Mineral zoning and gold occurrence in the Fortuna skarn mine, Nambija district, Ecuador

The Fortuna oxidized gold skarn deposit is located in the northern part of the Nambija gold district, southern Ecuador. It has been subdivided into four mineralized sites, covering a distance of 1km, which are named from north to south: Cuerpo 3, Mine 1, Mine 2, and Southern Sector. Massive skarn bodies occur in K-Na metasomatized volcanic and volcaniclastic rocks of the Triassic Piuntza unit. They appear to result from selective replacement of volcaniclastic rocks. Very minor presence of bioclast relicts suggests the presence of subordinate limestone. Endoskarn type alteration with development of Na-rich plagioclase, K-feldspar, epidote, actinolite, anhedral pyroxene, and titanite affects a quartz-diorite porphyritic intrusion which crops out below the skarn bodies in Mine 2 and the Southern Sector. Endoskarn alteration in the intrusion grades into a K-feldspar ± biotite ± magnetite assemblage (K-alteration), suggesting that skarn formation is directly related to the quartz-diorite porphyritic intrusion, the latter being probably emplaced between 141 and 146Ma. The massive skarn bodies were subdivided into a dominant brown garnet skarn, a distal green pyroxene-epidote skarn, and two quartz-rich varieties, a blue-green garnet skarn and light green pyroxene-garnet skarn, which occur as patches and small bodies within the former skarn types. The proximal massive brown garnet skarn zone is centered on two 060° trending faults in Mine 2, where the highest gold grades (5-10g/t) were observed. It grades into a distal green pyroxene-epidote skarn zone to the North (Cuerpo 3). Granditic garnet shows iron enrichment from the proximal to the distal zone. Diopsidic pyroxene exhibits iron and manganese enrichment from proximal to distal zones. The retrograde stage is weakly developed and consists mainly of mineral phases filling centimeter-wide veins, vugs, and interstices between garnet and pyroxene grains. The main filling mineral is quartz, followed by K-feldspar, epidote, calcite, and chlorite, with minor sericite, apatite, titanite, hematite, pyrite, chalcopyrite, and gold. Metal and sulfur contents are low at Fortuna, and the highest gold grades coincide with high hematite abundance, which suggests that retrograde stage and gold deposition took place under oxidizing conditions. Fluid inclusions from pyroxene indicate precipitation from high temperature—high to moderate salinity fluids (400 to 460°C and 54- to 13-wt% eq. NaCl), which result probably from boiling of a moderately saline (∼8-wt% eq. NaCl) magmatic fluid. Later cooler (180 to 475°C) and moderate to low saline fluids (1- to 20-wt% eq. NaCl) were trapped in garnet, epidote, and quartz, and are interpreted to be responsible for gold deposition. Chlorite analysis indicates temperature of formation between 300 and 340°C in accordance with fluid inclusion data. It appears, thus, that gold was transported as chloride complexes under oxidizing conditions and was deposited at temperatures around 300°C when transport of chloride complexes as gold carriers is not efficien

Magmatic-dominated fluid evolution in the Jurassic Nambija gold skarn deposits (southeastern Ecuador)

The Jurassic (approximately 145Ma) Nambija oxidized gold skarns are hosted by the Triassic volcanosedimentary Piuntza unit in the sub-Andean zone of southeastern Ecuador. The skarns consist dominantly of granditic garnet (Ad20-98) with subordinate pyroxene (Di46-92Hd17-42Jo0-19) and epidote and are spatially associated with porphyritic quartz-diorite to granodiorite intrusions. Endoskarn is developed at the intrusion margins and grades inwards into a potassic alteration zone. Exoskarn has an outer K- and Na-enriched zone in the volcanosedimentary unit. Gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn and occurs mainly in sulfide-poor vugs and milky quartz veins and veinlets in association with hematite. Fluid inclusion data for the main part of the prograde stage indicate the coexistence of high-temperature (500°C to >600°C), high-salinity (up to 65wt.% eq. NaCl), and moderate- to low-salinity aqueous-carbonic fluids interpreted to have been trapped at pressures around 100-120MPa, corresponding to about 4-km depth. Lower-temperature (510-300°C) and moderate- to low-salinity (23-2wt.% eq. NaCl) aqueous fluids are recorded in garnet and epidote of the end of the prograde stage. The microthermometric data (Th from 513°C to 318°C and salinity from 1.0 to 23wt.% eq. NaCl) and δ18O values between 6.2‰ and 11.5‰ for gold-bearing milky quartz from the retrograde stage suggest that the ore-forming fluid was dominantly magmatic. Pressures during the early retrograde stage were in the range of 50-100MPa, in line with the evidence for CO2 effervescence and probable local boiling. The dominance of magmatic low-saline to moderately saline oxidizing fluids during the retrograde stage is consistent with the depth of the skarn system, which could have delayed the ingression of external fluids until relatively low temperatures were reached. The resulting low water-to-rock ratios explain the weak retrograde alteration and the compositional variability of chlorite, essentially controlled by host rock compositions. Gold was precipitated at this stage as a result of cooling and pH increase related to CO2 effervescence, which both result in destabilization of gold-bearing chloride complexes. Significant ingression of external fluids took place after gold deposition only, as recorded by δ18O values of 0.4‰ to 6.2‰ for fluids depositing quartz (below 350°C) in sulfide-rich barren veins. Low-temperature (<300°C) meteoric fluids (δ18Owater between −10.0‰ and −2.0‰) are responsible for the precipitation of late comb quartz and calcite in cavities and veins and indicate mixing with cooler fluids of higher salinities (about 100°C and 25wt.% eq. NaCl). The latter are similar to low-temperature fluids (202-74.5°C) with δ18O values of −0.5‰ to 3.1‰ and salinities in the range of 21.1 to 17.3wt.% eq. CaCl2, trapped in calcite of late veins and interpreted as basinal brines. Nambija represents a deep equivalent of the oxidized gold skarn class, the presence of CO2 in the fluids being partly a consequence of the relatively deep setting at about 4-km depth. As in other Au-bearing skarn deposits, not only the prograde stage but also the gold-precipitating retrograde stage is dominated by fluids of magmatic origi

The granite hosted gold deposit of Moulin de Chéni (Saint-Yrieix district, Massif Central, France): petrographic, structural, fluid inclusion and oxygen isotope constraints

The Moulin de Chéni orogenic gold deposit is the only granite-hosted deposit of the Saint-Yrieix district, French Massif Central. It occurs in 338±1.5Ma-old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization. Formation of quartz veins and gold deposition occurred in two successive stages: an early "mesozonal” stage of quartz-sulfide (Fe-As-S) deposition, usually devoid of gold and a late "epizonal” stage of base metal and gold deposition. Both stages postdate peak metamorphism and granite intrusion. The genesis of the deposit is the result of four successive fluid events: (1) Percolation of aqueous-carbonic metamorphic fluids under an assumed lithostatic regime of 400-450°C, at a maximum depth of 13km; (2) Formation of the main quartz lodes with coeval K-alteration and introduction of As and S from aqueous-carbonic fluids percolating along regional faults. Arsenopyrite and pyrite deposition was linked to the alteration of Fe-silicates into K-feldspar and phengite at near-constant iron content in the bulk granite. Temperature was similar to that of the preceding stage, but pressure decreased to 100-50MPa, suggesting rapid uplift of the basement up to 7.5km depth; (3) The resulting extensional tectonic leads to the deposition of gold, boulangerite, galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process. Temperature and salinity decrease from 280 to 140°C and 8.1wt% eq. NaCl to 1.6wt% eq. NaCl, respectively; (4) Sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids (1.6wt% eq. NaCl to 0.9wt% eq. NaCl) under hydrostatic conditions at 200-150°

U-Pb, Re-Os, and 40Ar/39Ar geochronology of the Nambija Au-skarn and Pangui porphyry Cu deposits, Ecuador: implications for the Jurassic metallogenic belt of the Northern Andes

New U-Pb, Re-Os, and 40Ar/39Ar dates are presented for magmatic and hydrothermal mineral phases in skarn- and porphyry-related ores from the Nambija and Pangui districts of the Subandean zone, southeastern Ecuador. Nambija has been one of the main gold-producing centers of Ecuador since the 1980s due to exceptionally high-grade ores (average 15g/t, but frequently up to 300g/t Au). Pangui is a recently discovered porphyry Cu-Mo district. The geology of the Subandean zone in southeastern Ecuador is dominated by the I-type, subduction-related, Jurassic Zamora batholith, which intrudes Triassic volcanosedimentary rocks. The Zamora batholith is in turn cut by porphyritic stocks, which are commonly associated with skarn formation and/or porphyry-style mineralization. High precision U-Pb and Re-Os ages for porphyritic stocks (U-Pb, zircon), associated prograde skarn (U-Pb, hydrothermal titanite), and retrograde stage skarn (Re-Os, molybdenite from veins postdating gold deposition) of the Nambija district are all indistinguishable from each other within error (145Ma) and indicate a Late Jurassic age for the gold mineralization. Previously, gold mineralization at Nambija was considered to be Early Tertiary based on K-Ar ages obtained on various hydrothermal minerals. The new Jurassic age for the Nambija district is slightly younger than the 40Ar/39Ar and Re-Os ages for magmatic-hydrothermal minerals from the Pangui district, which range between 157 and 152Ma. Mineralization at Nambija and Pangui is associated with porphyritic stocks that represent the last known episodes of a long-lived Jurassic arc magmatism (∼190 to 145Ma). A Jurassic age for mineralization at Nambija and Pangui suggests that the Northern Andean Jurassic metallogenic belt, which starts in Colombia at 3° N, extends down to 5° S in Ecuador. It also adds a new mineralization style (Au-skarn) to the metal endowment of this bel

Thrust tectonics, crustal thickening, hydrocarbon and ore deposits in northern Central Andes

Thanks to numerous studies realized in cooperation with Peruvian institutions, we propose for the first time in the northern Peruvian Andes a crustal-scale balanced cross-section through the entire orogen to better understand structural architecture, crustal thickening and hydrocarbon-ore deposits genesis. Abundant industrial seismic data provided by Perupetro S.A. allowed to properly constrain the geometry of the forearc and retro-foreland basins (Calderon et al., 2017; Prudhomme et al., in press). Deep crustal structures and Moho geometries are constrained by a recent teleseismic receiver function study (Condori et al., 2017). The restoration, calibrated from new geochronological data and basins analysis, highlight an intermediate stage between the Incaic (late Cretaceous-early Eocene) and Andean (Neogene) orogenies corresponding to a phase of tectonic relaxation and extension. Shortening budgets established from surface and sub-surface data in the upper crust, and from crustal thickening in the middle-lower crust, make it possible to discriminate between the importance and role of each orogeny in the mountain building. The present stage of the balanced cross-section highlights a double-verging orogen, which could result from a total amount of shortening of 180 km fairly distributed between the Incaic and Andean orogenies. Important hydrocarbon and ore deposits located along the balanced cross-section are related to the geodynamic evolution of the successive Incaic and Andean thrust systems. In the forearc (Tumbes-Salaverry) and retro-foreland (Huallaga-Marañon) basins, 2D petroleum modellings have been done using sequential restorations in order to better target exploration. In the Western and Eastern cordilleras and the Subandean zone, significant ore deposits (Cu, Pb, Zn, Au, Ag…) are concentrated in sedimentary reservoirs of Incaic and/or Andean thrust anticlines. We explore and develop an innovative hypothesis, i.e., that there are strong interactions between mineralizing fluids (of both magmatic and sedimentary origin) and petroleum systems (oil shales and reservoirs). Indeed, both ore and oil types of deposits can be found in the same basins, with similar fluid migration and storage processes in sedimentary reservoirs

Systematic literature review of determinants of sedentary behaviour in older adults:a DEDIPAC study

BACKGROUND: Older adults are the most sedentary segment of society and high sedentary time is associated with poor health and wellbeing outcomes in this population. Identifying determinants of sedentary behaviour is a necessary step to develop interventions to reduce sedentary time. METHODS: A systematic literature review was conducted to identify factors associated with sedentary behaviour in older adults. Pubmed, Embase, CINAHL, PsycINFO and Web of Science were searched for articles published between 2000 and May 2014. The search strategy was based on four key elements: (a) sedentary behaviour and its synonyms; (b) determinants and its synonyms (e.g. correlates, factors); (c) types of sedentary behaviour (e.g. TV viewing, sitting, gaming) and (d) types of determinants (e.g. environmental, behavioural). Articles were included in the review if specific information about sedentary behaviour in older adults was reported. Studies on samples identified by disease were excluded. Study quality was rated by means of QUALSYST. The full review protocol is available from PROSPERO (PROSPERO 2014: CRD42014009823). The analysis was guided by the socio-ecological model framework. RESULTS: Twenty-two original studies were identified out of 4472 returned by the systematic search. These included 19 cross-sectional, 2 longitudinal and 1 qualitative studies, all published after 2011. Half of the studies were European. The study quality was generally high with a median of 82 % (IQR 69-96 %) using Qualsyst tool. Personal factors were the most frequently investigated with consistent positive association for age, negative for retirement, obesity and health status. Only four studies considered environmental determinants suggesting possible association with mode of transport, type of housing, cultural opportunities and neighbourhood safety and availability of places to rest. Only two studies investigated mediating factors. Very limited information was available on contexts and sub-domains of sedentary behaviours. CONCLUSION: Few studies have investigated determinants of sedentary behaviour in older adults and these have to date mostly focussed on personal factors, and qualitative studies were mostly lacking. More longitudinal studies are needed as well as inclusion of a broader range of personal and contextual potential determinants towards a systems-based approach, and future studies should be more informed by qualitative work

Incremental residential densification and urban spatial justice: The case of England between 2001 and 2011

Study of the relation between urban density and social equity has been based mostly upon comparative analysis at the city level. It therefore fails to address variations in intra-urban experience and sheds no light on the process of urban densification. Incremental residential development is particularly poorly recorded and under-researched, yet cumulatively it makes a substantial contribution to the supply of dwellings. The article presents a detailed examination of this form of development in England between 2001 and 2011, and considers its impact on urban spatial justice. We find that the incidence of soft residential densification was very uneven. It had disproportionately large effects on neighbourhoods that were already densely developed and that were characterised by lower income households with access to relatively little residential space. It thus contributed to an increase in the level of inequality in the distribution of residential space, increasing socio-spatial injustice

Quality indicators for patients with traumatic brain injury in European intensive care units

Background: The aim of this study is to validate a previously published consensus-based quality indicator set for the management of patients with traumatic brain injury (TBI) at intensive care units (ICUs) in Europe and to study its potential for quality measur

Changing care pathways and between-center practice variations in intensive care for traumatic brain injury across Europe

Purpose: To describe ICU stay, selected management aspects, and outcome of Intensive Care Unit (ICU) patients with traumatic brain injury (TBI) in Europe, and to quantify variation across centers. Methods: This is a prospective observational multicenter study conducted across 18 countries in Europe and Israel. Admission characteristics, clinical data, and outcome were described at patient- and center levels. Between-center variation in the total ICU population was quantified with the median odds ratio (MOR), with correction for case-mix and random variation between centers. Results: A total of 2138 patients were admitted to the ICU, with median age of 49 years; 36% of which were mild TBI (Glasgow Coma Scale; GCS 13–15). Within, 72 h 636 (30%) were discharged and 128 (6%) died. Early deaths and long-stay patients (> 72 h) had more severe injuries based on the GCS and neuroimaging characteristics, compared with short-stay patients. Long-stay patients received more monitoring and were treated at higher intensity, and experienced worse 6-month outcome compared to short-stay patients. Between-center variations were prominent in the proportion of short-stay patients (MOR = 2.3, p < 0.001), use of intracranial pressure (ICP) monitoring (MOR = 2.5, p < 0.001) and aggressive treatme