Diver-operated piston corer for nearshore use

A diver-operated piston corer suitable for collecting cores of >3 m length from fine-grained nearshore sediment has been developed. The corer uses a platform that rests on the sediment surface supporting both the operators and a derrick that maintains the piston at the sediment-water interface. The core is insected into and recovered from the sediment manually. The technique offers several advantages; low cost, minimal disruption of the sediment-water interface, little compaction of the sediment, the ability to collect longer length cores than is possible with gravity corers, and the ability to be deployed from relatively small boats. Dissolved ammonium and inorganic carbon data are presented from a 3.3-m core collected by this technique from Tomales Bay, California.     

Oceanic micrometeorological field experiments: An historical perspective

This paper provides an historical perspective on micrometeorological field experiments designed to evaluate air-sea interaction processes. Of course, marine meteorology is much older, and air-sea interaction has always been an inevitable part of it. But only in this century have the tools been developed to go from qualitative understanding towards quantitative measurements of interactions.     

Anisotropy beneath Hawaii from surface wave particle motion observations

Observed polarization ellipses for fundamental-mode surface waves observed at a digital station in Hawaii deviate from those expected for isotropic models of crust and mantle structure for that region. The anomalous motion occurs as rotations of the ellipse about all three axes in a cartesian corrdinate system. The largest and most consistent deviations occur as anomalous slopes of the ellipse about the horizontal axis transverse to the direction of propagation.The observed orientations and magnitudes of these angles can be explained by models of the upper mantle which contain olivine for which thea-axis dips significantly from the horizontal and which includes a sufficiently thick sedimentary layer (1 km) and a thicker than normal oceanic crust (15 km). The ellipses are also generally inclined from great circle paths about the vertical axis and are tilted about the axis aligned with the propagation direction. Both angles are small and difficult to measure, but the inclination angles are consistent with a model of the upper mantle in which thea-axis of olivine is preferentially oriented in an east-west direction.     

Lattice vibration spectra. LXVIII. Single-crystal Raman spectra of marcasite-type iron chalcogenides and pnictides,FeX2 (X=S,Se, Te; P,As, Sb)

Single-crystal Raman spectra of marcasite-type FeS₂, FeSe₂, and FeTe₂ and loellingite-type FeP₂, FeAs₂, and FeSb₂ are presented and discussed with reference to the energies of the two X-X stretching modes v _x-x (A _g, B _1g) and the four X₂ librations Rx₂ (A _g, B _1g, B _2g, B _3g). The main results obtained are that (i) the intraionic X-X bonds of FeS₂ marcasite and FeS₂ pyrite are nearly equal in strengths (mean values of the S-S stretching modes 418 and 420 cm^-1, respectively) and (ii) the interactions of the metal ions and the dumbbell-like X₂ units increase on going from the chalcogenides to the respective pnictides and from FeS₂ marcasite to pyrite (as shown from the frequencies of the X₂ librations).     

A review of methods used to determine the fractal dimension of linear features

An in-depth review of the more commonly applied methods used in the determination of the fractal dimension of one-dimensional curves is presented. Many often conflicting opinions about the different methods have been collected and are contrasted with each other. In addition, several little known but potentially useful techniques are also reviewed. General recommendations which should be considered whenever applying any method are made.     

Evaluation of drilling priorities using lead isotopes at the Lady Loretta lead-zinc-silver deposit, Australia

The weathered surface expression of the Lady Loretta lead-zinc-silver deposit outcrops almost continuously over a distance of about 4 km. Lead isotope ratios have been determined for samples, some of which contain > 4000 ppm Pb, from geochemically anomalous areas in order to assign drilling priorities to the anomalies.Twelve of the 43 samples analyzed contain isotopically homogeneous lead with ratios (²⁰⁷Pb/²⁰⁶Pb 0.9532–0.9549) similar to the expected targets for major ore deposits in the Mount Isa-McArthur River metallogenic province (²⁰⁷Pb/²⁰⁶Pb 0.955–0.962). Three main zones of interest can be outlined on the basis of lead isotopic data. The top priority is assigned to a 100-m-long section of the ironstone which coincides with the known outcrop of the ore. Lower priority for drilling is given to the two other zones which outcrop over smaller areas and have more radiogenic lead in their immediate surroundings. Several samples with anomalously high lead contents (> 1000 ppm) contain more radiogenic lead (²⁰⁷Pb/²⁰⁶Pb < 0.950) which was most likely derived from the weathering country rocks by supergene leaching and redeposition. Of the 22 samples containing ≥ 380 ppm Pb, lead isotopic analyses would have reduced the number deserving further attention to 10. Lead isotopic analyses in the early stages of exploration could have assisted in minimizing exploration expenditure at Lady Loretta.     

A Note on Robust Estimates

It is well known that the mean can be an unsatisfactory estimator of a true value if data are a poor approximation to a normal distribution or are too few in number for a normal distribution to be adequately delineated. Unfortunately, this knowledge is not always implemented in the evaluation of analytical data. The median may be used occasionally because it is recognised to be less affected by discrepent data. However, there are other 'robust' estimators which can be better than the simple median. This note complements a previous paper by the writer (1).     

Assessment of massive sulphide base metal targets using lead isotopes in soils

An assessment is made of the use of lead isotopes in soils as an exploration tool for concealed lead-rich base metal massive sulphide deposits, using four case histories in southeast Australia as examples. Case history 1 covers soil profiles (< 1 m depth) unrelated to mineralization in which the lead isotope ratios exhibit variation with depth and are different from those for massive sulphide deposits. Case history 2 covers six shallow (< 0.4 m depth) profiles from two traverses over the concealed Elura Zn-Pb-Ag deposit in central western New South Wales. For one traverse over completely concealed (blind) sulphides, no isotopic or geochemical signature of the orebody could be detected. In two profiles from the other traverse, for depths of 0.15 m and 0.3–0.45 m, the lead isotopic ratios in the soils are identical with those in the ore (the target isotope ratios). Case history 3 covers two occurrences of Silurian volcanogenic Cu-Zn-Pb mineralization at the Benambra prospect in northeast Victoria. The isotopic ratios for the soils are identical with those in the sulphides and the isotopic signature of the sulphides is also detectable in traverses where no obvious surface anomaly is developed. Case history 4 is an undrilled anomaly in Silurian shales and felsic volcanics where the isotope ratios in B horizon soils are consistent with those of the target isotopic signature.The information from these case histories suggests that the lead isotopic analysis of soils will be a useful exploration tool for concealed mineralization, although at the present stage of research it appears that its application may be limited to shallowly buried (< 100 m) targets or deeply buried targets with an extensive oxidation profile. Its main advantage over conventional geochemical techniques is its ability to discriminate between similar geochemical anomalies arising from different styles of mineralization, as illustrated by an example from Benambra.