Relations between stream sediment and source-rock mineralogy,Piney Creek Basin,Wyoming

The areal distribution of stream sediment and source-rock heavy mineralogy was studied to determine the mineralogical relations between source and derived sediment in the Piney Creek drainage basin of Wyoming. Heavy-mineral distribution in the streams was characterized using factor analysis. The results of analyses show that for an actively degrading stream system, the heavy-mineral composition of stream sediment is controlled to a considerable extent by the composition of local sediment sources and by continuous addition of detritus from bank cutting. Only the most common minerals from upstream sources persist as statistically significant variables downstream. In some cases the heavy-mineral mineral composition of stream sediment can be controlled by comparatively few, or volumetrically rare source rocks, even though more abundant source rocks supply a wide range of heavy minerals. Specific drainage configurations such as lakes and proximity of streams to major sediment sources significantly modify sediment mineralogy immediately downstream.     

Aircraft observations in the planetary boundary layer under stable conditions

An analysis of observations of airflow over Lake Ontario in a stably stratified atmosphere is presented. The relationship with theory is mentioned only in terms of what may be important to future work. Detailed air motion, potential temperature and mixing-ratio measurements are presented which show pervasive variability in the horizontal. There is no evidence of gravity waves. It is suggested that vertical mixing of the atmosphere may occur in stable conditions by a mechanism quite apart from the usual concept of the small-scale random eddy motion usually associated with surface convection. Vertical soundings are analyzed as well as two long constant-height observational runs.     

Small-scale gold distribution patterns in the Precambrian Kimberley Reef placer: A case-study at marievale GMC., East Rand Goldfield,South Africa

The Kimberley Reef is a Proterozoic gold-uranium-placer which was deposited during the Kimberley stage of the Upper Witwatersrand System, approximately 2.7 × 10⁹ years ago. The investigated site at Marievale GMC. is located towards the fanbase of the East Rand Goldfield. Geological, sedimentological, and geochemical parameters show that the placer formed in a fluviatil depositional environment (ca. 40 cm water depth) with a small-scale meandering stream pattern. Gold anomalies are elongated and frequently arcuate-shaped with sinuosities of ±1.5; their orientation reveals a high degree of variability on the scale of a few metres to tens of metres. They formed at the inside of meandering channel curves next to and alongside elongated conglomerate bodies which correspond to point bars. Concentrations of other heavy minerals formed according to their decreasing specific gravity at the outer, convex side and the downstream part of gold anomalies roughly in the order uraninite — pyrite and chromite — zircon. This sedimentary-controlled gold and heavy mineral distribution pattern was complicated by lateral channel migrations and frequent bed changes of streams, as well as subsequent faulting which had a depletioning effect on gold.