kromametri

Penunjuk pH sebagai suatu pendekatan untuk memantau kualiti atau kesegaran makanan semasa telah mendapat perhatian industri pembungkusan makanan. Penggunaan sumber semula jadi pigmen tumbuhan terutamanya daripada buah-buahan dan sayur-sayuran menjadi pilihan para pengguna untuk menggantikan pewarna sintetik dalam memastikan keselamatan makanan yang diambil setiap hari. Dalam kajian ini, ekstrak daripada bilberi telah digunakan sebagai pewarna sensitif pH. Perubahan warna sampel dikaji secara terperinci melalui kaedah kromametri dan juga kaedah spektrofotometri ultra-lembayung nampak. Warna merah terang terhasil dalam pH berasid, merah pudar pada neutral dan magenta ke kuning dalam pH beralkali. Keputusan kajian kromametri menunjukkan bahawa ekstrak bilberi berupaya mempamerkan perubahan warna yang jelas terhadap perubahan pH, iaitu terdapat perubahan nilai warna a* yang menyumbang kepada perubahan yang bererti dalam perbezaan warna keseluruhan (ΔE*). Nilai ΔE* juga ditentukan wujud hubungan linear dan kuantitatif terhadap julat pH tertentu. Oleh yang demikian, ekstrak bilberi didapati berpotensi sebagai bahan sensor untuk pH dalam membangunkan satu sensor pH bagi memantau kesegaran makanan terutamanya hasilan laut berbungkus memandangkan tahap kerosakan produk tersebut berkait rapat dengan perubahan pH ke arah alkali

Le contrôle du pouvoir discrétionnaire de l'administration par le juge administratif congolais

The present research examined the control exercised by the Congolese administrative judge on the discretionary power of the administration in a widely unfavourable context. The analysis of the court decisions states an indirect control over the discretionary power of the administration. The more elaborated and subtle controls are not practised yet. The exercised control is praiseworthy especially if we take into account multiple constraints which impose upon the mission of the judge in the current difficult context of Congo. It contains nevertheless many incapacities which affect seriously the efficiency. The improvement of the control of the discretionary power of the administration by the Congolese administrative judge crosses by the guarantee of good conditions of administration of the justice, the intensification of the capacities of the judges and the improvement of the quality of the laws. It also passes by the improvement of the control at present exercised on the legality of the administrative acts and by the emergence of more elaborated techniques of control.A global project of development of the administrative justice must be elaborated to improve the control of the discretionary power of the administration by the Congolese administrative judge.La présente recherche a examiné le contrôle exercé par le juge administratif congolais sur le pouvoir discrétionnaire de l’administration dans un contexte largement défavorable. L’analyse des décisions juridictionnelles fait état d’un contrôle exercé sur le pouvoir discrétionnaire de l’administration uniquement par le biais des éléments liés de l’acte administratif unilatéral. Les contrôles, plus élaborés et plus subtils, à l’instar de la censure de l’erreur manifeste d’appréciation ou de l’inobservation du principe de proportionnalité ne sont pas encore pratiqués. Le contrôle exercé est louable surtout si l’on tient compte de multiples contraintes qui s’imposent à la mission du juge dans le contexte difficile actuel du Congo. Il comporte néanmoins beaucoup d’insuffisances qui en entament sérieusement l’efficacité. L’amélioration du contrôle du pouvoir discrétionnaire de l’administration par le juge administratif passe par la garantie de bonnes conditions d’administration de la justice, le renforcement des aptitudes des juges et l’amélioration de la qualité des lois. Elle passe également par l’amélioration du contrôle actuellement exercé sur la légalité des actes administratifs et par l’émergence de techniques de contrôle plus élaborées. Les nombreux défis à la réalisation de ces mesures commandent d’envisager le renforcement du contrôle du pouvoir discrétionnaire dans un projet global de développement de la justice administrative à élaborer et à exécuter sur le court, le moyen et le long terme.(DROI 3) -- UCL, 201