Multivariate Analysis of an LA-ICP-MS Trace Element Dataset for Pyrite

Application of multivariate statistics to trace element datasets is reviewed using 164 multi-element LA-ICP-MS spot analyses of pyrite from the Moonlight epithermal gold prospect, Queensland, Australia. Multivariate analysis of variance (MANOVA) is used to demonstrate that classification of pyrite on morphological and other non-numeric factors is geochemically valid. Parallel coordinate plots and correlation cluster analysis using Spearman??s coefficients are used to discover unexpected elemental relationships without making assumptions a priori. Finally, principal component analysis and factor analysis are used to demonstrate the presence of sub-classes of pyrite. Corroborated with geological data, statistical analysis provides evidence for successive generations of hydrothermal fluids, each introducing specific metals, and for partial or complete replacement of different minerals. The data permit reinterpretation of Moonlight as a telescoped system where epithermal-Au (± base metals) is superposed onto early porphyry-Mo mineralization.     

Miniaturization of the flowing fluid electric conductivity logging technique

An understanding of the hydraulic properties of the aquifer and the depth distribution of salts is critical for evaluating the potential of ground water for conjunctive water use and for maintaining suitable ground water quality in agricultural regions where ground water is used extensively for irrigation and drinking water. The electrical conductivity profiles recorded in a well using the flowing fluid electric conductivity (FEC) logging method can be analyzed to estimate interval-specific hydraulic conductivity and estimates of the salinity concentration with depth. However, operating irrigation wells commonly allow limited access, and the traditional equipment used for FEC logging cannot fit through the small access pipe intersecting the well. A modified, miniaturized FEC logging technique was developed for use in wells with limited access. In addition, a new method for injecting water over the entire screened interval of the well reduces the time required to perform FEC logging.     

Development of saline ground water through transpiration of sea water

As vegetation usually excludes salt during water uptake, transpiration will increase the salinity of the residual water. If the source water is sea water, then the residual water may become highly saline. In the unconfined coastal aquifer of the tropical Burdekin River delta, northeastern Australia, areas of highly saline ground water with chloride concentrations up to almost three times that of sea water occur up to 15 km from the present coastline, and are attributed to transpiration by mangrove vegetation during periods of high sea level. Radiogenic ((14)C) carbon isotope analyses indicate that ground water with chloride concentrations between 15,000 and 35,000 mg/L is mostly between 4000 and 6000 years old, at which time sea level was 2 to 3 m higher than present. Stable isotope analyses of oxygen-18 and deuterium show no evidence for evaporative enrichment of this water. Oxygen-18, deuterium, and stable (delta(13)C) carbon isotope analyses of ground water and soil water point to a recharge environment beneath the mangrove forests during this postglacial sea level high stand. During that period, transpiration of the mangrove forests would have led to high chloride concentrations in the residual ground water, without inducing isotopic fractionation. Due to the higher density, this hypersaline water moved downward through the aquifer by gravity and has formed lenses of highly saline ground water at the bottom of the unconfined aquifer.     

Links between Indo-Pacific climate variability and drought in the Monsoon Asia Drought Atlas

Drought patterns across monsoon and temperate Asia over the period 1877–2005 are linked to Indo-Pacific climate variability associated with the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Using the Monsoon Asia Drought Atlas (MADA) composed of a high-resolution network of hydroclimatically sensitive tree-ring records with a focus on the June–August months, spatial drought patterns during El Niño and IOD events are assessed as to their agreement with an instrumental drought index and consistency in the drought response amongst ENSO/IOD events. Spatial characteristics in drought patterns are related to regional climate anomalies over the Indo-Pacific basin, using reanalysis products, including changes in the Asian monsoon systems, zonal Walker circulation, moisture fluxes, and precipitation. A weakening of the monsoon circulation over the Indian subcontinent and Southeast Asia during El Niño events, along with anomalous subsidence over monsoon Asia and reduced moisture flux, is reflected in anomalous drought conditions over India, Southeast Asia and Indonesia. When an IOD event co-occurs with an El Niño, severe drought conditions identified in the MADA for Southeast Asia, Indonesia, eastern China and central Asia are associated with a weakened South Asian monsoon, reduced moisture flux over China, and anomalous divergent flow and subsidence over Indonesia. Insights into the relative influences of Pacific and Indian Ocean variability for Asian monsoon climate on interannual to decadal and longer timescales, as recorded in the MADA, provide a useful tool for assessing long-term changes in the characteristics of Asian monsoon droughts in the context of Indo-Pacific climate variability.     

Cosmic‐ray exposure ages of pallasites

We analyzed cosmogenic nuclides in metal and/or silicate (primarily olivine) separated from the main‐group pallasites Admire, Ahumada, Albin, Brahin, Brenham, Esquel, Finmarken, Glorieta Mountain, Huckitta, Imilac, Krasnojarsk, Marjalahti, Molong, Seymchan, South Bend, Springwater, and Thiel Mountains and from Eagle Station. The metal separates contained an olivine fraction which although small, <1 wt% in most cases, nonetheless contributes significantly to the budgets of some nuclides (e.g., up to 35% for ²¹Ne and ²⁶Al). A correction for olivine is therefore essential and was made using model calculations and/or empirical relations for the production rates of cosmogenic nuclides in iron meteoroids and/or measured elemental concentrations. Cosmic‐ray exposure (CRE) ages for the metal phases of the main‐group pallasites range from 7 to 180 Ma, but many of the ages cluster around a central peak near 100 Ma. These CRE ages suggest that the parent body of the main‐group pallasites underwent a major break‐up that produced most of the meteorites analyzed. The CRE age distribution for the pallasites overlaps only a small fraction of the distribution for the IIIAB iron meteorites. Most pallasites and IIIAB irons originated in different collisions, probably on different parent bodies; a few IIIABs and pallasites may have come out of the same collision but a firm conclusion requires further study. CRE ages calculated from noble gas and radionuclide data of the metal fraction are higher on average than the ²¹Ne exposure ages obtained for the olivine samples. As the metal and olivine fractions were taken in most cases from different specimens, the depth‐dependency of the production rate ratio ¹⁰Be/²¹Ne in metal, not accounted for in our calculations, may explain the difference.     

A 421-d activity cycle in the BeX recurrent transient A0538–66 from MACHO monitoring

We present a ∼5-yr optical light curve of the recurrent Be/X-ray transient A0538–66 obtained as a by-product of the MACHO Project. These data reveal both a long-term modulation at P =420.8±0.8 d and a short-term modulation at 16.6510±0.0022 d which, within errors, confirms the previously found orbital period. Furthermore, the orbital activity is only seen at certain phases of the 421-d cycle, suggesting that the long-term modulation is related to variations in the Be star envelope.     

Initial Results from the Southern Edgeworth-Kuiper belt Survey

We present preliminary results of the analysis of the first 500 squaredegrees of the Southern Edgeworth-Kuiper belt Survey, a large sky survey whichran from January 2000 to January 2003 and comprises 2900° in total. Early testspredict that we should discover ～10 bright TNOs in our data, doubling the currentknown population.     

Can in-situ cosmogenic 14C be used to assess the influence of clast recycling on exposure dating of ice retreat in Antarctica?

Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods. In-situ cosmogenic ¹⁴C, in combination with longer lived nuclides such as ¹⁰Be, can be used to detect inheritance because the relatively short half-life of ¹⁴C means that in-situ ¹⁴C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ ¹⁴C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing ²⁶Al and ¹⁰Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance.     

Minor and trace elements in bornite and associated Cu-(Fe)-sulfides: A LA-ICP-MS studyBornite mineral chemistry

In situ laser ablation inductively-coupled mass spectroscopy (LA-ICP-MS) has been used to provide a baseline dataset on the minor element contents in hypogene bornite and accompanying Cu-sulfides from 12 deposits with emphasis on syn-metamorphic Cu-vein systems in Norway, and skarn, porphyry and epithermal systems in SE Europe.Bornite contains significant concentrations of both Ag and Bi, especially in the vein and skarn deposits studied and has the potential to be a major Ag-carrier in such ores. Concentrations of up to >1 wt.% of both elements are documented. Measured concentrations appear to be independent of whether discrete Ag- and/or Bi-minerals are present within the analyzed sulfide. Where bornite and chalcocite (or mixtures of Cu-sulfides) coexist, Ag is preferentially partitioned into chalcocite over co-existing bornite and Bi is partitioned into the bornite. Bornite is a relatively poor host for Au, which mimics Ag by being typically richer in coexisting chalcocite. Most anomalous Au concentrations in bornite can be readily tracked to micron- and submicron-scale inclusions, but bornite and chalcocite containing up to 3 and 28 ppm Au in solid solution can be documented. Selenium and Te concentrations in bornite may be as high as several thousand ppm and correlate with the abundance of selenides and tellurides within the sample. Selenium distributions show some promise as a vector in exploration, offering the possibility to track a fluid source. Bornite and chalcocite are poor hosts for a range of other elements such as Co, Ni, Ga and Ge, etc. which have been reported to be commonly substituted within sulfides. Hypogene bornite and chalcocite may have significantly different trace element geochemical signatures from secondary (supergene) bornite.