Neoproterozoic metamorphic events in the kekem area (central domain of the Cameroon north equatorial fold belt): P-T data

The Kekem area (southwestern part of the central domain of the Cameroon North Equatorial Fold Belt) is composed of high-grade migmatitic gneisses in which two lithological units are distinguished: (i) a metasedimentary unit (garnet- sillimanite-biotite-gneisses and garnet-biotite-gneisses) interpreted as a continental series; and (ii) meta-igneous rocks comprising mafic pyroxene gneisses, amphibolites, and orthogneisses. These units recrystallised under HT-MP conditions (T=700-800‹C, P . 0.5-0.8GPa) and were deformed in relation to a major tangential tectonic event with the NNE-SSW kinematic direction. The lithological association and its tectono-metamorphic evolution show striking similarities with the Banyo and Maham III gneisses, suggesting that the extensional depositional environment envisaged for this formation can be extended farther west. P-T calculations in this contribution provide new data on the Pan-African structural and metamorphic evolution of the metapelites and metabasites in the basement of the Kekem area. The results show two distinct events: (1) crystallization during a Pan-African high temperature metamorphic event and, (2) subsequent deformation and high temperature mylonitization. The data imply a high-temperature amphibolite-facies metamorphism along a clockwise P-T path. The recorded P-T involves a marked variation in pressure, which is typical of collisional crustal thickening. The contrasted metamorphic evolution between areas located to the south of the Central Cameroon Shear Zone(CCSZ; high pressure: Yaounde, Ntui-Betamba), and those located to the north (low pressure: Banyo, Tibati), along with widespread remains of Paleoproterozoic crust, suggest important crustal thickening during Pan-African tangential tectonics in southern Cameroon. As a consequence, the CCSZ is not simply a late Pan-African transpressive shear zone but appears to have been formerly a major intracontinental thrust zone.Key words: HT metamorphic event / Kekem/ Cameroon / Collisional crustal thickening / Neoproterozoic /North Equatorial Fold Belt.La region de Kekem est formee de gneiss anatectiques de haut-degre dans lesquels deux ensembles sont reconnus: (i) un ensemble metasedimentaire (gneiss a grenat, sillimanite et biotite, et gneiss a grenat et biotite) considere comme depose a lLinterieur dLun continent, (ii) des roches meta-ignees comprenant des gneiss a grenat et pyroxene,des amphibolites de composition mafique, et des orthogneiss. Ces deux ensembles ont recristallise (T=700-800‹C, P. 0,5-0,8GPa) et ont ete deformes en relation avec un episode majeur de tectonique tangentielle de direction cinematique NNE-SSW. Cette association lithologique et son evolution tectono-metamorphique montrent une similitude remarquable avec les formations panafricaines de Banyo et Maham III du domaine central de la chaine, suggerant que le contexte extensif de depot envisage pour ces dernieres peut etre etendu plus a lLouest. Les donnees nouvelles sur lLevolution tectono-metamorphique des metasediments et des metabasites panafricains du socle de la region de Kekem mettent en evidence un metamorphisme panafricain de haute temperature suivi dLune mylonitisation a haute temperature dans le facies amphibolite de haut degre selon un chemin P-T horaire. Les conditions P-T enregistrees se caracterisent par une variation de pression typique dLun epaississement crustal. LLevolution metamorphique panafricaine contrastee entre le domaine au sud du cisaillement Centre Camerounais(CCC; haute pression: Yaounde, Ntui-Betamba) et le domaine nord-CCC (basse a moyenne pression: Banyo, Tibati) ainsi que la presence ubiquiste de reliques dLune croute ancienne paleoproterozoique, suggerent un important epaississement crustal, lors dLun episode de tectonique tangentielle. Le CCC nLest donc pas un simple accident panafricain transpressif, mais apparait bien avoir ete prealablement un  chevauchement intracontinental majeur.Mots-cles : Metamorphisme de Haut degre/Kekem/ Cameroun/ Epaississement crustal/ Neoproterozoique /Chaine Nord Equatoria

Recent Innovations & Daily Problems. A new prosthesis in inguinal hernia repair:preliminary results of a pilot study.

Introduction: Elective surgery for inguinal hernia is affected by very low mortality « 1 per 10000 operation); in contrast, when surgery is carried out for complicated inguinal hernia, risks of postoperative complication are higher. TAPP is a world-wide accepted surgical practice in the treatment of elective bilateral or recurrent inguinal hernia, above all in young patients. Few exploratory studies were published on laparoscopic approach in the treatment of urgent complicated inguinal hernia. Aim of this study was to analyze feasibility (operative time, conversion rate), safety (postoperative morbidity, length of hospital stay) and quality of life (acute and chronic pain, return to work) of trans-abdominal pre-peritoneal laparoscopic hernia repair in acute incarcerated inguinal hernia. Rationale of laparoscopic trans-abdominal approach is the easier hernia reduction under vision and a better exploration of the abdominal cavity. Methods: from September 2012 to September 2013, 15 consecutive patients admitted in emergency at the Division of General Surgery of University "Sapienza", Polo Pontino, for acute incarcerated inguinal hernia were submitted to TAPP using 3 trocars (1 of 10 mm and 2 of 5mm) and polyester prosthesis fixed by fibrin glue. Exclusion criteria for laparoscopic approach were age III, previous abdominal surgery, signs of strangulated hernia. All of them were evaluated for operative time, conversion rate, postoperative morbidity, organ resection or other surgery required. All patients were scored for pain by Visual Analogic Scale (VAS) during postoperative in hospital stay at 7 days, 1,6 and 12 months after surgery. Results: median follow-up was 16 months and 12 as minimum. In all cases reduction of hernia was always possible and none conversion to open surgery was recorded, median operative time was 89 minutes (55-137 as range), omental resection was carried out in one patient (6,6%), no other organ resections needed, whereas contralateral hernia was diagnosed and repaired at the same time in 4 patients (26,6%). No major complications were observed, median blood loss was 100 ml, minor morbidity was contained to 18% represented by fever and wound infection of surgical umbilical scar. Median in hospital stay was 1,5 days with 1-5 days as range. Postoperative median acute pain, measured by visual analogic scale (VAS), was 2 (range:0-4), none patient referred any pain during follow-up. Median time of return to work was 6,5 days, ranged between 3 to 15 days. Patients' compliance to treatment and to follow-up was complete as well their satisfaction. Conclusions: In centres skilled for laparoscopy in emergency, TAPP could be considered a feasible and safe technique. In well-selected patients (especially if emolled in controlled clinical trial) TAPP could represent an alternative surgical approach for complicated incarcerated inguinal hernia to conventional open surgery even in urgency. The main advantages of laparoscopic approach are the ability to perform surgical hernia reduction under vision, a better exploration and evaluation of abdominal cavity and diagnosis and treatment of eventual contralateral defect of wall, otherwise often missed. Finally, the good control of acute and chronic pain, faster return to normal activity and work, better aesthetic results contributed to total satisfaction and compliance of the patients

Identifying high potential zones of gold mineralization in a sub-tropical region using Landsat-8 and ASTER remote sensing data: A case study of the Ngoura-Colomines goldfield, eastern Cameroon

© 2020 Elsevier B.V. Climatic conditions and vegetation constrain the use of optical satellite imagery as an exploration tool for hydrothermal ore mineralization in tropical and subtropical regions. In this investigation, Landsat-8 and ASTER satellite imagery were used to detect hydrothermal alteration zones associated with gold mineralization in the Ngoura-Colomines region, Eastern Cameroon. The study area contains several gold-bearing quartz veins associated with zones of pyritization, muscovite/sericite, iron oxides, and silicification. Principal Component Analysis (PCA), Independent Component Analysis (ICA), and specialized spectral band ratios were used to extract spectral information related to vegetation, iron oxide/hydroxide minerals, Al–OH, Fe-Mg–OH, carbonate group minerals, and silicification using Landsat-8 data at regional scale. Linear Spectral Unmixing (LSU) algorithm was implemented to ASTER VNIR + SWIR bands for detailed discrimination of hematite, jarosite, kaolinite, muscovite, chlorite and epidote at district scale. The Automated Spectral Hourglass (ASH) technique was employed to extract reference spectra directly from the ASTER bands for producing fraction images of end-members using the LSU. A comprehensive field survey was used to verify the remote sensing results. Petrographic study, X-ray diffraction analysis and reflectance spectroscopy indicated the presence of quartz, goethite and sericite, as well as the absorption features of Fe3+/Fe2+, Al–OH, OH/H2O and SiO2 in the alteration zones. Several hydrothermal alteration zones of iron oxide/hydroxide, clay, carbonate minerals and silicification zones were identified, which are spatially associated with known mining areas and gold occurrences in the study area. High potential prospects were also delineated, including the Ngoura-Colomines prospects and the newly discovered Yangamo-Ndatanga and Taparé-Tapondo prospects in the southwestern and southeastern parts of the study area. Consequently, satellite-based mineral prospectivity maps at regional and district scales were generated for the study area by implementing the fuzzy logic model to the most informative thematic layers derived from image processing results. The satellite-based prospectivity maps are reliable for exploration of new gold prospective zones in the Ngoura-Colomines goldfield