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Topic: Alluvial deposits

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  CO01693 - Silver Jack Dam - Colorado   (Site not responding. Last check: 2007-10-20)
Alluvial gravel deposits remain beneath the dam upstream and downstream of the cutoff trench.
The alluvial material is crudely stratified and predominantly clean to silty, sandy gravel and was logged in the wells of the cutoff trench as "sandy gravel, cobbles and boulders".
The underlying glacial till deposit consists predominantly of widely varying amounts of silt, gravel, cobbles and boulders and was described in the cutoff trench as "clayey to silty gravel and cobbles with blocks of shale and agglomerate".
www.usbr.gov /dataweb/dams/co01693.htm   (299 words)

 Alluvium - Wikipedia, the free encyclopedia
Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium.
Even small streams make alluvial deposits, but it is in the flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found.
The alluvial mud annually deposited by the Nile has enabled the Egyptians to grow crops since at least the 4th millennium BC without artificial fertilization.
en.wikipedia.org /wiki/Alluvial_deposit   (346 words)

 Alluvial fan - Wikipedia, the free encyclopedia
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
Alluvial fans are most likely to be found in desert areas subject to periodic flash floods from nearby thunderstorms in local hills.
Alluvial fans are very common around the margins of the sedimentary basins of the Basin and Range province of southwestern United States and northern Mexico.
en.wikipedia.org /wiki/Alluvial_fan   (334 words)

 Alluvial placer deposits, geology, exploration, mining, use - Page XI
Coarser gold is generally deposited in the upper reaches of a placer gulch, stream or river, and the finer grained gold is generally deposited in the lower reaches of placer watercourses.
The richest and coarsest gold and nuggets are commonly deposited in the layers with comparatively coarse sediment, and the finer gold particles are commonly deposited in the finer, sandy fractions of the sediment.
The source of the gold may be in the rocks along the shores; in sediments deposited by streams upon the coast; and in slightly auriferous stream or river terraces, sea terraces and gravel plains that border the coasts.
www.minelinks.com /alluvial/deposits10.html   (1394 words)

 Alluvial placer deposits, geology, exploration, mining, use - Page III
In the Carolinas and Georgia the placers and eluvial deposits commonly have gold with a fineness greater than 900 whereas the vein gold is generally much less than this value, in places being as low as 500.
Finally, it should be noted that alluvial gold, being derived from the oxidized ore, is of higher quality (fineness) than the average of the vein gold, and shows an increase in value downstream, due to surface refining action, as the size of the grains decreases.
It should be noted that the rim effect in placer gold evidently begins during oxidation of the primary deposits, because it is found in gold in the oxidized zones of auriferous deposits and in eluvial deposits.
www.kanada.net /alluvial/deposits2.html   (1541 words)

 Understanding Gold Deposits  - Arizona Outback - Home of Nugget Finder USA   (Site not responding. Last check: 2007-10-20)
In vein deposits, gold tends to occur in the free state, whereas in lodes it is usually bound up in the sulfide mineral.
The gold contained may be shed at the surface to form eluvial and alluvial deposits, or be carried in solution down the lode channel to be redeposited and enriched at the water table.
Secondary deposits are formed where gold shed from an outcropping vein or lode and is concentrated by the action of wind and water to form either: eluvial deposits in soil or slope debris near the outcrop; or alluvial deposits in stream channels.
www.arizonaoutback.com /understandgold.html   (2408 words)

 Geology of Quartz Deposits
Alluvial deposits are reported from several localities; one of these is near Vohemar near the northeast end of the island.
It is common for this type of deposit to be associated with veins in shale sandstone, or quartzite, and with pipes, pods, and associated forms in sandstones and quartzites.
Most of the deposits in bedrock are quartz veins, or flat-lying blanket deposits of milky quartz roughly parallel to the enclosing sediments, or a combination of these two types.
www.minsocam.org /msa/collectors_corner/arc/quartzdep.htm   (7444 words)

 Flint Hills geomorphology, Kansas
Alluvial deposits of chert gravel of presumed Neogene age are widespread and abundant on hill tops and high terraces throughout eastern Kansas.
Upland chert gravel deposits are widespread in southern Butler and northern Cowley counties--Figure 14.
This sediment is mainly alluvial sand and gravel of arkosic composition, which was derived from the Rocky Mountains, and is of late Tertiary and/or early Pleistocene age.
academic.emporia.edu /aberjame/field/flint/geomorph.htm   (2863 words)

 Soil Forming Factors: Deposits
Alluvial Deposits- rock debris that has been eroded into fine sediments that are subsequently transported by a mountain stream or river to the valley floor, as the gradient of the mountain decreases.
Alluvial deposits such as the Mississippi River Delta and China's vast alluvial plains have rich top soil and are known for being very fertile, crop growing regions.
Loess Deposits- Loess is comprised primarily of silt grains, with less significant anounts of clay and sand.
soil.gsfc.nasa.gov /soilform/deposits.htm   (2297 words)

 CA82903 - O'Neill Dam - California   (Site not responding. Last check: 2007-10-20)
In the left abutment, the bedrock typically consists of beds, from one to 60 feet thick, of poorly consolidated clayey and silty shales and fine-grained sandstone having an average bedding-plane dip of 45 degrees northeast.
The Pleistocene deposits are mostly silts, clays and clayey sands from stations 20+00 to 65+00.
The Recent alluvial deposits from station 65+00 to the left abutment are capped by a layer of lean clay except in the area of the former San Luis Creek where clean to silty and clayey sands were at the surface.
www.usbr.gov /dataweb/dams/ca82903.htm   (685 words)

 Pathways Subtopic Text   (Site not responding. Last check: 2007-10-20)
Alluvial deposits are the result of erosion of the surrounding mountainous regions by stream action, with the development of alluvial fans collecting along the basins below.
Alluvial fans are characterized by gently sloping alluvial deposits which are coarser near the apex in the mountains and grade toward finer deposits in the basins.
Within the interbedded alluvial deposits are layers of sand and gravel which extend into the central parts of the adjacent basins.
www-erd.llnl.gov /rescue/Topics/SCModel/pathways.html   (5882 words)

 Mojave Desert Tortoise Project Report: APPENDIX 3 - GEOLOGIC UNIT DESCRIPTIONS   (Site not responding. Last check: 2007-10-20)
The uppermost beds of the Coyote Lake basin at the southwest corner of the map area are part of an active playa that is reported to be a remnant of Pleistocene Lake Manix.
This unit consists of materials that make up the alluvial flats that lie between the edges of the fans that encroach on the bolson and the recent playa deposits that lie in the lower parts of its floor.
This deposit is thought by earlier workers to be derived from the light-colored quartz monzonite and granodiorite of the Paradise Range, which lies some 20 km to the west.
obelia.jde.aca.mmu.ac.uk /giscons/Tortoise/repapp3.htm   (2261 words)

 Alluvial fan Summary
An alluvial system is a landform produced when a stream or river, that is, some channelized flow (geologists call them all streams no matter what their scale) slows down and deposits sediment that was transported either as bedload or in suspension.
Thus, there is no preferred direction of deposition from side to side at the mouth of the stream, and as the alluvium accumulates it forms a cone-shaped pattern on the valley floor known as an alluvial fan.
Alluvial fans tend to have small slopes that may be no more than a foot every half a mile (a few tenths of a meter per kilometer).
www.bookrags.com /Alluvial_fan   (1893 words)

 Chert gravel
Alluvial deposits of chert gravel of presumed Neogene age are widespread and abundant on hill tops and high terraces throughout the region.
Alluvial deposits of chert gravel of presumed Miocene, Pliocene, and Pleistocene ages are widespread and abundant on drainage divides, isolated hill tops, and high terraces throughout eastern Kansas.
In a few cases, thin deposits of alluvial chert were discovered that are not identified as Olpe soil on the county reports.
www.emporia.edu /earthsci/chert/chert.htm   (5031 words)

 Gold Prospecting Techniques
Alluvial, eluvial and supergene deposits are secondary deposits formed by reworking of primary deposits.
Alluvial deposits are formed by the mechanical accumulation of grains, derived from pre-existing rocks, in streams and lakes.
Deposits of transported material containing gold also form on the surface of hillsides where it is concentrated at changes in gradient, such as, the base of a hill.
www.geologynet.com /gpros.htm   (8163 words)

 Southern California Areal Mapping Project home   (Site not responding. Last check: 2007-10-20)
Thus, modern wash deposits are unconsolidated sand-and-gravel deposits that occur in active channels of streams and rivers.
However, it is not helpful to lump all alluvial deposits as "wash deposits", so SCAMP geologic maps differentiate among various deposit-types that owe their origin ultimately to stream deposition in channel washes.
Distinguishing alluvial-fan and alluvial-valley deposits based on differences in their physical properties can be difficult (as between alluvial-valley deposits and deposits formed in the downstream toes of alluvial fans).
scamp.wr.usgs.gov /scamp/html/scg_surf_alluv.html   (1968 words)

 Alluvial (placer) gold diamond exploration and mining
The tropical alluvial deposits (placers) are saturated with water.
Since majority of tropical alluvial (placer) deposits have a limonite-cemented layer, under which the most interesting values are, the dredge must use a cutter head or wheel.
My experience, backed by figures, shows that an alluvial deposit with fine gold particles, in a large river system, can be evaluated with less than a 10% error, and often with less than a 5% error.
www.kanada.net /alluvial   (628 words)

 GEO_PLATE_F-17.HTML   (Site not responding. Last check: 2007-10-20)
Alluvial fans (C) are the result of this sedimentation process (Figure F-17.1).
Because of the high relief of source areas and the hydraulic characteristics, such as sporadic discharge, alluvial fans are commonly composed of coarse gravel and boulder-sized sediment near the mountain fronts.
Because alluvial fans (C) at the basin's edge trap most of the coarse sediment, deposits of the basin interior are generally fine- grained (terrigenous clay and silt) with carbonate and evaporite precipitates.
daac.gsfc.nasa.gov /geomorphology/GEO_4/GEO_PLATE_F-17.HTML   (783 words)

 Alluvial placer deposits, geology, exploration, mining, use - Page I
The term 'placer' is evidently of Spanish derivation and was used by the early Spanish miners in both North and South America as a name for gold deposits found in the sands and gravels of streams.
The bedrock in placer deposits is commonly referred to as the 'true bottom', although the term is little used today.
Eluvial, alluvial, beach and aeolian placers may become buried after their formation and are sometimes referred to as 'buried placers'.
www.minelinks.com /alluvial/deposits.html   (474 words)

 Alluvial deposit   (Site not responding. Last check: 2007-10-20)
An alluvial deposit is an accumulation of alluvium (sediment) sometimes containing valuable ore and gemstones or simply consisting of gravel or clay in the bed or former bed a river.
Texture and depositional history of near-surface alluvial deposits in the central part of the western San Joaquin Valley, California (SuDoc I 19.76:89-235)
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www.freeglossary.com /Alluvial_deposit   (314 words)

 s2chap5   (Site not responding. Last check: 2007-10-20)
Alluvial deposits that occur where the stream frequently floods over them are called flood plains.
The Anoka Sand Plain is a large alluvial deposit of the Mississippi River.
Sandy deposits are extensive throughout the central U.S.A. and occur throughout Minnesota with the largest areas north of the Twin Cities and in Wadena County.
www.soils.agri.umn.edu /academics/classes/soil2125/doc/s2chap5.htm   (1786 words)

 Diamonds | American Museum of Natural History
Basic alluvial operations along the Vaal River near Gong Gong, in South Africa, showing the trommel and washing pan.
Most of the diamond deposits first discovered were alluvial -- concentrations in streambed or riverbed sand and gravel.
The goal is relatively simple: to find a location where moving water has deposited diamonds in the bottom of a channel, possibly in a pocket or cleft.
www.amnh.org /exhibitions/diamonds/alluvial.html   (345 words)

 Formation of the Soils   (Site not responding. Last check: 2007-10-20)
The soils that formed from these alluvial deposits include the Comus, Rosman, Suncook, Toxaway, and Codorus soils on the flood plains and the Delanco and Kinkora soils on the terraces.
The Toxaway soils formed in part from alluvial deposits and in part from the decay of plants that grew on these soils when they were undrained.
The combined influence of relief and geologic erosion removes material from the surface of the steeper soils and deposits it on the alluvial bottoms; therefore, a soil surface on the steeper slopes is not maintained long enough to allow the other factors of soil formation to develop a well defined profile.
www.henderson.lib.nc.us /county/soil/Formation.htm   (1299 words)

 The importance of wetlands
The present valleys and river beds were formed in the aftermath of the last glacial periods (erosion, deposits of sand and gravel), followed by a return to the present climate (deposits of fine organic or mineral alluvial silt and ongoing erosion).
When the flow of water from the river basin has to cross these alluvial formations before joining rivers significant quantities of nitrates or pesticides contained in the water are eliminated by the action of bacteria trapped in the soil or by the vegetation.
This water is loaded with organic and mineral material causing erosion of the river basin and alluvial silt is deposited in the river bed.
www.nrpa.com /wetlands.htm   (466 words)

 ALN No. 51: Stefanov Fig. 4: Geologic map, alluvial fan deposits   (Site not responding. Last check: 2007-10-20)
Geologic map of alluvial fan deposits to the west of the White Tank Mountains located in central Arizona.
Deposits were mapped using band ratios of NS001 sensor data.
Age of deposits are: Y - Holocene; M - middle Pleistocene (Robinson et al.
ag.arizona.edu /OALS/ALN/aln51/stefanov4.html   (50 words)

 Diamond Information Atlanta: The Story of Diamonds   (Site not responding. Last check: 2007-10-20)
Those washed into rivers can collect into what are referred to as alluvial deposits while others may be carried hundreds of miles away.
Alluvial deposits yielded the first diamonds that were mined over 2,000 years ago in the Golconda region of India, between the Godavari and Krislina Rivers.
The story is told that these diamond deposits were discovered when a geologist saw a fox with a blue belly emerging from a hole.
www.therossjewelrycompany.com /diamonds.formation.html   (2363 words)

 Heavy Metals
During transport, sediment-bound metals are removed from the water column and stored in alluvial deposits for years, centuries, or even millenia before they are reintroduced to the aquatic environment.
My colleagues and I have been using a geochemical-geomorphological approach to gain a better understanding of the mechanisms through which heavy metals and other contaminants are transported, stored, and remobilized within fluvial environments over various temporal and spatial scales, particularly large river systems in South America.
by the delineation and mapping of alluvial stratigraphic deposits.
paws.wcu.edu /jmiller/heavymetalspage.htm   (293 words)

The alluvial valleys of the Calcasieu and Sabine rivers merge with the coastal marshlands in the latitude of southern Calcasieu and northern Cameron parishes.
All of the alluvial materials deposited in the Gulf Coastal Plain since the beginning of the rise in sea level at the close of the latest Pleistocene Ice Age are considered to be of Recent Age.
Deposits of this age occur in southwestern Louisiana throughout the area shown in white on Figure 1, that is, beneath the marshlands and alluvial valleys.
www.searchanddiscovery.com /documents/leblanc/index.htm   (8741 words)

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