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 (¹²C¹⁶O¹⁷O, ¹²C¹⁶O¹⁸O, ¹³C¹⁶O¹⁶O) in nanomolar quantities of CO₂ extracted from stratospheric air samples. CO₂ is separated from bulk air by gas chromatography and CO₂ isotope ratio measurements (ion masses 45 / 44 and 46 / 44) are performed using isotope ratio mass spectrometry (IRMS). The ¹⁷O excess (Δ¹⁷O) is derived from isotope measurements on two different CO₂ aliquots: unmodified CO₂ and CO₂ after complete oxygen isotope exchange with cerium oxide (CeO₂) at 700 °C. Thus, a single measurement of Δ¹⁷O requires two injections of 1 mL of air with a CO₂ mole fraction of 390 μmol mol⁻¹ at 293 K and 1 bar pressure (corresponding to 16 nmol CO₂ 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 ¹⁷O 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 ¹⁷O 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 CO₂ 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 δ¹³C, 0.07‰ (1σ) for δ¹⁸O and 0.55‰ (1σ) for δ¹⁷O for a sample of 10 measurements. This is sufficient to examine stratospheric enrichments, which at altitude 33 km go up to 12‰ for δ¹⁷O and up to 8‰ for δ¹⁸O with respect to tropospheric CO₂ : δ¹⁷O ~ 21‰ Vienna Standard Mean Ocean Water (VSMOW), δ¹⁸O ~ 41‰ VSMOW (Lämmerzahl et al., 2002). The samples measured with our analytical technique agree with available data for stratospheric CO₂

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