Structure,hydrothermal alteration and composition of the Rubiales Pb-Zn orebody (Lugo,Spain): Genetic model

The Rubiales Pb-Zn ore deposit, northwestern Spain, is situated in the Westasturian-Leonese zone, according to the division of the Hercynian Chain in the Iberian Peninsula (Julivert et al. 1972). The orebody is placed in a subvertical shear zone developed at the eastern limb of the Baralla syncline, within the middle and upper members of the lower Cambrian Transition Series. The deposit is a vertical lenticular mass with a N30°W direction. Its length is about 1200 m in a N-S direction by 600 m wide and has an average thickness of 30 m.Its mineralogy is simple: 99% of the sulphides consist of sphalerite and galena with a ratio of 7 to 1. The remaining 1% is mainly formed by pyrite and chalcopyrite with pyrrhotite traces. The deposit shows a large aureole of hydrothermal alteration which is the result of three consecutive processes: (1) sericitization of slates and ankeritization of limestones; (2) silicification of ankeritic rocks; and (3) chloritization of the lower part of the deposit.Since the deposit was discovered in 1967 there has been controversy concerning its origin. Two hypotheses have been considered so far: (1) a sedex model formation (Gilissen 1977; Vazquez 1987); and (2) a hydrothermal origin in a shear zone during the Hercynian Orogeny (Merayo et al. 1984; Arias 1988). The data herein presented support the second hypothesis.     

Construction of a high-resolution gridded rainfall dataset for Peru from 1981 to the present day

ABSTRACT

A new gridded rainfall dataset available for Peru is introduced, called PISCOp V2.1 (Peruvian Interpolated data of SENAMHI’s Climatological and Hydrological Observations). PISCOp has been developed for the period 1981 to the present, with an average latency of eight weeks at 0.1° spatial resolution. The merging algorithm is based on geostatistical and deterministic interpolation methods including three different rainfall sources: (i) the national quality-controlled and infilled raingauge dataset, (ii) radar-gauge merged precipitation climatologies and (iii) the Climate Hazards Group Infrared Precipitation (CHIRP) estimates. The validation results suggest that precipitation estimates are acceptable showing the highest performance for the Pacific coast and the western flank of the Andes. Furthermore, a meticulous quality-control and gap-infilling procedure allowed us to reduce the formation of inhomogeneities (non-climatic breaks). The dataset is publicly available at https://piscoprec.github.io/ and is intended to support hydrological studies and water management practices.     

Plate tectonics and volcanism in the gibraltar arc

Late Tertiary and Quaternary volcanism of southeastern Spain can be fitted in a platetectonics model, taking into account the post-Paleozoic evolution of the stable and semimobile Iberian areas and the new orogenic belts bordering the Mediterranean between Africa and the Iberian Peninsula.The occurrence and distribution of calc-alkaline and potassic volcanism suggest an oceanic crust sinking downwards from the Iberian plate. This active margin is causally related to the convergence and collision of Iberia and Africa during Late Cretaceous—Early Miocene time span.A pre-collision distensive phase is inferred from the stratigraphie and tectonic record between the Triassic and Late Cretaceous, while since the Late Miocene another distensive phase is related to the actualistic features.     

Zeolites in Tertiary coal from the Çayirhan mine, Beypazari, Turkey

The study focuses on the mineralogy of the upper coal seam accumulated at the top of the Çoraklar Formation (Miocene), Beypazari, Turkey. This coal seam is laterally extensive and averages 3.0 m thick, varying from 1.0 to 4.9 m. Analcime and clinoptiolite comprise up to 80% of the mineral matter (which also includes feldspars, quartz and pyrite and traces of dolomite, clay minerals and apatite) in the coal from the Cayirhan mine. Zeolites were formed when sodium-rich solutions altered aluminosilicate epiclastic material derived from contemporaneous volcanic activity. The allocthonous organic matter accumulated as a result of detrital plant and epiclastic material from an adjacent fresh-water environment being washed into a saline lake in sufficient quantities to form peat with a high mineral matter content (29.7% mean mineral matter content in raw coal). Subsequent syngenetic alteration of the volcanic glass incorporated into the peat resulted in zeolite formation. Alteration of sodium-rich epiclastic material by sodium-rich solutions resulted in the formation of analcime, whilst alteration of calcium-rich epiclastic material by sodium-rich solutions resulted in the formation of clinoptilolite.     

Stable isotope composition of F-Pb-Zn mineralization in the Valle de Tena (Spanish Central Pyrenees)

This study, dealing with the stable isotope (C, O, and S) geochemistry of F-Pb-Zn deposits, is part of an integrated metallogenetic study of the Valle de Tena (Central Pyrenees). The objective of this work is to place constraints on the origin of the mineralizing solutions and sources of sulphur and metals. Two types of mineralization have been identified: (1) stratabound ores linked to an emersion episode that occurred during the Namurian to Westfalian transition (Portalet mines), and (2) low-temperature hydrothermal veins related to post-Hercynian extensional tectonics (Yenefrito and Lanuza mines, and Tebarray occurrences). Stable isotopic study indicates that the source of mineralizing components was the local Upper Palaeozoic country rocks in the case of the stratabound Portalet deposit (biogenic sulphides and connate waters, modified by some meteoric input through a karst surface). In the case of vein deposits, stable isotopes point toward either modified connate water or marine water as the mineralizing fluid, with sulphur and metals derived from a mixture, in different proportions, of regional igneous and (meta)sedimentary country rocks. Received: 6 November 1995 / Accepted: 6 September 1996     

Principal Component Analysis of precipitation and rainfall regionalization in Spain

Summary A T-mode Principal Component Analysis (PCA) based on a network including 68 pluviometric gauges and their 12 mean monthly amounts of rainfall is attempted in order to describe the main patterns governing precipitation in Spain. The procedure is applied to a 12 × 12 intermonth covariance matrix; the unrotated components and two additional solutions deduced after varimax and oblimin rotations are presented and discussed. In all cases component scores are computed and their spatial distribution is discussed. Two regionalizations of Spanish rainfall are then obtained and compared in terms of group homogeneity. There follows a discussion concerning the main pluviometric characteristics of each region deduced from the best division.With 7 Figures     

Numerical modelling of surfacewater/groundwater flows for freshwater/saltwater hydrology: the case of the alluvial coastal aquifer of the Low Guadalhorce River, Malaga, Spain

This applied research deals with the numerical modelling and transient simulation of the joint surfacewater/groundwater flows that characterize the freshwater/saltwater hydrology of the coastal alluvial valley of the Low Guadalhorce River, Malaga, Spain. The MELEF model used was mainly adapted and calibrated for a simulation period of two hydrological years 1989/1990–1990/1991, before the current channelling of the river, where floods and low precipitations have been recorded. The model calibration process was performed with the aid of phreatic levels measured in numerous wells and piezometers, as well as recharges from precipitation and irrigation on the alluvial surface, which was also assessed by the hydrologic model SSMA-2. The present numerical approach can predict the forthcoming hydrology of the coastal alluvial of the Guadalhorce River after its final channelling.     

End-states of short-period comets and their role in maintaining the zodiacal dust cloud

Physical lifetimes and end-states of short-period comets are analysed in connection with the problem of the maintainance of the zodiacal dust cloud. In particular, the problem of the comet-asteroid relationship is addressed. Recent studies of the physical properties of Apollo-Amor asteroids and short-period comets (e.g., Hartmann et al., 1987) show significant differences between them, suggesting that they are distinct classes of objects. A few percent of the active SP comets might become asteroidal-like bodies in comet-type orbits due to the buildup of dust mantles. The remainder probably disintegrate as they consume their volatile content so their debris can only be observed as fireballs when they meet the Earth. Unobservable faint SP comets — i.e., comets so small (m 10¹⁴ g) that quickly disintegrate before being detected, might be a complementary source of dust material. They might be completely sublimated even at rather large heliocentric distances (r - 3 AU). Yet the released dust grains can reach the vicinity of the Sun by Poynting-Robertson drag. The mass associated with unobservable SP comets with perihelion distances q 3 AU might be comparable to that computed for the sample of observed SP co-mets with q 1.5 AU. It is concluded that SP comets (from the large to the unobservable small ones) may supply an average of several tons/sec of meteoric matter to the zodiacal dust cloud.