FULL DESCRIPTION OF THE PROPOSED PROJECT

Background

Evolution and economic potential of a variety of mineral deposits associated with valley channel systems have received considerable attention by researchers, as evidenced from recent international conferences and symposia in Russia (Placer symposia, 1997, 2000) and an International Symposium on Uranium deposits (2000); in Canada as part of the CANQUA Congress (2001); a special symposium on Quaternary economic deposits at the Durban INQUA (1999), at the Reno INQUA (2003), at the XI IAGOD conference in Namibia (2002), and many others.

Previously, only limited explanations were provided for valley ore accumulations. These were either considered separately to be gravity separations of minerals or hydrogenic accumulations (leachates). It is clearly necessary to consider the full spectrum of paleo-environmental conditions which controlled ore-forming processes in valleys, including their structural and paleoenvironmental setting and age.

Project rationale

The palaeodrainage channels, mostly discharging into preserved sedimentary basins, are widely distributed in Australia. Sedimentary infillings and development of major Tertiary palaeodrainage systems of south-central Australian. The presence of these palaeochannels presents numerous exploration problems and opportunities, and challenges traditional usages of geological, geophysical and geochemical exploration techniques. The processes of palaeochannel formation can, to some extent, highlight or even disguise exploration targets and, when understood, can be applied to advantage in mineral exploration.

Placer and other deposits associated with sediments in palaeochannels have been known in many places around the world since last century. Over the geologic period, the sediments weathered from mineral-bearing surface rocks of cratons were carried by palaeochannels discharging into sedimentary basins, and gold, diamond, uranium, clay minerals and heavy minerals may occur as placers or chemical occurrences in costal barriers or within channels. Widespread coaly deposits may be found to reach commercial significance in floodplains while groundwater resources are known from the sediments associated with the palaeochannels. Therefore, a systematical and detailed study of the palaeochannels can provide the possibility of locating channel deposits and even lode deposits.

In exploring and studying unknown buried channel deposits, one of the major difficulties is how to explore for such deposits beneath many metres of overburden over quite large areas without using systematic drilling. In exploration for mineral deposits in channel sediments, precise geometric definition of the palaeochannels becomes important. In recent years, many attempts at using combination of remote sensing, geological and geophysical techniques to successfully delineate palaeochannels have proven to be useful and important in delineation of palaeochannels.

In the present study, there are considerable uncertainties due to the unknown character of much of the material, that is, subsurface sediments. Recognition of important boundaries within the sedimentary sequences is readily achieved in some cases but is very difficult in others. Even when guided by past experience, the accuracy of geophysical models (imagery) and the estimation of the parameters of stream dynamics from both field and borehole observations sometimes is problematic.

Statement of the project

The main objective of this project is the analysis of fluvial channel systems in which mineral deposits occur. These range from distal gravitational accumulations (diamonds and heavy minerals) though proximal placer accumulations (Gold, PGE, Tin, etc.) to hydrogenic (leached) ore accumulations above geochemical barriers (Uranium, Molybdenum, TR, etc.). These sediment-hosted ore accumulations occur in valleys of various ages, including the recent past. The largest deposits occur in valleys developed in much earlier stages of landscape evolution, and are therefore clearly palaeochannel related.

Palaeochannels are of at least three types:

a) buried channels (thalwegs or overdeepened channels) in modern valleys.

b) abandoned (“dead”) valleys resulting from large-scale drainage basin reconfiguration and visible directly or indirectly in the present landscape, ie. Dead Sea.

c) fossil palaeochannels not visible in the present day relief, ie. basal palaeochannels incised into bedrock, and intra-formational palaeochannnels located at discontinuities.

Palaeochannels are the main concentrators of various kinds of terrestrial placers dated from Pre-Cambrian to Quaternary. They contain important resources of gold, PGE minerals, diamonds, tin, rare metals, etc. and are known in most placer regions through the world. Palaeochannels are also concentrators of leached deposits (ie. selenium, rhenium, yttrium, scandium, rare earths, etc.). Amongst these are known occurrences of Quaternary (Madagascar, Ukraine, Central Asia, Urals, Siberia), Pliocene (Yeellirrie, Australia, palaeochannel deposits of the Kyzyl-Kum Desert, Uzbekistan Republic), Neogene (Kazakhstan, palaeo-Don in Russia), Jurassic-Cretaceous ((Trans-Uralian area in Russia), Triassic (Colorado), and deposits of even older ages. Of special interest are Permian ultra-rich rare metal ores of the Tomtor deposits in Siberia, which for the most part are epigenetic leachates, but in part are placer deposits.

In arid regions, climatic variables are crucial in understanding the deposition of leached ores (ie. Australia, Nigeria, Mongolia, Western China, Kazakhstan and Uzbekistan Republic, etc.).

There is abundant evidence for active epigenetic changes which occur in palaeochannel placers themselves. These changes result in extensive supra-ore halos where elements of ore paragenesis are concentrated on surficial barriers. Those processes are most conspicuous in arid zones on land and above buried and submerged valleys which are located under recent and young alluvium, and contain the bulk of large gold, PGE or tin deposits. Preservation and scale of these ancient river channels depend on that so far as they are inherited by recent valleys. However, greater or lesser drainage restructuring is sine qua non for ancient valleys occurrence. The same is true of leached paleochannel uranium deposits.

Another important consideration is the coincidence of multiple ore-forming processes, and zonality of mineralization in paleochannels. For example, some paleochannels in the southern Urals display a regular transition from corundum, crystal and piezo-quartz in their upper reaches to gold placers downstream in middle stream, and to leached uranium deposits on the complex epigenetic geochemical barrier (reduction, hydrolysis, sorption, etc.) in their middle- and lower reaches. This epigenetic mineralization hasn’t facies limits and can spatially coincide with other placer mineralizations within paleochannels of the 2^st-5^rd order. Late Cenozoic landscapes of the south flank of the Trans-Urals peneplain were shaped in response to inherited planation and low rates of erosion related to gradual replacement of warm humide conditions by semi-arid conditions in the Miocene and by alteration of cold semi-humide and semi-arid conditions during the Pliocene-Quaternary

The project will concentrate on two aspects of paleochannels, namely:

a) valleys as records of environmental evolution, and

b) valleys as archives of various sedimentary deposits.

The main aims and expected outcomes / benefits of the project include: to test various techniques for successfully delineating the palaeochannels;

· to apply sedimentary geology to exploration for sedimentary mineral deposits;

· to estimate the history of environmental conditions affecting the cratons by establishing the history of sedimentation;

· to devise models for locating possible mineralisation related to the palaeochannels.

Model regions

The proposed investigation will consider the various tectonic and environmental situations wherein palaeochannels occur. The following models have been selected:

- Areas of neotectonic uplift (orogenesis) at the active continental margins (South American Andes) and in collision zones (Central Asian Highlands). In these areas climatic factors such as aridification and alpine glaciations are also important, and are direct responses to orogenesis.

– Ancient shields (cratons) are locales where young (Cenozoic) channels incise Paleozoic palaeochannels and rework their deposits; as a result, Paleozoic alluvium is an intermediate host for recent placers (for example, Kilo-Moto region in the Zaire Republic). Special emphasis should be put on the effects of climate (i.e. arid versus humid).

– Platforms ranging in age from ancient to youthful may feature several stratigraphic levels of palaeochannels (ie. basal channels or channels located at intra-formational discontinuities).

– Passive continental margins that have undergone destruction by rifting and eustatic sea level changes (Arctic Ocean shelf and adjacent coastal plains, including Chukotka Peninsula, North American and South African Atlantic coasts, West Indian coast, etc.). Extensive buried and submerged drainage systems are typical for such shelves. Horizontal tectonic displacements also cause re-orientation of valley systems (ie. Kolyma River mouth). Some beach placer deposits are the result of recent drainage changes associated with reconfiguration of coastal margins.

– Areas of major continental glaciations are locations where river systems are often drastically changed (ie. Yukon and MacKenzie Rivers in North America, and Northern European rivers in the area of the Scandinavian Ice Sheet). In addition to climatic (ice) factor, such drainage basins are also affected by glacial isostasy.

– Mid continental areas of aridification are synchronous with glaciation in high and temperate latitudes (ie., Mongolia, West China, Trans-Baikal area, and Pampa of Argentina, etc.).

– Other regions of drainage restructuring, such as those in the Carpathians and in Transylvania occur in mid-continental areas that are structurally stable and far from the effects of glaciation. Such drainage basin evolution is undoubtedly related to weathering and erosion cycles, and climate.

Still other regions may be included which highlight chronological and/or spatial variability of palaeochannels and their mineral occurrences. That opens the question of coincidence of ore-forming processes different in origin in palaeovalleys and a certain zonality of mineralization in palaeochannels. For one example, some palaeochannels in the Southern Urals display a regular transition from piezoquartz placers in the upper reaches to gold placers downstream and to infiltration uranium occurrences still lower.

Methodology and anticipated results

Evidence from existing geological maps should be utilised together with new field studies in an effort to improve our knowledge of the dimensions, trends and continuity of palaeochannels.

The preliminary stage of the work will include collecting and comparing published and unpublished data, and the interpretation of satellite and aerial photographs. Topography, digital elevation models (DEMs), Landsat, NOAA and radiometric images, magnetic, seismic, gravity, and transient electromagnetics (TEM), and airborne electromagnetics (AEM) methods, where available, should be integrated into the phase.

Materials utilized during the project include samples gained during field work and others taken from cores and cuttings. Field geological and geomorphological investigations will be performed in key regions and provinces of Canada, Australia, Russia, China, Kazakhstan, Uzbekistan, Chile, Argentina, India and other countries. These will consist of descriptions of outcrops, mines and quarry exposures, and cores. These samples should be examined for determination of sedimentary type and facies, environment of deposition, conditions of weathering, and some were subjected to petrological, mineralogical, and geochemical analysis.

A wide spectrum of laboratory analyses are planned. These include mineralogy, spectral, chemical, SEM, XRD, and isotopic analysis, and micromorphology. Laboratory results will be reported by age of deposits and by formational environment.

Regional paleotectonic and paleogeographic reconstructions at various scales will be made, depending on the size of the fluvial systems. Remote sensing mapping and computer modeling are planned. Comparative analysis of paleochannels and their related mineralization will be made with a view to tectonic, geomorphic and climatic settings. Therefore the methods of study on the palaeochannels can be summarized as below:

· detailed mapping of palaeochannels by using geological and geophysical techniques;

· detailed petrological, mineralogical and geochemical analyses of the channel fills;

· sequence stratigraphic and sedimentological analysis of channel fills;

· reviewing the palaeogeography adjacent to the nearshore basins.

Finally, the researchers will develop evolutionary models of palaeochannel mineralization types and histories.