Una introducción a la metalogenia de Cuba bajo la perspectiva de la tectónica de placas

Six main metallogenic epochs can be distinguished in the geological constitution of the island of Cuba. A first stage from Jurassic to Early Cretaceous times, included a rift episode involving materials from the Bahama and Yucatán continental paleomargin. Base metals sedex deposits (Pb-Zn-Cu) and Mn, associated with gold and silve r, are to be found in the detrital and carbonated series associated to this process. An arc (or arcs) of volcanic islands developed during the Aptian (Neocomian?)-Campanian stage. Three metallotects are to be found associated to the formation and development of this arc: a) the uppermost part of the suprasubduction zone mantle section, where bodies of ophiolitic chromitites occur, b) the back-arc volcanosedimentary submarine series, with volcanogenic deposits of massive sulfides (Kuroko and Cyprus type), Mn oxide exhalative mineralizations and zeolite deposits, and, c) the intrusive series and rocks in the axial zone of the arc, with iron and polymetallic skarn deposits, porphyry copper deposits and Au-Ag epithermal deposits. The first collisional process, between the Yucatán paleomargin and the Cretaceous volcanic arc, as well as the beginning of the collision between the Caribbean plate and the North-American plate, took place during the late Campanian-Danian stage. Orogenic gold mineralizations and, probably, tumgsten deposits date from this period. A volcanic arc, trending E-W, developed in eastern Cuba from Late Danian to Middle Eocene times. Major volcanogenic Mn deposits in Cuba are located within the Paleogene volcanic island arc in eastern Cuba. This volcanic activity also originated some major volcanogenic sulfide deposits, skarn and porphyry copper deposits, as well as zeolite deposits. Known metallotects in this geodynamic environment include: a) the volcanic and volcanosedimentary series located along the axial arc-back arc boundary, with volcanogenic sulfide deposits (Kuroko type) and Mn oxide volcanogenic deposits, and b) granitic intrusives related to the axial arc volcanic, with skarn and porphyry copper deposits. In western and central Cuba, in turn, piggy-back sedimentary basins associated to the collisional process between the Caribbean plate and the North-American plate developed during Danian-Middle Eocene times. Major orogenic gold mineralizations are associated with this process. A series of post-volcanic basins developed during the Middle Eocene-Late Eocene stages in eastern Cuba, some of which are associated to Mn resedimented mineralizations. Meanwhile, the development of sedimentary basins with olistostromes, associated to the collisional process, continued in central and western Cuba. Cuba finally joined the North-American plate at the end of this episode. Orogenic gold mineralizations may also occur in association with these processes. A shelf environment was established in Cuba from Late Eocene to Quatern a ry times. At that point, extensive Fe-Ni-Co laterite crusts (one of the largest examples of this type of deposit worldwide), bauxite crusts, gossan deposits (Fe, Au, Ag), resedimented Mn deposits, and marine and fluvial placer deposits, rich in noble metals, originated

Las cromititas ofiolíticas del yacimiento Mercedita (Cuba). Un ejemplo de cromitas ricas en Al en la zona de transición manto-corteza

The Mercedita deposit is located in the ophiolitic Massif of Moa-Baracoa (NE of Cuba) and is considered the most important podiform chromite deposit of America. Chromitite bodies, enclosed in hazbu rgite and residual dunites (mantle-crust transition zone). The chromite ore bodies are concordant with the main structures shown by the enclosing peridotites and also display pull-apart fractures. Chromite lenses enclose and substitute grabbro bodies (sills), that are concordant with the orientation of the host chromitite. Intergranular minerals are olivine, serpentine, and chlorite. Chromite has abundant, distributed solid inclusions of olivine and Na-rich pargasite (up 4 wt % Na2O), and minor laurite and millerite. Toward the contact with the included gabbro sills, abundant clinopy r oxene, plagioclase and rutile occur as inclusions in the chromite. The ores from Mercedita deposit are composed by refractary - grade chromite (Al-rich chromite), where A l 2 O 3 ranges between 25 and 33wt.%. The TiO2 values are relative ly high compared to the most common ophiolitic chromite, TiO2 content varies from 0.05 to 0.52 wt. %. Chromitites of the Mercedita deposit are poor in platinum-group elements (PGE), with total PGE ranging between 55.8 and 165.9 ppb and an average value of 90 ppb. From textural and geochemical data we propose a genetic model from the reaction of a back arc basin basalt, formed by melt-rock reactions, percolated through subhorizontal, porous dunitic channels and mixed with oxidized melts in suprasubduction zone mantle. Mixing of these two melts generated a hybrid melt whose bulk composition fell within the chromite liquidus field in the P-T- fO2 space (Hill and Roeder, 1974). Percolation of the hybrid melt through the dunitic channels promoted dissolution of preexisting silicate minerals and chromite crystallization

Rocas volcánicas de las series Inferior y Media del Grupo El Cobre en la Sierra Maestra (Cuba Oriental): volcanismo generado en un arco de islas tholeiítico

A set of 11 samples of igneous rocks from the lower and middle Cobre Group of the Sierra Maestra (SE Cuba) were analyzed. These rocks are volcanic and hypoabyssal bodies with porp hyritic texture and predominantly plagioclase phenocrystals. Their composition ranges from basalt to dacite and shows a tholeiitic trend with low K contents. The REE concentrations are low and, when normalized to chondrite, show a flat pattern with no relative enrichment in either LREE or HREE. In addition, these rocks present a slight enrichment in LILE and a strong Nb negative anomaly, typical of island arc tholeiites. Because of their geochemistry, the rocks of the Sierra Maestra are comparable to those of the Ke rmadec arc in the SW Pacific. Finally, the low REE content, the flat REE pattern, as well as the low uncompatible element contents, are similar to the IAT Series present in the Caribbean Volcanic Arcs. All these new data on the Pa l e ogene volcanism suggest that the tectonic models proposed for the origin of the Sierra Maestra Arc should be revised

Cromititas podiformes en la Faja Ofiolítica Mayarí-Baracoa (Cuba)

The Mayarí-Baracoa Belt occupies the easternmost part of the east-west-trending Cuban ophiolitic belt. It comprises t wo large, chromite-rich massifs: Mayarí-Cristal and Moa-Baracoa. Chromite deposits can be grouped into tree mining districts according to the chemistry of chromite ore: the Moa-Baracoa district (Al-rich chromite), the Sagua de Tánamo district (Al- and Cr-rich chromite) and the Mayarí district (Cr-rich chromite). Al-rich, Ti-rich chromites occur in the mantle crust transition (associated with harzbu rgites, dunites, plagioclase-bearing peridotites, gabbro sills and gabbro dikes), while Cr-rich, Ti-poor chromites occur in the deeper portions of the ophiolitic sequence (associated with harzbu rgites and dunites). The melts in equilibrium with the Al-rich chromites are close to the composition of the back-arc basin basalts (BABB), whereas the melts in equilibrium with the Cr-rich chromites are similar that of the boninite andesite. Chromite from Mayarí-Baracoa Ophiolite Belt formed when cal-alkaline melts (C), formed by melt-rock reactions, percolated through subhorizontal, porous dunitic channels and mixed with oxidized melts (H) in suprasubduction zone mantle. Mixing of these two melts generated a hybrid melt whose bulk composition fell within the chromite liquidus field in the P-T- fO2 space (Hill and Roeder, 1974). Percolation of the hybrid melt through the dunitic channels promoted dissolution of preexisting silicate minerals and chromite crystallization. Al-rich chromite from Moa-Baracoa should be formed in the distal parts of percolation channels at high fO2 , whereas Cr-rich chromite from Mayarí formed toward the proximal parts of the percolation channels under more reducing conditions

El placer lateral de playa Mejías (noreste de Cuba Oriental): un ejemplo de interacción de procesos aluviales y marinos en la concentración de minerales de elementos preciosos

The playa Mejías lateral placer is the most important placer in Cuba. Its mineralogical composition (magnetite, chromite, rutile, ilmenite, orthopyroxene) reveals that the ophiolites of the Mayarí-Baracoa Belt are the main source area. However, other sources are demonstrated for by the presence of 4 different morphological types of zircon crystals, and minerals related to listvaenitic mineralizations (calcosilicates, carbonates). Also, precious metals have been recognized . Previous to their fluvial transport, electrum grains were depleted in gold in the lateritic environment, producing silve r-rich rims to the electrum grains. The gold particles were transported by rivers as fine-sized particles of electrum with various compositions, and as Au-amalgam. During their fluvial transport, the smaller gold grains coalesced to form larger grains, and a final generation of highly pure gold cemented the subgrains. Then, the particles were deposited in a beach lateral placer, where the grains were leached by sea water, giving rise to corrosion textures. The particles of EGP minerals found are grains of osmium-rich laurite replaced by laurite veins associated with symplectitic intergrowths of a third laurite generation (having intermediate compositions between the above laurite generation) and iridioarsenite, as a consequence of serpentinization at the source. Leaching by sea water produces a depletion in osmium in the particles

Primitive Cretaceous island-arc volcanic rocks in eastern Cuba : the Téneme Formation

The Téneme Formation is located in the Mayarí-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Téneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Río Grande intrusive), and are overthrusted by serpentinized ultramafics. Téneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements « N-type MORB) and typical oceanic arc tholeiites (TiO2 = 0.5-0.8 %). Basaltic rocks exhibit low light REE/Yb ratios (La/Yb < 5), typical of intraoceanic arcs and are comparable to Maimón Formation in Dominican Republic (IAT, pre Albian) and Puerto Rican lavas of volcanic phase I (island arc tholeiites, Aptian to Early Albian). The mantle wedge signature of the Téneme Formation indicates a highly depleted MORB-type mantle source, without any contribution of E-MORB or OIB components. Our results suggest that Téneme volcanism represents a primitive oceanic island arc environment. If the Late Cretaceous age (Turonian or early Coniacian) proposed for Téneme Formation is correct, our results indicate that the Cretaceous volcanic rocks of eastern Cuba and the Dominican Republic are not segments of a single arc system, and that in Late Cretaceous (Albian-Campanian) Caribbean island arc development is not represented only by calc-alkaline (CA) volcanic rocks as has been suggested in previous works

On Deformations of n-Lie algebras

The aim of this paper is to review the deformation theory of $n$-Lie algebras. We summarize the 1-parameter formal deformation theory and provide a generalized approach using any unital commutative associative algebra as a deformation base. Moreover, we discuss degenerations and quantization of $n$-Lie algebras.Comment: Proceeding of the conference Dakar's Workshop in honor of Pr Amin Kaidi. arXiv admin note: text overlap with arXiv:hep-th/9602016 by other author

Pharmacological activation of LXR alters the expression profile of tumor-associated macrophages and the abundance of regulatory T cells in the tumor microenvironment

Liver X receptors (LXR) are transcription factors from the nuclear receptor family that are activated by oxysterols and synthetic high-affinity agonists. In this study, we assessed the anti-tumor effects of synthetic LXR agonist TO901317 in a murine model of syngeneic Lewis Lung carcinoma. Treatment with TO901317 inhibited tumor growth in wild-type but not in LXR-deficient mice, indicating that the anti-tumor effects of the agonist depends on functional LXR activity in host cells. Pharmacological activation of the LXR pathway reduced the intratumoral abundance of regulatory T cells (Treg) and the expression of the Treg-attracting chemokine Ccl17 by MHCIIhigh tumor-associated macrophages (TAM). Moreover, gene expression profiling indicated a broad negative impact of the LXR agonist on other mechanisms used by TAM for the maintenance of an immunosuppressive environment. In studies exploring the macrophage response to GM-CSF or IL-4, activated LXR repressed IRF4 expression, resulting in subsequent downregulation of IRF4-dependent genes including Ccl17. Taken together, this work reveals the combined actions of the LXR pathway in the control of TAM responses that contribute to the anti-tumoral effects of pharmacological LXR activation. Moreover, these data provide new insights for the development of novel therapeutic options for the treatment of cancer

Clinical value of next generation sequencing of plasma cell-free DNA in gastrointestinal stromal tumors

Gastrointestinal stromal tumor (GIST) initiation and evolution is commonly framed by KIT/PDGFRA oncogenic activation, and in later stages by the polyclonal expansion of resistant subpopulations harboring KIT secondary mutations after the onset of imatinib resistance. Thus, circulating tumor (ct)DNA determination is expected to be an informative non-invasive dynamic biomarker in GIST patients. We performed amplicon-based next-generation sequencing (NGS) across 60 clinically relevant genes in 37 plasma samples from 18 GIST patients collected prospectively. ctDNA alterations were compared with NGS of matched tumor tissue samples (obtained either simultaneously or at the time of diagnosis) and cross-validated with droplet digital PCR (ddPCR). We were able to identify cfDNA mutations in five out of 18 patients had detectable in at least one timepoint. Overall, NGS sensitivity for detection of cell-free (cf)DNA mutations in plasma was 28.6%, showing high concordance with ddPCR confirmation. We found that GIST had relatively low ctDNA shedding, and mutations were at low allele frequencies. ctDNA was detected only in GIST patients with advanced disease after imatinib failure, predicting tumor dynamics in serial monitoring. KIT secondary mutations were the only mechanism of resistance found across 10 imatinib-resistant GIST patients progressing to sunitinib or regorafenib. ctDNA evaluation with amplicon-based NGS detects KIT primary and secondary mutations in metastatic GIST patients, particularly after imatinib progression. GIST exhibits low ctDNA shedding, but ctDNA monitoring, when positive, reflects tumor dynamics

Peripheral organ equivalent dose estimation procedure in proton therapy

The aim of this work is to present a reproducible methodology for the evaluation of total equivalent doses in organs during proton therapy facilities. The methodology is based on measuring the dose equivalent in representative locations inside an anthropomorphic phantom where photon and neutron dosimeters were inserted. The Monte Carlo simulation was needed for obtaining neutron energy distribution inside the phantom. The methodology was implemented for a head irradiation case in the passive proton beam of iThemba Labs (South Africa). Thermoluminescent dosimeter (TLD)-600 and TLD-700 pairs were used as dosimeters inside the phantom and GEANT code for simulations. In addition, Bonner sphere spectrometry was performed inside the treatment room to obtain the neutron spectra, some relevant neutron dosimetric quantities per treatment Gy, and a percentual distribution of neutron fluence and ambient dose equivalent in four energy groups, at two locations. The neutron spectrum at one of those locations was also simulated so that a reasonable agreement between simulation and measurement allowed a validation of the simulation. Results showed that the total out-of-field dose equivalent inside the phantom ranged from 1.4 to 0.28 mSv/Gy, mainly due to the neutron contribution and with a small contribution from photons, 10% on average. The order of magnitude of the equivalent dose in organs was similar, displaying a slow reduction in values as the organ is farther from the target volume. These values were in agreement with those found by other authors in other passive beam facilities under similar irradiation and measurement conditions