Kinematic interpretation of remnant en-echelon rift segments of the southwestern Japan Sea

The southwestern Japan Sea and the margin of southwestern Japan feature parallel elongate extensional sub-basins and grabens. These structures are oblique to the trend of southwestern Japan and are interpreted as the remnant of an en-echelon array. Such a right-stepping remnant en-echelon pattern indicates sinistral rifting of the southwestern Japan block from Asia. The major extensional fault trends are parallel over a distance of 600 km. Infinitesimal kinematic relations show that it is unlikely that these faults initiated in response to rotation about the nearby pole determined from paleomagnetic studies. Rather, an earlier stage of rifting about a distant pole is indicated. The rotational pole of this early rifting was probably located at least 6000 km away from the rift and the pole of rotation was offset from the rift trend by a similar distance. Rifting about this distant rotational pole loosened the southwestern Japan continental block from the Asian mainland making it susceptible to a large rotation about a nearby pole.     

A note on the characteristics and possible origins of desert varnishes from Southeast Morocco. A reply to comments by R. I. Dorn

This reply to Dorn (1989) argues that a biotic origin is not the only way in which desert varnishes may be formed. It is suggested that a variety of initial conditions may result in similar end products. It is agreed that the dissimilar views of the authors may result from their different philosophies concerning the classification of Mn/Fe varnishes.     

An intercomparison of seawater filtration procedures

Filtration systems, used for the preparation of coastal seawater samples for trace analysis, have been intercompared to determine the extent of contamination arising during the filtration process. The results show that all the systems intercompared are able to provide uncontaminated filtrates for copper, nickel, cobalt and manganese and, with two exceptions, for cadmium and iron, at levels that would be encountered in uncontaminated coastal waters.     

Orographically-forced cold fronts — Mean structure and motion

Shallow cold fronts with a north-west/south-east orientation sometimes experience blocking by the coastal mountain range of south-eastern Australia and greatly increase their propagation speed on the eastern (seaward) side of the range while they advance more slowly to the west of the range. The violent behaviour of some cold-frontal passages, or southerly busters, is found to be at least orographically initiated, but the phenomenon does not exhibit the characteristics of a coastally-trapped density current. The head of the front has the character of an evolving density current and its propagation is well predicted by density current theory over more than half of its lifetime. Nevertheless, it differs from steady laboratory-simulated examples in that a horizontal roll-vortex just behind the front is found to be accelerating relative to the rate of advection of cold air behind the front. This implies that its evolution will be governed by warm air entrainment, a fact which is confirmed by the observations. General agreement between extensive airborne observations over the ocean and measurements made at selected points along the coast indicates the usefulness of these basic studies for future improvement to forecasting in the near-coastal region.     

Impact melting of the Cachari eucrite 3.0 Gy ago

Both the host phase and glass veins of the Cachari eucrite have been analyzed by microprobe and neutron activation analysis for their chemical compositions and by mass spectrometry for their ³⁹Ar-⁴⁰Ar gas retention ages. Cachari is chemically similar to other non-cumulate eucrites. The vesicular glass veins vary from pure glass, to devitrified glass, to areas that are substantially crystalline. The glassy areas have nearly the same concentrations of major and trace elements as the unmelted portions of Cachari, but some differences, probably due to preferential dissolution, occur along melt contacts. The glass formed by shock melting of Cachari host or of rock identical to it. ³⁹Ar-⁴⁰Ar data for the host and glass suggest distinctly different ages of 3.04 ±.07 Gy and 3.47 ±.04 Gy, respectively. The time of glass formation, which may also be the time of brecciation, is most likely given by the 3.0 Gy age of the host. The higher age for the glass is interpreted to represent incomplete Ar degassing during the 3.0 Gy event due to the greater resistance to Ar diffusion shown by the glass compared to the host. Event ages significantly younger than 4.5 Gy have now been determined for several eucrites and howardites and suggest a long dynamic regolith history for the parent body.     

Shopping perceptions of the inner city elderly

This paper offers an exploratory investigation of two behavioural constructs of elderly shoppers: (i) spatial information fields and (ii) retail evaluation criteria. The constructs of the elderly are examined with reference to comparable responses of a baseline group of non-elderly consumers. The data are elicited from samples of elderly and non-elderly apartment dwellers in Winnipeg's central area. The results disclose that the spatial information fields of the elderly are relatively restricted, largely as a result of their lower levels of mobility. The problem of limited transport availability for the elderly is also expressed in terms of the higher levels of importance which they assign to accessibility factors in the decision on where to shop for groceries. In terms of other retail evaluation criteria, the elderly and non-elderly express different degrees of concern about various grocery outlet characteristics and commodity traits. It is concluded that the elderly represent a distinctive group of shoppers whose special characteristics may be relevant to the formulation of consumer spatial choice models.     

Exploration rock geochemistry for gold, Parkes, New South Wales, Australia

The London-Victoria lode-type Au deposit near Parkes, New South Wales, was discovered in 1863 and became the subject of modern exploration in 1980 after about 75 years of little or no activity. The deposit lies within Palaeozoic tuffaceous, andesitic rocks. Soil geochemistry was the main technique used to define drill targets, and the deposit is now at an advanced state of assessment for probable development.Rock geochemistry is being investigated as an aid in drill-core interpretation in the search for extensions to the London-Victoria deposit and other similar deposits in the district.At an early stage of the rock-geochemical work it became clear that minor basemetal mineralization was also present in the structural hanging wall at between 30 and 70 m from the lode Au deposit. Interpretation of the geochemical signatures for major elements (Ca, Mg, Na, K, Fe) and trace elements (Cu, Pb, Zn, Mn) is confused by an overlap and merging of responses from the Au and base-metal mineralization. The measurement of bromine-soluble Sb, As, Bi, and Te, together with the more conventional major and trace elements, permits discrimination between geochemical halos related to the Au and those resulting from minor base metal mineralization.The results demonstrate the use of rock geochemistry for Au exploration, its usefulness in drawing attention to geological features, and the utility of bromine-soluble trace elements commonly associated with gold mineralization.     

The typing of Au and base-metal occurrences by plasma/mass spectrometry: initial results

This paper discusses the application of the newly developed ELAN 250 I.C.P./mass spectrometer to exploration geochemistry. This instrument combines an inductively coupled plasma with a quadrupole mass spectrometer. The combination of these two existing technologies makes it possible for the first time to perform stable-isotope and elemental analysis rapidly and concurrently.Particular attention is paid to the use of lead isotopes to type Au and base-metal occurrences. Data are presented on galena samples obtained from the Geological Survey of Canada and the Royal Ontario Museum. Consideration is also given to the potential usefulness of Pb isotopes and trace-element data to type mineral occurrences and to identify new ones.     

Some observations on the geochemistry of gold mineralization in the weathered zone at Norseman, Western Australia

At Norseman Au mineralization is hosted by parallel easterly dipping quartz reefs in a westerly dipping sequence of Archaean basaltic flows and As is strongly correlated with this mineralization. Near-surface exploration is hampered by an extensive cover of deeply weathered soils and a veneer of silty calcareous material, probably of aeolian origin, which, because of its low Fe content of < 5%, has a very low (< 10 ppm) and often indiscernible As signature over mineralization. At a test traverse over the southern end of the Mararoa quartz reef, drill sampling to 10 m depth in highly weathered in situ material beneath the calcareous veneer produced As anomalies which are strongly correlated with the extrapolation to surface of a shear zone hosting Au mineralization which is probably blind. The As anomalies can be extended into the surface horizon by manipulating the data to compensate for the low Fe content of the calcareous layer.The Au values in the drill samples were very low and poorly correlated with the extrapolation to surface of the Mararoa shear. However, the absence of a Au halo (at a 10 ppb detection limit) may be due to the shear being barren near surface, or may be due to the samples being taken from the strongly leached zones of a laterite profile. In the area of the test traverse at the southern Mararoa area, the upper horizons of the original laterite profile have been eroded away and the remaining horizons covered by a veneer of calcareous material. There is a better correlation of the Au values of the shallow drill samples with the projection to surface of a porphyry, which hosts minor low-grade Au mineralization.The results for Au dispersion around the Mararoa shear contrast with dispersion at the nearby Hinemoa Mine where gold mineralization crops out. Channel sampling in costeans showed that an Au anomaly (threshold 40 ppb) extends 50 to 150 m into oxidized wall rocks. This well defined halo may be due to the secondary dispersion of Au from the quartz reef into the ferruginous zone of the laterite profile.Gold in the leaves and twigs of Melaleuca pauperiflora F. Muell. from the traverse at the southern end of the Mararoa shear was determined by neutron activation analysis and found to be broadly correlated with the projected Au mineralization. However, the lack of correlation with the soil Au values to 10 m may be due to the plants taking up most of their water from below the depth of sampling.