Geochronology of Mexican mineral deposits. II: Veta Madre and Sierra epithermal vein systems, Guanajuato district

This paper presents two new high-resolution geochronological determinations for the epithermal deposits in the World-class Guanajuato mining district, in central Mexico. These are a Rb-Sr isochron age in illite at 28.47 ± 0.55 Ma for the Villalpando and San Juan de Dios low sulfidation veins of the Sierra group of veins, and a 40Ar/39Ar plateau age in adularia ("valencianite") at 30.20 ± 0.17 Ma for the La Valenciana ore shoot of the famous Veta Madre intermediate sulfidation vein. These determinations have greater accuracy, precision and trueness than the preexisting K-Ar determinations for similar adularia samples. The accuracy of such determinations supports the idea of a diachronic emplacement of intermediate and low sulfidation deposits in this district, the former being older than the latter, similar to other epithermal deposits in Mexico. Also, the ~2 m.yr. span between the Veta Madre and Sierra groups of epithermal veins is in agreement with other case studies, regardless of the size of the deposit

Datos geocronológicos preliminares de la colisión entre el Gran Arco-Isla Caribeño y la Plataforma Continental de Bahamas en el Segmento de La Española

In parallel to structural and metamorphlc studies, geochronologlcal Investigations have been initiated in eclogites and blueschists from the Samaná Peninsula complex, northern Hispaniola, using Sm-Nd, UPb, Rb-Sr and 40Ar/39Ar methods, to constraint subduction, collision and exhumation processes in the Caribbean-North America plate boundary zone. A garnet-omphacite- whole rock Sm-Nd isochron from eclogite yields an age of 86±47 Ma (l43Nd/l44Ndinitial= 0,512894±0,000057; MSWD=0,00036). Although imprecise, we interpret this age as dating the peak of eclogitic metamorphism and allows us to calculate an initial eNd value of +7,2, which suggests a relatively depleted source for the protolith and that the rock formed in an intra-oceanic island-arc setting without significant influence from continental crust. Whole rock trace elements and REE data and preliminary Pb and Rb-Sr analyses also support this interpretation. The 40Ar/39Ar analyses of phengite mineral separates from eclogite and blueschist were made to record the cooling age during retrograde metamorphism (Tc»325-3009C). Phengites of eclogite and blueschist yields average plateau ages of 36,30±0,l 3 Ma and 33,85±0,12 Ma, respectively. These Late Eocene to Early Oligocène ages are related to the regional exhumation of the high-P basement complex and are attributed to the initial oblique collision of the Bahama Platform beneath the Hispaniola arc

Geocronologia Ar-Ar de flogopitas del stock de Aguablanca (Badajoz). Implicaciones sobre la edad del plutón y de la mineralización de Ni-(Cu) asociada.

Ar-Ar dating of intercumulus phlogopite for both a websterite fragment within the mineralized breccia pipe of the Ni-(Cu) Aguablanca magmatic deposit; and the host gabbronorite has yielded ages of 335±2 to 338±3 Ma, i.e., Visean (Mississippian). These values are within error and suggest that the mineralization and the host rock are Variscan in age. Moreover this age is compatible with a previous model which interprets the sulfide mineralization as intrusive (vertical pipe) into the Aguablanca gabbronorites

The Aguablanca Ni–(Cu) sulfide deposit, SW Spain: geologic and geochemical controls and the relationship with a midcrustal layered mafic complex

The Aguablanca Ni–(Cu) sulfide deposit is hosted by a breccia pipe within a gabbro–diorite pluton. The deposit probably formed due to the disruption of a partially crystallized layered mafic complex at about 12– 19 km depth and the subsequent emplacement of melts and breccias at shallow levels (<2 km). The ore-hosting breccias are interpreted as fragments of an ultramafic cumulate, which were transported to the near surface along with a molten sulfide melt. Phlogopite Ar–Ar ages are 341– 332 Ma in the breccia pipe, and 338–334 Ma in the layered mafic complex, and are similar to recently reported U–Pb ages of the host Aguablanca Stock and other nearby calcalkaline metaluminous intrusions (ca. 350–330 Ma). Ore deposition resulted from the combination of two critical factors, the emplacement of a layered mafic complex deep in the continental crust and the development of small dilational structures along transcrustal strike-slip faults that triggered the forceful intrusion of magmas to shallow levels. The emplacement of basaltic magmas in the lower middle crust was accompanied by major interaction with the host rocks, immiscibility of a sulfide melt, and the formation of a magma chamber with ultramafic cumulates and sulfide melt at the bottom and a vertically zoned mafic to intermediate magmas above. Dismembered bodies of mafic/ultramafic rocks thought to be parts of the complex crop out about 50 km southwest of the deposit in a tectonically uplifted block (Cortegana Igneous Complex, Aracena Massif). Reactivation of Variscan structures that merged at the depth of the mafic complex led to sequential extraction of melts, cumulates, and sulfide magma. Lithogeochemistry and Sr and Nd isotope data of the Aguablanca Stock reflect the mixing from two distinct reservoirs, i.e., an evolved siliciclastic middle-upper continental crust and a primitive tholeiitic melt. Crustal contamination in the deep magma chamber was so intense that orthopyroxene replaced olivine as the main mineral phase controlling the early fractional crystallization of the melt. Geochemical evidence includes enrichment in SiO2 and incompatible elements, and Sr and Nd isotope compositions (87Sr/86Sri 0.708–0.710; 143Nd/144Ndi 0.512–0.513). However, rocks of the Cortegana Igneous Complex have low initial 87Sr/86Sr and high initial 143Nd/144Nd values suggesting contamination by lower crustal rocks. Comparison of the geochemical and geological features of igneous rocks in the Aguablanca deposit and the Cortegana Igneous Complex indicates that, although probably part of the same magmatic system, they are rather different and the rocks of the Cortegana Igneous Complex were not the direct source of the Aguablanca deposit. Crust–magma interaction was a complex process, and the generation of orebodies was controlled by local but highly variable factors. The model for the formation of the Aguablanca deposit presented in this study implies that dense sulfide melts can effectively travel long distances through the continental crust and that dilational zones within compressional belts can effectively focus such melt transport into shallow environments

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

Estudios isotópicos de Hf en zircones de granitoides pérmicos en el NW de México: Evidencia de mezcla de magmas generados a partir de la fusión de múltiples fuentes corticales

This study presents new Lu-Hf isotopic data for magmatic zircons from Permian granitoids interpreted to be associated with the early stages of subduction in NW Mexico. In-situ microanalyses by LA-MC-ICPMS technique indicate large variations in Hf isotopic compositions of zircons with the same age and from the same granitic rock sample (up to 15 epsilon Hf units). The range of initial epsilon Hf values for these Permian zircons is between -9.0 and -24.9, suggesting a mixture of magmas derived from melting of different crustal sources to generate the precursor magmas that formed the granitoids. The Hf crustal model ages for zircons vary in a range between 1.59�2.39 Ga, with most of the values between 1.6�1.8 Ga, indicating that Proterozoic basement rocks, similar to those present in NW Mexico today, were the source of melting to form the predecessor magmas for the Permian granitoids. The Hf isotopic data presented in this study indicates a complex process of crustal magma formation that cannot be revealed from just conventional whole rock geochemical and isotopic studies (e.g., major and trace elements and Sm-Nd isotopes). Our hypothesis about the evolution of crust/mantle input in magma genesis in NW Mexico from Proterozoic to the present proposes that the mantle played an important role in the initial stages of crustal formation (magmatism) during the Paleoproterozoic. Subsequently, from Mesoproterozoic to Permian time, the crust had a preponderant role in the generation of magmas. During the Jurassic and Cretaceous periods, the crustal input in magma formation starts to be significantly reduced in these subduction related magmas, to the point that Cenozoic felsic volcanic rocks have a large mantle component, but being this more extreme during the Quaternary, as basaltic lavas have an asthenospheric mantle signature with no evidence of crustal input (e.g., Pinacate Volcanic Field).En este trabajo se presentan datos isotópicos de Lu-Hf en zircones magmáticos de granitoides pérmicos asociados a subducción en el NW de Sonora, México. El microanálisis in situ realizado por la técnica de LA-MC-ICPMS muestra amplias variaciones en las composiciones isotópicas de Hf en zircones de la misma edad en una misma muestra de granitoide (hasta 15 unidades épsilon Hf). El rango de valores de épsilon Hf inicial para estos granitoides va desde -9.0 hasta -24.9. Esta variación sugiere una mezcla de magmas derivados de la fusión de diversas fuentes corticales que originaron a los granitoides pérmicos. Las edades modelo corticales de Hf para estos granitoides varían de 1.59 a 2.39 Ga, predominando el rango de 1.6-1.8 Ga, sugiriendo la fusión del basamento proterozoico que aflora en el noroeste de México para la formación de los granitoides pérmicos. Las relaciones isotópicas de Hf obtenidas ilustran la complejidad de los procesos de formación de magmas en la corteza continental. Esta complejidad raramente es revelada por estudios convencionales de geoquímica de elementos mayores y traza e isótopos de Sm-Nd en roca total. Nuestra hipótesis para la generación de magmas desde el Proterozoico al reciente en el NW de México establece que inicialmente el manto contribuyó de manera importante en la formación de magmatismo paleoproterozoico. Posteriormente, desde el Mesoproterozoico hasta el Pérmico la corteza ha jugado un papel significativo en la generación de magmas. Durante el Mesozoico la participación cortical se reduce y en el Cenozoico, y más aún en el Cuaternario, la contribución del manto se incrementa y es muy significativa, terminando con magmatismo astenosférico basáltico (e.g., El Pinacate)

El Escribano Granitoid Amphibole Ar/Ar age (539 ± 3 Ma): Cadomian volcanic arc (Ossa-Morena Zone)

El granitoide del Escribano es un cuerpo granítico-diorítico localizado en el borde norte del Sector de Obejo-Valsequillo-Puebla de la Reina en la Zona de Ossa-Morena (ZOM). Al sur está cubierto en discordancia por las arcosas y conglomerados de la Formación Torreárboles, que representa la base del Cámbrico Inferior trilobítico. Por el norte el contacto es mecánico (tectónico). Su enfriamiento ha sido datado por Ar/Ar sobre anfíboles en 539 ± 3 Ma, lo que confirma su pertenencia al arco volcánico cadomiense de la ZOMEl Escribano Granitoid is a granite-diorite body located on the northern edge of Obejo-Valsequillo-Puebla de la Reina Sector in the Ossa-Morena Zone (ZOM). It is covered unconformably by conglomerates and arkoses of Torreárboles Formation, which represents the base of trilobitic Lower Cambrian. To the north the contact is tectonic. The granitoid has been dated by Ar/Ar on amphibole at 539 ± 3 Ma, confirming its relationship to the Cadomian volcanic arc of the ZO