775 research outputs found
The giant Antamina deposit, Peru: intrusive sequence, skarn formation, and mineralisation
The Antamina Cu-Zn skarn, in the central Andes of Peru, is the largest skarn in the world with resources of ~2,968 Mt averaging 0.89% Cu, 0.77% Zn, 11 g/t Ag and 0.02% Mo as of 2015. The deposit measures ~2.5 km long by ~1.5 km wide with a vertical extension > 2.2 km and remains open at depth. The host rocks are structurally stacked limestones and marls of the Cretaceous Jumasha and Celendín formations. Skarn and mineralisation occur in and around the Antamina Porphyry Complex (APC), which consists of 4 porphyry centres emplaced between 10.95 ± 0.20 Ma and 10.24 ± 0.23 Ma (U-Pb zircon). The core of the main ore zone is composed of 3 contiguous porphyry centres (Oscarina, Taco-Bornita, Usupallares) oriented lengthwise from NE to SW; the fourth centre (Condorcocha) is located ~1 km north of Taco. This study combines field observations of cross-cutting relationships with U-Pb (zircon) and Re-Os (molybdenite) geochronology into a spatio-temporal model that explains how Antamina became a giant ore deposit.
At least 11 intrusive phases were identified at the Antamina deposit. The major porphyry phases documented in each intrusive centre at Antamina are classified as P1 (early), P2 (inter-mineralisation), and P3 (late inter-mineralisation). Sub-phases are denoted in alphabetical order as P2a, P2b, etc. General characteristics of the major phases are as follows: P1 is the causative skarn-forming intrusion in each porphyry centre. P1 ages range from 10.95 ± 0.20 Ma (Taco) to 10.24 ± 0.23 Ma (Usupallares). Endoskarn and exoskarn are genetically related to P1 porphyries. Stockwork quartz veins (≤ 40% volume) and hydrothermal biotite (potassic alteration) are locally abundant in the central porphyry complex. P2 intrusions cut P1 intrusions, related skarns, and early quartz veins. Quartz stockwork veins (± pyrite ± chalcopyrite ± molybdenite) extend outward from P2 porphyries and cross-cut P1 skarns. Locally, P2 contains xenoliths (up to several m long) of P1 exoskarn, P1 endoskarn, and refractory quartz vein fragments. P3 cross-cuts P1, P2, and early veins. Neither P2 nor P3 contain endoskarn alteration, although they do contain veins and disseminations of secondary biotite overprinted by sericite-chlorite alteration.
Molybdenite mineralisation occurs in two stages across the Taco-Bornita and Usupallares zones. Stage I molybdenite occurs in skarns; Re-Os ages include 10.58 ± 0.07 Ma and 10.44 ± 0.05 to 10.39 ± 0.05 Ma. Stage II molybdenite + quartz veins cut across P2 and P3 porphyries and Re-Os ages include 9.99 ± 0.04 and 9.68 ± 0.05 Ma. In general, U-Pb zircon and Re-Os molybdenite ages decrease from northeast to southwest along the structurally-controlled axis of the deposit. Together, these ages constrain the duration of magmatic-hydrothermal activity at Antamina to ~1.1 Ma.
The skarns formed in sequence with porphyry emplacement, then coalesced to form a continuous body of skarn that comprises the giant Antamina deposit. Systematic patterns of alteration and mineralisation are centred on the multi-phase porphyry centre; outward from this centre, alteration consists of hydrothermal biotite (i.e., potassic alteration) transitioning into endoskarn, exoskarn, bleached marble, and fluid escape structures in the most distal reaches of the deposit. Skarn garnet colour changes from pink to red to brown in endoskarn and from red to brown and green (from proximal to distal) in exoskarn. Garnet becomes more andradite-rich and grossularite-poor from proximal to distal skarns, and clinopyroxene becomes more hedenbergite-rich and diopside-poor along the same trend. Mineralisation and metal zoning shows an outward progression from Mo ± Cu in the central porphyry, to Cu (± Ag, Bi)-Zn-Pb from proximal to distal exoskarns. The ore mineralogy is dominated by molybdenite, chalcopyrite, bornite, and sphalerite with lesser galena and minor Bi-Ag-S minerals. Fluid inclusions in a unidirectional solidification texture (UST) sample consist of four types assigned to primary and secondary assemblages. Primary inclusions are highly saline with liquid-vapour-solid phases and contain up to 5 translucent daughters plus a triangular opaque daughter. Secondary inclusions display variable proportions of liquid-vapour-solid phases, and are generally less saline and more vapour-rich than primary inclusions. Primary inclusions homogenise by halite disappearance, whereas secondary inclusions homogenise to the liquid state. Lithostatic pressure estimates from primary fluid inclusions range from 1.2 to 0.95 kbar, which equates to formation depth range from ~4.6 to 3.5 km.
The formation of the giant Antamina skarn deposit is attributed to the emplacement of multiple fertile porphyries along a NE-trending fault zone into reactive wall rocks between 10.95 ± 0.20 Ma (oldest U-Pb zircon age) and 9.68 ± 0.05 Ma (youngest Re-Os molybdenite age). Miocene surface uplift (on the order of 3.5 km), coupled with Pleistocene glaciation, exposed the top of the deposit, preserving the ore body at a favourable erosional level
EUV and HXR Signatures of Electron Acceleration During the Failed Eruption of a Filament
We search for EUV brightenings in TRACE 171 {\AA} images and HXR bursts
observed during failed eruptions. We expect that if an eruption is confined due
to interaction with overlying magnetic structures then we should observe
effects connected with reconnection between magnetic structures and
acceleration of particles. We utilized TRACE observations of three well
observed failed eruptions. EUV images were compared to HXR spatial distribution
reconstructed from Yohkoh/HXT and RHESSI data. The EUV light curves of a
selected area were compared to height profiles of eruption, HXR emission and
HXR photon spectral index of power-law fit to HXR data. We have found that EUV
brightenings are closely related to the eruption velocity decrease, to HXR
bursts and to episodes of hardening of HXR spectra. The EUV brightened areas
are observed far from the flaring structure, in footpoints of large systems of
loops observed 30-60 minutes after the maximum of a flare. These are not
`post-flare' loops that are also observed but at significantly lower heights.
The high lying systems of loops are observed at heights equal to height, at
which eruption was observed to stop. We observed HXR source spatially
correlated with EUV brightening only once. For other EUV brightened areas we
estimated the expected brightness of HXR sources. We find that EUV brightenings
are produced due to interaction between the erupting structure with overlying
loops. The interaction is strong enough to heat the system of high loops. These
loops cool down and are visible in EUV range about 30-60 minutes later. The
estimated brightness of HXR sources associated with EUV brightenings shows that
they are too weak to be detected with present instruments. However, next
generation instruments will have enough dynamic range and sensitivity to enable
such observations.Comment: A&A accepte
Continuous-flow IRMS technique for determining the 17O excess of CO2 using complete oxygen isotope exchange with cerium oxide
This paper presents an analytical system for analysis of all single
substituted isotopologues (<sup>12</sup>C<sup>16</sup>O<sup>17</sup>O,
<sup>12</sup>C<sup>16</sup>O<sup>18</sup>O, <sup>13</sup>C<sup>16</sup>O<sup>16</sup>O) in nanomolar quantities
of CO<sub>2</sub> extracted from stratospheric air samples. CO<sub>2</sub> is
separated from bulk air by gas chromatography and CO<sub>2</sub> isotope ratio
measurements (ion masses 45 / 44 and 46 / 44) are performed using isotope ratio
mass spectrometry (IRMS). The <sup>17</sup>O excess (Δ<sup>17</sup>O) is
derived from isotope measurements on two different CO<sub>2</sub> aliquots:
unmodified CO<sub>2</sub> and CO<sub>2</sub> after complete oxygen isotope exchange with
cerium oxide (CeO<sub>2</sub>) at 700 °C. Thus, a single measurement of
Δ<sup>17</sup>O requires two injections of 1 mL of air with a CO<sub>2</sub>
mole fraction of 390 μmol mol<sup>−1</sup> at 293 K and 1 bar pressure
(corresponding to 16 nmol CO<sub>2</sub> each). The required sample size
(including flushing) is 2.7 mL of air. A single analysis (one pair of
injections) takes 15 minutes. The analytical system is fully automated for
unattended measurements over several days. The standard deviation of the
<sup>17</sup>O excess analysis is 1.7‰. Multiple
measurements on an air sample reduce the measurement uncertainty, as
expected for the statistical standard error. Thus, the uncertainty for a
group of 10 measurements is 0.58‰ for Δ
<sup>17</sup>O in 2.5 h of analysis. 100 repeat analyses of one air sample
decrease the standard error to 0.20‰. The instrument
performance was demonstrated by measuring CO<sub>2</sub> on stratospheric air
samples obtained during the EU project RECONCILE with the high-altitude
aircraft Geophysica. The precision for RECONCILE data is 0.03‰ (1σ) for δ<sup>13</sup>C, 0.07‰ (1σ) for δ<sup>18</sup>O and 0.55‰ (1σ) for δ<sup>17</sup>O for a sample of 10
measurements. This is sufficient to examine stratospheric enrichments, which
at altitude 33 km go up to 12‰ for δ<sup>17</sup>O
and up to 8‰ for δ<sup>18</sup>O with respect to
tropospheric CO<sub>2</sub> : δ<sup>17</sup>O ~
21‰ Vienna Standard Mean Ocean Water (VSMOW), δ<sup>18</sup>O ~
41‰ VSMOW (Lämmerzahl et al., 2002). The samples
measured with our analytical technique agree with available data for
stratospheric CO<sub>2</sub>
Coherent population oscillations with nitrogen-vacancy color centers in diamond
We present results of our research on two-field (two-frequency) microwave
spectroscopy in nitrogen-vacancy (NV-) color centers in a diamond. Both fields
are tuned to transitions between the spin sublevels of the NV- ensemble in the
3A2 ground state (one field has a fixed frequency while the second one is
scanned). Particular attention is focused on the case where two microwaves
fields drive the same transition between two NV- ground state sublevels (ms=0
-> ms=+1). In this case, the observed spectra exhibit a complex narrow
structure composed of three Lorentzian resonances positioned at the pump-field
frequency. The resonance widths and amplitudes depend on the lifetimes of the
levels involved in the transition. We attribute the spectra to coherent
population oscillations induced by the two nearly degenerate microwave fields,
which we have also observed in real time. The observations agree well with a
theoretical model and can be useful for investigation of the NV relaxation
mechanisms.Comment: 17 page
Homological methods in feature extraction of multidimensional images
We show that the newly developed homology algorithms are helpful in imaging problems on the example of an algorithm extracting one dimensional features from a noisy image. We indicate that in some situations the global nature of this algorithm may become advantageous when compared with the standard algorithms based on skeletonization and pruning. The algorithm works in every dimension. ©2009 IEEE.published_or_final_versionThe 2nd International Congress on Image and Signal Processing (CISP'09), Tianjin, China, 17-19 October 2009. In Proceedings of 2nd CISP, 2009, p. 1-
Longitudinal spin relaxation in nitrogen-vacancy ensembles in diamond
We present an experimental study of the longitudinal electron-spin relaxation
of ensembles of negatively charged nitrogen-vacancy (NV ) centers in diamond.
The measurements were performed with samples having different NV-
concentrations and at different temperatures and magnetic fields. We found that
the relaxation rate T1-1 increases when transition frequencies in NV- centers
with different orientations become degenerate and interpret this as
cross-relaxation caused by dipole-dipole interaction.Comment: 11 pages, 9 figure
Structure of the Afferent Terminals in Terminal Ganglion of a Cricket and Persistent Homology
We use topological data analysis to investigate the three dimensional spatial structure of the locus of afferent neuron terminals in crickets Acheta domesticus. Each afferent neuron innervates a filiform hair positioned on a cercus: a protruding appendage at the rear of the animal. The hairs transduce air motion to the neuron signal that is used by a cricket to respond to the environment. We stratify the hairs (and the corresponding afferent terminals) into classes depending on hair length, along with position. Our analysis uncovers significant structure in the relative position of these terminal classes and suggests the functional relevance of this structure. Our method is very robust to the presence of significant experimental and developmental noise. It can be used to analyze a wide range of other point cloud data sets
Лексическое наполнение современных газет российских немцев как реализация этнической функции языка
The purpose of our study was to determine the expression of the pro-apoptotic BAX protein in relation to the mutational status of BAX and p53 (as transcriptional activator of the BAX gene) in benign and malignant thyroid tissue. In 47 patients with thyroid tumours (14 follicular and 3 papillary carcinomas, 14 adenomas and 16 goitres), the DNA was screened for mutations of BAX (exon 1-6) and p53 (exon 5-8) by single-strand conformation polymorphism polymerase chain reaction (SSCP-PCR). Furthermore, the protein expression of BAX, p53 and p21 (which is also increased transcriptionally by p53) was investigated by immunohistochemistry. Surprisingly, we observed elevated BAX levels in patients with thyroid carcinomas compared with patients with adenomas (unpaired t-test: p<0.05) or with goitres (p<0.02). This is in clear contrast to other carcinomas where BAX is frequently inactivated which correlates to a poor prognosis (Sturm et al., 1999). There were no significant differences of the BAX levels between goitres or the adenomas. In the SSCP-PCR analysis, no BAX mutations were detectable. P53 mutation analysis by SSCP-PCR did not reveal any functional p53 mutations in the patients with carcinomas, adenomas or goitres. Nevertheless, patients with carcinomas showed an overexpression (preferentially cytoplasmic) of p53 protein compared with patients with benign tumours (p<0.05). The absence of p53 mutations suggests that the overexpressed p53 is wild type. This is in line with the expression profile of BAX and p21, which showed a higher protein expression in these p53 positive tumours (p<0.05 in the carcinomas compared with the non-malignant lesions). Consequently, the overexpressed p53 might be a correlate for dysregulation without loss of function. This, in turn, might be a reason for the good outcome of some patients with thyroid cancer
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